Sports nutrition energy metabolism and exercise part 1

Methods for the Measurement of Metabolic Rate

Human energy output can be assessed through direct and indirect calorimetry, along with the use of doubly labeled water This article will explore the advantages and disadvantages of these methods, as well as their applications.

Direct Calorimetry

Direct calorimetry measures heat production in a highly insulated chamber The chamber's walls are equipped with pipes that circulate water at a constant rate Heat generated by the subject is determined by the temperature difference between the incoming and outgoing water.

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Direct calorimetry is a highly accurate method for measuring the metabolic rate of athletes, but it is limited to resting measures and activities with minimal movement over extended periods (2–24 hours) This technique involves a controlled environment where oxygen is supplied, and carbon dioxide is absorbed, but it requires significant time to equilibrate heat loss and production, typically taking at least 30 minutes Additionally, the use of direct calorimeters, which can range from suit calorimeters to larger chambers, is impractical for most sports, varying environments, and large-scale population studies due to the complexity and cost of the necessary equipment.

Indirect Calorimetry

Closed Circuit Spirometry

The closed circuit system of indirect calorimetry utilizes a spirometer filled with 100% oxygen and a separate carbon dioxide absorbent to measure oxygen uptake As the individual breathes, the volume of gas in the spirometer decreases due to oxygen assimilation and CO2 removal, with the difference in volume indicating oxygen uptake, which is then converted to energy use by multiplying by 5 kcal/L However, this system has inherent issues, including the necessity for an air-tight design to ensure accurate measurements, the requirement for the subject to remain on the mouthpiece to prevent room air contamination, and the need for an adequate CO2 absorbent to avoid skewed results, particularly at high metabolic rates Additionally, the temperature of the gas can affect volume measurements, potentially leading to an underestimation of metabolic rate The spirometer must also have a large capacity to accommodate the oxygen needs during exercise, as a 30-minute session may require 40-90 liters of oxygen Furthermore, this method does not differentiate between energy sources, such as fats and carbohydrates, which, along with the bulkiness of the equipment and the proximity required for the subject, limits the application of closed-circuit spirometry in exercise studies.

FIGURE 5.1 Schematic of the closed circuit system for measuring energy expenditure.

Open Circuit Spirometry

The open-circuit system of indirect calorimetry prevents subjects from re-breathing purified air, as they inhale room air and exhale into the ambient environment During exhalation, the system measures the volume of air along with the expired O₂ and CO₂ content The difference between the inspired and expired volumes of O₂ is referred to as VO₂.

Open-circuit systems can be categorized into three variations: bag systems, computerized systems, and portable systems In each of these systems, the subject breathes through a mask or breathing valve, which directs the expired air into a large balloon or tube The concentrations of oxygen (O₂) and carbon dioxide (CO₂) are then measured using gas analyzers.

To accurately measure total air volumes, instruments such as turbines, pneumotachs, or gas meters are utilized The bag system captures the volume of exhaled air using a large meteorological balloon or a standard rubberized Douglas Bag, with the contents subsequently analyzed for gas volume and concentrations of O₂ and CO₂.

Values for gas volume and expired air are used to calculate oxygen uptake

The gas volume is corrected for temperature and water vapor to standard conditions (STPD: 0°C, 760 mmHg, and 0% relative humidity) to enable comparisons between measurements taken on Mt Everest and those at sea level The inspired gas volume is calculated from the expired volume and the concentrations of expired oxygen and carbon dioxide using the Haldane conversion These values are used to compute VO₂ and carbon dioxide production (VCO₂) A computerized system enhances this process by providing faster response times, allowing for breath-by-breath VO₂ calculations, unlike the Douglas Bag system, which measures VO₂ in larger increments ranging from 30 seconds to 10 minutes.

FIGURE 5.2 Schematic for the Open Circuit system for measuring breath-by-breath energy expenditure (bold arrows) and minute-by-minute averaging (dotted line).

132 Sports Nutrition: Energy Metabolism and Exercise

Modern technology and microprocessors have enabled the development of lightweight metabolic systems that weigh less than 1 kilogram, allowing athletes freedom of movement These systems, comprising less than 3% of an individual's weight, accurately measure energy expenditure without significantly impacting performance Portable metabolic/VO₂ systems have enhanced our understanding of athletic energy expenditures and provide valuable data on heart rates, making them essential for endurance athletes assessing their anaerobic thresholds Equipped with telemetry, these systems can deliver real-time data during workouts or competitions, whether set up on a track or in a vehicle for cyclists However, the major drawback is their high cost, approximately $30,000 USD.

Closed circuit systems maintain a consistent energy equivalent, irrespective of whether the energy source is carbohydrates or fats However, fats require more oxygen for energy production, consuming 213 mL O₂ per kcal compared to 198 mL O₂ per kcal for carbohydrates Additionally, fats generate a higher amount of CO₂ than carbohydrates, making it essential to understand the relationship between VCO₂ and energy sources.

VO 2 gives an indication of the specific source of the energy, whether fats or carbohydrates All open-circuit methods for computing energy expenditure rely on this axiom. The ratio of VCO 2 to VO 2 uptake is called the respiratory exchange ratio (RER), respiratory quotient (RQ), or simply the R value 2–4 Knowing the RER, one can consult standard tables and determine the non-protein energy production per liter of O 2 and insert that value into the equations to determine energy expenditure (Table 5.1) 19 The RER does not take protein metabolism for energy into consideration; therefore, it is sometimes referred to as the non-protein RER 2,4 The RER for carbohydrate is 1.0 and the reaction can be summarized by the following equation:

The oxidation of a single glucose molecule requires six O₂ molecules and produces six CO₂ molecules, resulting in a respiratory exchange ratio (RER) of 1.0 In contrast, the oxidation of fatty acids, such as palmitic acid, yields an RER of approximately 0.70, as it requires 23 O₂ molecules to produce 16 CO₂ molecules (16/23 = 0.696) Consequently, as the energy substrate shifts from fat to glucose, the RER increases from 0.7 to 1.0 For individuals consuming a balanced 50/50 mixture of carbohydrates and fats, the RER is 0.85 This ratio correlates with kcal production per liter of oxygen, with carbohydrates generating 5.047 kcal/liter (21 kJ/L) compared to fats, which produce 4.686 kcal/liter (19.6 kJ/L) Therefore, an athlete utilizing 100 liters of oxygen during an activity with this mixture would expend approximately 486 kcal (2036 kJ) of energy.

Open-circuit spirometry for measuring energy expenditure requires a steady state, as VCO₂ and VO₂ only reflect substrate utilization during this period Typically, during steady-state exercise, VCO₂ is lower than VO₂, resulting in an RER of ≤ 1.0 However, activities that generate significant lactic acid can lead to a disproportionate increase in VCO₂ relative to oxygen uptake, making spirometry ineffective for high-intensity anaerobic activities or those of insufficient duration to achieve steady state Additionally, individuals who feel uncomfortable with the equipment or perceive the testing as stressful may hyperventilate, increasing CO₂ output without affecting O₂ uptake, thus distorting the RER as a measure of substrate utilization These factors highlight the key limitations of indirect calorimetry.

The absolute VO₂, measured in liters per minute (L/min), reflects overall energy expenditure and varies with muscle mass, as larger muscle masses result in higher absolute VO₂ values Conversely, relative VO₂, expressed in milliliters of O₂ per kilogram of body weight per minute (mL/kg/min), allows for comparisons between individuals of different sizes, highlighting the importance of muscle mass as the primary metabolically active tissue.

D.B Dill introduced a system for expressing energy expenditure based on resting metabolic rate, which led to the development of the metabolic equivalent (MET) While research indicates that an oxygen uptake of 3.5 mL/kg/min or 1 kcal/kg/hr corresponds to one MET, this has not been conclusively verified The MET is widely utilized in clinical exercise testing and epidemiological studies; however, due to its imprecise nature, it is not recommended for representing the metabolic rates of athletes.

Doubly Labeled Water

Use of Open Circuit Technology

Energy expenditure during activity is usually measured by open-circuit spirometry.

Computerized systems are most effective for measuring energy expenditure during physical activities Some of these systems are stationary, designed for activities where participants remain close to the measurement device They have been utilized to assess energy costs for various exercises, including walking and running on treadmills, cycling on ergometers, swimming in flumes, rowing, stair stepping on ergometers, and arm cranking.

The bag technique of open-circuit spirometry is employed to measure VO2 during various activities such as cycling, swimming, and household chores, typically in confined spaces This method provides average responses over 1–10 minutes, depending on activity intensity and bag size, but does not offer breath-to-breath VO2 measurements Researchers must accompany subjects without hindering their movements, while subjects often wear a mouthpiece and support a breathing tube, which can be uncomfortable Additionally, gas exchange in the bags can lead to unreliable results if used for more than 10–15 minutes Consequently, bag measurements are usually limited to shorter durations for accuracy In contrast, miniaturized portable systems have transformed energy expenditure data collection, allowing for real-time measurements during various activities with minimal impact on movement and weight These advanced systems facilitate the assessment of energy expenditure in sports and daily tasks without tethering the subject.

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While these systems demonstrate high accuracy, they do present some minor issues The added weight of the equipment, typically around 1 kg, can elevate the energy expenditure during activities For adults, this additional weight is minimal, accounting for less than 2% of their body weight However, for children, the system's weight can significantly affect their energy costs during physical activities.

For accurate data collection, it is crucial that the systems are securely attached to the subject to prevent motion interference, which can alter energy costs Most systems require the use of a mask instead of a cumbersome breathing valve and mouthpiece for measuring expired gases However, an ill-fitting mask may lead to air leaks, affecting both the measured air volume and the fractions of expired gases Additionally, experience indicates that these systems can lose telemetry functionality when near electric fields, such as those from video displays Proper planning and consideration can mitigate these issues, ensuring reliable data collection for investigators.

Use of Heart Rate To Estimate Energy Expenditure

Ergometers

Ergometers and specialized machines have been created to accurately measure metabolic rates in various sports by simulating the specific actions involved These devices are primarily engineered to regulate effort, resistance, and speed during exercise.

Ergometers play a crucial role in sports nutrition and energy metabolism during exercise, with four primary types: cycle ergometers, rowing ergometers, treadmills, and cross-country ski machines Cycle ergometers have been utilized in research since the early 1900s and are essential for training cyclists Rowing ergometers, a more recent innovation from the fitness industry, and cross-country ski machines, popular in the 1980s and 1990s, serve as valuable training tools for competitive athletes Treadmills, introduced in research in the 1940s, quickly gained popularity among runners However, a limitation of these ergometers is their inability to replicate air and water resistance, which can lead to an underestimation of true energy expenditure during activities like swimming and rowing.

Cycle Ergometers

Cycle ergometers play a crucial role in physiological testing for athletes, offering vital insights into anaerobic and aerobic power There are two main types: upright and recumbent Upright ergometers, which closely replicate the posture of traditional cycling, are commonly used in exercise testing and can be equipped with clipless pedals and competitive-style handlebars for a more authentic experience In contrast, recumbent bikes position the legs horizontally, reducing blood pooling and active muscle mass, which limits the ability to maintain high work rates While recumbent cycles enhance comfort, they can decrease maximal aerobic power and are primarily utilized in fitness and rehabilitation settings rather than for athlete evaluation.

The workload of a cycle ergometer is determined by the pedal rate, resistance, or brake type on the flywheel A common method involves direct friction from a strap around the flywheel, which means that changes in pedaling rate affect the workload Therefore, understanding the resistance and pedal rate is essential for friction-braked designs Alternatively, resistance can be controlled electronically or electromagnetically, with modern micro-processors enabling a consistent workload irrespective of pedaling speed.

Work and power output on cycle ergometers can be quantified using various metrics Most manual-braked, friction-style ergometers measure resistance in kiloponds (kp), representing the friction applied by a kilogram mass The work output is calculated based on pedal frequency, the theoretical distance traveled per pedal rotation, and the resistance in kps For instance, pedaling at 60 rpm with 2 kp of resistance and a distance of 6 m per revolution results in a total work output of 720 kpm (2 kp × 60 rpm × 6 m/rev) While work can also be expressed in Newton meters or joules, this is less common Power, defined as work per unit of time, is generally measured in watts.

Athletes' energy expenditure can be measured in terms of ergometry without time limitations To convert kilopond meters (kpm) to watts, one can divide by 6.12 w/kgm/min For instance, a cyclist producing 720 kgm would have a power output of 118 watts.

Oxygen uptake can be estimated based on the work rate in kgm, with approximately 2 mL O₂ consumed per kgm For instance, an adult cycling at a rate of 720 kgm would require around 1440 mL (1.44 L) of O₂ per minute during exercise, calculated as 2 mL/kgm multiplied by 720 kgm This value represents the VO₂ needed solely for the work performed.

VO 2 , a constant for resting VO 2 needs to be added That amounts to approximately

300 mL of VO 2 for an adult Therefore, the total VO 2 for the above example would be approximately 1740 mL O 2 per minute.

The cycle ergometer is a valuable tool for evaluating anaerobic power, submaximal power, and maximal aerobic power, with testing protocols tailored to specific objectives Anaerobic power tests are brief, lasting 30 seconds or less, requiring maximal effort from the rider with resistance adjusted according to body mass Power measurements, reported in watts, include peak, mean, maximal, and minimum values in both absolute terms and relative to body mass Additionally, a graph depicting power decrements serves as an effective indicator of fatigue rates.

The graph illustrates the relationship between time and power, with time represented on the x-axis and power on the y-axis The slope of the line reflects the rate of power decrease during maximal effort.

Submaximal protocols on the cycle ergometer are often utilized to predict

VO₂max can be assessed using various submaximal tests, including the Astrand-Rhyming, PWC 170, and YMCA protocols Although these tests vary in stage lengths and workloads, they all involve a gradual increase in intensity and conclude before reaching maximal aerobic power The submaximal VO₂ or heart rate responses at each workload are then used in prediction equations or nomograms to estimate VO₂max Research indicates a moderate to strong correlation between the VO₂max predicted from these submaximal tests and the values obtained through maximal testing.

Protocols for assessing maximal aerobic power on a cycle ergometer typically involve incremental tests with gradually increasing workloads based on the subject's body mass and fitness level These tests usually last between 8 to 15 minutes Researchers have compared four exercise protocols with varying increment lengths (ramp/continuous increase, 1-, 2-, and 3-minute stages) while keeping the workload increase constant (watts/stage) The results indicated no significant differences in VO₂max among the protocols, suggesting that the length of the stage does not influence the physiological response to exercise when the work rate increase is consistent.

Recent advancements in computer and electronics technology have enabled the creation of compact flywheels compatible with standard bicycles By mounting the rear wheel on a stand and attaching the flywheel, cyclists can adjust resistance in real-time using electronic or manual brakes Innovative software allows users to simulate various competitive courses, including flat terrains, mountainous routes, and fitness tests, offering cyclists an engaging "virtual environment" for training These modern ergometers enhance the overall training experience, making it more enjoyable and effective.

Sports nutrition plays a crucial role in energy metabolism and exercise performance, particularly for competitive cyclists Advanced ergometers, often used in training, feature heart rate monitors that adjust resistance levels based on the cyclist's heart rate, optimizing workout efficiency.

Rowing Ergometers

Rowing ergometers replicate the experience of rowing on water while being used on land, featuring four main components: a flywheel, a dampening mechanism, a pulley with a handle, and a speed and power monitor The flywheel's spinning rate corresponds to the user's pulling strength, storing potential energy between pulls The dampening mechanism simulates water resistance through friction, which can be adjusted using air, a weighted belt, or water The pulley and handle function like oars, allowing the user to control the flywheel Lastly, the speed and power monitor tracks the flywheel's turnover rate and the force exerted on the pulley, providing valuable performance metrics.

There are two main types of rowing ergometers: static and dynamic Static ergometers, or stationary power heads, have a fixed flywheel, allowing the rower to slide back and forth on a seat In contrast, dynamic ergometers, known as floating power heads, feature a flywheel that moves with the rower, simulating more realistic rowing motions A study revealed that while there are some biomechanical differences, the power per stroke and total work remain similar between the two models.

Rowing ergometers simulate the four key phases of a rowing stroke: catch, drive, finish, and recovery During this continuous motion, various metrics are measured, with power and work being two primary variables Power (P) is determined by the formula $ P = \frac{E}{t} $, where energy (E) is divided by the time (t) taken for each stroke, and is measured in watts Work (W) is calculated as $ W = \frac{P}{t} $, expressed in joules, with the relationship that 1 watt equals 1 joule per second.

Rowing ergometers are essential tools for coaches and clinicians to evaluate athletic performance and training effectiveness Various protocols exist to assess aerobic capacity, with three common methods being continuous maximal tests, continuous incremental tests, and discontinuous incremental tests Continuous maximal tests, often referred to as "all-out" tests, typically last around 6 minutes, mirroring the duration of a 2000-meter race, which makes them ideal for simulating competitive conditions This protocol also measures the time taken to complete 2000 meters, demonstrating high test-retest reliability (r = 0.96), thus proving effective for tracking athlete progress.

A continuous incremental test, also known as a progressive exercise test, involves gradually increasing exercise intensity until the participant reaches their limit This method is effective for determining key fitness metrics such as anaerobic threshold and VO₂max, while also assessing the corresponding increases in cardiovascular, ventilatory, and metabolic responses related to exercise intensity.

Discontinuous incremental protocols feature gradual workload increases until fatigue, with short breaks in between each increment These breaks facilitate the collection of blood samples, enabling clinicians to measure blood lactate levels and identify the lactate threshold effectively.

Anaerobic power plays a crucial role in rowing performance, measured through maximal effort sprints on a rowing ergometer A 30-second test revealed strong correlations (r = −0.85 to −0.89) between various power metrics and performance in a 2000-meter rowing competition Notably, peak power explained approximately 76% of the variance in rowing time, underscoring the significance of this anaerobic phase in competitive rowing.

Treadmills

The treadmill enables users to walk or run at designated speeds while remaining stationary, facilitating easy connection to the spirometry system However, while it simulates walking or running, it does not fully replicate natural ambulation Research indicates that variations in air resistance between treadmill use and normal walking can reduce the energy expenditure associated with treadmill ambulation.

Motorized treadmills are commonly utilized for exercise testing and training, with workloads adjusted by changing speed or incline, reaching speeds of up to 12 miles per hour and grades of 25% They require users to support their own body weight, making the exercise "weight dependent." Treadmills can support individuals weighing up to 450 pounds, and their belt dimensions typically range from 16 to 22 inches in width and 45 to 60 inches in length, which is crucial for accommodating taller individuals or those with longer stride lengths Athletes favor larger treadmills, and many models feature handrails for added safety Some treadmills can measure heart rate through built-in sensors, although this can be challenging during high-intensity workouts While often used with metabolic systems, treadmills are large, difficult to transport, and can be expensive, especially those designed for athletes.

Cross-Country Ski Ergometers

Metabolic Rate During Swimming

Obtaining metabolic information during swimming is challenging due to the swimmer's movement and the risks associated with using electrical equipment in water Portable metabolic systems are essential in this context Four methods have been utilized to gather metabolic data: stationary swimming ergometers, swimming flumes, circular pools to mitigate turn-related issues, and backward extrapolation after swimming The stationary swimming ergometer has been in use for some time, where a swimmer is fitted with a belt connected to a pulley system that allows them to maintain a suspended weight This setup enables the measurement of expired gases through a breathing tube, allowing for the calculation of VO₂ using a standard metabolic system on the pool deck While effective, this method alters the swimmer's body position and dynamics, requiring them to exert more effort to maintain alignment.

FIGURE 5.3 Schematic of the side and top view of a swimming ergometer.

Since the early 1970s, swimming flumes have provided a unique training environment by recycling water currents past swimmers at a controlled velocity, allowing them to maintain a stationary position This setup enables accurate metabolic measurements similar to those obtained from swimming ergometers Unlike swim ergometers, swimming flumes allow athletes to use their natural swimming strokes in a more comfortable position However, the high cost of swimming flumes often exceeds the budgets of many athletic facilities.

Circular pools allow swimmers to swim continuously around a central platform housing a metabolic system, utilizing an arm with a breathing tube similar to a swim ergometer The swimmer's pace can be regulated by auditory signals or lights at the pool's bottom However, this setup alters the swimmer's body position, particularly affecting stroke mechanics, as one side of the body is engaged more than the other Despite their high cost, circular pools have effectively provided metabolic data In contrast, traditional swimming requires participants to navigate the pool's length, but current metabolic systems are inadequate for measuring these actions Additionally, using breathing apparatuses during swimming affects body position and increases resistance, leading to higher energy expenditure To address these challenges, researchers employ a backward extrapolation method using open-circuit spirometry, where swimmers complete a distance of 200–400 meters before quickly placing a breathing mask to measure VO₂ over three 20-second intervals, allowing for accurate calculations.

The result can be converted to kcal using the following formula: kcal/min = VO 2 (L/min) × 4.86 Kcal/L

Alternatively a curve can be constructed from the three 20-second VO 2 measures and extrapolated backward to what the VO 2 would have been during the last minute of swimming

The specificity of testing mode is crucial in athletic assessments, as an individual's responses to exercise tests can vary significantly based on the apparatus used Typically, maximal aerobic power is higher when measured on a treadmill compared to a cycle ergometer This difference arises because, during treadmill exercise, athletes must transport their body mass and engage a greater amount of active muscle mass, whereas cycling supports the body weight through the bike seat Faulkner et al highlighted that the increased VO₂max observed on treadmills is due to a larger stroke volume and enhanced muscle recruitment.

A study on sports nutrition and energy metabolism revealed that heart rates (HR) were higher during treadmill exercise compared to rowing at the same lactate levels, while maximal oxygen uptake (VO2max) was greater in rowing These variations were attributed to differences in posture and enhanced venous return during rowing Additionally, treadmill tests generally showed higher maximal aerobic power than swimming Notably, trained swimmers achieved higher values in swimming compared to cycling during maximal tests, whereas triathletes displayed superior maximal aerobic power in cycling than in swimming This underscores the significance of considering an athlete's training background when choosing the appropriate testing mode.

Maximal Metabolic Rate

Maximal metabolic rate, known as VO₂max, is influenced by the respiratory, cardiovascular, and muscle metabolic systems working together to generate energy Any dysfunction in these systems can restrict VO₂max; for instance, individuals with emphysema struggle to oxygenate their blood, hindering muscle energy production Similarly, a heart attack survivor may receive oxygen but face reduced blood pumping capacity, also limiting oxygen availability for muscle energy Sedentary, untrained individuals typically exhibit lower efficiencies across these systems, resulting in a compromised VO₂max compared to well-trained endurance athletes.

VO₂max, measured in milliliters per kilogram per minute (ml/kg/min), allows for effective comparison among individuals of varying sizes While it can also be expressed in absolute terms (liters per minute), this makes cross-size comparisons challenging since higher absolute values may merely indicate greater muscle mass Typically, larger individuals exhibit higher VO₂max in liters per minute due to increased muscle mass, but they tend to have lower values when expressed relative to body weight.

VO 2max when expressed per kilogram body mass For example, a football player may weigh 300 pounds (136 kg) and have 20% body fat His VO 2max expressed per

LO 2 /min may be 5 L/min, which is extremely high Yet when expressed per unit body mass, his VO 2max would only be 36.8 mL/kg/min, similar to a sedentary adult. The reason a larger individual has lower VO 2max when expressed per kilogram body mass, is that larger individuals have more supporting tissues (bone, tendon, adipose) that are not related to energy output The reverse is also true; smaller individuals have lower absolute VO 2max , but higher relative VO 2max than large individuals

To eliminate the influence of fat mass, some researchers have suggested expressing

VO2max per unit of fat-free mass (ml/kg FFM/min) is a valuable metric for assessing true gender differences in VO2max, as women typically have a higher fat mass due to genetic factors Generally, higher values of VO2max indicate better cardiovascular fitness.

VO₂max, measured in mL/kg/min or mL/kg FFM/min, indicates an individual's aerobic capacity For instance, a person with a VO₂max of 40 mL/kg/min can run at approximately 7 mph, while someone with a VO₂max of 60 mL/kg/min can reach speeds of 10.5 mph This highlights the significant advantage a high VO₂max provides to endurance athletes.

Maximal aerobic capacity, or VO₂max, is affected by various factors, including age, gender, and body composition Generally, VO₂max declines with age, leading to higher values in children compared to adults, partly due to their size-to-muscle mass ratio and the sedentary lifestyle of adults Adult men typically exhibit greater VO₂max than women, with average values of 40–45 ml/kg/min for men and 35–40 ml/kg/min for women These gender differences may stem from variations in body composition and hemoglobin concentrations, as women generally have a higher fat mass, which influences energy demands but not energy production When accounting for body fat, the differences in VO₂max between genders diminish significantly Men have a 10–20% higher hemoglobin concentration, enhancing their oxygen delivery to muscles Highly trained male endurance athletes can achieve VO₂max values exceeding 55 ml/kg/min, often reaching over 80 ml/kg/min, attributed to genetic factors and the adaptability of their respiratory, cardiovascular, and metabolic systems through intensive training In contrast, athletes engaged in anaerobic sports or resistance training typically have lower VO₂max than endurance athletes but higher than sedentary individuals.

FIGURE 5.4 Maximal aerobic power (VO 2max ) of various populations of elite athletes and normal adults These data are for men; women usually have lower values by approximately

Despite the VO2max levels of elite athletes remaining unchanged since 1960, endurance performances have significantly improved This enhancement can be attributed to advancements in training techniques, suggesting that factors beyond VO2max, such as anaerobic threshold and movement economy, are being optimized in endurance athletes.

Maximal oxygen uptake (VO₂max) is typically assessed through incremental exercise protocols that progressively increase work intensities while measuring VO₂ using open-circuit spirometry Various testing protocols and ergometers are available, with some practitioners opting for progressive speed during running or swimming The exercise mode should align with the athlete's sport for specificity; for instance, a trained runner may show lower VO₂max on a cycle ergometer compared to a treadmill There is no universal optimal test protocol, as the initial workloads should be low intensity (25–30% VO₂max) for warm-up, with each subsequent stage designed to prevent lactate build-up and premature fatigue Tests should aim to reach maximal capacity within 10–15 minutes, as shorter tests may be invalid due to lactate accumulation, while longer tests risk boredom or localized pain Consistency in testing protocols is essential for accurate performance comparisons.

VO 2max appears to have limits Data from the 1960s suggest that the zenith for

VO₂max is around 85 mL/kg/min, a figure supported by recent studies Despite this plateau in VO₂max levels, endurance performances continue to improve due to advancements in athletic equipment, such as lighter running shoes, reduced bicycle weights, modified swimming strokes, and ergonomically designed paddles for canoeing and kayaking However, these equipment enhancements alone do not fully explain the performance gains Therefore, it is likely that endurance training is affecting other critical factors, including anaerobic threshold and economy.

Anaerobic Threshold

The anaerobic threshold marks the transition from aerobic to anaerobic metabolism.

The anaerobic threshold is identified by measuring blood lactate levels during exercise, typically marked at a work rate, speed, metabolic rate, or heart rate when lactate reaches 4.0 mmol/L Commonly referred to as the ventilatory threshold, this term is used because it correlates closely with the lactate threshold and is simpler to measure.

The energy expenditure of athletes can be assessed without the need for blood samples Instead of directly measuring blood lactate levels at each stage, the anaerobic threshold is identified indirectly through methods used during progressive exercise testing.

1 Indirectly by a disproportionate rise in V E relative to VO 2 or VCO 2

2 A decrease in P ET O 2 with no change in P ET CO 2

3 A non-linear increase in V E /VO 2 relative to V E /VCO 2 65,66

When anaerobic metabolism surpasses a certain threshold, blood lactate accumulates, resulting in fatigue This lactate is buffered by bicarbonate (HCO₃⁻), which increases carbon dioxide (CO₂) production and causes metabolic acidosis due to excess hydrogen ions (H⁺) These physiological changes can be represented by specific equations.

Excess hydrogen ions (H+) and carbon dioxide (CO2) activate chemoreceptors, leading to increased ventilation beyond metabolic requirements This process effectively removes CO2 from the body, making VCO2 a valuable indirect marker for lactate production.

Identifying the anaerobic threshold (AT) is crucial for endurance athletes, as research indicates that AT can increase independently of maximal capacity This allows athletes to enhance performance by exercising at a higher percentage of VO₂max without the negative effects of lactic acid buildup Literature suggests that endurance athletes typically have AT levels exceeding 75% of VO₂max, potentially reaching up to 95%, while sprinters and college-aged individuals have lower AT levels of 60-70% and around 65% of VO₂max, respectively The differences in AT are attributed to enhanced lactate removal, increased mitochondrial function, and greater enzyme activity in trained individuals, enabling them to sustain higher intensities before relying on anaerobic energy sources However, periods of detraining can reverse these adaptations, causing AT to revert to pre-training levels Understanding one's AT is essential for effective training, as exercising just below this threshold allows athletes to maintain high intensity without lactate accumulation, leading to prolonged workouts and optimal aerobic training benefits.

Various techniques are employed to assess anaerobic threshold, with the graded exercise test on a treadmill or cycle ergometer being the most prevalent This test involves incrementally increasing exercise intensity at set intervals by adjusting the speed and incline on a treadmill or the resistance on a cycle ergometer.

Ventilatory measurements are taken during exercise tests, with blood lactate levels measured at each stage The anaerobic threshold (AT) is identified when ventilation (V_E) increases disproportionately to oxygen consumption (VO_2), typically represented on a graph with workload on the x-axis and V_E/VO_2 on the y-axis This threshold indicates a nonlinear rise in the graph Blood lactate levels can also be plotted against VO_2 or heart rate, with the point of curvilinear increase known as the lactate threshold or onset of blood lactate accumulation (OBLA), often marked at 4.0 mM/L, though it varies individually The AT can be expressed in absolute VO_2 (L/min), as a percentage of VO_2max, or in terms of heart rate, which is particularly relevant for athletes since heart rates are more easily monitored during training than VO_2.

To verify the accurate identification of the anaerobic threshold (AT), a second graded exercise test is typically conducted, where athletes perform exercises at varying intensities If the AT is correctly identified, the athlete's ventilation-to-oxygen consumption ratio (V E /VO 2) and blood lactate levels will remain stable at lower intensities, rise at the AT, and increase significantly at higher intensities Conversely, if these parameters do not show a marked increase, the AT has not been reached An alternative method for determining AT involves measuring running speed and corresponding heart rate, which is quick, straightforward, and can be executed outside a laboratory setting This method identifies the AT at the point where the speed-heart rate relationship becomes nonlinear, showing a strong correlation (r = 0.99) with AT measured via blood lactate, although some researchers have raised concerns about the reliability of this heart rate deflection in relation to the lactate threshold.

Economy of Human Movement

Economy refers to the energy expenditure required to cover a specific distance or maintain a certain speed, with athletes demonstrating good economy utilizing less oxygen at submaximal speeds This concept is crucial for prolonged exercise performance, as minimizing VO₂ helps preserve glycogen stores and delay fatigue Research indicates that endurance-trained runners exhibit lower oxygen uptake at a given pace compared to sprinters, with differences in energy cost potentially impacting performance over extended durations Variations in running economy can significantly influence outcomes in events like a 10K run, making this knowledge advantageous for endurance athletes such as runners, cyclists, swimmers, rowers, and paddlers Additionally, factors like gender affect economy, with women generally being less economical during high-speed running.

The energy expenditure of athletes can be influenced by various factors, including body composition, biomechanics, and training Effective muscle recruitment enhances performance economy, as repeated actions lead to better motor patterns and reduced extraneous muscle activity This is especially relevant in skill-based sports like swimming and canoeing Additionally, muscle fiber type plays a role, with Type I fibers offering greater mechanical efficiency for aerobic energy production compared to Type II fibers Physical attributes, such as leg length and upper body size, affect the number of strides or strokes needed, thereby impacting energy expenditure Equipment choices also matter; for instance, toe clips in cycling can enhance efficiency, while standing can decrease it However, the lack of sport-specific standards for measuring economy complicates comparisons, leading coaches and athletes to rely on repeated measures at various submaximal velocities to assess improvements in VO₂ per unit speed.

Resting Energy Expenditure

Understanding resting energy expenditure (REE) is crucial for athletes aiming to manage their weight, as it constitutes a significant part of daily energy expenditure Unlike basal metabolic rate (BMR), which represents the minimal energy needed for essential life functions in a completely rested state, REE reflects the energy required for normal body functions at rest Both REE and BMR are typically measured under similar conditions, with REE often being preferred due to its easier measurement process While the difference between BMR and REE is minimal, with REE measured after fasting and rest, both are expressed in kilocalories or kilojoules per hour, and individual rates can vary by ±20%.

Measurement of Resting Energy Expenditure

All calorimetry methods can be used to measure REE The procedure for REE involves obtaining two 5–7-minute continuous measures of VO 2 and VCO 2 , or one

In a controlled environment, individuals are measured for energy metabolism during a 15-minute collection period, discarding the initial 5 minutes Subjects lie supine for 30–45 minutes to ensure comfort, with spirometry equipment introduced to alleviate anxiety Following this rest, measurements are taken, often using a transparent hood or room calorimeter for more accurate basal metabolic rate (BMR) assessments Typically, BMR is measured over a 20–30-minute timeframe, contrasting with shorter 5–7-minute evaluations.

Estimating Resting Energy Expenditure (REE) can be complex due to the required equipment, time, and expertise Simplified methods utilize body mass, height, and age for calculations, with adult males averaging 1.0 kcal/kg/h and females 0.9 kcal/kg/h Energy expenditure is calculated by multiplying these constants by body mass The World Health Organization has established specific prediction equations based on age and gender, but discrepancies of over 15% exist among different estimation methods While most formulas consider gender and age, many overlook other significant factors that affect REE.

Factors Influencing REE

Daily Energy Expenditure of Athletes

Daily energy expenditure surpasses resting energy expenditure (REE) and varies based on lifestyle, occupation, and exercise Depending on their job, individuals can require 30–90% more energy than their REE For instance, those with sedentary jobs may need only 10–20% extra calories, while physically demanding occupations like roofing or bricklaying may necessitate an additional 80–90% On average, a college student consumes about 40–50% more calories daily than their REE, excluding exercise Generally, adults who engage in 30–45 minutes of exercise daily need only 10–14% more calories than what is required for rest and daily activities.

Athletes engaging in 3–5 hours of daily exercise require significantly more energy than their resting energy expenditure (REE) and lifestyle needs combined To address these increased demands, tables estimating energy expenditure for various activities have been created Specifically, Table 5.2 serves as a useful reference for determining the additional energy requirements of individuals training for specific sports, based on extensive research.

Energy needs vary significantly based on factors such as exercise duration, training intensity, and the athlete's size, age, and gender While some activities, like recreational basketball, may demand only a modest increase in energy, others, such as competitive endurance cycling or ultra-marathon running, can necessitate a substantial boost Utilizing measured resting energy expenditure (REE) can enhance the accuracy of these energy requirement estimates.

Understanding the resting energy expenditure (REE) allows for the calculation of total daily energy expenditure when combined with estimated lifestyle costs and exercise routines With this data, athletes, coaches, and clinicians can effectively assess the necessary energy consumption based on caloric intake.

TABLE 5.2 Energy Requirements of Various Sports Determined from Over 100 Sources

Cross-Country Runners 2600–3900 6.21–9.32 2500–3400 5.98–8.12 Cross-country Skiers 6000–15000 14.34–36.0 6569–8400 15.7–20.0

Long Distance Runners 2600–4000 6.21–9.56 2200–3500 5.26–8.36 Power Athletes* 2500–4000 5.98–9.56 - -

* power athletes = shotput, javelin, high jump, pole vault, divers7950_C005.fm Page 150 Wednesday, June 20, 2007 5:54 PM

To achieve the desired nutritional balance, a 20-year-old female runner weighing 112 pounds (∼51 kg) maintains her stable weight by balancing energy intake and expenditure Her resting energy expenditure (REE) is 1100 kcal per day, with an additional 330 kcal from her sedentary job During workouts, she burns approximately 840 kcal, resulting in a total energy expenditure of about 2270 kcal on training days and 1430 kcal on rest days To gain 5 pounds (2.267 kg) of muscle over the next 3 months, she would need to increase her caloric intake by roughly 100 kcal per day from carbohydrates or protein.

Weight gain = 2.267 kg = 2267 gm There are approximately 4 kcal/g of protein or carbohydrate

On workout days, her caloric intake should be approximately 2370 kcal, while on non-workout days, it should be around 1530 kcal To lose 5 pounds over the same period, she would need to reduce her daily energy intake by 101 kcal Although this is a theoretical example, various factors can affect total caloric needs Understanding the Resting Energy Expenditure (REE) and exercise Energy Expenditure (EE) allows coaches and clinicians to more accurately assess an athlete's nutritional requirements.

Summary

Endurance athletes can benefit from four key energy expenditure measures: maximal aerobic power (VO₂max), economy of movement, resting energy expenditure (REE), and estimates of anaerobic threshold (AT) While higher aerobic power is often linked to greater success in endurance sports, it is not the sole determinant of performance If two athletes possess identical aerobic power levels, the one with a higher anaerobic threshold or superior movement economy is more likely to excel.

Measuring energy expenditure is crucial for high-level endurance athletes, despite its complexity While direct calorimetry involves placing individuals in a closed chamber to directly measure heat production, it is impractical for athletes except for assessing resting metabolic rate In contrast, indirect calorimetry, which measures VO₂ and CO₂ production, is more suitable for athletes as it calculates energy use over short durations, such as minutes or hours This method has significantly advanced, enhancing its applicability for athletic performance assessment.

Sports nutrition plays a crucial role in understanding energy metabolism and exercise systems, enabling the measurement of metabolic rates during unhindered physical activity outside laboratory settings This method is particularly effective for assessing VO₂max, economy of motion, and estimating anaerobic thresholds To achieve accurate energy expenditure calculations, activities should be performed at low-to-moderate intensities in an aerobic state Currently, our ability to estimate the energy costs associated with very high-intensity exercise is limited, primarily due to the significant production of lactic acid during such activities.

Indirect calorimetry is not suitable for measuring energy expenditure over several days, leading to the development of doubly labeled water techniques This method, utilizing a double-isotope of water (²H₂¹⁸O), is ideal for assessing total energy expenditure over extended periods However, it cannot determine the specific energy cost of individual activities or test maximal aerobic power, anaerobic threshold, or economy of motion Consequently, indirect calorimetry remains the most effective method for measuring energy expenditure during specific activities, while doubly labeled water is best for estimating overall daily energy use Additionally, the high cost of doubly labeled water makes it impractical for routine use by athletes.

Understanding Resting Energy Expenditure (REE) is crucial for athletes seeking to manage their weight effectively, as it accounts for 50–65% of their daily energy expenditure REE is influenced by factors such as lean body mass, age, gender, size, climate, caloric intake, hormones, and exercise training While various methods exist to measure REE, portable indirect calorimetry systems are currently the most accessible and cost-effective To accurately estimate daily energy expenditure, athletes should consider their REE over 24 hours, lifestyle energy expenditure, and energy burned during exercise For endurance athletes, monitoring metabolic rate can enhance training programs, track performance, and evaluate potential As miniaturized metabolic systems become more available, the costs are expected to decrease, providing athletes with better access to these important measurements.

1 Young, D.S., Implementation of SI units for clinical laboratory data, Ann Intern Med 106, 14–129, 1987.

2 Schutz, Y., The basis of direct and indirect calorimetry and their potentials, Diabe- tes/Metabol Rev 11, 383–408, 1995.

3 Schutz, Y and Jéquier, E., Resting energy expenditure, thermic effect of food, and total energy expenditure In Handbook of Obesity, Bray, O.J., Bouchard, C., and James, W.P.T Eds., Marcel Dekker, Inc., New York, 1998, 433–455.

4 Consolazio, C.F., Johnson, R.E., and Pecora, L.J., Physiological Measurements of Metabolic Functions in Man, McGraw-Hill Book Company, New York, 1963, 1–98.

5 McArdle, W.D., Katch, F.I., and Katch, V.L., Exercise Physiology: Energy, Nutrition and Human Performance, Williams & Wilkins, Baltimore, 1996, 139–213.

6 Krogh, A and Lindhard, J., The relative value of fat and carbohydrate as sources of muscular energy, Biochem J 14, 290–363, 1920.

7 Bell, G.H., Emslie-Smith, D., and Paterson, C.R., Textbook of Physiology and Bio- chemistry, Churchill Livingstone, New York, 1976, 57–64.

8 Mellerowicz, H and Smodlaka, V.N., Ergometry: Basics of Medical Exercise Testing, Urban & Schwarzenberg: Munich, 1981, 1–23.

9 McLaughlin, J.E., King, G.A., Howley, E.T., Bassett, D.R., and Ainsworth, B.E., Validation of the Cosmed K4b2 portable metabolic system, Int J Sports Med 22, 280–284, 2001.

10 Harrell, J.S., McMurray, R.G., Baggett, C.D., Pennell, M.L., Pearce, P.F., and Bangdi- wala, S.I., Energy costs of physical activities in children and adolescents Med Sci Sports Exerc 37, 329–336, 2005.

11 Barbosa, T.M., Fernandes, R., Keskinen, K.L., Colaco, P., Cardoso, C., Silva, J., and Vilas-Boas, J.P., Evaluation of the Energy Expenditure in Competitive Swimming Strokes, Int J Sports Med Apr 11, Epub ahead of print, 2006

12 Duffield, R., Dawson, B., Pinnington, H.C., and Wong, P., Accuracy and reliability of a Cosmed K4b2 portable gas analysis system, J Sci Med Sport 7, 11–22, 2004.

13 Maiolo, C., Melchiorri, G., Iacopino, L., Masala, S., and De Lorenzo, A., Physical activity energy expenditure measured using a portable telemetric device in comparison with a mass spectrometer, Br J Sports Med 37, 445–447, 2003.

14 Strath, S.J., Bassett, D.R., Swartz, A.M., Thompson, D.L., Simultaneous heart rate- motion sensor technique to estimate energy expenditure, Med Sci Sports Exerc 33, 2118–2123, 2001

15 Bigard, A.X and Guezennec, C.Y., Evaluation of the Cosmed K2 telemetry system during exercise at moderate altitude, Med Sci Sports Exerc 27, 1333–1338, 1995

16 Gray, G.L., Matheson, G.O., and McKenzie, D.C., The metabolic cost of two kayaking techniques, Int J Sports Med 16, 250–254, 1995.

17 Smekal, G., Baron, R., Pokan, R., Dirninger, K., and Bachl, N., Metabolic and cardiorespiratory reactions in tennis players in laboratory testing and under sport- specific conditions, Wien Med Wochenschr 145, 611–615, 1995.

18 Zuntz, N and Schumburg, N.A.E.F., Studien zu Einer Pphysiologie des Macsches

19 Carpenter, T.M., Tables, Factors and Formulas for Computing Respiratory Exchange and Biological Transformations of Energy Carnegie Institution of Washington, Wash- ington, DC, 1964, 104.

20 Dill, D.B., The economy of muscular exercise Physiol Rev., 16, 263–291, 1936.

21 Bassett, D.R., Ainsworth, B.E., Swartz, A.M., Strath, S.J., O’Brien, W.L., and King, G.A., Validity of four motion sensors in measuring moderate intensity physical activity, Med Sci Sports Exerc 32, S471–480, 2000.

22 Klein, P.D., James, W.P.T., Wong, W.W., Irving, C.S., Murgatroyd, P.R., Cabrera, M., Dallosso, H.M., Klein, E.R., and Nichols, B.L., Calorimetric validation of the doubly labeled water method for determination of energy expenditure in man, Human Nutr Clin Nutr 38C, 95–106, 1984.

23 Schoeller, D.A., Energy expenditure from doubly labeled water: Some fundamental considerations in humans, Am J Clin Nutr 38, 999–1005, 1983.

24 Schoeller, D.A and Webb, P., Five-day comparison of doubly labeled water method with respiratory gas exchange, Am J Clin Nutr 40, 153–158, 1984.

25 Schoeller, D.A., Measurement of energy expenditure in free-living humans by using doubly labeled water, J Nutr 118, 1278–1289, 1988.

26 Wareham, N.J., Hennings, S.J., Prentice, A.M., and Day, N.E., Feasibility of heart- rate monitoring to estimate total level and pattern of energy expenditure in a population-based epidemiological study: The Ely young cohort feasibility study 1994–5.

27 Major P., Subtle physical activity poses a challenge to the study of heart rate Physiol Behav 63, 381–384, 1997.

28 Ott, A.E., Pate, R.R., Trost, S.G., Ward, D.S., and Saunders, R., The use of uniaxial and triaxial accelerometers to measure children’s free play physical activity, Pediatr Exerc Sci 12, 360–370, 2000.

29 Councilman, J.E., The Science of Swimming, Prentice Hall, Englewood Cliffs, 1968, 1–5.

30 Saitoh, M., Matsunaga, A., Kamiya, K., Ogura, M.N., Sakamoto, J., Yonezawa, R., Kasahara Y., Watanabe, H., and Masuda, T., Comparison of cardiovascular responses between upright and recumbent cycle ergometers in healthy young volunteers per- forming low-intensity exercise: Assessment of reliability of the oxygen uptake calculated by using the ACSM metabolic equation, Arch Phys Med Rehabil 86,1024–1029, 2005.

31 Paton, C.D and Hopkins, W.G., Tests of cycling performance, Sports Med 31, 489–496, 2001.

32 Knuttgen, H.G., Force, work, power and exercise, Med Sci Sports Exerc 10, 227–228, 1978.

33 American College of Sports Medicine ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription Baltimore:Williams & Wilkins, 1998.

34 MacDougall, J.D., Wenger, H.A., and Green, H.J., Physiological Testing of the High- Performance Athlete Champaign: Human Kinetics, 1991.

35 Howley, E.T and Franks, B.D., Health Fitness Instructor’s Handbook Champaign: Human Kinetics, 1997.

36 American College of Sports Medicine Guidelines for Exercise Testing and Prescrip- tion Physical Fitness Testing and Interpretation, 6th Edition, Baltimore: Lippincott Williams & Wilkins, 2000, pp 57–90

37 Zhang, Y.Y., Johnson, M.C., Chow, N., and Wasserman, K., Effect of exercise testing protocol on parameters of aerobic function, Med Sci Sports Exerc 23, 625–630, 1991.

38 Bernstein, I.A., Webber, O., and Woledge, R., An ergonomic comparison of rowing machine designs: Possible implications for safety, Br J Sports Med 36, 108–112, 2002.

39 Mahler, D.A., Andrea, B.E., and Andresen, D.C., Comparison of 6-min “all-out” and incremental exercise tests in elite oarsmen, Med Sci Sports Exerc 16, 567–571, 1984.

40 Schabort, E.J., Hawley, J.A., Hopkins, W.G., and Blum, H., High reliability of performance of well-trained rowers on a rowing ergometer, J Sports Sci 17, 627–632, 1999.

41 Riechman, S.E., Zoeller, R.F., Balasekaran, G., Goss, F.L., and Robertson, R.J., Prediction of 2000 m indoor rowing performance using a 30 s sprint and maximal oxygen uptake, J Sports Sci 20, 681–687, 2002.

42 Herk, H., Mader, A., Hess, G., Mucke, S., Muller, R., and Hollmann, W., Justification of the 4-mmol/l lactate threshold, Int J Sports Med 6, 117–130, 1985.

43 McMurray, R.G., Berry, M.J., Vann, R.T., Hardy, C.J., and Sheps, D.S., The effect of running in an outdoor environment on plasma beta endorphin, Ann Sports Med

44 Costill, D.L., Use of a swimming ergometer in physiological research, Res Quart.

45 McMurray, R.G., Effects of body position and immersion on recovery after swimming exercise, Res Quart 40, 738–742, 1969

46 Holmer, I., Physiology of swimming man Acta Physiol Scand Suppl 407, 1–55, 1974.

47 Pendergast, D.R., diPrampero, P.E., Craig, A.B., Wilson, D.R., and Rennie, D.W., Quantitative analysis of the front crawl in men and women, J Appl Physiol 43, 475–479, 1977.

48 Leger, L.A., Seliger, V and Brassard, L., Backward extrapolation of VO 2max values from the O 2 recovery curve, Med Sci Sports Exerc 12, 24–27, 1979.

49 Costill, D.L., Kovaleski, J., Porter, D., Kirwan, J., Fielding, R., and King, D., Energy expenditure during front crawl swimming: predicting success in middle distance events, Int J Sports Med 6, 266–270, 1985.

50 Astrand, P.O and Saltin, B., Maximal oxygen uptake and heart rate in various types of muscular activity, J Appl Physiol 16, 977–981, 1961.

51 Faulkner, J.A., Roberts, D.E., Elk, R.L., and Conway, J., Cardiovascular responses to submaximum and maximum effort cycling and running, J Appl Physiol 30, 457–461, 1971.

52 McArdle, W.D., Katch, F.I., and Pechar, G.S., Comparison of continuous and discontinuous treadmill and bicycle tests for max VO 2 , Med Sci Sports 5, 156–160, 1973.

53 Wicks, J.R., Sutton, J.R., Oldridge, N.B., and Jones, N.L., Comparison of the elec- trocardiographic changes induced by maximum exercise testing with treadmill and cycle ergometer, Circulation 57, 1066–1070, 1978.

54 Yoshiga, C.C and Higuchi, M., Heart rate is lower during ergometer rowing than during treadmill running, Eur J Appl Physiol 87, 97–100, 2002.

55 Roels, B., Schmitt, L., Libicz, S., Bentley, D., Richalet, J.P., and Millet, G., Specificity of VO 2max and the ventilatory threshold in free swimming and cycle ergometry: Comparison between triathletes and swimmers Br J Sports Med 39, 965–968, 2005.

56 Keller, B and Katch, F.I., It is not valid to adjust gender differences in aerobic capacity and strength for body mass or lean body mass, Med Sci Sports Exerc 23, S167, 1991.

57 Swain, D.P and Leutholtz, B.C., Metabolic Calculations Simplified Baltimore: Wil- liams & Wilkins, 1997.

58 Rowland T.W., Developmental Exercise Physiology Champaign: Human Kinetics, 1996.

59 Shvartz, E and Reibold, R.C., Aerobic fitness norms for males and females aged 6 to 75 years: A review, Aviat Space Environ Med 61, 3–11, 1990.

60 Saltin B and Astrand P.O., Maximal oxygen uptake of athletes, J Appl Physiol 23, 353– 358, 1967.

61 Rusko, H.K., Development of aerobic power in relation to age and training in cross- country skiers, Med Sci Sports Exerc 24, 1040–1047, 1992.

62 Beneke, R and Hutler, M., The effect of training on running economy and performance in recreational athletes, Med Sci Sports Exerc 37, 1794–1799, 2005.

63 Jones, A.M and Carter, H The effect of endurance training on parameters of aerobic fitness, Sports Med 29, 373–386, 2000.

64 Powers, S.K., Dodd, S., Deason, R., Byrd, R., and McKnight, T., Ventilatory threshold, running economy and distance running performance of trained athletes, Res Quart.

65 Ready, A.E and Quinney, H.A., Alterations in anaerobic threshold as the result of endurance training and detraining, Med Sci Sports Exerc 14, 292–296, 1982.

66 Wasserman, K., Whipp, B.J., Koyl, S.N., and Beaver, W.L., Anaerobic threshold and respiratory gas exchange during exercise, J Appl Physiol 35, 236–243, 1973.

67 Denis, C., Fouquet, R., Poty, P., Geyssant, A., and Lacour, J.R., Effects of 40 weeks of endurance training on anaerobic threshold, Int J Sports Med 3, 208–214, 1982.

68 Kohrt, W.M., O’Conner, J.S., and Skinner, J.S., Longitudinal assessment of responses by triathletes to swimming, cycling and running, Med Sci Sports Exerc 21, 569–575, 1989.

69 McLellan, T.M and Jacobs, I., Active recovery, endurance training, and the calculation of the individual anaerobic threshold, Med Sci Sports Exerc 21, 586–592, 1989.

70 Conconi, F., Ferrari, M., Ziglio, P.G., Droghetti, P., and Codeca, L., Determination of the anaerobic threshold by a noninvasive field test in runners, J Appl Physiol 52, 869–873, 1982.

71 Svedenhag, J and Sjodin, B., Maximal and submaximal oxygen uptakes and blood lactate levels in elite male middle- and long-distance runners, Int J Sports Med 5, 255–261, 1984.

72 Daniels, J and Daniels, N., Running economy of elite male and elite female runners, Med Sci Sports Exerc 24, 483–489, 1992.

73 Alexander, R.M., Walking and running, Am Scientist 72, 348–354, 1984.

74 Coyle, E.F., Sidossis, L.S., Horowitz, J.F and Beltz, J.D., Cycling efficiency is related to the percentage of type 1 muscle fiber, Med Sci Sports Exerc 24, 782–788, 1992.

75 Tanaka, K., Nakadomo, F., and Moritani, T., Effects of standing cycling and the use of toe stirrups on maximal oxygen uptake, Eur J Appl Physiol 56, 699–703, 1987.

76 Burfoot, A and Billing, B., The perfect pace Runner’s World, Nov, 1985, pp 39 +

77 Bursztein, S., Elwyn, D.H., Askanazi, J., and Kinney, J.M., Energy Metabolism, Indirect Calorimetry, and Nutrition Williams & Wilkins, Baltimore, 1989.

78 Matthews, C.E and Freedson, P.S., Field trial of a three-dimensional activity monitor: comparison with self report, Med Sci Sports Exerc 27, 1071–1078, 1995.

79 Arciero, P.J., Goran, M.I., and Poehlman E.T Resting metabolic rate in lower in women than men, J Appl Physiol 75, 2514–2520, 1993.

80 National Research Council Recommended Dietary Allowances 10 th edition, National Academy Press, Washington DC, 1989.

81 Altman, P.L and Dittmer, D.S., Metabolism Fed Am Soc Exper Biol., Bethesda,

82 Horton, T.J., and Geissler, C.A., Effects of habitual exercise on daily energy expenditure and metabolic rate during standardized activity, Am J Clin Nutr 59, 13–19, 1994.

83 Toth, M.J., and Poehlman, E.T., Effect of exercise on daily energy expenditure, Nutr Rev 54, S140–148, 1996.

84 Jacobs, I., Martineau, L., and Vallerand, A.L., Thermoregulatory thermogenesis in humans during cold exposure, Exerc Sport Sci Rev 22, 221–250, 1994.

85 Lammert, O and Hansen, E.S., Effects of excessive caloric intake and caloric restric- tion on body weight and energy expenditure at rest and light exercise, Acta Physiol Scand, 114, 135–141, 1982.

86 LeBlanc, J and Mercier, I., Components of postprandial thermogenesis in relation to meal frequency in humans, Canad J Physiol Pharm., 71, 879–883, 1993.

87 Miller, D.S., Gluttony 2: Thermogenesis in overeating man, Am J Clin Nutr 20, 1233–1239, 1967

88 Verboeket-Van de Venne, W.P.H.G., Westerterp, K.R., and Kester, A.D.M., Effect of the pattern of food intake on human energy metabolism, Br J Nutr 70, 103–115, 1993.

89 Zahorska-Markiewicz, B., Thermic effects of food and exercise in obesity, Eur J Appl Physiol 44, 231–235, 1980.

90 Shetty, P.S., Jung, R.T., James, W.P., Barrand, M.A., and Callingham, B.A., Post- prandial thermogenesis in obesity, Clin Sci 60, 519–525, 1981.

91 Poehlman, E.T., Melby, C.L and Badylek, S.F., Resting metabolic rate and post prandial thermogenesis in highly trained and untrained males, Am J Clin Nutr 47, 793–798, 1988.

92 Horton, E.S., Metabolic aspects of exercise and weight reduction, Med Sci Sports Exerc 18, 10–18, 1986.

93 Tremblay, A.E., Fontaine, E., Poehlman, E.T., Mitchell, D., Perron, L., and Bouchard, C., The effect of exercise-training on resting metabolic rate in lean and moderately obese individuals, Int J Obes 10, 511–517, 1986.

94 Davis, J.R., Tagiaferro, A.R., Kertzer R., Gerardo, T., Nichols, J., and Wheeler, J., Variation in dietary-induced thermogenesis and body fatness with aerobic capacity, Eur J Appl Physiol 50, 319–329, 1983.

95 Wilmore, J.H., Stanforth, P.R., Hudspeth, L.A., Gagnon, J., Warwick Daw, E., Leon, A.C., Rao, D.C., Skinner, J.S., and Bouchard, C., Alterations in resting metabolic rate as a consequence of 20 wk of endurance training: the Heritage Family Study,

96 Dolezal, B.A and Potteiger, J.A., Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals, J Appl Physiol 85, 695–700, 1998.

97 Lawson, S., Webster, J.D., Pacy, P.J., and Garrow, J.S., Effect of a 10-week aerobic exercise programme on metabolic rate, body composition and fitness in lean sedentary females, Brit J Clin Pract 41, 684–688, 1987.

98 Thorbek, G., Chwalibog, A., Jakobsen, K., and Henckel, S., Heat production and quantitative oxidation of nutrients by physically active humans, Ann Nutr Metabol

99 Ainsworth, B.E., Haskell, W.L., Whitt, M.C., Irwin, M.L., Swartz, A.M., Strath, S.J., O’Brien, W.L., Bassett, D.R., Schmitz, K.H., Emplaincourt, P.O., Jacob, D.R., and Leon, A.S., Compendium of physical activities: an update of activity codes and MET intensities, Med Sci Sports Exerc 32, S498–S504, 2000.

100 Short, S.H and Short, W.R., Four-year study of university athletes' dietary intake, J

6 The Measurement of Energy Expenditure and Physical Activity

Kelley K Pettee, Catrine Tudor-Locke, and Barbara E Ainsworth

II Definitions 160 III Conceptual Framework for Quantifying Energy Expenditure 164

IV Methods of Assessing Physical Activity and Energy Expenditure 165

1 Direct Measures of Energy Expenditure 167

2 Indirect Measures of Energy Expenditure 169

1 Direct Measures of Physical Activity 170

2 Indirect Measures of Physical Activity 175

Engaging in regular, moderate- to high-intensity physical activity offers significant health and performance benefits The physiological adaptations resulting from such activities depend on the frequency, duration, and intensity of the exercise This relationship is measured through energy expenditure (EE), which comprises energy used at rest (resting metabolic rate), during digestion (thermic effect of food), and during physical activity While resting metabolic rate constitutes the majority of daily EE, variations in activity-related EE have the most substantial impact on overall energy expenditure.

Sports nutrition plays a crucial role in energy metabolism and exercise, highlighting the variability in energy requirements among individuals and groups A 2000 position statement on nutrition and athletic performance underscored the importance of balancing energy intake with activity-related energy expenditure (EE) to improve athletic performance, sustain total and lean body mass, regulate metabolic and endocrine factors that control energy stores, and facilitate recovery between exercise sessions.

Accurately aligning athletes' energy intake with their energy expenditure (EE) necessitates effective methods for quantifying physical activity and exercise patterns Given the complexity of physical activity as a multidimensional behavior, precise measurement poses significant challenges, particularly for free-living individuals Cost-effective and reliable indirect methods for assessing activity-related EE are essential in addressing the energy needs of athletes This chapter aims to review the current techniques for quantifying free-living physical activity-related EE, starting with key terminology and a conceptual framework that will inform the discussion It will then focus on measurement techniques, particularly field methods suitable for evaluating activity-related EE in athletic populations.

To effectively operationalize constructs like cardiorespiratory fitness into measurable variables such as maximal oxygen consumption (VO₂max), it is essential to establish precise conceptual definitions The interchangeable use of different terms related to physical activity and energy expenditure (EE) by researchers has led to confusion and inconsistent study designs, hindering inter-study comparisons and standardized measurement practices Efforts to standardize terminology aim to create a universal framework for defining constructs, facilitating the operationalization of variables and enabling more accurate data interpretations and comparisons in studies linking physical activity to health and performance outcomes.

Physical activity and energy expenditure (EE) are distinct concepts, with physical activity defined as body movement resulting from skeletal muscle contraction, which leads to EE Various categories of physical activity exist and may overlap based on individual motivations For instance, a brisk walk may serve as transportation for one person while being part of an exercise regimen for another focused on managing blood pressure Additionally, exercise training and competitive sports represent a specialized subset of physical activity aimed at improving physical fitness or athletic performance.

The Measurement of Energy Expenditure and Physical Activity 161

TABLE 6.1 Definitions of Terms Related to the Measurement of Energy Expenditure and Physical Activity

Energy The capacity to do work.

Energy expenditure refers to the amount of energy required for biological processes Physical activity involves bodily movements generated by skeletal muscle contractions, which significantly elevate energy expenditure.

Physical Fitness A set of attributes (e.g., muscle strength and endurance, cardiorespiratory, flexibility, etc.) that people have to achieve that relate to the ability to perform physical activity.

Exercise Planned, structured, and repetitive bodily movement done to improve or maintain one or more components of physical fitness Exercise is a specific sub-category of physical activity.

Calorimetry methods are utilized to assess the rate and amount of energy expenditure both at rest and during physical activity A calorie is defined as the unit of energy needed to increase the temperature of 1 gram of water by 1 °C.

Kilojoules (kj) The unit of energy in the International System of Units 1,000

The Metabolic Equivalent (MET) is a unit that estimates the metabolic cost of physical activity, specifically oxygen consumption One MET is defined as the resting metabolic rate, which is approximately 3.5 ml O₂ per kg per minute or 1 kcal per kg per hour.

Duration The dimension of physical activity referring to the amount of time an activity is performed.

Frequency The dimension of physical activity referring to how often an activity is performed.

Intensity The dimension of physical activity referring to the rate of energy expenditure while the activity is performed.

Hours/Minutes Typical units of time used in quantifying the rate of energy expenditure or the period of physical activity measurement (e.g., kcal per minute or kcalãmin –1 ).

Tiêu đề	Energy Expenditure of Athletes
Tác giả	Robert G. McMurray, Kristin S. Ondrak
Trường học	Unknown University
Chuyên ngành	Sports Nutrition, Energy Metabolism, and Exercise
Thể loại	Lecture Notes/Document
Năm xuất bản	2007
Thành phố	Unknown City

Định dạng
Số trang	150
Dung lượng	10,74 MB