15 hypertrophy training mechanisms

The Lesson •The hypertrophy stimulus •Mechanisms of hypertrophy •How a muscle contracts •Types of muscle growth •How hypertrophy mechanisms relate to training •The variables to mani

Hypertrophy Training

Mechanisms of hypertrophy and application to training

UNIVERSITY

The Lesson

•The hypertrophy stimulus

•Mechanisms of hypertrophy

•How a muscle contracts

•Types of muscle growth

•How hypertrophy mechanisms relate to training

•The variables to manipulate in training

Stimulus to Fatigue

Overload: Acute disruption to homeostasis ie resistance training stress Adaptation: Process leading to functional improvement in

performance

Fatigue: reduction in the capacity to produce performance ie strength

(fitness)

Recovery: return to previous performance levels or better prior to

disruption

We want the RIGHT amount of stimulus to create a hypertrophy

adaptation! Then manage fatigue to create another overloading

hypertrophy stimulus again

Fitness Fatigue Model

Fitness (gains)

Performance

Fatigue

Time

Training

Overload

Stimulus

Recovery

What is the Hypertrophy Stimulus?

Initial Stimulus > Molecular Signaling > muscle protein synthesis

Initial Stimulus:

1 Mechanical Tension (Primary): mechanoreceptors within the

muscle sensitive to tension magnitude and duration at the fiber level

2 Metabolic Stress: accumulation of metabolites during training (lactate, H+, inorganic phosphates) generating fatigue

3 Muscle Damage: Disruption to muscle fiber structure

All 3 occur simultaneously at varying degrees and metabolic stress and muscle damage may be more related to effects of imposed mechanical tension on fibers

Potentials for Metabolic Stress and Muscle Damage

Metabolic Stress

Increased fiber recruitment

Increased myokine production

Increased cell swelling

Increased GH and testosterone levels

Concentric muscle contractions most energetically demanding

Higher repetition training, closer to failure, BFR, Super sets, drop sets

*additive effective to hypertrophy still uncertain

Muscle Damage

Increased inflammatory initiation

Satellite cell activity

Cell swelling

Too much damage limits hypertrophy

Eccentric muscle contraction most damaging

*Side effect of tension forces from contraction

Types of Hypertrophy

Muscle hyperplasia: increase in muscle cell number, evidence limited and not a primary contributor to growth

Myofibrillar hypertrophy: increase in size and amount of contractile elements of skeletal muscle

Sarcoplasmic hypertrophy: increase in all cellular components

(ribosomes, anerobic metabolism enzymes, T-tubules, etc)

Myofibrillar, fiber #

increase, sarcoplasm

unchanged

Sarcoplasmic, sarcoplasm increases, fiber #

unchanged

How Does a Muscle Produce Tension/Contract?

Muscle contracts (shortens and lengthens) by sliding filaments (actin and myosin) binding together and pulling the sarcomere closer together

Motor units are the nerve cells and muscle fibers they innervate You have small and large motor units that can innervate 2-3 fibers or up to 1000s of fibers

What Determines Level of Tension in a

Muscle?

More External Resistance DOES NOT mean more internal tension

1 Size Principle: Recruit low and high threshold motor units to have all fibers exposed to tension The motor units are activated in order from small (low threshold) to large (high threshold)

depending on the amount of force needed and rate of force

“Henneman’s Size Principle”

2 Force-Velocity Relationship: The fibers then must be contracted at highest forces possible which also means slow velocities as slow velocities allow for more binding of actin and myosin filaments

3 Length-tension Relationship: muscles produce more force at

certain lengths More force is produced at longer muscle length Long muscle lengths also add a passive force from the “stretch tension” add to the active tension of a muscle contracting

4 Internal moment arm: The leverage of a muscle on a joint

determines degree of force needed to create torque at the joint

5 Fatigue: Causes early recruitment of high threshold motor units, reduces contraction ability of fibers requiring unfatigued fibers to contribute to force production

How Do You Create High Tensions Lifting

Weights?

Hard sets! A set must be very challenging and close to muscular failure

to recruit high threshold motor units (HTMU) and maximal tension via slow velocities

Heavy loads >85% (1-5RM) will recruit HTMU early in the set and all reps will be stimulating via high tension

Light (15+ 1RM ) and moderate (6-15RM) loads will recruit HTMU later

in the set as fatigue is generated and more fibers must contribute to keep muscle contraction occurring So, the later reps will be more stimulating and early reps not as much

This gives notion to the idea of “effective” or “stimulating reps”

One set provides a level of magnitude of tension that increases as we approach muscular failure and the muscle fibers have a longer time duration of exposure to that tension

Is There a Dosage of Tension For Growth?

Hypertrophy

Too Many Sets Optimal Sets

No Sets Atrophy

RATE OF

GROWTH

Volume Dosage Inverse U shaped Curve

Programming Variables for Tension Stimulus

Volume: Dosage of stimulus = # of hard sets

Intensity: Degree of stimulus magnitude = % 1 rep max and proximity

to failure

Frequency: Organization of stimulus = training split

Exercise Selection: Regional stimulus= movement pattern choice and

muscles it involves

Exercise execution and tempo: Focus of stimulus = way in which you

move during a repetition and intention

Exercise order: Stimulus sequence and effectiveness = order of

movements

Rest periods: Removal of stimulus= time between sets

Summary

The main driving mechanism for hypertrophy is mechanical tension

Mechanical tension can be created with heavy and light load sets taken near or at proximity to muscular failure

A certain number of “hard sets” is needed to optimize hypertrophy

Metabolic stress and muscle damage may be additive factors to hypertrophy, but may also only be resultant factors of mechanical tension

Programming variables for hypertrophy revolve around how we will apply tension (stimulus) in an organized manner

Let’s Program!

Reference

Encyclopedia Britannica striated muscle; human biceps muscle

Available at:

https://www.britannica.com/science/muscle#/media/1/398553/4693

9 Access Date: July 28th 2020

Schoenfeld B Science and Development of Muscle Hypertrophy

Champaign, IL: Human Kinetics; 2021

Beardsley, C Hypertrophy: Muscle fiber growth caused by mechanical tension Strength and Conditioning Research Limited, 1 edition; 2019