076 Mechanisms of Muscle Growth

We care about hypertrophy as CrossFitters because lean body mass is highly correlated with strength in the advanced and within individuals over time.

There are two mechanisms of hypertrophy that appear to be primary:
1. Mechanical Tension
2. Metabolic Stress

CrossFitters, generally, should emphasize strategies that optimize for mechanical tension because of:
1. The effect that lower rep ranges have on strength
2. Access to equipment

There are other, what we might call “side effects” of hypertrophy training, that are not necessary for hypertrophy but often come along with hypertrophy training:
1. Muscle Damage (EIMD in research terms)
2. Muscle Soreness (DOMS in research terms)

Mechanical Tension

Any weight above your 30RM is enough tension to create a robust muscle growth response.

On the other hand, any weight below your 30RM is usually not enough tension to create a robust muscle growth response.  

Metabolic Stress

Metabolites and cell swelling appear to directly trigger muscle growth. 

In the gym, this is indicated by the burn and the pump that most people experience with higher rep ranges. 

This mechanism does not appear to be essential. You can get a great hypertrophic stimulus with just mechanical tension (e.g. sets in the 5-10 rep range).

Practical Application for CrossFitters

1. CrossFitters ought to bias lower rep ranges, which emphasize mechanical tension as a hypertrophic mechanism, and have a bigger effect on strength. 

2. CrossFitters in many cases ought to bias lower rep ranges, which emphasize mechanical tension, because most of the time they do not have access to bodybuilding machines. 

3. CrossFitters should select exercises so that their strength transfers to sport-specific skills. 

When you train this way, you will inevitably experience muscle damage and muscle soreness. 

Muscle Damage

Exercise can result in localized damage to muscle tissue.

Here’s what causes muscle damage:
1. New Exercises 
2. Low Training Status, for whom everything is a new exercise
3. Tension, volume, proximity to failure 

There appears to be a sweet spot. 

Avoiding damage altogether may result in less growth. 

Too much muscle damage could be detrimental to growth. 

Theoretically, we have to recover from the damage before the cells can grow. 

This is why I generally don’t like CrossFitters dropping in on classes, or doing Murph on Memorial Day, these things usually introduce novel stimuli that cause lots of muscle damage, fatigue, soreness and often interfere with the progression of that cycle.

Muscle Soreness

One would think that muscle damage and muscle soreness correlate perfectly. They do not. 

Muscle soreness could be caused by a combination of neural mechanisms, stress on fascia or stress on connective tissue. We don’t really know. 

You can have damage without soreness.  

BUT, soreness probably does mean some amount of damage. 

In short, getting really sore doesn’t mean you got a great stimulus. 

You mostly get sore from novel stimuli. 

This is one of the reasons that CrossFitters with lots of variety in their programs can be sore all the time without achieving very much, if any muscle growth. 

In summary, when it comes to side effects: 

Performance is probably the best indicator we have in the field of both damage and neuromuscular fatigue. 

If your performance is improving, hold or increase volume. 

If your performance is stable, hold volume and improve support. 

If your performance is falling, reduce volume.