Last month, I wrote a review for Greg Nuckols titled Training for Hypertrophy: The Case Against Muscle Damage. Today, I’d like to update and expand on that review. I’ll add a bit of evidence in favour of the “muscle damage” theory of muscle hypertrophy, to provide a more balanced view. Next, we’ll see what actually builds muscle (since muscle damage doesn’t seem to).
Evidence against muscle damage
To review, the evidence against muscle damage can be summed up as:
- Cardio (especially downhill running): damage without hypertrophy (Brentano and Kruel, 2011).
- Studies on blood-flow-restricted training: hypertrophy without damage (Lixandrão et al. 2018; Loenneke et al. 2014; Pearson and Hussain, 2015)
- Studies on beginners: more damage without more hypertrophy (Flann et al. 2011; Damas et al. 2016)
- Studies on anti-inflammatory drugs like ibuprofen: less inflammation, but just as much hypertrophy (Juneau, 2018)
On that last point, I want to highlight the work of Damas et al. (2016). They found that myofibrillar (muscle) protein synthesis was correlated with muscle hypertrophy in beginners only after 3 weeks of training, when muscle damage decreased.
In other words, when beginners start out, they get more damage, but that damage doesn’t seem to build muscle. And when damage goes down, you start seeing a strong positive correlation between muscle protein synthesis and muscle hypertrophy (r ≈ 0.9, and significant). By contrast, in the beginning, the correlation is actually negative (r ≈ -0.2 to -0.6), and not significant.
Evidence in favour of muscle damage
Schoenfeld (2016) recaps why muscle damage is theorised to enchance muscle hypertrophy. The four main mechanisms are:
- Satellite cell activity
- IGF-1 production
- Cell swelling
Expert reviews on muscle hypertrophy and muscle damage
In 2018, Damas et al. (2018) wrote that:
“Muscle damage is not the process that mediates or potentiates resistance training-induced muscle hypertrophy”.
Schoenfeld and Contreras (2018) responded in a letter to the editor. They concluded that:
“The question at hand is not whether muscle damage is the primary driver of hypertrophy; clearly it is not as compelling evidence indicates mechanical stress is predominant in this regard. The relevant question is whether muscle damage may enhance the hypertrophic response to regimented RT over time. And to this question, we contend that the current body of evidence is not sufficient to draw conclusions with any degree of confidence.”
Damas et al. (2018) replied. They concluded that:
“Based on current evidence the ball is on the other side of the court, i.e. the hypothesis of damage having a minor (or even large) role in explaining or potentiating muscle hypertrophy is speculative at this point.”
My take on muscle hypertrophy and muscle damage
Overall, this evidence leads me to conclude that damage may be be correlated to hypertrophy, without causing it. In other words:
- You lift
- It causes damage
- It causes something else
- That something else causes hypertrophy
How can you hypertrophy muscle then?
According to Schoenfeld (2016): “Mechanical tension may be the most important factor in training-induced muscle hypertrophy.” In animal models, it was found that peak tension and time under tension were important factors in stimulating hypertrophy, namely via mTOR, p70S6k and a process called “mechanotransduction”.
Think about it: what happens when you remove all tension? Well, you lose muscle mass quickly. In fact, according to NASA: “Studies have shown that astronauts experience up to a 20 percent loss of muscle mass on spaceflights lasting five to 11 days.”
20% in 5-11 days! That’s huge, and the kind of strong effect I like to see as an epidemiologist. Last, in terms of muscle hypertrophy, there is also something to be said for metabolic stress, but I’ll keep that one for another time.
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Muscle hypertrophy without muscle damage in concentric-only studies (https://www.ncbi.nlm.nih.gov/pubmed/28321637).