Mechanisms of Hypertrophy
So far we’ve discussed the benefits of strength training, what rep ranges you should use for your goals, and different types of progressive overload. In all these videos, we’ve mentioned muscle hypertrophy regularly, which simply refers to increasing the size of muscle fibers, which in turn, increases the size of muscles. Bigger muscles mean more strength. Yes, there is a difference between myofibrillar and sarcoplasmic hypertrophy, but we’re not going to go into all that. For now, let’s say that muscle hypertrophy is a good thing for strength, athleticism, and longevity. Although it’s not the only reason to strength train and I would argue, maybe not even the most important reason, it is an important one and so we’ll take it as a given that muscle hypertrophy is good, so let’s talk about the ways to increase it.
Mechanical Tension:
The first way is through mechanical tension. Lifting something heavy produces mechanical tension in muscle fibers and this tensile force makes them adapt. This stress doesn’t necessarily have to result in muscle damage - which will be discussed below - in order to stimulate growth and it might just be that this tension signals to the body that these fibers need to be bigger in order to handle this stimulus. As discussed in the progressive overload video, this stimulus should be increased in small increments in order to get the most out of the subsequent hormone response and muscle protein synthesis. A lot of the specifics here are not well understood, but there is certainly a correlation between lifting heavy and muscle growth - so making this a priority in your training is important.
Metabolic Stress:
The second way is through metabolic stress. Lifting something moderately heavy, but more times and with shorter rest periods puts metabolic stress on the muscle cells. Metabolic stress occurs from the production of metabolites, like lactic acid, the lack of oxygen in muscle fibers, an increase in reactive oxygen species, and cell swelling. All these things increase hormonal signaling for important substances like testosterone and growth hormone, which in turn increases muscle protein synthesis and thus the size of muscle cells. In some research this increase in size is consistent with the increase achieved by lifting heavier weights through mechanical tension. So here, lower weight and higher reps are your friend.
Muscle Damage:
Muscle damage gets a mention because it's talked about a lot in this hypertrophy conversation, but it seems like that might not actually cause muscle growth. Lifting something heavy and prolonging the eccentric phase, otherwise known as the muscle lengthening phase of a movement (think going down in a squat or lowering down in a push up), can produce a lot of muscle damage. Meaning small tears to the muscle fibers. This has been proposed as a driver of hypertrophy, but it seems that hypertrophy occurs independent of muscle damage and therefore has been called into question as a driver of hypertrophy by lots of researchers that know a lot more about this subject than me. I think it suffices to say, that even if there were a benefit to damaging muscle fibers, you’d want to use this sparingly as this is also the most likely reason for muscle soreness. Luckily, plenty of strength and hypertrophy can be achieved without muscle damage and therefore it should not be a goal of strength training. Being sore is not fun and it really seems it also provides no real benefit, which is definitely a relief. Hahaha.
Take Away:
The takeaway here is that increasing muscle hypertrophy is good for strength and longevity. In order to increase muscle size, your strength training workouts should combine mechanical tension and metabolic stress. You should take advantage of both these drivers of hypertrophy to work different mechanisms that lead to our desired outcome. Loading some exercises up heavy and doing sets of 8 to 12 reps will produce mechanical tension and reducing load and increasing reps to 12 to 15 will produce metabolic stress. This should all be done in a progressive fashion so that optimal adaptation occurs and muscle growth is stimulated through protein synthesis, which I’ll discuss in my next video.
TL;DR Video Explanation
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