Your Evidence based guide to building muscle (Part 1)

What causes muscle growth?

This is your ultimate guide to building muscle based on the best evidence we currently have. While there is so much nuance and so many conflicting studies it is nearly impossible to say anything with definitive authority, the following are principles that almost everyone in this field would agree on. Debates happen around the margins for sure, but unless you are a competitive bodybuilder, the following series will serve as a guide to 99% of what you could ever want to know about building muscle.

First off, let’s talk about how muscle growth actually occurs, because the latest evidence tells a story very different from what we thought we knew for a long time. Colloquially we like to say that ‘muscle is broken down and built back up,’ that you need to damage the muscle for it to grow. Although microtears and microtrauma to the muscle is present after a resistance training session, the best evidence we have suggests that this is not causative of muscle growth, but a byproduct. Soreness is not a good proxy for the effectiveness of your workout because the soreness we feel is actually a byproduct of damage not to the muscle itself, but fascia, which is a web-like substance running between your muscle and your skin. 

So if muscle damage is thought not to be an important factor in muscle growth, then what is? We are left with two plausible explanations. The less important of the two is referred to as metabolic stress. For a long time, the burning sensation that you feel in a muscle when exercising was thought to be lactic acid, but this is not true. Lactic acid is simply not present in the body. When your body needs to produce energy quickly it produces lactate, and is accompanied by the accumulation of hydrogen ions. It is the hydrogen ions accumulating in the environment local to the muscle that leads to that burning sensation. The production of these hydrogen ions and other byproducts of these energy production processes, is thought to be a significant stimulus for muscle growth. The ‘pump,’ that temporary enlargement of the muscle due to the capture and trapping of additional blood is also thought to be a powerful growth signal. 

But what is thought to be much more important than the first two potential causes of muscle growth is called mechanical tension, which affects your muscles at the level of their DNA. For a muscle to contract, the two ends of a muscle fiber pull closer together. Contract your bicep right now and you will feel how the muscle pulls on the tendon in your elbow joint, closing the space between your forearm and arm bone, your humerus. Within your bicep you have millions of individual muscle fibers, all of which will shorten when you contract that muscle. Take a set of bicep curls to failure and eventually more and more of those fibers will start contracting, and contracting harder and harder until they give up and the weight drops. It is through this process of the involuntary slowdown of the contraction that stimulates a process called mechanical tension, which works to send a powerful signal resulting in changes to your DNA. This process boosts Muscle Protein Synthesis, a hormonally driven process that decides whether your body is going to build new muscle, incredibly powerfully. The best assessment of exercise physiologists right now is that how much mechanical tension you can create in a muscle consistently over years has the biggest impact on whether that muscle will grow or not.