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November 16, 2021

Understanding Mechanical Tension, Part I: What Is Mechanical Tension?

It’s well-established that mechanical tension is the primary mechanism responsible for muscle hypertrophy (i.e., increases in muscle size). Simply stated, mechanical tension can be defined as the stress applied to a muscle, generally (although not exclusively) from an external resistance. Resistance can be applied to the muscle in various forms including but not limited to free weights, cable pulleys, pneumatics, hydraulics and body weight.

Here’s how things play out in practice. Let’s say you perform a set of dumbbell arm curls. During each repetition, the imposed load from the dumbbells place a stress on your arm flexors (i.e. biceps brachii, etc). Receptors in the working muscle fibers (i.e. mechanoreceptors) sense the applied forces and consequently convert the associated mechanical signals into chemical signals via a phenomenon called mechanotransduction. A cascade of intracellular (i.e. within the muscle fiber) enzymes then facilitate anabolic processes from these chemical signals, which drives the synthesis of proteins that build muscle. Numerous anabolic and catabolic pathways have been identified, and the extent of their activation/de-activation ultimately determines how much muscle you build.

Based on the aforementioned information, it may seem that using very heavy weights would necessarily be ideal for maximizing muscle mass; the heavier the better. After all, heavier loads impose greater forces on muscles, and thus there theoretically should be higher levels of mechanical tension created during such training, right? Well, if that were in fact the case, then powerlifting routines would be optimal for bodybuilding. Both controlled research and anecdotal experience in the field tell us that’s not the case.

How can this be?

Intrigued? Then stay tuned for Part 2 of this series, which will delve into the nuances of mechanical tension and discuss why the topic is much more complex than simply focusing on the absolute amount of weight lifted.