How-to: Muscle Building Mechanisms

Each exercise we choose in a workout routine usually stands out for the feeling it elicits. Some things burn, some things stretch, and some things just feel outright heavy. Usually, a combination of these things leaves the muscle you’re targeting exhausted by the end of the session and that’s how most people register that the job is done.

There’s a lot of vagueness to that style of training, and that lack of intentional decision making often leaves people confused about plateaus or a lack of progress despite genuine hard effort in their workouts.

To lend clarity, some background information on how your muscle responds to exercise can dramatically improve your workout efficiency.

The body is stimulated to change, adapt, or otherwise improve from one training session to the next because of the physical challenge you demanded of it. If you lifted something heavy, the body is triggered to get stronger to prevent that weight from being such an enormous challenge the next time. If you run some sprints until you’re too fatigued to continue, your body will adapt in such a way to make your heart, lungs, and energy utilization (carbohydrate, fat, etc.) during exercise more efficient to keep you going longer the next time.

When it comes to building muscle, there are three main mechanisms that seem to be the standout reasons for the body to want to grow. These are mechanical tension, metabolic stress, and muscle damage.

Mechanical Tension

Mechanical tension experienced by the workout muscle group appears to be the main trigger for growth. Mechanical tension is an expression of how many muscle fibres were required in order to complete the set of exercise, but more specifically, how fatiguing the set was to the muscle fibres that were recruited. In general, a muscle that has been taken to near failure (or near exhaustion) is a good measuring device for generating enough mechanical tension to cause growth. You know you’re there when the weight starts to feel progressively heavier throughout the set and your repetition speed slows to a crawl as the muscle fibres exhaust.

Metabolic Stress

The second mechanism, metabolic stress, is the experience of the working muscle fully exhausting its readily available energy stores during the particular set of exercise. The key difference between resistance training and, for example, long distance cardio, is that the muscles working during resistance training are not in a position to recover or produce enough sustainable energy for the continuation of the set. At some point the build-up of metabolic waste from the exercise will cause an unbearable localized burn in the working tissue and the end of a set. While metabolic stress can play a role in and of itself in stimulating a muscle to grow, the accumulated waste products actually help generate the previously described mechanical tension by inhibiting some of the working muscle fibres – thus causing more to be recruited, or, more to maximally exhaust as they are called upon to do more of the workload.

Muscle Damage

Nearly all work performed in a resistance training session will contribute some form of microscopic muscle damage to your body. While this does appear to be an independent reason for muscle growth, it isn’t necessarily something to strive for. That’s because in the effort required to generate mechanical tension and metabolic stress, muscle damage tends to just happen. While there are certain exercise styles that may emphasize more damage to occur, this shouldn’t be a main goal of a workout. Think of muscle damage as more of a kickstart to the muscle remodelling or growth process. Muscle damage gives a bit of a platform with which to repair or grow from, but also, requires the body to literally heal back to its original baseline before new growth can occur.

Knowing these mechanistic reasons for muscle growth should empower the trainee to have more problem solving and wherewithal to train in almost any situation. Start considering your current workout routines. Which mechanisms do you tend to emphasize? Which may be neglected? In the next blog I’ll discuss examples of exercises which would fall into each category, and how to start using this knowledge to better design your own workouts.

Best,

Eric