Your Body on Exercise: Physical & Mental Adaptations to Weight Training
May 8 2018

Your Body on Exercise: Physical & Mental Adaptations to Weight Training

By: VIDA Personal Trainer Patrick Merkel

“I want bigger arms,” “I want to be toned,” “I want broader shoulders.” Do these goals sound familiar? Too often, those of the fitness community set their sights on black-and-white goals without considering the other, and sometimes more important, adaptations to weight training. Sure, when done properly, weight training will get you bigger arms, broader shoulders, and a tighter look, but those hours spent sweating it out in the gym result in much deeper changes that often go unrecognized.

First, it is necessary to understand two of the essential principles of exercise: overload and adaptation. At the start of a new exercise program, or any physical activity with which you are unfamiliar, the body experiences stress (the difficulty of the exercise program.) As you continue to do this program over and over again, your body makes the necessary adaptations to deal with this stress, and thus, the exercise becomes easier over time. Once an exercise program that was once a challenge has become easy, your body goes on cruise control and you stop making fitness improvements. This is where overload comes into play. In order to keep improving your current fitness status, you must constantly stress your body by placing it in a situation in which it is unfamiliar. It is likely that many of us have experienced our body adapting to a certain lift over time. Given you are following an effective exercise program, it is likely that you can squat more weight today than you could ten weeks ago. Many will contribute this gain in strength to the muscles getting bigger, but there are other adaptations at play. Let’s dig into it!

Sometimes, it seems unfair; the beginners seem to make progress much quicker than those who have been training for years. This phenomenon is called the law of diminishing returns. The longer you train, the more adaptations you make in response to the stress, and results come at a much slower pace. A visual representation of this phenomenon is seen below:

Let’s use this representation as a guide for our journey through a weight training program. Notice the exponential growth in the beginning stages. This huge jump in strength gains is largely due to neuromuscular adaptations. Gabriel, Kamen, and Frost (2006) describe neuromuscular adaptations as an increase in neural output from the central nervous system to active muscle fibers. In short, the mind is being trained to better communicate with your muscles. Cool, right?!

As you become a more advanced weight-lifter, neural adaptations are less occurrent and other changes take place. The most widely-known change is hypertrophy. Muscular hypertrophy is the growth of muscle fibers. Don’t confuse this with hyperplasia, or a growth of new muscular cells. There is no current evidence showing the occurrence of hyperplasia in humans.

We can think of muscular hypertrophy as the first change that causes many other adaptations to occur. Humans have three subclasses of muscle fiber types: Type I, Type IIA, and Type IIX fibers. Type I fibers are also known as slow-twitch fibers and are most active in endurance training such as cardio, or everyday activity. Type IIA fibers are “hybrid” fibers which have some capacity to act during endurance events and some capacity to act during high-intensity events such as weightlifting. Finally, Type IIX fibers are fast-twitch fibers and respond to intense situations when quick bursts of energy are needed such as a sprint or during weight lifting. So how do these fiber types respond to weightlifting?

Because weightlifting is a high-intensity exercise; the Type IIA and Type IIX fibers are affected the most. Over time, morphological changes occur wherein the Type IIX fibers will turn into Type IIA fibers. With this change, the IIA fibers will hypertrophy leading to an expansion in size. With this expansion in size comes in increase in their capability to store glycogen, the muscles preferred energy source. The following chart displays how our body uses different energy stores based on the duration of the exercise event.

Note that no energy store is ever solely responsible for providing the body with energy. During weight lifting, we rely mainly on ATP (adenosine tri-phosphate) splitting, creatine phosphate (CP), and some anaerobic energy pathways. Through these pathways, the glycogen stored in our muscles is broken down to provide us with energy (ATP) to do work—in this case, lift weights. Thus, as we expand our muscles through hypertrophy, we are able to store more glycogen and, in turn, produce more energy to lift weights.

All these changes are contributing significantly to our ability to do work and can translate to daily activities such as walking down the street with a handful of groceries or moving furniture. With these adaptations in mind, I hope that as you develop your fitness goals, you look beyond the black-and-white cliché goals and consider the long-term effects and benefits of being a stronger individual—both mentally and physically. So what are you waiting for? It’s your set!

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