New insight into the molecular underpinnings of muscle development

By Angela Betsaida B. Laguipo, BSNAug 6 2020

In the world of weightlifting, some people gain more muscle faster than others, no matter what they do. Now, a novel human study may explain why this happens.

A team of researchers from the University of McMaster, alongside other investigators from Canada, the United Kingdom, and the United States, has found new answers through a new experiment wherein the participants exercised one leg and immobilized the other. The team has identified 141 genes that appear to regulate the growth of the skeletal muscles, which are tethered to the skeletons to control power and movement.

Study: Molecular Transducers of Human Skeletal Muscle Remodeling under Different Loading States. Image Credit: Anatomy Insider / Shutterstock

The study

In the study, which is published in the journal Cell Reports, young and healthy men built up muscle in one of their legs by following a prescribed regimen of weight training. They recruited ten men who underwent training for over ten weeks.

For the initial eight weeks, the other leg served as a non-exercising control. For the next two weeks, the non-exercising leg was immobilized entirely to a brace to keep it from bearing weight.

In just two weeks, the immobilized leg lost the same amount of muscle mass the opposite leg had gained in more than two months of weight training. The comparison of the genetic responses of the muscles in both legs of the same individual guided the researchers to isolate what helps exercise-related muscle growth accurately.

The muscle gain in the exercising limb is between 1 and 15 percent over the ten weeks, with an average of 8 percent. The muscle loss in the non-exercising or immobilized leg ranged between 1 and 18 percent, with an average of 9 percent. Put simply, the average participant lost muscle through inactivity at an approximately five times the rate he had gained it through weightlifting.

“The variation in muscle growth between people makes it very challenging to isolate what drives that growth. Using both legs of the same person to both load and unload muscles allowed us to make a direct comparison,” Dr. Tanner Stokes, lead author of the research, said.

Study implications

The novel experiment provided new insights that could help develop new methods against debilitating muscle loss in older people. This could potentially help in developing an “exercise pill” to combat weakness and frailty in old age. It could also help provide a drug to older people to prevent injuries of activity, mimicking the benefits of a workout.

Also, the study highlights the importance of building and retaining muscle for overall health and quality of life. The study is essential for helping keep older adults or seniors healthy and safe.

“If we can target those genes with lifestyle and drug therapies, we may be able to help seniors and others vulnerable to muscle loss,” Stuart Phillips, a professor of Kinesiology, said.

Skeletal muscle loading

Some types of exercise, including weightlifting, focuses on skeletal muscle loading that stressed the muscles. As a result, muscle fiber hypertrophy happens, which effectively builds muscles.

“Increased loading of skeletal muscle induces muscle fiber hypertrophy requiring the remodeling of myofibrillar and extracellular protein lattices. In contrast, unloading (UL) results in fiber atrophy, reductions in protein content, and a more fatigable tissue phenotype. In humans, voluntary loading (via resistance exercise training [RT]) leads to a highly heterogeneous physiological adaptation across individuals, which is associated with the differential molecular response,” the authors wrote in the paper.

Physical activity is an important way to promote overall health and wellbeing. The American Heart Association (AHA) recommends at least 150 minutes of moderate-intensity aerobic activity per week, or 75 minutes per week of vigorous aerobic activity. The agency also urges people to perform moderate- to high-intensity muscle-strengthening activity, including weights or resistance training, on at least two days per week.

Moderate-intensity aerobic exercises include activities such as water aerobics, brisk walking of at least 2.5 miles per hour, dancing, tennis, gardening, and biking. Vigorous-intensity activities include swimming laps, running, hiking uphill or with a heavy backpack, heavy yard work, tennis, aerobic dancing, jumping rope, and cycling 10 miles per hour, among others.

Very cool insights into the molecular underpinnings of muscle development https://t.co/TlMkyPLz3k pic.twitter.com/9wrsfEq1VB

— Brad Schoenfeld, PhD (@BradSchoenfeld) August 5, 2020