Relationship Between Body Mass and Muscle Strength: Correlation or Causation?

Author: Joey Harkins

Think of the strongest person you have ever met. Not in the pound-for-pound sense, but the individual that you can think of that can physically move objects that you might have thought could not possibly budge. This could be someone you played sports against in high school, someone you work with, or even someone you’ve seen on T.V. Chances are the person you’re thinking of isn’t too small. On the contrary, they’re probably one of the biggest people you’ve seen. There most definitely appears to be a relationship between body size and strength, but the question remains: is strength simply a product of increased body mass or are there more factors at play?

The answer to that question is that it may be a bit of both. While the world’s strongest
athletes are typically huge, they didn’t get there by eating at McDonald’s every day. While that would undoubtedly lead to increased body mass, it’s not going to make you stronger. Instead, these athletes must undergo rigorous strength training paired with proper recovery habits. During strength training, an athlete will stress his/her muscles by moving heavy loads. The weight of the load opposes the movement of the muscle, and when the load is great enough, it causes an adaptation to the targeted muscle. During the lift, tiny tears will occur within the skeletal muscle body. Following exercise, assuming the athlete undergoes healthy recovery techniques (nutrition, sleep, etc.), proteins within the muscle will work to not only repair the tears, but to initiate growth. This growth will help the muscle to move heavier loads without accumulating as much damage.

From this, we can see how increases in muscle size can lead to increased strength. Over
time, strength training will result in increased lean muscle mass, meaning body weight that is supplied solely by the muscles. When a muscle gets bigger, we say that its cross-sectional area increases. There is a direct relationship between cross-sectional area and force production by a muscle (McArdle 2015). At the cellular level, muscle cells or myocytes are filled with contractile units called sarcomeres. Sarcomeres are made up of fibers called actin and myosin, which interact and overlap when stimulated. During a muscle contraction, actin and myosin will increase their overlap, shortening the sarcomere and the entire muscle. When a muscle increases its cross-sectional area following resistance training, additional sarcomeres are formed, leading to more cross-bridges created between actin and myosin. This means that with increased muscle size, more contractile units can work together to produce more force and move heavier loads.

So how do muscles adapt to resistance training? When completing resistance training, all
loads within exercises should be based off the athlete’s one repetition max (1RM). This value indicates the absolute heaviest load the individual can move for that particular exercise. 1RM is normally calculated using different formulas, as a true 1RM is very difficult to perform. In a study done by Gerson et. al in 2002, the researchers wanted to investigate the effects of different types of resistance training on muscle adaptations. 32 untrained males were split into groups and put through different resistance training programs. The first group, or low rep group, completed 3-5 repetitions of a high percentage of their 1RM in three separate exercises throughout the 8-week program. The second group, or intermediate rep group, completed 9-11 reps of an intermediate percentage of their 1RM. The third group, or high rep group, completed 20-28 reps at a lower percentage of their 1RM throughout the program. By the end of the program, the groups’ final 1RM was compared to their original 1RM at the beginning of the study as well as characteristics
of their muscles before and after the testing. The low rep group not only saw the largest jump in 1RM, but their muscle size had increased dramatically. (Gerson, et. al 2002)

Gerson’s study is a great example of how our muscles adapt to heavy loads in strength
training. Because the low rep group was lifting the heaviest weight relative to their 1RM, the
stress put on their muscles was greater than the groups that completed more reps at lighter weights. The increased stress caused more micro-tears to occur within their muscles, and as the muscle recovered, more sarcomeres (contractile units) were formed to prepare the muscles for resisting heavy loads in the future. This increase in sarcomere formation not only made the subjects in the study better at lifting heavy loads, but also increased the size of their muscles.

The process of increasing muscle size is known as hypertrophy. Hypertrophy occurs when
synthesis of muscle proteins occurs faster than muscle degradation (Schoenfeld 2010). As
discussed already, increases in muscle size (cross-sectional area) lead to increases in muscle strength. This is why it is not uncommon for athletes to try to attain hypertrophy by any means necessary. Though this hypertrophy can be aided by ample rest, recovery exercises, and nutrition, many athletes will try to exacerbate strength gains by supplementation. Though supplementation of products like protein powder and creatine monohydrate have been proven to be essentially harmless and even beneficial, some known techniques may not be in the athlete’s best interest.

We have all heard the stories of athletes using steroids in order to boost their
performance. Though steroids are banned in just about every professional and collegiate athletic league, many athletes still get caught taking them. So why take them in the first place, if they almost surely mean the end of your athletic career? A study done by Bhasin, et. al in 1996 wanted to challenge the concept that steroid use would increase performance. Anabolic steroids like testosterone have many important functions within the body, one of which leading to increases in muscle mass. The study took adult males and split them into four groups: placebo without exercise, placebo with exercise, testosterone without exercise, and testosterone with exercise. By the end of the study, significant differences could be observed between the groups that supplemented testosterone versus those who took the placebo. The steroid groups saw significant increases in cross-sectional areas of their arms and legs as well as huge increases in 1RM’s. Though testosterone paired with exercise yielded the largest difference, there is no doubt
that steroids increase general muscle strength and size even in the absence of exercise. So it’s no doubt why athletes may be tempted to begin taking steroids. With the aid of anabolic steroids, these athletes could crush baseballs, bike faster, and lift heavier, however, they are deemed immoral and unhealthy, and are frowned upon (to say the least) by the athletic community.

The reason I bring up the use of steroids is that they further demonstrate that increases in
lean muscle mass lead to greater force output. Increased strength is helpful in all walks of life, but I would not encourage the use of steroids to achieve this strength. A study done by Basaria et. al in 2010 wanted to investigate the adverse effects brought on by the use of testosterone supplementation. The study took 209 elderly men (average age of 74) with limitations in mobility and strength and allowed them to go about their daily lives, but with added doses of testosterone or a placebo. The researchers measured the groups’ strength throughout the study as well as factors relating to their cardiovascular, respiratory, and dermatologic health. By the end of the study, the testosterone group reported far more adverse effects, showing much higher risk of heart, lung, and skin problems (Basaria 2010). This study is important, because it shows that while anabolic steroids like testosterone may lead to strength gains, taking them may put you at higher risk of serious, life-threatening disease.

A better idea for maximizing strength gains is to focus on healthy recovery habits in
addition to your strength program. No matter how hard you exercise in the weight room, it will be incredibly difficult to sustain strength gains if work is not also done after you leave the gym. To optimize the effects of strength training, one must also eat meals with a balance of protein to aid muscle recovery, healthy carbohydrates and fats to provide energy, and greens for additional nutritional support. A healthy diet paired with ample amounts of sleep will be crucial to attaining the strength gains you work so hard for.

Being stronger is incredibly important, not just as we compete in athletics, but as we age.
As we get older and our bodies begin to age, the ability to move independently will be prolonged by increased strength. Everyday actions such as carrying bags of groceries, getting up from the couch, and grabbing something from on top of the fridge get exponentially more difficult as we age. Maintaining muscle strength can help us to continue our lifestyle habits and live happy,
healthy lives.

Works Cited

Basaria, Shehzad et al. Adverse Events Associated with Testosterone Administration. The New England Journal of Medicine, vol. 363, no. 2, 8 July 2010.

Bhasin, Shalender; et al. The Effects of Supraphysiologic Doses of Testosterone on Muscle Size and Strength in Normal Men. The New England Journal of Medicine, vol. 335, no. 1, 1996.

Gerson, Campos E.R; et. al. Muscular adaptations in response to three different resistance-
training regimens: specificity of repetition maximum training zones. (88), 50-60.
European Journal of Applied Physiology, 2002.

McArdle, William D. Exercise Physiology. 8th ed., Wolters Kluwer, 2015.

Schoenfeld, B. (2010). The Mechanisms of Muscle Hypertrophy and Their Applications to
Resistance Training. Journal of Strength and Conditioning Research, 24(10), 2857-2872.