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How does exercise change your body?

This is an excerpt from Smarter Workouts 2nd Edition by Pete McCall.

The COVID-19 pandemic of 2020-2021 exposed systemic vulnerabilities in the overall health of the U.S. population. The pandemic can be credited with a significant shift in the number of individuals in the United States who perceive the value of fitness and exercise as a mode of preventive health care. Individuals with healthy lifestyles and no comorbidities were significantly more resilient and experienced fewer severe outcomes from COVID-19, while those with preexisting health conditions such as obesity, diabetes, and cardiovascular disease experienced significantly higher hospitalization and mortality rates.

For years it has been recognized that regular, consistent physical activity, specifically exercise, can enhance the strength of the body’s natural immune system, with extensive data from the pandemic era providing more evidence. For example, individuals who exercise and participate in physical activity consistently could experience a 31 percent lower risk of acquiring an infectious disease and a 37 percent lower risk of premature death if an infectious disease is contracted (Chastin et al. 2021). In addition, a study of nearly 50,000 patients with COVID-19 found that individuals who did not engage in regular physical activity were

• 2.26 times more likely to be hospitalized,
• 1.73 times likely to require care in an intensive care unit (ICU), and
• 2.49 times more likely to die from COVID-19 (Sallis et al. 2021).

One outcome of the pandemic experience is that many individuals have joined health clubs with the intent of exercising to achieve and maintain optimal health. As of 2025, a record 81 million individuals in the United States hold memberships to a gym, health club, or fitness studio, representing a 26 percent increase in membership from 2019—a sign that many individuals are choosing exercise as a means of preventive health care (Health & Fitness Association 2026).

Many health-care providers promote the benefits of physical activity and encourage patients to exercise; however, few know how to provide proper instructions on how to start a program, leaving it up to you, the individual, to figure it out on your own. A common first step when starting an exercise program is to join a health club or a fitness studio, and while that is an important step, it does not provide specific guidance on the most effective type of exercise for your particular needs. Let’s face it, you understand the benefits of regular exercise and know that following one could result in significantly improved health; yet, identifying the best type of exercises for your needs can be difficult.

One example of the difficulty of identifying the most effective exercise program for your needs is that exercise scientists, medical professionals, and public health officials have for years recommended the health benefits of achieving at least 75 minutes of vigorous-intensity physical activity or 150 minutes of moderate-intensity physical activity every week, as established by the U.S. Department of Health and Human Services Physical Activity Guidelines; however, the primary mode of exercise promoted is walking, or other low- to moderate-intensity activity, most likely because of its accessibility (U.S. Department of Health and Human Services 2018).

It’s important to note that other than recommending specific exercises for either “bone strengthening” or “muscle strengthening” or both, there is little-to-no guidance provided in the federal guidelines on the role that strength training exercise should play in an overall physical activity program. This is a huge gap in information that misses the opportunity to promote strength training as a beneficial form of exercise.

There is a rapidly accumulating body of evidence suggesting that increasing lean muscle mass via strength training can provide significant health benefits compared to low- to moderate-intensity aerobic exercise. In a comprehensive review of the literature, Tyler and Thanos provide evidence suggesting that strength training is an effective means of improving the health and function of your cardiovascular, musculoskeletal, neuropsychological, and metabolic systems. The study authors note that, “Not only is resistance training preventative medicine through its reduction in disease risk and enhancement of health and wellness, but it is also an effective intervention through its alleviation of disease signs and symptoms” (Tyler and Thanos 2023, 5).

Likewise, in a review of peer-reviewed studies, Abou Sawan and colleagues found that, “Health benefits of resistance training extend beyond those attributed to increasing muscle mass and strength and include reduced mortality risk. Participation in resistance training can increase physical and cognitive function, improve cancer survival and manage metabolic health” (Abou Sawan et al. 2023, 5). (Note: Strength training, resistance training, and weightlifting all refer to the same activity: using external resistance to increase levels of lean muscle mass and force output; for simplicity, strength training will be used in this text to refer to this mode of exercise.)

The evidence suggests that the health benefits from strength training are more extensive than those provided by performing low- to moderate-intensity aerobic exercise alone. Therefore, according to existing guidelines, it’s important to add at least two, and ideally three, days of strength training per week to ensure optimal health benefits from exercise. However, even as exercise guidelines recommend strength training, they do not provide instructions on the type of strength training exercise to perform, and so you’re left to your own devices, which often means looking to the Internet and social media for answers.

While many resources provide lots of helpful information, it’s important to recognize that many common exercise programs are derived from bodybuilding, only adding to the confusion surrounding what to do in strength training workouts. That’s because the focus of a bodybuilding program is usually muscle-isolation exercises involving only a single joint or muscle group at a time, meaning the individual body parts are used as separate, discrete units. An example is the knee extension machine, which requires you to be in a seated position as you move a weight by straightening your legs. Yes, this action can strengthen the larger muscles of your upper thigh, but those muscles are designed to work with both your hip and knee while you’re standing on your feet, not while sitting down.

Efficient human movement requires multiple muscle groups working simultaneously to generate the force to move your body. For this reason, combined with the fact that using more muscles can increase energy expenditure during a workout, strength training programs for achieving optimal health should emphasize multijoint movement patterns, not isolated muscle actions.

More Excerpts From Smarter Workouts 2nd Edition

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