By Jason R. Karp, PhD, Special AFS Contributor

Years ago, I applied to be a personal trainer in a gym. Taking one look at my runner’s body, the owner said to me, “Go work out for a couple of months and come back to reapply.” Happy as I was with my runner’s body, I never went back.

But it occurred to me that most people in the fitness industry care more about what you look like than what you know. Regardless of how big your pecs or sexy your calves are, there are basic things that every fitness professional needs to know. Here’s three of them:

The Science and Research on Weight Loss and Weight Maintenance

Despite weight loss being the biggest reason why people buy a gym membership or hire a personal trainer, most fitness professionals are not familiar with the research on weight loss and weight maintenance. For example, although there is much talk in the fitness industry about strength training leading to an increase in resting metabolic rate, which helps clients lose weight, strength training does not chronically increase resting metabolic rate.

In the absence of pathology, people lose weight only when caloric expenditure is greater than caloric intake. When that occurs, resting metabolic rate actually decreases. It is never elevated when losing weight. Each pound of muscle burns only 6 to 7 calories per day (and you can’t add that many pounds of muscle). Research does not support strength training for weight loss, but rather for the preservation of muscle mass while trying to lose weight. Since weight loss is the biggest reason why people seek our help, you better be a weight loss expert if you’re a fitness professional and offer weight loss programs at your club.

Specific Health and Fitness Outcomes of Different Workouts and Training Programs

Fitness professionals need to know how to design clients’ workouts based on science and research that cause specific physiological changes and organize all of their workouts into a progressive, systematic training program that enables their clients to accomplish their specific goals and achieve greater fitness and health. Exercise contraindications, the development of muscular strength, muscular endurance, cardiovascular endurance, flexibility, and body composition all must be taken into consideration.


Since most of the fitness industry is focused on various forms of strength training, whether it be with or without equipment and one-on-one or in a group setting, fitness professionals need to know how muscles and tendons work to move our bodies, including correct and safe techniques for exercises, lever systems, muscle architecture, contraction types, force-length and force-velocity relationships of muscle, and so on. 

I wonder how much of the above that gym owner knew who turned me away for a job. At least he had big biceps.

More from this Author:

Creating Running Programs in Your Fitness Business

14-Minute Metabolic Workouts to Implement Into Your Fitness Business


A competitive runner since sixth grade, Dr. Jason Karp quickly learned how running molds us into better, more deeply conscious people, just as the miles and interval workouts mold us into faster, more enduring runners. This passion that Jason found as a kid placed him on a yellow brick road that he still follows all these years later as a coach, exercise physiologist, bestselling author of 8 books and 400+ articles, speaker, and educator. He is the 2011 IDEA Personal Trainer of the Year. His REVO₂LUTION RUNNING™ certification has been obtained by fitness pros and coaches in 21 countries. His books can be found on Amazon.

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