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Don’t Overlook the Underweight

With all the attention on helping clients lose weight, it’s easy to forget about the populations that actually want to gain body mass.

How many times have you read a news story that began with alarming statistics about the growing obesity crisis in the United States? As fitness professionals, we have dedicated our energies to devising effective interventions to help our clients lose weight to better their health. However, it is important to remember that the weight management principles and programs used for the overweight or obese do not apply to any clients who don’t need or want to shed pounds. In other words, we cannot take a “one size fits all” approach to weight management.

Weight management is a comprehensive science. As such, it involves practices that facilitate not only body fat reduction but healthy gains in lean body mass
as well. Although many clients stand to benefit from both outcomes, as an industry we all too often view weight management exclusively from a weight loss or
body mass reduction perspective. In the process, we overlook clients who want or need to gain weight, such as high-
performance athletes, those afflicted with cancer or HIV/AIDS and people recovering from eating and body image disorders.

This article outlines some important principles of weight management often overlooked by personal trainers and group fitness instructors. It is imperative that readers stay within the scope of their practice whenever discussing weight management issues with clients.

Principle 1: Begin
With the End in Mind

First and foremost, listen very carefully to the goals of any client hoping to gain body mass. Question the client’s motivation, and listen for responses that suggest poor body image or psychological problems. Are lean body mass gains desired for athletic competition? Are there medical issues to consider? Is the client being picked on at school or pressured at work? The answers to these questions will inform how you need to proceed. You may be the first contact this client has reached out to, and you want to be encouraging while remaining within your own abilities and scope of practice. Be prepared to refer the client to other professionals as needed.

Principle 2:
Measure Carefully!

It makes little sense to help a client set a weight goal if you don’t have the ability to measure the progress of that goal. Ideally, every fitness center would have access to hydrostatic weighing or dual-energy X-ray absorptiometry (DEXA) techniques to ensure accurate measurement of body composition. Unfortunately, even in the weight-obsessed United States, this is not the case. That said, you should use the highest-quality body composition assessment techniques available. Be prepared to explain the limitations of your methods to the client. If you possess little more than a cheap pair of skinfold calipers or if your body composition assessment skills are limited, you need to refer the client to a professional who can obtain more accurate measurements. Never track a client’s progress in gaining lean body mass using nothing more than a bathroom scale.

Principle 3: Be Willing
to Use the “F” Word

In the politically correct times in which we live, it is understandable that you might hesitate to utter the word fat. But you need to get over this hesitation, because the practice of weight management is not for the faint-of-heart. By verbally distinguishing between the terms fat mass and fat-free mass when talking to clients in your day-to-day practice, you will be less likely to rely on weight alone to gauge the client’s progress. That’s because weight is the product of body mass and gravity. Fat mass and fat-free mass are what make up that body mass. Relying on weight depicted on a scale means you can’t track water fluctuations, clothing weight variability or even calibration drifts in the scale, all of which influence the accuracy of a body composition assessment. Without more sophisticated and accurate assessment tools, you cannot measure percent fat and percent lean body mass. Yet it is precisely those constituents that we need to measure and track carefully in order to monitor the client’s progress.

Principle 4: Explain
the Concept of
Energy Expenditure

It is important to teach clients trying to gain lean body mass about the concept of energy expenditure and its role in the weight gain process. They need to understand how physical energy expenditure and energy storage influence weight gain or loss. Encourage your weight gain–oriented clients to maintain levels of cardiorespiratory endurance appropriate to their age and gender in accordance with Chapter 4 of ACSM’s Guidelines for Exercise Testing and Prescription (American College of Sports Medicine 2006). Recommend that clients eat a healthy diet in accordance with the federal government’s MyPyramid. Suggest that clients make resistance training their primary form of physical activity (Kraemer et al. 2002).

Principle 5: Remember That Metabolism Is Not Magic

If you work with clients interested in gaining lean body mass, you need to recognize and share the importance of metabolism. Stress that metabolism involves both energy expenditure and energy storage. This will help clients more readily understand that physical activity energy expenditure cannot exceed the amount of calories consumed in their diet. This will help dispel the common myth that it is possible to simultaneously lose body fat and gain lean body mass. It is up to the competent fitness professional to educate clients accordingly and to structure long-term exercise and nutrition programs that do not conflict with each other.

Principle 6: The Role
and Restrictions of Resistance Training

As mentioned earlier, it is important to include resistance training in any program for weight gain–oriented clients. However, it is equally important that you (and your clients) recognize the limitations of resistance training in producing meaningful gains in lean body mass. One meta-analysis reviewed studies that examined the impact of resistance training on weight management and found that gains in lean body mass tend to be modest at best (Donnelly et al. 2003). The reviewers found that lean body mass gains were approximately 0.8 kilogram (kg), or 1.8 pounds, of in resistance training studies that lasted 8–16 weeks, and about 1.3 kg, or 2.8 pounds, in studies that lasted 18–52 weeks (Donnelly et al. 2003).

Principle 7: When Lives Change, So Should Goals

Just as it is important to assess body composition and other parameters of physical fitness at the start of a weight-gain program, it is also important to regularly assess and review the client’s progress (or lack thereof) toward achieving his or her goal. The primary reason for regular and ongoing reassessment is twofold: (1) it takes a long time to see changes in lean body mass gains; and (2), clients can experience abrupt lifestyle changes that will affect their progress and even the very nature of their original weight-gain goals. For example, consider an 18-year-old male client who worked with you for a year to gain body mass in order to be more competitive in football during his senior year of high school. Assuming that both his exercise intensity and his diet were altered to achieve this goal, this client may need an adjustment in diet and physical activity level if he stops playing football in college. In the same way that you guided the client toward his body mass gains, you should be prepared (using a similar methodology) to tailor his program as his lifestyle and fitness demands change over his life span. There are no strict guidelines for how often you should reassess a client’s goals; this will depend on a variety of factors, such as the client’s health and the goals themselves.

Balancing the Scale

The purpose of this article was to remind readers that the science of weight management does not apply only to clients who want to lose weight. There was no intention to minimize the importance of helping overweight and obese clients achieve their weight management goals through proper diet and exercise. But we do need to take a moment to consider the needs of clients who want to gain lean body mass safely. Scientific principles for accomplishing this are just as important as those being incorporated on the other side of the weight management scale. n

If you work with clients interested
in gaining lean body mass, you need to
recognize and share the importance of

Sidebar: 7 Simple Strategies for Weight Gain

  1. Find out why the client wants to gain weight.
  2. Get the most accurate body measurements possible.
  3. Don’t hesitate to use the word fat with clients.
  4. Explain in simple terms how energy expenditure and storage affect weight.
  5. Teach the client about basic metabolism principles.
  6. Combine resistance exercise into the program but recognize its limitations.
  7. Review and revise weight loss goals when the client’s lifestyle changes.


American College of Sports Medicine (ACSM). 2006. ACSM’s Guidelines for Exercise Testing and Prescription (7th ed.). Baltimore: Lippincott Williams & Wilkins.
Donnelly, J. E., et al. 2003. Is resistance training effective for weight management? Evidence-Based Preventive Medicine, 1 (1), 21–29.
Kraemer, W. J., et al. 2002. American College of Sports Medicine Position Stand: Progression models in resistance training for healthy adults. Medicine & Science in Sports & Exercise, 34 (2), 364–80.

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