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What Fitness Pros Need to Know About Strength Training for GLP-1 Users

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Man and woman participating in strength training for GLP-1 users

Strength Training for GLP-1 Users

GLP-1 medications have changed the landscape of weight management, often resulting in significant and sometimes rapid weight loss. While these medications can be an effective tool for improving metabolic health and reducing body weight, the rate of weight loss raises an important consideration: not all weight lost is body fat.

Along with fat loss, individuals may also lose lean body mass, including valuable muscle tissue. Preserving muscle mass is essential for maintaining strength, functional ability, metabolic health, and long-term weight management. This creates an important opportunity for fitness professionals to play a supportive role. Through appropriately designed resistance training, thoughtful exercise programming, and an emphasis on recovery, personal trainers can help clients prioritize muscle preservation and physical function while navigating weight loss with GLP-1 medications.

Why Do GLP-1 Users Lose Muscle?

Research has and continues to show that GLP-1s are effective in weight loss. Two trials, the STEP 1 trial and the SURMOUNT-1 trial reported that once-weekly semaglutide use led to weight reductions of 15% and 20% of initial body weight. However, these trials also found that approximately 30% to 40% of the lost weight was lean body mass. This is due to the rapid rate at which weight is often lost on these types of medications.

Rapid weight loss, which is defined as greater than one kilogram of weight loss per week (greater than 2.2 lbs/week) results in greater muscle mass loss than slow weight loss. A 2015 study compared rapid weight loss (defined in this study as at least 5% of initial body weight loss in 5 weeks) to slow weight loss (5% of initial body weight loss in 15 weeks). The amount of weight lost in both groups was nearly the same; however, a significant reduction of body fat was observed in the slow weight loss group compared to the rapid weight loss group. In addition, a significant reduction in lean mass, total body water, and resting metabolic rate (RMR) was seen in the RAPID weight loss group as compared to the slow weight loss group.

During periods of rapid weight loss, the body experiences changes in energy availability and protein metabolism that can make maintaining muscle mass more challenging. When calorie intake drops substantially, the body must adapt to having less energy available to support its normal functions. Although stored body fat provides much of the energy needed during weight loss, muscle tissue can also be affected.

Two important processes influence whether muscle mass is maintained or lost:

  • Muscle protein synthesis decreases: Muscle protein synthesis is the process by which the body builds and repairs muscle proteins. When energy and protein intake are insufficient, the body’s ability to support muscle repair, recovery, and growth may be compromised.

  • Muscle protein breakdown may increase relative to synthesis: The body is constantly breaking down and rebuilding muscle proteins. During significant calorie restriction, muscle protein breakdown can exceed synthesis, resulting in a negative muscle protein balance over time.

When the body is in a substantial energy deficit, it may also rely more heavily on amino acids (the building blocks of protein) to support energy production and other metabolic processes. This can increase the risk of losing lean tissue, particularly when dietary protein is inadequate and resistance training is absent or insufficient.

Hormonal changes associated with weight loss can further influence muscle maintenance. For example, testosterone, which plays an important role in muscle protein synthesis and the maintenance of lean body mass, may decrease during periods of substantial energy restriction, particularly in some men. Changes in other hormones involved in metabolism and muscle regulation may also contribute to the body’s response to prolonged calorie restriction.

Why this matters for clients taking GLP-1 medications: These medications can significantly suppress appetite, making it difficult for some individuals to consume enough total calories and protein to support muscle maintenance. When substantial weight loss occurs alongside inadequate protein intake and insufficient resistance training, the risk of losing muscle increases.

Why Strength Training is Important

Muscle mass is pivotal for long-term metabolic and overall health.

Body mass index (BMI) is often used to track weight loss and risk levels of developing obesity-related conditions. However, as BMI takes into account one’s height and weight, but not muscle mass, it may not be the best tool for assessing risk. An individual’s BMI may be lower, but if they have lost muscle mass, they may still be at risk for disease. Research continues to find skeletal muscle as an independent marker of biological health, meaning low muscle mass is associated with cardiovascular disease risk and higher muscle mass increases insulin sensitivity.

Skeletal muscle is an important place where the body burns down fat to be used for energy, also known as lipid oxidation. Skeletal muscle plays a special role in controlling how much fat the whole body stores or uses by using aerobic metabolism (energy production that requires oxygen).

Muscle is extremely metabolically active, meaning it requires a lot of energy – or calories – to maintain. It contributes a substantial amount to resting energy expenditure and one’s metabolism.

An additional possible side effect of rapid weight loss is a loss of bone density. Strength training, specifically weight-bearing compound strength training (think free weights over machines) can help combat the loss of bone density that may accompany weight loss.

How to Program Strength Training

When working with clients taking GLP-1 medications, resistance training should prioritize maintaining muscle mass, preserving functional strength, and supporting long-term health. The goal is not simply to burn more calories, but to provide an appropriate training stimulus that the client can recover from and sustain.

Consider the following programming strategies:

1. Prioritize Full-Body Strength Training

Aim for 2–3 nonconsecutive days of full-body resistance training each week. Focus on compound movements that recruit multiple muscle groups and reinforce functional movement patterns, including squats, pushes, pulls, hip hinges, and loaded carries.

2. Apply Progressive Overload Gradually

As exercises become easier, progressively increase the challenge by adjusting resistance, repetitions, sets, or exercise complexity. For example, when a client can comfortably complete 8–12 repetitions with good technique and appropriate effort, consider increasing the resistance or advancing the exercise variation.

3. Incorporate Balance and Core Stability

Include exercises that challenge balance, coordination, and trunk stability. These components support everyday movement, functional independence, and overall physical performance.

4. Prioritize Strength and Movement Quality Over Caloric Expenditure

GLP-1 medications can substantially reduce appetite and overall energy intake. When a client is already experiencing a significant energy deficit, adding excessive exercise volume may contribute to fatigue and make adequate nutrition and recovery more difficult.

Rather than asking, “How can I help this client burn more calories?” consider asking, “What training stimulus can this client adequately recover from while maintaining strength, muscle mass, and function?”

5. Monitor Recovery and Training Tolerance

Pay attention to how clients respond to exercise from session to session. Monitor factors such as:

  • Exercise performance and perceived exertion
  • Recovery between workouts
  • Sleep quality and energy levels
  • Muscle soreness and fatigue
  • Training motivation
  • Changes in strength and exercise tolerance

Clients may experience fluctuations in energy and exercise capacity, so be prepared to adjust training intensity, volume, or exercise selection as needed. Flexibility in programming is essential.

6. Measure Progress Beyond the Scale

Body weight alone provides an incomplete picture of a client’s progress. If weight is decreasing while strength, physical function, and training quality are being maintained, that is valuable information.

Consider tracking multiple indicators of progress, including:

  • Functional strength and movement competency
  • Muscular endurance and stamina
  • Body composition, when appropriate
  • Circumference measurements
  • Changes in exercise performance and tolerance
  • Ability to perform everyday activities

Ultimately, success should be measured by more than pounds lost. Maintaining muscle, improving strength, preserving functional capacity, and supporting overall health are important outcomes that personal trainers can help clients achieve while navigating weight loss with GLP-1 medications.

Finally, remember to stay within scope of practice for a fitness professional. Do not advise on dosage, side effects, or medication adjustments. The fitness professional’s role is to support safe exercise, promote healthy behaviors, and reinforce adherence to medical guidelines.

Additional Resources

If you are looking for more information on working with clients on a GLP-1 medication, to include additional considerations and programming examples, check out the Strength Training for GLP-1 Clients e-learning module, a one-hour recording of a webinar presented in conjunction with Insure Fitness Group this September.

Additionally, for those seeking to go even further in-depth, NETA will be rolling out a three-hour continuing education workshop on Training GLP-1 Clients during our 2027 Virtual Fit Fest next February.

References

Darci Revier

Darci Revier, DHSc
CSCS, E-RYT 200

Director of Education

Darci Revier is NETA’s Director of Education. She obtained her masters degree in Human Nutrition from the University of Bridgeport, her doctorate in Health Science and Exercise Leadership from California University of Pennsylvania, and holds certifications through the NSCA, ACE, NASM, and USAW. She began working in fitness, nutrition and health promotion with members of the United States Marine Corps in 2008, joining NETA as a presenter in 2015 and transitioning to her current full-time role in 2018. Follow Darci on Instagram.

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