The rapid adoption of GLP-1 receptor agonists (GLP-1 RAs) such as semaglutide (Ozempic, Wegovy) has revolutionized the treatment of type 2 diabetes and obesity. However, for personal trainers working with clients on these medications, the conversation cannot simply stop at weight loss. A critical, yet often overlooked, aspect of GLP-1 usage is its potential impact on skeletal muscle, metabolic health, and long-term functional capacity.
As a personal trainer, you are in a unique position to preserve, protect, and enhance your clients’ muscle mass during this powerful (and sometimes risky) pharmacological journey. This article explores the emerging science around GLP-1 agonists and muscle loss, why resistance training is essential, and how to reposition your services as a critical safeguard against metabolic decline and sarcopenia in an age of rapidly advancing pharmacological interventions.
Understanding the GLP-1 Landscape
GLP-1 RAs mimic the incretin hormone GLP-1, enhancing insulin secretion, suppressing glucagon, and slowing gastric emptying. These actions collectively contribute to better glycemic control and reduced appetite, supporting significant weight loss in individuals with obesity and/or type 2 diabetes (Ellingsgaard et al., 2011; Janus et al., 2019). However, it is imperative to note that the scale doesn’t tell the whole story.
To illustrate, weight loss from GLP-1 RAs may include significant lean mass loss, a concern that’s often ignored by both prescribers and patients (Old et al., 2025; Sargeant et al., 2019). And therein lies the opportunity for well-informed fitness professionals.
GLP-1 Use and Lean Mass Loss: What the Research Says
1. Reductions in Skeletal Muscle Mass
Multiple studies have shown that GLP-1 RAs can lead to reductions in lean body mass (LBM). Sargeant et al. (2019) noted that patients on GLP-1 therapy often experience disproportionate losses in muscle mass relative to fat loss, raising red flags for sarcopenia and functional decline. While these drugs excel in reducing total body weight, the composition of that weight loss matters profoundly.
Old et al. (2025) echoed this caution, suggesting that even when GLP-1 therapy is accompanied by resistance training, the preservation of LBM may be inconsistent. These findings are particularly concerning for aging populations or those already at risk for sarcopenia.
2. Variable Effects on Muscle Function
On a more optimistic note, some studies suggest GLP-1 RAs may improve insulin sensitivity, which could indirectly benefit muscle metabolism (Jiao et al., 2024). For example, Osaka et al. (2023) found that older adults on GLP-1 therapy combined with basal insulin experienced favorable appendicular muscle mass changes. Exendin-4, a GLP-1 analogue, may also downregulate muscle atrophy markers such as myostatin (Kamiya et al., 2022).
Nevertheless, the heterogeneity of these effects—combined with limited long-term data—underscores the need for a proactive, exercise-based approach to muscle retention.
The Sarcopenia-Metabolism Connection
Sarcopenia, or age-related muscle loss, is not merely an aesthetic concern. It is deeply intertwined with metabolic dysfunction, insulin resistance, and systemic inflammation (Beaudart et al., 2014; Su et al., 2019). Clients losing muscle while taking GLP-1 medications may face unintended consequences, including:
- Reduced resting metabolic rate
- Impaired glucose disposal
- Increased frailty
- Decreased functional independence
Evans and Cummings (2024) note that weight loss without concurrent resistance training often accelerates these problems, especially in older adults. This means trainers cannot afford to treat weight loss as a win if muscle mass is not being preserved or built.
Resistance Training as a Muscle-Sparing Intervention
1. Combining GLP-1 Therapy with Strength Training
Bonfante et al. (2024) and Zhao et al. (2022) have demonstrated that resistance training, especially when combined with aerobic exercise or GLP-1 therapy, supports muscle preservation and metabolic health. These interventions enhance muscle protein synthesis, neuromuscular function, and even bone density—effects that counteract the catabolic tendencies of weight loss.
Grønfeldt et al. (2020) further highlighted the benefits of blood flow-restricted training in preserving strength in populations unable to lift heavy weights, which may be especially useful for deconditioned clients or those on calorie-restricted diets.
2. Hormonal and Molecular Considerations
GLP-1 RAs influence various hormonal pathways that intersect with exercise physiology. For example:
- GLP-1 enhances muscle microcirculation, improving insulin’s metabolic action (Chai et al., 2014).
- Interleukin-6 (IL-6), often elevated post-exercise, stimulates endogenous GLP-1 production, suggesting a synergistic relationship between exercise and gut-brain hormonal regulation (Ellingsgaard et al., 2011).
- Resistance training modulates myostatin, a negative regulator of muscle growth, offering another mechanism for muscle retention (Kamiya et al., 2022).
These pathways demonstrate that exercise—especially resistance-based—is not merely compatible with GLP-1 therapy but potentially amplifies its metabolic benefits while mitigating muscle-related risks.
Positioning Yourself as an Expert in the GLP-1 Era
The increasing prescription of GLP-1 RAs represents both a public health breakthrough and a call to action for fitness professionals. Trainers who understand the physiological complexity of these medications can provide smarter programming, stronger client outcomes, and standout market positioning.
Here’s how to get started:
- Educate yourself on GLP-1 mechanisms, side effects, and contraindications (see references).
- Screen for sarcopenia risk factors: Ask about fatigue, recent weight loss, and grip strength.
- Build customized resistance programs: Prioritize strength training, compound lifts, and progression models.
- Collaborate with healthcare teams: Physicians and dietitians will appreciate having a trainer on board who “gets it.”
- Track progress objectively: Use metrics like DEXA scans, grip strength, and muscle circumference, not just the bathroom scale.
As research continues to evolve, it’s clear that GLP-1 users need resistance training more than ever. They need accountability, structure, and targeted interventions—exactly what personal trainers are equipped to offer.
GLP-1 receptor agonists represent a powerful tool in fighting obesity and diabetes, but with great power comes great responsibility. As a trainer, you can be the muscle-centric safeguard your clients need. Protect their lean mass. Empower their performance. And use your platform to ensure that “weight loss” doesn’t come at the cost of functional vitality.
In summary, GLP-1s may be trending. But muscle is forever.
References
Beaudart, C., Rizzoli, R., Bruyère, O., Reginster, J., & Biver, E. (2014). Sarcopenia: burden and challenges for public health. Archives of Public Health, 72(1). https://doi.org/10.1186/2049-3258-72-45
Bonfante, I., Duft, R., Mateus, K., Trombeta, J., Chacon‐Mikahil, M., Velloso, L., … & Cavaglieri, C. (2024). Combined training and hormones/enzymes with insulinotropic actions in individuals with overweight and type 2 diabetes mellitus: A randomized controlled trial. European Journal of Sport Science, 24(1), 97–106. https://doi.org/10.1002/ejsc.12057
Chai, W., Zhang, X., Barrett, E., & Liu, Z. (2014). Glucagon-like peptide 1 recruits muscle microvasculature and improves insulin’s metabolic action in the presence of insulin resistance. Diabetes, 63(8), 2788–2799. https://doi.org/10.2337/db13-1597
Ellingsgaard, H., Häuselmann, I., Schuler, B., Habib, A., Baggio, L., Meier, D., … & Donath, M. (2011). Interleukin-6 enhances insulin secretion by increasing glucagon-like peptide-1 secretion from L cells and alpha cells. Nature Medicine, 17(11), 1481–1489. https://doi.org/10.1038/nm.2513
Evans, W., & Cummings, S. (2024). Weight loss–induced muscle mass loss. JAMA, 332(16), 1394. https://doi.org/10.1001/jama.2024.17212
Grønfeldt, B., Nielsen, J., Mieritz, R., Lund, H., & Aagaard, P. (2020). Effect of blood-flow restricted vs heavy-load strength training on muscle strength: Systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 30(5), 837–848. https://doi.org/10.1111/sms.13632
Jiao, R., Lin, C., Cai, X., Wang, J., Wang, Y., Lv, F., … & Ji, L. (2024). Characterizing body composition modifying effects of a GLP-1 receptor-based agonist: A meta-analysis. Diabetes, Obesity and Metabolism, 27(1), 259–267. https://doi.org/10.1111/dom.16012
Kamiya, M., Mizoguchi, F., & Yasuda, S. (2022). Amelioration of inflammatory myopathies by GLP‐1 receptor agonist via suppressing muscle fibre necroptosis. Journal of Cachexia, Sarcopenia and Muscle, 13(4), 2118–2131. https://doi.org/10.1002/jcsm.13025
Old, V., Davies, M., Papamargaritis, D., Choudhary, P., & Watson, E. (2025). The effects of GLP-1 receptor agonists on mitochondrial function within skeletal muscle: A systematic review. Journal of Cachexia, Sarcopenia and Muscle, 16(1). https://doi.org/10.1002/jcsm.13677
Osaka, T., Hamaguchi, M., & Fukui, M. (2023). Favorable appendicular skeletal muscle mass changes in older patients with type 2 diabetes receiving GLP-1 receptor agonist and basal insulin co-therapy. Clinical Medicine Insights: Endocrinology and Diabetes, 16. https://doi.org/10.1177/11795514231161885
Sargeant, J., Henson, J., King, J., Yates, T., Khunti, K., & Davies, M. (2019). A review of the effects of GLP-1 receptor agonists and SGLT2 inhibitors on lean body mass in humans. Endocrinology and Metabolism, 34(3), 247–259. https://doi.org/10.3803/enm.2019.34.3.247
Su, Y., Hirayama, K., Han, T., Izutsu, M., & Yuki, M. (2019). Sarcopenia prevalence and risk factors among Japanese community-dwelling older adults living in a snow-covered city according to EWGSOP2. Journal of Clinical Medicine, 8(3), 291. https://doi.org/10.3390/jcm8030291
