GLP-1s Are Reshaping Your Gym Floor. The Question Is What You Do About It.

A few years ago, if you had told me that a weekly injection would become one of the biggest forces in the fitness industry, I am not sure I would have believed you. Yet here we are.  

Walk onto almost any gym floor and a real share of the people training are also on a GLP-1 medication such as semaglutide or tirzepatide. They are losing weight, often a lot of it, and they are doing it faster than most diet and exercise programs alone could manage.

That is genuinely good news for a lot of people. But there is a quieter story sitting underneath the headline weight loss numbers, and it is one the fitness industry is uniquely placed to do something about.

What the weight loss is actually made of

When someone loses weight on a GLP-1, not all of that loss is fat. A portion of it is lean tissue, and some of that lean tissue is skeletal muscle mass. The step 1 and surmount trials, the large studies behind semaglutide and tirzepatide, found that roughly 30 to 40 percent of the weight lost was lean body mass rather than fat.  

More recent work has refined the picture. A 2026 systematic review and meta-analysis in the International Journal of Obesity reported that after twelve months of therapy, skeletal muscle mass fell by around 3 percent and lean body mass by around 1 percent, alongside meaningful reductions in visceral fat. Researchers at UC Davis have also noted that some of the earlier, scarier lean mass figures were partly explained by losses from the liver and other organs rather than muscle alone, which is reassuring. But those same researchers are clear that limiting muscle wasting through exercise and quality protein still matters a great deal.

Why does this matter so much? Because skeletal muscle is not just about strength or how you look in the mirror. It is the body's largest site for glucose uptake, a major driver of metabolic rate, and one of the clearest markers we have for healthy aging. Prado, Phillips, Gonzalez and Heymsfield made this case directly in The Lancet Diabetes and Endocrinology in 2024, in a paper titled, fittingly, Muscle Matters.  

When you lose muscle, you lower your metabolic engine, which is the exact thing you need running to keep the weight off after the medication stops. And most people do stop. A large share discontinue within a year, and when they do, weight tends to come back. If muscle was lost on the way down and never rebuilt, that return is even harder to manage.

This is where the Fitness Industry shines!

Here is the part I find genuinely exciting. The single most effective tool we have for protecting and rebuilding muscle during weight loss (after optimal protein consumption is equated) is not a new drug. It is resistance training. The exact thing the fitness industry already delivers every single day.

The evidence keeps stacking up. A 2025 review in Frontiers in Clinical Diabetes and Healthcare concluded that resistance training is crucial for preserving lean mass during weight loss, and that pairing GLP-1 therapy with structured strength work and enough protein delivers additive benefits. In 2025, a joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and  

The Obesity Society recommended strength training at least three times per week, plus at least 150 minutes of aerobic activity, for people using these medications. And a six month study of 200 adults, presented in 2025, showed that people who received guidance on resistance training and protein lost about 13 percent of their body weight but only around 3 percent of their muscle. That is the whole game in one sentence. Same weight loss, very different outcome, decided largely by training and protein.

So, the question I want to put to the industry is a simple one. How are you helping your members?

Not in a vague, motivational sense. Specifically. If a member walks in next week and tells you they have just started on a GLP-1, what happens next? Do you have a way to put a number on where their muscle is today? Do you have a plan to protect it? Will you know in three months whether your programming actually worked, or will you be guessing?

You cannot manage what you do not measure

This is the part I think the industry has under-appreciated. Encouraging resistance training is the right instinct, but without a baseline you are flying blind. The scale will go down on a GLP-1 no matter what you do, so the scale tells you almost nothing about whether you are protecting the right tissue. A member can lose twenty pounds, feel like a runaway success, and quietly be shedding the muscle that protects their long-term health.

A baseline body composition measurement changes that conversation completely. It separates fat loss from muscle loss, and it lets you follow skeletal muscle mass over time so you can actually see whether the training is doing its job.

This is where the Evolt 360 Body Composition Analyzer is built differently from a lot of what is on the market. It assesses skeletal muscle mass using multi-frequency bioelectrical impedance, rather than estimating it from body weight, and it produces a consistent, repeatable read that you can track from one scan to the next.  

For a population on GLP-1 medications, where weight is dropping quickly, that repeatable trend line is the thing that actually tells the story. A single number on a single day is interesting. The same number tracked across months is what proves your program is working.

There is one more piece I think is genuinely useful here, and it speaks straight to the protein problem. The literature is consistent that protein intake during weight loss should sit somewhere around 1.2 to 2.0 grams per kilogram per day to help preserve muscle, and increasingly researchers are expressing that target relative to lean tissue rather than total body weight. That distinction matters, because appetite suppression on a GLP-1 makes it very easy to fall well short without realizing it. The Evolt 360 establishes an individualized suggestion based on the member’s own body composition, goal, activity level and activity type, not a generic figure off a chart. It hands your members and your coaches a concrete starting target and discussion point to further individualise and discuss with their health care professional. It does not replace a clinician's advice, and it should not, but it gives the everyday conversation a real number to work from.

The responsibility, and the opportunity

GLP-1 prescribing is a medical decision, and it belongs with medical providers. The fitness industry's job is not to prescribe medication. But exercise prescription has always been the fitness industry’s domain, and right now the science is pointing squarely at the doorstep.  

The people best placed to make sure this generation of weight loss is good quality weight loss, the kind that builds long term health rather than quietly eroding it, are the coaches, trainers and operators who see these members several times a week.

That is a real responsibility. It is also, if you choose to see it this way, one of the biggest opportunities the industry has had in years. The clubs and studios that build a simple, repeatable process around this, baseline the member, train them properly, give them a protein target, then re-measure to prove it worked, are going to stand out. They will keep members longer, get better results, and have the data to show for it.

So, I will ask it one more time, because I think it is the question that matters most this year.  

Your members are already walking through your doors on these medications. How are you helping them?

Guest Author, Kylie Zimmerle, Product Manager, Evolt Health

References

1. Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine, 2021.

2. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 2022.

3. GLP-1 agonists and changes in body mass and composition in adults with overweight or obesity: a systematic review and meta-analysis. International Journal of Obesity, 2026.

4. Prado CM, Phillips SM, Gonzalez MC, Heymsfield SB. Muscle matters: the effects of medically induced weight loss on skeletal muscle. The Lancet Diabetes & Endocrinology, 2024.

5. GLP-1 agonists and exercise: the future of lifestyle prioritization. Frontiers in Clinical Diabetes and Healthcare, 2025.

6. American College of Lifestyle Medicine, American Society for Nutrition, Obesity Medicine Association, The Obesity Society. Joint advisory on nutrition and physical activity for adults using incretin-based therapies, 2025.

7. Johnson B, et al. Suboptimal protein intake for hypocaloric diet needs while using GLP-1 receptor agonists. Journal of the International Society of Sports Nutrition, 2025.

8. Resistance training and protein intake during GLP-1 receptor agonist therapy (six-month study of 200 adults). Presented at the European Congress on Obesity, 2025.