I’ve had several clients start GLP-1 medications this year, semaglutide, tirzepatide, different doctors, different reasons. The pattern that’s actually useful to understand isn’t the drug itself. It’s what happens to muscle while the weight comes off, and how much of that outcome is actually still in the coach’s hands.
A meaningful share of the weight lost is muscle, not fat
Across the current research, somewhere between a quarter and nearly forty percent of total weight lost on GLP-1 therapy is lean mass rather than fat, with the higher end showing up more on the newer, higher-dose compounds. That’s not a rounding error. Muscle tissue burns roughly three times the resting calories per kilogram that fat does, so losing it doesn’t just change how someone looks, it lowers the metabolic rate that’s supposed to keep the weight off long term.
The mechanism is straightforward once you say it out loud: appetite suppression controls how much a person eats. It has no say in whether the body pulls the deficit from fat or muscle. Without a strong enough signal telling the body which tissue to protect, it protects neither particularly well.
Backing off intensity is the instinct, and it’s backwards
A client eating less, moving through a rougher stretch of nausea or fatigue some weeks, looks like someone who needs an easier program. The instinct to lighten the load is understandable. It’s also exactly the wrong direction. Resistance training is the clearest signal available for telling the body which tissue is worth keeping. Remove that signal at the same time appetite is already suppressed, and there’s nothing left pushing the loss toward fat instead of muscle.
What the current research actually supports
This isn’t a hunch. The S-LITE trial found that clients doing supervised resistance and aerobic training alongside GLP-1 therapy didn’t just lose weight faster, they gained lean mass, something the medication alone never produced. Several major research groups (Exeter, Ohio State, Rice among them) currently have active trials running specifically on this question, so the picture is still filling in. But the practical direction already converging across the research is consistent: structured resistance training two or more times a week, protein intake in the 1.2 to 1.6 grams per kilogram of bodyweight range, spread across meals rather than loaded into one, and close attention to whether appetite suppression is quietly cutting into recovery, not just calories.
What this actually looks like in a session
Don’t assume. Ask directly whether appetite has dropped enough to affect how much they’re eating around training days specifically, not just in general. A client who used to eat comfortably before a session may now be training on much less, which changes what they can recover from that week. Prioritize compound resistance work over pure cardio volume, since cardio alone does nothing to protect lean tissue and these clients need every protective signal they can get. Keep an eye on energy and GI symptoms when picking session timing, since nausea and reflux are common enough on these medications to matter for scheduling, not just performance. And loop the client’s prescriber in on what’s actually being planned, since decisions like this sit better made together than guessed at from either side alone.
The medication isn’t doing this part of the job
It was never going to. Appetite control and muscle preservation are two different problems, and only one of them has a drug attached to it. The other one is still, entirely, the program.
Ramses
Personal Trainer and Group Fitness Instructor