You finally found something that works. Now your body is playing by a completely different set of rules.
Beard Guy showed up to a Tuesday morning run feeling like someone had unplugged him from the wall. Heart rate was fine. Sleep was fine. Stress was manageable. But the legs? The legs had apparently filed for early retirement and forgotten to send the memo.
It wasn’t overtraining. It wasn’t a bad night. It was dose day.
If you are a type 2 diabetic training on a GLP-1 medication like Mounjaro, Ozempic, or Wegovy, you already know that something is different. You might not be able to name it yet, but you feel it. The effort that used to produce a certain result is producing something else now. Sometimes less. Sometimes just… different.
My Garmin, which I have lovingly nicknamed Judge Judy for reasons that will become obvious to any athlete who has ever been handed a “status: unproductive” verdict they did not see coming, took one look at my training load and body battery and banged the gavel. The watts, the pace, the effort scores from six months ago? Inadmissible. All of it. Court has ruled that the athlete who existed before dose day is no longer a reliable witness, and the sooner you stop calling him to the stand, the better.
This is not a post about whether GLP-1s are right for you. That conversation lives between you and your doctor. This is about what training actually looks like once you are on one, why your energy behaves the way it does, and how to stop fighting your body and start working with it.
What to Actually Expect From Your Energy
Here is the thing nobody tells you when you start a GLP-1: the fatigue you feel is not your blood sugar crashing. It is your body quietly forgetting to ask for food.
For me, Tuesday is dose day, but the shot does not happen until after my hard bike session is done. That is not a coincidence. That is a scheduling decision I made on purpose, and it is one of the first things I tell any athlete I coach who is on a GLP-1. Protect your hard efforts. Dose around them, not into them.
By Tuesday afternoon, after the shot, Beard Guy is operating at somewhere between sixty and seventy percent. Wednesday is a long slow run day, which works out fine because the engine is idling anyway. Mad Anthony is watching the numbers from the booth and noting that output is down, recovery metrics are soft, and the body battery looks like it has been running a background app nobody authorized. Thursday is an easy bike, which fits the energy curve almost perfectly. Friday brings a harder swim, and by then the energy is starting to return. Saturday and Sunday are where the longer bike and harder run sessions live, and that is where I expect to actually perform.
That is not luck. That is the week I built around a Tuesday dose.
The research on GLP-1 medications and endurance athletes is thin at best. What the science does tell us is that the energy dip most athletes experience is tied less to the drug itself and more to what the drug does to your appetite. GLP-1s suppress the food noise that most of us rely on as a hunger signal. You simply stop feeling hungry, which means you stop eating enough, which means you show up to a Saturday long ride running on fumes you did not know were low. Judge Judy does not care why the tank is empty. She just delivers the verdict.
The fix is not complicated, but it requires intention. You have to eat on a schedule, not on a signal. Carbohydrates are still your training fuel, and the medication does not change that math. I wear a CGM twenty-four hours a day, which means I have real-time data telling me what my glucose is doing before, during, and after every session. My control outside of training is solid, sitting at roughly ninety-eight percent time in range week to week. So when the energy dip hits on dose day, I already know it is not a glucose problem. That distinction matters, because the instinct for any type 2 diabetic is to blame blood sugar first. Sometimes the answer is simpler: you just did not eat enough Tuesday.
When the Dose Hits and Why Your Stomach Goes Quiet
Gastric emptying sounds like a medical term someone invented to make a simple concept sound complicated. What it actually means is that your stomach is moving food through more slowly than it used to. For most people, that translates to feeling full longer, which is part of how GLP-1 medications do their job. For athletes, it means something a little more inconvenient: the hunger signal that used to tell you to eat before a workout has gone mostly silent.
Here is what that looks like in practice. It is approaching noon on a Wednesday. Beard Guy has already knocked out his long slow run. He looks at the clock, does the math, and realizes he has not eaten since breakfast. The thing is, he is not hungry. Not even a little. No growling, no focus fade, no craving. Nothing. So he sits there and debates whether he actually needs to eat or whether his body is just being efficient.
He eats anyway. And the moment the food hits, he realizes he was hungry the entire time. The notification just never came through.
That is gastric emptying at work. The cue is gone. The need is not.
This is where dose timing matters, and why it is the first conversation I have with any athlete I coach who is starting a GLP-1. Tuesday is my dose day. The shot happens after my hard bike, not before. By Tuesday afternoon the medication is doing its job, and by Wednesday the stomach has gone quiet. Wednesday through Friday, Beard Guy is essentially eating on a schedule because there is no internal alarm telling him to. Mad Anthony is logging this as a feature, not a bug, as long as the calories and carbohydrates are actually going in on time.
The athletes who struggle most on GLP-1s are not the ones with bad training plans. They are the ones who stopped eating because they stopped feeling hungry and never connected those two things to their flatlined workouts three days later.
My doctor brought me into this medication slowly, starting at a low dose and increasing it gradually over several months until we landed where we needed to be. That slow titration is probably why I avoided the GI issues that give GLP-1s a bad reputation. Nausea, bloating, and reflux are real side effects, but they are often worse when the dose goes up too fast too soon. If your first few weeks on a GLP-1 felt like a gut renovation project, that is worth a conversation with your doctor. It does not have to feel that way.
Where Do You Go From Here
Training on a GLP-1 is not impossible. It is not even that complicated once you understand what the medication is actually doing and why your body is responding the way it is. The energy dip is real. The absent hunger cue is real. The quiet stomach on a Wednesday morning is real. But none of those things have to derail your training if you plan around them instead of fighting through them.
There is a lot more to cover on this topic. Glucose management during training, fueling strategy when you have no appetite, and what your data is actually telling you when Judge Judy hands down a verdict you did not expect. This is a conversation worth continuing.
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Coach Tony Hampton is a triathlon and endurance multisport coach based in Fort Wayne, Indiana, with a growing focus on health and wellness coaching. He holds certifications through IRONMAN U, ESCI, Stryd Run Power, TriDot Pool School, and Precision Nutrition (PN Certified Master Coach).
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