Preserving Muscle on GLP-1: A Hybrid Athlete's Protocol

The Muscle Loss Problem

GLP-1 medications are effective at producing weight loss. What the headlines rarely mention is that not all of that lost weight is fat. Clinical trials consistently show that 25-40% of weight lost on semaglutide (Ozempic, Wegovy) is lean body mass in sedentary populations (Wilding et al., 2021; Rubino et al., 2022).

For a sedentary person losing 15 kg on semaglutide, that could mean 4-6 kg of lost lean mass — muscle tissue, but also contributions from bone mineral density, organ mass, and connective tissue. A 2024 meta-analysis by Heymsfield and colleagues confirmed this range across multiple GLP-1 trials.

For endurance athletes, this is a serious concern. Lean mass loss means reduced power output, compromised running economy at higher intensities, weaker functional strength (critical for HYROX stations), and potential injury risk from musculoskeletal imbalance. The power-to-weight benefit of losing fat can be partially or fully offset if you lose too much muscle along the way.

The good news: these numbers come from sedentary study populations who did not exercise or optimize protein intake. Active intervention changes the ratio substantially. The question is how much — and that is what this protocol and my body composition tracking attempt to answer.

My Preservation Protocol

My approach rests on three pillars, each addressing a different mechanism of lean mass loss. No single intervention is sufficient — the combination is what matters.

Pillar 1: Resistance training

Mechanical tension on muscle fibers is the primary stimulus for muscle retention during weight loss. Without resistance training, the body has no reason to preserve energetically expensive muscle tissue in a caloric deficit.

Pillar 2: Protein intake

Protein provides the raw material for muscle protein synthesis. In a caloric deficit — which GLP-1 creates by suppressing appetite — inadequate protein accelerates lean mass loss. Higher protein intakes partially buffer this effect.

Pillar 3: Training load maintenance

Endurance training volume provides an additional stimulus to the muscles used in running, cycling, and swimming. Reducing training volume during GLP-1 treatment removes this stimulus and accelerates lean mass loss in the working muscles. Maintaining volume while managing the caloric deficit is the balancing act.

Resistance Training Program

The goal of resistance training on GLP-1 is not hypertrophy — it is retention. The programming reflects this: moderate volume, heavy enough loads to provide mechanical tension, compound movements that hit multiple muscle groups efficiently, and a frequency that fits alongside endurance training without creating excessive fatigue.

I kept it straightforward: full-body resistance training maintained throughout the 5-week GLP-1 protocol. No reduction in training frequency, no reduction in volume, no concessions. The resistance sessions ran alongside a full Ironman training block — swimming, cycling, running — which meant time efficiency mattered more than elaborate periodization.

The approach was full-body sessions rather than a traditional split. With endurance training taking priority in terms of hours, I could not afford to dedicate separate days to push, pull, and legs. Full-body sessions meant every muscle group got stimulus in every session, which is the right strategy when the goal is preservation rather than hypertrophy.

Working weights stayed the same throughout. No strength regression. That was the litmus test I cared about — if my numbers started dropping, it would signal either insufficient protein, insufficient recovery, or actual lean mass loss. None of those alarms went off.

Progression strategy

In a caloric deficit, expecting continuous strength gains is unrealistic. The goal is to maintain current working weights as long as possible. I track every session and consider a 5% drop in any lift a signal that recovery or protein intake needs attention.

Over the 5-week protocol, I saw zero regression in working weights across any lift. No exercise dropped in load. In a caloric deficit, that is the outcome you want — not improvement, just stability. The fact that I could walk into the gym in week 5 and move the same weight I moved in week 1 tells me the protocol held.

Subjectively, I looked and felt more lean. The mirror changed before the scale did, which is what you expect when fat is coming off and muscle is staying. For a baseline reference: my InBody scan from January 2026 (pre-GLP-1) showed 94.1 kg total body weight with 50.9 kg skeletal muscle mass. I do not have a follow-up InBody scan yet to compare directly — the body fat estimates I track come from circumference measurements and a regression model, not InBody or DEXA. Those circumference results are detailed below.

Protein Strategy

The protein challenge on GLP-1 is practical, not theoretical. Everyone agrees high protein intake preserves muscle during weight loss. The problem is that GLP-1 suppresses appetite, and protein is the most satiating macronutrient. Eating 1.8-2.4g per kilogram of body weight when you are rarely hungry requires deliberate planning.

Daily targets

I target 1.8-2.4g protein per kilogram of body weight per day, adjusted based on training load. Higher-volume days (long runs, brick sessions) warrant the upper end of the range; rest days can stay at the lower end.

My daily protein intake ranged from 140g to 190g depending on training load. At a body weight of approximately 92.5 kg during the protocol, that works out to roughly 1.5-2.1 g/kg per day — within the recommended range for muscle preservation during weight loss. Heavy training days pushed toward the upper end; rest days sat closer to the lower bound.

I did not follow a rigid protein timing protocol. The priority was hitting the daily total. On days when appetite was suppressed (typically 1-3 days post-injection), liquid protein sources made the difference between hitting the target and falling short.

Timing around training and injections

Protein timing matters more on GLP-1 because the window of normal appetite is narrower. I front-load protein in the morning (when appetite is typically least suppressed) and immediately post-training (when the body signals need most clearly). The 24-48 hours after injection are the hardest for hitting protein targets — I rely more heavily on liquid protein during this window.

Rather than a precise meal-by-meal breakdown, my approach was pragmatic: protein first at every eating opportunity, and when appetite was too low for a full meal, a protein shake closed the gap. The 24-48 hours after injection were the hardest window for hitting protein targets — liquid sources became essential insurance during those days.

Practical tactics for low-appetite days

• Protein shakes as insurance. When solid food is unappealing, a 40g whey shake takes 30 seconds to drink. This is not optimal nutrition — it is damage control for days when eating feels impossible.
• High-protein snacks. Greek yogurt (20g per serving), jerky, protein bars, and cottage cheese provide protein without requiring a full meal.
• Prioritize protein first in every meal. Eat the protein source before carbs and fats. If appetite runs out mid-meal, at least the protein was consumed.
• Batch cook protein sources. Having pre-cooked chicken, hard-boiled eggs, and prepared tofu in the fridge removes the decision overhead on low-energy days.

Training Load Management

For endurance athletes, the temptation during GLP-1 treatment is to reduce training volume because of lower energy intake. This is a mistake. Reducing the stimulus to working muscles accelerates lean mass loss. The goal is to maintain training volume while managing the caloric deficit through strategic fueling.

What I maintained

• Weekly running volume (kilometers and frequency)
• Long run duration and progression
• Key quality sessions (tempo, intervals, threshold work)
• Cycling volume for triathlon preparation

What I adjusted

• Easy day intensity. On days when energy was low (usually 24-48 hours post-injection), easy runs were truly easy — Zone 1, no pushing.
• Session fueling. Every session over 60 minutes included intra-workout carbohydrate, even easy runs. The caloric deficit cannot come from training fuel.
• Recovery protocols. Sleep, hydration, and post-session nutrition received extra attention. The margin for recovery error is smaller in a deficit.

The bottom line: I did not miss a single training session due to GLP-1 during the 5-week protocol. The full Ironman training block continued — swimming, cycling, running, plus resistance training. Energy levels stayed consistent. No recovery issues that I could attribute to the medication rather than normal training fatigue.

This is worth emphasizing because many GLP-1 protocols recommend reducing training volume during the initial phase. I did not do that. Whether I could have maintained this at a higher dose is an open question — at 2.5 mg tirzepatide, the caloric deficit was modest enough that fueling was never compromised. On the bike, I consumed 100+ grams of carbohydrates per hour with no GI issues whatsoever.

Body Composition Results

A note on methodology: I do not use DEXA scans. My body fat estimates come from regular circumference measurements fed into a linear regression model. This is less precise than DEXA — it cannot isolate lean mass from fat mass with clinical accuracy. But it is practical, repeatable, and the directional trends over 5 weeks are clear enough to draw conclusions.

For a baseline reference, my InBody scan from January 26, 2026 (before starting GLP-1) measured 94.1 kg total body weight with 50.9 kg skeletal muscle mass. I do not have a follow-up InBody scan for direct comparison.

Circumference measurements (5-week change)

Measurement	Feb 22	Mar 22	Change
Waist	87.5 cm	85.5 cm	-2.0 cm
Belly	86.0 cm	82.5 cm	-3.5 cm
Chest	107.0 cm	105.0 cm	-2.0 cm
Hips	~99 cm	~99 cm	stable
Thighs	~62 cm	~62 cm	stable

Estimated body fat

• Feb 22 (start): 13.0% (circumference-based estimate)
• Mar 22 (5 weeks): 11.3% (circumference-based estimate)

The pattern is telling. Fat loss was concentrated in the trunk and midsection — waist, belly, and chest all decreased meaningfully. Hips and thighs stayed stable, which suggests the leg musculature used in running and cycling was preserved. The limb measurements holding steady while trunk measurements dropped is consistent with fat loss, not lean mass loss.

Lean mass preservation rate

The key metric is what percentage of total weight lost was lean mass versus fat mass. The clinical trial average for sedentary participants is 25-40% lean mass loss. With my protocol, the goal is to push this well below 20%.

Without DEXA, I cannot calculate an exact lean-mass-to-fat-mass loss ratio. What I can say with confidence:

• Total weight lost: approximately 4.5 kg (94.5 kg to ~90 kg measurement weight)
• Body fat estimate change: 13.0% to 11.3% (-1.7 percentage points)
• Trunk circumferences: decreased 2.0-3.5 cm across waist, belly, and chest
• Limb circumferences: stable — no measurable decrease in thigh or hip measurements
• Working weights: maintained — no regression in any resistance exercise
• Clinical trial context: sedentary populations lose 25-40% of total weight as lean mass

The circumstantial evidence points in the right direction: fat came off the midsection, limbs stayed the same size, and strength did not decrease. A DEXA scan would give precise numbers, but the convergence of these indicators suggests the three-pillar protocol worked. I plan to get a follow-up InBody scan to put harder numbers on this.

What the Research Says

My protocol is informed by — but not limited to — the current evidence base. Here is a brief overview of what the research supports and where gaps remain.

Established evidence

• Resistance training preserves lean mass during weight loss. This is well-established across multiple contexts, not specific to GLP-1. A 2024 systematic review confirmed that resistance training during pharmacological weight loss significantly reduced lean mass loss compared to medication alone.
• Higher protein intake reduces lean mass loss. Intakes of 1.6g/kg and above are consistently associated with better lean mass outcomes during caloric deficit (Phillips & Van Loon, 2011).
• Endurance training provides partial protection. Running and cycling preserve leg musculature through regular use, though the effect on upper body is minimal.

Open questions

• Optimal protein threshold on GLP-1 specifically. Most protein research was conducted without concurrent GLP-1 use. Whether the altered gut motility and absorption affect protein utilization is not yet established.
• GLP-1 and muscle protein synthesis directly. Some preclinical data suggests GLP-1 receptor agonists may have direct effects on muscle protein synthesis beyond the caloric deficit. This is not yet confirmed in human studies.
• Long-term lean mass outcomes. Most GLP-1 trials are 52-68 weeks. The long-term trajectory of lean mass — especially after reaching weight maintenance — is not well-studied.

For the full protocol and journey context, return to the GLP-1 pillar page. For how these body composition changes affected race performance, see my race results with data.

Frequently Asked Questions

How much muscle do you lose on Ozempic or Wegovy without doing anything about it?

Clinical trials show that 25-40% of total weight lost on semaglutide is lean body mass in sedentary populations (Heymsfield et al., 2024). For a person losing 15 kg, that could mean 4-6 kg of lean mass — including muscle, bone density contribution, and organ mass. Active intervention with resistance training and adequate protein can substantially reduce this ratio, though no protocol eliminates it entirely.

How much protein should an endurance athlete eat on GLP-1?

The general recommendation for muscle preservation on GLP-1 is 1.6g protein per kg body weight per day. For endurance athletes with high training volume, I target 1.8-2.4g/kg. The challenge is practical: GLP-1 suppresses appetite, and protein is the most satiating macronutrient. I use protein shakes, high-protein snacks between meals, and strategic timing around training to hit these targets.

Can you build muscle while on Ozempic or Mounjaro and losing weight?

Building net new muscle while in a caloric deficit is difficult for anyone and likely impossible at the rate of weight loss typical on GLP-1. The realistic goal is preservation — maintaining as much existing lean mass as possible while losing predominantly fat. Some beginners to resistance training may see initial strength gains through neural adaptation, but this is not the same as significant muscle hypertrophy.

How often should you strength train on GLP-1?

Research on muscle preservation during weight loss consistently shows that 2-3 resistance training sessions per week, targeting all major muscle groups, is the minimum effective dose. I train 3x/week with a focus on compound movements (squats, deadlifts, presses, rows). For endurance athletes, the challenge is fitting this around swim/bike/run volume without overtraining.

Does endurance training protect against muscle loss on GLP-1?

Endurance training alone provides some stimulus to the muscles being used (primarily legs in running and cycling), but it does not adequately protect upper body musculature or provide the mechanical tension needed for full-body lean mass preservation. Runners on GLP-1 without resistance training may preserve leg muscle reasonably well but lose significant upper body and core lean mass. A combined approach is essential.