You’ve just finished your long Sunday ride. Three hours on the bike, or a half marathon at marathon pace. Your legs are heavy, fatigue has set in, and yet you feel light — too light, maybe. Over the past few weeks, you’ve noticed your thighs shrinking, your arms losing their tone, the scale showing a dropping number without any clear reason why.
I see this scenario regularly in my practice. Cyclists, runners, triathletes who train seriously and lose muscle without even realising it. Many default to the same reflex: “proteins are for bodybuilders, not for me.” And that’s exactly where the problem begins.
Preserving muscle mass in endurance sports is not a gym goal. It’s about performance, health, and athletic longevity. Let me explain why — and above all, how to approach it practically.
Why endurance training melts muscle
When you run or cycle for hours, your body needs energy. It first draws on your glycogen stores, then on fat. But when those reserves run out — and they do, especially during long rides or high-intensity sessions — your body turns to another source: the amino acids in your muscles. This is called muscle catabolism.
Endurance exercise is, by nature, a catabolic effort. Research published in Physiological Reports shows that in cyclists, muscle loss is not limited to the legs: it affects all muscles that are not directly engaged in the sporting movement. The longer the effort and the greater the energy deficit, the stronger the catabolic signal.
Type I muscle fibres — the ones you recruit in endurance — have limited hypertrophic potential. They’re built to last, not to grow. In practical terms, your training doesn’t build muscle — it wears it down. And if you don’t compensate for that wear through nutrition, you progressively lose your muscle capital.
Why does this matter? Because less muscle means less power. A runner who loses muscle mass loses propulsive force. A cyclist whose thighs shrink loses watts. And beyond pure performance, muscle loss weakens joints, increases injury risk, and compromises your ability to handle heavy training loads.
The key role of protein (without bulking up)
This is the most common misunderstanding I encounter: “if I eat more protein, I’ll bulk up“. No. To gain muscle mass, you need a significant caloric surplus, specific hypertrophy training, and a favourable hormonal context. Endurance athletes rarely meet all three of those conditions.
For you, protein doesn’t serve to build muscle. It serves to repair what training destroys. Every long ride, every interval session damages muscle fibres. Protein provides the building blocks — amino acids — needed for muscle protein resynthesis. It’s maintenance, not construction.
The scientific evidence is clear on this point. Research published in PLoS ONE on trained endurance runners showed that protein requirements sit well above standard recommendations. The researchers established an average need around 1.65 g/kg/day, with a recommendation of 1.83 g/kg/day — significantly more than the older estimates of 1.2 to 1.4 g/kg/day based on nitrogen balance.
A protein intake between 1.6 and 1.8 g per kilogram of body weight per day is a minimum for serious endurance athletes. That’s comparable to strength athletes’ requirements — and it often surprises my clients when I tell them. But the data are there: endurance exercise oxidises amino acids during effort, and you need to compensate for those losses.
As Nicolas Aubineau, sports dietitian, emphasises, protein is essential after exercise because it directly contributes to muscle protein resynthesis in the tissues damaged during training. Protein isn’t a bonus — it’s a pillar of recovery.
When and how to eat protein to preserve your muscle mass
Total daily protein intake is essential, but timing also matters. Here are the principles I recommend to my athletes.
The post-exercise window: the decisive moment. Within 30 minutes of your session, your body is particularly receptive to nutrients. This is what’s called the anabolic window. A rapidly absorbed protein source — such as whey or a liquid dairy product — taken during this period kickstarts the muscle repair process. A well-formulated recovery drink combining protein and carbohydrates is often the most practical solution in the field.
Spread your intake throughout the day. Rather than concentrating all your protein in a single meal, distribute it across three to four servings. Breakfast, lunch, snack, dinner: each meal should contain a quality protein source. Eggs, poultry, fish, legumes, dairy — variety is your best ally.
Needs vary from one athlete to another. I deliberately don’t give specific gram amounts in this article, because your needs depend on your weight, training volume, metabolism, and goals. What works for a 60 kg cyclist riding ten hours a week doesn’t apply to an 80 kg ultra-trail runner in preparation. This is exactly the role of a tool like Ograal: personalising intake based on your actual profile. You’ll find nutritional recommendations tailored to your discipline and activity level.
Prioritise complete proteins. Not all proteins are equal. Animal proteins (eggs, fish, meat, dairy) contain all essential amino acids in optimal proportions. If you’re vegetarian or vegan, you can achieve a complete profile by carefully combining legumes, grains, and nuts — but this requires more rigorous planning.
Other levers: sleep, carbohydrates, strength training
Protein is central, but it’s not the whole picture. Preserving your muscle mass in endurance depends on a set of factors that work in synergy.
- Sleep is your best natural anabolic. It’s during deep sleep that your body secretes growth hormone and muscle repair peaks. If you sleep poorly or not enough, even the most optimal diet won’t suffice. Aim for at least seven to eight hours of quality sleep, and treat sleep as a training tool in its own right.
- Carbohydrates protect your muscles. This is a point many endurance athletes overlook. When your glycogen stores are full, your body doesn’t need to tap into muscle protein for energy. Consuming enough carbohydrates before, during, and after exercise limits catabolism. Carbohydrates also play a role in glycogen resynthesis and post-exercise muscle anabolism.
- Strength training is an ally, not an enemy. Two to three short strength sessions per week, focused on functional movements (squats, lunges, core work), send a powerful signal to your body: “keep this muscle, I need it.” You won’t bulk up — your endurance training takes care of that — but you’ll maintain your strength, stability, and muscular integrity.
- Avoid prolonged caloric deficits. Losing weight is a common goal among cyclists and runners. But an overly aggressive or prolonged restriction directly attacks muscle mass. If you want to refine your body composition, do it gradually, while maintaining a high protein intake and periodising your restriction phases outside competition periods.
From theory to practice
Preserving your muscle mass in endurance isn’t complicated. It’s a matter of simple principles applied consistently: enough protein, well distributed, at the right time, accompanied by appropriate carbohydrates, sleep, and a minimum of strength work. The real challenge is translating those principles into actual meals, tailored to you and your training schedule.
That’s exactly what Ograal does. The app offers personalised nutritional recommendations based on your discipline, training volume, and goals. No more calculating, doubting, or navigating contradictory advice. You know what to eat, when, and why — and your muscles will thank you.
Discover your personalised nutrition plan on Ograal and give your body what it truly needs to perform, last, and stay strong.
Ingrid Gallerini
Sports Dietitian — Ograal
