Why Endurance Athletes Also Need Protein: 5 Reasons From Muscle Maintenance to Training Adaptation

1Endurance Training Also Breaks Down Muscle; It's Not Just Weight Training That Consumes Protein

Many believe "muscle breakdown" is exclusive to weightlifting. The opposite is true: prolonged, moderate to high-intensity endurance exercise is itself a chronic consumption of protein.

During exercise, the body increases whole-body protein turnover — simultaneously breaking down muscle protein (MPB) and attempting to synthesize it (MPS). As exercise duration extends, some amino acids are oxidized for energy, serving as an additional energy source. Reviews indicate that during prolonged moderate to high-intensity exercise, amino acid oxidation can account for approximately 5–10% of total energy expenditure, with branched-chain amino acids being the primary ones oxidized (Witard et al., Sports Med 2025; Fritzen et al., Annu Rev Nutr 2019).

What does this mean? It means that with every long training session, a portion of your muscles is "disassembled." If you don't replenish protein, breakdown will continue to outweigh synthesis, leading to a gradual loss of lean body mass over time.

• Witard OC, et al. Protein Nutrition for Endurance Athletes: A Metabolic Focus on Promoting Recovery and Training Adaptation. Sports Med 2025;55(6):1361-1376. PMID:40117058.
• Fritzen AM, et al. Dietary Fuels in Athletic Performance. Annu Rev Nutr 2019;39:45-73. PMID:31136266.

2Protein's Core Mission: Maintaining Condition, Not Just "Muscle Building"

For endurance athletes, protein's most important role is to shift the net balance back to positive — allowing muscle synthesis to keep pace with breakdown, maintaining existing lean body mass and the muscle condition required for athletic performance.

This is different from "getting strong." Endurance athletes don't need to pursue the maximum rate of muscle hypertrophy, but they do need sufficient protein intake to counteract the catabolic stress of training, keeping muscles in a "continuously usable" state (Jäger et al., J Int Soc Sports Nutr 2017).

More importantly, training adaptation itself is a process of "protein creation": mitochondrial biogenesis, increased capillary density, and upregulation of aerobic enzyme activity — all these changes that make you stronger require protein synthesis to materialize (Morton et al., Int J Sport Nutr Exerc Metab 2026; Witard 2025). Without sufficient protein raw materials, adaptation is just "training" but not necessarily "growing."

• Jäger R, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20. PMID:28642676.
• Morton JP, et al. Nutritional Periodization: Strategies to Enhance Training Adaptation and Recovery. Int J Sport Nutr Exerc Metab 2026;36(3):279-304. PMID:41130458.
• Witard OC, et al. Sports Med 2025 (Same as Section 1).

3How Much? Recommended Protein Intake for Endurance Athletes

The International Society of Sports Nutrition (ISSN) position is that the recommended protein intake for individuals who exercise regularly is approximately 1.2–2.0 g per kg of body weight per day; endurance-focused athletes with high training volumes typically fall within the range of 1.2–1.6 g/kg/day (Jäger 2017).

In contrast, the reference intake for an average sedentary adult is approximately 0.8 g/kg/day. This means that a 70 kg endurance athlete needs about 84–112 g of protein daily, which is more than double that of an average person—and this doesn't even account for additional consumption on long training days.

In practice, distributing the total amount across meals is more effective than consuming it all at once: consuming approximately 0.25–0.4 g/kg per meal (or 20–40 g of high-quality protein per meal) can more steadily stimulate muscle protein synthesis (Jäger 2017). For a 70 kg person, this means about 18–28 g per meal, spread across three meals plus a post-exercise dose.

• Jäger R, et al. J Int Soc Sports Nutr 2017 (Same as Section 2).

• Schematic diagram · Data source: Jäger et al., J Int Soc Sports Nutr 2017; for endurance athletes, a range of 1.2–1.6 g/kg/day is recommended, with 1.4 g/kg/day used as a median for illustration.

4Post-Exercise: Carbohydrates with Protein to Care for Both Glycogen and Muscles

Post-endurance exercise nutrition typically focuses on a "dual-track approach": replenishing glycogen while also supporting muscle recovery.

Research shows that co-ingesting carbohydrates and protein after exercise, compared to carbohydrates alone, further supports glycogen resynthesis and muscle recovery (Alghannam et al., Nutrients 2018). Reviews on nutrient timing also indicate that early post-exercise protein supplementation (with carbohydrates) significantly aids in initiating recovery, although the "strict timing window" is not as narrow as commonly believed—total intake and daily consumption patterns are equally crucial (Kerksick et al., J Int Soc Sports Nutr 2017).

For endurance athletes, a practical approach is to consume a carbohydrate and protein recovery solution within 30–60 minutes after a long training session or competition, and then return to regular meals. This can facilitate faster recovery on that day and smoother transition to the next day's training.

• Alghannam AF, et al. Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion. Nutrients 2018;10(2). PMID:29473893.
• Kerksick CM, et al. International society of sports nutrition position stand: nutrient timing. J Int Soc Sports Nutr 2017;14:33. PMID:28919842.

5Get Your Protein Right with SiS Recovery Powders

Applying the above logic to products, both SiS recovery powders can help you get enough protein, though they have different focuses:

How to choose:

• If you follow a vegan diet, want to control sugar intake, and also need vitamins and minerals → REGO Rapid Recovery is more suitable.
• If you want to replenish a large amount of glycogen after exercise, don't mind higher sugar, and are fine with whey protein → BETA Recovery is more suitable, as it has a more concentrated amount of protein and carbohydrates.

Neither product is "protein-only"; rather, they integrate protein into a comprehensive "post-exercise recovery" strategy—which is precisely what endurance athletes need most.

• Schematic diagram · Data source: SiS official product page (REGO Rapid Recovery per 50g / BETA Recovery per 100g).

• Schematic diagram · Data source: SiS official product page; fat rounded to 0.1g.

• Schematic diagram · Data source: SiS official product page.

• SiS official product page: REGO Rapid Recovery (scienceinsport.com/shop-by-need/recovery/rego-recovery-powder)
• SiS official product page: BETA Recovery (scienceinsport.com/shop-by-need/recovery/beta-recovery-powder)

Conclusion

To connect the dots: Endurance training breaks down muscles and increases protein turnover → Protein's role is to maintain muscle status and facilitate training adaptation → Approximately 1.2–1.6 g/kg daily, distributed across meals and post-exercise → Use a recovery strategy with carbohydrates and protein to fill the gap. Endurance athletes don't need to treat protein as a "muscle builder," but incorporating it into their daily routine is fundamental for training to truly translate into progress.

• Jäger R, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20. PMID:28642676. DOI:10.1186/s12970-017-0177-8.
• Kerksick CM, et al. International society of sports nutrition position stand: nutrient timing. J Int Soc Sports Nutr 2017;14:33. PMID:28919842. DOI:10.1186/s12970-017-0189-4.
• Witard OC, et al. Protein Nutrition for Endurance Athletes: A Metabolic Focus on Promoting Recovery and Training Adaptation. Sports Med 2025;55(6):1361-1376. PMID:40117058. DOI:10.1007/s40279-025-02203-8.
• Morton JP, et al. Nutritional Periodization: Strategies to Enhance Training Adaptation and Recovery. Int J Sport Nutr Exerc Metab 2026;36(3):279-304. PMID:41130458. DOI:10.1123/ijsnem.2025-0073.
• Fritzen AM, et al. Dietary Fuels in Athletic Performance. Annu Rev Nutr 2019;39:45-73. PMID:31136266. DOI:10.1146/annurev-nutr-082018-124337.
• Alghannam AF, et al. Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion. Nutrients 2018;10(2). PMID:29473893. DOI:10.3390/nu10020253.