Ultramarathon Physiology: What HCPs Should Know?

Ultramarathon Metabolism: What Happens to the Body During Extreme Distances?

Ultramarathon metabolism has become a growing area of scientific focus as extreme-distance events attract more endurance athletes worldwide. A new real-world study published in Nutrients provides unprecedented insight into how the body responds when pushed beyond 100 km, revealing profound calorie loss, widespread muscle damage, and complex hormonal fluctuations that differ by race and distance. The physiological cost of completing 230 km, the study shows, is not merely an extension of shorter races but a distinct metabolic challenge.

Real-World Ultramarathon Physiology Insights for HCPs

To understand clinically relevant metabolic changes that occur during ultramarathons, researchers conducted a prospective observational study during the 2024 TorTour de Ruhr, a non-stop event in Germany. This unique field environment allowed investigators to capture real-time physiological stress that laboratory simulations cannot replicate.

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A total of 43 experienced endurance athletes (average: 37 ultramarathons completed) participated across three distances, 100 km, 160.9 km (100 miles), and 230 km. Blood and saliva analyses measured biomarkers of muscle damage (CKM, LDH) and key metabolic hormones, including leptin, ghrelin, insulin, glucagon, GLP-1, and irisin. Continuous glucose monitoring (CGM) was used in a subgroup, while nutrition intake and symptom burden were documented throughout the race.

Despite high carbohydrate intake, nearly 79% of total calories, athletes were unable to match expenditure, leading to severe energy deficits. On average, runners lost 6,797 kcal, but the 230 km group recorded losses surpassing 18,364 kcal, demonstrating massive physiological strain with ultra-long distances.

Hormonal, Metabolic, and Muscular Shifts During Extreme Distances

HCPs monitoring endurance athletes will find the hormonal responses particularly relevant. The study recorded:

• Leptin: Significant whole-group decline, most pronounced in the 230 km runners
• Ghrelin: Increased (p = 0.0083), intensifying hunger signaling
• Insulin: Decreased (p = 0.0033), promoting fuel mobilization
• Glucagon: Increased (p = 0.0139), supporting glucose release
• Irisin: Significantly elevated (p = 0.0160), suggesting adaptive muscle remodeling

Interestingly, glucose levels from CGM systems stayed stable and within normal range, despite the calorie deficit. This indicates a strong compensatory response as the body shifts fuel pathways to preserve brain and muscle function during prolonged exertion.

Muscle damage was significant across all distances, with marked rises in CKM and LDH, confirming widespread structural stress. Athletes also reported high post-race GASE symptom scores, including nausea, appetite loss, muscle pain, and exhaustion—symptoms clinicians frequently observe in ultra-endurance athletes.

Clinical Implications for Recovery, Nutrition, and Athlete Monitoring

For clinicians, sports nutritionists, and physiologists, this study reinforces the need for individualized fueling plans, balanced macronutrient support, and targeted recovery strategies tailored to race distance. The hormonal disruptions observed, particularly leptin suppression, insulin reduction, and glucagon activation, indicate that extreme distances may temporarily alter endocrine function, delaying recovery if nutritional deficits persist.

The study emphasizes that 230 km events represent a fundamentally different metabolic state, requiring specialized monitoring and post-race rehabilitation protocols to restore muscle integrity, replenish energy stores, and stabilize hormonal balance.

As ultramarathons gain participation across all age groups, these findings offer critical insights for HCPs supporting athletes through preparation, race-day nutrition, and post-event recovery.

Source:

MDPI