What happens to your body during an ultramarathon? Recent study reveals necessary metabolic changes

A recent prospective observational study published within the journal Nutrients tracked ultramarathon athletes over 100 km, 100 miles (160.9 km) and 230 km to evaluate metabolic, hormonal and muscular stresses under real-world conditions.

The study results showed significant energy deficits (averaging nearly 6,800 kcal) in addition to significant muscle damage and hormonal changes occurring across all distances, with some markers showing the biggest changes within the 230km group quite than consistent deterioration with distance traveled.

These results highlight the urgent need for personalized recovery and energy strategies for extreme endurance athletes and highlight that while severe physiological stress occurs as early as 100 km, the biological cost of running 230 km is different and significantly higher than that of running 100 km.

Growing interest in ultra-endurance events

Ultra-endurance sports have seen continued growth over the past decade, with hundreds of athletes now competing in events lasting longer than 24 hours. While the physiological disadvantages of those breeds, particularly their extreme demands for energy availability and immune function, are well-known, most existing research has focused on shorter time periods or controlled laboratory environments that lack ecological validity and the flexibility to reflect real breed conditions.

Consequently, understanding how levels of physiological stress vary with distance stays a major gap in current exercise science.

Moreover, there’s little data on key appetite-stimulating hormones, equivalent to leptin and ghrelin, during such events. Understanding these physiological fluctuations is critical because sustained negative energy balance can impair endocrine function and delay recovery, potentially jeopardizing long-term health.

Study design and athlete monitoring

The current study goals to fill these knowledge gaps and inform future sport policy by utilizing data from the TorTour de Ruhr 2024, a grueling non-stop ultramarathon event in Germany. Study data was collected from 43 experienced endurance athletes (16 women and 27 men) who were divided into three groups based on their race distance: 100 km, 160.9 km and 230 km. Crucially, these athletes were very experienced and had accomplished a mean of 37 ultramarathons.

Study data included a comprehensive physiological profile of all enrolled participants, derived from a mixture of blood biomarkers, digital monitoring and surveys:

Biochemical evaluation: Blood and saliva samples were collected immediately before the race and on the finish line to measure and compare markers of muscle damage, particularly creatine kinase muscle type (CKM) and lactate dehydrogenase (LDH). Hormones that control energy metabolism, including leptin, ghrelin, insulin, Glucagon, GLP-1and irisin were also recorded and included in subsequent statistical analyses.

Glucose monitoring: A subset of 17 participants received continuous glucose monitoring (CGM) systems to trace their interstitial glucose levels in real time during their respective races.

Weight loss plan and Symptom Tracking: Participants were required to trace and report their food and fluid intake using the Food Database GmbH, Bremen, Germany (FDDB) database app. As well as, they accomplished the final assessment of uncomfortable side effects (GASES) Questionnaire to evaluate physical symptoms equivalent to nausea and muscle pain.

Notably, only 39 of the 43 participants included accomplished their respective races and their data sets formed the premise for statistical evaluation, including descriptive statistics, the Kolmogorov-Smirnov normality test, and the Wilcoxon matched pairs signed rank test.

Extreme deficits and hormonal changes

Study analyzes showed that despite eating a high-carbohydrate weight loss program (which accounted for nearly 79% of intake), study participants were unable to fulfill their calorie needs and as an alternative experienced severe deficits. Specifically, the mean estimated energy deficit across all distances was calculated to be 6,797 kcal. Notably, this deficit varied significantly by distance, with the 230 km group having a deficit of as much as 18,364 kcal. This extreme calorie deprivation was observed to trigger a cascade of hormonal adaptations, although not all hormones showed statistically significant distance-dependent differences.

Key findings included:

Appetite regulationLeptin decreased significantly at the general group level, with the biggest decrease occurring within the 230 km group, while there was only a trend toward reduction within the 100 km group and no significant change within the 160.9 km group. In contrast, ghrelin, the hunger hormone, increased (p = 0.0083).

Metabolic shifts: insulin Levels decreased (p = 0.0033), while glucagon levels increased (p = 0.0139). This mutual shift has already been shown to assist the body mobilize stored fat and sugar to fuel the brain and muscles. Surprisingly, despite the huge calorie deficits, CGM The info showed that glucose levels remained stable and inside normal ranges, demonstrating the body’s remarkable ability to keep up homeostasis under stress.

Irisin release: The study also found a major increase in irisin (p = 0.0160), a muscle hormone (myokine) related to fat metabolism, suggesting that extreme exercise stimulates adaptive metabolic remodeling.

GLP-1one other hormone examined within the study, showed no significant pre- and post-effects, further highlighting the heterogeneous hormonal responses to extreme endurance training.

Impact on ultra-endurance recovery

The current study establishes the severe disruptions in metabolic and structural integrity induced by ultramarathon running, supported by observations of a major increase CKM And LDH (marker of muscle damage) and post-race climbs GASES Scores (reported increase in nausea, lack of appetite, muscle pain and fatigue).

Future dietary protocols should likely emphasize balanced carbohydrate, fat and protein strategies, including adequate protein intake to support muscle resilience and recovery, while maintaining adequate carbohydrate availability to stabilize energy supply and endocrine function, thereby improving not only athletic performance but in addition physiological well-being.