As ultra-endurance events continue to grow in popularity-with races now routinely exceeding 24 hours in duration-new research highlights the significant physiological strain placed on even elite athletes. A prospective observational study published in Nutrients analyzed metabolic, hormonal, and muscle stress in ultramarathoners completing distances of 100, 160.9, and 230 kilometers during the 2024 TorTour de Ruhr in Germany.The findings reveal ample energy deficits and hormonal disruption across all distances, underscoring the need for tailored recovery and fueling strategies to mitigate the substantial toll these races take on the body.
Even seasoned ultramarathon runners experience significant energy depletion, muscle breakdown, and hormonal shifts during races, with longer distances leading to the most substantial physiological strain, according to new research.
Study: Does Distance Matter? Metabolic and Muscle Challenges of a Non-Stop Ultramarathon with Sub-Analysis Based on Race Distance. Image Credit: lzf/Shutterstock
A recent prospective observational study published in the journal Nutrients tracked ultramarathon athletes competing in distances of 100 kilometers (62 miles), 160.9 kilometers (100 miles), and 230 kilometers (143 miles) to assess metabolic, hormonal, and muscle stress under real-world conditions. Understanding the physiological toll of extreme endurance events is crucial for optimizing athlete health and recovery.
The study revealed substantial energy deficits – averaging nearly 6,800 calories – along with significant muscle damage and hormonal changes across all distances. Notably, some markers showed the most pronounced alterations in the 230-kilometer group, rather than a uniform worsening with increased mileage. These findings highlight the need for individualized recovery and fueling strategies for endurance athletes.
Researchers found that while significant physiological stress occurs even at 100 kilometers, the biological cost of running 230 kilometers is distinct and considerably more severe than running 100 kilometers.
Growing Interest in Ultra-Endurance Events
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Ultra-endurance sports have seen consistent growth over the past decade, with thousands of athletes now participating in events lasting more than 24 hours. While the physiological demands of these races – particularly their extreme energy requirements and impact on immune function – are well-established, most existing research has focused on shorter durations or controlled laboratory settings. These controlled environments may not accurately reflect the challenges athletes face during actual races.
Therefore, understanding how the extent of physiological stress evolves with distance remains a significant gap in sports science.
Data on key hormones regulating appetite, such as leptin and ghrelin, during these events is also limited. Tracking these hormonal fluctuations is essential, as prolonged negative energy balance can disrupt endocrine function and delay recovery, potentially jeopardizing long-term health.
Study Design and Athlete Tracking
This study aimed to address these knowledge gaps and inform future sports policies by analyzing data from the TorTour de Ruhr 2024, a grueling, non-stop ultramarathon held in Germany. Data was collected from 43 experienced endurance athletes (16 women and 27 men) divided into three groups based on their race distance: 100 km, 160.9 km, and 230 km. The athletes were highly experienced, having completed an average of 37 previous ultramarathons.
The study data included a comprehensive physiological profile of all participants, derived from a combination of blood biomarkers, digital monitoring, and surveys:
Biochemical Analysis: Blood and saliva samples were collected immediately before the race and at the finish line to measure and compare markers of muscle damage, specifically creatine kinase (CKM) and lactate dehydrogenase (LDH). Hormones regulating energy metabolism, including leptin, ghrelin, insulin, glucagon, GLP-1, and irisin, were also recorded and included in subsequent statistical analyses.
Blood Glucose Monitoring: A subgroup of 17 participants used continuous glucose monitoring (CGM) systems to track their interstitial glucose levels in real-time during their respective races.
Dietary and Symptom Tracking: Participants tracked and reported their food and fluid intake using the Food Database GmbH (FDDB) application. They also completed the General Assessment of Effects (GAZ) questionnaire to evaluate physical symptoms such as nausea and muscle pain.
Ultimately, data from 39 of the 43 participants who completed their races were used for statistical analysis, including descriptive statistics, the Kolmogorov-Smirnov normality test, and the paired Wilcoxon signed-rank test.
Extreme Deficits and Hormonal Changes
The study analyses revealed that despite a carbohydrate-rich diet (representing nearly 79% of intake), participants were unable to meet their caloric needs, demonstrating significant energy deficits. The average estimated energy deficit across all distances was 6,797 calories. This deficit varied considerably by distance, with the 230-kilometer group experiencing deficits up to 18,364 calories. This extreme caloric deficit triggered a cascade of hormonal adjustments, although not all hormones showed statistically significant differences based on distance.
Key findings included:
Appetite Regulation: Leptin levels decreased significantly across the entire group, with the most pronounced drop occurring in the 230-kilometer group. The 100-kilometer group showed only a trend toward reduction, while the 160.9-kilometer group showed no significant change. Conversely, ghrelin, the hunger hormone, increased (p = 0.0083).
Metabolic Changes: Insulin levels decreased (p = 0.0033), while glucagon increased (p = 0.0139). This reciprocal change is known to help the body mobilize stored fats and sugars to fuel the brain and muscles. Surprisingly, despite the massive caloric deficits, CGM data showed that glucose levels remained stable and within a normal range, demonstrating the body’s remarkable ability to maintain homeostasis under stress.
Irisin Release: The study also noted a significant increase in irisin (p = 0.0160), a hormone derived from muscle (myokine) linked to fat metabolism, suggesting that extreme exertion stimulates adaptive metabolic remodeling.
GLP-1, another hormone evaluated in the study, did not show significant results before and after, further highlighting the heterogeneous hormonal responses to extreme endurance exercise.
Implications for Ultra-Endurance Recovery
This study establishes the severe disruptions to metabolic and structural integrity induced by ultramarathon running, supported by observations of significant increases in CKM and LDH (markers of muscle damage) and post-race GAZ scores (increased reports of nausea, loss of appetite, muscle pain, and exhaustion). The findings underscore the importance of understanding the physiological demands placed on athletes during these events.
Future nutritional protocols should likely emphasize balanced carbohydrate, fat, and protein strategies, including adequate protein intake to support muscle resilience and recovery, while maintaining sufficient carbohydrate availability to stabilize energy supply and endocrine function, thereby improving both athletic performance and physiological well-being.
