Project FURTHER: A Physiological, Biomechanical, and Psychosocial Profile of an All-Female 6-Day Ultramarathon Race

Background
Ultramarathon performance reflects a complex interplay of physiological, biomechanical, and psychosocial factors, yet data from multi-day events remain limited, particularly in females. The demands and key determinants of performance in these events, including the longest ratified world-record event, the 6-day ultramarathon, are not well-characterized. This study aimed to provide a comprehensive, multi-disciplinary profile of the demands and performance determinants in an all-female 6-day ultramarathon.

Methods
10 heterogenous female athletes (27–48y, Tier 2–5, V̇O2 peak: 21.0–62.9 ml∙min–1·kg–1) ran a self-paced, certified 6-day ultramarathon. Data were collected over the preceding year, 2–4d pre-race, during the race, and post-race. We assessed V̇O2 peak with ventilatory thresholds and running economy; haemoglobin mass; body composition; total daily energy expenditure (TDEE, via doubly-labelled water) and dietary energy intake (EI); continuous heart rate, glucose, and core temperature; neuromuscular and cognitive fatigue; biomechanical parameters; in-race blood sampling to assess inflammatory markers; and psychosocial outcomes.

Results
All athletes achieved personal distance records over 6 days (463.6±199.6 km), with the top athlete covering 901.8 km, breaking the female world record. Exercise intensity was low (~46±6%V̇O2 peak), but demands were extreme: up to 20 h·day−1 racing with 82,699±17,192 steps·day−1, total sleep 5.2±1.9 h·day−1, 4188±1109 kcal·day−1 EI, and 6698±2071 kcal·day−1 TDEE; including three of the highest female TDEEs reported. Average active race pace was 8:41±2:27 min:sec·km−1 and the average decline in running velocity from the first 2 days to the last 2 days was 9±13.1%. There was no evidence of neuromuscular or cognitive fatigue 24 h post-race. The top athlete, who ran 258.2 km farther than the next finisher, had similar lab-tested physiology compared to the next four top finishers, but spent the most time on course with the highest TDEE, EI, running and total step count, and exhibited significantly greater neuromuscular fatigue, inflammatory markers, sleep deprivation, and pacing decline. The only clear difference between the top athlete and the next 4 athletes was years of running experience (29 vs. 9.7±7.4 years).

Conclusions
The 6-day ultramarathon imposes an extreme physical and psychological challenge. Success may depend less on physical capacity and biomechanical efficiency than on the ability to persevere through fatigue.