PURPOSE: This case-report characterised the respiratory, cardiovascular, and nutritional/gastrointestinal (GI) responses of a trained individual to a novel ultra-endurance exercise challenge.
METHODS: A male athlete (age 45 y, mass 80.7 kg, stature 1.71 m, V̇O2max 54.8 mL∙kg-1∙min-1) summited 100 mountains on foot (all elevations >600 m) in 25 consecutive days, and cycled between five base-camps throughout the UK. Laboratory measures of pulmonary function (spirometry, whole-body plethysmography, single-breath rebreathe), respiratory muscle strength (maximum static mouth-pressures), and cardiovascular structure and function (echocardiography, electrocardiography, large vessel ultrasound, flow-mediated dilatation) were assessed at baseline and at 48 h post-challenge. Dietary intake (4-d food diary), self-reported GI symptoms, and plasma endotoxin concentrations were assessed at baseline, pre/post mid-point (day 13), pre/post penultimate point (day 24), and at 48 h post-challenge.
RESULTS: The participant completed the challenge with a total exercise time of 142 h (5.3±2.8 h∙d-1), distance of 1141 km (42.3±43.9 km∙d-1), ascent of 33804 m (1252±807 m∙d-1), and energy expenditure of 80460 kcal (2980±1451 kcal∙d-1). Relative to baseline, there were post-challenge decreases in pulmonary volumes and capacities (6 - 32%), expiratory flows (9 - 28%), maximum expiratory mouth-pressure (19%), and maximum voluntary ventilation (29%). Heart rate variability had deteriorated, manifesting in a 48% decrease in the root mean square of successive differences (RMSSD) and a 70% increase in the low-frequency/high-frequency ratio (LF/HF). There were no notable changes in any other index of cardiovascular structure or function. Pre- to post-challenge endotoxin concentrations were elevated by 60%, with a maximum increase of 130% after a given stage, congruent with an increased frequency and severity of GI symptoms.
CONCLUSIONS: This is the first study of the integrative physiological responses to an ultra-endurance exercise challenge. The findings extend our understanding of the limits of physiological function and may inform medical best-practice for personnel supporting ultra-endurance events.