Commentaries on Viewpoint: Sacrificing economy to improve running performance—a reality in the ultramarathon? ECCENTRIC LOAD OF LONG-TERM RUNNING AND ENERGY INTAKE HAVE A MAJOR ROLE IN THE ULTRAMARATHON

TO THE EDITOR: The analyses of ultraendurance athletes have provided new insights into the limits of human performance capacity and into medical complications when going beyond the physical limits. Ultradistance running poses a unique stress on the athlete. In their Viewpoint, Millet et al. (3) argued that determinants of performance in ultraendurance are subjected to a compromise between two main parameters: energy cost and lower limb tissue injury. The latter results from a complex combination of extrinsic factors (training errors including lack of specific strength, inappropriate footwear, inappropriate running surface, and terrain) and intrinsic factors (poor flexibility, biomechanical lower extremity malalignment, anthropometry, previous injury, running experience). Concerning the former, environmental conditions, training, and perhaps most importantly fluid and fuel intake all contribute to energy balance state and so race performance. In fact, nutrient intake during ultradistance races has been found to be below the estimated energy cost (1). Despite a low relative intensity the energy cost of running (expressed in mlO2) is increased during ultradistance trail running races (2) compared with level running. This induces a marked negative energy balance state that was shown to reduce serum leptin concentrations during ultramarathon race (5). Thus suboptimal nutrition certainly would result in decreased performance under these circumstances. Finally, it is proposed that the most important factor linking both parameters explaining ultramarathon tolerance is the eccentric load of long-term running causing an association between skeletal muscle damage and impaired renal function through dehydration, rhabdomyolysis, and hemolysis (4) further exacerbated without optimal nutrition intake.