Energy Cost of Running During a Bout of 80.5-km Treadmill Running

Abstract

Success in ultraendurance running is composed of many interrelated variables. Notably the involvement of the cardiovascular system has been proposed to explain variance in performance. At present, there is limited data on the changes in the energy cost of running (Cr) during bouts of ultraendurance running. Therefore, the purpose of this study was to identify changes and adjustments in Cr and respiratory variables over an 80.5-km treadmill time trial (TT). Participants were instructed to complete 80.5 km on a motorized treadmill and to cover the distance in the fastest possible time. Respiratory variables ( QUOTE o2 [oxygen consumption], QUOTE co2 [carbon dioxide production], and RER [respiratory exchange ratio]) were measured via indirect calorimetry every 16.1 km at a set speed of 8 km/h. Running speed and heart rate were continually monitored throughout the 80.5-km TT. Average run time to completion was 7 hours 28 minutes 9 seconds ± 1 hour 25 minutes 12 seconds at a mean speed of 10.8 ± 1.5 km/h (pace, 5:34 ± 1:04 min/km). QUOTE o2 increased by 21.8% from the start of the TT to completion (31.19 ± 2.89 vs 38.0 ± 6.41 mL∙min–1∙kg–1, respectively), while RER decreased from the start to 32.2 km whereupon RER plateaued. There was a significant increase of 24.2% in Cr (P < .001) from the start to completion of the TT. The current study indicated adjustments in QUOTE o2, Cr, and substrate utilization during an 80.5-km treadmill TT. Results indicated a shift to fatty acid oxidation as a main fuel source over a bout of 80.5 km, which corresponded with the increase in Cr. These findings may influence pacing strategies and overall success of performance in ultraendurance events.