Efeito da velocidade inicial no desempenho e alterações mecânicas da corrida em ultramaratona de 6 horas

Abstract

The aim of this study was to describe the pacing strategy adopted by runners during a 6-hour ultramarathon running race and investigate whether a slow-start affect overall performance, ratings of perceived exertion (RPE), ratings of fatigue (ROF) and running mechanics. Sixteen ultrarunners were recruited and took part of the first part of this study (descriptive). During the second part (experimental), 10 participants performed a third additional testing session. The study consisted of three sessions: 1) critical speed test; 2) self-paced 6-hour ultramarathon running race; and 3) 6-hour ultramarathon with initial speed manipulation. During the first race, the athletes were instructed to achieve the greatest possible distance in a 6-hour run in an athletics track. Four weeks later, they performed a second 6-hour ultramarathon, in which they were requested to run the initial 36 minutes (i.e. first 10% of the race) at speeds ~18% below their mean speed of the initial 36 min of the first race (self-paced). During both races, RPE, ROF and running mechanics were measured in consistent time-intervals. Our results showed that, in general, athletes adopted a sigmoid pacing strategy (F = 32.90; P < 0.001; ηp2 = 0.69), increasing linearly their RPE (F = 30.27; P < 0.001; ηp2 = 0.67) and ROF (F = 56.04; P < 0.001; ηp2 = 0.79). The contact times increased (F = 9.43; P < 0.001; ηp2 = 0.39) and aerial times decreased (F = 9.77; P < 0.001; ηp2 = 0.39) after 1 hour of the race, whereas the stride length was lower (F = 9.92; P < 0.001; ηp2 = 0.40) after 2 hours and stride frequency did not change (F = 0.90; P = 0.45; ηp2 = 0.06) during the first race. Despite lower normalised mean speeds during the first 10%-time interval (P < 0.001), and greater speeds at 50% (P < 0.001) and 90% (P = 0.034) of the second race, overall performance was not different between races (57.5 ± 10.2 vs. 56.3 ± 8.5 km; P = 0,298). However, runners decreased their RPE (F = 3.46; P < 0.001; ηp2 = 0.28) and ROF consistently throughout the second race (F = 2.30; P = 0.010; ηp2 = 0.20). Moreover, contact times were higher and aerial times shorter during the second race, during the first lap (P < 0.001) and at 30 minutes (P < 0.004). The stride length was lower during the first lap (P < 0.001), 30 minutes (P < 0.001) and 1 hour (P = 0.047), whereas stride frequency was lower only at 30 minutes (P < 0.001). Decreasing initial speed by ∼18% might not affect 6-hour ultramarathon performances, but it lowers the development of RPE and ROF. Finally, running mechanics seem to be affected mainly by changes in running speed.