Abstract des Autors

The aim of this study was to investigate the increase in energy cost of running occurring at the end of a triathlon and a marathon event and to link them to the metabolic and hormonal changes, as well as to variations in stride length. Seven subjects took part in 3 experimental situations: a 2h15min triathlon (30 min swimming, 60 min cycling and 45 min running), a 2h15min marathon (MR) where the last 45 min were run at the same speed as the triathlon run (TR), and a 45 min isolated run (IR) done at triathlon speed. The results show that energy cost during MR was higher than during TR (+8.9%). Similar observations were made for pulmonary ventilation (+7.9%) and heart rate (+6.3%). Moreover, the values were significantly greater than the values obtained during the IR. TR and MR lead to greater weight loss (2.4+/-0.3 kg) than IR (1+/-0.2 kg). The triathlon and the marathon produced a large decrease in plasma volume (respectively 19.6+/-1.4% and 12.9+/-1.1%) compared to IR (2+/-0.4%). Plasma renin activity was higher for the triathlon and the marathon than for the IR. MR produces a significantly greater increase in plasma free fatty acids (F.F.A.) than TR and IR. In addition, the F.F.A. at the end of TR were significantly higher than IR. At the end of the trial the mean stride lengths for TR and IR were greater (+15%) than for MR. This study, carried out with subjects running overground, confirms the decrease in running efficiency previously shown at the end of a laboratory triathlon, and demonstrates that this decrease is lower than that occurring during a marathon. Verf.-Referat