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 2h 15 min triathlon (30 min swimming, 60 min cycling
and 45 min running), a 2 h 15 min marathon (MR) were 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 (p <
0.01) (+ 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 (p < 0.01) (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 (p < 0.01). MR produces a significantly greater increase in plasma free fatty
acids (F.F.A.) than TR(p < 0.05) and IR(p < 0.01). In addition, the F.F.A. at the
end of TR were significantly higher than IR (p < 0.05). At the end of the trial the
mean stride lengths for TR and IR were greater (+ 15 %) (p < 0.01) 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.
Key words
Triathlon - marathon - dehydration - running efficiency - energy cost of running -
stride length
