Morning-to-evening differences in oxygen uptake kinetics in short-duration cycling exercise.

This study analyzed diurnal variations in oxygen (O(2)) uptake kinetics and efficiency during a moderate cycle ergometer exercise. Fourteen physically active diurnally active male subjects (age 23+/-5 yrs) not specifically trained at cycling first completed a test to determine their ventilatory threshold (T(vent)) and maximal oxygen consumption (VO(2max)); one week later, they completed four bouts of testing in the morning and evening in a random order, each separated by at least 24 h. For each period of the day (07:00-08:30 h and 19:00-20:30 h), subjects performed two bouts. Each bout was composed of a 5 min cycling exercise at 45 W, followed after 5 min rest by a 10 min cycling exercise at 80% of the power output associated with T(vent). Gas exchanges were analyzed breath-by-breath and fitted using a mono-exponential function. During moderate exercise, the time constant and amplitude of VO(2) kinetics were significantly higher in the morning compared to the evening. The net efficiency increased from the morning to evening (17.3+/-4 vs. 20.5+/-2%; p<0.05), and the variability of cycling cadence was greater during the morning than evening (+34%; p<0.05). These findings suggest that VO(2) responses are affected by the time of day and could be related to variability in muscle activity pattern.

Modification of cycling biomechanics during a swim-to-cycle trial.

The aim of this study was to investigate the effects of drafting, i.e., swimming directly behind a competitor, on biomechanical adaptation during subsequent cycling. Eight well-trained male triathletes underwent three submaximal sessions in a counterbalanced order. These sessions comprised a 10-min ride on a bicycle ergometer at 75% of maximal aerobic power (MAP) at a freely chosen cadence. This exercise was preceded either by a 750-m swim performed alone at competition pace (SCA trial; swimming-cycling alone), a 750-m swim in a drafting position at the same pace as during SCA (SCD trial; swimming-cycling with drafting), or a cycling warm-up at 30% of MAP for the same duration as the SCA trial (CTRL trial). The results indicated that the decrease in metabolic load when swimming in a drafting position (SCD trial) was associated with a significantly lower pedal rate and significantly higher mean and peak resultant torques when compared to the SCA trial, p < 0.05. These results could be partly explained by the lower relative intensity during swimming in the SCD trial when compared with the SCA trial, involving a delayed manifestation of fatigue in the muscles of the lower limbs at the onset of cycling.

Drafting during swimming improves efficiency during subsequent cycling.

PURPOSE: The aim of the present study was to investigate the effects of drafting (i.e., swimming directly behind a competitor) while swimming with a wet suit on physiological parameters and cadence during subsequent cycling. METHODS: Eight well-trained male triathletes underwent two submaximal sessions conducted in a counterbalanced order. One of these sessions (SAC) consisted of a 750-m swim, performed at competition pace, followed by a 15-min ride on a bicycle ergometer at 75% of maximal aerobic power and at a freely chosen cadence. During the other session (SDC) the subjects swam 750 m in a drafting position at the same pace as during SAC and then performed the 15-min cycling test at the same intensity as during SAC. RESULTS: The main result indicated that cycling efficiency was significantly improved when the cycling session was preceded by a swimming bout performed in drafting position compared with an isolated swimming bout (+4.8%, P < 0.05). CONCLUSION: These results could be partly explained by the lower relative intensity observed during swimming in the SDC trial when compared with the SAC trial. This study suggests the relative importance of swimming condition and highlights the advantage of drafting during the swimming portion of a sprint triathlon.