Continuous heart rate monitoring over 1 week in teenagers aged 11-16 years.

Heart rate (HR) was monitored in 66 French pubertal boys (B, n = 28) and girls (G, n = 38) aged 11-16 years to evaluate habitual physical activity (HPA) over a 1-week period in the winter. The HR and the percentage of heart rate reserve (%HRR) were taken to be indexes of the metabolic activity for the whole day and for the different parts of the day. The HPA was evaluated from the time spent each day below 50%HRR, between 50%-70%HRR and above 70%HRR, which related to the time spent in no or low physical activity (NLPA), moderate physical activity (MPA) and vigorous physical activity (VPA), respectively. No sex differences were observed in the average %HRR each day [%HRRmean, [B 30 (SD 4)%; G 32 (SD 4)%]] or in NLPA [B 715 (SD 61) min, G 711 (SD 81) min] and VPA [B 19 (SD 16) min, G 21 (SD 21) min] throughout the week. During school days, daily %HRRmean was 7% smaller in 14-16 year olds compared to 11-13 year olds. This was linked to a decrease in MPA and a concomitant increase in NLPA (P < 0.05). Daily %HRRmean varied significantly during the week (range: 28-34% HRR). There were significant differences among the periods of the day (P < 0.05). The HR was the greatest during physical education lessons [128 (SD 11) beats x min(-1)], recreation [113 (SD 15) beats x min(-1)] and lunch break [108 (SD 12) beats x min(-1)] and the lowest during the evening [94 (SD 10) beats x min(-1)]. It was only during the lunch breaks that %HRRmean was greater (P < 0.05) on school days than on free days. Of all the teenagers studied 32% were considered active during the week.

Time-of-day effects in maximal anaerobic leg exercise.

Time of day variations in maximal anaerobic leg exercise were studied in 23 men mean age 23 (SD 3) years. All the subjects performed two anaerobic tests (force-velocity and multi-jump tests) and those familiar with sprinting ran an additional 50-m dash (n = 16). The maximal anaerobic powers for cycling and jumping (Pcycling and Pjump) and maximal anaerobic velocity (vpeak) were performed consecutively in the same order for all tests. The force-velocity and force-power relationships were established to determine Pcycling. The flight time (tf) and the ground contact time (tc) were recorded from five consecutive jumps on a jump-ergometer to calculate Pjump. The vpeak was measured between the 35th and the 45th m during the dash-run. The test schedules were at 0900, 1400 and 1800 hours on separate days in random order. Rectal temperatures (Tre) and body mass (mb) were measured before each test. The Tre increased significantly from 0900 to 1800 hours (P < 0.001) but mb did not vary during the day (P > 0.05). The Pcycling and Pjump were higher at 1400 and 1800 hours than at 0900 hours. The differences between the morning and the afternoon reached 3% (P < 0.05) for Pcycling and 5%-7% for Pjump (P < 0.01). The time-of-day effect was significant for tf (P < 0.05) but not for tc. During the dash-run tests, the differences almost reached significance for vpeak between 0900 and 1800 hours (P = 0.0544). No significant variations were observed between 1400 and 1800 hours for cycling, jumping and running tests. A time-of-day effect in the maximal anaerobic power of cycle and multi-jump tests existed. Such variations would have pronounced effects when expressed in competitions.