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) a nd girls (G, n = 38) aged 11-16 years to evaluate habitual physical ac tivity (HPA) over a 1-week period in the winter. The HR and the percen tage of heart rate reserve (%HRR) were taken to be indexes of the meta bolic activity for the whole day and for the different parts of the da y. The HPA was evaluated from the time spent each day below 50%HRR, be tween 50%-70%HRR and above 70%HRR, which related to the time spent in no or low physical activity (NLPA), moderate physical activity (MPA) a nd 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 VP A [B 19 (SD 16) min, G 21 (SD 21) min] throughout the week. During sch ool 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 concomita nt increase in NLPA (P < 0.05). Daily %HRRmean varied significantly du ring the week (range: 28-34% HRR). There were significant differences among the periods of the day (P < 0.05). The HR was the greatest durin g physical education lessons [128 (SD 11) beats . min(-1)], recreation [113 (SD 15) beats . min(-1)] and lunch break [108 (SD 12) beats . mi n(-1)] and the lowest during the evening [94 (SD 10) beats . 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.