This study investigated the validity of the CSA activity monitor for assessment of
the total amount of physical activity in adolescent athletes. Activity data were compared
to data on daily energy expenditure and its derivatives measured by the doubly labeled
water method. Seven athletes (speed skaters) with a mean age of 18.2 ± 1.1 y were
monitored twice (off-season and pre-season) by the activity monitor for eight consecutive
days. The primary training during the off-season period was running whereas the pre-season
period mainly involved skate training (i.e. inline skating, slideboard training, and
skating imitations). Activity counts were significantly correlated to all energy estimates
during the off-season period (r = 0.93 - 0.96; P < 0.01) whereas not during the pre-season
period (r = 0.32 - 0.57). A two-way multivariate analysis of variance showed a significant
period effect for activity counts (668 ± 163 vs. 548 ± 91; P = 0.026) whereas not
for total daily energy expenditure (15.7 ± 2.1 MJ × d-1 vs. 16.0 ± 1.0 MJ × d-1; P = 0.71). The relationship between activity counts and total daily energy expenditure
seems to be affected by different training conditions. Therefore these circumstances
have to be carefully considered in the interpretation of activity monitor data.
Accelerometer, doubly labeled water, energy expenditure, physical activity.