Association between Physical Activity, Sedentary Time and Healthy Fitness in Youth.

Purpose: To examine the associations between objectively measured physical activity (PA), sedentary time, and health-related fitness; and to investigate the combined association of PA and sedentary time on health-related fitness in youth.

Methods: PA and sedentary time were assessed with accelerometers in 2506 youth aged 10-18 years (M age=13.2+/-2.3). Participants were classified as active (>=60 min/day MVPA) versus inactive (<60 min/day MVPA), and as low versus high sedentary (according to the median value of sedentary time/day) and thereafter grouped as active/low sedentary, active/high sedentary, inactive/low sedentary, and inactive/high sedentary. Five physical fitness tests (body mass index [BMI], push-ups, curl-ups, sit and reach, and the PACER test) were assessed with FITNESSGRAM and participants were categorized as being in the healthy versus the unhealthy fitness zone (HFZ). A fitness composite score was calculated using the individual fitness tests z-score. Regression models were used to examine the relationship between PA, sedentary time and physical fitness.

Results: Time spent in MVPA (min/day) ([beta]=0.002, p<0.001) was significantly associated with the fitness score independent of sedentary time. Sedentary time was not associated with physical fitness independent of MVPA. Compared to the inactive/high sedentary group (referent), being categorized as active/low sedentary was associated with an increased likelihood of being in the HFZ for sit and reach (OR=2.55, 95% CI: 1.96-3.32) and having a higher fitness composite score (OR=1.38, 95% CI: 1.13-1.69).

Conclusions: Time in MVPA was associated with better physical fitness independent of sedentary time. Participants classified as active/low sedentary had higher odds of being in the HFZ, for flexibility, and to have a better fitness composite score. These findings suggest that time in MVPA contributes to better physical fitness in youth.