Reinforcing value of interval and continuous physical activity in children.

During play children engage in short bouts of intense activity, much like interval training. This natural preference for interval-type activity may have important implications for prescribing the most motivating type of physical activity, but the motivation of children to be physically active in interval or continuous fashion has not yet been examined. In the present study, ventilatory threshold (VT) and VO2 peak were determined in boys (n=16) and girls (n=16) age 10+/-1.3 years. Children sampled interval and continuous constant-load physical activity protocols on a cycle ergometer at 20% <VT on one day and 5% >VT on another day. The physical activity protocols were matched for energy expenditure. Children then completed an operant button pressing task using a progressive fixed ratio schedule to assess the relative reinforcing value (RRV) of interval versus continuous physical activity. The number of button presses performed to gain access in interval or continuous physical activity and output maximum (O(max)) were the primary outcome variables. Children performed more button presses (P<0.005) and had a greater O(max) (P<0.005) when working to gain access to interval compared to continuous physical activity at intensities >VT and <VT. This suggests that interval-type physical activity was more reinforcing than continuous constant-load physical activity for children when exercising both >VT and <VT. Children likely participate in short-duration bouts of activity at a high-rate during natural play because it is more reinforcing than longer, continuous activity.