Purpose. During play children engage in intermittent bouts of activity less than 15 seconds in duration, much like interval training. These short bouts comprise 95% of their total physical activity. Despite this observed natural preference for interval-type activity, the reinforcing value of interval relative to continuous exercise has not yet been examined.; Methods. 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 exercise on a cycle ergometer at 20% VT on one day and 5% >VT on another day. The exercise protocols were matched for energy expenditure on each day. After sampling the exercise protocols children played a computer game to assess the RRV of interval versus continuous exercise by having children work to earn access to either interval or continuous exercise in 1-min blocks for a total of 7 min (fixed ratio schedule; 4, 8, 16, 32, 64, 128, 256). The amount of time children earned and the total amount of button presses they performed for interval or continuous were compared.; Results. There were no differences in the amount of time earned (P = 0.07) or work performed (P = 0.34) for interval exercise >VT and VT. Children performed more button presses (P≤0.01) during the computer game for access to interval compared to continuous exercise >VT and VT. Children also earned a greater proportion of minutes for interval compared to continuous exercise >VT (P = 0.02), but not VT (P=0.20).; Conclusions. Interval exercise was more reinforcing than continuous exercise for children when exercising both >VT and VT. These results support the notion that children participate in short-duration bouts of activity at a high-rate during natural play because that type of activity is more reinforcing than longer, continuous activity.
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