Reinforcing value of interval and continuous exercise above and below the ventilatory threshold
Barkley, Jacob Edward
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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 VO 2 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< or =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.