Anaerobic threshold and the determination of training target heart rates in premenarchal girls.

The capability of children to respond to endurance training with increased aerobic capacity is unclear. Prepubertal subjects may require higher target heart rates than adults to increase VO2 max, and previous studies failing to demonstrate aerobic trainability in children may have involved inadequate exercise intensity. In this study, heart rates at the anaerobic threshold, measured noninvasively as the ventilatory breakpoint (VBP), were determined during treadmill testing of 12 premenarchal girls to establish a metabolic-based target rate. The mean heart rate at VBP was 171 beats/min (+/- 12 SD) with a range from 147 to 194 beats/min. Although a wide intersubject variability was observed, the rates at VBP exceeded those predicted by standard formulas for calculating target heart rates in adults by over 10 beats/min in a majority of the girls. These data indicated that target heart rate guidelines designed for training older individuals may not adequately stress oxygen delivery systems in prepubertal subjects.