What limits endurance in normal children?

We have compared the results of a standard progressive maximal exercise test to those of an endurance exercise test in 22 healthy school children (13 girls, 9 boys, mean age 14.8 years) in order to examine whether it is possible to extrapolate results from a maximal test to predict their endurance capacity. All children performed a standard progressive maximal exercise test (15 W increments every minute until exhaustion) and an endurance test (individually calculated loads to mimic cycling at 20 km/h against a windforce 5 of Beaufort for 30 minutes) on 2 separate days. In both tests metabolic [oxygen uptake (Vo 2 ), CO 2 production, blood lactate accumulation], ventilatory [minute ventilation (V E )], and circulatory variables were measured. From the maximal test the threshold of lactate accumulation (LT) was determined. Thirteen children were capable of enduring the 30 minute exercise (Group l), and 9 could not complete the endurance test (Group 2). These two groups were comparable with respect to age, height, and baseline lung function. Children in Group 2 had a higher mean weight ( P < 0.005) than those in Group 1. Eight of the 9 children in Group 2 were girls, whereas Group 1 consisted of 5 girls and 8 boys. There was no significant difference between Group 1 and 2 in the mean values of Vo 2 max, maximal respiratory exchange ratio (R max), V E max, LT, oxygen pulse, and other variables obtained during the maximal exercise tests. Lactate accumulation during the endurance test in Group 2 was larger than in Group 1 ( P < 0.005). This confirms that lactate metabolism is a key factor that determines endurance capacity. The endurance time also correlated significantly ( P < 0.01) with the ratio between V E and maximal voluntary ventilation (MVV). We conclude that exercise endurance in healthy children correlates with variables related to lactate metabolism. It appears that a load at or lower than the LT can be sustained for 30 minutes in the great majority of healthy children. © 1993 Wiley‐Liss, Inc.