WHAT LIMITS ENDURANCE IN NORMAL-CHILDREN

We have compared the results of a standard progressive maximal exercis e test to those of an endurance exercise test in 22 healthy school chi ldren (13 girls, 9 boys, mean age 14.8 years) in order to examine whet her it is possible to extrapolate results from a maximal test to predi ct their endurance capacity. All children performed a standard progres sive maximal exercise test (15 W increments every minute until exhaust ion) and an endurance test (individually calculated loads to mimic cyc ling at 20 km/h against a windforce 5 of Beaufort for 30 minutes) on 2 separate days. In both tests metabolic [oxygen uptake (V(O2)), CO2 pr oduction, blood lactate accumulation], ventilatory [minute ventilation (V(E))], and circulatory variables were measured. From the maximal te st the threshold of lactate accumulation (LT) was determined. Thirteen children were capable of enduring the 30 minute exercise (Group 1), a nd 9 could not complete the endurance test (Group 2). These two groups were comparable with respect to age, height, and baseline lung functi on. Children in Group 2 had a higher mean weight (P < 0.005) than thos e in Group 1. Eight of the 9 children in Group 2 were girls, whereas G roup 1 consisted of 5 girls and 8 boys. There was no significant diffe rence between Group 1 and 2 in the mean values of V(O2) max, maximal r espiratory exchange ratio (R max), V(E)max, LT, oxygen pulse, and othe r variables obtained during the maximal exercise tests. Lactate accumu lation 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 th at determines endurance capacity. The endurance time also correlated s ignificantly (P < 0.01) with the ratio between V(E) and maximal volunt ary ventilation (MVV). We conclude that exercise endurance in healthy children correlates with variables related to lactate metabolism. It a ppears that a load at or lower than the LT can be sustained for 30 min utes in the great majority of healthy children.