Effect of prolonged inactivity on aerobic fitness of children.

Prolonged bed rest diminishes maximal aerobic power in adults, but no information is available regarding the physiologic responses to extended periods of inactivity in children. This study evaluated the impact of 9 weeks of bed rest on recovery peak VO2 in 5 children ages 7-11 years (3 boys, 2 girls) treated for femoral fractures. Beginning 2 weeks after initial ambulation during convalescence, maximal treadmill testing with measurement of gas exchange parameters was performed monthly for 4 months and again at 6 and 9 months. The difference between peak VO2 on the initial test and subsequent plateauing of peak VO2 on subsequent serial tests was considered indicative of alterations resulting from prolonged bed rest. Peak VO2 increased 13.3% to a plateau at 3 months while maximal aerobic power did not change significantly in five healthy control subjects. Between tests 1 and 3 treadmill endurance time improved 98% in the subjects and 1% in controls. These findings suggest (1) habitual activity in children accounts for approximately 13% of aerobic fitness levels, (2) following prolonged inactivity, aerobic fitness is regained by 3 months, and (3) improvements in performance far exceed those accounted for by changes in peak VO2 following extended bed rest in children.