Transient Oxygen Uptake and Heart Rate Responses at the Onset of Relative Endurance Exercise in Prepubertal Boys and Adult Men*

Abstract

Performance and physiologic responses to relative endurance exercise were compared in 21 prepubescent boys (C, mean ± SD, age = 10.2 ± 0.28 yrs) and 21 adult men (A, age = 30.0 ± 1.23 yrs). Relative endurance exercise consisted of pedaling a bicycle ergometer for 8 min at an initial power output of 103 ± 1.0% V̇O₂max (mean ± SE) for the C and 105 ± 1.1% V̇O₂max for the A (P > 0.05). Standard open circuit Spirometrie techniques were used to measure V̇O₂, and HR was monitored via a bipolar ECG. The physiologic (V̇O₂ or HR) responses were graphed and a one-component exponential equation fit to the data. Few differences (P > 0.05) were evident in power output characteristics (RPM or total% dropoff) between C and A. However, many C-A differences were evident in physiologic responses. C have a faster V̇O₂ half-time (t1/2) than that of As (C 17.2 ± 0.74 s vs A 28.5 ± 1.31 s, P < 0.05). Also, the HR 11/2 values (C 24.8 ± 1.96 s vs A 41.0 ± 2.94 s, P < 0.05) indicate that C reached their asymptotic HR more quickly than A. Apparently, young C have quicker V̇O₂ and HR responses to relative endurance exercise. Whether a threshold age exists where the Cs responses “mature” remains the subject of subsequent investigations.

Key words

relative endurance - supramaximal - heart rate - oxygen consumption - kinetics