Oxygen uptake kinetics during treadmill running in boys and men

The purpose of this study was to compare the kinetics of the oxygen uptake (VO2) response of boys to men during treadmill running using a three-phase exponential modeling procedure. Eight boys (11-12 yr) and eight men (21-36 yr) completed an incremental treadmill test to determine lactate threshold (LT) and maximum VO2. Subsequently, the subjects exercised for 6 min at two different running speeds corresponding to 80% of VO2 at LT (moderate exercise) and 50% of the difference between VO2 at LT and maximum VO2 (heavy exercise). For moderate exercise, the time constant for the primary response was not significantly different between boys [10.2 +/- 1.0 (SE) s] and men (14.7 +/= 2.8 s). The gain of the primary response was significantly greater in boys than men (239.1 +/- 7.5 vs. 167.7 +/- 5.4 ml . kg (-1). km-(1); P < 0.05). For heavy exercise, the VO2 on kinetics were significantly faster in boys than men (primary response time constant = 14.9 +/- 1.1 vs. 19.0 +/- 1.6 s; P < 0.05), and the primary gain was significantly greater in boys than men (209.8 +/- 4.3 vs. 167.2 +/- 4.6 ml . kg(-1). km(-1); P < 0.05). The amplitude of the VO2 slow component was significantly smaller in boys than men (19 +/- 19 vs. 289 +/- 40 ml/min; P < 0.05). The VO2 responses at the onset of moderate and heavy treadmill exercise are different between boys and men, with a tendency for boys to have faster on-kinetics and a greater initial increase in VO2 for a given increase in running speed.