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 exerc
ise) and 50% of the difference between VO2 at LT and maximum VO2 (heavy exe
rcise). For moderate exercise, the time constant for the primary response w
as 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). T
he amplitude of the VO2 slow component was significantly smaller in boys th
an men (19 +/- 19 vs. 289 +/- 40 ml/min; P < 0.05). The VO2 responses at th
e 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.