Effects of baseline metabolic rate on pulmonary O2 uptake on-kinetics during heavy-intensity exercise in humans.
We hypothesised that initiating heavy-intensity exercise from an elevated baseline metabolic rate would result in slower Phase II O2 uptake V(O2) kinetics and a greater overall 'gain' in V(O2) per unit increase in work rate. Seven healthy males performed a series of like-transitions on a cycle ergometer: (1) from light exercise to 'moderate' exercise (80% of the gas exchange threshold, GET; L-->M); (2) from light exercise to 'heavy' exercise (40% of the difference between GET and V(O2) peak; L-->H); (3) from moderate exercise to heavy exercise (M-->H). The Phase II time constant (tau) was significantly (P<0.01) greater in the M-->H condition (48+/-11 s) compared to the L-->M and L-->H conditions (26+/-6 s versus 27+/-4 s, respectively). Moreover, the end-exercise 'gain' values were significantly different between the three conditions (L-->M, 8.1+/-0.7 mL min-1 W-1; L-->H, 9.7+/-0.4 mL min-1 W-1; M-->H, 10.7+/-0.7 mL min-1 W-1; P<0.05). This 'non-linearity' in the pulmonary V(O2) response to exercise might be attributed, at least in part, to differences in the metabolic properties of the muscle fibres recruited in the abrupt transition from a lower to a higher work rate.
Wilkerson
Daryl P
DP
School of Sport and Health Sciences, University of Exeter, St. Luke's Campus, Heavitree Road, Exeter EX1 2LU, United Kingdom.
Jones
Andrew M
AM
D000328:Adult; D001481:Basal Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012016:Reference Values