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A raised metabolic rate slows pulmonary O 2 uptake kinetics on transition to moderate‐intensity exercise in humans independently of work rate
Author(s) -
Bowen T. Scott,
Murgatroyd Scott R.,
Can Daniel T.,
Cuff Thomas J.,
Lainey Allison F.,
Marjerrison Andrea D.,
Spencer Matthew D.,
Benson Alan P.,
Paterson Donald H.,
Kowalchuk John M.,
Rossiter Harry B.
Publication year - 2011
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2011.058321
Subject(s) - work rate , cycle ergometer , chemistry , oxygenation , heart rate , kinetics , medicine , cardiology , intensity (physics) , circulatory system , zoology , biology , blood pressure , physics , quantum mechanics
During exercise below the lactate threshold (LT), the rate of adjustment (τ) of pulmonary O 2 uptake () is slowed when initiated from a raised work rate. Whether this is consequent to the intrinsic properties of newly recruited muscle fibres, slowed circulatory dynamics or the effects of a raised metabolism is not clear. We aimed to determine the influence of these factors on using combined in vivo and in silico approaches. Fifteen healthy men performed repeated 6 min bouts on a cycle ergometer with work rates residing between 20 W and 90% LT, consisting of the following: (1) two step increments in work rate (S1 and S2), one followed immediately by the other, equally bisecting 20 W to 90% LT; (2) two 20 W to 90% LT bouts separated by 30 s at 20 W to raise muscle oxygenation and pretransition metabolism (R1 and R2); and (3) two 20 W to 90% LT bouts separated by 12 min at 20 W allowing full recovery (F1 and F2). Pulmonary O 2 uptake was measured breath by breath by mass spectrometry and turbinometry, and quadriceps oxygenation using near‐infrared spectroscopy. The influence of circulatory dynamics on the coupling of muscle and lung was assessed by computer simulations. The in R2 (32 ± 9 s) was not different ( P > 0.05) from S2 (30 ± 10 s), but both were greater ( P < 0.05) than S1 (20 ± 10 s) and the F control bouts (26 ± 10 s). The slowed kinetics in R2 occurred despite muscle oxygenation being raised throughout, and could not be explained by slowed circulatory dynamics ( predicted by simulations: S1 = R2 < S2). These data therefore suggest that the dynamics of muscle O 2 consumption are slowed when exercise is initiated from a less favourable energetic state.