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1 Canadian Centre for Activity and Aging, The University of Western Ontario, London, Ontario, Canada; School of Kinesiology, The University of Western Ontario, London, Ontario, Canada
2 Department of Kinesiology, The University of Toledo, Toledo, Ohio, USA
3 Canadian Centre for Activity and Aging, The University of Western Ontario, London, Ontario, Canada; School of Kinesiology, The University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada
* To whom correspondence should be addressed. E-mail: jkowalch{at}uwo.ca.
The effect of prior heavy-intensity (HVY) exercise on subsequent moderate-intensity (MOD) phase II pulmonary O2 uptake kinetics (
VO2) was examined in young adults exhibiting relatively fast (FK; VO2 < 30s; n=6) and slow (SK; VO2 > 30s; n=6) VO2 kinetics. Subjects performed 4 repetitions of a MOD1-HVY-MOD2 protocol on a cycle ergometer with work rates corresponding to 80% estimated lactate threshold (
L) (MOD1; MOD2), and 50% difference between L and VO2peak (HVY); each transition lasted 6 min and each was preceded by 6 min cycling at 20W. VO2 and heart rate (HR) were measured breath-by-breath and beat-by-beat, respectively; concentration changes of muscle deoxy- (HHb); oxy- (O2Hb) and total-hemoglobin (HbTOT) were measured by near-infrared spectroscopy (Hamamatsu NIRO 300). VO2 was lower (P<0.05) in Mod2 than Mod1 in both FK (Mod2, 20 (±5)s; Mod1, 26 (±5)s) and SK (Mod2, 30 (±8)s; Mod1, 45 (±11)s); linear regression analysis showed a greater "speeding" of VO2 kinetics in subjects exhibiting a greater MOD1 VO2. HR, O2Hb and HbTOT were elevated (P<0.05) in Mod2 compared to Mod1. The delay prior to an increase in HHb (HHb TD) was reduced (P<0.05) in Mod2, while the MRT-HHb was reduced (P<0.05) in FK (Mod2, 22 (±3)s; Mod1, 32 (±11)s) but not different in SK (Mod2, 36 (±13)s; Mod1, 34 (±15)s). We conclude that improved muscle perfusion in MOD2 may have contributed to the faster adaptation of VO2, especially in SK, however a possible role for metabolic inertia in some subjects cannot be overlooked.
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