title: Prior heavy-intensity exercise speeds VO2 kinetics during moderate-intensity exercise in young adults.
abstract: The effect of prior heavy-intensity warm-up exercise on subsequent moderate-intensity phase 2 pulmonary O2 uptake kinetics (tauVO2) was examined in young adults exhibiting relatively fast (FK; tauVO2 < 30 s; n = 6) and slow (SK; tauVO2 > 30 s; n = 6) VO2 kinetics in moderate-intensity exercise without prior warm up. Subjects performed four repetitions of a moderate (Mod1)-heavy-moderate (Mod2) protocol on a cycle ergometer with work rates corresponding to 80% estimated lactate threshold (moderate intensity) and 50% difference between lactate threshold and peak VO2 (heavy intensity); each transition lasted 6 min, and each was preceded by 6 min of cycling at 20 W. VO2 and heart rate (HR) were measured breath-by-breath and beat-by-beat, respectively; concentration changes of muscle deoxyhemoglobin (HHb), oxyhemoglobin, and total hemoglobin were measured by near-infrared spectroscopy (Hamamatsu NIRO 300). tauVO2 was lower (P < 0.05) in Mod2 than in Mod1 in both FK (20 +/- 5 s vs. 26 +/- 5 s, respectively) and SK (30 +/- 8 s vs. 45 +/- 11 s, respectively); linear regression analysis showed a greater "speeding" of VO2 kinetics in subjects exhibiting a greater Mod1 tauVO2. HR, oxyhemoglobin, and total hemoglobin were elevated (P < 0.05) in Mod2 compared with Mod1. The delay before the increase in HHb was reduced (P <0.05) in Mod2, whereas the HHb mean response time 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.
authors.affiliation: School of Kinesiology, 3M Centre, Canadian Centre for Activity and Aging, The Univ. of Western Ontario, London, Ontario, Canada N6A-3K7.
authors.forename: Brendon J
authors.initials: BJ
authors.lastname: Gurd
authors.forename: Barry W
authors.initials: BW
authors.lastname: Scheuermann
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D006801:Humans; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D018482:Muscle, Skeletal / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*
chemical_list: D010100:Oxygen