Prior heavy-intensity exercise speeds V{middle dot}O2 kinetics during moderate-intensity exercise in young adults

1 Canadian Centre for Activity and Aging, 2 School of Kinesiology, and 3 Department of Physiology and Pharmacology, The University of Western Ontario London, Ontario, Canada; and 4 Department of Kinesiology, The University of Toledo, Toledo, Ohio Submitted 16 September 2004 ; accepted in final form 29 November 2004 The effect of prior heavy-intensity warm-up exercise on subsequent moderate-intensity phase 2 pulmonary O 2 uptake kinetics ( O 2 ) was examined in young adults exhibiting relatively fast (FK; O 2 < 30 s; n = 6) and slow (SK; O 2 > 30 s; n = 6) O 2 kinetics in moderate-intensity exercise without prior warm up. Subjects performed four repetitions of a moderate (Mod 1 )-heavy-moderate (Mod 2 ) protocol on a cycle ergometer with work rates corresponding to 80% estimated lactate threshold (moderate intensity) and 50% difference between lactate threshold and peak O 2 (heavy intensity); each transition lasted 6 min, and each was preceded by 6 min of cycling at 20 W. O 2 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). O 2 was lower ( P < 0.05) in Mod 2 than in Mod 1 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 O 2 kinetics in subjects exhibiting a greater Mod 1 O 2 . HR, oxyhemoglobin, and total hemoglobin were elevated ( P < 0.05) in Mod 2 compared with Mod 1 . The delay before the increase in HHb was reduced ( P < 0.05) in Mod 2 , whereas the HHb mean response time was reduced ( P < 0.05) in FK (Mod 2 , 22 ± 3 s; Mod 1 , 32 ± 11 s) but not different in SK (Mod 2 , 36 ± 13 s; Mod 1 , 34 ± 15 s). We conclude that improved muscle perfusion in Mod 2 may have contributed to the faster adaptation of O 2 , especially in SK; however, a possible role for metabolic inertia in some subjects cannot be overlooked. near-infrared spectroscopy; muscle deoxygenation; heart rate; muscle oxygen utilization; warm-up exercise Address for reprint requests and other correspondence: J. M. Kowalchuk, School of Kinesiology, 3M Centre, Canadian Centre for Activity and Aging, The Univ. of Western Ontario, London, Ontario, Canada N6A-3K7 (E-mail: jkowalch{at}uwo.ca )