Prior heavy-intensity exercise speeds VO2 kinetics during moderate-intensity exercise in young adults

The effect of prior heavy-intensity warm-up exercise on subsequent moderate-intensity phase 2 pulmonary O-2 uptake kinetics ((tau V) over dot O-2) was examined in young adults exhibiting relatively fast (FK; tau(V) over dot O-2 < 30 s; n = 6) and slow (SK; tau (V) over dot O-2 > 30 s; n = 6) (V) over dot 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 (V) over dot O-2 (heavy intensity); each transition lasted 6 min, and each was preceded by 6 min of cycling at 20 W. (V) over dot 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). tau(V) over dot 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 (V) over dot O-2 kinetics in subjects exhibiting a greater Mod(1) tau(V) over dot 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 (V) over dot O-2, especially in SK; however, a possible role for metabolic inertia in some subjects cannot be overlooked.