Effects of prior short multiple-sprint exercises with different intersprint recoveries on the slow component of oxygen uptake during high-intensity exercise

This study compares the effects of two short multiple-sprint exercise (MSE) (6 x 6 s) sessions with two different recovery durations (30 s or 180 s) on the slow component of oxygen uptake ((V) over dotO(2)) during subsequent high-intensity exercise. Ten male subjects performed a 6-min cycling test at 50% of the difference between the gas exchange threshold and (V) over dotO(2peak) (Delta 50). Then, the subjects performed two MSEs of 6 x 6 s separated by two intersprint recoveries of 30 s (MSE30) and 180 s (MSE180), followed 10 min later by the Delta 50 (Delta 50(30) and Delta 50(180), respectively). Electromyography (EMG) activities of the vastus medialis and lateralis were measured throughout each exercise bout. During MSE30, muscle activity (root mean square) increased significantly (p <= 0.04), with a significant leftward-shifted median frequency of the power density spectrum (MDF; p <= 0.01), whereas MDF was significantly rightward-shifted during MSE180 (p = 0.02). The mean (V) over dotO(2) value was significantly higher in MSE30 than in MSE180 (p < 0.001). During Delta 50(30), (V) over dotO(2) and the deoxygenated hemoglobin ([HHb]) slow components were significantly reduced (-27%, p = 0.02, and -34%, p = 0.003, respectively) compared with Delta 50. There were no significant modifications of the (V) over dotO(2) slow component in Delta 50(180) compared with Delta 50 (p = 0.32). The neuromuscular and metabolic adaptations during MSE30 (preferential activation of type I muscle fibers evidenced by decreased MDF and a greater aerobic metabolism contribution to the required energy demands), but not during MSE180, may lead to reduced (V) over dotO(2) and [ HHb] slow components, suggesting an alteration in motor units recruitment profile (i.e., change in the type of muscle fibers recruited) and (or) an improved muscle O-2 delivery during subsequent exercise.