Effects of short-term endurance training on muscle deoxygenation trends using NIRS

Purpose: This study examined changes in cardiorespiratory responses and muscle deoxygenation trends to test the hypothesis that both central and peripheral adaptations would contribute to the improvements in VO2max and simulated cycling performance after short-term high-intensity training. Methods: Eight male cyclists performed an incremental cycle ergometer test to voluntary exhaustion, and a simulated 20-km time trial (20TT) on wind-loaded rollers before and after training (60 min x 5 d(.)wk(-1) x 3 wk at 85-90%VO2max). Near-infrared spectroscopy (NIRS) was used to evaluate the trend in vastus medialis hemoglobin/myoglobin deoxygenation (Hb/Mb-O-2) during both tests pre- and posttraining. Results: Training induced significant increases(P less than or equal to 0.05) in maximal power output (367 +/- 63 to 383 +/- 60 W), VO2max (4.39 +/- 0.66 to 4.65 +/- 0.57 L(.)min(-1)), and maximal O-2 pulse (22.7 +/- 3.2 to 24.6 +/- 2.8 mL O(2)(.)beat(-1)) during the incremental test, but maximal muscle deoxygenation was unchanged. 20TT performance was significantly faster (27:32 +/- 1:43 to 25:46 +/- 1:44 min:s; P :5 0.05) after training without a significant increase (P > 0.05) in the VO2 (4.02 +/- 0.52 to 4.04 +/- 0.51), heart rate (176 +/- 9 to 173 +/- 8 beats(.)min(-1)) or O-2 pulse (22.4 +/- 3.2 to 23.5 +/- 2.8 mL O(2)(.)beat(-1)). However, mean muscle deoxygenation during the 20TT was significantly lower after training (-550 +/- 292 to -707 +/- 227 mV, P +/- 0.05), and maximal deoxygenation showed a trend toward significance (-807 +/- 344 to -1009 +/- 331 mV, P = 0.08), suggesting a greater release of oxygen from Hb/Mb-O-2 via the Bohr effect. Conclusion: The significant improvement in induced by short-term endurance training in well-trained cyclists was due primarily to central adaptations, whereas the simulated 20TT performance was enhanced due to localized changes in muscle oxygenation.