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 VO(2max) 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 x wk(-1) x 3 wk at 85-90% VO(2max). 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 post-training.
Results: Training induced significant increases (P </= 0.05) in maximal power output (367 +/- 63 to 383 +/- 60 W), VO(2max) (4.39 +/- 0.66 to 4.65 +/- 0.57 L x min(-1)), and maximal O(2) pulse (22.7 +/- 3.2 to 24.6 +/- 2.8 mL O(2) x 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 </= 0.05) after training without a significant increase (P > 0.05) in the VO(2) (4.02 +/- 0.52 to 4.04 +/- 0.51), heart rate (176 +/- 9 to 173 +/- 8 beats x min ) or O pulse (22.4 +/- 3.2 to 23.5 +/- 2.8 mL O(2) x 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 -1,009 +/- 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 VO(max) 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.