Vastus medialis muscle oxygenation trends during a simulated 20-km cycle time trial

In this study we examined the oxygenation trend of the vastus medialis musc le during sustained high-intensity exercise. Ten cyclists performed an incr emental cycle ergometer test to voluntary exhaustion [mean (SD) maximum oxy gen uptake 4.29 (0.63) 1(.)min(-1); relative to body mass 60.8 (2.4) ml(.)k g(-1.)min(-1)] and a simulated 20-km time trial (20TT) on a wind-loaded rol ler system using their own bicycle (group time = 23-31 min) in two separate sessions. Cardio respiratory responses were monitored using an automated m etabolic cart and a wireless heart rate monitor. Tissue absorbency, which w as used as an index of muscle oxygenation, was recorded simultaneously from the vastus medialis using near-infrared spectroscopy. Group mean values fo r oxygen uptake, ventilation, heart rate, respiratory exchange ratio, power output, and rating of perceived exhaustion were significantly (P less than or equal to 0.05) higher during the incremental test compared to the 20TT [4.29 (0.63) 1(.)min(-1) vs 4.01 (0.55) 1(.)min(-1), 120.4 (26) 1(.)min(-1) vs 97.6 (16.1) 1(.)min(-1), 195 (8) beats(.)min(-1) vs 177 (9) beats(.)min (-1), 1.15 (0.06) vs 0.93 (0.06), 330.1 (31) W vs 307.2 (24.5) W, and 19 (1 .5) vs 16 (1.7), respectively]. Oxygen uptake and heart rate during the 20T T corresponded to 93.5% and 90.7%, respectively, of the maximal values obse rved during the incremental test. Comparison of the muscle oxygenation tren ds between the two tests indicated a significantly greater degree of deoxyg enation during the 20TT [-699 (250) mV vs -439 (273) mV; P less than or equ al to 0.05] and a significant delay in the recovery oxygenation from the 20 TT. The mismatching of whole-body oxygen uptake and localised tissue oxygen ation between the two tests could be due to differences in muscle temperatu re, pH, localised blood flow and motor unit recruitment patterns between th e two tests.