Effect of acute normobaric hypoxia on quadriceps integrated electromyogram and blood metabolites during incremental exercise to exhaustion.

This investigation analysed the effects of environmental hypoxia (EU) on changes in quadriceps integrated electromyogram (iEMG) and metabolite accumulation during incremental cycle ergometry. Trained male subjects (n = 14) were required to complete two maximal oxygen uptake (VO(2max)) tests, one test during EH (F(1)0(2) = 0.135), the other during normoxia (F(1)0(2) = 0.2093). The EMG were recorded at each exercise intensity from the vastus lateralis, rectus femoris and vastus medialis muscles over 60 cycle revolutions. Mean integral values were then calculated. Blood was collected from the radial vein of consenting subjects (n = 8) at the end of each exercise intensity. Oxygen saturation of arterial blood (S(a)O(2)) was estimated using pulse oximetry. Gas exchange variables were collected on-line every 15 s. The results indicated that, without exception, EH significantly reduced total exercise time. Mean time to exhaustion in EH was 26.34 (SD 2.58) min compared with 35.25 (SD 4.21) min during N. The S(a)O(2) values indicated that severe arterial desaturation had been achieved by EH. Mean values for VO(2max) obtained in EH were 49 ml*kg* min(-1), compared with 59 ml*kg*min(-1) attained in N. Plasma lactate and ammonia concentrations were both significantly higher in EH. Increases in lactate and ammonia concentration were highly correlated in both N and EH. The onset of plasma lactate and ammonia accumulation occurred at the same exercise intensity in N. The iEMG responses of all three quadriceps muscles tended to be greater in the EH trials, although this difference was not significant. The basis for iEMG nonsignificance may have been related to large within sample variation in iEMG, sample size and the severity of the hypoxia induced.