Abstract:
This research comprised 2 studies. The purpose of the first study was to assess the acute responses of on physiological variables, blood biochemistry such as hemoglobin, hematocrit, and serum hypoxic-inducing factor 1 (HIF-1α) and vascular endothelial growth factor (VEGF), and muscle oxygenation parameters such as oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb), total hemoglobin and myoglobin (tHb), and tissue oxygen index (TSI) at the vastus lateralis under normobaric hypoxic condition in rugby sevens. Seven male rugby sevens players volunteered for this study. They were members of the Thailand rugby sevens national team and had no exposure to high altitude (>1500 m) at least 6 months before the start of the experiment. In a single blinded randomized design, each participant underwent an incremental running test on a motorized treadmill to determine peak oxygen uptake (VO2peak) in normobaric normoxia (FiO2=20.9%) and after 3 h exposure to normobaric hypoxia (FiO2=14.5%). Arterial oxygen saturation (SaO2), heart rate (HR), and rated of perceived exertion (RPE) were continuously measured throughout the experiment. Blood sample was collected for determining HIF-α and VEGF concentrations at rest and blood lactate concentration before and at 3 min after exercise. The results showed that hemoglobin concentration and serum HIF-1α were significant increased (p<0.05), While VEGF levels was significant decreased (p<0.05) after 3 h exposure to hypoxia compared with their baseline. Moreover, SaO2, VO2peak, VEpeak, HRpeak and time to exhaustion were significant decreased (p<0.05), while RPE and peak blood lactate and were unchanged as compared to baseline. There was also a significant reduction in O2Hb (p<0.05) but not HHb, tHb, and TSI. The purpose of the second study was to determine the effects of repeated sprint training under normobaric hypoxic (FiO2 14.5%) on sea-level aerobic capacity, running based repeated sprint ability, and muscle oxygenation parameters in rugby sevens. Fourteen male rugby sevens players, age between 18-33 years, participated in the study. They, matched by their VO2peak, were divided into 2 groups: the hypoxic group (RSH, n=7) and the normoxic group (RSN, n=7). Both RSH and RSN group completed 18 sessions of repeated sprint training on a motorized treadmill in either normobaric hypoxic (FiO2=14.5%) or normoxic (FiO2=20.9%) environments, respectively, over a periods of 6 weeks (3 sessions per week). Each training session consisted of 3 sets of 6-s × 10 sprints at 140% velocity at VO2peak (vVO2peak) with 20-s interval of passive recovery and 4 min between each set. Before and after 6 week of training period, VO2peak, serum HIF-1α and VEGF levels, muscle oxygenation at Vastus lateralis, along with running based repeated sprint ability (RAST) were measured and analyzed. Independent sample t-test and paired t-test were used for statistical analysis. The H test of Kruskal-Wallis and Wilcoxon Signed Rank test were used to compare differences in dependent variables between groups and within groups for non-parametric statistical analysis. The level of significance was set at p-value < 0.05. The results showed that after 6 weeks of training RSH induced significant increases in VO2peak, serum HIF-1α and VEGF concentrations, and improvement of TSI and HHb at vastus lateralis compared to prior training but not RSN. In addition, there was a significant decrease in fatigue index, but not peak power and mean power, during running based repeated sprint ability test only in RSH. In conclusion, our results indicated that an addition of 6-wk of sprint training in normobaric hypoxia to normal training had a positive effect on aerobic performance and repeated sprint ability compared to similar training at normoxia. These improvements were concomitant with significant increases in serum HIF-1α and VEGF as well as improvement of muscle oxygenation.