Abstract
VO2max, efficiency and economy play important roles in endurance performance. These improvements have been elicited separately through endurance and sprint interval training (SIT) and intermittent hypoxic exposure (IHE). However, there is limited data of the interaction of SIT and IHE on endurance performance. Therefore the purpose of this study was to compare the effects of IHE, SIT, and a combination of IHE/SIT on VO2max and submaximum energy costs. 20 healthy male subjects (age: 26 ± 4yrs, ht: 179 ± 7cm, wt: 85 ± 18kg, VO2max: 52.32±14.32ml/kg/min) were split into 4 groups for a 2 wk training study. The 4 groups consisted of a normoxic control group (NC) (n=5), a normoxic training group (NST) (n=5), an intermittent hypoxic control group (IHC) (n=5) and an intermittent hypoxic training group (IHST) (n=5). All volunteers spent ~ 10 days within 12 day period in a hypoxic enclosure. The IHE and normoxic conditions were blinded to the participants. The intermittent hypoxic and normoxic groups were exposed for 3 hours to a simulated altitude of 90.34 ± 1.35 mmHg and ~149 mmHg PiO2, respectively. The training groups performed 6 SIT sessions on a cycle ergometer over a 2 wk period. Each SIT session included 4-7 x 30 second all out sprints with a resistance of 7.5% of body weight. Hypoxic or normoxic exposure was conducted immediately after each SIT session. Pre and post maximal (incremental ramp @ 35watts/min) and submaximal cycle ergometer tests (60 min @ 10% below ventilatory threshold) were conducted 1 wk before and after the last IHE or normoxic exposure. The following variables were measured: VO2max, gross efficiency (GEF), net efficiency (NEF) and economy (EC). A mixed model repeated measures ANOVA was used to analyze the differences between IHE, SIT and IHST. Post intervention, there were no significant effects between the 4 groups for VO2max (p=0.307), GEF (p=0.207), NEF (p=0.349), and EC (p=0.349). There was a significant (~6%) increase in GEF due to training (Pre: 14.3%, Post: 15.2%, p=0.029). While the change was not significant, NEF (increase 1.3%, p=0.068) and EC (increase 3.3%, p=0.14) did tend to increase due to training. The significant change in GEF was the result of a significant (~7%) decrease in kcals/min (Pre: 11.3 kcal/min, Post: 10.5kcal/min, p=0.031) due to training. Two weeks of IHE, SIT or IHST does not have a significant effect on VO2max, GEF, NEF or EC. Therefore, 2 wks of IHE to a simulated altitude of ~4000 m or a combination of the two training interventions are ineffective in improving VO2max or submaximum energy costs in males with above average fitness. However, sprint interval training is effective in increasing gross efficiency during submaximal exercise.