Physiological responses to very short duration hypoxic exposure and its use for improving sprint performance during intermittent exercise
Altitude training has been the subject of much research over the past forty year. However, research has focused on endurance performance and prolonged exposures to hypoxia have generally been employed to bring about improvements in performance. Few studies have investigated the responses to very short duration altitude exposures and its effects on performance. Moreover, research into the benefits of altitude training for improving the restoration of sprint performance during high intensity intermittent sports remains scarce. Therefore, this thesis aimed to determine the very acute responses to hypoxic exposure and the efficacy of repeated very short duration hypoxic exercise on recovery of sprint performance during intermittent activity. In addition, the thesis also aimed to determine the effect of such a training modality on oxidative stress levels and cellular damage during repeated sprint activity. Study one investigated the acute cerebral and skeletal oxygenation and cardiorespiratory responses to a single bout of very short duration (15 mm) hypoxic exposure (3048 m; F102 = 0.143) at rest and during exercise, and compared these to normoxic values. Both exercise conditions were performed at 65% of AP4lR max. The results of the study found that very short duration, hypoxic training stimulated significantly greater decreases in cerebral TOl over normoxic exercise (55.73 ± 2.77 and 64.02 ± 7.28%, respectively). Cerebral AHHb (31.07 ± 14.20 pmoFL 1 ) was also found to be significantly greater during hypoxic exercise than normoxic exercise (6.42 ± 8.04 pmoFLj and resting hypoxia (19.06 ± 7.40 pmohL 1 ). Skeletal TOI was not significantly different across all test conditions. However, skeletal AHH b (32.22 ± 20.81 pmolL 1 ) was significantly greater during hypoxic exercise than during resting hypoxia (10.23 ± 6.97 pmolL 1 ). Oxygen uptake and respiratory rate were not significantly different between normoxic and hypoxic exercise conditions, with mean V02 being 1.89 ± 0.03 and 1.83 ± 0.34 Lmin 1 for normoxic exercise and hypoxic exercise, respectively. Mean respiratory rates were 27.32 ± 6.27 and 24.63 ± 5.24 breaths.min for normoxic exercise and hypoxic exercise, respectively. These significant differences between conditions suggest greater 02 extraction rates during very short duration hypoxic exercise than during normoxic exercise or resting hypoxia. It was therefore proposed that a short course of very short duration hypoxic exposure may elicit improvements in the efficiency of 02 uptake and utilisation during intermittent exercise and subsequently lead to a reduction in oxidative stress during such activities. Resulting from the findings of study one, study two investigated the cerebral and skeletal oxygenation, cardiorespiratory and haematological changes in response to very short duration (15 mm) hypoxic training (HT) 3 times per week for three weeks compared to comparable normoxic training (NT). In addition, the study also evaluated the effectiveness of the hypoxic training programme on restoring sprint performance during an intermittent performance test (IPT) and the effects this protocol had on oxidative stress levels, as determined by MDA analysis. The results found that very short duration HT significantly increased RBC and F -id postintervention by 8.39% and 5.89% respectively, whilst Hb increase by 5.38% postintervention, though this was not to a level of significance. In contrast the NT group reported non-significant decreases post-intervention for Hb (3.36%) and RBC (0.61%), whilst Hd decreases significantly (5.31%). No significant differences were reported for MDA either pre or post-intervention or between groups. No significant differences were reported between the HT and NT groups or pre and post-intervention for any cerebral or skeletal tissue oxygenation variables. However, the HT showed greater increases in skeletal AHHb over the NT group during the sprint efforts of the IPT (79.99 ± 30.17 and 55.46 ± 29.00 pmolL 1 , respectively). Similar observations were also reported during the IPT's recovery periods, with mean AHHb being 64.53 ± 23.04 and 48.29 ± 28.31 pmoFL 1 , for the HI and NT groups, respectively. Additionally, no significant differences were found for sprint Wmean and Wak between the groups post-intervention. However, the HT group increased Wmean by 11.99% post-intervention compared to the 3.75% increase by the NT group. Comparable increases were also noted for W 3k, with the HT group improving 11.82% post —intervention and the NT group improving only 3.45%. No significant differences were found between the HI and NT groups or pre and post-intervention for V02 or respiratory rate during both sprint and recovery periods. However, the HI group generally showed non-significant decreases in both parameters, whilst the NT group showed no change from pre-intervention levels. This thesis found that despite significant improvements in haematological variables in the HT group over the NT group, very short duration hypoxic training does not improve the restoration of sprint performance during intermittent activity significantly more than comparable normoxic training. However, in general, the hypoxic training group did elicit greater levels of improvement. Thus, the results of this thesis may reflect more, the relatively low number of participants in the studies, and not that the changes reported were meaningless. Improvements of approximately 5% in blood parameters and almost 12% in power output are still likely to be of interest to the intermittent sports performer, as such improvements may make a difference during critical periods of a match or race.
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