Lindsay, T., Ansley, L., Neary, J. P., Hunter, A., St Clair Gibson, A., Skowno, J., & Noakes, T. D. (2009). Changes in pacing strategy in response to an acute shift to and from hypoxia. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

This study described changes in pacing profile and physiology in response to a mid-exercise change in ambient oxygen concentration (FIO2). Male cyclists (N = 8) completed two 20-km time-trials in random order. In one trial, the first 10 km was normoxic (FIO2 = 21%) and the second 10 km was hypoxic (FIO2 = 15% ~2,700 m). The order was reversed in trial two. Ss were blinded to the conditions. The trials were done inside a chamber set at normobaric pressure. Ss acclimatized to the initial FIO2 for 10 minutes before each trial. Expired gases (4, 14 km), cardiac output (continuous), and blood gases (taken at 0, 4, 9, 14, and 19 km) were measured. Ss used their own bicycles on an electrically braked cycle trainer. Power output was averaged over 2 km.

Power output was lower in hypoxia at every interval except 12 and 14 km. Power output for the final 2 km was 116% of the mean power output for the second 10 km in normoxia, but only 102% in hypoxia. Ventilation during hypoxia was higher at 14 km and oxygen pressure during hypoxia was lower at every interval. Cardiac output for the final 2 km was lower in hypoxia.

Power output changed less than 210 sec after switching to FIO2. Descriptively, pacing during the first 10 km was similar in both conditions, but absolute power output was lower in hypoxia. The attenuated hypoxic end-spurt was consistent with other studies. Cardiac output during the end-spurt was lower during hypoxia and thus was not limiting. Instead, the end-spurt seemed to be related to the altered ventilation and oxygen pressure. However, altered power output during the first 500 m (~60 seconds) and a quick power output response after changing FIO2 suggests that pacing changes are not merely a result of peripheral fatigue. Indeed, the initial power output was likely determined during the 10 minutes pre-trial equilibration period and/or from sensations in the first minute of exercise. Changes in power output with altered FIO2 may have involved a rapid oxygen sensing response.

Implication. The initial anticipatory component for a performance is based on sensation. The sensations occur before performance and in the initial stages of the activity. Therefore, it is important that strategies of control and deliberate performance-specific activities that cover the activities immediately before an activity and the transition into the performance are most important for setting the pace of an activity.

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