Abstract
PurposeTo determine how immune markers are affected by acute hypoxic exercise at the same relative intensity.MethodsTwelve endurance-trained males (age: 28 ± 4 years, dot{V}O2max: 63.7 ± 5.3 mL/kg/min) cycled for 75 min at 70 % of altitude-specific dot{V}O2max, once in normoxia (N) and once in hypobaric hypoxia equivalent to 2000 m above sea-level (H). Blood and saliva samples were collected pre-, post- and 2 h post-exercise.ResultsParticipants cycled at 10.5 % lower power output in H vs. N, with no significant differences in heart rate (P = 0.10) or rating of perceived exertion (P = 0.21). Post-exercise plasma cortisol was higher in H vs. N [683 (95 % CI 576–810) nmol/l vs. 549 (469–643) nmol/l, P = 0.017]. The exercise-induced decrease in CD4:CD8 ratio was greater in H vs. N (−0.5 ± 0.2 vs. −0.3 ± 0.2, P = 0.019). There were no significant between-trial differences for adrenocorticotropic hormone, plasma cytokines, antigen-stimulated cytokine production, salivary immunoglobulin-A or lactoferrin. However, there was a main trial effect for concentration [F(11) = 5.99, P < 0.032] and secretion [F(11) = 5.01, P < 0.047] of salivary lysozyme, with this being higher in N at every time-point.ConclusionWhether the observed differences between H and N are of sufficient magnitude to clinically impair host defence is questionable, particularly as they are transient in nature and since other immune markers are unaffected. As such, acute hypoxic exercise likely does not pose a meaningful additional threat to immune function compared to exercise at sea level, provided that absolute workload is reduced in hypoxia so that relative exercise intensity is the same.
Highlights
Various forms of hypoxic training are used by competitive endurance athletes, both to acclimatise before competition at altitude (Fulco et al 2000) and to improve exercise performance at sea level (Levine and Stray-Gundersen 1997; Stray-Gundersen et al 2001)
This is in agreement with the current study where there was no effect of hypoxia on post-exercise plasma concentrations of IL-6, or any of the other measured cytokines, when cycling at 70 % of altitude specific V O2max
The results of the current study suggest that this exercise-induced decrease is more pronounced when exercising in hypobaric hypoxia, even when relative exercise intensity is the same
Summary
Various forms of hypoxic training are used by competitive endurance athletes, both to acclimatise before competition at altitude (Fulco et al 2000) and to improve exercise performance at sea level (Levine and Stray-Gundersen 1997; Stray-Gundersen et al 2001). Taking into account this augmented stress response to exercise, coupled with reports of increased resting levels of adrenaline, cortisol and interleukin-6 at high altitude (Mazzeo et al 2001), it seems reasonable to hypothesise that hypoxic training might pose a greater threat to immune function compared to equivalent training at sea level Both anecdotal evidence from athletes and coaches, and scientific literature point towards an increased incidence of opportunistic infectious illness during and immediately after altitude training (Bailey et al 1998; Gore et al 1998). To determine whether the differences in responses observed are due to hypoxia per-se, rather than this increase in relative exercise intensity, it is useful to instead match trials based on a fraction of altitude-specific V O2max This is of greater relevance to endurance athlete populations, since they will typically train at a similar, or even a lower, relative exercise intensity at altitude as when they are at sea level (Gore et al 1998)
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