Background: Progressive exercise-induced dehydration may impair aerobic exercise performance (AEP). However, no systematic approach has yet been used to determine how pre-exercise hypohydration, which imposes physiological challenges differing from those of a well-hydrated pre-exercise state, affects AEP and related components such as peak oxygen consumption [Formula: see text] and [Formula: see text] at lactate threshold [Formula: see text].
Objective: To determine, using a systematic approach with meta-analysis, the magnitude of the effect of pre-exercise hypohydration on AEP, [Formula: see text] and [Formula: see text].
Design: This was a systematic review with meta-analysis of well-controlled studies.
Data sources: MEDLINE, SPORTDiscus and CINAHL databases and cross-referencing. INCLUSION CRITERIA FOR SELECTING STUDIES: (1) well-controlled human (≥ 18 years) studies; (2) pre-exercise hypohydration induced at least 1 h prior to exercise onset; (3) pre-exercise body mass loss in the hypohydrated, experimental condition was ≥ 1% and ≥ 0.5% than the well-hydrated, control condition; (4) following the dehydrating protocol body mass change in the control condition was within - 1% to + 0.5% of the well-hydrated body mass.
Results: A total of 15 manuscripts were included, among which 14, 6 and 6 met the inclusion criteria for AEP, [Formula: see text] and [Formula: see text], respectively, providing 21, 10 and 9 effect estimates, representing 186 subjects. Mean body mass decrease was 3.6 ± 1.0% (range 1.7-5.6%). Mean AEP test time among studies was 22.3 ± 13.5 min (range 4.5-54.4 min). Pre-exercise hypohydration impaired AEP by 2.4 ± 0.8% (95% CI 0.8-4.0%), relative to the control condition. Peak oxygen consumption and [Formula: see text], respectively, decreased by 2.4 ± 0.8% (95% CI 0.7-4.0%) and 4.4 ± 1.4% (95% CI 1.7-7.1%), relative to the control condition. Compared with starting an exercise hypohydrated, it is respectively likely, possible and likely that AEP, [Formula: see text] and [Formula: see text] benefit from a euhydrated state prior to exercise. Meta-regression analyses did not establish any significant relationship between differences in body mass loss and differences in the percent change in AEP or [Formula: see text]. However, [Formula: see text] was found to decrease by 2.6 ± 0.8 % (95% CI 0.7-4.5%) for each percent loss in body mass above a body mass loss threshold of 2.8%.
Conclusion: Pre-exercise hypohydration likely impairs AEP and likely reduces [Formula: see text] (i.e., the aerobic contribution to exercise was lower) during running and cycling exercises ≤ 1 h across different environmental conditions (i.e., from 19 to 40 °C). Moreover, pre-exercise hypohydration possibly impedes [Formula: see text] during such exercises.