Impact of Pre-exercise Hypohydration on Aerobic Exercise Performance, Peak Oxygen Consumption and Oxygen Consumption at Lactate Threshold: A Systematic Review with Meta-analysis

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 ( V ˙ O 2 peak ) and V ˙ O 2 at lactate threshold ( V ˙ O 2 LT ) . Objective To determine, using a systematic approach with meta-analysis, the magnitude of the effect of pre-exercise hypohydration on AEP, V ˙ O 2 peak and V ˙ O 2 LT . 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, V ˙ O 2 peak and V ˙ O 2 LT , 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 V ˙ O 2 LT , 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, V ˙ O 2 peak and V ˙ O 2 LT 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 V ˙ O 2 LT . However, V ˙ O 2 peak 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 V ˙ O 2 LT (i.e., the aerobic contribution to exercise was lower) during running and c