Background: How hypohydration impacts non-bodyweight (BW)-dependent muscle performance and vertical jumping ability remains to be determined using meta-analytic procedures.
Objectives: Our objective was to determine the impact of hypohydration on muscle endurance, strength, anaerobic power and capacity and vertical jumping ability using a meta-analytic approach.
Data sources: Studies were located using database searches and cross-referencing.
Synthesis methods: Effect summaries were obtained using random-effects models; method of moments mixed-effects analysis-of-variance-like procedures were used to determine differences between groups; and restricted maximum likelihood random-effects meta-regressions were performed to determine relationships between variables, impact of confounders, and interaction effects.
Results: A total of 28 manuscripts met the inclusion criteria, producing six (upper body muscle endurance), ten (lower body muscle endurance), 14 (upper body muscle strength), 25 (lower body muscle strength), nine (muscle anaerobic power), nine (muscle anaerobic capacity), and 12 (vertical jumping ability) effect estimates. Hypohydration impaired overall muscle endurance by 8.3 ± 2.3% (P < 0.05), with no significant difference between upper body (-8.4 ± 3.3%) and lower body (-8.2 ± 3.2%). As a whole, muscle strength fell by 5.5 ± 1.0% (P < 0.05) with hypohydration; the difference between lower (-3.7 ± 1.8%) and upper (-6.2 ± 1.1%) body was non-significant. Anaerobic power (-5.8 ± 2.3%) was significantly altered with hypohydration, but anaerobic capacity (-3.5 ± 2.3%) and vertical jumping ability (0.9 ± 0.7%) were not. No significant correlations were observed between the changes in any of the muscle performance variables or vertical jumping ability and the changes in hypohydration level. Using an active procedure to dehydrate participants decreased muscle performance by an additional 5.4 ± 1.9% (2.76-fold) (P = 0.02) compared with using a passive dehydration procedure. Trained individuals demonstrated a 3.3 ± 1.7% (1.76-fold) (P = 0.06) lesser decrease in muscle performance with hypohydration than did untrained individuals.
Conclusion: Hypohydration, or factors associated with dehydration, are likely to be associated with practically important decrements in muscle endurance, strength, and anaerobic power and capacity. However, their impact on non-BW-dependent muscle performance is substantially mitigated in trained individuals or when hypohydration is induced passively. Conversely, it is possible that body water loss (~3% BW) may improve performance in BW-dependent tasks such as vertical jumping ability.