Physiologic and Lactate Dynamics During Voluntary Breath-Hold: A Systematic Review and Meta-Analysis.

This meta-analysis systematically examined the effects of voluntary breath-holding (BH) on blood lactate concentration and classified all available data according to apnea modality into static apnea (STA) and dynamic apnea (DYN) groups. Given the observed heterogeneity across studies, subgroup analyses were conducted to explore physiologic differences related to apnea type, training status, and environmental condition as well as to investigate the influence of the diving reflex on lactate metabolism. The study further aimed to quantify the degree of anaerobic activation induced by voluntary BH and to compare variations in lactate dynamics and metabolic responses across different experimental conditions. Fourteen studies published between 2005 and 2024, encompassing 32 experimental groups and 315 participants, were included. All investigated voluntary BH interventions-dry STA, wet STA, DYN, and depth diving (depth)-compared with control conditions. Analyses followed PRISMA 2020 guidelines using a random-effects model to calculate pooled standardized mean differences with correction for small-sample bias. Subgroup analyses examined lactate variation by apnea type, training status, and environment. Pearson's correlation (r) analysis evaluated the relationship between breath-hold duration and changes in blood lactate concentration. Pooled results revealed a significant increase in blood lactate after BH (P<0.00001) with substantial heterogeneity (I2=79%). Significant differences were observed between STA and DYN (P<0.01) and between trained and untrained participants (P<0.05), whereas blood lactate concentrations were elevated relative to baseline under both dry and wet conditions as well as during dynamic apnea and depth diving, but no significant differences were observed between environmental conditions.. Under the wet condition, a moderate negative correlation (r=-0.54, P=0.047) indicated that prolonged apnea stabilized rather than linearly increased lactate levels. Voluntary BH significantly elevates blood lactate concentration, reflecting enhanced anaerobic metabolism and an adaptive physiologic responses. The findings indicate that training status and apnea modality exert greater influence on lactate dynamics than environmental factors and that prolonged wet apnea may induce metabolic stabilization through intensified diving reflex activation. Clinically, these findings indicate that, particularly under wet STA breath-hold conditions, blood lactate levels do not increase linearly with apnea duration (r=-0.54), potentially masking underlying physiologic strain during hypoxic exposure. This physiologic pattern may be clinically relevant to hypoxia-related adverse events. Accordingly, these findings underscore the importance of careful risk assessment and heightened safety awareness during breath-hold activities, especially under wet STA conditions.