Water-based exercise effects on cardiac autonomic response: A systematic review

This systematic review focused on heart rate variability (HRV) responses either during and after a water-based session or training. We included studies that assessed acute (during exercise and recovery) and chronic HRV responses to water-based exercise (WBE). The sample of the studies could be teenage (aged older than 10), with no maximum age limit, regardless of sex, health and level of physical activity. Studies that used compressed air devices (scuba diving), passive hydrotherapy, immersion only after exercise, or immersion without exercise were excluded. We performed this search during the second fortnight of July 2022 using the PubMed, Scopus, CINAHL, Embase, SciELO, SPORTDiscus databases, and a man-ual search. Two independent reviewers conducted eligibility analysis and data extraction. We used the "risk of bias" table, available in RevMan (Version 5.3), to assess the risk of bias for the selection, detection and attrition domains. The search resulted in 3528 articles, of which 20 became part of this review, totaling 317 subjects (240 in the acute effects analysis and 77 in the chronic analysis). There was great diversity in the characteristics of the exercise among the studies. Seventeen studies analysed the effect of a single exercise session, and three others analysed the chronic effect. Twelve studies compared exercises in-and out-of -water. When compared to the baseline, WBE and land-based exercises (LBE) did not affect parasympathetic modulation in five studies. On the other hand, two studies showed a lower parasympathetic modulation reduction during WBE compared to LBE. During post-WBE recov-ery, parasympathetic modulation was similar to other moments in seven studies and higher for LBE in only one study. Three studies showed a possible accelerated recovery of HRV indices post-WBE. Chronically, WBE resulted in better parasympathetic modulation in three studies. The assessment of risk of bias resulted in 75% or more of the studies presenting a high or an unclear risk in selection criteria, sample randomization and blinding outcomes for evaluators. Water immersion can influence cardiac autonomic modulation during exercise, with a lower reduction in parasympathetic modulation than LBE. WBE has positive chronic effects on cardiac autonomic modulation in people who have altered functions of the autonomic nervous system, although the number of studies is still scarce. (c) 2023 Elsevier Masson SAS. All rights reserved.