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Abstract

Previous studies have shown mechanistic neurophysiological evidence to foster motor cortical and plasticity alongside improved cerebral perfusion. Although evidence remains limited, these neural effects suggest passive immersion may enhance force output capacity. PURPOSE: This study aimed to investigate the acute effects of passive water immersion in a seated position on lower-extremity isometric strength as measured by isometric mid-thigh pull (IMTP) performance on land. METHODS: Thirty-three active young adults (age: 22.64 ± 4.18 years, height: 174.55 ± 10.28 cm, mass: 81.45 ± 18.77 kg) completed both land and water conditions (LC and WC), with pre- and post-tests using within subjects repeated measures design. In the LC, participants performed two maximal-effort IMTP trials before and after 45 min of seated rest on land, while in the WC, the same protocol was completed before and after 45 min of chest-deep immersion at a thermoneutral temperature of 34.0 ± 0.5 °C. The absolute peak force (PF) reliability was assessed with ICCs and outcomes were analyzed using a two-way repeated-measures ANOVA with effect size (ηp2). Significance was set at p < .05. Results: Both LC and WC showed excellent inter-trial reliability of PF (ICCs ≥ 0.986, CVs 2.3 – 3.3%). Significant main effects of time were observed for all PF related outcomes (p < .001, ηp2 = .385 – .425), with an additional effect of condition for NetPF (PF – Body weight; condition: p < .05, ηp2 = .121). No significant interactions were found. Conclusions: This is the first study to investigate whether the neurophysiological mechanisms previously demonstrated with passive water immersion can translate into isometric force-generating capacity of the lower extremities. In the present study, although not statistically significant, the observed trend suggests that passive water immersion may help in blunting time-related decreases in maximal isometric strength.

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