Effect of Prolonged Water Immersion on Isometric Mid-thigh Pull Performance: A Feasibility Study and Preliminary Analysis

Water immersion may enhance muscle strength by increasing cerebral blood flow and activating the cerebral cortex due to an upwardly directed hydrostatic pressure gradient. Early evidence shows that grip strength improves when individuals are partially immersed in water compared to on land. However, it remains unclear whether this effect can be confirmed under conditions involving the activation of a larger muscle mass. PURPOSE: The purpose was to investigate the effects of prolonged water immersion on lower-extremity maximal isometric strength using the isometric mid-thigh pull (IMTP) test. METHODS: Six male recreationally active young adults (age = 24.3 ± 3.4 years; height = 177.7 ± 6.5 cm; mass = 73.4 ± 12.3 kg) participated in the study. Each participant completed both land and water conditions in a randomized order, with a minimum 7-day gap between sessions. In the land condition, participants performed two IMTP trials, separated by a 1-minute rest, before and after sitting on a chair for 45 minutes on land. In the water condition, participants completed the same IMTP trials, but before and after sitting submerged to the xiphoid process in water for 45 minutes. The water was maintained at a thermoneutral temperature of 29.5°C ± 0.2°C. A standardized warm-up was conducted before each set of two IMTP trials. Bar height was adjusted to ensure participants engaged isometrically with the IMTP rig at a hip angle of 140-150° and a knee angle of 125-145°. Raw and body-weight (BW) normalized peak force were recorded using a force platform. Paired t-tests were used to assess pre- and post-sitting differences in IMTP peak force for both land and water conditions. RESULTS: Raw and BW normalized peak force were reduced following prolonged sitting on land (2336 ± 646 N vs. 2475 ± 697 N; p = 0.026) (2.9 ± 0.4 vs. 3.1 ± 0.3 BW; p = 0.023). Raw and BW normalized peak force were not different following prolonged sitting in water (2460 ± 541 N vs. 2468 ± 547 N; p = 0.840) (3.1 ± 0.3 vs. 3.1 ± 0.3 BW; p = 0.782). CONCLUSION: These findings suggest that prolonged water immersion may stimulate sufficient motor cortex activity to maintain maximal leg muscular strength after extended periods of sitting.