ABSTRACT
Purpose: This study aimed to investigate the effects of underwater walking for 6 weeks at 60% of the predicted maximum heart rate on respiratory muscle strength of elderly people as well as its sustained effects on respiratory muscle strength. Methods: The participants were 43 healthy elderly men, who were randomly divided into the continuous group (n=21) and the non-continuous group (n=22). Initially, both groups performed 30 min of underwater walking four times a week for 6 weeks, after which the continuous group continued the same for another 6 weeks, whereas the non-continuous group was prohibited from performing any exercise, except for daily activities. The walking speed during underwater walking was adjusted such that the exercise intensity was 60% of the predicted maximum heart rate, with the water depth up to the fourth intercostal space or higher. Outcome Measures: The maximal inspiratory pressure (PImax), maximal expiratory pressure (PEmax), and vital capacity (VC) were measured before exercise and 6, 8, 10, and 12 weeks after exercise. Results: The PImax and PEmax were significantly higher after 6 weeks of exercise than those before exercise. In the continuation group, PEmax increased significantly at 12 weeks of exercise compared to that at 6 weeks, whereas PImax did not show a significant increase. In the non-continuous group, PEmax decreased significantly from the 10th week onwards as compared to that at 6 weeks and showed a significantly lower value than that of the continuous group. The PImax of the non-continuous group decreased significantly at 12 weeks compared to that at 6 weeks. The VC after the 6-week underwater walking program did not differ from the pre-exercise value, with no significant difference observed between the two groups. Moreover, the VC in both groups showed no significant changes after 12 weeks of underwater walking compared to that after 6 weeks. Conclusions: Because underwater walking involves moving forward while resisting water pressure, it is necessary to activate the expiratory abdominal muscles to stabilize the trunk. Notably, the respiratory muscle strength in the non-continuous group decreased 4-6 weeks after the underwater walking program was terminated.