Effects of sitting posture in bathtub bathing on joint torque and brain activities

The purpose of this study was to investigate how the posture during bathtub bathing affects the body and mind. Although many studies discussed comfort and safety of bathing, little has been studied from the perspective of biomechanics and neuroscience. In our two experiments, we manipulated bathers’ posture and measured changes in biomechanical loads (torque at joints) and cerebral blood flowin frontal brain regions. Additionally, we also collected subjective evaluation of physical relaxation for each posture. The results of experiments with male subjects in the 20 s to 30 s showed that extending legs, in comparison to flexing legs, induced a physically relaxed state, which was revealed by subjective evaluation. Furthermore, we found significant decrease of joint torque in the ankle and hip and a significant increases of joint torque in the knee when legs were extended than when flexed. Our measurements indicated inhibition of neural activity in the left ventrolateral prefrontal region during leg extension. These results motivate further exploration of the possibility that physical relaxation with a less confined bathing posture may induce “liberation from verbal thinking”.