Y. Shimoyama

The effect of water immersion on short-latency somatosensory evoked potentials in human

BackgroundWater immersion therapy is used to treat a variety of cardiovascular, respiratory, and orthopedic conditions. It can also benefit some neurological patients, although little is known about the effects of water immersion on neural activity, including somatosensory processing. To this end, we examined the effect of water immersion on short-latency somatosensory evoked potentials (SEPs) elicited by median nerve stimuli. Short-latency SEP recordings were obtained for ten healthy male volunteers at rest in or out of water at 30°C. Recordings were obtained from nine scalp electrodes according to the 10-20 system. The right median nerve at the wrist was electrically stimulated with the stimulus duration of 0.2 ms at 3 Hz. The intensity of the stimulus was fixed at approximately three times the sensory threshold.ResultsWater immersion significantly reduced the amplitudes of the short-latency SEP components P25 and P45 measured from electrodes over the parietal region and the P45 measured by central region.ConclusionsWater immersion reduced short-latency SEP components known to originate in several cortical areas. Attenuation of short-latency SEPs suggests that water immersion influences the cortical processing of somatosensory inputs. Modulation of cortical processing may contribute to the beneficial effects of aquatic therapy.Trial RegistrationUMIN-CTR (UMIN000006492)

Comparison of once and twice weekly water exercise on various bodily functions in community-dwelling frail elderly requiring nursing care

Previous research suggests that water exercise (WE) improves bodily functions of the frail elderly, but there is as yet no research on the effect of once weekly WE. This study aims to compare the effects of once and twice weekly WE on bodily functions of frail elderly requiring nursing care in six months. The design is a prospective cohort study. Participants were assigned to two different exercise groups (once weekly group or twice weekly group; n=35). Once weekly group participate in a 60-min exercise session once a week, for six months while twice weekly group attended the session twice a week. Exercise sessions were divided into a 10-min warm-up on land and 50 min of exercise in water. The 50-min WE program consisted of 20 min walking, 10 min activities of daily living (ADL) exercise, 10 min stretching and strength exercises, and 10 min relaxation in water. Muscle strength, flexibility, balance, mobility and ADL disability were measured before the beginning of intervention and three months and six months after the program had started. Significant differences between the once and twice weekly groups were found in flexibility and balance at 3-months and 6-months and lower muscle strength and ADL disability only at 3-months. These results from present study suggested that the effects of WE frequency in the fail elderly who require nursing care were different for each bodily function.

Effects of water immersion on short- and long-latency afferent inhibition, short-interval intracortical inhibition, and intracortical facilitation

OBJECTIVE The aim of the present study was to investigate the effect of water immersion (WI) on short- and long-latency afferent inhibition (SAI and LAI), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). METHODS Motor evoked potentials (MEPs) were measured from the first dorsal interosseous (FDI) muscle of fifteen healthy males before, during, and after a 15-min WI at 30°C up to the axilla. Both SAI and LAI were evaluated by measuring MEPs in response to transcranial magnetic stimulation (TMS) of the left motor cortex following electrical stimulation of the right median nerve (fixed at about three times the sensory threshold) at interstimulus intervals (ISIs) of 20 ms to assess SAI and 200 ms to assess LAI. The paired-pulse TMS paradigm was used to measure SICI and ICF. RESULTS Both SAI and LAI were reduced during WI, while SICI and ICF were not significantly different before, during, and after WI. CONCLUSIONS WI decreased SAI and LAI by modulating the processing of afferent inputs. SIGNIFICANCE Changes in somatosensory processing and sensorimotor integration may contribute to the therapeutic benefits of WI for chronic pain or movement disorders.

Does installation of the backstroke start device reduce 15-m start time in swimming?

ABSTRACT The purpose of this study was to determine the installation of the backstroke start device reduces 15-m time. Thirteen college swimmers participated in this study. The aerial start and underwater motions were recorded with two digital video cameras. The center of mass (CM) of the swimmer, angular displacements and velocities of the shoulder, hip and knee joints were calculated. As an indicator of performance, the 5- and 15-m times were measured. The 5- and 15-m times in the backstroke start device condition were significantly shorter than in the non-backstroke start device condition. The vertical velocities of the CM at hand-off and toe-off in the backstroke start device condition were significantly greater than in the non-backstroke start device condition, while there was no significant difference in the CM horizontal velocity at toe-off. As a result, the height of the great trochanter at entry of the fingertips, with the backstroke start device, was 15 cm higher than in the non-backstroke start device condition. In addition, the CM horizontal velocities at 5 m in the backstroke start device condition were significantly greater than those of the non-backstroke start device. Thus, the use of the backstroke start device may reduce the 15-m time by diminution of the entry area.

Functional Role of the Front and Back Legs During a Track Start with Special Reference to an Inverted Pendulum Model in College Swimmers.

This study investigated factors that determine the velocity of the center of mass (CM) and flight distance from a track start to devise effective technical and physical training methods. Nine male and 5 female competitive swimmers participated in this study. Kinematics and ground reaction forces of the front and back legs were recorded using a video camera and force plates. The track start was modeled as an inverted pendulum system including a compliant leg, connecting the CM and front edge of the starting block. The increase in the horizontal velocity of the CM immediately after the start signal was closely correlated with the rotational component of the inverted pendulum. This rotational component at hands-off was significantly correlated with the average vertical force of the back plate from the start signal to hands-off (r = .967, P < .001). The flight distance / height was significantly correlated with the average vertical force of the front plate from the back foot-off to front foot-off (r = .783, P < .01). The results indicate that the legs on the starting block in the track start play a different role in the behavior of the inverted pendulum.

Whole-Body Water Flow Stimulation to the Lower Limbs Modulates Excitability of Primary Motor Cortical Regions Innervating the Hands: A Transcranial Magnetic Stimulation Study

Whole-body water immersion (WI) has been reported to change sensorimotor integration. However, primary motor cortical excitability is not affected by low-intensity afferent input. Here we explored the effects of whole-body WI and water flow stimulation (WF) on corticospinal excitability and intracortical circuits. Eight healthy subjects participated in this study. We measured the amplitude of motor-evoked potentials (MEPs) produced by single transcranial magnetic stimulation (TMS) pulses and examined conditioned MEP amplitudes by paired-pulse TMS. We evaluated short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using the paired-TMS technique before and after 15-min intervention periods. Two interventions used were whole-body WI with water flow to the lower limbs (whole-body WF) and whole-body WI without water flow to the lower limbs (whole-body WI). The experimental sequence included a baseline TMS assessment (T0), intervention for 15 min, a second TMS assessment immediately after intervention (T1), a 10 min resting period, a third TMS assessment (T2), a 10 min resting period, a fourth TMS assessment (T3), a 10 min resting period, and the final TMS assessment (T4). SICI and ICF were evaluated using a conditioning stimulus of 90% active motor threshold and a test stimulus adjusted to produce MEPs of approximately 1–1.2 mV, and were tested at intrastimulus intervals of 3 and 10 ms, respectively. Whole-body WF significantly increased MEP amplitude by single-pulse TMS and led to a decrease in SICI in the contralateral motor cortex at T1, T2 and T3. Whole-body WF also induced increased corticospinal excitability and decreased SICI. In contrast, whole-body WI did not change corticospinal excitability or intracortical circuits.

Water immersion decreases sympathetic skin response during color–word Stroop test

Water immersion alters the autonomic nervous system (ANS) response in humans. The effect of water immersion on executive function and ANS responses related to executive function tasks was unknown. Therefore, this study aimed to determine whether water immersion alters ANS response during executive tasks. Fourteen healthy participants performed color–word-matching Stroop tasks before and after non-immersion and water immersion intervention for 15 min in separate sessions. The Stroop task-related skin conductance response (SCR) was measured during every task. In addition, the skin conductance level (SCL) and electrocardiograph signals were measured over the course of the experimental procedure. The main findings of the present study were as follows: 1) water immersion decreased the executive task-related sympathetic nervous response, but did not affect executive function as evaluated by Stroop tasks, and 2) decreased SCL induced by water immersion was maintained for at least 15 min after water immersion. In conclusion, the present results suggest that water immersion decreases the sympathetic skin response during the color–word Stroop test without altering executive performance.

P688: Water flow stimulation increases excitability of primary motor cortex at rest and during movement – a transcranial magnetic stimulation and EEG study

Question: Previous research have found that water immersion induced attenuation of short and long latency afferent inhibition, whereas no change in the excitability of primary motor cortex (MI) was observed because of low stimulus intensity (Sato et al., 2013). Consequently, we investigated whether the MI excitability increased by increasing the stimulus intensity by water flow. Methods: Ten healthy subjects participated in three separate experiments. We evaluated the motor-evoked potential (MEP) recruitment curve produced by a single transcranial magnetic stimulation (TMS) pulse at increasing stimulus intensities (experiment 1) and short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using the paired magnetic stimulation technique (experiment 2) before and after 15 min of intervention periods. Three interventions were set at immersion of their right hand with water flow (flow trial), without flow (immersion trial), and no immersion control (control trial). SICI and ICF were evaluated using a conditioning stimulus of 80% active motor threshold and a test stimulus adjusted to produce MEPs of approximately 1-1.2 mV, and were tested at intra-stimulus interval of 3 ms and 10 ms, respectively. In experiment 3, movement-related cortical potentials (MRCPs) were evaluated to examine the MI excitability during movement with flow trial alone. Results: With flow trial alone, the slope of MEP recruitment curve significantly increased (experiment 1) and the water flow stimulation led to a decrease in SICI and an increase in ICF in the contralateral motor cortex (experiment 2) after intervention. In contrast, there was no significant difference with immersion and control trials. Furthermore, the amplitude of motor potential (MP) in MRCPs significantly increased after 15 min of water flow intervention (experiment 3). Conclusions: We concluded that water flow stimulation increases the MI excitability at rest and during movement and differentially modulates excitability in motor cortical circuits.