Water Immersion to the Femur Level Affects Cerebral Cortical Activity in Humans: Functional Near-Infrared Spectroscopy Study

Differences in the prefrontal cortex responses of healthy young men performing either water-based or land-based exercise at light to moderate intensity

Cerebral blood flow increases more during water-based exercise than land-based exercise owing to the effects of end-tidal CO₂ (PETCO₂) and mean arterial pressure (MAP) changes due to water immersion. However, it is unclear whether oxygenated hemoglobin (oxy-Hb) concentrations in the prefrontal cortex (PFC) are increased more by water-based or land-based exercise. We hypothesized that oxy-Hb concentrations in the PFC are higher during water-based exercise than land-based exercise when the exercise intensity is matched. To test this hypothesis, 10 healthy participants (age: 24.2 ± 1.7 years; height: 1.75 ± 0.04 m; weight: 69.5 ± 5.2 kg) performed light- to moderate-intensity cycling exercise in water (water-based cycling (WC); chest-high water at 30 °C) and on land (LC). Stroke volume, cardio output, heart rate, MAP, respiratory rate, PETCO₂, and oxy-Hb in the PFC were assessed during 15 min of exercise, with exercise intensity increased every 5 min. Both WC and LC significantly increased oxy-Hb concentrations in the PFC as exercise intensity was increased (intensity effect: p < 0.001). There was no significant difference in oxy-Hb concentrations during WC and LC in most prefrontal areas, although significant differences were found in areas corresponding to the left dorsolateral PFC (exercise effect: p < 0.001). Thus, WC and LC increase oxy-Hb concentrations in the PFC in a similar manner with increasing exercise intensity, but part of the PFC exhibits enhanced oxy-Hb levels during WC. The neural response of the PFC may differ during water-based and land-based exercise owing to differences in external information associated with water immersion.

Efficacy and safety of aquatic exercise in knee osteoarthritis: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

To examine the efficacy and safety of aquatic exercise for people with knee osteoarthritis.

DATA SOURCES

PubMed, Web of Science, Embase, CENTRAL, CNKI and WanFang databases were searched from 1966 to September 2022.

REVIEW METHODS

Randomized controlled trials evaluating aquatic exercise for people with knee osteoarthritis compared with no exercise and land-based exercise were included. The Grading of Recommendations Assessment, Development and Evaluation system was used to evaluate the certainty of evidence.

RESULTS

Twenty-two studies with 1394 participants were included. Compared with no exercise (13 trials with 746 participants), low-to high-certainty evidence revealed that aquatic exercise yielded significant improvements in patient-reported pain (SMD -0.58, 95% CI -0.82 to -0.33), stiffness (SMD -0.57, 95% CI -1.03 to -0.11) and physical function (SMD -0.35, 95% CI -0.52 to -0.18) immediately postintervention. A sustained effect was observed only for pain at three months postintervention (SMD -0.48, 95% CI -0.91 to -0.06). The confidence intervals demonstrated that the pooled results do not exclude the minimal clinically important differences. There were no significant differences between the effects of aquatic exercise and land-based exercise (13 trials with 648 participants) on pain (SMD -0.12, 95% CI -0.29 to 0.04), stiffness (SMD -0.17, 95% CI -0.49 to 0.16) or physical function (SMD -0.13, 95% CI -0.28 to 0.02). No study reported a serious adverse event in relation to aquatic exercise.

CONCLUSION

Aquatic exercise provides a short-term clinical benefit that is sustained for at least three months postintervention in terms of pain in people with knee osteoarthritis.

Evaluation of the Feasibility of a Two-Week Course of Aquatic Therapy and Thalassotherapy in a Mild Post-Stroke Population

Strokes are a leading cause of disability in developed countries. Patients with disabilities need rehabilitation to improve their physical functioning, mental status, and quality of life. Currently, no high-quality evidence can be found attesting the benefits of any of the interventions that are nowadays used. Water-based exercise may improve the physical conditions and quality of life of people in the post-stroke phase. The objective of this study is to test whether aquatic therapy in an enriched environment at the seaside (a thalassotherapy center) could play a role in this condition. A quasi-experimental prospective study consisting of a specific program assessed 62 patients with a mild–moderate disability pre- and post-2 weeks of intensive treatment. They followed a thalassotherapy regimen including aquatic therapy in a sea water pool at 32–34 °C for 45 min daily five times a week. The outcomes measured were the Berg Balance scale, the Timed Up and Go test, the 10-meter walking test, the 6-min walking test, the Pain Visual Analogue Scale, the WHO Well-being index, EuroQoL VAS and EuroQoL 5D. We observed a significant improvement in all outcomes measured (p < 0.001, except mobility EuroQoL p < 0.05), except in the other four dimensions of the EuroQoL 5D and 10-metre walking test (NS). Conclusion: A two-week intensive course of aquatic therapy and thalassotherapy may be beneficial in the short term by reducing pain and improving the functional status and overall well-being of post-stroke patients.

Acute effects of contrast bath on sympathetic skin response in patients with poststroke complex regional pain syndrome

PURPOSE

Complex regional pain syndrome (CRPS) is one of the common complications in stroke patients. Sympathetic dysfunction is usually considered underlying pathology. The evidence for contrast bath (CB) used in the treatment of CRPS is limited. The aim of the study is to investigate the possible effects of CB on the sympathetic activity in poststroke CRPS.

MATERIALS AND METHODS

Stroke patients with CRPS (CRPS group) and without CRPS (control group) were included in the study. Age, gender, duration of stroke, aetiology, plegic side, dominant hand, spasticity level, Brunnstrom stages, and comorbidities were recorded. CB was performed for one session to the plegic side of the CRPS and control groups. Sympathetic skin responses (SSR) was recorded from the plegic and healthy hands of participants at pre-CB and post-CB.

RESULTS

Each group consisted of 20 participants. No significant difference was detected in stroke duration, aetiology, and Brunnstrom stages between groups. Elbow spasticity level was significantly higher in CRPS group (p = .034). SSR amplitudes of plegic hands were significantly decreased after CB in CRPS and control groups (p = .0002, p = .013 respectively). Also, CB reduced the SSR amplitude of healty side in CRPS group (p = .003). There was no statistically significant change in SSR latency or percentage changes of SSR amplitude and latency after CB in both groups.

CONCLUSION

CB leads to a significant reduction in sympathetic activity of plegic side of stroke patients. Also, CB to the plegic side has an inhibitory effect on sympathetic activity of healty side in poststroke CRPS. ClinicalTrials.gov ID: NCT04198532.

Influence of Aquatic Therapy in Children and Youth with Cerebral Palsy: A Qualitative Case Study in a Special Education School

Cerebral palsy results in the progressive loss of motor functions, with a negative impact on daily activities and participation. Despite the well described benefits of aquatic therapy in children, little is known about the effects of the same in school settings. This study aimed to describe the experience of children and youth with cerebral palsy participating in an aquatic therapy program within a special education school considering their educational and therapeutic perspectives. A qualitative descriptive case study with embedded units was developed, comprising 27 participants. This study employed purposeful sampling to include children and youth with cerebral palsy from the Asociación Ayuda a la Paralisis Cerebral (APACE) special education school, together with their parents, the special education teachers, and health care professionals. Data were collected via non-participant observation, semi-structured and informal interviews, focus groups, and researcher field notes. A thematic analysis was conducted, revealing the following themes: (a) the connection with the environment; (b) postural improvements and mobility; (c) the opportunity to perform tasks; (d) learning and transfer. A motivating environment leads to physical, cognitive and social benefits, both at school and in the home. Aquatic therapy was viewed as a means for learning and participation. These findings may enhance understanding regarding the potential benefits of implementing multidisciplinary aquatic therapy programs in specialist school settings.

The effect of aquatic physical therapy in patients with stroke: A systematic review and meta-analysis

Objective: The purpose of this study was to evaluate the literature reports of qualitative and quantitative results of physical therapy treatments in the alternative aquatic setting for individuals affected by strokes. Method: PRISMA guidelines were used to carry out the systematic review and meta-analysis. Three bibliographic databases were searched: MEDLINE, PEDro, and the Cochrane Library. Papers included in the study were required to: (a) have a randomized controlled trial (RCT) design of research; and (b) be published in English; (c) be published during the last 10 years (2008-2018). Only randomized controlled trials were employed in the study. The quality of the clinical trials to be included was evaluated according to the Jadad scale. The internal validity was assessed according to the PEDro scale. Results: Eleven RCTs were initially identified in the systematic review. Eight of these were involved in the meta-analysis comparing outcomes and follow-up. Eight studies received a Jadad score of three, indicating a high level of quality. The remaining three studies achieved a lower score which indicated lower qualitative level. Nearly all of the results of the quantitative analysis were statistically significant (P < 0,05) and most of them favored of the experimental group subject to aquatic treatment. Conclusion: Aquatic physical therapy may be a valid means for the rehabilitation of people affected by stroke. The integration of this methodological approach with conventional physical therapy should be considered. However, more studies; a larger number of participants; and varying lengths of follow-up times are necessary.

Priming Effects of Water Immersion on Paired Associative Stimulation-Induced Neural Plasticity in the Primary Motor Cortex

We aimed to verify whether indirect-wave (I-wave) recruitment and cortical inhibition can regulate or predict the plastic response to paired associative stimulation with an inter-stimulus interval of 25 ms (PAS25), and also whether water immersion (WI) can facilitate the subsequent PAS25-induced plasticity. To address the first question, we applied transcranial magnetic stimulation (TMS) to the M1 hand area, while alternating the direction of the induced current between posterior-to-anterior and anterior-to-posterior to activate two independent synaptic inputs to the corticospinal neurons. Moreover, we used a paired stimulation paradigm to evaluate the short-latency afferent inhibition (SAI) and short-interval intracortical inhibition (SICI). To address the second question, we examined the motor evoked potential (MEP) amplitudes before and after PAS25, with and without WI, and used the SAI, SICI, and MEP recruitment curves to determine the mechanism underlying priming by WI on PAS25. We demonstrated that SAI, with an inter-stimulus interval of 25 ms, might serve as a predictor of the response to PAS25, whereas I-wave recruitment evaluated by the MEP latency difference was not predictive of the PAS25 response, and found that 15 min WI prior to PAS25 facilitated long-term potentiation (LTP)-like plasticity due to a homeostatic increase in cholinergic activity.

Comparison of motor skill learning, grip strength and memory recall on land and in chest-deep water

Immersion in chest-deep water may augment explicit memory in healthy adults however, there is limited information on how this environment might affect implicit memory or motor learning. The purpose of this study was to compare the speed and accuracy for learning a motor skill on land and in chest-deep water. Verbal word recall and grip strength were included to gain a more complete understanding of the intervention. Sixty-two younger adults (age = 23.3 ± 3.59 yrs.) were randomly assigned to either a water group immersed to the xiphoid or a land group. Participants in both groups completed the same eight practice trials of a mirror-drawing task on two separate days. Outcome measures for this task included time and error numbers to complete each drawing. The number of words recalled using a 12 word recall test, and peak grip strength using a hand dynamometer were measured each day of testing. The influence of environment and repeated practice on each outcome measure were assessed with an analysis of variance and effect sizes (ES). Time and errors for both groups significantly decreased with practice (p < 0.01, ES = 0.11-0.28), however the drawing time was greater in water than on land for trials 1, 5, and 6 (ES = 0.50-0.55). There was a 7% increase in words recalled (9.24 ± 1.19 vs 8.60 ± 1.19) and a 16% increase in grip strength (405 ± 104 vs 342 ± 83) for water than land groups (ES 0.54-0.64). Healthy adults in chest-deep water and on land display comparable mirror-drawing speed and accuracy after minimal practice. Curiously, water immersion may augment verbal word recall and grip strength abilities.

Water Immersion Affects Episodic Memory and Postural Control in Healthy Older Adults

BACKGROUND AND PURPOSE

Previous research has reported that younger adults make fewer cognitive errors on an auditory vigilance task while in chest-deep water compared with on land. The purpose of this study was to extend this previous work to include older adults and to examine the effect of environment (water vs land) on linear and nonlinear measures of postural control under single- and dual-task conditions.

METHODS

Twenty-one older adult participants (age = 71.6 ± 8.34 years) performed a cognitive (auditory vigilance) and motor (standing balance) task separately and simultaneously on land and in chest-deep water. Listening errors (n = count) from the auditory vigilance test and sample entropy (SampEn), center of pressure area, and velocity for the balance test served as dependent measures. Environment (land vs water) and task (single vs dual) comparisons were made with a Wilcoxon matched-pair test.

RESULTS

Listening errors were 111% greater during land than during water environments (single-task = 4.0 ± 3.5 vs 1.9 ± 1.7; P = .03). Conversely, SampEn values were 100% greater during water than during land environments (single-task = 0.04 ± 0.01 vs 0.02 ± 0.01; P < .001). Center of pressure area and velocity followed a similar trend to SampEn with respect to environment differences, and none of the measures were different between single- and dual-task conditions (P > .05).

CONCLUSIONS

The findings of this study expand current support for the potential use of partial aquatic immersion as a viable method for challenging both cognitive and motor abilities in older adults.

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.

Site Specificity of Changes in Cortical Oxyhaemoglobin Concentration Induced by Water Immersion

Our previous studies have shown that water immersion (WI) changes sensorimotor processing and cortical excitability in the sensorimotor regions of the brain. The present study examined the site specificity of the brain activation during WI using functional near infrared spectroscopy (fNIRS). Cortical oxyhaemoglobin (O₂Hb) levels in the anterior and posterior parts of the supplementary motor area (pre-SMA and SMA), primary motor cortex (M1), primary somatosensory cortex (S1), and posterior parietal cortex (PPC) were recorded using fNIRS (OMM-3000; Shimadzu Co.) before, during, and after WI in nine healthy participants. The cortical O₂Hb levels in SMA, M1, S1, and PPC significantly increased during the WI and increased gradually along with the filling of the WI tank. These changes were not seen in the pre-SMA. The results show that WI-induced increases in cortical O₂Hb levels are at least somewhat site specific: there was little brain activation in response to somatosensory input in the pre-SMA, but robust activation in other areas.

Water Sensation During Passive Propulsion for Expert and Nonexpert Swimmers

This study determined whether expert swimmers, compared with nonexperts, have superior movement perception and physical sensations of propulsion in water. Expert (national level competitors, n = 10) and nonexpert (able to swim 50 m in > 3 styles, n = 10) swimmers estimated distance traveled in water with their eyes closed. Both groups indicated their subjective physical sensations in the water. For each of two trials, two-dimensional coordinates were obtained from video recordings using the two-dimensional direct linear transformation method for calculating changes in speed. The mean absolute error of the difference between the actual and estimated distance traveled in the water was significantly lower for expert swimmers (0.90 ± 0.71 meters) compared with nonexpert swimmers (3.85 ± 0.84 m). Expert swimmers described the sensation of propulsion in water in cutaneous terms as the "sense of flow" and sensation of "skin resistance." Therefore, expert swimmers appear to have a superior sense of distance during their movement in the water compared with that of nonexpert swimmers. In addition, expert swimmers may have a better perception of movement in water. We propose that expert swimmers integrate sensations and proprioceptive senses, enabling them to better perceive and estimate distance moved through water.

Age-Related Changes in Postural Sway Are Not Consistent Between Land and Aquatic Environments

BACKGROUND AND PURPOSE

Quantifying how the environment (land vs water) influences age-related changes in postural sway is important for the development of new therapies that improve balance. The authors are not aware of any previous studies that have compared postural sway in an aquatic environment between age groups or when water depth and/or perturbations are incorporated into the comparison. The purpose of this study was to compare the effect of water depth and jet intensity on postural sway in older and younger adults.

METHODS

Sixteen older (age = 62.8 ± 9.56 years) and 15 younger (age = 22.5 ± 1.85 years) adults participated. Participants stood quietly for 90 seconds on land and at various water depths and jet intensities while center of pressure (CoP) sway was recorded using a force platform.

RESULTS

Statistical comparisons revealed that CoP range and area measurements were different between land and aquatic conditions (P = .04 - .001). For example, CoP sway area in chest deep water (8.51 ± 2.97 cm) was greater than on land (2.41 ± 1.37 cm; effect size = 2.05). Furthermore, CoP sway area at the 60% jet intensity (71.4 ± 31.2 cm) was substantially greater than at the 20% jet intensity (12.4 ± 6.23 cm; effect size = 1.89). Surprisingly, the proportion of change across water depths and jet intensities was not consistent between older and younger groups as indicated by significant age by environment interactions (P = .03 - .001). Follow-up tests indicated that older adults swayed less than younger adults in water at the level of the hip (effect sizes = 0.42-0.94) and when water jets were applied at a 60% jet intensity (effect sizes = 0.63-1.97).

CONCLUSIONS

Water immersion to the chest with high jet intensities produces the greatest CoP sway in both groups. This is likely a result of buoyancy and perturbation intensity. Less sway in the older group may reflect a strategy that reduces degrees of freedom for this group when faced with these stability challenges.

Regional Changes in Cerebral Oxygenation During Repeated Passive Movement Measured by Functional Near-infrared Spectroscopy

The aim of this study is to investigate the influence of passive movement repetition frequency at 1.5-Hz and 1-Hz on changes in cerebral oxygenation and assess the temporal properties of these changes using functional near-infrared spectroscopy (fNIRS). No significant differences in systemic hemodynamics were observed between resting and passive movement phases for either 1.5-Hz or 1-Hz trial. Changes in cortical oxygenation as measured by fNIRS in bilateral supplementary motor cortex (SMC), left primary motor cortex (M1), left primary somatosensory cortex (S1), and left posterior association area (PAA) during passive movement of the right index finger revealed greater cortical activity at only 1.5-Hz movement frequency. However, there were no significant differences in the time for peak oxyhemoglobin (oxyHb) among regions (bilateral SMC, 206.4 ± 14.4 s; left M1, 199.1 ± 14.8 s; left S1, 207.3 ± 9.4 s; left PAA, 219.1 ± 10.2 s). Therefore, our results that passive movement above a specific frequency may be required to elicit a changed in cerebral oxygenation, and the times of peak ΔoxyHb did not differ significantly among measured regions.

Human Physiology in an Aquatic Environment

Water covers over 70% of the earth, has varying depths and temperatures and contains much of the earth's resources. Head-out water immersion (HOWI) or submersion at various depths (diving) in water of thermoneutral (TN) temperature elicits profound cardiorespiratory, endocrine, and renal responses. The translocation of blood into the thorax and elevation of plasma volume by autotransfusion of fluid from cells to the vascular compartment lead to increased cardiac stroke volume and output and there is a hyperperfusion of some tissues. Pulmonary artery and capillary hydrostatic pressures increase causing a decline in vital capacity with the potential for pulmonary edema. Atrial stretch and increased arterial pressure cause reflex autonomic responses which result in endocrine changes that return plasma volume and arterial pressure to preimmersion levels. Plasma volume is regulated via a reflex diuresis and natriuresis. Hydrostatic pressure also leads to elastic loading of the chest, increasing work of breathing, energy cost, and thus blood flow to respiratory muscles. Decreases in water temperature in HOWI do not affect the cardiac output compared to TN; however, they influence heart rate and the distribution of muscle and fat blood flow. The reduced muscle blood flow results in a reduced maximal oxygen consumption. The properties of water determine the mechanical load and the physiological responses during exercise in water (e.g. swimming and water based activities). Increased hydrostatic pressure caused by submersion does not affect stroke volume; however, progressive bradycardia decreases cardiac output. During submersion, compressed gas must be breathed which introduces the potential for oxygen toxicity, narcosis due to nitrogen, and tissue and vascular gas bubbles during decompression and after may cause pain in joints and the nervous system.

Whole-hand water flow stimulation increases motor cortical excitability: a study of transcranial magnetic stimulation and movement-related cortical potentials

Previous studies examining the influence of afferent stimulation on corticospinal excitability have demonstrated that the intensity of afferent stimulation and the nature of the afferents targeted (cutaneous/proprioceptive) determine the effects. In this study, we assessed the effects of whole-hand water immersion (WI) and water flow stimulation (WF) on corticospinal excitability and intracortical circuits by measuring motor evoked potential (MEP) recruitment curves and conditioned MEP amplitudes. We further investigated whether whole-hand WF modulated movement-related cortical activity. Ten healthy subjects participated in three experiments, comprising the immersion of participants' right hands with (whole-hand WF) or without (whole-hand WI) water flow, and no immersion (control). We evaluated MEP recruitment curves produced by a single transcranial magnetic stimulation (TMS) pulse at increasing stimulus intensities, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) using the paired TMS technique before and after 15 min of intervention. Movement-related cortical potentials (MRCPs) were evaluated to examine primary motor cortex, supplementary motor area, and somatosensory cortex excitability upon movement before and after whole-hand WF. After whole-hand WF, the slope of the MEP recruitment curve significantly increased, whereas SICI decreased and ICF increased in the contralateral motor cortex. The amplitude of the Bereitschaftspotential, negative slope, and motor potential of MRCPs significantly increased after whole-hand WF. We demonstrated that whole-hand WF increased corticospinal excitability, decreased SICI, and increased ICF, although whole-hand WI did not change corticospinal excitability and intracortical circuits. Whole-hand WF modulated movement-related cortical activity, increasing motor cortex activation for the planning and execution of voluntary movements.

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.

Brain mapping after prolonged cycling and during recovery in the heat

The aim of this study was to determine the effect of prolonged intensive cycling and postexercise recovery in the heat on brain sources of altered brain oscillations. After a max test and familiarization trial, nine trained male subjects (23 ± 3 yr; maximal oxygen uptake = 62.1 ± 5.3 ml·min(-1)·kg(-1)) performed three experimental trials in the heat (30°C; relative humidity 43.7 ± 5.6%). Each trial consisted of two exercise tasks separated by 1 h. The first was a 60-min constant-load trial, followed by a 30-min simulated time trial (TT1). The second comprised a 12-min simulated time trial (TT2). After TT1, active recovery (AR), passive rest (PR), or cold water immersion (CWI) was applied for 15 min. Electroencephalography was measured at baseline and during postexercise recovery. Standardized low-resolution brain electromagnetic tomography was applied to accurately pinpoint and localize altered electrical neuronal activity. After CWI, PR and AR subjects completed TT2 in 761 ± 42, 791 ± 76, and 794 ± 62 s, respectively. A prolonged intensive cycling performance in the heat decreased β activity across the whole brain. Postexercise AR and PR elicited no significant electrocortical differences, whereas CWI induced significantly increased β3 activity in Brodmann areas (BA) 13 (posterior margin of insular cortex) and BA 40 (supramarginal gyrus). Self-paced prolonged exercise in the heat seems to decrease β activity, hence representing decreased arousal. Postexercise CWI increased β3 activity at BA 13 and 40, brain areas involved in somatosensory information processing.

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

Background

Water 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.

Results

Water 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.

Conclusions

Water 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 Registration

UMIN-CTR (UMIN000006492)