The Effects of 10-Minute Outdoor Cold-Water Immersion on Postural Stability.

INTRODUCTION: Decreased body temperature after accidental cold-water immersion can impair fine motor control, muscular function, and cognition. Similar impairments to postural stability could further increase the risk of musculoskeletal injury before a complete recovery is made. The purpose of this study was to evaluate how changes in core temperature, skin temperature, and shivering magnitude after cold-water immersion impact postural stability. We also sought to assess how those outcomes recovered following active rewarming. We hypothesized that relatively colder foot temperature, lower core temperature, and greater shivering magnitude would correlate with reduced postural stability immediately after cold-water immersion. We further expected that postural stability would not recover to near-baseline levels after rewarming.

MATERIALS AND METHODS: Twenty-nine active duty service members (28 M/1 F) participated in a 10-minute immersion to the neck in cold water (1.3 °C) as part of the requirements to complete a military cold-weather training course. The training exercise occurred outdoors in prevailing environmental conditions (air temperature: -4.2 °C). All participants provided informed consent for their research data to be used, in accordance with a protocol approved by the Naval Health Research Center Institutional Review Board. Tri-axial acceleration, core, and skin temperature were continuously recorded. Postural stability was evaluated during three 60-second periods of quiet standing on a force platform-indoor baseline, post-immersion after changing into dry clothes, and after 40 minutes of active rewarming. We quantified shivering magnitude and frequency from acceleration and explored how changes in core temperature, skin temperature, and shivering magnitude impacted postural stability outcomes after cold-water immersion and subsequent rewarming.

RESULTS: Participants exhibited post-immersion increases in root-mean-square (RMS) center of pressure velocity (68.74 ± 41.59 mm/s) and 95% confidence ellipse area (1769.51 ± 1355.44 mm2) compared to baseline (RMS: 8.63 ± 2.12 mm/s; ellipse area: 87.63 ± 42.58 mm2; P < .001), indicating impaired postural stability. Post-immersion core temperature reductions and higher post-immersion shivering magnitude were associated with increased RMS velocity (temperature: r = -0.52, P = .19; shivering: r = 0.93, P < .001) and 95% confidence ellipse area (temperature: r = -0.44, P = .048; shivering: r = 0.69, P = .001). Although RMS velocity and 95% confidence ellipse area improved after rewarming (RMS: 14.33 ± 4.64 mm/s, P < .001; ellipse area: 252.88 ± 134.82 mm2, P < .001), both measures remained at a deficit compared to baseline. We found no significant association between foot temperature and postural stability, but higher post-immersion mean skin temperature was moderately correlated with larger post-immersion RMS velocity (r = 0.71, P = .002) and 95% confidence ellipse area (r = 0.57, P = .015). Greater differences between minimum and baseline core temperature were moderately associated with greater baseline to post-immersion increases in both postural stability outcomes. Similarly, greater differences between minimum and post-rewarming core temperature were moderately associated with greater improvements in both postural stability outcomes from post-immersion to post-rewarming.

CONCLUSIONS: Our results suggest that effective recovery of core temperature and cessation of shivering may be insufficient to mitigate the detrimental effects of cold-water immersion on postural stability. This may have significant implications for service members and first responders in the field, where impaired postural stability raises questions about their ability to move safely, operate under load, and effectively perform critical tasks.