327-OR: Does Exercise in Cool Water Result in a Greater Decrease in Blood Glucose Concentration than Exercise in Thermoneutral Water or on Land in People with Type 1 Diabetes?

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Introduction: It is unclear whether exercise in cool water, typical of many popular beaches, increases the risk of hypoglycaemia in individuals with type one diabetes mellitus (T1DM). Objective: To test the hypothesis that exercise in cool water results in a greater decrease in blood glucose concentration than does exercise in thermoneutral water or on land in individuals with T1DM. Methods: Eight overnight-fasted individuals (aged 18 to 40 years) with T1DM completed 3 x 60-min cycling sessions on an ergometer at 40% of their on-land V̇O2peak under the following conditions; while immersed in cool water (22°C), in thermoneutral water (32°C) or on land at thermoneutrality (22°C). At regular time intervals, the following variables were measured: concentration of blood glucose and plasma insulin, skin blood flow and skin temperature, and rate of carbohydrate and fat oxidation. Results: Blood glucose concentration did not change during cycling in cool or thermoneutral water (p>0.05), but decreased during cycling on land (p<0.05). During 60 minutes of on-land recovery at 24°C after cycling in cool water, blood glucose concentration increased significantly (~2 mmol/L, p<0.05), but not after cycling in thermoneutral water or on-land. The concentration of plasma insulin decreased during and early after cycling in cool water (p<0.05). Conclusion: Exercise in cool water in people with type 1 diabetes mellitus does not cause a greater decrease in blood glucose concentration than does exercise in thermoneutral water or on land, but increases blood glucose early during on-land recovery probably as a result of a transient decrease in plasma insulin concentration.