In amateur athletes with type 1 diabetes, a 9-day period of cycling at moderate-to-vigorous intensity unexpectedly increased the time spent in hyperglycemia, which was associated with impairment in heart rate variability
In type 1 diabetes, autonomic dysfunction may occur early as a decrease in heart rate variability (HRV). In nondiabetic populations, the positive effects of exercise training on HRV are well documented. However, exercise in individuals with type 1 diabetes, particularly if strenuous and prolonged, can lead to sharp glycemic variations, which can negatively impact HRV. This study explores the impact of a 9-day cycling tour on HRV in this population, with a focus on exercise-induced glycemic excursions.
Research Design and Methods
Twenty amateur athletes with uncomplicated type 1 diabetes cycled 1500km. HRV and glycemic variability were measured by heart rate and continuous glucose monitoring. Linear mixed models were used to test the effects of exercise on HRV, considering concomitant glycemic excursions and subject characteristics as covariates.
Nighttime HRV tended to decrease with the daily distance traveled. The more time the subjects spent in hyperglycemia, the lower the parasympathetic tone was. This result is striking given that hyperglycemic excursions progressively increased throughout the 9 days of the tour, and to a greater degree on the days a longer distance was traveled, while time spent in hypoglycemia surprisingly decreased. This phenomenon occurred despite no changes in insulin administration and a decrease in carbohydrate intake from snacks.
In sports enthusiasts with type 1 diabetes, multiday prolonged exercise at moderate-to-vigorous intensity worsened hyperglycemia with the latter being negatively associated with parasympathetic cardiac tone. Considering the putative deleterious consequences on cardiac risks, future work should focus on understanding and managing exercise-induced hyperglycemia.