Blood Glucose Response during Exercise in the Heat in Adults with Type 1 diabetes

Abstract

Decreases in blood glucose levels during aerobic exercise are a major concern for individuals with type 1 diabetes (T1D), especially if levels drop below the normal range (hypoglycemia). However, the extent to which blood glucose may decline during a given intensity of aerobic exercise in the heat is unclear. Therefore, we examined the changes in blood glucose in individuals with T1D during intermittent exercise in the heat performed at progressively greater exercise intensities. Fifteen, physically active (VO2peak of 44.7 ± 5.5 mL·kg−1·min−1) adults (28 ± 6 years) with T1D (hemoglobin A1c: 7.7 ± 1.1%, duration of diabetes: 13 ± 7 years) participated in the study. The participants were permitted to eat a light meal of their choice at least 90 min prior to the start of the experimental trial. Following instrumentation, participants entered a temperature controlled chamber maintained at 35°C where they rested for 30 min. Thereafter they were required to perform three successive 30 min bouts of semi‐recumbent cycling at Light (~35% of VO2peak), Moderate (~52% of VO2peak) and High intensity (~65% of VO2peak) levels. Each exercise bout was followed by a 30‐min recovery. Core body temperature was measured continuously. Blood glucose concentrations were measured every 15 min throughout the entire protocol. Participants ingested glucose tablets as required if blood glucose fell below pre‐specified levels. Core temperature increased gradually above baseline resting (37.10 ± 0.28°C) by 0.35± 0.28°C, 0.62± 0.28°C and 1.04± 0.34°C at the end of Light, Moderate and High intensity exercise bouts, respectively. Baseline resting glucose was 11.17 ± 3.16 mmol·L−1 and remained relatively unchanged throughout each exercise/recovery transition with the exception that blood glucose was reduced (p<0.05) during the High intensity exercise bout (7.38 ± 2.32 and 7.55 ± 3.04 mmol·L−1 at 15‐ and 30‐min of exercise) relative to the prior recovery period (9.65 ± 3.36 mmol·L−1 as measured at 30‐min of recovery) following the Moderate intensity exercise (9.05 ± 3.53 and 8.47 ± 3.71 mmol·L−1 at 15‐ and 30‐min of exercise). Finally, no changes in blood glucose occurred in the last recovery cycle following the High intensity exercise bout (7.33 ± 2.18 and 8.10 ± 2.80 mmol·L−1 at 15‐ and 30‐min of recovery). Eleven of the fifteen participants required glucose supplementation. Two out of the fifteen participants developed hypoglycemia (blood glucose <4.0 mmol·L−1). For one participant this occurred in the early stages of recovery following the Moderate intensity exercise (subsequently took 20 grams of glucose tabs) whereas for the second it occurred during both Moderate (subsequently ingesting 12 grams of glucose tabs) and High intensity exercise (subsequently ingesting 20 grams of glucose tabs) bouts. In conclusion, individuals with T1D performing prolonged exercise in the heat are likely to require glucose supplementation to reduce the risk of hypoglycemia, especially at higher work intensities.Support or Funding InformationFunding support provided by the Canadian Institutes of Health Research (grant no. 286363, funds held by Dr. Glen P. Kenny)