Participation in regular physical activity provides numerous health benefits for individuals with type 1 diabetes mellitus (T1DM). However, the blood glucose response to exercise is affected by a number of factors including the intensity and duration of exercise, circulating insulin levels and supplemental carbohydrate. Since variable blood glucose responses to exercise may contribute to fear of hypoglycaemia, poor adherence to regular exercise and lower than average fitness levels, the aim of this study was to determine the reproducibility of the blood glucose response to moderate-intensity exercise in individuals with T1DM.

The participants cycled for two 30-minute bouts at 55% VO2 peak separated by a 30 minute rest period on two separate occasions under basal insulin conditions following an overnight fast. The participants basal insulin infusion rates were optimised prior to their first study using fasting blood glucose levels and these rates were matched during their second study. Activity levels and diet were also matched the day before each study. Blood samples for glucose and lactate were collected at regular intervals during each study and respiratory gases were collected during exercise to determine the rate of oxygen consumption.

Nine participants completed both exercise studies. Blood glucose levels were stable prior to exercise on both occasions with no difference in pre-exercise levels (5.7 ± 0.2 mmol/L and 5.9 ± 0.1 mmol/L; p>0.05). During exercise, blood glucose levels fell at a rate of approximately 0.02 mmol/L.min-1 and continued to decline at a slower rate during recovery reaching similar nadirs at 30 minutes post-exercise (3.9 ± 0.2 mmol/L and 3.6 ± 0.2 mmol/L; p>0.05). There were no significant differences in blood glucose levels before, during or after exercise between studies.

The blood glucose response to exercise is highly reproducible in individuals with T1DM under optimised basal insulin conditions in the fasted state.