Intermittent high-intensity exercise does not increase the risk of early postexercise hypoglycemia in individuals with type 1 diabetes.

E xercise is generally recommended for individuals with type 1 diabetes because it is associated with numerous physiological (1,2) and psychological (3,4) benefits. However, participation in exercise can also increase the risk of experiencing severe hypoglycemia, during both exercise (5) and recovery (6). Unfortunately, there are no evidence-based guidelines for safe participation in intermittent high-intensity exercise (IHE), which characterizes most team and field sports, manual labor occupations, and spontaneous play in children. This is because the response of blood glucose levels to this type of exercise is not known, as previous research on intermittent exercise has employed exercise protocols that do not accurately reflect the high-intensity work–to–recovery ratios observed in intermittent sports (7,8). Therefore, the aim of this study was to investigate the effect of IHE that simulates the high-intensity work–to–recovery ratios observed in intermittent sports on blood glucose levels and glucoregulatory hormones in individuals with type 1 diabetes in order to assess the risk of hypoglycemia. RESEARCH DESIGN AND METHODS — Eight volunteers with type 1 diabetes (aged [ SD] 18.6 2.1 years, BMI 22.1 1.5 kg/m, VO2peak 42.4 7.3 ml kg 1 min , type 1 diabetes duration 7.0 4.6 years, and HbA1c 7.0 0.4%), who were free of complications and not taking any prescribed medication other than insulin, gave informed consent to participate in the study in accordance with both the University of Western Australia and Princess Margaret Hospital Human Ethics Committees. The participants visited the laboratory on three separate occasions, first for a familiarization session followed by either a control rest (CON) or IHE trial administered in a random counterbalanced order. At 8:00 AM on CON and IHE trials, the participants injected their usual morning insulin into the abdomen (mean dose 9.4 4.8 units), or in the case of one participant on subcutaneous insulin infusion pump, their usual insulin bolus was infused. Following this, all participants consumed their normal breakfast, which was standardized to be identical on both visits. An antecubital vein was subsequently cannulated for blood sampling, while capillary blood was sampled from a hyperemic earlobe every 15 min for determination of blood glucose levels, which peaked postprandially and then began to decline. As blood glucose levels approached 11 mmol/l, either the CON or IHE protocol was commenced (112 27 min after insulin injection). This procedure was designed to simulate a “real life” situation in which insulin is injected and food is consumed before morning exercise. The IHE protocol was based on timemotion analyses of various intermittent sports (9–11) and spontaneous play in children (12) and consisted of 11 4-s maximal sprints repeated every 2 min on a cycle ergometer for a total duration of 20 min. In contrast, the CON protocol required the participants to be seated on the cycle ergometer for 20 min without exercise. Capillary blood from the hyperemic earlobe and venous blood from the cannulated antecubital vein were sampled during both protocols and for the first hour of recovery. Data were analyzed using two-way repeated-measures ANOVA and paired samples t tests using the SPSS 11.0 for Windows software package. Statistical significance was accepted at P 0.05. Data are expressed as means SD.