Background High-intensity interval training (HIIT) is characterized by brief periods of high-intensity aerobic exercise interspersed with periods of rest or active recovery and has been reported to be more effective than moderate-intensity continuous training for improving several health outcomes. However, safety and efficacy of HIIT in high-risk patient populations, like type 2 diabetic patients, needs to be established. This study aims to analyze the acute effects of HIIT in postprandial blood glucose levels in patients with type 2 diabetes.

Methods This was a randomized crossover study. Twelve individuals with type 2 diabetes (diagnosed at 5.83±3.13 years; six men and six women; age 58.67±5.35 years; glycated hemoglobin 7.08±1.18 %; body mass index 30.07±5,64 kg/m2) treated with oral hypoglycemic agents (metformin, N=5; metformin+sitagliptin, N=4; metformin+vildagliptin, N=3) underwent a single exercise session of high-intensity interval training on treadmill and a control session of seated rest with one week apart in a random order. Exercise session consisted in a 5-min warm-up followed by 5 series of 3-min brisk walking at 70% of heart rate reserve (HRR), interspersed with 3-min at 30% HRR. In the end a 5-min cool-down was carried, totaling a 40-min exercise session. Treadmill speed and grade were adjusted to induce the defined intensity. Training zones were calculated with Karvonen HRR method. Sessions were held in the morning period during standardized breakfast postprandial state. Capillary blood glucose was measured at baseline (fasting state), immediately before sessions (0 min), during sessions (10, 20 and 30 min) immediately after sessions (40 min) and during recovery (50, 60, 70, 80 and 90 min).

Results After exercise start, blood glucose levels were always lower compared to control. However, two-way ANOVA (conditionxtime) with repeated measures only identified statistically significant diferences at minute 20 (155.92±51.13 vs. 110.58±47.07 mg/dl, p=0.034), 30 (148.50±55.58 vs. 95.08±44.77 mg/dl, p=0.017), 40 (137.42±48.60 vs. 91.17±38.71 mg/dl, p=0.017) and 50 (134.00±52.91 vs. 94.25±38.33 mg/dl, p=0.047). No acute adverse events occurred during exercise or recovery: no symptomatic hypoglycemia, hyperglycemia, no symptoms of myocardial ischemia or stroke and no musculoskeletal injuries.

Conclusions HIIT appears to be an effective and safe exercise strategy to acutely control blood glucose in patients with type 2 diabetes.

Trial funding and registration Diabetes em Movimento® is funded by Portuguese Foundation for Science and Technology with reference SFRH/BD/47733/2008 and is registered in Current Controlled Trials with reference ISRCTN09240628.