Effects of sprint interval training on insulin sensitivity, glucose tolerance, and central circulation in sedentary, overweight women
Trilk, Jennifer Lee
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Sprint interval training (SIT) increases muscle oxidative capacity and V.O2max, but whether insulin sensitivity, glucose tolerance and central circulatory capacity are improved is unknown. PURPOSE: To examine the effects of SIT on insulin sensitivity, glucose tolerance, V.O2max and its determinants (Qmax, SVmax, HRmax, (a-v)O2 diffmax) in sedentary, overweight women. METHODS: Twenty-eight women were randomly assigned to SIT (n = 14; age = 30 ± 7 yr, BMI = 36 ± 6 kg/cm2; V.O2max 22 ± 4 ml/kg∙min) or control (CON, n = 14; age = 31 ± 6 yr, BMI = 35 ± 6 kg/cm2; V.O2max 20 ± 3 ml/kg∙min) groups. SIT trained 3 d/wk (4-7, 30-s maximal-effort sprints on a stationary cycle ergometer with 5% body weight as resistance and 4 min active recovery between sprints), while CON remained sedentary (exercise ≤ 1 day/wk). Pre- and post-intervention, a 2-hr oral glucose tolerance test (OGTT) was performed to assess changes in fasting insulin and glucose, area under the curve for insulin (I-AUC) and glucose (G-AUC), the homeostasis model assessment for insulin resistance (logHOMA-IR) and the insulin sensitivity index (ISI). V.O2max and HRmax were measured during a cycling graded exercise test, and a 20-min ride at 50% V.O2max was used to estimate maximal cardiac output (Q.max), stroke volume (SVmax), and (a-v)O2 diffmax by CO2-rebreathing. Data were analyzed using a mixed-model, repeated measures ANOVA. RESULTS: Changes in fasting glucose (SIT: -6% vs. CON: -1%), I-AUC (SIT: -19% vs. CON: -7%), and G-AUC (SIT: -5% vs. CON: -4%) were not different between SIT and CON (P > 0.05). LogHOMA-IR decreased (P = 0.005) more in SIT (-25%) than in CON (0%). A greater improvement in fasting insulin (SIT: -22% vs. CON: -4%) and ISI (SIT: 30% vs. CON: 0%) was clinically-meaningful but not significant (P > 0.05). SIT increased over CON (P < .05) for V.O2max (12% vs. -1%), Q.max (10% vs. -6%) and SVmax (11% vs. -4%). Changes in HRmax and (a-v)O2 diffmax were not different between groups (P > 0.05). CONCLUSION: SIT improves insulin sensitivity without affecting glucose tolerance and improves V.O2max by increasing SVmax and Qmax in sedentary, overweight women.