Summary of recent studies assessing acute SI responses to exercise
| Reference | Participants | Study type | Exercise type and intensity | Outcome measure | Authors' conclusions and comments |
| de Matos et al22 | Twenty-seven obese patients or obese patients with insulin resistance. | Exercise intervention. | Acute 60 min of aerobic exercise on a cycle ergometer at 60% of peak oxygen consumption. | Compared with paired eutrophic controls, obese subjects had higher basal levels of p-JNK and p-IRS-1(ser612), and reduced HSP70. Exercise reduced p-IRS-1(ser612) for both obese and obese insulin-resistant subjects. A main effect of exercise was observed for HSP70. | A single session of exercise promotes changes that are characteristic of a reduction in cellular stress. Such changes may contribute to an exercise-induced increase in SI. |
| Rynders et al38 | Eighteen adults with prediabetes. | Randomised controlled trial of acute responses to exercise. | Moderate intensity exercise at LT versus high intensity exercise (75% of the difference between LT and peak O2 consumption versus control (1 hour of seated rest). One hour after exercise, subjects undertook an OGTT. | SI improved by 51% following moderate intensity exercise and 85% following high-intensity exercise. | Acute exercise had an immediate and intensity-dependent effect on improving postprandial glycaemia and SI. |
| Newsom et al39 | Eleven sedentary, obese adults. | Randomised controlled trial. | Three experimental trials: (1) exercise at 50% VO2 peak for~70 min (expending ~350 Kcal); (2) exercise at 65% VO2 peak for ~55 min to expend 350 kcal; (3) no exercise. Exercise was undertaken in the afternoon and SI assessed the following morning. | Seventy minutes of exercise at 50% VO2 peak increased insulin sensitivity by 35% compared with control condition. Whereas the 55 min of exercise at 65% VO2 peak produced average increase in SI of 20% compared with control condition, this was not statistically significant. | A prolonged single session of exercise at a moderate intensity improved SI the next day in obese adults. This may be more effective than a shorter duration bout at a higher intensity. |
| Malin et al40 | Fifteen patients with prediabetes aged 49.9±3.6 years. | Randomised, controlled, cross-over trial, with control condition. | Three trial conditions: (1) 1 hour rest (control); (2) 200 kcal cycle ergometer exercise bout at LT; and (3) 200 kcal cycle ergometer exercise bout at 75% of difference between lactate threshold and VO2 peak. A 75 g OGTT was undertaken 1 hour postexercise/control. | Compared with control, exercise lowered skeletal muscle IR independently of exercise intensity, but hepatic and adipose IR was increased. Glucose-stimulated insulin secretion did not differ between conditions, but postprandial glucose levels were lower postexercise. | Exercise promoted insulin sensitivity in skeletal muscle post exercise. The increase in IR in adipose and hepatic tissue may further promote glucose uptake and glycogen restoration in the muscles. |
| Ortega et al43 | Ten healthy young men. | Randomised cross-over trial with control condition. | SIT of 4 × 30 s sprints versus continuous low intensity exercise at 46% VO2 peak versus moderate intensity exercise at 77% VO2 peak versus control. Intravenous glucose tolerance tests undertaken 30 min, 24 hours and 48 hours postexercise. | All exercise conditions improved SI for at least 48 hours compared with the control condition. Thirty minutes postexercise the improvements induced by SIT were greater than for either of the continuous exercise bouts. | All exercise bouts improved SI, and in the short term (30 min postexercise) SIT was more effective than low or moderate intensity continuous exercise at improving SI. |
| Terada et al44 | Ten patients with diabetes aged 45–75 years. | Randomised, controlled, cross-over trial, with control condition. | Four exercise conditions each of 60 min duration: (1) HIIT (repetitions of 3 min at 40% VO2 peak and x 1 min at 100% VO2 peak) in fasted state; (2) HIIT postbreakfast; (3) Moderate intensity exercise (55% of VO2 peak) in fasted state; and (4) moderate intensity exercise, postbreakfast; plus no exercise (control). | HIIT reduced overnight and fasting glycaemia the day after the exercise by more than moderate intensity exercise. Exercising in a fasted state rather than ‘post-breakfast’ attenuated postprandial glycaemic increments. Compared with the control condition, HIIT in a fasted state produced significant improvements to: 24-hour mean glucose, fasting glucose, postprandial glycaemic increment, glycaemic variability and time spent in hyperglycaemia. | HIIT resulted in acute benefits to glycaemic regulation, which were further enhanced by undertaking the exercise in a fasted state. |
| Whyte et al45 | Ten overweight/obese men aged 26.9±6.2 years. | Randomised, controlled, cross-over trial. | Three trial conditions: (1) four maximal 30 s sprints, with 4.5 min recovery between each (SIT); (2) a single maximal ES matched with SIT for work done; and (3) no exercise (CON). Oral glucose tolerance tests were undertaken on the days following each of the above. | SI Index was 44.6% higher following ES than CON, but did not differ significantly between SIT and CON. On the day following exercise, fat oxidation in the fasted state was increased by 63% and 38%, compared with CON, in SIT and ES, respectively. | A single ES, which may represent a more time-efficient alternative to SIT, can increase SI and increase fat oxidation in overweight/obese sedentary men. |
ES, extended sprint; HIIT, high intensity interval training; LT, lactate threshold; OGTT, oral glucose tolerance test; SI, insulin sensitivity; SIT, sprint interval training.