Sjoros TJ, Heiskanen MA, Motiani KK, et al. Increased insulin-stimulated glucose uptake in both leg and arm muscles after sprint interval and moderate-intensity training in subjects with type 2 diabetes or prediabetes [published online ahead of print March 13, 2017]. Scand J Med Sci Sports. 2017;1-11.
To evaluate the effects of sprint interval training (SIT) and moderate-intensity continuous training (MICT) on glucose and fatty acid uptake in peripheral muscles of the arms and legs, including the effects on insulin sensitivity in those muscles.
Randomized controlled trial; participants were randomly assigned to engage in either SIT or MICT to compare effects of exercise on glucose and insulin parameters.
Twenty-six sedentary individuals aged 40 to 55 years, with diagnosis of either type 2 diabetes mellitus or prediabetes. Based on exclusion criteria, none of the participants smoked, used narcotics, had chronic disease or defect that hindered daily life, had a history of anorexia nervosa/bulimia or asthma, currently or previously exercised regularly, or had a peak oxygen consumption (VO2peak)>40 mL/kg/min (VO2peak is positively correlated with physical fitness). The SIT group included 9 men and 4 women; the MICT group included 7 men and 6 women.
Study Parameters Assessed
Both SIT and MICT groups trained 6 sessions within 2 weeks in controlled laboratory conditions. Sprint interval training included 4 to 6 bouts of all-out cycling for 30 seconds followed by a 4-minute recovery period (either doing nothing or very light cycling). Training began with 4 bouts per session and was increased by 1 after every other session to 6 maximum.
These results suggest that regular exercise can, in a relatively short period of time (2 weeks), help reduce glucose levels in patients with impaired glucose control.
Each session of MICT consisted of 40 to 60 minutes of cycling at a 60% intensity of peak VO2. Training began with 40 minutes per session and was increased by 10 minutes after every other session to the maximum of 60 minutes. Both exercise training modes also included a 5-minute low-intensity warmup and cool-down period before and after each session.
A hyperinsulinemic euglycemic clamp study (participants received infusions of insulin and glucose, used to measure insulin sensitivity) was performed before and after the study, as well as an oral glucose tolerance test (OGTT). Positron emission tomography (PET) analysis with labeled tracers was used to measure glucose and free fatty acid (FFA) uptake in the thigh and arm muscles.
Primary Outcome Measures
The following parameters were measured before and after the exercise sessions: weight, body mass index (BMI), fat (%), fat-free mass, VO2peak, glycosylated hemoglobin (HbA1c), hemoglobin, hematocrit, fasting glucose, fasting insulin, fasting FFA, OGTT 2-hour glucose, OGTT 2-hour insulin, glucose area under the curve (AUC) in OGTT, insulin AUC in OGTT.
Both SIT and MICT exercise sessions led to a 25% increase in whole-body insulin-stimulated glucose uptake. There was significantly increased insulin-stimulated glucose uptake in all thigh and upper arm muscles. Two weeks of SIT or MICT induced dramatic 138% (P<0.001) and 93% (P<0.001) increases in quadriceps femoris (QF) glucose uptake, respectively.
In both groups, fatty acid uptake was increased in QF muscle but not in hamstrings or biceps and triceps brachii.
Peak VO2 improved by 5% (P=0.013) in the SIT group, with no significant improvement in the MICT group.
This study shows that both SIT and MICT can improve measures of glucose control in patients with diabetes or prediabetes. Both interval and continuous training improved overall insulin sensitivity and significantly increased glucose and FFA absorption in the QF; glucose absorption was increased in other muscles as well. These results suggest that regular exercise can, in a relatively short period of time (2 weeks), help reduce glucose levels in patients with impaired glucose control. Regular exercise trains muscles to better respond to insulin and promotes absorption of glucose and fatty acids from the serum.1 When we recommend exercise for our patients with prediabetes or type 2 diabetes mellitus, we can encourage them to engage in either continuous or interval training, whichever form is more comfortable (or achievable) for them, and let them know that both can help control their condition.
Although fasting glucose did not deviate from pre- and post-study levels, HbA1c did decrease in post-study analysis. The decrease in HbA1c is likely related to a postprandial decrease in glucose level, given that exercise has been shown to lower postprandial glucose for up to 24 hours, depending on duration and intensity.2,3
This study involved only a very small number of participants and did not consider potential effects of female menstrual cycling or menopause hormonal therapy, 2 important limitations. Estrogen hormones can affect some women’s insulin resistance: premenstrual insulin resistance can occur,4 and hormone replacement therapy in postmenopausal women can lower insulin resistance.5 However, the results of this study are encouraging and can inform our exercise recommendations for patients with diabetes or prediabetes.