Exercise for glucose control in diabetes and prediabetes

Relation

Sjoros TJ, Heiskanen MA, Motiani KK, et al. Increased insulin-stimulated glucose uptake in both leg and arm muscles after sprint intervals and moderate-intensity exercise in patients with type 2 diabetes or prediabetes [published online ahead of print March 13, 2017].Scand J Med Sci Sports. 2017;1-11.

Study objective

To evaluate the effects of sprint interval training (SIT) and moderate intensity continuous exercise training (MICT) on glucose and fatty acid uptake in peripheral muscles of the arms and legs, including the effects on insulin sensitivity in these muscles.

Draft

Randomized controlled trial; Participants were randomly assigned to undergo either SIT or MICT to compare the effects of exercise on glucose and insulin parameters.

Participant

26 sedentary people aged 40 to 55 years with a diagnosis of type 2 diabetes mellitus or prediabetes. Based on the exclusion criteria, none of the participants smoked, used narcotics, had a chronic illness or defect that interfered with daily life, had a history of anorexia nervosa/bulimia or asthma, currently or previously exercised regularly, or had peak oxygen consumption (VO_2tip) > 40 ml/kg/min (VO_2tippositively 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 for 6 sessions within 2 weeks under controlled laboratory conditions. Sprint interval training included 4 to 6 rounds of full cycling for 30 seconds, followed by a 4 minute recovery period (either doing nothing or very light cycling). Training started with 4 bouts per session and increased by 1 to a maximum of 6 after every other session.

These results suggest that regular exercise in a relatively short period of time (2 weeks) can help reduce glucose levels in patients with impaired glucose control.

Each MICT session consisted of 40 to 60 minutes of cycling at an intensity of 60% of maximal VO₂. Training began with 40 minutes per session and increased by 10 minutes after every other session to a maximum of 60 minutes. Both exercise modes also included a 5-minute low-intensity warm-up and cool-down period before and after each session.

A hyperinsulinemic euglycemic clamp study (participants received insulin and glucose infusions to measure insulin sensitivity) and an oral glucose tolerance test (OGTT) were performed before and after the study. Positron emission tomography (PET) analysis with labeled tracers was used to measure glucose and free fatty acid (FFA) uptake in thigh and arm muscles.

Primary outcome measures

The following parameters were measured before and after the training sessions: weight, body mass index (BMI), fat (%), fat-free mass, VO_2tipglycosylated hemoglobin (HbA_1c), 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.

Key insights

Both SIT and MICT training sessions resulted in a 25% increase in insulin-stimulated glucose uptake throughout the body. There was a significantly increased insulin-stimulated glucose uptake in all thigh and upper arm muscles. Two weeks of SIT or MICT resulted in a dramatic 138% (P<0.001) and 93% (P<0.001) increases glucose uptake by the quadriceps femoris (QF).

In both groups, fatty acid uptake was increased in the QF muscle, but not in the hamstrings or biceps and triceps brachii.

Top VO₂improved by 5% (P=0.013) in the SIT group, with no significant improvement in the MICT group.

Practice implications

This study shows that both SIT and MICT can improve glucose control measures in patients with diabetes or prediabetes. Both interval and continuous exercise improved overall insulin sensitivity and significantly increased QF glucose and FFA absorption; Glucose absorption was also increased in other muscles. These results suggest that regular exercise in a relatively short period of time (2 weeks) can help reduce glucose levels in patients with impaired glucose control. Regular exercise trains muscles to respond better to insulin and promotes the absorption of glucose and fatty acids from the serum.¹When recommending exercise to our patients with prediabetes or type 2 diabetes mellitus, we can encourage them to do either continuous or interval exercise, 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 differ from pre- and post-study values, HbA_1cdecreased in the post-study analysis. The decrease in HbA_1cis likely related to a postprandial decrease in glucose levels, as exercise has been shown to decrease postprandial glucose levels for up to 24 hours, depending on duration and intensity.^2.3

This study included only a very small number of participants and did not consider possible effects of the female menstrual cycle or menopausal hormone therapy, two important limitations. Estrogen hormones can affect insulin resistance in some women: premenstrual insulin resistance may occur,⁴and hormone replacement therapy in postmenopausal women can reduce insulin resistance.⁵However, the results of this study are encouraging and can inform our exercise recommendations for patients with diabetes or prediabetes.