Miriam E. Tucker
August 04, 2014
Walking at alternating levels of intensity improves insulin sensitivity in people with type 2 diabetes, whereas walking at a continuous pace but expending the same amount of energy does not, a new study finds.
The results were published online August 4, 2014 in Diabetologia by Kristian Karstoft, MD, of the Center of Inflammation and Metabolism, Rigshospitalet, Copenhagen, Denmark, and colleagues.
“These results suggest that training with alternating intensity, and not just training volume and mean intensity, is a key determinant of changes in whole-body glucose disposal in individuals with type 2 diabetes,” Dr. Karstoft and colleagues write.
The lack of effect of the continuous-intensity walking is “surprising and is in disagreement with other studies,” the authors say, and is not due to lack of training.
“We believe that the high training volume alone was not enough to elicit changes and that the spikes and/or variability in training intensity in the [interval] group were necessary for the improvements seen in metabolic outcome,” they state.
Glucose Levels, Body Weight Drop With Interval Training
In the study, a total of 32 non–insulin-treated patients with type 2 diabetes were randomized to continuous-walking training, interval-walking training of equivalent energy expenditure, or a nontrained control group. All were instructed to stop taking glucose-lowering, lipid-lowering, and antihypertensive medications a week before baseline testing.
The continuous walking was of moderate intensity, at 55% or more of the individual’s peak-energy expenditure rate for walking. For the interval walking, participants alternated 3 minute intervals of fast (70% or greater of peak-energy expenditure) and slow (about 40% or greater of peak-energy expenditure). The control subjects were simply told to continue their habitual lifestyles.
Both types of 60-minute training sessions were carried out 5 times per week for 4 months in the patients’ own environments. Subjects in both groups wore a device that monitored their activity levels and that also gave audible signals to the interval-walking group to ensure matching of the training intensity to that of the continuous group.
Before and after the intervention, hyperglycemic clamps were used to measure insulin secretion, glucose isotope tracers were infused to measure glucose metabolism, and skeletal-muscle biopsies were taken to assess insulin signaling.
Average glucose levels dropped only in the interval group, from 9.0 mmol/L (162 mg/dL) preintervention to 8.7 mmol/L (157 mg/dL) postintervention, while rising slightly in both the continuous-exercise and control groups.
The investigators determined that this and other improved parameters of glycemic control were likely due to increased insulin sensitivity (49.8% increase in the insulin-sensitivity index, P < .001) and increased peripheral glucose disposal (by 14.5%, P <.05), both of which were seen only in the intermittent-exercise group.
Improved insulin signaling in skeletal muscle was also found only in the intermittent exercise group, while there were no changes in insulin secretion in any of the 3 groups.
Improved body composition also occurred only in the interval group — average weight loss was 4.2 kg (9 lb) — but changes in body weight explained only 25% of the improvements seen, indicating that other factors contribute, the authors say.
“Whether these beneficial effects extrapolate to hard end points in the long term must be determined in order to justify the clinical utility of interval training for individuals with type 2 diabetes,” they conclude.
This study was primarily funded by the Danish Center for Strategic Research in Type 2 Diabetes, supported by the Danish Agency for Science. The authors declare that there is no duality of interest.
Diabetologia. Published online August 4, 2014. Article
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