Lead author Kristian Karstoft, MD, from the Centre of Inflammation and Metabolism in the Faculty of Health Sciences at the University of Copenhagen, Rigshospitalet, in Denmark mentioned that, the improvements in glycemic control were dependent on improvements in insulin sensitivity without compensatory deteriorations in beta cell function.
Dr. Karstoft said, "The whole idea was to find a realistic training intervention for type 2 diabetic patients, exercise has been recommended for patients with diabetes for a long time, but how to get them to do exercise is less agreed upon."
In this study, the investigators evaluated 2 walking training interventions in patients with T2DM who were receiving a variety of antidiabetic medications except insulin. They randomly assigned patients to a control group (n = 8), a continuous-walking training group (CWT; n = 12), or to an interval-walking training group (IWT; n = 12). The active training groups were instructed to train for 1 hour, 5 times a week, for the 4-month study period. Their activity was monitored using a heart rate monitor and a training computer that included an accelerometer.
IWT consisted of walking fast for 3 minutes, slow for 3 minutes, and repeating throughout each session. Continuous walkers stayed at the same speed throughout each session.
The groups were fairly well matched at baseline for age (57 - 61 years) and body mass index (29.0 - 29.7 kg/m2). Their median HbA1c was 6.4% for the control group, 6.6% for the CWT group, and 6.9% for the ITW group. The IWT group initially had a higher fasting glucose level and higher glucose on a 2h oral glucose tolerance test.
The researchers used continuous glucose monitoring (CGM) to evaluate glycemic control at baseline and at 4 months. They used a hyperglycemic clamp to measure insulin secretion and sensitivity and disposition index at the same time points.
Dr. Karstoft added that, "We looked at the feasibility, which showed that it was possible to do this training for type 2 diabetic subjects, with overall adherence of 89% with no difference between the groups." The CWT and IWT groups exercised for 57 to 61 min/session and 4.4 to 4.6 sessions/week, and there was no statistically significant difference between them. The dropout rate was less than 10% in each group.
The training computer showed that the 2 training groups trained at the same level of intensity overall, which was 72.7% (standard deviation [SD], ± 3.6%) for the CWT group and 70.5% (SD, ± 2.0%) for the IWT group. However, the latter group achieved this overall level by varying the intensity between the slow and fast walking periods. The groups were equivalent in their total energy expenditures.
At the end of the study, the control group had no change in their maximal oxygen consumption (VO2max), whereas participants in the IWT group had an increase of 16% (SD, ± 4%; P < .05).
"We showed improvements in glycemic control but only in the interval walking training group," Dr. Karstoft said. Compared with baseline, the IWT group had mean and maximal decreases in CGM glucose levels of 0.8 mmol/L (P = .05) and 2.8 mmol/L (P < .05). The control arm showed a decline in glycemic control of 1.2 mmol/L (SD, ± 0.4 mmol/L; P < .05) as measured by CGM, compared with baseline. The CWT group showed no changes in glycemic control between baseline and 4 months.
Insulin sensitivity increased in the IWT group by 57% (SD, ± 17%; P < .05) with no significant change in insulin secretion (3 ± 6%). The insulin disposition index increased by about the same amount (60%, P < .05) as the insulin sensitivity for the IWT group, but the index remained fairly constant for the control and CWT groups.
Additionally, interval walkers lost an average of 4 kg of body weight, whereas continuous walkers did not change their body weights after the intervention. Dr. Karstoft explained that a phenomenon of "post-exercise oxygen consumption" may have helped account for this finding in light of the fact that the 2 walk training groups had the same energy intake.
He and his colleagues concluded that walking training in a real-world setting is feasible for patients with T2DM. The IWT regimen was superior to CWT in improving glycemic control even though participants following the 2 regimens expended the same amount of energy. The improvements in glycemic control with IWT were associated with improvements in insulin sensitivity and in the absence of compensatory decreases in beta cell function, as reflected by the heightened insulin disposition index.
"The recommendation is that exercise should be undertaken, but it should be of a certain intensity. And based on that, we would recommend interval training approaches," Dr. Karstoft said.
European Association for the Study of Diabetes (EASD) 48th Annual Meeting: Abstract 600. Presented October 3, 2012.