Feasibility and preliminary efficacy of high intensity interval training in type 2 diabetes☆
Introduction
Current physical activity or exercise recommendations for patients with type 2 diabetes (T2D) suggest a minimum of 150 min per week of moderate to vigorous aerobic exercise [1]. However, data are conflicting as to whether or not individuals with T2D benefit more from participating in high intensity exercise. Recent meta-analyses have highlighted the variability in the response to various exercise protocols and have suggested that a greater exercise dose predicts greater decreases in glycated hemoglobin A1c (HbA1c) [2]. Conversely, greater exercise intensity per se has been shown to lead to greater improvements in HbA1c in some meta-analyses [3] but not others [2], [4].
Similarly, while high intensity exercise has been indicated to improve insulin sensitivity [5], [6], [7], the mechanisms by which exercise intensity affects insulin sensitivity are not well understood. Acute increases in non-oxidative glucose disposal [8], [9], [10] or chronic preferential reduction in intra abdominal adipose tissue (IAAT) [11], just to name a few, may be more prominent following high intensity exercise and contribute to enhanced insulin sensitivity. Recently, more attention has been directed toward the effect of high intensity exercise on IAAT due to its role in the pathogenesis of insulin resistance and T2D. Nonetheless, studies have shown conflicting results with some studies showing preferential reductions in IAAT with higher intensity exercise irrespective of energy expenditure [12], [13], [14] while others report no differences [15], [16]. Thus, whether exercise intensity can be tailored to favor preferential reductions in IAAT and HbA1c remains inconclusive.
While the benefits of high intensity exercise requires further research, there are several concerns regarding the feasibility of implementing high intensity exercise, particularly in older, sedentary or overweight participants with comorbidities such as T2D. Primary perceived barriers include concerns over the risk of injury [17], poor adherence [18], and low self-efficacy in the ability to implement exercise [19]. One approach to minimizing the barriers to high intensity exercise may be the use of interval exercise training which alternates between high intensity exercise bouts and lower intensity recovery periods. Interestingly, while only a few previous studies [20], [21], [22] have prescribed interval training in people with T2D, all demonstrated preferable effects with one study [20] reporting greater reductions in HbA1c and IAAT than other studies identified in a meta-analysis [2]. Unfortunately, this latter study did not have a moderate intensity exercise comparison group and it is unknown whether the greater than expected benefits were due to the intervention itself or to some characteristics of the participants.
As recently suggested by Hawley et al., high intensity interval training may be a potent therapeutic intervention to improve blood glucose concentrations and body composition [23]. Nonetheless, to our knowledge there has not yet been a randomized trial that compares the feasibility and chronic effects of high intensity interval exercise (HI-IE) and moderate intensity continuous exercise (MI-CE) interventions in T2D. The objective of this pilot study was to compare the feasibility (recruitment, adherence and retention) of HI-IE versus MI-CE in patients with T2D. Secondary outcomes of interest included investigation of the preliminary efficacy of HI-IE and MI-CE in improving HbA1c and estimates of IAAT. Compensatory changes in daily steps and energy intake throughout the study were also investigated.
Section snippets
Design
This was a 12-week, single center, parallel-group randomized trial (ClinicalTrials.gov registration number: NCT01144078) conducted in Edmonton, Alberta, Canada. Ethical approval was obtained from the University of Alberta Health Research Ethics Board.
Participants
Initial recruitment was conducted through newspaper advertisement and websites. These recruitment strategies briefly outlined the inclusion criteria: (1) men and women between 55 and 75 years (y) of age; (2) diagnosed with T2D; (3) able to exercise
Recruitment
Between June 2010 and February 2011, 126 participants were screened. The intervention was delivered between September 2010 and June 2011. Fig. 1 shows the flow of the participants from recruitment to follow-up. Of the 126 individuals screened, 59 did not meet the initial inclusion criteria and were excluded. The most common reasons for exclusion were time constraint to exercise 5 days per week (n = 18) and loss of interest (n = 17). Subsequently, another 49 were excluded after briefly meeting with
Discussion
To our knowledge, this is the first randomized trial to compare the feasibility of high intensity interval and moderate intensity continuous exercise training in individuals with T2D. The results suggest that both interventions are feasible and provide high satisfaction to participants. While the recruitment rate for this study (12%) is similar to a larger study investigating the effects of different exercise interventions on glycemic control [33], [34], the key finding is that, for the subset
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgements
Funding for this study was provided by the Alberta Diabetes Institute. Mr. Terada was supported by a studentship from the Alberta Diabetes Institutes and an Art Quinney Award. The authors would like to thank the study participants for their time and efforts, Dr. Ronald Dlin for his assistance with the screening of participants, Mr. Scott MacLeod for assistance with data analysis, and the staff of Saville Sport Center (University of Alberta South Campus) for accommodating our study.
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Clinical trial registration number: NCT01144078