Abstract
Objective: To examine the acute and chronic effects of structured exercise on glucose outcomes assessed by continuous glucose monitors in adults with type 2 diabetes.Methods: PubMed, Medline, EMBASE were searched up to January 2020 to identify studies prescribing structured exercise interventions with continuous glucose monitoring outcomes in adults with type 2 diabetes. Randomized controlled trials, crossover trials, and studies with pre- and post-designs were eligible. Short-term studies were defined as having exercise interventions lasting ≤2 weeks. Longer-term studies were defined as >2 weeks.Results: A total of 28 studies were included. Of these, 23 studies were short-term exercise interventions. For all short-term studies, the same participants completed a control condition as well as at least one exercise condition. Compared to the control condition, exercise decreased the primary outcome of mean 24-h glucose concentrations in short-term studies (−0.5 mmol/L, [−0.7, −0.3]; p < 0.001). In longer-term studies, mean 24-h glucose was not significantly reduced compared to control (−0.9 mmol/L [−2.2, 0.3], p = 0.14) but was reduced compared to pre-exercise values (−0.5 mmol/L, [−0.7 to −0.2] p < 0.001). The amount of time spent in hyperglycemia and indices of glycemic variability, but not fasting glucose, also improved following short-term exercise. Among the shorter-term studies, subgroup, and regression analyses suggested that the timing of exercise and sex of participants explained some of the heterogeneity among trials.Conclusion: Both acute and chronic exercise can improve 24-h glucose profiles in adults with type 2 diabetes. The timing of exercise and sex of participants are among the factors that may explain part of the heterogeneity in acute glycemic improvements following exercise.
Highlights
Meta-analyses have repeatedly confirmed that, on average, regular exercise training causes meaningful improvements in glycemic control in people with type 2 diabetes (T2D) [1, 2]
Given the heterogeneity identified in previous meta-analyses, we explored differences among the short-term trials with pre-specified and novel subgroup comparisons, as well as meta-regression analyses, to examine the impact of factors such as exercise timing, dietary standardization, medications, type of Continuous glucose monitors (CGM), sex, and baseline glycemic control
In the study by Godkin et al [30], the effect of a single bout of exercise was compared to control after the first session of exercise and after a session of exercise performed after 6 weeks of exercise training
Summary
Meta-analyses have repeatedly confirmed that, on average, regular exercise training causes meaningful improvements in glycemic control in people with type 2 diabetes (T2D) [1, 2]. These meta-analyses typically included glycated hemoglobin (A1C) as a primary outcome and showed a high degree of heterogeneity among trials [2]. A1C does not provide information on what aspect of glycemic control has been improved (i.e., two people with very different daily glucose profiles can have the same A1C) and does not allow direct comparisons between short-term and longer-term responses to exercise. In addition to mean daily glucose concentration, CGM permit measures such as glucose concentrations over specific periods (e.g., post-prandial periods), the amount of time within specific glucose ranges (e.g., below 3.9 mmol/L), or other outcomes such as glucose variability, which can be associated with oxidative stress [3] and potentially other diabetes-related complications [4]
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