Abstract
In the context of type 2 diabetes, inter-individual variability in the therapeutic response of blood glucose control to exercise exists to the extent that some individuals, occasionally referred to as “non-responders,” may not experience therapeutic benefit to their blood glucose control. This narrative review examines the evidence and, more importantly, identifies the sources of such inter-individual variability. In doing so, this review highlights that no randomized controlled trial of exercise has yet prospectively measured inter-individual variability in blood glucose control in individuals with prediabetes or type 2 diabetes. Of the identified sources of inter-individual variability, neither has a prospective randomized controlled trial yet quantified the impact of exercise dose, exercise frequency, exercise type, behavioral/environmental barriers, exercise-meal timing, or anti-hyperglycemic drugs on changes in blood glucose control, in individuals with prediabetes or type 2 diabetes. In addition, there is also an urgent need for prospective trials to identify molecular or physiological predictors of inter-individual variability in the changes in blood glucose control following exercise. Therefore, the narrative identifies critical science gaps that must be filled if exercise scientists are to succeed in optimizing health care policy recommendations for type 2 diabetes, so that the therapeutic benefit of exercise may be maximized for all individuals with, or at risk of, diabetes.
Highlights
Type 2 diabetes mellitus (T2DM) is characterized by persistent hyperglycemia (Table 1) that increases the risk of retinopathy, nephropathy, neuropathy, and cardiovascular-related mortality
Glycated hemoglobin (HbA1c) levels, fasting plasma glucose, and the 2-h plasma glucose value during a 75-g oral glucose tolerance test (OGTT) are the three variables used by clinicians to measure blood glucose control, and to diagnose and monitor treatment in those at risk of developing diabetes and in patients with T2DM (American Diabetes Association, 2018a) (Table 1)
We found that only interval walking training improved continuous glucose monitoring (CGM)-derived glucose control but that this was in the presence of greater weight loss than the continuous walking group
Summary
Type 2 diabetes mellitus (T2DM) is characterized by persistent hyperglycemia (Table 1) that increases the risk of retinopathy, nephropathy, neuropathy, and cardiovascular-related mortality. They calculated the technical error of measurement for these variables to determine the frequency of exercise-induced adverse outcomes, reporting that 12, 10, and 13% of their sample population had an “adverse response” in systolic blood pressure, triglycerides, and HDL-cholesterol, respectively, following exercise training (Bouchard et al, 2012) While this elegant approach, which was used by Phillips et al (2017), provides evidence that non-responders to exercise exist in the context of cardiometabolic risk factors, surprisingly the authors of neither study presented inter-individual changes in blood glucose control. While current guidelines (Table 2) for preventing and treating T2DM clearly state how many minutes of exercise should be accumulated each week and how frequent exercise sessions should be (American Diabetes Association, 2018b), precise guidance on what a moderate to vigorous intensity equates to is lacking
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