Randomized clinical trials show that aerobic exercise training improves glycemic control in patients with type 2 diabetes mellitus (T2DM).1 However, interindividual variability is large.2 This may be explained by genetic variability,3 but ambient hyperglycemia4 and pancreatic β-cell function5 may also contribute. We examined whether changes in glycemic control following a 12- to 16-week aerobic exercise training intervention were influenced by the pretraining glycemic state in 105 individuals with impaired glucose tolerance or T2DM.
Individuals with impaired glucose tolerance or type 2 diabetes mellitus underwent 12 to 16 weeks of moderate-intensity exercise training, 5 days per week for 60 minutes per day. Individual subject data points are plotted on both panels; the x-axis represents the pretraining variable, and the y-axis indicates the exercise-induced change, such that the data points above the axis indicate an exercise-induced increase and vice versa. Open circles represent impaired glucose–tolerant subjects, and open triangles represent subjects with type 2 diabetes mellitus. The solid line represents the regression curve, and the dotted line represents the 95% confidence interval. A, There was a nonlinear quadratic relationship between pretraining 2-hour oral glucose tolerance test (OGTT) level and the training-induced change in 2-hour OGTT level (y = 0.06x2 − 1.5x + 7.6 [r2 = 0.26; P = .06] [N = 105]). For every 1-mmol/L increase in pretraining 2-hour glucose level above 13.1 mmol/L (the inflection point of the curve), there was a 0.2-mmol/L loss of improvement in 2-hour glucose level following exercise (to convert glucose to milligrams per deciliter, divide by 0.0555). B, There was also a nonlinear quadratic relationship between pretraining hemoglobin A1c (HbA1c) level and the training-induced change in HbA1c level (y = 0.31x2 − 3.8x + 11.7 [r2 = 0.33; P = .02] [n = 52]). For every 1–percentage-point increase in pretraining HbA1c level above 6.2% (the inflection point of the curve), there was a 0.2–percentage-point loss of improvement in HbA1c level following exercise. C, An inverse linear relationship between pretraining HbA1c level and the training-induced change in aerobic fitness was found (y = −0.11x + 0.91 [r = −0.38; P = .006] [n = 52]). For every 1–percentage-point increase in pretraining HbA1c level, there was 0.11-L/min loss of improvement in maximal oxygen uptake (V̇o2max) following exercise training.
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