Aim/hypothesis: In people with type 2 diabetes, exercise improves glucose control (as reflected in HbA₁(c)) and physical fitness, but it is not clear to what extent these exercise-induced improvements are correlated with one another. We hypothesised that reductions in HbA₁(c) would be related: (1) to increases in aerobic fitness and strength respectively in patients performing aerobic training or resistance training; and (2) to changes in strength and aerobic fitness in patients performing aerobic and resistance training.
Methods: We randomly allocated 251 type 2 diabetes patients to aerobic, resistance, or aerobic plus resistance training, or to a sedentary control group. Peak oxygen consumption VO₂(peak), workload, treadmill time and ventilatory threshold measurements from maximal treadmill exercise testing were measured at baseline and 6 months. Muscular strength was measured as the maximum weight that could be lifted eight times on the leg press, bench press and seated row exercises.
Results: With aerobic training, significant associations were found between changes in both VO₂(peak) (p = 0.040) and workload (p = 0.022), and changes in HbA₁(c.) With combined training, improvements in VO₂(peak) (p = 0.008), workload (p = 0.034) and ventilatory threshold (p = 0.003) were significantly associated with changes in HbA₁(c.) Increases in strength on the seated row (p = 0.006) and in mid-thigh muscle cross-sectional area (p = 0.030) were significantly associated with changes in HbA₁(c) after resistance exercise, whereas the association between increases in muscle cross-sectional area and HbA₁(c) in participants doing aerobic plus resistance exercise (p = 0.059) was of borderline significance.
Conclusions/interpretation: There appears to be a link between changes in fitness and HbA₁(c). The improvements in cardiorespiratory fitness with aerobic training may be a better predictor of changes in HbA₁(c) than improvements in strength.