Associations between physical fitness and HbA₁(c) in type 2 diabetes mellitus

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.

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.

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.

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.