Movement, not fitness, seems to mediate glucose control in diabetics.
Does physical activity in type 2 diabetics help even if fitness levels do not improve? Researchers reanalyzed the data from the HART-D trial and found that the HbA1c levels improved by just over 25% and body fat percentage along with waistlines decreased--even without improvements in cardiorespiratory fitness. The movement of physical activity seems to improve diabetic control regardless of changes in fitness.
PositiveTip: Don't give up on moving, even if you feel your fitness level is not improving.