Association of aerobic fitness level with exercise-induced hypoglycaemia in Type 1 diabetes

To determine the impact of physical fitness level on hypoglycaemia risk during exercise in people with Type 1 diabetes.

A total of 44 patients [34 adults (aged 22-70 years) and 10 adolescents (aged 12-18 years)] with Type 1 diabetes, treated with insulin pump therapy, underwent a standardized exercise session. Cardiorespiratory fitness (maximum oxygen uptake) was measured and classified, based on established norms for age and sex, into either poor (< 25th percentile) or good fitness level (> 25th percentile). Plasma glucose levels were measured every 10 min, each patient performed physical activity at 60% maximum oxygen uptake either on a treadmill for 1 h or on a bicycle for 30 min. Frequency of hypoglycaemia (plasma glucose < 4 mmol/l) and decline in plasma glucose levels during exercise were assessed.

In all, 23 patients had a good exercise fitness level. Hypoglycaemic events occurred in 17/23 patients (74.0%) in the good fitness level group compared with 8/21 patients (38.0%) in the poor fitness level group (P = 0.02). Both groups had similar pre-exercise plasma glucose levels. The plasma glucose values during exercise in the good fitness level group compared with the poor fitness level group were: plasma glucose nadir 3.9 ± 1.6 vs 5.5 ± 2.4 mmol/l (P = 0.01) and plasma glucose change -4.6 ± 3.4 vs. -2.1 ± 3.1 mmol/l (P = 0.01). The correlation between the plasma glucose nadir and maximum oxygen uptake was r = -0.38 (P = 0.01).

Patients with good fitness level seem to be more prone to hypoglycaemia during exercise. This could be the result of better insulin sensitivity and the fact that they tend to exercise at greater work thresholds. These results are a step toward a better understanding of the association between physical fitness and exercise-induced hypoglycaemia.