[Physical exercise in the diabetic. The importance of understanding endocrine and metabolic responses (author's...

During physical activity in normals, metabolic control is well regulated despite major changes in metabolic fuels, glucose and non esterified fatty acids (NEFA). Release of NEFA from adipose tissue is stimulated by a decrease of insulin and blood glucose as well as by an increase of growth hormone, catecholamines and adrenergic stimulation. The increase in glucose utilisation by muscle during physical activity is balanced by an increase in glucose production by the liver. This hepatic glucose production is due to glycogenolysis (beginning of exercise) and by gluconeogenesis (later in time). The metabolic pathways are favoured by decreased insulin and blood glucose levels induced by physical activity and by increased levels of epinephrine, cortisol and glucagon. On the other hand in insulin-dependent diabetics, these compensatory mechanisms might be seriously unbalanced because of non physiologic insulin levels. In well controlled diabetics, moderate physical activity induces the same changes in energetic fuels as in normal controls. When a diabetic exercises after insulin injection, the levels of circulating insulin are always higher than in non-diabetics where blood insulin levels decrease. In diabetics on insulin this supra-normal level of insulin during physical activity decreases hepatic glucose production and increases peripheral glucose uptake with a resultant tendency to hypoglycemia. On the other hand, in poorly controlled diabetics, physical activity can induce a rise in blood glucose. Increased hepatic glucose output, decreased peripheral utilisation of glucose and increased growth hormone, glucagon, epinephrine and cortisol levels might even lead to development of ketosis. Physical activity can disturb the stability of diabetes when insulin levels are either too low or too high leading to high and low blood glucose responses respectively. The benefit of physical activity in the diabetic will therefore depend upon the degree of diabetes control; ideal control is not always easy to obtain or to maintain. Thus, to derive maximum benefit to health both the diabetic and the physician should clearly understand how to adapt treatment to physical activity (prevention of hypoglycemia, change in insulin doses, etc.).