[Insulin resistance among relatives of patients with NIDDM. Significance of physical fitness and muscle metabolism].

To explore the possible role of a reduced physical fitness for the diminished insulin sensitivity in first-degree relatives of NIDDM patients, 21 relatives and 22 matched control subjects were examined employing a hyperinsulinaemic (insulin infusion rate 0.6 mU/kg/min) euglycaemic clamp combined with the isotope dilution technique (3-3H-glucose), the forearm technique and indirect calorimetry. During hyperinsulinaemia glucose disposal (Rd) was significantly diminished in the relatives (p < 0.01). Maximal oxygen uptake (VO2 max) was 15% lower in the relatives than in the controls (p = 0.03). There was a highly significant correlation between Rd and VO2 max in both groups. In multiple linear regression analyses with Rd as the dependent variable VO2 max significantly determined the level of Rd (p < 0.01), whereas forearm blood flow and anthropometric data did not. We concluded that the insulin resistance in healthyfirst degree relatives of patients with NIDDM is associated with a diminished physical work capacity. Whether this finding is ascribable to environmental or genetic factors remains to be determined.