Exercise augments the absorption of isophane (NPH) insulin

In order to determine the effect of exercise on the rate of absorption of an isophane (NPH) insulin, 7 normal men were studied on two separate occasions using the euglycaemic clamp technique. On one day subjects undertook 60 min of exercise on a treadmill (5 km h-1, 5 degrees slope) 180 min after injection of human isophane (NPH) insulin (0.25 U kg-1), while on the control day they remained at rest throughout the 420 min study. Serum insulin concentrations rose in parallel after injection achieving similar values at 180 min on exercise and control days (13.7 +/- 1.2 (+/- SE) vs 12.0 +/- 1.5 mU l-1; NS), respectively. After the onset of exercise, insulin concentrations rose markedly to a peak of 29.8 +/- 2.2 mU l-1 after 50 min of exercise (p less than 0.001), compared with a slight fall on the control day to 10.4 +/- 1.7 mU l-1 (NS). At the end of the exercise period, serum insulin concentrations returned rapidly to control day values. Glucose infusion requirements rose significantly during the exercise period from 2.8 +/- 0.5 mg kg-1 min-1 to a peak at 235 min of 11.1 +/- 1.2 mg kg-1 min-1 (p less than 0.001), compared with an increase on the control day from 2.0 +/- 0.6 to 2.5 +/- 0.6 mg kg-1 min-1 (NS) over the same period. These results demonstrate an enhanced rate of absorption of an isophane (NPH) insulin during exercise in normal subjects.