Blood Fibrinolytic Activity in Man

Abstract

This investigation was undertaken in normal subjects to define the relationship between the intensity of exercise and magnitude of fibrinolytic response and to examine the effect of diurnal variations on the exercise response. Fibrinolytic activity was measured on fibrin plates and expressed as mm². Diurnal variations occurred with lowest activity at 8:00 AM (mean, 66 mm²), and peak activity between 5:00 and 8:00 PM (mean, 266 mm², P<0.001). Five minutes of maximal treadmill exercise caused a marked increase in mean activity from 90 to 658 mm² (P<0.001). Five minutes of 70% maximal exercise produced no significant increase, but 30 minutes increased activity to 626 mm² (P<0.005). In contrast, 30 minutes of 40% maximal exercise produced a small elevation from 80 to 173 mm² (P<0.005). Maximal and 40% maximal exercise evoked greater responses at 4:00 PM than 8:00 AM. Exercise produces increases in fibrinolytic activity which are related to the relative intensity of exercise, its duration, and the time of day it is performed. Short bursts of intense exercise cause marked increases, but more prolonged bouts of moderate exercise are required to produce similar increases. The increases with prolonged mild exercise are small and comparable to those observed during resting diurnal variations.