EFFECTS OF EXERCISE INTENSITY, DURATION, AND TIME OF DAY ON FIBRINOLYTIC-ACTIVITY IN PHYSICALLY ACTIVE MEN

The purposes of this investigation were to determine: 1) whether the f ibrinolytic responses to acute, submaximal exercise were best related to intensity, duration, or total caloric expenditure; and 2) whether t he time of day exercise is performed affects the fibrinolytic response . Twelve physically active men ((x) over bar age = 34.8 +/- 4.0 yr) pe rformed four 30-min exercise sessions: 50% VO2max, a.m. and p.m:, and 80% VO2max a.m. and p.m. Blood samples were analyzed for tissue plasmi nogen activator (TPA) activity and plasminogen activator inhibitor-1 ( PAI-1) activity. Data were analyzed using a three-way ANOVA with repea ted measures. TPA activity: preexercise TPA did not differ among the f our sessions. TPA increased with exercise in all sessions except the 5 0% a.m. session. Exercise at 80% increased TPA more than 50% (P < 0.00 1) and evening sessions increased TPA more than morning sessions (P < 0.05). PAI-1 activity: preexercise PAI-1 activity was higher during th e morning than evening and significantly decreased with exercise in al l sessions except the 50% p.m. session. It was concluded that changes in fibrinolytic activity appear to be influenced primarily by exercise intensity rather than duration or total caloric expenditure. Addition ally, time of day of exercise performance significantly influenced fib rinolytic activity.