FIBRINOLYTIC RESPONSE TO HIGH AND LOW-INTENSITY EXERCISE

Abstract

Fibrinolysis, the capacity to lyse inappropriate or excessive clot, increases during exercise. This response protects against atherothrombotic events and is related to both exercise intensity and duration. The purpose of the present study was to compare fibrinolytic response to high-intensity exercise versus long-duration, equicaloric low-intensity exercise. Ten healthy males (mean age = 26.6 ± 3.9 years, mean weight = 78.2 ± 12.3 kg, mean height = 177.7 ± 6.7 cm) were evaluated during two constant-load exercise tests on a cycle ergometer. The high-intensity test (HIT) was performed for 20 minutes at an intensity above lactate threshold (LT). During the low-intensity test (LIT), subjects exercised at 90% of LT until caloric expenditure was equivalent to the HIT (mean duration = 39.2 ± 4.3 min). Immediately before, immediately after, and one hour after exercise, fasting blood samples were obtained. Plasma from samples was analyzed for tissue pasminogen activator (tPA), which increases fibrinolytic activity, and plasminogen activator inhibitor-1 (PAI-1), the main circulating inhibtor of tPA. Changes in tPA and PAI-1 were assessed using a two-factor repeated measures analysis of variance (RMANOVA). Plasma PAI-1 activity significantly (P < 0.05) decreased during HIT (pre-exercise = 16.1 ± 1.7 AU/ml, post-exercise = 10.7 ± 2.4 AU/ml), but not during LIT (pre-exercise = 15.6 ± 1.8 AU/ml, post-exercise = 13.3 ± 1.4 AU/ml). There was a non-significant increase in plasma tPA activity during HIT (pre-exercise = 1.5 ± 0.2 IU/ml, post-exercise = 2.16 ± 1.3 IU/ml) and LIT (pre-exercise = 1.5 ± 0.3 IU/ml, post-exercise = 1.6 IU/ml) (P = 0.06 for RMANOVA). These results suggest high intensity exercise, performed above LT, elicits a greater fibrinolytic response than equicaloric exercise performed below LT.