Fibrinolytic Response In Relation To Exercise Intensities Centered Around Lactate Threshold

Abstract

BACKGROUND: Potential for blood coagulation increases as a function of physical exertion. This response is typically matched by an increase in fibrinolytic activity. The magnitude of fibrinolytic response has been directly associated with blood lactate concentration and may exhibit a threshold-type response similar to lactate threshold (LT). PURPOSE: To determine if there is a fibrinolytic threshold based on aerobic exercise intensity. METHODS: Eight healthy males (mean ± SD, age 24 ± 3 year, height 182 ± 9 cm, weight 83 ± 17 kg) completed a maximal cycle test and 4 submaximal cycle tests on non consecutive days. Cycling intensities for 20 minute submaximal tests were based on percentages (90%, 95%, 100%, 105%) of LT. Blood samples were obtained via clean venipuncture prior to and immediately following submaximal exercise to obtain platelet-poor plasma. tPA and PAI-1 activity were assessed using bio-functional immunosorbent assay (Biopool International, Sweden) whereas tPA antigen was analyzed using enzyme-linked immunosorbancy assay (American Diagnostica inc., Stamford, CT). Data were analyzed using repeated measures analysis of variance. RESULTS: There was no significant difference among pre-exercise values for tPA activity (90% LT = 0.37 ±0.18 IU/ml, 95% LT = 0.45 ± 0.31 IU/ml, 100% LT= 0.34 ± 0.16IU/ml, 105% LT=0.43± 0.32 IU/ml) or antigen (90% LT = 16.30 ±6.61 ng/ml, 95%LT= 13.93 ±3.00 ng/ml, 100% LT = 15.33 ± 5.56 ng/ml, 105% LT = 19.92 ± 6.94 ng/ml). Following exercise at 90% and 95% of LT, tPA activity (2.31 ± 1.23 IU/ml and 2.25 ± 1.59 IU/ml) was lower (P < 0.05) than post-exercise values for both the 100% and 105% of LT trials (2.92 ± 1.81 IU/ml and 3.13 ± 2.17 IU/ml, respectively). This effect was also true for tPA antigen, as post-exercise values for 90% and 95% of LT (20.63 ±5.95 ng/ml and 15.84 ± 7.90 ng/ml) were significantly (P < 0.05) lower than 100% and 105% LT (26.96 ± 9.92 ng/ml and 32.68 ± 7.78 ng/ml, respectively). PAI-1 did not change significantly following acute exercise for any of the trials. CONCLUSION: Our results suggest that submaximal exercise performed slightly below lactate threshold, elicits a significant fibrinolytic response. However, exercise at and even slightly above lactate threshold results in significantly higher fibrinolytic response than what is observed in the sub-threshold domain.