This study was designed to examine the relationship between foot impact force and the magnitudes of the changes in markers of intravascular hemolysis during distance running. Fourteen male distance runners (VO2 max = 66.1 +/- 5.0 ml.kg-1.min-1, mean +/- SD) completed two treadmill runs and a resting control procedure. The two treadmill tests involved running at 215 m.min-1 for 10,000 footstrikes at elevations of either +6% (uphill) or -6% (downhill). Mean foot impact force was 11% greater with the downhill than the uphill running. The three procedures were ordered randomly and separated by 7 days. Hemoglobin concentration (Hb), hematocrit (Hct), plasma free hemoglobin (PFHb), and haptoglobin (Hp) concentrations were assayed in blood samples collected via venipuncture 15 min and immediately before exercise, and immediately, 1 h, and 2 h after the exercise. Repeated measures ANOVA revealed that Hp was significantly decreased and PFHb was significantly increased after treadmill running (P less than 0.05) and that these changes were significantly greater with downhill than uphill running (P less than 0.05). These findings support the theory that mechanical trauma to red blood cells occurring at footstrike is a major cause of hemolysis during running.
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