Effect of shoe cushioning on the development of reticulocytosis in distance runners

Abstract

We studied erythropoietic activity in relation to the rearfoot cushioning of shoes worn by 14 male runners before, during, and the morning after a 17-day period of increased training mileage. The percentage of retic ulocytes in the red blood cell count (normal, Resting blood samples were obtained at baseline and on three mornings (Days 11, 13, and Day 18, which followed the completion of the increased training period). No significant differences were found between the groups in red blood cell count, hematocrit, or total hemoglobin, haptoglobin, plasma-free hemoglobin, and serum ferritin levels. The groups did not differ in percent reticulocytes at baseline (0.2% firm-sole versus 0.2% soft-sole), on Day 11 after running 280 km (0.8% firm- sole versus 0.8% soft-sole), or on Day 13 after 48 hours of rest (1.3% firm-sole versus 1.0% soft-sole). However, on Day 18 after running 430 km, reticulocyte counts were 29% higher (P < 0.05) in firm-sole than soft-sole (2.2% versus 1.7%, respectively). The overall change in percent reticulocytes was linearly correlated with Peak g (r = 0.57, P < 0.05). Although marked reticulocytosis occurred in both groups, it was significantly more pronounced in the firm-sole group. The positive correlation between per cent reticulocytes and Peak g suggests that shoe rear foot cushioning is one determinant of the erythropoietic response to increased training mileage in distance run ners.