Endurance exercise training increases medullary and extramedullary hematopoiesis

Increases in hematocrit are a well known adaptation to exercise training. It is not known if exercise training induces changes in hematopoietic tissues that facilitate increases in hematocrit. The colony forming unit GEMM assay was used to assess the effects of ten weeks of progressive treadmill training on the hematopoietic progenitor content in several tissues of four week old C57Bl/6 mice. Red blood cell progenitors increased by 3.1, 4.7, 2.8, and 1.3 fold (p<0.008 for all) in bone marrow, spleen, blood, and liver, respectively. White blood cell progenitors increased by 1.3 and 3.2 fold (p<0.026 for both) in bone marrow and blood, respectively. Finally, multipotent white and red blood cell progenitors increased by 3.4, 4, and 9.7 fold (p<0.007 for all) in bone marrow, spleen, and blood, respectively. This data indicates that endurance exercise training can increase the hematopoietic progenitor content of bone marrow, blood, spleen, and liver. Increased hematopoiesis in these tissues may help facilitate endurance training associated increases in hematocrit.