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1Departments of Anatomy and of Physiology and Kinesiology, Kansas State University, Manhattan, Kansas; and 2Departments of Health and Kinesiology, Texas A&M University, College Station, Texas
Submitted 20 January 2005 ; accepted in final form 24 June 2005
A single bout of eccentric exercise results in muscle damage, but it is not known whether this is correlated with microcirculatory dysfunction. We tested the following hypotheses in the spinotrapezius muscle of rats either 1 (DH-1; n = 6) or 3 (DH-3; n = 6) days after a downhill run to exhaustion (90–120 min; –14° grade): 1) in resting muscle, capillary hemodynamics would be impaired, and 2) at the onset of subsequent acute concentric contractions, the decrease of microvascular O2 pressure (PmvO2), which reflects the dynamic balance between O2 delivery and O2 utilization, would be accelerated compared with control (Con, n = 6) rats. In contrast to Con muscles, intravital microscopy observations revealed the presence of sarcomere disruptions in DH-1 and DH-3 and increased capillary diameter in DH-3 (Con: 5.2 ± 0.1; DH-1: 5.1 ± 0.1; DH-3: 5.6 ± 0.1 µm; both P < 0.05 vs. DH-3). At rest, there was a significant reduction in the percentage of capillaries that sustained continuous red blood cell (RBC) flux in both DH running groups (Con: 90.0 ± 2.1; DH-1: 66.4 ± 5.2; DH-3: 72.9 ± 4.1%, both P < 0.05 vs. Con). Capillary tube hematocrit was elevated in DH-1 but reduced in DH-3 (Con: 22 ± 2; DH-1: 28 ± 1; DH-3: 16 ± 1%; all P < 0.05). Although capillary RBC flux did not differ between groups (P > 0.05), RBC velocity was lower in DH-1 compared with Con (Con: 324 ± 43; DH-1: 212 ± 30; DH-3: 266 ± 45 µm/s; P < 0.05 DH-1 vs. Con). Baseline PmvO2 before contractions was not different between groups (P > 0.05), but the time constant of the exponential fall to contracting PmvO2 values was accelerated in the DH running groups (Con: 14.7 ± 1.4; DH-1: 8.9 ± 1.4; DH-3: 8.7 ± 1.4 s, both P < 0.05 vs. Con). These findings are consistent with the presence of substantial microvascular dysfunction after downhill eccentric running, which slows the exercise hyperemic response at the onset of contractions and reduces the PmvO2 available to drive blood-muscle O2 delivery.
skeletal muscle; downhill running; microvascular adaptation; capillary hemodynamics; oxygen exchange
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