Rat hindlimb muscle blood flow during level and downhill locomotion

Duringeccentrically biased exercise (e.g., downhill locomotion), whole bodyoxygen consumption and blood lactate concentrations are lower thanduring level locomotion. These general systemic measurements indicatethat muscle metabolism is lower during downhill exercise. This studywas designed to test the hypothesis that hindlimb muscle blood flow iscorrespondingly lower during downhill vs. level exercise. Muscle bloodflow (determined by using radioactive microspheres) was measured inrats after 15 min of treadmill exercise at 15 m/min on the level (L,0°) or downhill (D, 17°). Blood flow to ankle extensormuscles was either lower (e.g., white gastrocnemius muscle: D, 9 ± 2; L, 15 ± 1 ml · min¹ · 100 g¹) or not different(e.g., soleus muscle: D, 250 ± 35; L, 230 ± 21 ml · min¹ · 100 g¹) in downhill vs. levelexercise. In contrast, blood flow to ankle flexor muscles was higher(e.g., extensor digitorum longus muscle: D, 53 ± 5; L, 31 ± 6 ml · min¹ · 100 g¹) during downhill vs.level exercise. When individual extensor and flexor muscle flows weresummed, total flow to the leg was lower during downhill exercise (D,3.24 ± 0.08; L, 3.47 ± 0.05 ml/min). These data indicate thatmuscle blood flow and metabolism are lower during eccentrically biasedexercise but are not uniformly reduced in all active muscles; i.e.,flows are equivalent in several ankle extensor muscles and higher inankle flexor muscles.