HIGHLIGHTED TOPIC Skeletal and Cardiac Muscle Blood Flow Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle

Kano, Yutaka, Danielle Padilla, K. Sue Hageman, David C. Poole, and Timothy I. Musch. Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle. J Appl Physiol 97: 1138–1142, 2004. First published May 7, 2004; 10.1152/japplphysiol. 00334.2004.—To utilize the rat spinotrapezius muscle as a model to investigate the microcirculatory consequences of exercise training, it is necessary to design an exercise protocol that recruits this muscle. There is evidence that the spinotrapezius is derecruited during standard treadmill exercise protocols performed on the uphill treadmill (i.e., 6° incline). This investigation tested the hypothesis that downhill running would effectively recruit the spinotrapezius muscle as assessed by the presence of an exercise hyperemia response. We used radioactive 15m microspheres to determine blood flows in the spinotrapezius and selected hindlimb muscles of female SpragueDawley rats at rest and during downhill (i.e., 14° incline; 331 5 g body wt, n 7) and level (i.e., 0° incline; 320 11 g body wt, n 5) running at 30 m/min. Both level and downhill exercise increased blood flow to all hindlimb muscles (P 0.01). However, in marked contrast to the absence of a hyperemic response to level running, blood flow to the spinotrapezius muscle increased from 26 6 ml min 1 100 g 1 at rest to 69 8 ml min 1 100 g 1 during downhill running (P 0.01). These findings indicate that downhill running represents an exercise paradigm that recruits the spinotrapezius muscle and thereby constitutes a tenable physiological model for investigating the adaptations induced by exercise training (i.e., the mechanisms of altered microcirculatory control by transmission light microscopy).