Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle

Abstract

I. Musch. Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle. J Appl Physiol 97: 1138 -1142. 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 15-m microspheres to determine blood flows in the spinotrapezius and selected hindlimb muscles of female SpragueDawley rats at rest and during downhill (i.e., Ϫ14°incline; 331 Ϯ 5 g body wt, n ϭ 7) and level (i.e., 0°incline; 320 Ϯ 11 g body wt, n ϭ 5) running at 30 m/min. Both level and downhill exercise increased blood flow to all hindlimb muscles (P Ͻ 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 Ϯ 6 ml ⅐ min Ϫ1 ⅐ 100 g Ϫ1 at rest to 69 Ϯ 8 ml⅐ min Ϫ1 ⅐ 100 g Ϫ1 during downhill running (P Ͻ 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). skeletal muscle; blood flow; microvascular adaptation DIRECT OBSERVATION OF SKELETAL muscle microcirculation by intravital microscopy is key to understanding microvascular control, capillary hemodynamics, and O 2 exchange. Unfortunately, there are very few muscles anatomically and optically suitable for transmission light microscopy. Of these, the rat spinotrapezius muscle possesses the following singular advantages: 1) it can be exteriorized and transilluminated without disruption of the nervous or primary vascular supplies (2,12,28,40); 2) it comprises a mosaic of the three principal fiber types found in mammalian muscle (8); and 3) the oxidative capacity approximates that found in the untrained human quadriceps (8,22). Consequently, it is not surprising that intravital microscopy of the spinotrapezius has been integral to our understanding of muscle microcirculation in health (4,21,23,25,31,37,39) and chronic diseases such as heart failure (15), Type 1 diabetes (18), and hypertension (13).Within the past two years, it has been possible to measure spinotrapezius capillary hemodynamics during muscle contractions (17,33). This raises the exciting possibility that the spinotrapezius can be utilized to understand the effects of physiological adaptations, for example, to exercise training on capillary hemodynamics and O 2 exchange in contracting muscle. Unfortunately, conve...

Effects of aging and exercise training on spinotrapezius muscle microvascular Po2 dynamics and vasomotor control

“…1). The lack of a net hyperemic increase to the spinotrapezius muscle between rest and exercise is similar to that demonstrated previously (44,65) and is consistent with the idea that the spinotrapezius muscle is not recruited during level or incline running (65).…”

“…Based on the results of the Pm O 2 study, we conducted a follow-up investigation to determine the effects of exercise training on resistance artery vasomotor control in the spinotrapezius muscle with advancing age. Bulk blood flow was also measured at rest and during exercise to confirm previous findings (44) that the spinotrapezius muscle does not demonstrate a net hyperemic increase during inclined treadmill running. Knowledge of the effects of exercise on skeletal muscle Q O 2 and vasomotor control is important in resolving the exercise intolerance demonstrated in the elderly population.…”

“…This is unlikely, as the training program did not elicit an increase in the activity of the sentinel oxidative enzyme citrate synthase in the spinotrapezius muscle of either group (Table 1). To our knowledge, only downhill running recruits (44) and elicits training-induced adaptations in the oxidative capacity of the spinotrapezius muscle (37). Therefore, given the linear relationship between recruitment/intensity and oxidative capacity (16), the lack of change in citrate synthase activity in both young and aged groups (Table 1) suggests that the spinotrapezius muscle is not recruited during inclined exercise training.…”

Intracellular calcium accumulation following eccentric contractions in rat skeletal muscle in vivo: role of stretch-activated channels

“…The spinotrapezius muscle has formed a cornerstone of our understanding of muscle microcirculatory control (18,21,24,29,34). As well as possessing optical properties requisite for intravital microscopy, it is composed of all three major muscle fiber types (10) and has an oxidative capacity similar to that found in the human quadriceps (30).…”

The Effects of Aging on Capillary Hemodynamics in Contracting Rat Spinotrapezius Muscle

“…The rat spinotrapezius muscle is a postural muscle, originating in the lowerthoracic and upper-lumbar region of the vertebral column and inserting on the scapula, which also functions to stabilize the scapula, for example, during downhill treadmill running (Kano et al, 2004). The left spinotrapezius muscle was exposed and exteriorized as described previously (Poole et al, 1997;Kindig et al, 2002;Russell et al, 2003), in a manner which preserves the vascular network and neural connections supplying the muscle (Bailey et al, 2000).…”