Abstract
Muscle contraction mechanically changes vessel geometry and consequently muscle circulation. Lengthening of muscle fiber straightens capillary tortuosity and further increase in muscle fiber length reduces blood flow by extending the capillary while reducing its diameter. The direction of capillary to the fiber long axis will modify the extent of capillary lumen diameter change due to lengthening muscle fiber. During passive stretching in human subjects, the relationship between changes in blood volume (determined by near-infrared spectroscopy: NIRS) and fascicle length differed among the three heads of triceps surae muscles with different fascicle length and pennation angle. Muscle thickness, muscle curvature, and muscle fascicle angle are potential determinants of intramuscular pressure during muscle contraction. Muscle circulation is impeded more in short bulging muscles with great curvature of fibers than in long slender muscles with less curvature. The different response of circulatory parameters across the synergist muscles in the calf and heterogeneity of muscle circulation in the same muscle were observed, partly due to the difference in the pennation angle of the muscle fascicle. The muscle architecture will influence venous outflow by changing the muscle pumping action. This is possibly an indirect way of modifying vasodilation due to difference in muscle architecture.
