Skeletal Muscle Afferents

The constellation of cardiovascular and respiratory responses evoked by the stimulation of skeletal muscle afferents has been termed "the exercise pressor reflex." The purpose of the exercise pressor reflex is to deliver oxygenated blood to metabolically active tissues (that is, the exercising muscles) and to remove carbon dioxide and hydrogen ions from these tissues. In addition, the exercise pressor reflex contributes significantly to the increase in cardiac output evoked by dynamic exercise. The reflex increases sympathetic discharge to the vascular beds of dynamically exercising muscles, an effect that partly counters the increase in vascular conductance, which, in turn, is caused by the increase in muscle metabolism. The exercise pressor reflex also plays an important role during static exercise. The afferent limb of the exercise pressor reflex is composed of group III and IV afferents, which together are called "thin fiber afferents." Groups Ia, Ib, and II play no role in evoking this reflex.