McCALL, G.E., K.L. GOSSELINK, A.J. BIGBEE, R.R. ROY, R.E. GRINDELAND, and V.R. EDGERTON. Muscle afferent-pituitary axis: A novel pathway for modulating the secretion of a pituitary growth factor. Exerc. Sport Sci. Rev., Vol. 29, No. 4, pp 164-169, 2001. Evidence is presented for a novel muscle-neuro-endocrine pathway for modulating the secretion of an unidentified pituitary growth factor by proprioceptive input from skeletal muscle afferents. Exercise stimulates the release of this growth factor, whereas chronic unloading associated with bed rest or spaceflight abrogates the normal exercise stimulus.