Muscular reflex and baroreflex influences on heart rate during isometric contractions.

Isometric hindlimb contractions were induced in anaesthetised dogs by stimulation of appropriate spinal ventral roots. During such contractions there were appreciable reflex systemic pressor responses accompanied by small increases in heart rate. The heart rate responses during contractions were small because the primary cardioacceleratory reflexes from muscle were partly masked during contractions by opposing baroreceptor-cardiodepressor reflexes.