BUCK, JOE A, LOUIS R. AMUNDSEN, and DAVID H. NIELSEN. Systolic blood pressure responses during isometric contractions of large and small muscle groups.Med. Sci. Sports Exercise.Vol. 12, No. 3, pp. 145–147, 1980. The purpose of this study was to test for a difference between the systolic blood pressure responses to voluntary contractions of large and small muscle groups of the upper extremity. Systolic blood pressure was measured at approximately 20 sec intervals during sustained isometric contractions of the index finger adductors and handgrip muscles contracting at 40% of maximal voluntary contraction (MVC). Contractions were terminated when EMG activity exceeded 10% of maximal activity of selected accessory muscles or when the 40% MVC Tension could no longer be held constant (±10%). The slopes of the regression lines representing systolic blood pressure responses to sustained isometric contraction of a small and large muscle group of the upper extremity were significantly different (p<.001). Older theories that pressor responses are determined only by the % MVC and not by the mass of contracting muscle need to be reexamined.