Sex differences in the fatigability of arm muscles depends on absolute force during isometric contractions

Women are capable of longer endurance times compared with men for contracti ons performed at low to moderate intensities. The purpose of the study was 1) to determine the relation between the absolute target force and enduranc e time for a submaximal isometric contraction and 2) to compare the pressor response and muscle activation patterns of men [26.3 +/- 1.1 (SE) yr] and women (27.5 +/- 2.3 yr) during a fatiguing contraction performed with the e lbow flexor muscles. Maximal voluntary contraction (MVC) force was greater for men (393 +/- 23 vs. 177 +/- 7 N), which meant that the average target f orce (20% of MVC) was greater for men (79.7 +/- 6.5 vs. 36.7 +/- 2.0 N). Th e endurance time for the fatiguing contractions was 118% longer for women ( 1,806 +/- 239 vs. 829 +/- 94 s). The average of the rectified electromyogra m (%MVC) for the elbow flexor muscles at exhaustion was similar for men (31 +/- 2%) and women (30 +/- 2%). In contrast, the heart rate and mean arteri al pressure (MAP) were less at exhaustion for women (94 +/- 6 vs. 111 +/- 7 beats/min and 121 +/- 5 vs. 150 +/- 6 mmHg, respectively). The target forc e and change in MAP during the fatiguing contraction were exponentially rel ated to endurance time (r(2) = 0.68 and r(2) = 0.64, respectively), whereas the change in MAP was linearly related to target force (r(2) = 0.51). The difference in fatigability of men and women when performing a submaximal co ntraction was related to the absolute contraction intensity and was limited by mechanisms that were distal to the activation of muscle.