The Sex Difference in Muscle Fatigability Occurs in Young Adults But Not in Old Adults

Abstract

1893 The duration that an isometric contraction can be sustained at a submaximal intensity is longer in young women compared with young men. This effect has not been examined thoroughly in old adults. PURPOSE: The purpose of this study was to compare the time to task failure for a sustained isometric contraction performed at a submaximal intensity with the elbow flexor muscles by young and old men and women. Methods: Twenty-seven young (14 men, 13 women, 18–35 years) and 18 old adults (10 men, 8 women, 65–80 years) sustained an isometric contraction at 20% of maximal voluntary contraction (MVC) torque until the target torque could no longer be achieved for at least 5 s. Results: The young adults were stronger than the old adults (mean ± SEM; 69 ± 3 N•m vs 46 ± 3 N•m, P < 0.05) and the men were stronger than the women (69 ± 3 N•m vs 44 ± 3 N•m, P < 0.05). The time to task failure was longer for the young women (1099 ± 130 s) compared with the young men (646 ± 125 s, P < 0.05), but there was no difference for the old women and men (1278 ± 165 s vs 1444 ± 148 s, P > 0.05). Furthermore, the time to task failure was longer for the old adults (864 ± 90 s vs 1370 ± 111 s, P < 0.05). Mean arterial pressure (MAP), heart rate, and average electromyographic activity (EMG) of the elbow flexor muscles increased during the fatiguing contraction (p< 0.05) for all subjects. However, the increase in MAP (P = 0.05) and EMG (p< 0.05) were greater for the young and old men compared with the young and old women. Furthermore, the EMG activity was greater at the start of the contraction for the old adults compared with the young adults for all muscles and increased at a greater rate throughout the contraction (p< 0.05). Conclusion: Old adults did not exhibit the sex difference in the duration of a sustained submaximal contraction that was observed in young adults. Also, the duration of the fatiguing contraction was longer for the old adults compared with the young adults. These differences in duration were not accompanied by parallel changes in the pressor response and in muscle activation. Supported by an ACSM Research Endowment award to SKH and an NIH award (NS43275) to RME.