title: Stressor-induced increase in muscle fatigability of young men and women is predicted by strength but not voluntary activation.
abstract: This study investigated mechanisms for the stressor-induced changes in muscle fatigability in men and women. Participants performed an isometric-fatiguing contraction at 20% maximal voluntary contraction (MVC) until failure with the elbow flexor muscles. Study one (n = 55; 29 women) involved two experimental sessions: 1) a high-stressor session that required a difficult mental-math task before and during a fatiguing contraction and 2) a control session with no mental math. For some participants (n = 28; 14 women), cortical stimulation was used to examine mechanisms that contributed to muscle fatigability during the high-stressor and control sessions. Study two (n = 23; nine women) determined the influence of a low stressor, i.e., a simple mental-math task, on muscle fatigability. In study one, the time-to-task failure was less for the high-stressor session than control (P < 0.05) for women (19.4%) and men (9.5%): the sex difference response disappeared when covaried for initial strength (MVC). MVC force, voluntary activation, and peak-twitch amplitude decreased similarly for the control and high-stressor sessions (P < 0.05). In study two, the time-to-task failure of men or women was not influenced by the low stressor (P > 0.05). The greater fatigability, when exposed to a high stressor during a low-force task, was not exclusive to women but involved a strength-related mechanism in both weaker men and women that accelerated declines in voluntary activation and slowing of contractile properties.
authors: Exercise Science Program, Department of Physical Therapy, Marquette University, Milwaukee, Wisconsin.
authors: Manda L
authors: ML
authors: Keller-Ross
authors: Hugo M
authors: HM
authors: Pereira
authors: Jaclyn
authors: J
authors: Pruse
authors: Tejin
authors: T
authors: Yoon
authors: Bonnie
authors: B
authors: Schlinder-Delap
authors: Kristy A
authors: KA
authors: Nielson
authors: Sandra K
authors: SK
authors: Hunter
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D003071:Cognition; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009044:Motor Cortex / Q000503:physiopathology*; D018763:Muscle Fatigue; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000294:innervation*; D012737:Sex Factors; D013315:Stress, Psychological / Q000150:complications* / Q000503:physiopathology / Q000523:psychology; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D014836:Volition; D055815:Young Adult
keywords: gender; muscle fatigue; sex differences; transcranial magnetic stimulation; voluntary activation