title: Sex Differences in Arm Muscle Fatigability With Cognitive Demand in Older Adults.
abstract: BACKGROUND
  Muscle fatigability can increase when a stressful, cognitively demanding task is imposed during a low-force fatiguing contraction with the arm muscles, especially in women. Whether this occurs among older adults (>60 years) is currently unknown.
  
  
  OBJECTIVE
  We aimed to determine if higher cognitive demands, stratified by sex, increased fatigability in older adults (>60 years). Secondarily, we assessed if varying cognitive demand resulted in decreased steadiness and was explained by anxiety or cortisol levels.
  
  
  METHODS
  Seventeen older women (70±6 years) and 13 older men (71±5 years) performed a sustained, isometric, fatiguing contraction at 20% of maximal voluntary contraction until task failure during three sessions: high cognitive demand (high CD=mental subtraction by 13); low cognitive demand (low CD=mental subtraction by 1); and control (no subtraction).
  
  
  RESULTS
  Fatigability was greater when high and low CD were performed during the fatiguing contraction for the women but not for the men. In women, time to failure with high CD was 16±8 minutes and with low CD was 17±4 minutes, both of which were shorter than time to failure in control contractions (21±7 minutes; high CD mean difference: 5 minutes [95% confidence interval {CI}, 0.78-9.89], p=0.02; low CD mean difference: 4 minutes [95% CI, 0.57-7.31], p=0.03). However, in men, no differences were detected in time to failure with cognitive demand (control: 13±5 minutes; high CD mean difference: -0.09 minutes [95% CI, -2.8 to 2.7], p=1.00; low CD mean difference: 0.75 minutes [95% CI, -1.1 to 2.6], p=0.85). Steadiness decreased (force fluctuations increased) more during high CD than control. Elevated anxiety, mean arterial pressure, and salivary cortisol levels in both men and women did not explain the greater fatigability during high CD.
  
  
  CONCLUSIONS
  Older women but not men showed marked increases in fatigability when low or high CD was imposed during sustained static contractions with the elbow flexor muscles and contrasts with previous findings for the lower limb. Steadiness decreased in both sexes when high CD was imposed.
  
  
  CONCLUSIONS
  Older women are susceptible to greater fatigability of the upper limb with heightened mental activity during sustained postural contractions, which are the foundation of many work-related tasks.
authors.affiliation: Department of Physical Therapy, Marquette University, PO Box 1881, Milwaukee, WI, 53201, USA, hugo.maxwell@hotmail.com.
authors.forename: Hugo M
authors.initials: HM
authors.lastname: Pereira
authors.forename: Vincent C
authors.initials: VC
authors.lastname: Spears
authors.forename: Bonnie
authors.initials: B
authors.lastname: Schlinder-Delap
authors.forename: Tejin
authors.initials: T
authors.lastname: Yoon
authors.forename: April
authors.initials: A
authors.lastname: Harkins
authors.forename: Kristy A
authors.initials: KA
authors.lastname: Nielson
authors.forename: Marie
authors.initials: M
authors.lastname: Hoeger Bement
authors.forename: Sandra K
authors.initials: SK
authors.lastname: Hunter
mesh_terms: D000367:Age Factors; D000368:Aged; D000375:Aging / Q000523:psychology*; D001007:Anxiety / Q000503:physiopathology / Q000523:psychology; D062186:Arterial Pressure; D001696:Biomechanical Phenomena; D003071:Cognition; D005260:Female; D006339:Heart Rate; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D007537:Isometric Contraction; D008297:Male; D055641:Mathematical Concepts; D008875:Middle Aged; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology*; D012307:Risk Factors; D012463:Saliva / Q000378:metabolism; D012737:Sex Factors; D013315:Stress, Psychological / Q000378:metabolism / Q000503:physiopathology* / Q000523:psychology*; D013997:Time Factors; D019415:Torque; D034941:Upper Extremity
chemical_list: D006854:Hydrocortisone