title: Muscle weakness, fatigue, and torque variability: effects of age and mobility status.
abstract: BACKGROUND
  Whereas deficits in muscle function, particularly power production, develop in old age and are risk factors for mobility impairment, a complete understanding of muscle fatigue during dynamic contractions is lacking. We tested hypotheses related to torque-producing capacity, fatigue resistance, and variability of torque production during repeated maximal contractions in healthy older, mobility-impaired older, and young women.
  
  
  METHODS
  Knee extensor fatigue (decline in torque) was measured during 4 min of dynamic contractions. Torque variability was characterized using a novel 4-component logistic regression model.
  
  
  RESULTS
  Young women produced more torque at baseline and during the protocol than older women (P < 0.001). Although fatigue did not differ between groups (P = 0.53), torque variability differed by group (P = 0.022) and was greater in older impaired compared with young women (P = 0.010).
  
  
  CONCLUSIONS
  These results suggest that increased torque variability may combine with baseline muscle weakness to limit function, particularly in older adults with mobility impairments.
authors.affiliation: Department of Kinesiology, University of Massachusetts, 108 Totman Building, 30 Eastman Lane, Amherst, Massachusetts, 01003, USA.
authors.forename: Jane A
authors.initials: JA
authors.lastname: Kent-Braun
authors.forename: Damien M
authors.initials: DM
authors.lastname: Callahan
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Fay
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Foulis
authors.forename: John P
authors.initials: JP
authors.lastname: Buonaccorsi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000502:physiology; D004185:Disability Evaluation; D005260:Female; D006304:Health Status; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D051346:Mobility Limitation; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018908:Muscle Weakness / Q000503:physiopathology*; D012044:Regression Analysis; D019415:Torque
keywords: aging; contraction; physical function; power; sarcopenia