title: Association of Muscle Endurance, Fatigability, and Strength With Functional Limitation and Mortality in the Health Aging and Body Composition Study.
abstract: Mobility limitation is highly prevalent among older adults and is central to the loss of functional independence. Dynamic isokinetic muscle fatigue testing may reveal increased vulnerability to disability and mortality beyond strength testing.
  
  
  
  We studied community-dwelling older adults enrolled in the Health Aging and Body Composition study (age range: 71-82) free of mobility disability and who underwent isokinetic muscle fatigue testing in 1999-2000 (n = 1,963). Isokinetic quadriceps work and fatigue index was determined over 30 repetitions and compared with isometric quadriceps maximum torque. Work was normalized to leg lean mass accounting for gender-specific differences (specific work). The primary outcome was incident persistent severe lower extremity limitation (PSLL), defined as two consecutive reports of either having a lot of difficulty or being unable to walk 1/4 mile or climb 10 steps without resting. The secondary outcome was all-cause mortality.
  
  
  
  There were 608 (31%) occurrences of incident PSLL and 488 (25%) deaths during median follow-up of 9.3 years. After adjustment, lower isokinetic work was associated with significantly greater risks of PSLL and mortality across the full measured range. Hazard ratios per standard deviation lower specific isokinetic work were 1.22 (95% CI 1.12, 1.33) for PSLL and 1.21 (95% CI 1.13, 1.30) for mortality, respectively. Lower isometric strength was associated with PSLL, but not mortality. Fatigue index was not associated with PSLL or mortality.
  
  
  
  Muscle endurance, estimated by isokinetic work, is an indicator of muscle health associated with mobility limitation and mortality providing important insight beyond strength testing.
authors.affiliation: Division of Nephrology, Department of Medicine, University of Washington Kidney Research Institute, Seattle. broshanr@uw.edu.
authors.forename: Baback
authors.initials: B
authors.lastname: Roshanravan
authors.affiliation: Department of Anesthesiology and Pain Medicine, University of Washington, Seattle.
authors.forename: Kushang V
authors.initials: KV
authors.lastname: Patel
authors.affiliation: Veterans Affairs Pittsburgh Healthcare System, University of Pittsburgh School of Medicine, Pennsylvania.
authors.forename: Linda F
authors.initials: LF
authors.lastname: Fried
authors.affiliation: Division of Nephrology, Department of Medicine, University of Washington Kidney Research Institute, Seattle.
authors.forename: Cassianne
authors.initials: C
authors.lastname: Robinson-Cohen
authors.affiliation: Division of Nephrology, Department of Medicine, University of Washington Kidney Research Institute, Seattle.
authors.forename: Ian H
authors.initials: IH
authors.lastname: de Boer
authors.affiliation: Laboratory of Epidemiology and Population Sciences, National Institute on Aging, Bethesda, Maryland.
authors.forename: Tamara
authors.initials: T
authors.lastname: Harris
authors.affiliation: School of Population and Public Health, University of British Columbia, Vancouver, Canada.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Murphy
authors.affiliation: Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Satterfield
authors.affiliation: Florida Hospital & Sanford-Burnham-Presbys Translational Research Institute for Metabolism and Diabetes, Orlando.
authors.forename: Bret H
authors.initials: BH
authors.lastname: Goodpaster
authors.affiliation: General Internal Medicine Section, San Francisco Veterans Affairs Medical Center, California.
authors.forename: Michael
authors.initials: M
authors.lastname: Shlipak
authors.affiliation: Department of Epidemiology, University of Pittsburgh School of Medicine, Pennsylvania.
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.affiliation: Division of Nephrology, Department of Medicine, University of Washington Kidney Research Institute, Seattle.
authors.forename: Bryan
authors.initials: B
authors.lastname: Kestenbaum
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D005260:Female; D006801:Humans; D035002:Lower Extremity; D008297:Male; D051346:Mobility Limitation; D018763:Muscle Fatigue; D053580:Muscle Strength / Q000502:physiology*; D010807:Physical Endurance
keywords: Fatigue; Mobility; Muscle; Sarcopenia; Strength