Baback Roshanravan1, Kushang V Patel2, Linda F Fried3, Cassianne Robinson-Cohen4, Ian H de Boer4, Tamara Harris5, Rachel A Murphy6, Suzanne Satterfield7, Bret H Goodpaster8, Michael Shlipak9, Anne B Newman10, Bryan Kestenbaum4. 1. Division of Nephrology, Department of Medicine, University of Washington Kidney Research Institute, Seattle. broshanr@uw.edu. 2. Department of Anesthesiology and Pain Medicine, University of Washington, Seattle. 3. Veterans Affairs Pittsburgh Healthcare System, University of Pittsburgh School of Medicine, Pennsylvania. 4. Division of Nephrology, Department of Medicine, University of Washington Kidney Research Institute, Seattle. 5. Laboratory of Epidemiology and Population Sciences, National Institute on Aging, Bethesda, Maryland. 6. School of Population and Public Health, University of British Columbia, Vancouver, Canada. 7. Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis. 8. Florida Hospital & Sanford-Burnham-Presbys Translational Research Institute for Metabolism and Diabetes, Orlando. 9. General Internal Medicine Section, San Francisco Veterans Affairs Medical Center, California. 10. Department of Epidemiology, University of Pittsburgh School of Medicine, Pennsylvania.
Abstract
BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: Muscle endurance, estimated by isokinetic work, is an indicator of muscle health associated with mobility limitation and mortality providing important insight beyond strength testing.
BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: Muscle endurance, estimated by isokinetic work, is an indicator of muscle health associated with mobility limitation and mortality providing important insight beyond strength testing.
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