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Background: While some studies report muscle strength is associated with mortality, independent of aerobic physical activity (PA), in older people, there are less data in women and lack of studies adjusting the association for objective measures of PA and physical performance. We prospectively examined this association in 5,061 multiethnic (White, 48.2%; Black, 34.0%; Hispanic, 17.9%) women ages 63-99 (mean 78.3) with complete information for analysis in the Objective Physical Activity and Cardiovascular Health Study.Methods: Quartile categories of dominant hand grip strength (<14, 14-18, 18.1-22.5, >22.5 kg) and EPESE categories of time to complete five consecutive unassisted chair stands (>16.6, 16.6-13.7, 13.6-11.2, <11.2 sec) were the muscle strength exposure measures. Primary covariables included age, race-ethnicity, current smoking, BMI, and number of comorbidities. Accelerometer measured moderate-to-vigorous PA (MVPA) and total sedentary time, and gait speed during a self-paced 8 meter walk test were further assessed as confounding factors. Cox regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI).Results: There were 306 (5.5%) all-cause deaths during a mean 3.3 year follow-up. Adjusting for primary covariables, significant inverse trends in mortality were observed across categories of grip strength, HR (95% CI) = 1.00 (ref), 0.70 (0.53, 0.93), 0.77 (0.56, 1.05), 0.59 (0.41, 0.87), trend p = .007, and chair stands, 1.00, 0.82 (0.62, 1.09), 0.76 (0.55, 1.04), 0.53 (0.36, 0.77), trend p <.001. Further adjustment for MVPA attenuated these associations which remained statistically significant, 1.00, 0.72, 0.81, 0.66, trend p = .032, and 1.00, 0.91, 0.88, 0.65, trend p = .033, respectively. Similarly, adding sedentary time or gait speed to the primary covariables did not eliminate significance of the inverse mortality trends with either muscle strength measure. Adjusting for primary covariables, each 1-standard deviation (6.2 sec) faster chair stand time was associated with 12% lower mortality risk (p = .004), which was attenuated to 8% risk reduction (p = .04) when further controlling for MVPA. Adjusting for primary covariables and MVPA, each 1-standard deviation (6.8 kg) increment in grip strength was associated with 13% lower mortality risk (p = .04), and this inverse association was generally consistent across subgroups defined by age (interaction p = .78), race-ethnicity (p = .19), and BMI (p = .88). Controlling for gait speed opposed to MVPA resulted in consistent findings.Conclusions: Higher muscular strength is associated with lower mortality in older women, independent of device-measured MVPA and sedentary time, and measured gait speed, an indicator of aerobic fitness. If results are confirmed, in addition to guideline recommendations regarding aerobic PA, promoting skeletal muscle strength is an important component of aging well.