Associations between independent or concurrent decline in upper and lower limb strength and cognitive impairment

BACKGROUND: Skeletal muscle strength decline is related to cognitive impairment (CI). The longitudinal decline of upper and/or lower limb strength and CI remain poorly reported. We aimed to investigate the effects of independent or concurrent decline in upper and lower limb strength over a two-year period, on the future risk of CI. METHODS: We studied 2,443 participants (43.1% females) aged ≥ 60 years from the China Health and Retirement Longitudinal Study. The upper limb muscle strength (handgrip strength) and lower limb muscle strength (chair-rising time) were obtained at wave 1 (2011), and wave 2 (2013). At wave 3 (2015), 4 (2018), and 5 (2020) cognitive function was measured. According to the upper and lower limb muscle strength changes over two years, participants were classified into 4 groups: Stable-both (no decline in upper and lower limb strength), Upper decline-only (with a decline in upper limb strength only), Lower decline-only (with a decline in lower limb strength only), and Decline-both (with a decline in both upper and lower limb strength). We investigated the association between two-year muscle strength status and incident CI using discrete-time Cox regression. RESULTS: Over two years, participants with "Stable-both", "Upper decline-only", "Lower decline-only" and "Decline-both" were 60.6%, 18.2%, 16.0%, and 5.2%, respectively. There were 480 (19.65%) incident cases of CI over a mean follow-up of 5.73 years. Participants with "Lower decline-only" and "Decline-both" had increased risk of incident CI (HR = 1.62, P < 0.001, and HR = 1.80, P = 0.005, respectively). The associations remained significant when excluding participants with upper and lower limb muscle strength weakness at wave 1. However, the results were significant only in males and not in females. CONCLUSIONS: A decline in muscle strength, particularly in the lower limbs or both upper and lower limbs, increases the risk of future CI, regardless of the baseline muscle strength. Therefore, dynamic monitoring of upper and lower limb strength is essential for early identification of individuals at risk of CI.