A Finnish study involving 338 older adults (average age 66) has found that greater muscle strength is associated with better cognitive function.
Muscle strength was measured utilising handgrip strength, three lower body exercises such as leg extension, leg flexion and leg press and two upper body exercises such as chest press and seated row.
Handgrip strength, easy to measure, has been widely used as a measure of muscle strength, and has been associated with dementia risk among the very old. However, in this study, handgrip strength on its own showed no association with cognitive function. But both upper body strength and lower body strength were independently associated with cognitive function.
It may be that handgrip strength is only useful for older, more cognitively impaired adults.
These are gender-specific associations — muscle strength was significantly greater in men, but there was no difference in cognitive performance between men and women.
The finding is supported by previous research that found a link between walking speed and cognition in older adults, and by a 2015 study that found a striking correlation between leg power and cognition.
This 10-year British study involved 324 older female twins (average age 55). Both the degree of cognitive decline over the ten year period, and the amount of gray matter, was significantly correlated with high muscle fitness (measured by leg extension muscle power). The correlation was greater than for any other lifestyle factor tested
 . Muscle strength and cognition in ageing men and women: The DR's EXTRA study. European Geriatric Medicine [Internet]. 2017 ;8(3):275 - 277. Available from: http://www.sciencedirect.com/science/article/pii/S1878764917300712
 . Kicking Back Cognitive Ageing: Leg Power Predicts Cognitive Ageing after Ten Years in Older Female Twins. Gerontology [Internet]. 2015 . Available from: http://www.karger.com/?doi=10.1159/000441029