Researchers in the UK studied 324 twins average age 55 at baseline and then 12 years later. It was found that those who scored better on cognitive processing tests and had better visual memory had better lower leg power at baseline. Researchers picked twins as they would have more similar genetic make up.
MRI imaging also demonstrated more gray matter volume at 12 years after baseline leg power assessment. An increase in 40 watt leg explosive power correlated with an average of 3.3 years lower cognitive age.
Leg power was chosen as the measure for fitness because it was “sensitive to low-intensity physical activity”, has functional carryover and declines with age more than physical strength. The Leg Extensor Power Rig was used for measuring this.
Authors acknowledge that this study does not prove causality between physical fitness and brain aging, however it it supports a probable causal relationship. Physical activity levels are correlated with slower brain aging and its possible that leg power is a good measure for physical activity.