Research reveals stronger people have healthier brains - A study of nearly half a million people has revealed that muscular strength, measured by handgrip, is an indication of how healthy our brains are. This finding exists in the general population as well as people experiencing schizophrenia.
Source: http://www.manchester.ac.uk/discover/news/research-reveals-stronger-people-have-healthier-brains/I dislike measuring overall strength levels by handgrip alone. Grip is only one small factor with strength, not your whole body