My grand pop told me to judge a man by his handshake. Men with soft effeminate hands, beware! But, now research is indicating that there is so much more to grip strength:
https://www.naturalnews.com/2018-05-24-your-handshake-may-be-a-good-indicator-of-how-healthy-your-brain-is.html
“A hand grip may be a normal, everyday thing for men and women alike but a recent study showed that the strength of a handshake can indicate a person’s brain health. Using the data of 475,397 people from the general population in the U.K., and 1,162 participants who were diagnosed with schizophrenia, researchers discovered that grip strength is connected to the performance of the visual memory and reaction time of a person. This study has been proven in two groups where one has participants over 55 years old and the other has participants younger than 55. Aside from visual memory and reaction time, tests conducted during the research also included examinations for reasoning, prospective memory and number memory.
According to Dr. Joseph Firth, an Honorary Research Fellow at The University of Manchester and Research Fellow at NICM Health Research Institute at Western Sydney University, people who are stronger tend to have better functioning brains, particularly when age, gender, body weight and education are taken into account. The cross-sectional analysis was done between 2007 and 2010 using the baseline assessment for the UK Biobank. As part of the test, participants were categorized for more focused studies and results; those with records of non-affective disorders were tested separately from those with no history of mental illnesses.
https://academic.oup.com/schizophreniabulletin/advance-article/doi/10.1093/schbul/sby034/4942313
It looks like there really was something in grand pop’s advice.