Stronger hands lengthen your life

It's not really a discovery, or study. The article is implying that stronger hands help prevent falls. And because falls are _the_ (emphasis theirs) leading cause of injury-related death for people who are 65+, stronger hands help in living longer lives because of lower injury rates.

Stronger hands means a person's is able to use them to hold on to something, to prevent or slow-down the fall, and reducing the risk of serious, life threatening injury.