One of the nawafil prayers whose benefits have been highly mentioned in many ahadith is the chast prayer offered soon after sun rise till the afternoon zawal time.
One of the fadail mentioned is that by offering two rakats of chast one offers sadaqa of all the joints (>300) . Reflecting on this I recall that almost all elderly people of our community whom I know get osteoarthritis sometime in their lives but what is amazing is that my grandparents both of whom have passed away were regular in their chast prayers and till the time of their death none of them complained of pain in any of their joints( although both crossed 85 years) ! I wonder if there are more examples around ?