An effective ground stroke in tennis requires topspin, producing a ball that dive-bombs as it crosses the net and then skips forwards low and fast.

British researchers who tested several racquet designs found that a heavier racquet with a higher centre of mass increases both ball speed and topspin. “You can hit the ball harder and it will still land in bounds,” says Dr Tom Allen, lead author of the study, which appeared in the Journal of Sports Sciences. The problem is, a heavier racquet can slow your stroke. Allen suggests adding lead tape to the top of the racquet, on the outside of the rim. Start with five grams. Test it, and if your swing feels normal, add another layer of lead. Keep adding lead as long as you don’t notice a difference in your swing.