Sore muscles are "knot" a problem if you own a lacrosse ball. Better than a good ol' tennis ball, which isn't always firm and often slides around on a wood floors or walls, a rubbery lacrosse ball is just hard enough to put pressure on certain trigger points under you feet and on your legs. Stash one in your gym bag for a self-massage on the go. Source: Frank Baptiste, a strength and conditioning specialist and founder of FranklyFitness
