We're fans of running, HIIT, and plyo, but for the love of all things holy, give your knees a break this year. They may not have let you in on their secret yet, but your knees love those activities a lot less than you do. Before you become irate: we're not suggesting you stop doing these workouts (unless you hate them, in which case, refer back to slide two) — simply that you supplement your high-impact routine with some low-impact strengthening exercises. Pilates and yoga, anyone? We'll never tell you to ditch Barry's or Orangetheory (because we can't imagine life without them), but mixing things up will help extend the life of your joints and allow for many more workouts for years to come.