Embracing a willingness to train around injuries is the mark of a champion (or at least the mark of someone who is dedicated to achieving fitness). If you have broken your ankle, weight-bearing exercises that place stress on the joint-such as running and free-weight exercises like lunges and squatting-are certainly out. But there are many ways to work around your situation. With nothing more than some effort and creativity on your part, you still can make substantial physical progress despite your injury.
Exercising with a Broken Ankle
Avoid any exercises that place direct stress on the ankle joint itself, or any other exercises that your physician has expressly prohibited. Remember that moderation and reasonableness are the keys to moving past your injury as quickly as possible with the least possible negative impact. Use your head instead of your ego, and steer clear of banned exercises.
Stick to upper body training during your injury; take some time to increase the strength and tone of your "better half." Devote at least two training days per week to working the muscles of the upper body, with one mitigation day for the muscles of the legs to prevent substantial atrophy while you are recovering from your condition. Good upper body exercises during this period include the bench press, seated military press, one-arm rows, and even dips and pull-ups, if you have a training partner or other spotter who can catch you as you descend to avoid placing undue stress on the ankle. Be creative, and focus on what you can do instead of lamenting the things you can't.
Train your uninjured leg using unilateral lower body exercises like hyperextensions, reverse hyperextensions, leg extensions, hamstring curls and one-legged calf raises. You might even be able to exercise the muscles of the upper leg on your injured side using certain machines like the hamstring curl and leg extension machines (depending on the size of the cast and whether you can fit your leg into the machine without discomfort or pain). If you decide to pursue this route, exercise care and stop at the first sign of any pain from your broken ankle, even if you are not explicitly placing weight on the leg at that particular moment.
Perform simple cardio on crutches on the track if you feel the need for a bit of light endurance training. Keep things light and simple, sticking to workouts of 20 to 30 minutes tops, and go at a measured pace. You are not going to be able to break any land speed records during this time, but you will be able to burn a few extra calories while dealing with a broken ankle if you are smart and careful.