I've checked the internet for some possible exercises and I think this is the easiest one : The Tower Pulls--Stretching your supporting calf muscles plays a key role in restoring your ankle flexibility and range of motion as you recover from a broken fibula. Sit upright in a firm chair. Place your injured foot in the center of a towel. Grab a hold of the towel with both hands. Gently pull on the towel until you feel a stretch in your calf area. Hold this stretch for 15 seconds. Slowly return to the original position. Relax for 10 seconds. Repeat this exercise 10 times.