Muscle tear in calf muscle

This is the second time I have torn a muscle in the calf of my leg while playing tennis. First in my right leg and then in the left one. My doctor says I should do some warm-up exercises before I play to avoid this occurring again. What I would like to know is if there is any connection to lack of vitamins and the easy tearing of leg muscles, or if any specific vitamin can strengthen the muscles. Also which specific warm-up exercises should I do and for how long before I play. I belong to a health club so I have access to all exercise equipment. Also I must mentions that I am 50 years old but in very good physical shape. Thank you