Calf muscle injuries often involve your calf growing tighter and tighter as a result of pounding on the road, so your first point of call is to ensure this tightening is kept to a minimum.
Stretching (stand on a step with your forefoot and lower your heel into the gap behind), compression socks and rolling your calf muscles with a massage stick (not unlike a rolling pin) all play a significant role. The rolling pin is a great way of finding tight spots, and by working them hard it fires the required nerve endings within your muscle to stimulate faster recovery. From here any return to actual running has to be slow and incremental.
Start with 10min jogging on grass and progress that by just a few minutes each time you run. There’s some research that suggests getting up on your toes is a proficient way to reduce tightening, working to the theory that you’re using it in a slightly different way, thus reducing the fatigue that one set of muscles accumulates. So in a steady run, if you’re feeling any stress, a few ‘toe’ efforts over 20secs could help reduce tightening.
And, of course, always remember to check your running shoes. Are they the right kind for your particular form? Are they correct for the surface you’re running on? And have you owned them for less than 400-500 miles or six months?
Older shoes compress and lose their cushioning and support, which of course means your calf is working harder and is, therefore, more likely to tighten. Fortunately for triathletes, work in the pool can help a lot, as either water running or simply cracking on with your usual swimming session uses the aerobic system while allowing the calf to rest.