Must admit, I've suffered on and off from calf muscle pulls and tears ever since I started running twenty one years ago. It's the only injury I've ever consulted a Physio about, and it cost me quite a lot of money! Even when I was stretching on a regular basis (thirty minutes a day) and doing all the relevant exercises recommended by the physio, it still came back. If truth be known that's one of the reasons I've stopped racing because, at my end of the age scale, it takes longer and longer to return to racing fitness after injury.
As Revenged says in his post, mid to forefoot strikers are more prone to this sort of injury, and I'm definitely a forefoot striker. However, since I stopped racing last January I've had no recurrence of the problem. It may be because, when I go out now, I'm only out for enjoyable runs as opposed to hard training - such as intervals, hill reps, cruise sessions, etc.. Or it may be because I've started wearing orthotics - which supposedly re-align the ankle, knee and pelvic joints to make one more 'balanced' - but can't see how they could affect my calf muscles.
Anyhow, such is my level of fitness at the moment I've started doing a few reps to quicken up again. Hope it's not inviting disaster!
Cheers!