I went on a run last week after a layoff of 4 days. About 3 ks into the run, I started to get quite tight calf muscles. Considering that I have done quite a bit of running over the past 4 months , used to get tight calves but thought that I had finally escaped their clutches, I was a bit annoyed. I may not have warmed up enough - but I generally usually don't so nothing much was new there --- I changed my running form a little bit in action by lifting my knees a little higher and concentrated on driving them forward instead of driving my feet forward - and the pain did go away. So - was it my form ? , the lack of sufficient warmup? the early hills in the run??