It happened to me a few times during my first winter on fixed. It was

painful to say the least! Could feel it for ages afterwards.
What worked for me was
1. Moving my cleats as far back as they would go, which unloads the calf muscle quite a bit. Fortunately my frame design means I still clear the front wheel by a smidgeon (but nobody turns the bars that much at speed anyway).
2. I made a habit of stretching my muscles a lot more when I'm not riding, so it's not so much of a shock when I get on and ride.
3. Warmer clothing for my legs and waterproof/windproof tights on the coldest days.