Calf muscle seizure

I am a 51 years old male
I have been running in sub zero weather in Montr

[hyepod]

I am a runner too, but also a podiatrist.  This is probably unlikely, but have you considered DVT (deep venous thrombosis)?  In other words, a clot deep within the calf.  Is it swollen or reddened?  I must say, though, I have seen DVT's without those signs.  In any case, a DVT is a medical emergency....just so you know.