Cramps in upper legs, calves, and feet.

[kazana]

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I very often get cramps in my upper legs (the back of the leg, whatever that muscle group is called), the calves, and my feet.
I'm not sure what could be causing that, so I'm hoping the Gym might know.

The cramps typically occur in the evening, when I go to bed, but the cramps in my feet (toes curling up and that stuff) happen at any given time during the day. Whenever I just lie still and try to relax or sit on my partner while giving her a massage I can almost guarantee that my feet will cramp.

I usually thought it might be a lack of water or magnesium. But by now I'm drinking around 2-3 liters (.5-.8 gallons) every day, and a lot more when I'm being active in sports.
I don't drink much coffee or any other forms of caffeine. On average probably 1-2 cups a day.
I'm also taking cal/mag supplements, so I don't think I have a deficit in that area, either.
I couldn't spot any differences in frequencies when I'm active in sports or not. (Obv my calves cramp when I push too hard playing soccer, but that's to be expected if I'm not fit enough.)

What I have noticed, though, is that during the last couple months while I was on an Atkins diet, I had a lot fewer cramps. As soon as I started adding sugar to my diet again afterwards, the cramps immediately appeared. That could just be coincidence, but who knows, maybe that is related?

So do any of the health gurus around here have any ideas or suggestions what could be causing this?