Mainly legs, though sometimes other muscles like abs. I’ve even had my fingers cramp. As for why those muscles, I have no idea. Just know that salt, and sometimes Mg, helps or completely fixes it.
I went from adding salt only to my coffee (1 cup) in the morning, to also adding it to my tea (1 cup). I salt the crap out of my food, and will add things like (real, no wheat) soy sauce or fish sauce to my natto or other foods.
I’m hoping cool weather will mean fewer cramps.
But we read about other people’s experiences… I never thought other people are anything like me regarding diet though it’s easy for me as my SO needs the HCHF diet he is thriving on 
He is the one who eats oatmeal for breakfast and he is fine for the next 9 hours (his most active time). Wow. But as we both need bigger meals and I saw the same from other family members, it’s hard to wrap my head around tiny meals - but I met such people so I am aware it works for some, even many.
I am sure I eat less salt than before. I dropped carbs, fat and salt compared to my old high-carb days. I think my protein intake is similar but as I never tracked back then, I can’t possibly know. It’s almost impossible for me to eat too little sodium (zero for 5 days did the trick but I had no idea about electrolytes and it wasn’t bad, per se, just odd) but I can overdo it and that’s horrible.
But salt seems easy, one tries some amount and quickly see if that works for them or not. Or just do whatever feels right. I lightly salt my food and it works.
I am curious about that too… It’s always my calves when I lack Magnesium. (It seems to be always Magnesium for me but I eat the same perfect amount of sodium every day as far as I know anyway.) And I never get cramps when I eat little sodium (I had none on a 5 day fast once). And I only get cramps on keto with little to no meat and no Mg supplement.
Maybe this is something that is explained so early in Medical School that everybody knows it, but while I’ve seen hundreds of people talk about it over the years, I’ve never heard an explanation for it. I call it “oddly specific” cramping, and I tend to get it in my right leg far more than my left, and if not my right lower leg, then I get it in two toes on my right foot. If my big toe is #1 and I count to the right, it’s numbers 3 and 4. Just those two and it will wake me up in the middle of the night. If my calf cramps, I have to stand up to stretch it back out. I can’t recall my left calf ever cramping.
Oddly specific. The best thing I’ve done for that is to take a mix of Real Salt (the brand) and potassium chloride salt - 1/4 teaspoon of both in water or sometimes lemonade. I also added Magnesium Glycinate. I’ve added the Real Salt and KCl once a day and then twice a day if I’m fasting. The last few months, I’ve done it once a day while fasting and haven’t had the cramps at all.
And speaking of oddly specific, my right ankle and really my leg below the knee has seemed slightly bigger than my left for as long as I can remember. I remember noticing it in 2013. I figure if it was a dangerous blood clot I’d be dead by now. Thankfully, it doesn’t hurt; my wife has an issue with her left ankle and foot being swollen and it does hurt. She had pretty much every test they could think of but no reason was found.
I think we’re not as symmetrical left to right as we’d like to think.
redmond Real salt is also my salt of choice. I am more familiar with exercise-associated muscle cramps, which are generally spasmatic and involuntary contractions of skeletal muscles that occur during or immediately after exercise. They result in bulging or knotting of the muscle and usually occur in multi-joint muscle groups when contracting in a shortened position (i.e., quadriceps, hamstrings, and calf).
Athletes have historically blamed electrolyte imbalance, nutrition, or dehydration for their cramps. However, with these types of cramps, a Nobel scientist researching them says cramping is almost always triggered by hyperactive nerves pounding fatiguing muscles during exercise. They did muscle biopsies and blood work on those athletes who were cramping and did not find any problems with dehydration or a lack of electrolytes. As muscles fatigue, motor neurons that induce contraction (or shortening) of the muscle fibers begin to fire uncontrollably into the muscle. It’s this loss of neuromuscular control that triggers the onset of a cramp.
I find that explanation a little puzzling. Since I’m not thinking about things that happen during or immediately after exercise, maybe it’s an entirely different phenomenon.
If I find that my cramps don’t happen when I drink my electrolyte mix, I’m perfectly willing to believe it’s just a coincidence. After all, it’s not placebo controlled, randomized study. In that scenario, I have the cramps some number of times (true) and then based on some reading or conversations I’ve had with other people, I mix up my brew and drink it daily. After some period, I think “the electrolytes must have fixed it,” (also true) and since I’d rather not go through that regularly I keep drinking it and whatever caused the cramps goes away for some other reason.
The part that makes me hesitate is that the “…electrolyte imbalance, nutrition, or dehydration…” belief is very widespread - it comes from lots of people. That means a vast number of people have had the same coincidence. I have no idea what the real probability of the drink having fixed it or not having fixed is - and the second one is the important one here. Assuming having cramps or not and drinking the electrolytes are independent variables, the probability of a widespread coincidence goes down as the number having the coincidence goes up.
I went through a totally unrelated thing where I had a coincidence that seemed to fix a problem and ended up taking massive amounts of an herbal thing for years. I eventually concluded, “I hate placebos.”
This makes sense. And at least for me, it’s the weaker side / area, or the one that’s slightly injured from a former cramp, that cramps again. Thinking maybe the stronger muscle is able to withstand a greater stress level.
If it works for you, then continue to use it. It does not matter if there is merit in your mix or if it is the placebo effect; it works for you.
I follow something similar, though I have a soft water system at home that adds potassium to the water. I think I get enough potassium, so I usually don’t supplement potasium.
And it’s NOT the placebo effect, because if I DON’T do this, it gets worse. Even this morning, I had to change what I do for body weight training because of cramps in my feet in a certain position.
And if you’ve ever had a lower leg cramp that comes on at night while you’re sleeping and have to jump out of bed because it’s no painful, you might not know what we’re discussing. But I have had those enough that I’d rather up my salt (and Mg) intake than have them again.
Yeah, why is it always at night? That is when I am most likely to get the cramps as well. The worst is when the hamstring cramps. It is a large muscle and difficult to get to relax and uncramp. Almost scary when it happens.
Definitely - for me, it’s “Oh, I’m in for it now… 
” That cramped knot of muscle is like a baseball, a hard painful little bugger, and I sit up in bed and stretch it as best I can, like you’d normally stretch the back of your legs; takes effort and patience. And if it relaxes then I have to go really slow in lying back down and straightening out or the darn thing will seize up again.
@VirginiaEdie and @OldDoug I would also like to know why they are at night. Yes, a hamstring cramp would be brutal. Mine tend to be near my calves, maybe the fibularus longus?
If I keep up with salt and the like, I tend not to have these too often, thankfully. Because trying to get that muscle to lengthen again is a bear.
I can see that the hamstring would be worse.
Personally, I can’t quite figure out why cramps become more prevalent at times and less prevalent at times. I’d guess it has to do with the weather (hotter = more cramps), but I’m not 100% sure.
I have them occasionally, but I had them even more often before Keto, especially when I was flying long distance a lot. Yep, always at night.
I definitely never experienced something like that… My cramps are polite, they only happen when I wake up (so it’s always in the morning) and it’s just a few seconds of unpleasant feeling (it just goes away almost immediately, lucky!), barely painful (and my pain tolerance is pretty low)… My biggest problem with it that it means I have Magnesium problems (and my body doesn’t function right due to it) and it sounds dangerous and I need to do something before it impacts something even more serious. The feeling itself is no big deal, really. I still hope I never will get it again.
A stubborn hamstring cramp sounds horrible… It’s ALWAYS my calf. The only one I ever got before keto happened in a pool, that was more stubborn, more painful and somewhat scary…
Am I a weirdo that it never comes at night? Or it’s my ability that keeps me from waking at night? But it’s not perfect, a few things can wake me (a full bladder never ever cut it, I like that) and pain surely could… 
Calf cramps are nasty too. That’s a strong muscle and it’s tough to get it to lengthen and relax and stay relaxed. It’s a workout for the comparatively small muscles on the front of the lower leg. 
Does anyone get irritable when they are low on salt? I have twigged that this may be happening to me, but not sure if it is just coincidental events
I do lots of exercise as part of my career. So I get irritable when I forget to keep up with my electrolyte needs.