A Calf Cramp Does Not Have Just One Cause

I woke in the night with a cramp in my calf.

It is a pain that is hard to forget once you have had it. And those who get it often will have been told more than once to drink more water, or that they are short of minerals.

Water and electrolytes do not explain all of it

That was long taken for granted. But there are studies that actually compared the blood of people who cramped with those who did not.

Among long-distance runners, and in a study that enrolled some two hundred triathlon competitors in advance and followed them, no clear difference in electrolyte levels or degree of dehydration appeared between the two groups. What matched better was how fast they had run and whether they had cramped before.

This does not settle the matter, though. In situations like long work in the heat, where a great deal of salt is lost in sweat, there are researchers who still hold that the balance of water and salt plays a part. It is a subject not yet narrowed to a single cause.

I look at this as something small happening inside a narrow compartment. Muscle is wrapped in fascia. It is a compartment that cannot swell freely. (Sweat Is Not Only for Cooling You Down)

When conditions inside the compartment grow tight, several things go wrong at once. A cramp is closer to that going-wrong showing itself briefly and hard. So I separate out three strands — energy, pressure, and nerve.

The first two strands — the energy it takes to release, and the pressure that blocks it

Let me start with what is not well known.

Muscle does not spend energy only when it contracts. If anything, releasing takes energy. The calcium that caused the contraction has to be pumped back where it came from for the muscle to release, and that pumping spends energy.

So when energy is short, a muscle does not so much clench as fail to let go. That a cramping muscle goes hard as stone is closer to not having the strength to let go than to squeezing hard.

The second strand overlaps here. When pressure inside the compartment rises, that pressure presses the small vessels from outside. Blood flow drops.

With less blood flow, less oxygen and energy come in. Then the first of these gets worse. Short of the strength to release it goes hard, going hard raises the pressure further, and the rising pressure drops the flow further still. It becomes a loop.

That stretching the calf by hand releases a cramp works on breaking this loop.

The third strand — sometimes it tilts on the nerve side

Muscle has two sensors. The muscle spindle measures how far the muscle has been stretched, and the Golgi tendon organ measures how much force is on the tendon.

The signals these two send have to balance for a muscle to contract at a fitting strength. When that balance tilts one way, the nerve driving the muscle grows over-excited. This is the explanation gaining ground at present. Even so, in the laboratory some people do not cramp even with the conditions set up, so it does not explain everything on its own.

And there are cases where that nerve is pressed not at the calf but much further up. For those in whom rubbing the calf helps only for the moment, I look at the lower back and the foot together. (Your Back Hurts, and I Look at Your Foot)

There is a reason it happens especially at night

Lying down, the foot bends of itself toward the sole. The calf muscle is then left already shortened as far as it goes. A muscle that is already short grows excited more readily.

So a cramp at night and a cramp during exercise are not under the same conditions. There is a trial in which a group who slowly stretched their calves before sleep had fewer cramps at night, and that fits with the above in stretching a shortened muscle out beforehand.

So what I ask

• When it happens — after exercise, in sleep, or on standing up after long sitting
• One side or both — if it repeats on one side only, I look harder at the nerve side
• Whether anything comes with it — whether numbness comes too, whether the feet are cold

It is because where to look differs depending on which it is. The same word "cramp" does not point at the same thing.

Where this story continues

The case where numbness comes along and the tests come back normal I have written down separately in When Your Hands and Feet Tingle and You Cramp Often but the Tests Are Normal. That piece deals with breathing and the body's acid-base environment.

When to see a doctor first

If cramps repeat on one side only and strength drops away, if the calf swells and feels hot, or if the calf seizes and makes you stop after only a short walk rather than in sleep — before a story like this, examination and testing come first.

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Sources

• A study that enrolled participants in advance and found that running speed and previous cramping matched better than dehydration or sodium change — British Journal of Sports Medicine, 2011
• A review setting out that the cause of exercise-associated cramp is not yet settled and that both views stand opposed — Sports Medicine, 2019
• A trial confirming fewer night cramps in a group who stretched their calves before sleep — Journal of Physiotherapy, 2012

Written by Dr. Heo Ji-young (Ph.D. in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)