The Mechanics of Cramp

Inside every muscle are hundreds of muscle fibres and each of these contain muscle filaments. These slide past each other when the muscle is relaxed.

When the muscle needs to generate force (in order to walk, run or kick) the filaments lock together and the muscle contracts. A signal is given to the muscle and it is washed with a salt (sodium) solution. The filaments then need to unlock and relax before contracting again. In this case the filaments are washed with a calcium solution, relaxing the fibres as you propel forwards. Muscle fibres are therefore in a continuous cycle of contraction and relaxation.

However, painful cramp is out of control muscle contraction, locking the muscle in a very painful spasm, which can often last for several agonising minutes…or a lot longer.

Many muscles are attached to more than two bones. Muscles are arranged opposite each other, e.g. the muscles in the shin of our leg allow us to bend our ankle upward, while the calf muscle allows us to bend our ankle downward.


In the illustration aside, the calf muscle can be seen contracting when flexed (Diagram 2).

Cramp occurs in Diagram 3 when the calf muscle has locked in the contracted position and so it is hard to touch and extremely painful.

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