The popular theory explaining why exercise induces muscle cramping is that the muscle becomes fatigued causing the golgi tendon organ (a proprioceptive sensory receptor) within the muscle to stop doing it’s job of sensing muscle tension. Under normal circumstances, the Golgi tendon organ causes inhibition of the muscle, allowing the muscle to relax. Without this feedback loop, the muscle stays contracted and you get a cramp.
Dehydration and electrolyte loss have also been cited as being the cause of cramping, though there is growing evidence to the contrary. It may be that the coupling of the two factors play a part. There is another theory out there that isn’t well known, but clinically I see evidence of this theory almost daily.
Anatomical slings are chains of muscles, fascia and ligaments that function together to allow movement. Thomas Myers is largely credited for the identification of these slings in his book, Anatomy Trains. Myers identified ten slings or “myofascial meridians.” To that list can be added myofascial subsystems that also work in unison to create functional movement (there are five), such as the deep longitudinal subsystem. That’s 15 slings around our body, helping us move.
These slings act like springs and are designed to store energy when stretched, then release this energy as the sling contracts. When a muscle in the sling is inhibited, it breaks the sling. The nervous system tries to compensate for this by tightening another part of the sling. An example would be a hamstring getting tighter for an inhibited gluteus maximus, or a calf muscle getting tighter for a inhibited hamstring etc. Get where I’m going with this? If one muscle is tightening to take up the slack for another muscle in the sling it is effectively doing the job of two muscles. It is getting twice as much neural drive (signal from the brain) and it is going to get fatigued…. and eventually cramp. In case your wondering, plantar fascia can be caused by the exact same mechanism.
The fix is to identify the compensations that exist within the relevant sling and correct them so as each muscle is getting the appropriate neural drive and is working in unison with it’s other sling members. No overworking = no cramps!