Cramps during exercise

A cramp is a sudden, involuntary, spasmodic contraction of a muscle or group of muscles

There are two commonly held theories behind cramping during exercise:

1. Cramps are the result of an electrolyte (salt to fluid ratio) imbalance related to dehydration. This is the most common belief founded on an observation of increased chloride levels in sweat in the early 20th century. More recent studies of competing marathon runners and ironmen have not found a significant difference in the concentration of salts in the plasma of crampers and non-crampers. They also noted less overall body-weight loss (a very crude measure of dehydration) in crampers when compared with those who did not cramp. This means that as yet there has been no association found between fluid/electrolyte levels and cramping. However it is worth noting that there are limitations to this research for instance failure to measure competitiors fluid and electrolyte ingestion and digestion during the event.

2. Cramps are caused by a dysfunctional reflex control of the motor nerve due to fatigue. To explain it very simply; research has found that as a muscle fatigues the muscle reflexes that encourage contraction increase, and the reflexes that inhibit contraction decrease, with the net effect being involuntary muscular contraction due to too many “contract” messages being received by the muscle tissue.

The second theory appears to make more sense. If cramps were due to electrolyte imbalances then cramps would be widespread, affecting all muscles in the body equally. Instead we usually cramp in the active muscles that are placed in a shortened position for example calves during swimming. However as yet no one has been able to reproduce cramps in a controlled manner in a laboratory setting, so we do not really know what causes them. Based on the available research our advice is to stretch if you are cramping, or likely to cramp, and to avoid overloading a muscle. Practically this means not going too hard too fast in endurance events, pace yourself. Same principle for shorter bursts of exercise (sprints or weightlifting) stay within your limitations, and increase your efforts gradually. And of course being well hydrated is always a good idea!

What are your experiences with cramps? We'd love to hear from you!