Muscle Cramping

By Scot Willingham

Today, we talk about muscle cramps – causes, relief, and prevention.

While many reasons exist for cramping, as well as types of cramping, this article addresses what experts call Exercise-Associated Muscle Cramping (EAMC). When you hear runners, triathletes or cyclists say, “My hamstrings started cramping up on that last hill. I backed off a little and felt OK. But, then when I tried to jump back up to the field, I cramped again.”—they are referring to EAMC.

EAMC refers to a localized cramp in a particular muscle or muscle group. It occurs during intense or prolonged exercise, such as maximum force contractions or ultra-endurance events (e.g. marathon, IronMen, long cycling road events,). The cramp will be intense but usually will fade with reduced movement and typically within 5 minutes. However, it recurs easily when either of the two conditions is imposed again—maximum force or more repetitive, constant work.

This type of cramping is unrelated to what has been labeled “heat cramping” or cramps caused by medical conditions. Nor the systemic, generalized spasticity seen in elite triathletes near the finish.

Old Research

Much of the cramping research prior to 1990 originated from anecdotal stories in the late 1800’s describing workers who were enduring high temperature and humidity conditions while performing hard manual labor, profusely sweating, and experiencing cramping. An early study (Talbott & Michelsen, 1933) found depleted chloride levels (an electrolyte) in Hoover Dam workers.

The association of profuse sweating and depleted electrolytes became the assumed cause of muscle cramping and can be found in literature today. Over time, more electrolytes have been added to the list.

This resulted in the traditional electrolyte depletion hypothesis which suggests fluid changes from profuse sweating create systemic electrolyte imbalances. This imbalance causes either a depletion of electrolytes necessary for muscle use or, by increasing serum osmolality, creating mechanical changes in nerves and their environment.

The corollaries of the traditional electrolyte depletion hypothesis are that:

1. “salty” sweating, a term without any scientific definition, creates a higher loss of electrolytes and increased risk for EAMC.
2. Dehydration (fluid loss) creates an electrolyte imbalance.
3. Heat creates either profuse “salty” sweating or dehydration.

This hypothesis and its corollaries are not supported by the latest research.

New Research

Recent studies have found that the above associations do not occur in EAMC. Three prospective studies (Schwellnus et al., 2004; Sulzer et al., 2005; Maughan, 1986) have found no abnormal serum electrolyte concentrations associated with EAMC in athletes.

It has been suggested that sodium loss would create EAMC, and this loss occurs through sweating and exhalation during an event. Sweating would be the main source of fluid loss. Sweat being hypotonic (having a low number of solutes [e.g. electrolytes such as sodium]), a large fluid loss would have to accompany a clinically significant sodium loss. Yet, a literature review found no study that showed athletes with EAMC more dehydrated than controls (athletes of the same gender, competing in the same race with similar finish times).

What has been verified recently is altered neuromuscular control associated with repetitive activities that use either increased intensity above training levels or are involved in durations longer than conditioning levels. In other words, a repetitively used muscle fatiguing against a higher force/intensity demand or duration beyond its conditioning level could be a major component of localized muscle cramping.

Nervous system alterations occur in the muscle spindle and Golgi tendon organs. Signals from these afferents alter spinal muscle control by increased excitatory activity and decreased inhibitory activity in the motor loop. The resulting hyper-activity creates cramping. As some athletes are more prone to cramping, it cannot be ruled out that there is also a genetic component to EAMC.

Relief and Prevention

Passive stretching has been observed to alleviate EAMC. This could simply mean—stop actively contracting the muscle. Note that the anecdotal story includes, “when I backed off, it stopped cramping.”

As far as prevention, it appears that there may be several avenues open to athletes.

During training:

• Include progressively more intense and longer workouts to acclimate the muscle by duplicating or surpassing the intensity and distance of the race event

• Condition the affected muscles and muscle groups by increasing fatigue resistance

During the event:

• Reduce the force demands (such as shifting to a smaller gear in cycling)

Scot Willingham, MA, ACSM, CSCS, USAC is a neuromuscular re-educator that coaches cyclists and other endurance athletes while working as a strength and conditioning rehabilitation expert in NYC. He is a recent graduate of Teachers College, Columbia University’s Motor Learning department. Motor Learning is the field that researches human motor control and is used as the foundation for many pedagogical decisions in physical education, sports coaching, movement teaching and rehabilitation.

Further Reading: http://www.sportsscientists.com/2008/01/featured-series-on-science-of-sport.html)

References:

Maughan, R.J. (1991) Fluid and electrolyte loss and replacement in exercise. Journal of  Sports Sciences, 9:117-142, 1991.

Schwellnus, M.P. (2009). Cause of exercise associated muscle cramps (EAMC)—Altered neuromuscular control, dehydration, or electrolyte depletion?, British Journal of Sports Medicince,43: pp. 401-408.

Sulzer, N.U., Schwellnus, M.P. & Noakes, T.D. (2005). Serum electrolytes in Ironman triathletes with exercise-associated muscle cramping. MSSE, 28(5 Suppl): S167.

Talbott JH and Michelson J. “Heat cramps: a clinical and chemical study.” Journal of Clinical Investigation. 1933, Volume 12, p 533-49.