Posts Tagged ‘hyper-excitable motor nerve’

Exercise Associated Muscle Cramps

Monday, March 6th, 2017

Posted March 6, 2017

By Michelle Snow, MA, AT, CSCS

Muscle cramps are often associated with heat and dehydration. A 2003 study looked at the number of heat related illnesses during a football season. Seventy-three percent of these illnesses were related to muscle cramping.1  Dehydration has long been blamed as the cause of exercise associated muscle cramps (EAMC). The most common theory places blame on salty sweat removing electrolytes from the body.

However, if EAMCs are heat and dehydration related, why do people experience cramping during cold weather events or while swimming in cold water? And, why does stretching almost immediately relieve the EAMC?

Unfortunately, to date, very little evidence and research has found a cause for EAMC. Two theories have been developed to help explain what may contribute to cramping, the dehydration and electrolyte imbalance theory and the altered neuromuscular control theory.

Initially, it was believed fluid and electrolyte disturbances may cause EAMC. This theory hypothesized that sweating caused a loss of fluid and electrolytes. This would lead to contraction of the interstitial space and a loss of interstitial volume. The increase in surrounding ionic concentrations and mechanical deformation of the nerve endings leads to a hyper-excitable motor nerve and a spontaneous contraction.

The theory was based on observation that athletes who experienced EAMC would often have significant fluid and electrolyte losses at the time of the cramp.4 However, it has been shown that losses in fluids and electrolytes, plasma, blood volume and body weight are similar in individuals who experience EAMC and those who do not experience cramping. Even when given a sports drink that reflected individual fluid losses, approximately seventy percent of participants still experienced EAMC.2

Due to these discrepancies, the second theory regarding a neuromuscular etiology has the strongest support from current research. This theory hypothesizes that neuromuscular fatigue alters the reflex control mechanisms of both the muscle spindle and golgi tendon organ, eliciting muscle cramping.4

The muscle spindle responds to length changes in the muscle. As length increases, the muscle spindle increases impulses to the agonist muscle to contract and decreases impulses to the antagonist muscle so it relaxes. The golgi tendon responds to length changes in the tendon and causes the agonist muscle to relax. Both work together to protect the muscle from over stretching. However, with fatigue, it has been noted that the muscle spindle activity increases while the golgi tendon activity decreases.2 This may explain why muscle cramps occur later in activity once the muscle has fatigued.

In most studies, fatigue has been the most common contributing factor to muscle cramping. This may be caused by an increase in exercise intensity and/or duration. It has also been found that those who have a history of EAMC are more likely to cramp again during other bouts of exercise. Current injury or previous history of injury may also play a role in EAMC. And, it has been found that male athletes are more likely to cramp than female athletes due to the greater proportion of fast-twitch fibers4.

The most effective treatment for acute fatigue-induced muscle cramps is static stretching of the affected muscle. It is thought that static stretching activates the golgi tendon organ by increasing tension in the tendon, causing increased afferent reflex inhibition.4  While the old method of using pickle juice may not change the blood plasma concentrations of electrolytes, it has been found that the acetic acid in pickle juice may trigger a reflex that increases neurotransmitter inhibition to cramping muscles.3 This has been found to effectively shorten the duration of EAMC.

However, it may not be an effective treatment for athletes who develop stomach duress or acid reflux after consumption. Even though there is little evidence to support the dehydration-electrolyte theory, it is still recommended that athletes remain hydrated to prevent heat illness. It is important to continue to recommend athletes to consume enough fluid so that not more than two percent of body weight loss occurs due to perspiration.

Other treatments have been recommended, however, little research has been completed to determine how effective they may be. Plyometric exercises and eccentric exercise may be incorporated for athletes who chronically experience muscle cramps. One study looked at strengthening the gluteus medius to help an athlete who struggled with hamstring muscle cramping. With the agonistic relationship of the hamstring and the gluteus medius, it was proposed that the weak glut might increase the amount of work the hamstring needed to do,  fatiguing the hamstring more quickly. The athlete targeted in this study was able to complete 3 triathlons without EAMC following 3 weeks of the targeted strengthening.4

Further research is needed to explain what causes exercise associated muscle cramps. Fatigue plays a significant role in muscle cramping. However, it does not explain how some athletes experience cramps, while others do not. The most effective treatment is static stretching of the affected muscle.

Resources

1. Cooper, E. R., Ferrara, M. S., Broglio, S. P. (2006). Exertional Heat Illness and Environmental Conditions during a Single Football Season in the Southeast. Journal of Athletic Training, vol. 41, 332-336.

2. Miller, Kevin. The Neurological Evidence for Muscle Cramping. NATA Symposium, June 2011, New Orleans Convention Center, New Orleans, LA. Conference Presentation.

3. Miller, K. C., Mack, G. W., Knight, K. L., Hopkins, J. T., Draper, D. O., Fields, P. J., Hunter, I. (2010). Reflex Inhibition of Electrically Induced Muscle Cramps in Hypohydrated Humans. Medicine and Science in Sports and Exercise, vol. 42, no. 5, 953-961.

4. Nelson, N. L., Churilla, J. R. (2016). A Narrative Review of Exercise-Associated Muscle Cramps: Factors that Contribute to Neuromuscular Fatigue and Management Implications. Muscle and Nerve, vol. 54, no. 2, 177-185.

 

Save

Save

Save