New York Flyers: News on the Run: Muscle Cramping During Exercise

Reyna F

A common sports nutrition question I receive is about muscle cramping. We have all experienced it and it is not a pleasant feeling. I can tell you exactly when I will get a muscle cramp. In late March, when I do my first long, hard bicycle ride of more than fifty miles, I will get a cramp in my calf sprinting up the hill on Hudson Terrace. Why does this occur? It will be obvious if you continue reading.

WHAT IS A MUSCLE CRAMP?

Muscle cramping is a common, painful, physiological disturbance of skeletal muscle. Many athletes are regularly frustrated by exercise-induced muscle cramp (EIMC) and until recently there have been few scientific studies on the topic. When I first researched the topic in 2005, I found only two current scientific studies and one review article on the topic. Since then, the number of studies have increased and the results have been similar. Meanwhile, there has been a perpetuation of myths as to the cause and treatment of EIMC.

Why do we sometimes experience muscle cramps while exercising? Is it due to dehydration, not enough to eat, insufficient training, or some other reason? Here is my attempt to find the truth of what causes muscle cramps and how they can be prevented.

Is it dehydration? First is a study of ten male cyclists who cycled for 30 minute bouts who were hypohydrated (under hydrated) with a loss of an average of 3% of their bodyweight. This study found that mild hypohydration with minimal neuromuscular fatigue does not seem to predispose individuals to cramping. Thus, cramps may be more associated with neuromuscular fatigue than dehydration/electrolyte losses. The effect of greater fluid losses on cramp threshold frequency needs to be researched. In addition, this was an extremely small subject group of only males. (Med Sci Sports Exerc. 2010 Nov;42(11):2056-63). Three percent hypohydration does not affect threshold frequency of electrically induced cramps. Miller KC, Mack GW, Knight KL, Hopkins JT, Draper DO, Fields PJ, Hunter I.)
Is it electrolytes? In a study researching triathletes suffering from EIMC after the 2000 South African Ironman Triathlon, eleven athletes formed the cramping group. Nine non-cramping triathletes were matched for race finishing time and body mass formed the control group. Post-race sodium concentration was significantly lower in the cramping group than the control group but was within the normal clinical range of post-race serum sodium concentrations. There were no significant differences between the two groups for post-race serum electrolytes, glucose, hemoglobin concentrations or hematocrit. The authors of the study concluded that acute EIMC in Ironman triathletes is not associated with a greater percent body mass loss or clinically significant differences in serum electrolyte concentrations. The increased EMG activity of cramping muscles may reflect increased neuromuscular activity. However, this is another example of a small subject group. (Medicine, Science and Sports Exercise 2005 July;37(7):1081-5)

Is it electrolytes and hydration? Another study researched whether EIMC in distance runners is related to changes in serum electrolyte concentrations and hydration status. Seventy-two runners participating in an ultra-distance road race were followed up for the development of EIMC. Twenty-one runners who suffered from acute EIMC during the race formed the cramp group, while 22 runners with no history of EIMC during the race formed the control group. There were no significant differences between the two groups for pre-race or post-race body weight, per cent change in body weight, blood volume, plasma volume, or red cell volume. The immediate post-race serum sodium concentration was significantly lower in the cramp group than in the control group. The immediate post-race serum magnesium concentration was significantly higher in the cramp group than in the control group. The study authors concluded that there are no clinically significant alterations in serum electrolyte concentrations and there is no alteration in hydration status in runners with EIMC participating in an ultra-distance race. (British Journal of Sports Medicine 2004 Aug;38(4):488-92)

In a study of Ironmen racers, 43 out of 209 triathletes reported EIMC and were compared to the 166 who did not report EIMC after an Ironman. There were no significant differences between groups in any pre-race-post-race serum electrolyte concentrations and body weight changes. The development of EIMC was associated with faster predicted race times and faster actual race times, despite similarly matched preparation and performance histories in subjects from both groups. A regression analysis identified faster overall race time (and cycling time) and a history of cramping (in the last 10 races) as the only two independent risk factors for EIMC.

The results from this study add to the evidence that dehydration and altered serum electrolyte balance are not causes for EIMC. Rather, endurance runners competing at a fast pace, which suggests that they exercise at a high intensity, are at risk for EIMC. (Br J Sports Med. 2011 Jun;45(8):650-6. Epub 2010 Dec 9. Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. Schwellnus MP, Drew N, Collins M.)

WHAT DOES THIS MEAN ABOUT FOR THE ELECTROLYTE AND HYDRATION HYPOTHESIS?

A review of the four human studies that evaluated hydration and electrolyte status, and although two out of the four had an extremely small sample size, shows that they all concluded hydration and electrolyte status do not have a significant impact on EIMC. Obviously more research in this area is necessary.

To support this, I found the most recent review article on the topic. Review articles are always interesting to read since they summarize the scientific studies on a specific subject. The review examined current scientific evidence in support of (1) the "electrolyte depletion" and "dehydration" hypotheses and (2) the "altered neuromuscular control" hypothesis in the aetiology of EIMC.

Scientific evidence in support of the "electrolyte depletion" and "dehydration" hypotheses for the aetiology of EIMC comes mainly from 18 anecdotal clinical cases, and one small (n = 10) case-control study. Results from four prospective cohort studies do not support these hypotheses. The reviewer surmised that the "electrolyte depletion" and "dehydration" hypotheses do not offer plausible pathophysiological mechanisms with supporting scientific evidence that could adequately explain the clinical presentation and management of EIMC.

Scientific evidence for the "altered neuromuscular control" hypothesis is based on results from research studies in human models of muscle cramping, epidemiological studies in cramping athletes, and animal experimental data. Schwellnus concluded that the “altered neuromuscular control” hypothesis is the likely cause of EIMC. (Br J Sports Med. 2009 Jun;43(6):401-8. Epub 2008 Nov 3. Cause of exercise associated muscle cramps (EIMC)--altered neuromuscular control, dehydration or electrolyte depletion? Schwellnus MP.)

Ok. So now we know EIMC is probably not caused by dehydration or electrolyte depletion. What evidence do we have that it is something else? Here is a study for our Ironmen and women.

A case-control study of 433 Ironmen found those who self-reported EIMC were taller, heavier, and had faster Ironman times. What I found interesting was an association among a positive family history for EIMC and a history of tendon and/or ligament injuries. This study concluded that a history of EIMC is associated with:

(1) exercising at a higher intensity during a race that may result in premature muscle fatigue,
(2) an inherited risk (positive family history), and
(3) a history of tendon and/or ligament injury.
(Clin J Sport Med. 2011 May;21(3):204-10. Factors associated with a self-reported history of exercise-associated muscle cramps in Ironman triathletes: a case-control study. Shang G, Collins M, Schwellnus MP.)

Now a study for the ultra runners of the club. Out of 49 runners participating in a 56 km race, 20 runners reported EIMC (EIMC group) during or within 6 hours after the event. Runners in the EIMC group tended to report on average longer training sessions during the 3 days before the race. Significant risk factors for EIMC were a past history of EIMC, faster running pace at the early stage of a race (28km split) and possibly pre-race muscle damage. (Br J Sports Med. 2011 Nov;45(14):1132-6. Epub 2011 Mar 13. Increased running speed and pre-race muscle damage as risk factors for exercise-associated muscle cramps in a 56 km ultra-marathon: a prospective cohort study. Schwellnus MP, Allie S, Derman W, Collins M.)

For those who prefer technical explanations, I have one for you too. Disturbances at various levels of the central and peripheral nervous system and skeletal muscle are likely to be involved in EIMC and may explain the diverse range of conditions in which cramp occurs. Disturbance in the activity of proprioceptors may occur through faulty posture, shortened muscle length, intense exercise and exercise to fatigue, resulting in increased motor neuron activity and motor unit recruitment. (Sports Medicine 1996 Jun;21(6):409-20)

SO WHAT DOES THIS ALL MEAN?

There is greater evidence supporting the theory that EIMC is due to tight muscles, muscle fatigue, a history of tendon and/or ligament injury, exercising at a high intensity and/or family history vs. hydration and electrolyte theories.

It doesn’t mean the hydration and electrolytes are not important. Although they may not impact EIMC, they are essential for many other muscular and bodily functions.

WHAT CAN WE DO TO PREVENT EIMC?

You can’t change your family or injury history. But you can do some things to prevent EIMC. According to some researchers, the key to prevention of EIMC is to reduce the risk of developing premature muscle fatigue. (Clin Sports Med. 2008 Jan;27(1):183-94, ix-x. Muscle cramping in athletes--risk factors, clinical assessment, and management. Schwellnus MP, Drew N, Collins M.)

How do you do that? By proper training and conditioning that includes weight lifting and stretching. If you bike ride, make sure you are positioned properly on your bicycle. This can be done by going to a bike fit specialist.

WHAT SHOULD YOU DO IF YOU GET EIMC?

The most effective immediate management of EIMC is rest and passive stretching. (Clin Sports Med. 2008 Jan;27(1):183-94, ix-x. Muscle cramping in athletes--risk factors, clinical assessment, and management. Schwellnus MP, Drew N, Collins M.)