Water and electrolyte balance are important for the function of all organs. Water provides the medium for biochemical reactions within cell tissue and is essential for maintaining an adequate blood volume. Each body water compartment contains electrolytes. Sodium chloride is the main electrolyte in sweat, with potassium, magnesium and calcium also present in smaller quantities.
Exercise associated muscle cramps (EAMC) are one of the most common problems encountered by medical staff at endurance events, such as marathons and triathlons. EAMC is defined as a painful spasmodic involuntary contraction of skeletal muscle that occurs during or immediately after exercise. Several researchers claim that ‘heat cramps’ or ‘sweat cramping’ and EAMC are defined differently, defining heat cramping as sustained, spreading, sharply painful muscle contractions, describing the end of the continuum of EAMC.
Several theories have been proposed to explain the cause and course of treatment of muscle cramps during exercise. However, it does not seem that there is conclusive evidence to support any of the proposed arguments and the area remains under controversy and misconception. Two main theories are proposed:
Dehydration and serum electrolyte theory
Muscle cramps related to exercise, were first reported over 100 years ago in laborers working in hot, humid environments such as mines and steamships. These laborers added salt to their drinks to relieve EAMC, leading to the electrolyte and dehydration hypotheses. However, these reports were based on anecdotal evidence alone and no mechanism was proposed to explain how serum electrolyte imbalances can result in muscle cramping. In addition, hydration status and electrolyte balance were not measured.
Mechanisms in cramping remain unclear. It is proposed that large sodium losses in sweat contribute to cramping by contracting the extra-cellular fluid space and may change ion channels to make neuromuscular junctions or muscle units hyper-excitable, causing involuntary and sustained contractions. A study by Stofan et al in 2005, tested the hypothesis that NCCA football players prone to heat cramps lose more fluid and sodium through sweating. 10 football players were recruited for the study; five of them had a history of cramping, while 5 served as controls. Sweat loss, sweat electrolytes and fluid intake were measured during a pre season two a day practice session. Athletes in the cramping group did not incur a larger fluid deficit than the non cramping group, their sweat rate was higher, and their sodium intake greater. During the season, the cramping group experience several cramping episodes despite high sodium intakes. The researcher’s results did not fully support their hypothesis, yet they indicated that sodium supplements are needed to prevent cramps.
Although EAMC is often associated with exercise in the heat, cramping has also been reported in cold conditions without an increase in core temperature. In addition, extreme cold has been associated with EAMC in swimmers, passive heating alone does not result in cramping, and cooling does not relieve muscle cramps. On the contrary, cooling can make muscle cramps worse.
Sodium levels within the extra-cellular fluid should remain within a range of 130-160mmol/l to keep cells, tissues and organs functioning properly. The body has appropriate defense mechanisms to protect against the development of a sodium deficit during exercise, releasing sodium from internal body stores. Contraction of the extra-cellular fluid volume by as little as 1L (~7%) can release 140mmol of sodium.
It has been argued by several researchers that EAMC has not been associated with a significant change in serum electrolytes and hydration status in triathletes and runners. A research study by New-Butler et al in 2006, examined whether athletes who ingest additional sodium during an Ironman event maintain higher sodium than those that do not. 145 athletes competing in the 2001 South Africa Ironman took part in the study, and were divided into an experimental group and control group. The experimental group was handed 40 tablets with 620mg sodium chloride each, while the control group was handed 40 placebo tablets. Athletes were advised to consume 1-4 tablets every hour. The sodium supplements did not change serum sodium response, indicating that additional sodium supplements are not needed during Ironman events to maintain sodium within the normal range. Clinical measures of dehydration were not different between groups.
Muscle fatigue theory
Skeletal muscle cramping is an abnormality of skeletal muscle relaxation. It has been suggested that EAMC is the result of altered alpha-motoneuron activity, possibly resulting from an imbalance between muscle spindle and Golgi tendon organ discharge associated with fatigue. With high intensity muscle activity and fatigue, muscle spindle output is increased, leading to an increased motoneuron activity.
It is suggested that EAMC occurs only in muscles that were involved in repetitive contractions. The majority of runners with complaints of EAMC report a subjective feeling of muscle fatigue before the onset of cramping. This suggests that EAMC is a result of an abnormality of neuromuscular control at the spinal level in response to intense, fatiguing exercise. Muscle fatigue disrupts the functioning of the peripheral muscle receptors by causing an increased firing rate of type Ia and II muscle spindle afferents, as well as decreasing the type Ib afferent activity from the golgi tendon organs.
It is documented that the muscles prone to cramping span across two joints, and it has been observed that cramping can occur when muscles are in a shortened position. This will decrease the tension in the tendons of the muscle during contraction and further decrease the inhibitory afferent activity from the type Ib afferent of the golgi tendon organ. Passive stretching is the most effective therapy to relieve acute muscle cramping as it increases muscle tension.
A survey of 1300 marathon runners found that older age, longer history of running, higher body mass index, shorter daily stretching routine and a family history of cramping were all related to EAMC. In addition, high intensity running, long duration, subjective muscle fatigue and hill running were identified as specific conditions associated with EAMC.
It is suggested that hydration and electrolytes may help prevent EAMC’s up to a certain threshold of muscular fatigue. It is hypothesized that beyond that specific personal threshold, hydration and electrolyte supplements will not be an effective strategy to prevent EAMC. Those that support the dehydration and sodium electrolyte theory aim to differentiate between heat cramps, or sweat cramps, and exercise associated muscle cramps. However, the definitions provided do not seem to differ significantly, creating confusion.
Reading countless research articles and talking to many athletes led me to support the muscle fatigue theory. One athlete mentioned that he got cramping in his hip flexors transitioning from cycling to running while racing. After reviewing his bike fit, it turned out that his saddle was too far forward, causing those muscle to over work. Other athletes mentioned they get cramping towards the end of an event, once again supporting the muscle fatigue hypothesis.
Unfortunately, there are no suggested prevention methods or treatment options for fatigue induced EAMC. It seems that incorporating an adequate stretching routine in the athletes’ training program and perhaps strengthening of the muscles that are susceptible to cramping may help as a preventative measure.
Just because I do not believe muscle cramps are related to sodium levels, does not mean that sodium replacement during endurance events is not important... However, you get all the electrolytes you need from your sports drink and there is no need to take sodium pills as well.
The next related questions are how much sodium is needed during endurance events? How much water? How much weight is it safe to lose? Is it normal to gain weight during an Ironman event? All materials for future posts...
Comments and questions are more than welcome :)
2 comments:
Great post Noa. Worth the wait. I would be interested in hearing more about the stretching/strengthening of vulnerable muscle groups. Also, is there a downside (other than cost) to taking electrolyte supplements as an insurance policy?
Thanks Dave. I think the main thing is to make sure you have done the right amount, and kind of training prior to your race. I don't think there is a need to take extra electrolyte supplements, other than your sports drink during a race as an insurance policy. I typically recommend athletes take a few salt tabletes with them, just in case, but thats mainly for the placebo effect... Increasing serum sodium above normal levels may lead to dehydration, while diluting serum sodium will lead to hyponatremia... its a very fine balance! More on that in another post, sometime in the next couple of weeks :)
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