Muscle Cramps: Hydration, Salt and Fatigue

The heat and humidity this summer has many of our clients suffering from muscle cramps. Looking at past research and theories on muscle cramps, we must conclude that the elusive question of what causes muscle cramps remains unanswered.

The three main causes cited for causing EAMC (Exercise Associated Muscle Cramps) are:

  • Loss of serum electrolytes (sodium, potassium, magnesium, chloride, calcium) because of dehydration.
  • Pre-mature muscle fatigue caused by performing exercise at a higher relative exercise intensity or duration, when compared with normal training.
  • Inhibited range of motion as a result of tight muscles.

The loss of serum electrolytes happens when you train and neglect to consume enough fluids. This dehydration occurs in all weather, training intensity, or terrains. However, it is most detrimental when you train in hot, humid conditions.  It is detrimental because electrolytes are lost through sweat and perspiration.  Electrolytes are a group of ions required by the body to stimulate multiple neurological reactions. The five primary electrolytes are sodium, potassium, chloride, magnesium and calcium. Sodium, potassium and chloride are the most important for muscle contraction.
Many people believe all muscle cramps can be explained by a lack of potassium, but most physiologists do not.

While there is no replicated scientific evidence to date, most scientists believe it is the depletion of sodium and chloride, that causes cramping because of the role they play in maintaining fluid balance in the body. How does depletion of sodium and chloride effect training? As an athlete exercises for an extended duration in hot weather, their core body temperature increases. This leads to dehydration. Blood pressure will decrease, and the heart rate rises. One of the ways the body tries to compensate for this is to release hormones that increase sodium permeability in the kidneys. This, in turn, increases the uptake of water into the kidney. These combined responses slow the decrease in blood pressure, and the body reserves water and sodium for necessary core body functions. When there is a higher percentage of water in and outside of cells than electrolytes, athletes experience hyponatremia. This disrupts the balance of electrolytes inside and outside of cells, causing a decrease in neural signals within the muscle, thus decreasing performance.

The only instance I found that may somewhat support the theory that sodium loss causes EAMC was a case report of an experienced triathlete during the course of the Western Australian Ironman Triathlon. The athlete’s sodium levels stayed relatively the same from before the start of the race to transition number two. However, from transition number two to the end of the race, the athlete lost 2% of his body weight due to fluid loss. “The athlete slowed during the run phase of the race after his core temperature rose to critically high levels.  As he slowed and his core temperature increased, there was an unusually rapid reduction in blood sodium that preceded cramping, despite presenting with signs of dehydration.” (5)

Other studies have hypothesized a decreased serum sodium concentration would cause muscle cramping but have proved to be inconclusive (2, 4). Noakes et. al. studied Ironman South Africa athletes to analyze serum electrolyte levels, and even though the decrease in sodium concentrations was significant, the difference compared to a control group was within the normal clinical range of post-race serum sodium concentrations. They were unable to correlate decreased sodium concentration to an increase in exercise-associated muscle cramping. Instead, they concluded “the increased activity of cramping muscles post-race may reflect increased neuromuscular activity.”(2)

The second hypothesized cause of EAMC, is pre-mature muscle fatigue.  “No mechanism explains how such imbalances in serum electrolytes result in localized muscle cramping. The “muscle fatigue” hypothesis suggests that EAMC is the result of an abnormality of neuromuscular control at the spinal level in response to fatiguing exercise. The development of premature muscle fatigue appears to explain the onset of EAMC.”(3) The diagnosis of EAMC is made clinically, and the most effective immediate management of EAMC is rest and passive stretching. The key to the prevention of EAMC is to reduce the risk of developing premature muscle fatigue. (6)

Hunter Allen, a USA cycling Level 1 coach, agrees that rest and stretching are the best way to prevent muscle cramps. If you exercise your muscles when they are already in a stretched (weakened) state, you will not gain fitness or strength. As you exercise without stretching, your muscles will become tight and they aren’t able to work in the range of motion necessary for optimal muscle recruitment. If you add the extreme conditions and intensity of a race, the muscles may not be able to respond without cramping. He recommends massage and yoga to keep muscles open.

You can’t use a “one size fits all” approach to muscle cramping since the cause will vary person to person. A veteran Ironman-distance triathlete could complete in an extremely hot and humid Austin 70.3 and need 2L of IV at the finish, but never get muscle cramps.  However, someone new to endurance racing could race a sprint triathlon in the same conditions and complain of calf cramps during the run.

The best prevention of exercise-associated muscle cramping would be:

  • Sodium load during taper week:  This has to be customized per diet and hydration plan. I wont give general recommendations here. I have athletes use The Right Stuff and pre-drink the week prior so the body has time to absorb and manage total fluid status.
  • Drink 16 ounces of an electrolyte drink such as nuun before your workout in hot conditions, and sip an electrolyte drink during workouts lasting 60 minutes or longer in hot conditions. To prevent bloating and discomfort, the electrolyte drink should be non-carbonated and have low concentrations of carbohydrate. Carbonation and high sugar content inhibits the digestion and absorption of the electrolytes and glucose.
  • If you usually eat a low-sodium diet, speak with your doctor about adding salt to your meals on the days you work out for 60 minutes or longer in hot conditions. If your diet consists of packaged foods and eating out, you consume enough salt to compensate for loss during exercise and should not add it to your meals.Work with a Sports Nutritionist to create a customized training nutrition plan. They will help you determine the amount of gels, chomps, water, and electrolyte drink you should be consuming per workout.
  • Avoid pre-mature muscle fatigue by:
    •  Scaling down your workouts during hot and humid conditions: Don’t force the pace of a run even if it was scheduled to be a sub-threshold workout. Your heart rate will naturally be higher as the mercury rises, so if it’s in the ‘endurance’ zone instead of the ‘recovery’ zone during your warm-up, back-off and adjust the workout even though you feel like your exertion level is low.
    • Staying loose: Befriend a foam roller and use it religiously, attend yoga class, or get a massage.
    • Avoiding weekend warrior syndrome: If you haven’t been riding your bike all summer and decide to head out on a four hour ride in 93’ temps with 90% humidity, you are setting yourself up for muscle fatigue and nail-biting muscle cramps.

What to do when you get a cramp?  Once you get a cramp, you cannot make it disappear right away. This is why prevention is key. Most cramps are relieved through light stretching, massage, and hydration.

During a race, walk through the aid stations, sip de-fizzed cola, and stretch the affected area. If you feel a stitch in your side during a run, try to slow your rate of breathing and consciously breathe deeper into your abdominal cavity or reach hands overhead to stretch the affected side.  You can try to run through a stitch if you can manage the discomfort. Cramps in the quadriceps or calves should be slowly stretched and massaged as well, followed by suggested prevention tips above.

1.    Laursen PB, Watson G, Abbiss CR, Wall BA, Nosaka K.  Hyperthermic fatigue precedes a rapid reduction in serum sodium in an Ironman triathlete: a case report. Int J Sports Physiol Perform. 2009 Dec, 4(4):533-7.
2.    Sulzer NU, Schwellnus MP, Noakes TD. Serum electrolytes in Ironman triathletes with exercise-associated muscle cramping. Med Sci Sports Exerc. 2005 Jul, 37(7):1081-5.
3.    Schwellnus MP. Muscle cramping in the marathon: aetiology and risk factors. Sports Med. 2007, 37(4-5):364-7.
4.    Maughan RJ. Exercise-induced muscle cramp: a prospective biochemical study in marathon runners. J Sports Sci. 1986 Spring, 4(1):31-4.
5.    Laursen PB, Watson G, Abbiss CR, Wall BA, Nosaka K. Hyperthermic fatigue precedes a rapid reduction in serum sodium in an Ironman triathlete: a case report. Int J Sports Physiol Perform. 2009 Dec, 4(4):533-7.
6.    Schwellnus MP, Drew N, Collins M.  Muscle cramping in athletes–risk factors, clinical assessment, and management.  Clinical Sports Med. 2008 Jan, 27(1):183-94, ix-x.
7.    Hunter Allen’s theory on cramping

Semantics of Hydration

cross published: Trifuel
Recently while running up Pikes Peak,  I came upon a fellow with good intentions explaining hydration to a woman who was new to mountain running. He said: “You don’t need to carry water with you during the race, they have plenty of aid stations. Besides, most people over-hydrate anyway.” In this particular instance, this man was referring to drinking too much water as being overhydrated, but using the phrase “overhydrate” without explanation of or differentiation between water and electrolytes can give two very different implications.

The problem with telling an athlete unfamiliar with the semantics of hydration is that the person receiving this message, might interpret that to mean they should not drink a lot during the race. However, telling them to drink an electrolyte and carbohydrate drink when they are thirsty is a completely different message. This question of semantics might not make a difference to an experienced athlete who uses the term hydration interchangeably with drinking electrolytes, but for someone new to running at altitude, it should be clarified. Dr. Tim Noakes, one of the initial authors involved in creating protocols for hydration recommendations in endurance sports, has now done an about face in his latest book “Waterlogged” published in 2012. This article does not delve into the controversial debate surrounding the book, but instead focuses on differences in terminology related to hydration status.

Semantics are important when it comes to hydration to distinguish between two common terms associated with sweating: dehydration and hyponatremia. Differentiating terminology related to over and under consuming fluids and the concern for each is important. Consuming an insufficient amount of water that results in total body water weight loss is a condition called dehydration. Drinking too much water during exercise can cause water intoxification, (exercise associated hyponatremia (EAH)), a condition defined by dangerously low serum sodium levels. The media has used the terms dehydration and exercise associated hyponatremia (EAH) to mean the same and in doing so it has falsely led readers to assume that the symptoms for the two different conditions are the same. Due to specific events like the Boston Marathon which gained a lot of hype and press in 2002 when athletes over consumed water and/or total fluid including carbohydrate beverages, guidelines have been created and recommendations on fluid intake have been updated.

Dehydration, or insufficient water status in the body, is important because water makes up 45% – 75% of our body weight (60% average) and is tightly regulated to within 0.2 – 0.5% of our daily body mass. A reference range is used because each person’s water mass percentage will vary depending on fluid consumption and body composition. The more lean mass and glycogen stores a person has, the higher the percentage of water in body composition. The main symptom of mild dehydration is thirst, but as the percentage of water loss increases, perceived exertion, core temperature, and heart rate may increase.

The goal of hydration plans is not to prevent weight loss but to reduce the amount of it. There has been debate whether or not dehydration affects performance, and each person’s tolerance to it will vary. It is recommended that athletes minimize weight loss to 2 – 3% of body weight in exercise lasting longer than 90 minutes. Many professional marathon runners accumulate much higher percentages of body weight loss than the recommendation without perceived decrement to their performance. However, the physiological adaptations that take place as a result of their training in combination with the elevated threshold for discomfort elite athletes exhibit; make them the minority, not the norm.

Determining accurate water loss using sweat rates is difficult since there are several sources of error, including respiratory loss of water and water as a byproduct of the breakdown of glycogen, fat, and protein. In addition, sweat rates focus on the loss of body weight which can be altered without a change in body water status. However, sweat rates are the least burdensome for athletes to use to measure body water status and can provide approximations for a variety of environments and intensities of training.

Exercise associated hyponatremia (EAH) can occur when a person is in a state of water balance or water deficit (dehydration), but it is usually associated with excessive water intake. In general, if a person consumes an electrolyte beverage when they are thirsty, EAH can be avoided. However, if a person drinks electrolyte containing beverages excessively (as if trying to prevent sweat loss), they can experience EAH. Exercise associated hyponatremia is usually asymptomatic and even though we usually associate excessive intake of water with weight gain, many times there is no change in body weight. The only way to diagnose EAH is to have your blood drawn for evaluation of sodium levels. Exercise associated hyponatremia is diagnosed when serum sodium levels fall below 135 mmol/L. Symptoms of EAH include feeling bloated, a ‘puffy’ appearance, nausea, and vomiting. These are all symptoms that can be experienced from simply participating in an endurance event. EAH is not a condition one would experience after a normal training day, so just because you feel bloated, you most likely are not experiencing EAH. Studies have found that even a moderate intake of sodium as part of a carbohydrate electrolyte drink prevented dramatic changes in serum sodium levels, and sodium intake while exercising in the heat is necessary in preventing EAH due to sodium loss that occurs when an athlete tries to match fluid intake with sweat loss.

The balance of water inside and outside of cells in relation to the concentration of sodium and chloride determines sodium balance. Hew-Butler et al. found that athletes who lost up to 3.8% of their body weight after Ironman South Africa (2006) still maintained serum sodium and plasma volume, showing us that our bodies work to maintain the balance of water, sodium and chloride inside and outside of cells. Weight loss >4% may result in a disturbance to sodium balance however, this depends on sex, amount and type of fluid ingested during event, and sweat rate. Pahnke et al. found that men had a higher overall sweat rate than women during the 2003 Hawaii IronmanⓇ Triathlon World Championship in Kailua-Kona, Hawaii and women on average drank more of a sodium containing beverage than the men, which attenuated their decline in sodium levels. Out of the men and women who completed this race, those that lost >4% body weight did not show a significant change in their serum sodium concentrations. The average concentration of sodium per pound of sweat is 400 – 500 mg, but it can range as high as 1100 mg. This large degree of variability is why it is difficult to make definitive recommendations about the use of salt tablets.

Some research has shown sodium supplementation does not affect sodium loss or performance during a 12.5 hour Ironman competition but it did minimize total weight loss in subjects who consumed 700 mg/hr salt compared to those that did not during Ironman South Africa. In addition, in the same race, none of the athletes that finished the race had EAH defined as < 135 mmol/L sodium regardless if they consumed a salt tablet or not. Most athletes did not fully replace or match fluid intake with loss. This is important because if they did try to match loss through intake, serum sodium levels most likely would have decreased. However, by not matching sweat loss with fluid intake, their kidneys preserved sodium concentration levels while total body mass (mostly water) decreased. Many professional Ironman athletes positively attribute their success in Kona, HI to salt supplementation during the race. The training and acclimatization that a professional athlete does in preparation for Kona cannot be compared to an age group triathlete with less fitness, experience, and who trains in a different environment.

Key points:

  • Monitoring your sweat rate is a great way to follow trends in your rate of water loss from different types and duration of workouts and also comparing the same workout in two different environments; however, it is very easy to become caught up in the numbers and almost obsessed with fluid in and fluid out. Don’t try to make this equation equal to zero.
  • Instead of fighting your sweat rate, accept it and learn to become comfortable with it. Yes, we want to drink as much fluid and electrolytes as is comfortable within reason, but the other half of this is that you also have to train. You have to train enough that your body acclimates to the environment (e.g., hot and humid) and you mentally learn to manage the discomfort of sweating.
  • Hydrating in advance of training and rehydrating 24 – 48 hours in advance and after workouts in which you lose > 2% body weight is important. You can work with a sports nutritionist or dietitian to determine how much and what types of fluid to use, but in general, you should replace 24 oz (750 ml) per pound of weight lost. Drink these fluids throughout the day and not in one sitting. During this time, urine color is not necessarily an accurate indicator of hydration status.
  • To enhance hydration status the week preceding a half or full Ironman distance race in a hot and humid environment, consume electrolytes (calcium, magnesium, potassium, sodium and chloride) in addition to water. These will enhance total body water status.
  • Replenishing glycogen stores will also enhance hydration status since up to three grams of water is drawn into cells and stored in muscle bound to a gram of glycogen. Carbohydrate loading may not be necessary to accomplish this. It depends what kind of nutrition plan you are currently following (e.g., low carbohydrate or paleolithic) and the training you completed the week before your event.
  • There are different opinions on using thirst as a reminder to drink. Consuming a carbohydrate beverage that contains sodium has shown to increase palatability and stimulate thirst (McKinley). From our experience we have noticed that thirst works for lower intensity workouts completed in moderate environments for shorter durations. When it comes to a half or full ironman distance triathlon, fatigue and fitness of the athlete can affect their ability to recognize when they are thirsty. Sometimes their mental status is skewed due to fatigue or low energy intake and they don’t recognize thirst.
  • The efficiency at which you sweat increases with fitness, so you may notice that as soon as you step outside on a hot and humid day, you begin to sweat buckets. This is good – your natural AC is turning on!

Regina Hammond has a Master’s Degree in Sports Nutrition and works for Trismarter Triathlon Coaching and Nutrition ( Staying abreast of the latest research she believes in an individualized approach to nutrition. With a background in competitive swimming, biking and running, she understands what it takes to be a competitive triathlete and works with clients on performance fueling plans, periodized nutrition plans, weight loss, and behavior change.


  • Almond, C.S., Shin, A.Y., Fortescue, E.B., Mannix, R.C., Wypij, D., et al. Hyponatremia among runners in the Boston Marathon. N Engl J Med. 2005;352:1550-1556.
  • Anastasiou et al. Sodium Replacement and Plasma Sodium Drop During Exercise in the Heat When Fluid Intake Matches Fluid Loss. Journal of Athletic Training. 2009;44(2);117-123.
  • Speedy, D.B., Thompson, J.M., Rodgers, I., Collins, M., Sharwood, K., Noakes, T.D. Oral salt supplementation during ultradistance exercise. Clin J Sport Med. 2002;12:279–84.
  • Hew-Butler, T.D., Collins, M., Bosch, A., Sharwood, K., Wilson, G., Armstrong, M., et al. Maintenance of plasma volume and serum sodium concentration despite body weight loss in Ironman triathletes. Clin J Sport Med. 2007;17:116–22.
  • Hew-Butler, T.D., Sharwood, K., Collins, M., Speedy, D.B., Noakes, T.D. Sodium supplementation is not required to maintain serum sodium concentrations during an Ironman triathlon. Br J Sports Med. 2006;40:255–9.
  • Speedy, D. B., Noakes, T. D., Rogers, I. R., Thompson, J. M., Campbell, R. G., Kuttner, J. A. et al. Hyponatremia in ultradistance triathletes. Medicine and Science in Sports and Exercise. 1999; 31,809–815.
  • Rehrer, N.J. Fluid and electrolyte balance in ultra-endurance sport. Sports Med. 2001;31:701–15.
  • Speedy, D.B., Noakes, T.D., Kimber, N.E., Rogers, I.R., Thompson, J.M., Boswell, D.R., et al. Fluid balance during and after an Ironman triathlon. Clin J Sport Med. 2001;11:44–50.
  • Institute of Medicine. Dietary Reference Intakes for Water, Sodium, Chloride, Potassium and Sulfate, Washington, D.C: National Academy Press, pp. 73-185, 2005.
  • Hew-Butler, et al. Statement of the Second International Exercise-Associated Hyponatremia Consensus Development Conference, New Zealand, 2007. Clin J Sport Med. 2008;18:111–121.
  • Greenleaf, J.E. Problem: thirst, drinking behavior, and involuntary dehydration. Med Sci Sports Exerc. 1992;24:645–656.
  • Noakes, T.D. Fluid replacement during marathon running. Clin J Sport Med. 2003;13:309–318.
  • Olsson, K. E., & Saltin, B. Variation in total body water with muscle glycogen changes in man. Acta Physiologica Scandinavica. 1970;80,11-18.
  • Maughan, R.J., Shirreffs, S.M., Leiper, J.B. Errors in the estimation of hydration status from changes in body mass. J Sports Sci., 2007 May;25(7):797-804.
  • Pahnke, M.D., Trinity, J. D. Zachwieja, J. J., Stofan, J. R., Hiller, W.D., Coyle, E. F. Serum Sodium Concentration Changes Are Related to Fluid Balance and Sweat Sodium Loss. Med. Sci. Sports Exerc. 2010;42(9):1669–1674. (Funded by Gatorade Sports Science Institute)