Cramp Killing

Since this site is primarily about heat endurance and the athlete I'd like to start off with an ariticle titled "Cramp Killing" by Dr. Douglas Stoddard which will also be published in April 2006 Edition of The Racing Post www.theracingpost.us .

Douglas W. Stoddard MD, M Sport Med, Dip Sport Med, ES.
Medical Director-Toronto Sports & Exercise Medicine Institute (SEMI)
Medical Director-Medion Corporation (eload, emend, Zone Caps)

"If you have never felt the pain and discomfort of cramping during your cycling training or competitions, consider yourself lucky. Cramping will definitely slow you down, unfocus your mind, and often will lead to the dreaded “DNF”; or, worse, the medical tent or nearest hospital. No doubt many of you have experienced these feelings and situations, especially if you are cranking out the bigger miles in hotter temperatures. Fortunately, there is help!

The History of Cramping

For as long as “hot endurance” events have been around, cramping has kept company. This is contrasted to “cold endurance” events, which tax the system in very different ways compared to those performed in the heat and are rarely associated with cramping. Based on my experience tending to cyclists suffering from heat related illnesses, the incidence of cramping in hot endurance sports is increasing. This would have to be related to the increasing length of endurance events coupled with the hotter temperatures in which they are run.

Where and Why Do You Cramp?

Cramping typically occurs in muscles being used the most. For example, tennis players can experience cramping in their forearms. Runners may experience them in their calves, and cyclists in their quads. Cramping typically hits later in the event, when fatigue and other physiological disturbances (see below) are at their peak.

There two cramping theories currently talked about. The more established theory, which I will call the “Electrolyte Theory”, relates cramping to electrolyte disturbances. These occur due to sweating, and inadequate replenishment of the lost electrolytes. The electrolytes mentioned most are sodium and potassium, as normal levels of both of these ions are crucial for normal neuromuscular function. Some relevant “sweat facts” are as follows:

1. Human sweat typically contains anywhere from 700-1200 milligrams of sodium per liter, but may be as high as 2500-3000 mg/liter. It also contains 180-240 milligrams of potassium per liter.
2. Most sports drinks contain between 200-400 milligrams per liter of sodium, and 50-120 milligrams per liter of potassium.
3. Average sweat rates are about 1 liter per hour in the heat, though there will be wide variation from person to person.
4. Your gastrointestinal tract (stomach/intestines) is limited in the amount of fluid it can absorb-an average for most people would be around 1 liter per hour, though, again, wide variation does occur.
5. You probably do not drink a liter of fluid per hour.

And therein lies the problem. If cramping is due to electrolyte imbalances (and this author believes very much that it plays a key role) then the above numbers tell the story of how easy it is to drop your sodium and potassium levels with prolonged sweating. This is not helped by a low rehydration rate and the low electrolyte levels in your sports drink. You have a problem.

Furthermore, while sodium and potassium are likely the most important electrolytes to consider, calcium, zinc and magnesium are also worth considering, as there are many anecdotal reports of how supplementing with these minerals has helped cramping athletes.

A newer theory, which I will call the “Spinal Reflex Theory”, explains cramping as being the result of neurological alterations which occur at the spinal cord level, and these alterations secondarily cause muscles to cramp. The physiology with this one is somewhat involved, but the idea is that fatiguing muscle sends various nervous signals to the spinal cord, which secondarily sends reflex nervous impulses back to the muscle that causes spasm and cramping.

Both of these theories are relevant, but in my opinion, do not tell the whole story. Human physiology is complex and composed of many interdependent processes. Other important factors to consider are:

1. Dehydration, resulting from large volumes of water lost in sweat
2. Lactic Acidosis (lactic acid build-up) resulting from working close to or at your anaerobic/lactate threshold
3. Hypoglycemia (low blood sugar), or bonking, or hitting the wall, resulting from inadequate replacement of easily absorbed, useable carbohydrates

Combine these with electrolyte abnormalities, and you have the recipe for cramping. Any “spinal reflex” contribution, if it exists, would have to be affected by these abnormal physiological states anyway. Therefore, cramping, along with the many other heat related symptoms including headaches, nausea, dizziness, vomiting and diarrhea, is likely related to all of these abnormalities working together.

Prevention

If these four abnormal physiological states are responsible for cramping, prevention is a fourfold proposition:

1. To prevent dehydration-DRINK! You may be fine allowing yourself to become slightly dehydrated-certainly enough has been written on the topic and exactly matching losses with replacement fluid may not be 100% necessary. But, trying to get as close as possible to replacing what you are losing is still the goal i.e. if you lose a liter per hour, you must try to put back at as close to this amount as you can tolerate. Weighing yourself before and after your event will give you an idea of how much water loss you have experience. Remember, 1 liter of fluid = 1 kilogram = 2.2 pounds. For help in determining hydration needs you can use a hydration calculator tool like the one at http://www.eload.net/Calculator/FluidCalc.htm which will be up sometime in April ‘06.
2. To reduce electrolyte depletion, use a sports drink that contains physiological quantities of electrolyte. As mentioned, you will run into problems using drinks that have significantly less electrolyte in them than what you are losing in your sweat. Furthermore, look for a drink that recognizes that the ratio of sodium: potassium in sweat is about 4:1, which means that the ratio in the drink should be about the same. Some drinks have more potassium than sodium in them, ignoring these fundamental physiological ratios. Additionally, addition of zinc, magnesium and calcium is beneficial. Salt tablets are an inexact way of replenishing lost sodium, and may not contain other valuable electrolytes.
3. To reduce lactic acid accumulation, use a sports drink that contains a lactic acid buffer. Not many do. MultiCitrate is an excellent buffer, as this compound is converted in your body to bicarbonate, and bicarbonate is the most important substance in the body for buffering lactic acid. Bicarbonate itself is not generally included in sports drinks because it is irritating to the gastrointestinal tract, therefore MultiCitrate is definitely the way to go.
4. To reduce hypoglycemia, use a sports drink that has easily absorbed and readily useable carbohydrates in them. High glycemic, easily digested and absorbed, glucose (dextrose) remains the best choice. Dextrose is the carbohydrate used in intravenous fluids when rapid carbohydrate replacement is required. Dextrose easily passes through your gut wall into the blood stream, and requires no processing by your liver before your muscles can use it. It is also non-irritating to your gut, and is not too sweet. Carbohydrates to avoid include fructose, or fruit sugar, which is very sweet, can cause gastrointestinal irritation and requires processing by your liver before your muscles can use it. You want a sugar that requires minimal processing so the energy is available when you need it-NOW! Additionally, ingesting a lot of long chain carbohydrates, like maltodextrin, amylopectin and amylose, can contribute to gastrointestinal upset by leaving undigested remnants in your intestine. This is especially prevalent when you are involved in high intensity work.

In conclusion, cramping is a prevalent problem in endurance athletes of all kinds. The abnormal physiological processes that contribute are dehydration, electrolyte imbalances (especially sodium), lactic acidosis and hypoglycemia. When present together, all of these factors act synergistically to alter the way in which muscles contract and relax, leading to cramping. Optimal prevention means addressing all of these processes as thoroughly as possible, and a properly formulated sports drink is the first place to start."