You’re at mile 18 of your marathon race. Things are starting to get tough–you’re starting to feel tired, but you’re able to maintain your pace. A couple of minutes later, though, you start to feel your calf muscles tighten, and your pace slows. Soon enough, your calf muscles completely “lock up” and you can’t get them to relax. You have to stop and walk because of the tightness and pain in your muscles. 

As you’re stretching your calves on a nearby curb, you might be wondering, why did this happen to me? What leads to these muscle cramps? And what can I do to prevent this in the future?

Muscle cramps are a common and frustrating issue for endurance athletes. A heavy bout of cramps can turn a great race into a “struggle fest” to make it to the finish line. Gaining a better understanding of the science behind muscle cramps will help you prepare better for your next race, lessening the likelihood that “cramping up” keeps you from hitting your goal time.

What is a muscle cramp and why does it occur?

Exercise-associated muscle cramps (EAMCs) are “painful, involuntary contractions of a skeletal muscle during or shortly after exercise”¹. EAMCs can range in severity, but in most cases they dissipate over time without need for medical attention or serious intervention. EAMCs tend to occur in muscles that cross two joints (examples: your quadriceps on the front of your thigh, your calves on the back of your lower leg). The incidence of cramps with exercise increases in hotter months of the year, but cramping can occur in any weather. 

Traditionally, EAMCs were thought to occur because of dehydration and loss of electrolytes due to heavy sweating during exercise. However, there is more scientific  evidence that is contrary to this explanation than there is in support of it. Multiple studies that compared cramping vs. non-cramping athletes during endurance competitions show that there was no difference in serum electrolyte levels (how much electrolytes are in your blood) between the two groups, both during and after competition^2,3. Another study showed that EAMCs occurred as the subjects became fatigued with exercise, regardless of whether they were well-hydrated or dehydrated⁴. So, it is unlikely that dehydration and electrolyte loss alone are major factors in cramping during your race. 

A different explanation for muscle cramps during endurance exercise is fatigue. Muscle fatigue can be defined as a progressive, exercise-induced reduction in the ability of a muscle to produce force or power. So, as you run for longer periods of time, it becomes more difficult for your muscles to produce the same amount of force that they could at earlier stages in the race. Eventually, you begin to run slower, even though you may feel that you’re working hard as ever to keep pace. 

But how does this muscle fatigue lead to cramps? By altering something called neuromuscular control⁵. Your muscles are controlled by your nervous system (the “neuro” in neuromuscular), which can be broken down into two basic parts: 1) the central nervous system, which is your brain and spinal cord and 2) your peripheral nervous system, which are the nerves that branch off of your spinal cord to connect to all of the muscles in your body. Signals for muscles to contract and relax are first sent by your brain, then travel down your spinal cord, and are finally sent to the muscle through peripheral nerves. When you get fatigued during a race, the amount, intensity, and duration of these signals can change. This change in the signals (also called neuroexcitability) is thought to be what causes cramps to occur–if your muscles are receiving too much input to contract but not enough input to relax, then they will not relax as they should. This inability for muscles to relax after contracting is the cramping that you experience. 

So, changes to neuroexcitability appear to be the driver behind muscle cramps, and muscle fatigue can affect this neuroexcitability. However, it’s important to point out that there are several other factors that can either alter your nervous system function or contribute to muscle fatigue¹. They include:

• Underlying illness
• Side effects of medication
• Lack of adequate sleep prior to competition
• Improper nutrition – depleted glycogen stores going into competition OR not replenishing glycogen stores during the race (glycogen is what is broken down into fuel for your muscles–your body stores a limited amount that can easily be used during exercise.)
• Under-preparation in training for the race – being comfortable and efficient in running at race pace for a prolonged period of time 
• Dehydration (this can lead to reduced performance and fatigue)
• Unacclimatized to the environment (Heat and humidity can raise your body temperature with exercise, which can cause your heart rate to stay higher than normal, and this can cause you to fatigue quicker than usual.)
• Overexcitation of the nervous system (Being overly “nervous” or anxious about the competition can influence neuroexcitability.)

Preventing muscle cramps: 8 questions to ask yourself

Look at the factors listed above. In order to address your cramping issues, you have to take a look at more than just your running workouts, and do more than just drink more Gatorade or eat more bananas. You have to take a holistic look at yourself as an athlete. Ask yourself these questions: 

• Do you understand the effects of any medications that you take – have they been shown to potentially cause muscle cramps or spasms? 
• Do you get enough sleep to wake up in the morning feeling well-rested? (Adults typically need about 7-9 hours of sleep per night.)
• How much time was spent or distance was run at or near your goal race pace? How comfortable did you feel running at that pace?
• Have you been doing any strength training and/or plyometrics to prepare your muscles, bones, tendons, and joints to be strong enough to handle running for hours at a time? (You take on loads of 3-5x your bodyweight with each step.)
• Do you have an eating plan to “carbo-load” for a couple of days leading up to the race so that your muscle glycogen stores are maximized? 
• Do you have a plan for your in-race nutrition and hydration?  What will you eat or drink during a long race, and how often will you take nutrition and hydration? (Your body can run low on carbohydrates to use as fuel after ~2-3 hours of running.)
• Have you thought about how you’ll alter your race plan if the weather is hotter/more humid than you would expect? 
• Do you have a race day routine that will help you manage your nerves so you’re not overexcited?

Give these questions some consideration before your next big race, especially if you frequently deal with EAMCs.

What should I do if I begin to cramp during a race?

The quickest way to get rid of a cramp during a race is to stop running and stretch the area that is cramping^6,7. You can also do some gentle self-massage while stretching. If the cramping becomes intense or is happening in several different muscles at the same time, you may need to have someone help you stretch out.

Also, continuing to hydrate with water or a sports drink can be helpful, but keep in mind that it takes 13 minutes or longer for those fluids to be absorbed into the bloodstream⁸. There is limited evidence that drinking a small amount of pickle juice can alleviate cramps faster than drinking plain water⁹. However, most races don’t give away pickle juice at water stops, so if you plan on using it, bring your own.

Final thoughts and Resources

I decided to do a deep-dive on the research on EAMCs because I have personally experienced muscle cramps while running a marathon. I know how frustrating it is to spend months preparing for a race, only for it to be derailed in the last few miles. Previously, I did not take into account all of the different factors that affect the fatigue that leads to muscle cramps. Now that I know better, I will do better the next time. And now that you understand muscle cramps, I hope you’ll do the same.

Want to learn more about proper hydration during your runs? Check out my Instagram post here.

Written by: Brian Barney PT, DPT CSCS

References

1. Miller KC, McDermott BP, Yeargin SW, Fiol A, Schwellnus MP. An Evidence-Based Review of the Pathophysiology, Treatment, and Prevention of Exercise-Associated Muscle Cramps. J Athl Train. 2022;57(1):5-15. doi:10.4085/1062-6050-0696.20
2. SULZER NU, SCHWELLNUS MP, NOAKES TD. Serum electrolytes in ironman triathletes with exercise-associated muscle cramping. Medicine & Science in Sports & Exercise. 2005;37(7):1081-1085. doi:10.1249/01.mss.0000169723.79558.cf 
3. Schwellnus MP. Cause of exercise associated muscle cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion? British Journal of Sports Medicine. 2008;43(6):401-408. doi:10.1136/bjsm.2008.050401 
4. Jung AP, Bishop PA, Al-Nawwas A, Dale RB. Influence of Hydration and Electrolyte Supplementation on Incidence and Time to Onset of Exercise-Associated Muscle Cramps. J Athl Train. 2005;40(2):71-75.
5. Nakagawa K, Miyamoto N, Kanosue K. Neural mechanisms of Muscle Cramp. Sports Performance. Published online 2015:79-90. doi:10.1007/978-4-431-55315-1_8 
6. Bertolasi L, De Grandis D, Bongiovanni LG, Zanette GP, Gasperini M. The influence of muscular lengthening on cramps. Ann Neurol. 1993;33(2):176–180. doi:10.1002/ana.410330207
7. Maquirriain J, Merello M. The athlete with muscular cramps: clinical approach. J Am Acad Orthop Surg. 2007;15(7):425–431. doi:10.5435/00124635-200707000-00007
8. McDermott BP, Anderson SA, Armstrong LE, et al. National Athletic Trainers’ Association position statement: fluid replacement for the physically active. J Athl Train. 2017;52(9):877–895. doi:10.4085/1062-6050-52.9.02
9. Miller KC, Mack GW, Knight KL, et al. Reflex inhibition of electrically induced muscle cramps in hypohydrated humans. Med Sci Sports Exerc. 2010;42(5):953–961. doi:10.1249/MSS.0b013e3181c0647e