What Causes Cramps While Running

What Causes Cramps While Running

India Lewis

If you’ve never felt the debilitating pain of a muscle cramp when out training consider yourself lucky! In this post, we take a look at what causes cramps while running and most importantly, what you can do to keep them at bay.

Ask 100 people who’ve run a marathon about cramping and you’ll spot the slight wince on the faces of those who’ve experienced cramping around the 20-mile mark!

The sensation comes on quickly, starting with a slight tightening of your quads, glutes, hamstrings or calves before finally feeling like your leg muscles are being gripped in the jaws of a gator with each attempt to flex the muscle sheer agony!

Why Your Legs Cramp While Running

Before we dive into looking at just what causes cramps while running, first it’s important to understand why your legs cramp.

Modern research has found that there are two main types of muscle cramping:

  • Cramp caused by dehydration and electrolyte defficiency.
  • Cramps caused by muscle fatigue.

Cramp caused by dehydration and electrolyte defficiency

Typically, this was always thought to be the cause of leg cramps. The logic went that towards the end of a marathon or long run in the heat, you’d have sweated out most your electrolytes and would be experiencing some dehydration.

The loss of fluids and electrolytes cause neuromuscular junctions to repeatedly tense, resulting in cramping.


  • Excess sweating
  • Poor re-hydration during exercise
  • Poor re-hydration before exercise


Symptoms include:

  • Starts out slowly with micro-muscle twitches that are only slightly noticeable.
  • Usually happens in the bigger leg muscles such as hamstrings and quadriceps.
  • Cramping isn’t consistent and comes and goes.


  • Start drinking as soon as you notice the symptoms, preferably something with high electrolyte content or salts.
  • Icing (which isn’t practical during a race) and massage.

This great video below from Angelo dela Cruz is packed full of useful tips and is definitely worth a watch!

Cramps caused by muscle fatigue

Cramps brought on by muscle fatigue are often directly caused by muscles not being allowed to properly tense and relax. Typically, this is why fatigue cramps tend to occur in calf muscles.


  • Age
  • Reduced flexibility.
  • Going too long too quickly


Symptoms of cramps caused by muscle fatigue are often difficult to spot as unlike cramps caused by dehydration, muscle fatigue cramps come on suddenly and with little warning.

Typically, if you’ve been staying hydrated and taking on electrolytes you can be confident that you’re experiencing this type of cramping.


Runners have also long used compression when running as a way to try and stave off calf muscle cramps. While there’s little research to conclusively prove if this works or not, there’s plenty of anecdotal evidence to suggest that it does.

So there you have it, hopefully, now you have a better understanding of what causes cramps while running and know exactly what to do should your legs start to tighten during your next run.

Brooks Running