Over the last 2 seasons I had been struggling with sudden inner thigh cramps (feel like spasms, very painful and immobilize the leg) that have onset around mile 60 of Z3 rides/races. Most of my riding is triathlon. Through a lot of research and fit modification I've been able to alleviate it. I wanted to share what I've learned to hopefully help other riders who experience similar problems.
Cramping has generally been attributed to electrolyte imbalance, which is partly to blame but provides more questions than answers. For instance, if cramping is related to electrolytes, how come inner thigh cramps usually target only one leg or a specific area? And how come they occur more often while cycling and rarely while running?
It's because more often with inner thigh cramping the culprit is exercise induced arterial endofibrosis. Basically muscular inflammation of the groin muscles causes an artery in that area to get temporarily blocked; the resulting decrease in blood supply to the lower adductors and vastus medialis and is what causes the cramp. There are fit and geometry factors that can speed up the cramping. The endofibrosis occurs more often in cyclists who have seen a few seasons, which is why you don't usually see the problem when you first started riding, but it comes later once your fitness has improved substantially. It's also very common in triathletes, who have well developed adductors from running that, once inflamed, are much larger than those of a non-runner.
Factors that accelerate endofibrosis: Aero position, and knees tracking inward/toes pointed inward leading to overuse of adductors and gracilis on recovery phase of pedal stroke.
The solution I found was really very simple. Adjust float on your cleat so your toes and knees are pointed sufficiently outwards. You should be using your glutes when spinning up on the recovery stroke, not your adductors. The more you use the adductors/gracilis to pull, the quicker they get inflamed and the quicker you will cramp. During my last IM race I was able to delay cramping until mile 111, which was near perfect. Breaking aero position and spinning lightly (easing up on power) is also good way to prevent a cramp when you feel it coming on slightly.
Anyway, hope that helps. Please feel free to add your own experiences/findings
Some sources:
http://cyclingtips.com.au/2011/11/ex...-endofibrosis/
http://sportsmedicine.about.com/od/b...riopathy_2.htm
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-Albert Einstein, collected from assorted memoirs
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