this happened to me a few months ago but it was my fault cuz i was pushing myself too hard and was not fueled well enough for my efforts (yea and i was brakeless). i ran out of electrolytes was my issue. i was riding along with a friend and i felt it coming but though i could push thru it but didn't happen so i pulled over and stretched but that sucker stayed even after 5 min of doing it. He told me to buy a tomato and it will do the trick. sure nuff it worked and now after that i make sure i keep an energy bar or something with electrolytes to keep me going. but fueling well enough can play a part in avoiding it