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Pre-tied shoes cause MAJOR left calf cramp

In utter pain I threw the shoe down and tried to relax (tough to do when it looks like the muscle's practically up at my knee!). This WORKED in practice, but following the bike ride my legs were rubbery and stretching my foot out caused a serious cramp. I was barely able to walk later and the pain lasted a week afterwards. Luckily in the heat of the battle I was able to complete the run.