Your achilles tendon connects the two major calf muscles to the back of the heel. Under too much stress, it tightens and becomes irritated. Tendinitis accounts for 11 per cent of all running injuries; eight per cent of Runner's World survey respondents have had it in a 12-month period.
Are you at risk?
If youâ€™ve dramatically intensified your training, have tight, weak calves or have been imperfectly dipped in the waters of invincibility, youâ€™re vulnerable.
Can you run through it?
Forget the classic PE teacherâ€™s mantra. â€œIf you have any pain during or after running, stop,â€ says sports podiatrist Amol Saxena. Catch minor strains early and a few days off can heal them; keep running and it could take six months to clear.
Ice five times a day and strengthen your calves with eccentric heel drops: stand with the balls of your feet on a step. Raise up on both feet, then take your strong foot off the step. Lower on your injured foot, dropping your heel below the step. Raise, and put your other foot back on the step. Do 20 reps.
Prevent a relapse
Strong calves protect your achilles, so do those daily heel drops. Avoid aggressive calf stretching, and donâ€™t wear flip-flops or high-heeled shoes.
Shannon Rowbury, 1500m bronze medallist at the 2009 World Championships, wears compression socks for hard workouts to relieve achilles tightness.
How to proceed
Stop running: Severe pain and swelling above your heel â€“ even when youâ€™re not running.
Run with caution: Dull pain around your heel at the end of your run that lingers afterwards but goes away when iced.
Go run: No pain when you pinch the tendon, starting at the heel and working your way up towards your calf.