A few years ago, just when I’d started training for a big race, I strained my Achilles tendon.  Being an Irishman, I couldn’t, of course, bring this evidence of age and infirmity to the attention of an actual physician.  However, I consulted the oracles of the internet and they were, for once, very consistent in their advice:  “Wait a few days until the pain has faded and then work steadily on ankle strengthening exercises.  Most importantly, lay off running for at least 3 weeks.”