Achilles pain is one of the most stubborn running problems. The good news: complete rest is rarely the answer.
A pain-monitoring approach used in research:
Pain during activity up to 5 out of 10 is acceptable
It should settle back to baseline by the next morning
It shouldn’t get worse from week to week
The core of treatment is load: slow, heavy calf raises, done consistently for weeks to months. Rest alone doesn’t make a tendon stronger. More: tendon health: load is the medicine.