« Should I run if my knee hurts the day after? »

Short answer: it depends on when the pain shows up, not on how strong it is.

Pain that appears the morning after and fades within a day is usually load-related and rarely a reason to stop. Pain that appears during the run, and gets worse as you go, is the one that stops the session.

What the sources say A 2019 review in the British Journal of Sports Medicine on running and knee osteoarthritis found no association between recreational running and joint degradation, and a lower prevalence than in sedentary controls. It says nothing about running through pain, which is a different question.

What we could not establish Whether the 24-hour rule holds for people who started after forty specifically. The studies do not separate that group.

What members with ten years in say Three of them independently described the same rule: if it is gone by the next run, keep going; if it is there two runs in a row, see someone.

This is not medical advice, and the difference between load pain and injury pain is exactly what a physiotherapist is for.