The short answer is anytime they’re injured. An athlete should seek medical attention anytime they are injured. But if you’re doing an exercise routine and you’re sore or stiff that can be normal. Determining whether it’s normal or not normal is really up to the patient. If it’s normal for them then they can give it a little bit of time. If it doesn’t get better, follow up with the doc that time. However, something’s that a little not right or instability in the joint or something that is causing them significant dysfunction in their daily lives is a good time to follow up with a physician.