Knee - after intense exercise, the back of the knee (especially a little below the midline) feels tight and it's hard to straighten my leg fully. usually feel ok after 2-3 days but symptoms reappear after next workout session. possible reasons?

Strain: It appears that you have muscle or ligament strain. Try an anti inflammatory after exercise Good Luck

ECS: The area describes sounds like the upper portion of your calf (gastrocnemius/sole is complex). It sounds like you may be suffering from “exertions compartment syndrome”. You could also have a popliteal cyst (Bakers cyst) that can change in size making it difficult to extend the knee until it shrinks again. You should see an orthopedic surgeon in your area.