I ended up with a tight knee yesterday,i fell off after scraping the kerb(only at about 7 mph so no harm done). My knee is grazed but after my fall i did another 7 or 8 miles to hopefully stop it from stiffening up. It was pretty stiff last night, but today it's fine. I think that getting blood flowing to a strain or a pull or a knock is better than resting it immediately after the injury occurs.