I accidently reirritated an old (46yrs) right knee injury when my bicycle turned suddenly to the left coming downhill and hitting the rear bumper of an suv. As the bike was turning left my right lower leg hit the rear bumper. That must have twisted my knee. I got home as best I could walking the bike and applied ice at least twice before I fell asleep with my leg elevated. Felt better the next day. Staying in very low gears I ran a small errand that I had previously promised to a neighbor. The next day the bottom of my right knee cap could take much weight. I elevated it even more and started taking motrin. With my previous injury I lost my anterior crusiate ligament and started getting arythritis in the knee. Was told to start riding a bicycle 38 yrs ago and been doing ever since. I t has been 5 days now since my reinjury. My question is when should I start applying heat.