Here it goes. I don't usually run for the sake of running, my running is usually pretty much limited to the multi-sprint sports I enjoy (tennis and football...the European kind), but I'm a 32 yo in very good cardiovascular shape and athletic. Some of my friends invited me to run with them in a mountain running race. There were 2 categories, "pro" who ran over a semi-maraton distance (21 km) and "amateur" who ran over a distance of just over 7 km (about 4.5 miles). We participated in the "amateur" race. Given the fact that I had a holiday scheduled and other commitments I only "trained" twice for this race, the target being to see how I do in running uphill/downhill...etc, both times we did some trail/woods running with something like 1/3 of the distance of road running. First time we did about 10-11 km, and the second time about 14 km. The first run was a couple of weeks before the race, then I went on holiday for a week and the second run was a few days before the race. At the end of the first run I felt slight discomfort on the outside of my left knee, but it went away totally in a couple of days. At the end of the second run (the 14 km one), which was on a Wednesday I felt serious discomfort (pain) in the same location. I iced it, did some stretches, applied some local anti-inflammatory creams and took some Ibuprofen as the race was going to be on Saturday. I ran the Saturday race with some elastic bandage on my left knee and finished in a very respectable 3rd place in my age bracket and 5th overall for that amateur section. However...although the distance of the race was shorter than my training runs...the uphill/downhill sectors were much more aggressive, there were some sectors with climbing that involved rope/chains, a couple of small mountain river crossings and there was a long and aggressive/rocky downhill at the end of it. By the time I got to that downhill sector I was feeling the same pain on the outside of my knee (this time it was worse in my right one...presumably because I've been "saving" the left one during the race) and I frankly couldn't run that part of the race the way I know I could have done with "healthy" knees...I lost a lot of time there, but running that downhill quickly was just too painful. During the following 2-3 days I felt pain when walking uphill/downhill and when going up and especially down some stairs. Walking on "straight" floor wasn't as big of a problem. About a week later I was able to play some tennis but felt slight discomfort (not too painful) during longer/more demanding rallies. I only consulted "Doctor Google" about this and I'm pretty sure it's the so called "ITBS" or a problem with inflammation of the Iliotibial Band...most likely caused by my poor running form. I'm looking for second opinions from more experienced runners and recommendations of strengthening exercises and/or stretches that help prevent this issue for the future. If this issue comes up again I'm going to have to talk about it with some physio/doctor but for now I think some "on my own" work might be enough as a preventive measure. Thanks in advance .