Had ACL reconstruction in Jan 2011. They used my hamstring tendons. I was running during that following summer although it was sporatic at best (just didn't feel like running). The recovery process was pretty painful early on but overall was easy i thought. It took some time to get the confidence back to attempt to run. My PT had me doing a lot of leg lifts, bridges, squats, stationary bike, stuff like that. Hamstring bruising last a long time. This past year I put in some serious training. Got up to maybe 70 a week with workouts and racing, no problems with the knee or hamstrings whatsoever. I will tell you that my knee does feel different, not necessarily in a bad way, just different. Ive also played roller hockey, snowboarded, water skied all after the surgery with no problems. Im not doing workouts or racing as much as i did in college, but i think if i was in that type of college training/racing system; the knee could easily handle it.