Actually, it's pretty much almost the exact opposite.... Train your hamstrings. If you've had a previous ACL injury, you need to focus on your hamstrings, not your quads as much. An explosive athlete is going to have their hamstrings about 120% of the strength of their quads. Look at a sprinter's legs, their hamstrings almost look like biceps. By overworking your quad's in relation to your hammys you create a lot more stress on your ACL. Too much hamstring strength CAN relate to PCL injuries in some sports, and lower back injuries, but most likely in skiing, you're not putting a lot of pressure on your PCL.. Focus on Squats, Deadlifts, and power cleaning... Good luck man, don't think about your injury, just think about how much fun you're having on the hill and how lucky you are to be skiing! you got it, good luck