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(scientific muscle @ Sep. 19 2006,00:54)</div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">Fausto, it wasn't that I worked different muscles, it was the fact that when I lift I do only 20 reps per exercise....but on saturday I was doing sprints in the football game for several hours! My lower body muscles are not conditioned to that kind of work/endurance output!</div>
Probably so, since endurance work can build up a lot of lactic acid. However, a lot of guys' workouts here wouldn't really work all the muscles used in sprinting very well, IMO.
For instance, you've mentioned doing squats with your heels on a 2x4 and that you like the emphasis that it places on your quads. However, you may be losing the glute and hammy work that ATG squats sitting back a bit more can give. Other than isolation exercises, stiff leg deads can help here, but I don't recall if you do them. Another one is calves. I'm not convinced that most here will get much calf development without either calf raises, or a pulling movement (power cleans, for example) that has you go up on your toes.
Another one is hip flexors. They are certainly used in sprinting. This one is a little harder to do in a compound exercise, I've been trying some hanging leg raises as an ab/hip flexor combo. Maybe there is something better.
I'm not sure where you got sore or if it could have been avoided without endurance work. However, the point remains that even as great an all-around exercise as squats may not quite get all the muscles used in sprinting, especially if not done really ATG going well below parallel.