You use higher weights for a variety of reasons. One of the most important is the angle of your body involved in the leg press movement. This gives you a significant mechanical advantage in itself. In theory, a 45 degree press (very common) will allow you to press almost 50% more weight than your best squat. In practice the difference is more than that because the squat involves smaller stabilising muscles as well (i.e. less isolation) as well as the muscles in the upper body.

One thing that people should not consider is the research that shows that the CNS is what stimulates muscle growth, not the muscle stress per se. The CNS recognises the load on overall musculature in the squat and the ensuing hormonal response results in greater protein syntheisis (i.e. bigger and strong muscles). The CNS also gets used to exerting force in a manner that is closer in reality to the athletic movement, meaning that there should be greater carryover to athletic sports. As I said before, leg press is a tool that is fine for bodybuilding purposes. For everyone else, just work on your squat. Bigger squat will mean bigger leg press numbers anyway.

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Height 5'7 Reach approx 7'0
BW @ 23 Jul 08: 145lbs (>13%bf)
Re-training start: Jul 08 (post injury+3 mths rehab)

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