My comments on this from doing a little bit of everything over the years:
1) The notion that sliding saves knees by itself is a fallacy. If you could guarantee you never stuck, that would be great. But what causes catastrophic knee injuries is the knee going in two different directions -- which is what happens when the tib/fib part of the leg sticks and the femur keeps going, as happens when you suddenly stick.
2) Planting doesn't necessarily cause knee problems. How fast you approach the line, your weight balance, your timing -- all those things determine how much stress your knee will take. And I've found most knee pain comes from...
3) ...the knee bend itself, and that's true whether I'm planting or sliding. Your approach leading up to that point is what will determine how much stress is on the knee at delivery.
I slide about six inches these days, if that. But I can bowl in my tennis shoes if need be. Like someone else said, I actually get more pain sometimes in my right knee during the power step -- but that's because there's an old baseball injury in that leg.
I wouldn't recommend a planted step to someone with a fast approach, nor would I recommend everyone go to a super-slide approach that looks like you're curling, either.
Jess
