JAS wrote:

I really don't have a clear visual of these concepts, can anyone help? Tighten abdominals? Pelvic thrust?

O.K. but only as it pertains to skiing...  -he,he!

Stand up, now get into the ski position. let your shoulders roll forward slightly, relax your arms and let them just hang... Reach up and feel how loose your ab's are right now...

Now pinch your glutes tightly together, You'll notice your pelvic move fwd. a little bit. Now go ahead and move (thrust) it fwd. a tad more, your glutes will now be fully engaged... (This is the same as "Hips up"...)  Hold this position and roll your shoulders back and puff your chest out slightly' (slightly pinching shoulder blades) keeping your head up/level, you'll notice a very solid core position and your ab's should automatically be engaged... (tightened) reach up and check your ab's now...

Abdominals support approx: 60% of the lower Back and are a huge part of torso balance and stabilization. There's No need to make a conscience move to tighten them while skiing. Proper form will do that. But, if they are not being kept toned and sharp they will not engage as effectively as they should regardless...

Hope that makes some sense!