Upper body stabilisation, promotes good posture, good for fore, and aft balance discovery.
Take your poles and place them both across the small of your back, then hold them in place by hooking your arms around them so they sit between your inner elbows and back. Hold your hands to the front again.
Using your uphill arm, push the uphill side of the poles forwards.
Pushing the uphill side of your body forwards with the poles forces the upper body into a better posture. Having the poles behind you changes your centre of balance and therefore restricts the possibility for leaning backwards without feeling off-balance.