Those contortions are caused by Poser's default, of using 'spline interpolation' for motion. Check out pages 224 - 228 of the manual to understand this better. The 'Break Spline' button on the animation control panel can help this problem, to a point. I think that converting a figure's entire group of keyframes to 'linear', before starting any animation, is the better way to go. Then, if you need to smooth out a particular motion, you can switch the keyframes back to spline, for only those body parts (or objects) that need them.