Re: Jan Childress vs. Timothy Hwang
Dr. Shie Ming Hwang uses two primary solo exercise drills to develop this skill.
1) standing in cat stance (90-98 % of weight on rear leg) and rotating the waist from side to side (knees and head remain forward facing). The arms swing relaxed at eye and shoulder level (resembling Yang style posture called "single whip".
2) standing in cat stance (90-98 % of weight on rear leg) and arching the waist to the rear(knees and hips remain forward).
Both of these drills burn the rear leg's quadriceps immensely as you relax (weight underside) causing your skeletal frame to sink and rise.
Then you do the same with non-resistive push hands patterns with a partner to build flow.
Then you allow the partner to push at will without pattern.