See "Sitback" Video above: Whether Form or Push Hands, how well we "sitback" is the Acid test of how good any of our postures will be. If we have back pain, try checking how well you sitback during form practice. There needs to be a "tuck" under of the buttocks to coincide with contraction of abdominal muscles to pull back...
Tom is tall as well and needs to sitback with a crease appearing in the front as Master Hwa articulates. These types of problems can be traced to incorrect form practice, push hands shows up these errors. Hence, the statement from Master Hwa: "if we do push hands before having internal discipline (basic contraction of abdomen to mobilize body during sitback, forward lean, walking practice) it is putting the cart before the horse". Sometimes people think they got it but push hands will show things with a glare. Tom is not sitting back and has to use arm strength, that goes hand in hand with nervous tension, it makes the arm rigid, rigidizing the whole body in the process. Muscle Tension as I explain below is not the bugaboo people make it out to be in Tai Chi, but we should eschew nervous tension that inhibits body movement.
Sitting our posterior into any chair, couch,etc., is a perfect analogy for sitback in Tai Chi. Try it and observe what happens to angle of back, you get that crease he talks about. Just watch that you do not stick the rear end out, tuck it under to sit. Keep this anology in mind during form. This is basic sitback, there are variations of sitback. Also, all need abdominal contraction and proper "tuck under" to mobilize forward and back movements.
As my teacher has said, "TENSION is abhorred" in Tai Chi. I hear people all the time say they take Tai Chi to "relax" because they have so much TENSION. However, we want muscle tension in Tai Chi for it is none other than "JIN" in all of its forms. Substitute the word "ENERGIZED" for TENSION and then work to eliminate nervous tension. This is all about posture, core alignment, nerve impulses and cultivating that muscle tension...ENERGIZING. Substitute ENERGIZED for TENSION and understand the sameness but don't think to eliminate muscle tension, instead think that it is an integral and dynamic part of the engine that drives JIN.
My student Tom Kostusiak says: "When I first started doing Classical Tai Chi with Sifu Roach several years ago, I experienced back pain while playing the form. Sifu pointed out that I was not sitting back and tucking in properly during this time as well. As I progressed with correcting my posture my back pain subsided. Upon further investigation, it became clear that incorrect posture was the cause of the pain problem (for me) as I was not properly aligned to perform the moves. So while I agree that being able to consciously relax the muscles is important, posture plays a significant role in making sure that our core is properly aligned in order to perform the movements themselves."
As for me, I broke my hip in 2000 because of a roller blading accident...yes, roller blading. My lower back was in agony for a couple years, all that after doing Wu's Style many years, it did not help I started Classical Tai Chi in 2003...voila'...That lower back pain is gone now, no Ibuprofen for me either. My upper back pain from years at a computer, disappeared after I started this, about a year. I have no knee pain but I used to when I did styles where back foot was splayed out. So much knee pain I could not squat, that is gone. It is possible to do this and cause ache because of overdoing it. However, it is also certainly possible as Tom has said to do things incorrectly and create pain. That is why it is critical to check, check and recheck everything you do in Classical Tai Chi...after all, everyone is a distance student.
If anyone had reason to gloss over things it would be me more than 99.9% of the Tai Chi community. Why? Because, I have 35 years experience in Tai Chi, 30 in Wu Style alone, and a fat head when I started this. Speaking for myself, I learned to put the ego on the back shelf to learn this the right way. How did I do that, not easy but I learned to know "Treasure" when I see it.