In Tai Chi, Don't try to use your legs

Chen Yingjun told me that in 2004, in Austrália. It sounds contradictory at first, because when our posture is corrected by a Taijiquan (Tai Chi) Master, our thighs burn because of the effort.

The more you try to use your legs, the less you’ll actually use them.Chen Yingjun

The explanation is simple: in Taijiquan (Tai Chi), power ought to be natural. If you try to develop power directly, you’ll use the body mechanics you have right now, and not the new body mechanics you want to learn. This is very logical, as you don’t know the new mechanics yet. So, how would you do it? You should always look for the correct posture in Taijiquan (Tai Chi). Sure, it isn’t easy to change the way your body works, but in time the new will supersede the old, a new and better motor coordination will develop, and you’ll be able to channel all the weight to your feet while you relax the whole body – including the legs.
This is in total agreement with one of the first instructions i got from Grandmaster Chen Xiaowang. I asked him how the shape of the lower back should be, and he answered:

It’s not about the lower back, it’s about relaxing here (tapping his hand on his upper thighs)Chen Xiaowang