The human body is a complex mechanical and chemical system, so it is no wonder that people try to explain taiji in terms of modern science. I am not against it, although I think it is a difficult thing to do (see other blog post
here). But I do think in terms of modern science. I believe that taiji is really about how to move your body in the most efficient manner, using the least force to achieve the biggest effect.
But trying to use modern science to explain taiji is not easy, because our bodies are just too complex. We learn about levers in mechanics, but the human body is not a simple set of levers. We have so many levers interconnected, working together and against each other, that it is very difficult for the human brain to grasp.
So while using modern science to explain taiji can help us to better understand taiji, understanding the science behind it does not mean we can actually put it into practice. The only way to do that is to actually practise, and feel it for ourselves. Only through practice can our bodies actually move in the way that taiji requires so that we can achieve the biggest effect with the smallest force.