I've started reading Tai Chi Dynamics by Robert Chuckrow, who is a physics professor and explains Tai chi in terms of physics. It's quite a fascinating book and I'm really intrigued by his explanation of how to work with the muscles of the body, because I think it aptly demonstrates how energy work is approached, in terms of attempting to force it to go somewhere as opposed to flowing with it. With contractive muscular force, a lot more pressure is put on the muscle to perform an action. Weight lifters tend to use their muscles in a contractive way. Obviously this can make them very strong, but it also decreases the flexibility they have. Also muscular contraction can only be done for a short time because of the sharp build up of lactic acid.
With extension applied to the muscles, the muscles are stretched in a way that is natural to them...they are kept relaxed instead of contracted. Muscular extension allows a person to perform longer...the lactic acid doesn't build up as fast.
I tried one of the exercises he includes in the book. You relax an arm that you have extended in front of you as much as possible. You gently squeeze your fingers as if you were holding a ribbon in your hand. You then replicate this motion in the muscles in your arm. It's a very subtle movement, and different from how I normally move my arm. There's not as much effort involved, and at the same time it does seem that the chi or internal energy is freed up...it flows more. I will continue working with this to see what I can do with it. Chuckrow notes that when the muscles in the body aren't using contractive force, they become relaxed and the body acts like a container of fluid. Pressure is increased equally across all parts of the body.
Personally I find this fascinating. Having done a fair amount of Taoist breath work, I know that the fire breathing is similar to the contractive use of muscles...sharp and contained. It seems more powerful, but the water approach is more like the extending of muscles. It gradually builds up the force and it can be sustained much longer.
I've only read part of the first chapter and I can already say I really like this book. Check it out if you get a chance!