If you asks a modern tai-chi practitioner about microcosmic circulation, most likely he or she will not know what you're talking about. True, many tai-chi practitioners don't do microcosmic nowadays. In a previous post, I explained the opening of Ren and Du mais (任督二脈) through practicing a form (Wu's style) of tai-chi Nei Gung (check Here). Most tai-chi practitioners do it as "soft exercise" don't do Nei Gung, no wonder they have never heard about opening Ren/Du and have never understand what is microcosmic circulation! Having said that many tai-chi practitioners are familiar with a related concept: "point focus or point meditation" (守意), the most common being "focus at Daintian" (意守丹田).
How is the progress of point focus or point meditation like? And how is it related to microcosmic circulation? These are the questions that I am going to discuss below.
Doing tai-chi in slow-motion has been called "silk reeling". A concept familiar to most tai-chi practitioners. And through slow motion (or silk reeling), one can better feel chi filling one's body. And, as a best practice, one should also do some zhan zhuang groundwork before reeling silk.
When one progresses, the next step is to do silk reeling with a spiral-undertone. It is called "spiral silk jing" (纏絲勁). This is a way of training defined connecting muscles group to contract synchronically. Physically it is just like wriggle water out of a towel. And just like wriggling a towel, one needs two fixed points. These are points a practitioner needs to focus his mind on (守意).
What is the relevancy of doing microcosmic circulation or practice to open one's Ren and Du Mais(任督二脈)? The reason is that in turning one's body left or right in different ways, one needs to choose one point along one's spinal cord as the focused point. And only through doing microcosmic or tai-chi Nei Gung's relevant exercise can one have a strengthened spinal cord that one can feel and can be focused pointedly along it.
Unlike some old (mythical) thinking like "open the Ren and Du Mais (通任督) as the ultimate achievement", my opinion is that doing so is a necessary step towards an advanced level tai-chi. This is another post for tai-chi enthusiasts.