Any physical activity can generate chi. Physical activities that use rotation in our hip joints can generate the greatest amount of chi. As such, the most simple exercise to generate a large amount of chi is jogging. And it is of the best exercise for young people. The problem is jogging demands an inordinate amount of physical exertion on our leg muscles (not to mention our knee joints). And for good and for bad it requires our body to burn a huge amount of energy. The slim and physically fit bodies of marathon runners is a clear demonstration of the huge benefit (including endurance training!) of jogging. And it will be quite prohibitive for people of lesser physical stamina which include the majority of middle-aged people, and all recovering patients.
Tai chi (and chi kung) goes another route. It employs methods to directly generate chi through activating our hip joints with minimal exertions on our leg muscles. There are many tricks (as mentioned from time to time in this blog). One interesting trick is the use of imbalance to achieve our chi generation objective.
Shaking our body to activate our hip joints to generate chi is the most common method. The possible negative side effects of shaking is that the chi thus generated is difficult to manage. In spiritual combat (神打), fictional legends (for example "possessed oneself with Monkey king") are used to control the random movements of a practitioner. And self-induced chi kung (自發功) needs the close supervision of a qualified master. I have seen videos in Youtube of folks experimenting with self body shaking to generate chi for spiritual purposes seemingly without a clear understanding of possible negative side-effects. Readers interested to experiment with such practice are therefore cordially warned here.
The use of imbalance is a better option. It might not be as speedy as self shaking, but definitely safer, easier to practise and can be incorporated into most internal martial art, meditation, or chi kung systems (Sufi dance is a form of controlled use of imbalance for spiritual purpose).
In master Wang Xiangzai's I-chuen system, nano-movement using the imbalance state of a common combat stance is used. One simply consciously creates certain imbalance when doing combat stance. A dynamic process of balance-imbalance can generate the required chi to spread over our body. Our focused mind is to manage such chi for even distribution inside our body (hence an absent-minded state won't work).
In tai chi, it is more simple. It is achieved through the standard bow stance and seated stance. When activating chi through imbalance, a student does the stances as zhan zhuang, with one additional trick: stretched your toes outwards and upwards to create the sense of imbalance. With some good practice, this "imbalance training method" can be applied while doing the standard tai chi form. This use of imbalance is particularly applicable for Wu-style, and other styles that use the "creek stance" (川字步) which is more imbalanced in the first place.