Got a problem with your joints? The conventional wisdom is do flexibility exercise, or join a yoga class. Without a proper diagnosis of the problem, such advice can create more injuries rather solve the problem. Yes, it is not all about being flexible.
The thing is if one's joint is loose, doing exercise that requires excessive ranges of motion or positioning (e.g. using a pec deck or Nautilus pullover machine or doing yoga asana) may cause more harm than good. Why do people have loose joints? There are two reasons: One is due to in-born weak physique, and two is caused by joint injuries. Exercises with excessive ranges of motion or positioning are more suitable for people with strong but tight joints (professional guidance of course is still required here, a co-ordination with one's breathing will be an essential element).
To train up a loose joint, limited or no movement exercise is required. In this respect, zhan zhuang (chi standing meditation) is an excellent option. Through the practice of zhan zhuang, chi will be made to flow towards the affected joints where tendons will be activated to contract bringing the joints back to their rightful positions and strengthening them in the process. Aligning and strengthening through chi is not through conscious movement, but rather through subtle (or micro, half-conscious) movements activated by one's breathing mechanism together with chi generation and flow.
After one has built a good foundation through zhan zhuang, one can further strengthen one's loose joints through tai-chi movements. Needless to say it is important to have a smooth flow of chi during the movements, otherwise effectiveness will be close to nil.
PS: For the benefits of those having loose joints and who don't like to pick up zhan zhuang, the following advice is offered:
Participate in high-resistance weight training with reduced ranges of motion. This type of exercise program should be guided by a physiotherapist. An example of an exercise used to tighten the shoulder joints is the dumbbell bench press. The resistance used permits four to six repetitions at a very slow tempo and should always be done under supervision. All exercises and stretches encouraging excess mobility of the loose joints should be strictly prohibited.