In spiritual meditation and internal martial art, there is always a dilemma between Yin and Yang. A meditative mind (Yin) is most conducive to chi generation, on the other hand, if our increasing chi-power is not engaged in some "positive" (Yang) work, our mind will be prompt to wander around, inviting hallucination or chi out-of-control, resulting in a condition known as chi-kung or kundalini syndrome.
The general conception is that spiritual meditation works more on the Yin side through solitary folded leg, seated meditation with little regard to physical body building. This approach is not totally right. The fact is that if a practitioner's joints are not properly aligned, which is usually the case for novice meditators, he will feel very uncomfortable in a seated meditative pose. The result will be very shallow meditative state, if meditation can be done at all. Some prior training in standing or moving chi-kung exercise, a Yang aspect, can greatly facilitate one's seated spiritual meditative practice. In addition, to avoid possible hallucinatory side effect, Tao and Zen masters will guide their practitioners' mind with time-tested spiritual conceptions (like the concept of Emptiness in Buddhism and the concept of Tao in Taoism, which is itself a long subject that cannot be dealt into any detail here, interested readers can refer to some of my other posts on the subject). These more rationalistic guidelines can serve as a balancing Yang towards one's deep meditation, which in Yin in nature. Our mind or ego will therefore not wander around (or in psychotic cases, disintegrated), and therefore can have an opportunity to be enlightened to a higher level of consciousness, which Jung called the Individuation process.
The practice of martial arts doesn't necessarily need any chi-kung practice. Chi-kung, called Nei-gung in martial art, is the core technique of an internal martial art like tai-chi. Having said that it should not be his only training routine, if he is interested to study actual physical combat. In his Nei-gung practice, the internal martial artist will generate chi and will use this chi to strengthen his muscles, tendons and bones, generally make him more "fit to fight" as his training progresses. The dilemma is that chi will be maximized with a meditative mind, but in combat situations, one's mind need to be alerted to his opponent. Failing to solve this dilemma will result in an internal martial artist having a high level of Nei-gung power but unable to tackle actual combat situation. Under this constraint, an internal martial artist, in my opinion, is usually more prepared for self-defense than for ring-combat which demands a more intensive Yang side training . From another perspective, internal martial art clearly puts more attention to the Yang side when compared with spiritual meditation, and therefore chi-kung syndrome seldom falls upon a practitioner .
In the middle ground between spiritual meditation and internal martial art, there are a lot of masters or schools teaching people the art of chi-kung, which may include anything combining some meditative practice and some slow-movement practice, with or without foot-work. Some problems can arise in this middle ground without any solid guidance for practice. For example, moving arms around in a relaxed body with a meditative mind can generate chi, but may move your chi around uncontrollably with negative consequence. Of course, finding a professional master is also very important, if anything goes wrong, he might guide you back. This is the negative aspect of going towards the Yin. For the benefit of my readers who might just happen to be learning some form of such
chi-kungs, my advice is that it is always safer to lean towards more on
the side of nei-gung, i.e. use chi to do the more difficult task of
opening and alignment one's muscles and joints, than do the "lazy" way of swinging around, allowing one's chi a kind of uncontrolled free-flow.
Another negative aspect of going into the Yin is a "recreational chi-generation" like "recreational" OBE or divinity seeking without the guidance of time-tested spiritual guidance like the classics from the tradition of Tao and Zen meditation. This is a much more complex subject to be even able to be touched on the surface here.
A leaning towards all or most on the Yang side? Probably one is not doing chi-kung at all!
All in all, a correct balance is required in practices where the generation of chi is an essential ingredient. How the balance is to be stroke will depend on a practitioner's objective as well as on the physical and mental conditions of an individual practitioner, the beauty is in the detail, as always it is.