It is not surprising that people in this mental state open themselves up to possible demonic influence. Yoga is not for Christians. Most martial arts teachers include meditation as part of their instruction. The mental conditioning that meditation brings is largely responsible for the amazing physical feats that advanced martial artists do. Focusing the attention on the single task, such as breaking many boards with a bare hand, is brought about by achieving the impassive Zen mental state.
Christians have no business being involved in the martial arts, even at the most elementary level.
The author is not applying this statement to the subject of wars, which in his estimation sometimes are justified.