Practitioners of tai-chi chi-kung and zhan zhuang will tell you that they can generate enough energy to circulate around their bodies and achieve the objective of "Muscles as one" (肌肉如一) without using sexual energy. And fair to say, people with a good discipline of exercise (like jogging, swimming, or mind-body exercise such as tai-chi) do experience a higher libido level than folks leading a more sedentary lifestyle. In other words, an activation of libido is part and parcel of a practice that can generate chi (jogging can generate chi, but not as efficient as doing tai-chi; of course I'm not saying that tai-chi is categorically better than jogging, I'm only comparing chi-generation efficiency, and that's why tai-chi is better for older people to practice than jogging).
Meditation is a form of mind-body exercise in Taoist practice. In Hui Ming Jing (and many other Taoist texts), meditative practice without energy generation will be frowned upon and considered as no-use like a piece of cold rock kind of sitting.
In Taoist meditation, energy will be generated by three sources in the initial practice:
1. Energy generated by the breathing muscles, being channeled into a single point (dantian's aperture 竅).
2. Energy generated by the hands - both as energy generator and balancer, again which is channeled to the dantian.
3. Energy generated by the folded legs (a source of powerful energy, that's why tai-chi practitioners put a lot of emphasis in opening the groin area, the ball-and-socket joins [胯], that's way the best way to practice meditation is to have folded legs rather than simple seated position on a chair. Since we are talking about this topic, I might as well add that for zhan zhuang (站樁), there is a seated position but with legs lifted up or not fully grounded so as to help liberate energy from the groan area).
The concentrated energy in the dantian aperture can then be directed to flow upwards along the spine as microcosmic circulation.
The "problem" is with the muscles in the Hui-Yin (會陰) (with anus & vicinity) will be activated to direct energy to the dantian aperture. In the process, in young males, the sex organ is likely to be stimulated causing a heightened sexual drive and possibly with an erection too.
It is actually a clever way for the Taoist to turn an embarrassment (and a hindrance to focused meditation) into yet another source of energy. The level of libido will be reduced after the energy has been led up through the spinal cord. And according to the text, eventually a Taoist master can be so proficient and conditioned in re-directing the sexual energy, he will no longer afraid of having any sexual urge (since it is a conscious action of re-direction, a modern man should not be afraid of losing one's libido because of Taoist meditation!)