Prana = life-force, & is generally received from the breath, sunlight & food.
It is also built up by other means: in the body via toning up the glands which in turn increases the life-force in the glands. When a body part works optimally, it is able to store more life-force, & in the glands, each time a yoga posture is done, the relevant gland that is activated by doing the posture, squirts out hormones from that gland/s. The gland starts to regenerate: & correspondingly, we start to have more vitality. Vitality is also life-force.
As the mental/emotional "blocks" in the body lessen, prana moves more freely around the body = more life-force. These mental/emotional blocks are stored in the body & they block prana moving in those areas.
As the energy revives, via "stretching", mental & emotional energy is released from the little chakras which are on the meridians & which are also known as acupuncture points. More energy is able to flow along these meridians, increasing the life-force not only in the body but also mentally & emotionally creating mental & emotional vitality.
As the system is revived with movement & pranayama, the whole body .
As the nerve impulses come to operating in a more harmonious manner, the life-force is revived within the body.
concentration/dharana = focusing the mind "draws" our prana inwards, which means in effect that we are not dissipating it. We are building it up internally.
Meditation/dhyana = as we allow the mental/emotional/visual inner content to flow unimpeded in meditation, we are again allowing the internal "blockages" a safe release.....& more prana is able to take up the space that these "blockages" have vacated..
Sound, whether in a mantra or in chanting the ancient yoga truths, work on both body parts & the corresponding brain area, building up the life-force in both.
Yama = restraint/control
Yoga philosophy gives techniques for behavioural & attitudes to conduct our life so that we do not dissipate the prana, we build it up instead.
We also learn how to restrain the breath in practicing yoga pranayama (breathing techniques). We hold the breath in, which creates increased absorption, & we hold the breath out: this stores the inhaled prana. And with bandhas: physical body movements which lock/squeeze parts of the body, & in turn restrain absorbed prana, then when we come out of the lock, we receive a concentrated "burst" of prana.
Pranayama therefore is the control of our life -force, we can build it up within ourself & we can restrain it, meaning that we can contain it, store it. This means that we don't waste it.