Peacedog wrote:"....many yoga and chi gung systems use breathe retention as well, primarily for increasing your chi."
This is true. It should be noted, however, that such retentions of the breath are invariably performed with a stationary physical posture, not while moving around with active steps and changes of posture while holding the breath.
Yogic pranayama with breath retention is preferrably practiced in a relaxed seated meditation position with legs crossed, with the body as still as possible externally, and with movement of the breath alone internally. Additionally, breath retention while performing other yogic postures (asanas) is normally only done while holding the final shape of the asana at full extension, or while in repose at the completion of the asana when fully returned to the beginning position, prior to performing another asana.
Similarly, most chi-kung routines recommend breath retention only while holding a stationary posture, whether standing or seated or reclining, but not while performing the transitional movements from one posture to the next one, and not while performing a 'moving chi-kung' exercise with active steps and frequent changes of posture such as Tai-Chi Chuan.
In both traditions, yoga and chi-kung, it is understood that the potential risk of internal injury is likely when changing the anatomical shape and position of the internal organs, and the spatial relationships among them, while retaining the breath with internal compression. This is why retention breathwork is usually recommended and reserved only for stationary postures.
Doc