The purpose of this article is to inform fighters and coaches in the mixed martial arts about the nature of instability training, and to provide guidance for those who wish to engage in it.The term ‘instability training’ was chosen over other commonly used terms, like ‘core stability training’, because it emphasises the training goal, which is to create instability in each exercise, not stability. In this article, the term ‘core’ refers to the musculature that supports the trunk (i.e. rib cage and spine), upper extremity (shoulder girdle) and lower extremity (pelvic girdle). All of these muscles work together as an integrated whole to maintain balance, rather than in isolation4 and core stability (or balance) is controlled through complex neuronal communication between peripheral sensors within the core musculature and central brain structures.6