This document discusses the physiological effects of mixed martial arts (MMA) competition and training. It notes that MMA involves elements of various martial arts and comprises rounds of fighting that are won by submission, decision, or knockout. Weight classes range from flyweight to super heavyweight. MMA requires a high level of aerobic and anaerobic fitness as well as muscular strength. However, there is little research on the impacts of weight cutting and regaining on performance, optimal training protocols, or talent identification for MMA athletes. More study is needed to fully understand the physiological demands of MMA competition and how to best prepare fighters.