The purpose of this review is to explore existing research on the physiological aspects of difficult rock climbing. Findings will be categorized into the areas of an athlete profile and an activity model. An objective here is to describe high-level climbing performance; thus the focus will primarily be on studies that involve performances at the 5.11/6c (YDS/French) level of difficulty or higher. Studies have found climbers to be small in stature with low body mass and low body fat. Although absolute strength values are not unusual, strength to body mass ratio is high in accomplished climbers. There is evidence that muscular endurance and high upper body power are important. Climbers do not typically possess extremely high aerobic power, typically averaging between 52-55 ml.kg(-1).min(-1) for maximum oxygen uptake. Performance time for a typical ascent ranges from 2 to 7 min and oxygen uptake (VO2) averages around 20-25 ml.kg(-1).min(-1) over this period. Peaks of over 30 ml.kg(-1).min(-1) for VO2 have been reported. VO2 tends to plateau during sustained climbing yet remains elevated into the post-climb recovery period. Blood lactate accumulates during ascent and remains elevated for over 20 min post-climbing. Handgrip endurance decreases to a greater degree than handgrip strength with severe climbing. On the basis of this review, it appears that a specific training program for high-level climbing would include components for developing high, though not elite-level, aerobic power; specific muscular strength and endurance; ATP-PC and anaerobic glycolysis system power and capacity; and some minimum range of motion for leg and arm movements.