Limits to human performance

Introduction In 1950, Maurice Herzog and Louis Lachenal became the first climbers to reach the summit of an 8000 m peak (Annapurna, 8091 m). Since that pioneering achievement, tens of thousands of mountaineers have ventured to Nepal, Pakistan, Tibet and China to climb the 14 peaks that rise above 8000 m. Some have succeeded. Some have died in the attempt. Climbing above 8000 m is a severe test of human performance (West, 2000). The attendant drama has long been riveting to a vast popular audience and has also helped inspire a wealth of research on high-altitude medical physiology (Houston, 1998; Hultgren, 1997; Richalet, 1999; Roach et al., 1999). Remarkably, few studies have quantified risk (Town, 1986; Pollard and Clarke, 1988; Huey and Eguskitza, 2000), even though the reality of Himalayan mountaineering tragedies is apparent (Krakauer, 1997). Many questions need to be addressed. How risky is reaching the summit of an 8000 m peak? Does supplemental oxygen enhance survival (Huey and Eguskitza, 2000)? Does the size of a team influence success rate or death rate? How do factors such as height, steepness, difficulty and weather affect success and mortality? Does risk of death from different causes (e.g. avalanche versus illness) change with altitude (Pollard and Clarke, 1988)? Answers to such questions can ultimately provide insight into what limits human performance in an extreme environment and also provide mountaineers with information relevant to risk-taking. We can now begin to address such questions. The necessary historical data derive from extensive interviews obtained over many years by E. Hawley and by X. Eguskitza supplemented by published records in the mountaineering literature (e.g. American Alpine Journal, Alpine Journal, Himalayan Journal and High and scores of books). To search for patterns in these data, we adopt analytical techniques that were developed for evolutionary studies of Natural Selection on organisms (Endler, 1986; Schluter and Nychka, 1994). For example, we attempt to determine whether rates of success or of death correlate with factors such as mountain height, use of supplemental oxygen or team size. Our analyses are still preliminary but nevertheless provocative. We begin by reviewing some of the physical and physiological challenges associated with high-altitude mountaineering. Then, we will use available mountaineering data to test two hypotheses: (i) that the success rate in reaching the summit is inversely related to a mountain’s height and (ii) that death rates are directly related to mountain height. 3115 The Journal of Experimental Biology 204, 3115–3119 (2001) Printed in Great Britain © The Company of Biologists Limited 2001 JEB3350