Figure 1. Model fitting for events with three progression periods. Performances of the Oxford-Cambridge boat race, Vasaloppet cross-country ski and speed ski record (for covering a 100-m distance) in seconds. doi:10.1371/journal.pone.0003653.g001 Discussion Our study is the first to model the performance evolution of outdoor sport events influenced by physiological, technological and environmental factors. Although the studied events largely differ in longevity, duration and physical environment (ice, snow, water, ground, air), the piecewise decaying exponential model describes a common evolutive pattern. Older events BPs follow a progression with high curvature coefficients suggesting the same rapid improvement in the early phase and a profile made up of two or three periods over the XIXth and XXth centuries. In addition, the initial b state that we estimated here is lower than the value previously calculated for Olympic sports (46% vs 60%), which may be due to the fact that here we took into account all records starting at day 0, whereas national Track & Field or Speed Skating competitions had already started long before the first Olympic games [1]. This emphasizes the particular status of these sport monuments in their own discipline. Robert Fogel [18] previously used the term ‘‘techno-physiolog- ical evolution’’ to describe human health and anthropometric Sport Performance Evolution Figure 2. Model fitting for events with two progression periods. Performances of the Elfstedentocht speed skating race (normalized distance of 200 km) in hours and of the Channel crossing swimming in minutes. doi:10.1371/journal.pone.0003653.g002 gains over the last three centuries. Similar improvements occured over the XXth century (enhanced physical training, higher number of participants, nutritional practice, biological knowledge and medical advances) in sports like rowing [19], cross-country skiing [20,21], speed skating [22] or cycling [23], which are sports with high aerobic requirements. Indeed, these events present similar progression patterns (a and b coefficients) than those obtained in Olympic disciplines performed in a controled environment and quantified by world records [1]. Predictions of the BP asymptotic limits from the piecewise exponential model suggest that the achievement of human limits may occur during the XXIth century. Furthermore, our model suggests that the limits will be rapidly reached in events highly dependent on physiological capabilities, e.g. expected performance improvements over the next century in Oxford–Cambridge, Vasaloppet and Elfstedentocht are lower than 2%. The most recent of these events, the Hawaii Ironman, may have already achieved its asymptotic value (b9 value: 99.64%) although it has been challenged since three decades only. The performance evolution for this event may be based on its rapidly growing popularity and benefits from the advances previously made in the three sports involved in triathlon (swimming, cycling, running). These results compared to those published for world records [1] suggest that environmental and climatic conditions, though influencing a year to year performance progression, do not modify the secular trend toward ultimate performance achievement. Maximal boat speed in transatlantic records largely depends on environmental conditions (north Atlantic depression speed and numbers) rather than on individuals’ physical power. Tools have been developed to control, at least partly, environmental factors for the athlete’s benefits: e.g. navigation equipments allow for information to be transmitted to, or from, the boat in order to PLoS ONE | www.plosone.org 3 November 2008 | Volume 3 | Issue 11 | e3653