Physiological demands of running during long distance runs and triathlons

The aim of this review article is to identify the main metabolic factors wh ich have an influence on the energy cost of running (Cr) during prolonged e xercise runs and triathlons. This article proposes a physiological comparis on of these 2 exercises and the relationship between running economy and pe rformance. Many terms are used as the equivalent of 'running economy' such as 'oxygen cost', 'metabolic cost', 'energy cost of running', and 'oxygen c onsumption'. It has been suggested that these expressions may be defined by the rate of oxygen uptake ((V)over dotO(2)) at a steady state (i.e. betwee n 60 to 90% of maximal (V)over dotO(2)) at a submaximal running speed. Endurance events such as triathlon or marathon running are known to modify biological constants of athletes and should have an influence on their runn ing efficiency. The Cr appears to contribute to the variation found in dist ance running performance among runners of homogeneous level. This has been shown to be important in sports performance, especially in events like long distance running. In addition, many factors are known or hypothesised to i nfluence Cr such as environmental conditions, participant specificity, and metabolic modifications (e.g. training status, fatigue). The decrease in ru nning economy during a triathlon and/or a marathon could be largely linked to physiological factors such as the enhancement of core temperature and a lack of fluid balance. Moreover, the increase in circulating free fatty aci ds and glycerol at the end of these long exercise durations bear witness to the decrease in Cr values. The combination of these factors alters the Cr during exercise and hence could modify the athlete's performance in triathl ons or a prolonged run.