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.