Eur J Appl Physiol DOI 10.1007/s00421-010-1372-3 123 ORIGINAL ARTICLE Metabolic rate and gross eYciency at high work rates in world class and national level sprint skiers Øyvind Sandbakk · Hans-Christer Holmberg · Stig Leirdal · Gertjan Ettema Accepted: 18 January 2010  Springer-Verlag 2010 Abstract The present study investigated metabolic rate (MR) and gross eYciency (GE) at moderate and high work rates, and the relationships to gross kinematics and physical characteristics in elite cross-country skiers. Eight world class (WC) and eight national level (NL) male sprint cross- country skiers performed three 5-min stages using the skat- ing G3 technique, whilst roller skiing on a treadmill. GE was calculated by dividing work rate by MR. Work rate was calculated as the sum of power against gravity and fric- tional rolling forces. MR was calculated using gas exchange and blood lactate values. Gross kinematics, i.e. cycle length (CL) and cycle rate (CR) were measured by video analysis. Furthermore, the skiers were tested for time to exhaustion (TTE), peak oxygen uptake (VO 2peak ), and maximal speed (V max ) on the treadmill, and maximal strength in the laboratory. Individual performance level in sprint skating was determined by FIS points. WC skiers did not diVer in aerobic MR, but showed lower anaerobic MR and higher GE than NL skiers at a given speed (all P < 0.05). Moreover, WC skiers skated with longer CL and had higher V max and TTE (all P < 0.05). In conclusion, the present study shows that WC skiers are more eYcient than NL skiers, and it is proposed that this might be due to a bet- ter technique and to technique-speciWc power. Keywords Cross-country skiing · Cycle length · Skating · Work rate Introduction Energy delivery and mechanical eYciency are two key factors in endurance performance. Traditionally, cross- country skiers are tested for energy delivery capacity, and research over the last few decades has shown that world class skiers have been among the endurance athletes with the highest maximal oxygen uptake (VO 2max ) (Holmberg et al. 2007; Ingjer 1991; Saltin and Astrand 1967). Although a considerable number of studies have been done on work economy in cross-country skiing (HoV et al. 1999; HoVman 1992; HoVman et al. 1990a, b, 1994; Mahood et al. 2001; Mikkola et al. 2007; Millet et al. 1998a, b, 2002, 2003; Osteras et al. 2002), limited research has been done on mechanical eYciency (HoVman et al. 1995; Niinimaa et al. 1978). No study has compared eYciency between cross-country skiers of diVerent performance levels. Generally, two deWnitions have been used to express eYciency in endurance sports. Gross eYciency (GE) is deWned as the ratio of work generated to the total energy expended metabolic rate (MR), expressed as a percentage (Sidossis et al. 1992). In addition, work economy is often studied when the work rate is unknown, determined by measuring the steady-state oxygen uptake and the respira- tory exchange ratio (RER) at a given sub-maximal speed (Moseley and Jeukendrup 2001; Saunders et al. 2004). GE is regarded as reXecting the eYciency of the entire human Communicated by Susan Ward. Ø. Sandbakk (&) · S. Leirdal · G. Ettema Human Movement Science Programme, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway e-mail: oyvind.sandbakk@svt.ntnu.no H.-C. Holmberg Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, Östersund, Sweden