Abstract The aim of this study was to determine the effect of endurance training on the relationship between mechanical stride descriptors (stride rate and stride rate variability) and the aerobic energy cost that would be decreased by training in an all-out supra-lactate threshold run. Six long distance runners (175 ± 6 cm; 72 ± 9 kg; 27 ± 4 years) performed two identical track tests before and after 8 weeks of supra-lactate threshold training: an incremental test and a constant load test at 50% of the velocity difference between the lactate threshold and O 2max (vD50). During the constant load test, aerobic energy cost (EC), stride rate (SR) and stride rate variability (SRV) were measured. The constant load tests were carried out before and after training at the same absolute intensity, in order to compare stride mechani- cal descriptors. Our results show that after eight weeks of intermittent running at vD50, the velocity associated with O 2max (v O 2max ) increases (p = 0.03) due to the decrease of run- ning economy (RE, p = 0.02), and not due to an increase in O 2max (p = 0.5). EC remained unchanged with training (p > 0.1), but SRV was significantly reduced (p < 0.03). No relationship was observed before and after training between the stride rate variability and the aerobic energetic cost (rs < 0.5; p > 0.05). This study indicates that because of the initial level of the runners, endurance training has not induced an increased O 2max , but a decrease of the SRV. Further studies have to be conducted with more subjects in order to elucidate the mech- anisms underlying this decrease in SRV which is observed with training. ˙ V ˙ V ˙ V ˙ V ˙ V Keywords: Oxygen kinetics, training, running, stride rate variability. Introduction Numerous authors have shown that mechanical parameters such as stride frequency and stride rate variability are related to the oxygen cost (Högberg, 1952ab; Cavanagh & Williams, 1982; Candau et al., 1998). These authors have suggested that runners naturally choose the most economical stride rate and they have demonstrated significant relationships between this rate and the oxygen consumption during supra-lactate thresh- old constant-load exercise. Moreover, an increase in stride rate variability (SRV) has been reported during fatigue. It has been suggested that since a large variability is not favourable for maintaining an optimal step frequency, the increase in step rate variability observed during fatigue could partly explain the increase in aerobic energy cost (EC) observed at the end of the exercise (Candau et al., 1998). Therefore step rate variability could be related to the aerobic energy cost during supra-lactate threshold constant load exer- cise. However, no study has investigated the possible modi- fications of this SRV with training and its relationships with the kinetics of oxygen uptake or EC. Figure 1 illustrates a typical increase of the oxygen kinet- ics. For moderate constant-load cycle exercise (i.e., below lactate threshold) it has been shown that endurance training influences the kinetics of oxygen uptake. Moreover, several studies have reported that following an endurance training Accepted: 10 May, 2001 Address correspondence to: Jean Slawinski, Centre de Médecine du Sport CCAS, 2 Avenue Richerand, F-75010 Paris, France. Tel.: ++33 1 4202 0818; Fax: ++33 1 4239 2083; E-mail: jeanslawinski@hotmail.com Effect of Supra-Lactate Threshold Training on the Relationship between Mechanical Stride Descriptors and Aerobic Energy Cost in Trained Runners J. Slawinski 1 , A. Demarle 1 , J.-P. Koralsztein 2 and V. Billat 1 1 Laboratoire d’Etude de la Motricité Humaine, Faculté des Sciences du Sport, Université de Lille 2, France 2 Centre de Médecine du Sport, Caisse Centrale des Activités Sociales, Paris, France Archives of Physiology and Biochemistry 1381-3455/01/10902-110$16.00 2001, Vol. 109, No. 2, pp. 110–116 © Swets & Zeitlinger