Lactate threshold responses to a season of professional British youth soccer

Objective: To examine the changes in aerobic endurance performance of professional youth soccer players throughout the soccer season. Methods: Nine youth soccer players were tested at six different time points throughout the soccer season by sub-maximal blood lactate assessment, using an incremental treadmill protocol. Whole blood lactate concentration and heart frequency (Hf) were determined at each exercise stage. Running velocities at the first lactate inflection point (v-T_lac) and at a blood lactate concentration of 4 mmol l^-1 (v-4mM) were determined. Results: Running velocity at the two lactate thresholds increased from the start of pre-season training to the early weeks of the competitive season, from 11.67 (0.29) to 12.96 (0.28) km h^-1 for v-T_lac, and from 13.62 (0.25) to 14.67 (0.24) km h^-1 for v-4mM (p<0.001). However, v-T_lac and v-4mM when expressed relative to maximum heart frequency (Hf_max) remained unchanged. The Hf to blood lactate concentration relationship was unchanged after the pre-season training period. The two expressions of lactate threshold did not reveal differences between each other. Conclusion: Running velocity at v-T_lac and v-4mM increased significantly over the pre-season period, but v-T_lac and v-4mM were unchanged when expressed relative to Hf_max. This finding may indicate that increased endurance performance may be mainly attributable to alterations in Vo_2max. Although lactate assessment of soccer players is useful for determining endurance training adaptations in soccer players, additional assessment of the other two determinants of endurance performance (Vo_2max and running economy) may provide more useful information for determining physiological adaptations resulting from soccer training and training interventions.