Purpose: We compared incline and level training sessions as usually used in elite 400-m runners through stride kinematics and muscular activity measurements.
Methods: Nine highly trained 400-m runners (international and French national level) performed two maximal velocity sprints: 1) 300-m on level ground (LEV) and 2) 250-m on an incline ground (INC) characterized by a mean +/- SD grade of 5.4 +/- 0.7%. Kinematics (250 Hz) and electromyography parameters (root mean square [RMS] and integrated electromyography [iEMG] measurements) were analyzed (from 40- to 50-m phases).
Results: INC induced a decrease in running velocity compared to LEV (6.28 +/- 0.38 vs 7.56 +/- 0.38 m.s) explained by a reduction in stride length (-14.2%) and stride rate (-7.4%) and by an increase in push-off time (+26.4%). Kinematics analysis indicated that the lower limbs were more flexed during INC running. Concerning the level of activity of the lower limb muscles, the major findings pointed out the decrease in RMS for semitendinosus and biceps femoris muscles during the contact phase and for vastus lateralis during its concentric phase. However, iEMG of both semitendinosus and biceps femoris muscles remained constant during both contact and push-off phases.
Conclusion: Our results are clearly different from those of previous studies carried out at similar absolute velocities in both LEV and INC conditions, which were not the case in this study. The lower running velocity marking INC running was associated with a decrease in the activation of the hamstrings. Trainers should particularly consider this lower level of activation of the hamstrings muscles during INC maximal sprint.