Lower limb mechanical asymmetry during repeated treadmill sprints.

Stride mechanical imbalances between the lower limbs may be detrimental to performance and/or increase injury risks. This study describes the time course and magnitude of asymmetries in running mechanical variables during repeated treadmill sprints and examines whether inter-limb differences in sprinting mechanics increase with fatigue. Thirteen non-injured male athletes performed five 5-s sprints with 25-s recovery on an instrumented treadmill, allowing the continuous (step-by-step) measurement of running kinetics/kinematics and spring-mass characteristics calculation. For each variable, bilateral leg asymmetry (BLA%) between the left and the right leg was defined as: {[(high value-low value)/low value]×100}. BLA% for propulsive power and horizontal forces averaged ∼12-13%, while lower values occurred for step-averaged values of running velocity, resultant and vertical forces (all ∼4%). For all sprints, kinematic BLA% ranged from 1.6±1.0% (swing time) to 9.0±5.3% (aerial time). BLA% for vertical and leg stiffness was 6.4±4.9% and 7.6±3.6%, respectively. While distance covered decreased across repetitions (P<0.05), there was no significant interaction between sprint repetitions and leg side for any of the mechanical variables studied (all P>0.05). Although inter-limb differences were observed for many running kinetics/kinematics and spring-mass characteristics during repeated treadmill sprints, the lack of interaction between sprint repetitions and leg side suggests that lower limbs fatigued at a similar rate.