Kinematic alterations after two high-intensity intermittent training protocols in endurance runners

Purpose: This study aimed to evaluate running kinematic characteristics during the early and late stages of 2 high-intensity intermittent training (HIIT) protocols with similar external load but different average running pace, as well as to compare the fatigue-induced changes during both HIIT protocols at a kinematic level. Methods: Eighteen endurance runners were tested on a track on 2 occasions: 10 runs of 400 m with 90-120 s recovery between running bouts (10 x 400 m), and 40 runs of 100 m with 25-30 s recovery between running bouts (40 x 100 m). Heart rate was monitored during both protocols; blood lactate accumulation and rate of perceived exertion were recorded after both exercises. A high-speed camera was used to measure sagittalplane kinematics at the first and last runs during both HIIT protocols. The dependent variables were spatial-temporal parameters (step length and contact and flight time), joint angles during support (relative angles of the hip, knee, and ankle), and foot strike pattern. Results: High levels of exhaustion were reached by the athletes during both workouts (blood lactate accumulation >12 mmol/L, rate of perceived exertion >15; peak heart rate (HRpeak) > 176 bpm). A within-protocol paired t test (first vs. last run) revealed no significant changes (p >= 0.05) in kinematic variables during any of the HIIT sessions. A between-protocol comparison with the first run of each protocol revealed the effect of running speed on kinematics: +2.44 km/h during the 40 x 100m: shorter contact and flight time (p <= 0.01) and longer step length (p = 0.001); greater hip flexion (p = 0.031) and ankle extension (p = 0.001) at initial contact; smaller knee and ankle flexion (p < 0.001) at midstance; and greater hip extension at toe-off (p < 0.001). Conclusion: HIIT sessions including runs for 15-90 s and performed at intensity above the velocity associated with maximal oxygen uptake did not consistently perturb the running kinematics of trained endurance runners. (C) 2019 Published by Elsevier B.V. on behalf of Shanghai University of Sport.