Validation of a new method to measure contact and flight times during treadmill running

The purpose of this study was to validate a new method to measure contact and flight times during treadmill running and to test its reliability and sensitivity. Fifteen well-trained runners performed 7 sets of running at different speeds (from 10 to 22 km·h). Contact and flight times were simultaneously recorded by a high-speed video system (gold standard method) and a new method based on laser technology (SportJump System Pro). Athletes were classified according to their foot strike pattern (rearfoot vs. midfoot and forefoot). The new method overestimated the contact time and underestimated the flight time with respect to the gold standard method (p < 0.001). However, relationships and intraclass correlation coefficients (ICCs) between both systems were very strong (r and ICC > 0.99, p < 0.001). Contact time differences between the 2 systems depended on running speed (p < 0.001) but not on foot strike pattern or runners' body mass. This allowed to correct the differences in contact time and flight time. The new method was sensitive for detecting small differences in contact time (<20 ms) when the running speed increased and when the type of foot strike patterns changed. Additionally, a low intraindividual step variability (coefficient of variation = 2.0 ± 0.5%) and high intra- (ICC = 0.998) and interobserver (ICC = 0.977) reliability were shown. In conclusion, the new method was validated, being reliable and sensitive for detecting small differences in contact and flight times during treadmill running. Therefore, it could be used to compare biomechanical variables between groups in cross-sectional studies and to verify the influence of some independent variables (i.e., training, running economy, or performance) on running biomechanics.