Adaptación, validación y aplicación de una nueva tecnología para valorar la biomecánica de la carrera de resistencia

Abstract

Long-distance running performance depends on several factors such as physiology (VO2max, anaerobic threshold, running economy, age, gender, muscle fibre composition, fatigue and ethnicity), environment (air/wind, temperature, humidity, altitude and slope), psychology (intervention, focus of attention and music), training (endurance, resistance, heat acclimation and altitude training) and biomechanics (anthropometry, “legstiffness”, flexibility, foot strike pattern and spatio-temporal parameters). Nowadays, the real influence of some of these variables is still unknown. In particular, the influence of some biomechanical parameters such as foot strike pattern and/or spatio-temporal parameters on running economy, their relationship with physiological parameters and the impact on running performance are controversial topics of discussion. It is possible that the technological limitations of the measuring instruments have generated this discrepancy. The present Thesis would try to explain these issues by the following aims: 1- adapt and validate a new method to measure spatio-temporal variables (i.e. contact and flight times, step rate and length) during treadmill running, which would allow to register automatically a high and representative number of steps of both feet, 2- analyze the influence of foot strike pattern (rearfoot vs midfoot/forefoot) on running economy and other biomechanical variables, 3- examine simultaneously the influence of anthropometric, physiological and biomechanical variables on running performance. The validation of the new method (SportJump System Pro; a contact laser platform inserted in a treadmill and connected to a specific software) was performed with 15 runners, who completed 7 sets of running between 10 and 22 km·h-1 . Contact and flight times were registered with a high-speed video camera (gold standard method) and the new method. The new technology overestimated the contact time and underestimated the flight time at every running speed. However, these differences between both methods did not depend on runners’ foot strike pattern or mass, and they were corrected according to running speed. In conclusion, the new method was validated, being reliable and sensitive for detecting small changes in running spatio-temporal parameters, being the analysis tool used in next experimental phases of this Thesis. The analysis of the influence of foot strike pattern on running economy and biomechanical variables was performed by comparing biomechanical and physiological Abstract variables of 10 rearfoot and 10 midfoot/forefoot well-trained runners with a similar level of performance in a half-marathon. No differences were observed in VO2max, aerobic and anaerobic thresholds. Nevertheless, rearfoot strikers were between 5.0 and 9.3% more economical than midfoot/forefoot strikers at submaximal speeds. Step rate and length were not different between groups, but rearfoot strikers showed longer contact time and shorter flight time than midfoot/forefoot strikers at all running speeds. Thus, the differences in contact and flight time could explain running economy differences. Finally, the influence of anthropometric, physiological and biomechanical variables on running performance was examined analyzing 48 runners of different level. They were divided into 4 groups according to their performance level in a half-marathon. Significant differences between groups and correlations with performance were observed in training-related (experience and km per week), anthropometrics (mass, body mass index and sum of six skinfolds), physiological (VO2max, aerobic and anaerobic thresholds and running economy) and biomechanical variables (foot strike pattern). Higher level runners showed shorter contact time than lower level runners at the same running speed. However, this was due to the higher percentage of midfoot/forefoot runners in the best group of runners. Taking into account runners’ foot strike pattern and speed, these differences disappeared. Step rate and length were not different between groups at the same running speed. Therefore, running spatio-temporal variables (contact and flight time, step rate and length) were not sensitive to performance. To sum up, the adaptation and validation of the new method to measure running spatio-temporal parameters allowed us to obtain the following conclusions: 1- rearfoot strikers are more economical than midfoot/forefoot strikers at submaximal running speeds, 2- midfoot/forefoot strikers have an approximately 10% shorter contact time than rearfoot strikers, which could be beneficial at high running speeds (> 20 km·h-1 ), 3- running spatio-temporal parameters (contact and flight time, step rate and length) seem not to be sensitive to performance level.