Metabolic and mechanical changes in ultra-endurance running races and the effects of a specific training on energy cost of running

The present thesis is divided into two parts. Part I: The objectives of the first part were to examine the factors affecting the ultra-endurance performance and in particular which aspects influence the cost of running (Cr). Consequently, we defined how the Cr and running mechanics changed during different types (i.e. level and uphill) of ultra-endurance races. Finally, we proposed a specific training protocol for improving the Cr in high-level ultra-marathoners. We assessed the Cr by measuring the oxygen consumption at one (or more) fixed speeds using a metabolic unit. Further, for the running mechanics measurement and the spring-mass model parameters computation we used video analysis. Other parameters such as maximal muscle power of the lower limbs (MMP), morphological properties of the gastrocnemius medialis and Achilles tendon stiffness were also measured. Our studies showed that the maximal oxygen uptake, the fraction of it maintained throughout the race and the Cr are the main physiological parameters affecting the ultra-endurance performance, both in level and uphill competitions. Moreover, low Cr values were related to high MMP, vertical stiffness (kvert), low foot print index (FPI), Achilles tendon stiffness and external work. These results indicate that MMP, kvert and FPI are important factors in determining ultra-endurance performance. Also, our studies reported that during ultra-endurance competitions athletes tend to change their running mechanics after a certain time (~4 hours) rather than after a certain distance covered. Then, by adding strength, explosive and power training to the usual endurance training it is possible to lower the cost of running leading to a better performance. From these conclusions we suggest new training protocol for the ultra-marathoners including strength, explosive and power training which maintain a correct and less expensive running technique during ultra-endurance events. Part II: The aim of the second part was to develop and validate a customized thermoplastic polyurethane insole shoe sensor for collecting data about the ground reaction forces (GRF), contact and aerial times. This prototype allowed us to collect vertical GRF and contact time by using piezoresistive force sensors (RFS). Our final model was composed by a rubber insole, five RFSs, an s-beam load cell, an acquisition device (NI myRIO) and a battery case. By using this device we can collect data on field, avoiding the restrictions imposed by the laboratory environment