Author(s): HANLEY, B., CHATZAKIS, P., ZACHAROGIANNIS, E., PARADISIS, G., BISSAS, A., Institution: LEEDS BECKETT UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 864

INTRODUCTION:
Ultradistance races are longer than a marathon or last more than 6 h. Pacing profiles of ultrarunning events show considerable variation in running speed, and linking these variations to biomechanical responses could assist in developing training practices. Although such long-distance events require enormous physical effort, biomechanical measurements at regular intervals during competitive ultrarunning have not been undertaken. The aim of this study was to analyse changes in key biomechanical parameters during a 12-h track ultramarathon race.
METHODS:
Eight ultramarathon runners (7 men, 1 woman; 48 y (± 5), 1.72 m (± 0.10), 73.7 kg (± 10.4)) participated. Three stationary digital cameras (120 Hz) were used to record the runners as they ran through the calibrated section of the home straight. Video data were collected at the end of each hour (after 1 h, 2 h, etc.). The collected video files were imported into SIMI Motion (Simi Reality Motion Systems GmbH, Germany) for analysis. Spatiotemporal and angular data were calculated using coordinate data obtained using the 3D still image measurement tool. Global stiffness characteristics were calculated using estimated peak vertical ground reaction forces via the methods of Morin et al. (2005).
RESULTS:
There was an overall effect of running time on step length, flight time, duty factor, foot behind distance, foot angle at initial contact, knee angle at midstance and leg stiffness. There were no changes in thigh, knee, shank or ankle angles. The winner of the race completed 127 km over the 12-h duration (mean speed: 10.59 km/h), more than 15 km ahead of the runner-up. He was the only athlete who consistently recorded a flight time (mean: 0.051 s), with the longest mean step (1.09 m), shortest contact time (0.317 s), lowest duty factor (0.431), and the smallest thigh (57°) and knee angles (144°) at initial contact.
CONCLUSION:
There was a decrease in step length as the race progressed, caused by a reduction in flight time and shorter distances to the foot behind the body at toe-off. The athletes ran with double support phases after the 4th hour and thus had a grounded running style. That the race winner achieved a flight phase on every analysed lap highlights one biomechanical advantage he enjoyed over his competitors. There was no change in mean cadence and it is possible the athletes sacrificed step length to maintain a steady cadence. This might have helped with withstanding fatigue given it means a consistent firing rate for the lower limb muscles and is evidence of ultrarunners’ self-optimisation of stride characteristics. There were increases in leg stiffness during the race, which were important in the context of better running economy. Overall, the athletes maintained their lower limb joint angles, showing the effect of long-term training on their capabilities to maintain stable running techniques.

References
Morin et al., JAB, 2005, 21(2), 167–180.