Abstract
Research into the biomechanical manifestation of fatigue during exhaustive runs is
increasingly popular but additional understanding of the adaptation of the spring-mass
behaviour during the course of strenuous, self-paced exercises continues to be a challenge
in order to develop optimized training and injury prevention programs. This study
investigated continuous changes in running mechanics and spring-mass behaviour during
a 5-km run. 12 competitive triathletes performed a 5-km running time trial (mean performance:
̴17 min 30 s) on a 200 m indoor track. Vertical and anterior-posterior ground reaction
forces were measured every 200 m by a 5-m long force platform system, and used to
determine spring-mass model characteristics. After a fast start, running velocity
progressively decreased (− 11.6%; P<0.001) in the middle part of the race before an end spurt in the final 400–600 m.
Stride length (− 7.4%; P<0.001) and frequency (− 4.1%; P=0.001) decreased over the 25 laps, while contact time (+ 8.9%; P<0.001) and total stride duration (+ 4.1%; P<0.001) progressively lengthened. Peak vertical forces (− 2.0%; P<0.01) and leg compression (− 4.3%; P<0.05), but not centre of mass vertical displacement (+ 3.2%; P>0.05), decreased with time. As a result, vertical stiffness decreased (− 6.0%; P<0.001) during the run, whereas leg stiffness changes were not significant (+ 1.3%;
P>0.05). Spring-mass behaviour progressively changes during a 5-km time trial towards
deteriorated vertical stiffness, which alters impact and force production characteristics.
Key words
leg spring behaviour - stride parameters - stiffness - pacing strategy - middle distance
running
