Abstract
We investigated the changes in step temporal parameters and spring-mass behaviour
during the running phase of a major international triathlon competition. 73 elite
triathletes were followed during the 2011 World Championships Grand Final. The running
speed, ground contact and flight times were assessed over a 30 m flat section at the
beginning of the 4 running laps and towards the finish line, by using a high-frequency
camera (300 Hz). The leg and vertical stiffness, and vertical displacement of the
mass centre were calculated from step temporal characteristics. A concomitant decrease
in running speed, vertical stiffness and leg stiffness was reported during the 4 running
laps, except towards the finish line, where these parameters increased. Running biomechanics
was not affected between the beginning and the end of the 10 km run, when triathletes
were compared for the same running speed (1.68±0.16 m vs. 1.70±0.17 m for step length,
3.18±0.11 Hz vs. 3.16±0.15 Hz for step rate, 12.87±3.14 kN.m − 1 vs.12.76±3.05 kN.m − 1 for Kleg, 31.18±4.71 kN.m − 1 vs.30.74±3.88 kN.m − 1 for Kvert, at lap1 and finish, respectively). Multiple regression models revealed
that both step rate change and step length change were correlated with running speed
change and that the standardized partial regression coefficient was higher for step
length change than for step rate. Independent of the cofounding effect of speed and
despite the neuromuscular fatigue previously shown after long-duration events, the
lower limb mechanical stiffness and the overall spring-mass regulation were not altered
over the 10 km triathlon run in elite competitors. This study showed also that step
length explained, to a greater extent than step frequency, the running speed variance
in elite triathletes.
Key words
biomechanics - elite triathletes - running pattern - stiffness