The bouncing mechanism of running in children
The bouncing mechanism of running in children
The bouncing mechanism of running
The effect of age and body size on the bouncing mechanism of running was studied in children 2-16 years of age. The natural frequency of the bouncing system (fs) and the external work required to move the center of mass of the body were measured using a force platform.
At all ages, during running below ±11 km h-1, the freely chosen step frequency (f) is about equal to fs (symmetric rebound), independent of speed, although it decreases with age from 4 Hz at 2 years to 2.5 Hz above 12 years. The decrease of step frequency with age is associated with a decrease in the mass-specific vertical stiffness of the bouncing system k/m due to an increase of the body mass m with a constant stiffness k. Above 12 years, k/m and f remain approximately constant due to a parallel increase in both k and m with age.
Above the critical speed of ±11 km h-1, independent of age, the rebound becomes asymmetric, i.e. f < fs. The maximum running speed (V,-- f ,max ) increases with age while the step frequency at V,-- f ,max remains constant (±4 Hz), independent of age.
At a given speed, the higher step frequency in preteens results in a mass-specific power against gravity less than that in adults. The external power required to move the centre of mass of the body is correspondingly reduced.
More information: Bénédicte Schepens
Main publications of the lab on that topic
SCHEPENS B., WILLEMS P.A. & CAVAGNA G.A. (1998) The mechanics of running in children. J. Physiol., London 509: 927-940
SCHEPENS B., WILLEMS P.A., CAVAGNA G.A. & HEGLUND N.C. (2001) Mechanical power and efficiency in running children. Pflugers Arch. 442: 107-116
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