title: A simple method for measuring stiffness during running.
abstract: The spring-mass model, representing a runner as a point mass supported by a single linear leg spring, has been a widely used concept in studies on running and bouncing mechanics. However, the measurement of leg and vertical stiffness has previously required force platforms and high-speed kinematic measurement systems that are costly and difficult to handle in field conditions. We propose a new "sine-wave" method for measuring stiffness during running. Based on the modeling of the force-time curve by a sine function,this method allows leg and vertical stiffness to be estimated from just a few simple mechanical parameters: body mass, forward velocity, leg length, flight time, and contact time. We compared this method to force-platform-derived stiffness measurements for treadmill dynamometer and overground running conditions, at velocities ranging from 3.33 m.s-1 to maximal running velocity in both recreational and highly trained runners. Stiffness values calculated with the proposed method ranged from 0.67 % to 6.93 % less than the force platform method, and thus were judged to be acceptable. Furthermore, significant linear regressions (p < 0.01) close to the identity line were obtained between force platform and sine-wave model values of stiffness. Given the limits inherent in the use of the spring-mass model, it was concluded that this sine-wave method allows leg and stiffness estimates in running on the basis of a few mechanical parameters, and could be useful in further field measurements.
authors.affiliation: Physiology Laboratory, PPEH Res. Unit, Univ. of Saint-Etienne, France.
authors.forename: Jean Benoît
authors.initials: JB
authors.lastname: Morin
authors.forename: Georges
authors.initials: G
authors.lastname: Dalleau
authors.forename: Heikki
authors.initials: H
authors.lastname: Kyröläinen
authors.forename: Thibault
authors.initials: T
authors.lastname: Jeannin
authors.forename: Alain
authors.initials: A
authors.lastname: Belli
mesh_terms: D000328:Adult; D000465:Algorithms; D003198:Computer Simulation; D004548:Elasticity; D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D010808:Physical Examination / Q000379:methods*; D012420:Running / Q000502:physiology*; D013314:Stress, Mechanical