Factors Affecting Peak Vertical Ground Reaction Forces in Running

Nine subjects (6 males, 3 females) ranging in body mass from 90.9 to 45.5 kg ran repeated trials across a force platform while being filmed at 50 fps. The subjects ran five barefooted trials at each of three speeds: 3.35, 3.83, and 4.47 m s-I. Force data were collected on-line and analyzed for the magnitude and temporal characteristics of the initial impact (FZ1) peak and the active (Fz2) peak of vertical ground reaction force (VGRF). Multiple regression and correlation analysis were used to study the relationship between the magnitudes of these kinetic data and kinematic and anthropometric data taken from the film and from measurements of the subjects. The results support the general conclusion that speed and, indirectly, body mass are significant effectors of the magnitudes of FZ1. In addition, other factors that correlate significantly with FZ1 are reciprocal ponderal index (RPI) and stature; halfstride length, step length, leg length, and vertical hip excursion during a halfstride cycle; and hip offset, contact angle, and dorsiflexion angle at contact. Body mass correlates highly with FZ2 (r = 0.95). Other significant factors correlating with Fz2 are RPI, stature, vertical hip excursion, dorsiflexion angle, hip offset, half-stride length, and step length. These data support earlier findings that speed and the effective mass of the leg at contact are important effectors of the magnitude of IF, . In addition, the kinematic and anthropometric parameters that contribute significantly to the variability in FZ1 and Fz2 are generally cross-correlated with body size and/or running speed.