Hamill, Joseph, Research Quarterly for Exercise and Sport
Identification of Variable Types for Prediction of Impact Forces
Lower extremity injury during impact activities can be the result of chronic or acute loads to the body. The type of load associated with the movement might be reflected by the biomechanical variables used to characterize the activity. For example, discrete point values are typically associated with minimum or maximum values, analogous with acute loads. Average values obtained across some defined time period which minimize the effect of discrete peak values would appear to be more closely aligned with the concept of chronic loads. The purpose of the study was to assess the effects of selected variable types (reflecting body loads) on the prediction of impact forces. Ten subjects performed a total of 75 drop landings (0.6 m) across three days. High speed video (200 Hz) and force platform data (1000 Hz) were obtained from both lower extremities during the impact phase of landing. Impact forces associated with peak forefoot (F1) and rearfoot (F2) contact were identified for each subject-leg-trial. Anthropometric data were obtained and joint kinetic values computed as well as selected lower extremity kinematic values. A multiple regression procedure was used (|alpha~ = 0.05) to predict F1 and F2 values from kinematic and joint kinetic variables of the following three types: discrete point (D), interval average (A) and combination (C) which included D and A variables. Results of the prediction models across subjects ranged from 24.2% explained variance (EV) (A, F2, kinematic) to 89.0% EV (C, F2, joint kinetic). C models were identified as the best overall predictors for F1 and F2 across all subjects, accounting for 68.6% overall EV. D accounted for 1.3 times the EV versus A, overall. Joint kinetic variables were more effective than kinematic variables (1.9 times EV) for the prediction of impact forces while F2 models exhibited 1.2 times greater EV than F1 models. Results from the study indicated that F1 and F2 are better predicted using D variable types, suggesting that variables related to acute loading are important to examine when investigating mechanisms of lower extremity impacts.
Ground Reaction Forces in Elite Runners With Cerebral Palsy
The purpose was to examine the ground reaction forces (GRF) of elite runners with cerebral palsy (CP). Because of lack of information on kinetic running parameters of individuals with CP, prevalence of lower extremity injuries at the knee joint with elite athletes with CP, success of using kinetic techniques for clinical analyses of walking gait of individuals with CP, and concern for joint and tissue stress from suspected compensatory movements, a need exists to determine the GRF of elite runners with CP to develop a baseline on trained individuals. Using the USCPAA classification system, 7 male Ss included Class 5 (n = 1); Class 6 (n = 3), Class 7 (n = 2), and Class 8 (n = 1) athletes who qualified for the 1992 Paralympic Games in Barcelona, Spain (mean age = 22.43 yrs; mean ht = 178.89 cm; mean wt = 621.45 N; and mean yrs of competitive experience = 8.86). Regarding CP involvement of the lower extremities, 4 Ss had involvement in both legs; 1 S was primarily left-side involved; 1 S was predominantly right-side involved; and 1 S had no leg involvement. Data collection occurred in the Biomechanics Laboratory during the Paralympic Invitational Training Camp at Ball State University during July, 1992. GRF data were collected using a Kistler 9281 B force platform at a sampling rate of 1000 Hz. A Zenith 386 computer using ASYST and FADAP software was used for data storage and analysis. Force recordings were normalized to body weight. Variables were stance time, peak impact, time to peak impact, and average vertical ground reaction force (AVGRF). Ss ran at 2 speeds: a self-selected aerobic training pace (SSATP) and a near race pace (NRP). AVGRF for each class was:
SSATP (%BW) SD NRP (%BW) SD Class 5 139. …