The effect of gait speed and load carrying on the reliability of ground reaction forces

Many risk factors for instability have been identified, but gait stability is difficult to measure and quantify. Conventional methods to assess gait stability are based on perturbing the subject until a fall is produced resulting in information about the boundary of stable gait patterns. Without perturbing the gait control, this study focuses on the reliability of successful weight transfers during various gait speed and load carrying. Participants walked on a treadmill under fifteen conditions (five load positions x three speeds) while vertical ground reaction forces were recorded for a number of consecutive steps. The first four statistical moments (i.e. mean, standard deviation, skewness and kurtosis) of the distributions of several kinetic parameters were calculated based on the series of recorded steps. Changes were seen in all four moments of various parameters for several speed and loading conditions. The results suggest that alterations are made in both the basic gait pattern and in the tradeoff point between accuracy of execution of the gait pattern and successful completion of the task. Changes in the higher moments suggest that some loading positions and higher speeds reduce the reliability of the execution of gait patterns while other loading positions may actually increase the reliability. (C) 2002 Elsevier Science Ltd. All rights reserved.