The impact of sampling frequency on ground reaction force variables.

New portable and low-cost technologies for assessing limb loading may be useful in non-laboratory environments, but have relatively low sampling frequencies. The lowest recommended sampling frequency for impact kinetics has not been investigated. The purpose of this study was to determine the effect of sampling frequency on metrics of impact kinetics during landing, walking, and running. This was a retrospective analysis of bilateral drop vertical jumps, unilateral drop landings, treadmill running, and flat, inclined, and declined treadmill walking. Landing data were collected at 1920 Hz while walking and running data were collected at 1440 Hz. Impact kinetics were computed at the highest possible sampling frequency, and then data were continuously down-sampled to determine the impact on the following computed metrics: peak impact force, average LR, and impulse. The minimum sampling frequency to compute each outcome with 90%, 95%, and 99.5% accuracy when compared to the original sampling frequency were determined. To achieve 90% of the true value of impact force, a sampling frequency of 180 Hz was needed for running, 62 Hz for bilateral landing, and 48 Hz for remaining tasks. For average LR, a sampling frequency of 1440 Hz was need for running, 63 Hz for inclined walking, 192 Hz for bilateral landing, and 48 Hz for the remaining tasks. For impulse, 48 Hz was required for all tasks. The results of this study provide future researchers with a guide for selecting the sampling frequency required to accurately assess impact kinetics during walking, landing, or running.