Advances in motion analysis.

Time magnification in motion photography allows the observation of events in the stride cycle that normally are beyond the resolution of the human eye. Quantitative analysis goes a stage further by measuring the stride in terms of timing, distance, and angular variables. Motion analysis is a good technique for detecting left-right asymmetries of gait, and the nature of the asymmetries has some value in locating the site of a lameness. Repeated analyses of the same horse allow an objective assessment of the effects of local anesthesia, surgical treatment, or medication. It is anticipated that this will be one of the most useful clinical applications of motion analysis in the clinical setting. This article reviews the hardware and software available for cinematographic and videographic gait analysis. Manual digitization is tedious and time consuming, but these drawbacks are partially overcome by semi-automated systems, which use point prediction to estimate the location of the markers. Fully automated systems rely on the use of contrasting markers attached to the horse's skin overlying the anatomic landmarks. In some joints, skin motion relative to the underlying bones is sufficient to introduce significant errors in joint angle calculations unless appropriate correction algorithms are applied.