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Summary Surface electrodes were used to record electromyographic (EMG) activity of the long digital extensor muscle on the right hindlimb of 8 Thoroughbred horses for 8 s at the walk and 8 s at the trot before (unfatigued) and after (fatigued) an exercise test. The exercise test was performed on a motorised treadmill set on a 10% grade. Each test started at a speed of 6 m/s which was increased by 1 m/s each minute until the horse fatigued as indicated by its inability to keep pace with the treadmill with minimal encouragement. Observations were made on the horses prior to conditioning (untrained state) and after 8 weeks of regular exercise (trained state). The mean root‐mean‐square (rms) values of EMG bursts collected in each experimental trial were determined for each horse and group means were derived from the mean of independent subjects. Statistical comparisons for differences in rmsEMG were related to gait, fatigue and training. Mean rmsEMG at the trot was consistently higher than at the walk (P<0.05). At the walk, mean fatigued rmsEMG tended to be higher than the mean unfatigued rmsEMG in the untrained state and was significantly higher in the trained state (P<0.05). At the trot, mean fatigued rmsEMG was higher (P<0.05) than mean unfatigued rmsEMG in both the untrained and trained states. Training did not have an effect on mean rmsEMG of unfatigued muscles at the walk or the trot (P>0.05). However, fatigued muscles experienced higher EMG activity in the trained state at the walk (P<0.05). A similar tendency was observed at the trot. Results of this study suggest that surface EMG measurement may be useful for evaluating fatigue in exercising horses.

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This study uses computed tomography and computer aided design software (I-DEAS'") for the development of a three-dimensional electronic solids model of the lower limb of the horse. Data from two millimeter transverse contiguous slices of the distal forelimb of a yearling horse were acquired from a computed tomographic scanner and then transferred to a computer system via magnetic tape. Outline of the bony tissue for each scan slice was first obtained with a feature extraction algorithm. A solids model for each skeletal segment of the specimen was then reconstructed with I-DEAS'" and subsequently displayed with various graphics options. The reconstructed electronic solids model would be useful for the study of 3D joint mechanics and finite element analysis of the bony structures, as well as for diagnostic purposes providing CT images could be obtained antemortem.

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