Camera speeds for optoelectronic assessment of stride-timing characteristics in horses at the trot

Robert L. Linford From the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616.

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 DVM, PhD

Summary

Quantitated locomotion analysis is increasingly being used during assessment and treatment of gait disorders in human beings. Locomotion analysis is also thought to have potential for enhancing the assessment of lameness in horses. Availability of highspeed video recording systems has simplified the process of quantitated locomotion analysis; however, the high cost of such systems has limited their use for routine clinical assessment in horses. The temporal resolution of 500- to 1,000-image/s (Hz) recording systems is beyond what has been considered necessary for precise quantitation of short-duration events in horses at the trot; however, it is uncertain whether the temporal resolution of more economical 60-Hz recording systems is adequate.

To determine whether a recording rate of 60 Hz is satisfactory for assessment of stride-timing values in horses at the trot, the stride-timing values calculated from 60-Hz recordings were compared with those calculated from 1,000-Hz recordings that had been simultaneously made for 5 horses trotting on a horizontal treadmill at a speed of 3.0 m/s. The left forefoot of each horse was fitted with an instrumented horseshoe that illuminated and quenched light-emitting diodes (led) in view of both cameras precisely at toe contact, heel contact, heel lift, and toe lift. The exact pattern and timing of foot placement and lift was referenced by the illumination pattern of the led. Recordings of 10 consecutive strides were reviewed, image by image for each horse, and the elapsed time at each important stride event was tabulated. Stride-timing values were then arithmetically calculated from the elapsed time values for each recording system.

Significant differences were not found between the stride-timing values obtained from the 1,000-Hz recordings and those obtained from the 60-Hz recordings for any timing variable assessed. For each timing variable, the mean value of the 60-Hz measurements for the 10 strides of each horse was within 3.3 milliseconds (ms) of the mean value of the 1,000Hz measurements for the same 10 strides, with the exception of the 60- and 1,000-Hz assessments of the toe-heel contact interval for 1 horse, which differed by 6.9 ms. On the basis of the 60- and 1,000-Hz recordings, the overall mean ± SD values for the stride, stance, swing, and breakover durations were, respectively, 731.4 ± 16.0 ms, 320.7 ± 15.2 ms, 410.7 ± 18.7 ms, and 60.5 ± 9.9 ms. The toe-heel contact interval was 7.6 ± 8.8 ms.

The instrumented shoe and led mechanism provided a unique, simple, and accurate method for quantitation of stride timing, with clear visual references for placement and lift. Using the shoe for optoelectronic assessment, it was found that a recording rate of 60 Hz was adequate to study stride-timing characteristics of horses trotting at 3.0 m/s when 10 strides were studied per horse. Temporal resolution of the 60-Hz recordings was not sufficient to study the foot-landing pattern for individual strides. Further studies are recommended to determine whether the 60-Hz rate is satisfactory for kinematic quantitation of timing and other stride variables. The optoelectronic methods that were used to assess stride timing in this study could readily be used in conjunction with kinematic studies to verify the accuracy of kinematic methods for quantitating stride-timing values. The cost of the 60-Hz video recording system used for this investigation was 30 times less than that of the 1,000-Hz system. Sixty-hertz video recording systems may provide a basis for increased usefulness and application of quantitated locomotion analysis techniques during clinical evaluation and treatment of gait disorders in horses.

Summary

Quantitated locomotion analysis is increasingly being used during assessment and treatment of gait disorders in human beings. Locomotion analysis is also thought to have potential for enhancing the assessment of lameness in horses. Availability of highspeed video recording systems has simplified the process of quantitated locomotion analysis; however, the high cost of such systems has limited their use for routine clinical assessment in horses. The temporal resolution of 500- to 1,000-image/s (Hz) recording systems is beyond what has been considered necessary for precise quantitation of short-duration events in horses at the trot; however, it is uncertain whether the temporal resolution of more economical 60-Hz recording systems is adequate.

To determine whether a recording rate of 60 Hz is satisfactory for assessment of stride-timing values in horses at the trot, the stride-timing values calculated from 60-Hz recordings were compared with those calculated from 1,000-Hz recordings that had been simultaneously made for 5 horses trotting on a horizontal treadmill at a speed of 3.0 m/s. The left forefoot of each horse was fitted with an instrumented horseshoe that illuminated and quenched light-emitting diodes (led) in view of both cameras precisely at toe contact, heel contact, heel lift, and toe lift. The exact pattern and timing of foot placement and lift was referenced by the illumination pattern of the led. Recordings of 10 consecutive strides were reviewed, image by image for each horse, and the elapsed time at each important stride event was tabulated. Stride-timing values were then arithmetically calculated from the elapsed time values for each recording system.

Significant differences were not found between the stride-timing values obtained from the 1,000-Hz recordings and those obtained from the 60-Hz recordings for any timing variable assessed. For each timing variable, the mean value of the 60-Hz measurements for the 10 strides of each horse was within 3.3 milliseconds (ms) of the mean value of the 1,000Hz measurements for the same 10 strides, with the exception of the 60- and 1,000-Hz assessments of the toe-heel contact interval for 1 horse, which differed by 6.9 ms. On the basis of the 60- and 1,000-Hz recordings, the overall mean ± SD values for the stride, stance, swing, and breakover durations were, respectively, 731.4 ± 16.0 ms, 320.7 ± 15.2 ms, 410.7 ± 18.7 ms, and 60.5 ± 9.9 ms. The toe-heel contact interval was 7.6 ± 8.8 ms.

The instrumented shoe and led mechanism provided a unique, simple, and accurate method for quantitation of stride timing, with clear visual references for placement and lift. Using the shoe for optoelectronic assessment, it was found that a recording rate of 60 Hz was adequate to study stride-timing characteristics of horses trotting at 3.0 m/s when 10 strides were studied per horse. Temporal resolution of the 60-Hz recordings was not sufficient to study the foot-landing pattern for individual strides. Further studies are recommended to determine whether the 60-Hz rate is satisfactory for kinematic quantitation of timing and other stride variables. The optoelectronic methods that were used to assess stride timing in this study could readily be used in conjunction with kinematic studies to verify the accuracy of kinematic methods for quantitating stride-timing values. The cost of the 60-Hz video recording system used for this investigation was 30 times less than that of the 1,000-Hz system. Sixty-hertz video recording systems may provide a basis for increased usefulness and application of quantitated locomotion analysis techniques during clinical evaluation and treatment of gait disorders in horses.

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