A cross sectional survey of forelimb loading bias and examination of centre of pressure and the association with workload between counter-clockwise and clockwise trained Thoroughbred racehorses in New Zealand

Abstract

Background: Musculoskeletal injury (MSI) is one of the major reasons for wastage of horses in the racing industry. The use of a pressure plate may be useful in the early detection of lameness by measuring the Centre of Pressure (CoP). High-intensity asymmetric training and workload are associated with asymmetry in the load distribution of the forelimbs of Thoroughbred racehorses. At present, there is no published data on asymmetry in the load distribution of clockwise trained racehorses. Objectives: To investigate the difference in load distribution of the forelimbs between clockwise and counter-clockwise trained Thoroughbred racehorses and the CoP displacement in association with workload. Methods: CoP data were measured in 17 counter-clockwise, 30 clockwise and 10 in both directions trained Thoroughbred racehorses. A 0.5 m Footscan pressure plate was used for data collection. Horses stood squarely positioned with their forelimbs in the centre of the pressure plate for a duration of 66.7 seconds while measuring at a sampling frequency of 15 Hz. Duplicate static images were performed with once the left limb and once the right limb placed first to calculate loading distribution between the forelimbs. CoP data were filtered and amplitude, velocity and frequency of the CoP displacement were calculated. Results: The loading of the right forelimb was 54.31% in the counter-clockwise trained group, 52.95% in the clockwise trained group and 57.07% in the both directions trained group. There were no significant differences in loading between the three groups. The mean amplitude was 0.80±0.34 mm, the mean velocity was 0.89±0.38 mm/s and the mean frequency was 0.34±0.05 Hz. There was a significant decrease in frequency with accumulated gallops (R2=0.162, p=0.002) as well as total cumulative gallop distance (R2=0.124, p=0.007). Conclusion: The loading of the right forelimb was higher than the loading of the left forelimb, irrespective of training direction and workload. This implies a biologically normal level of asymmetry and laterality. The decrease in frequency with a higher workload suggest a greater postural stability within racehorses with a higher workload. However, further research is required to investigate possible changes in the frequency due to a higher workload.