The impact of cumulative bone fatigue on musculoskeletal injury risk in racing Thoroughbreds.

Objective Overview

• This study investigates how cumulative bone fatigue contributes to the risk of musculoskeletal injuries (MSI) in racing Thoroughbred horses by analyzing their stride data recorded through wearable technology.

Background and Purpose

• Musculoskeletal injuries in racehorses typically develop gradually rather than occurring suddenly.
• These injuries arise due to repeated mechanical loading cycles, or cumulative bone fatigue, sustained over time while galloping and racing.
• Wearable technology now allows researchers to accurately record stride characteristics like speed and number of strides.
• The purpose of the study was to estimate bone fatigue accumulation from stride data and examine how different rates of bone fatigue relate to injury risk.

Study Design and Methods

• Data was collected from 3168 race starts by 405 Thoroughbred horses beginning their race careers in Tasmania, Australia between 2011 and 2016.
• Bone fatigue accumulation was estimated for each horse based on the speed (meters/second) and total number of strides each horse took during races.
• The percentage of bone fatigue accumulated was calculated over various time frames such as:
• Entire career
• Active racing career
• Preparation periods
• Rolling windows of 1 to 5 race starts to capture short-term and intermediate workloads
• These values were then converted into workload rates representing how quickly bone fatigue accumulated.
• A Cox proportional-hazard regression model was applied to analyze the effect of these workloads on the time until the first musculoskeletal injury occurred (71 first MSI events identified).
• Results of the hazard analysis were presented as Hazard Ratios (HR) with 95% Confidence Intervals (CI) to quantify injury risk.

Key Findings

• Horses with higher rates of bone fatigue accumulation over just one race start had a significantly greater risk of injury (HR = 3.37, 95% CI: 1.01–11.22; p = 0.048).
• Similarly, higher overall career bone fatigue accumulation rates strongly increased injury risk (HR = 1.80, 95% CI: 1.53–2.11; p < 0.001).
• When looking at an intermediate period covering the previous four starts:
• Low workload rates (less than 0.25 of bone fatigue accumulation rate) resulted in a restricted mean survival time (RMST) to injury of 760 days and a 2.89-fold higher risk of MSI compared to medium workloads.
• High workload rates (≥0.75) showed a much higher risk, with a RMST of 405 days and an 8.51-fold increased risk of injury relative to medium workload horses (0.25-0.75) which had a RMST of 1027 days.
• This indicates that both very low and very high bone fatigue workloads are associated with shorter times to injury with medium workloads being associated with better musculoskeletal health.

Implications and Conclusions

• The study suggests monitoring bone fatigue accumulation through wearable technology can help identify horses at higher risk of musculoskeletal injury before symptoms appear.
• Timely adjustments to training and race workloads could be implemented to mitigate this risk by maintaining bone fatigue accumulation within a moderate, safer range.
• These insights can inform more effective, data-driven training programs aimed at enhancing racehorse safety and longevity.
• Overall, the ability to quantify skeletal stress offers a promising tool for improving injury prevention practices in the Thoroughbred racing industry.