Stirred Not Shaken: A Study of Head Kinematics and Cognitive Changes in Horseracing: A Longitudinal Pilot Study

Abstract

Abstract Introduction: In sport emerging research of cumulative head kinematics that participants are exposed to, have revealed changes structurally and functionally within the brain, with the potential for long term alterations. Quantifying this exposure is an important consideration for all sports. In horseracing the style of riding adopted by jockeys causes minimal interference to the horse’s movement but places them in an inherently unstable position. This pilot study seeks to define and quantify the head kinematics encountered by jockeys while training racehorses and how these change throughout a year. The secondary aim is to examine whether this level of exposure to head accelerations influences short term cognitive function. Methods: Two male and two female professional flat jockeys were instrumented with head mounted Inertial Measurement Units to record head kinematics encountered while riding. Data were collected during morning riding out at 3 time points over a year. A short battery of tests to measure executive function, manual dexterity and visual function were conducted immediately before and after the riding. Peak and mean linear and rotational head kinematics for each ride were calculated. In addition, a novel cumulative metric quantifying the number of head accelerations (linear and rotational) above levels measured while running (> 3g and > 400 rad/sec²) was measured. Pre and post riding scores from the test battery were analysed using a paired samples t-test. Results: The average head kinematics measured were resultant linear (peak acceleration 5.8g mean 1.02g), resultant rotational velocity (peak 10.37 rad/sec and mean 0.85 rad/sec) and resultant rotational acceleration (peak 1495 rad/sec² and mean 86.58 rad/sec²). The average duration an acceleration event (acceleration ‘pulse’) lasted for was 575.5 ms peak and 127 ms mean for linear and 813 ms peak and 89.4 ms mean for rotational accelerations. The cumulative metric showed that a jockey is exposed to 300 linear accelerations and 445 rotational accelerations above daily living levels per hour. The test battery showed small changes in executive function post exposure, but these were not significant. Significant improvement in manual dexterity performance (Grooved pegboard non dominant hand) and a deterioration in visual performance (significant receding of near point convergence and near point accommodation) were seen post exposure. Discussion: This pilot study is the first to quantify and investigate head kinematics in this population while riding out in the mornings. The levels measured were low however, the effect of the long-repeated exposure to above daily living head accelerations is not clear. A measurable decline in executive function and dexterity did not occur after riding however a significant decline in a measure of visual function was identified. Conclusions: This study has demonstrated the feasibility of measuring head kinematics in professional jockeys as well as considering acute functional changes. This work lays the foundation for future large-scale research within this industry to monitor the kinematics and effects identified and understand the variables that might influence them in the short and longer term. It is important to begin to establish what level of risk might be posed by the cumulative exposure to sub concussive head kinematics because of riding.