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

The purpose of this longitudinal pilot study was to add to the body of research relating to head kinematics/vibration in sport and their potential to cause short-term alterations in brain function. In horseracing, due to the horse’s movement, repeated low-level accelerations are transmitted to the jockey’s head. To measure this, professional jockeys (2 male, 2 female) wore an inertial measurement unit (IMU) to record their head kinematics while riding out. In addition, a short battery of tests (Stroop, Trail Making Test B, choice reaction time, manual dexterity, and visual function) was completed immediately before and after riding. Pre- and post-outcome measures from the cognitive test battery were compared using descriptive statistics. The average head kinematics measured across all jockeys and days were at a low level: resultant linear acceleration peak = 5.82 ± 1.08 g, mean = 1.02 ± 0.01 g; resultant rotational velocity peak = 10.37 ± 3.23 rad/s, mean = 0.85 ± 0.15 rad/s; and resultant rotational acceleration peak = 1495 ± 532.75 rad/s2, mean = 86.58 ± 15.54 rad/s2. The duration of an acceleration event was on average 127.04 ± 17.22 ms for linear accelerations and 89.42 ± 19.74 ms for rotational accelerations. This was longer than those noted in many impact and non-impact sports. Jockeys experienced high counts of linear and rotational head accelerations above 3 g and 400 rad/s2, which are considered normal daily living levels (average 300 linear and 445 rotational accelerations per hour of riding). No measurable decline in executive function or dexterity was found after riding; however, a deterioration in visual function (near point convergence and accommodation) was seen. This work lays the foundation for future large-scale research to monitor the head kinematics of riders, measure the effects and understand variables that might influence them.