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Article

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

by
Emma Edwards
1,*,
Bert Bond
1,
Timothy P. Holsgrove
2,
Jerry Hill
3,
Ryan Baker
1 and
Genevieve K. R. Williams
1
1
Exeter Head Impact, Brain Injury and Trauma (ExHIBIT) Research Group, Department of Public Health and Sport Science, Faculty of Health and Life Sciences, University of Exeter, Exeter EX1 2LU, UK
2
Department of Engineering, Faculty of Environment, Science and Economy, University of Exeter, Exeter EX4 4QJ, UK
3
British Horseracing Authority, Holborn Gate, 26 Southampton Buildings, London WC2A 1AN, UK
*
Author to whom correspondence should be addressed.
Vibration 2024, 7(4), 1171-1189; https://doi.org/10.3390/vibration7040060
Submission received: 20 August 2024 / Revised: 11 November 2024 / Accepted: 25 November 2024 / Published: 27 November 2024
(This article belongs to the Special Issue Vibrations in Sports)
Browse Figures
Versions Notes

Abstract

:
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.

1. Introduction

There is growing evidence of a link between collisions in sport and the brain pathology termed chronic traumatic encephalopathy [1,2,3]. In addition, there is also increasing concern around the exposure to sub-concussive head accelerations/vibrations in both occupational [4,5] and sport [6,7] settings. Due to this concern, many sports have quantified the head kinematics experienced during participation and identified whether any short-term brain changes can be measured. To achieve this, inertial measurement units (IMUs) have been utilised to measure both linear (using accelerometers) and rotational (using gyroscopes) head kinematics [8]. While early research focused on head impacts [9,10], the head accelerations resulting from forces transmitted through the body also need to be considered [11,12]. Using standard tests to detect cognitive changes after exposure to head accelerations has given mixed results [6,13], and any relationship between the two factors is likely to be complex [4,14]. Further research is needed to assist the understanding of lower level head kinematics and possible short-term cognitive changes.
In horseracing, the posture adopted by jockeys places them in an inherently unstable position [15]. Rates of concussion per hour of participation are suggested to be high compared to other sports [16]. Investigations examining equestrian falls give the thresholds for a 50% risk of concussion from a fall as 59 g, 28 rad/s, and 2700 rad/s2 [17]. However, in monitoring annual cognitive testing over a 5-year period, cognitive decline was identified in several jockeys, which was not linked to medically diagnosed concussion [18]. While the authors suggested that chronic stress may underlie this, there may be other causes for this noted decline.
This study seeks to measure the head kinematics experienced by jockeys while riding horses (not during falls). In competitive races, an average peak resultant linear acceleration of 6.18 ± 4.12 g and peak resultant rotational velocity of 11.76 ± 13.1 rad/s have been reported at the head [19]. However, as races generally last for under 10 min, exposure to these levels will be short. Alongside racing, professional jockeys also train racehorses (termed riding out) for several hours each morning. In New Zealand, researchers measured morning track riding and found that while the jockey absorbed much of the horse’s movement through the body, linear displacements of 3.46 ± 0.98 g (largely in a vertical direction) were measured at the jockey’s head [20]. The current literature lacks agreement on the values above which levels of head acceleration should be reported (particularly in non-impact scenarios), and it has been suggested that all, irrespective of magnitude, may be relevant [11,12,21]. Miller et al. published a systematic review of head kinematics measured during daily activities, providing an indication of the levels that might be considered non-injurious [12]. However, this review included single events (head turn, shake, or jump), which are unlikely to occur repetitively for long periods. The authors acknowledged that the true non-injurious threshold needs to take into consideration repeated frequent long-term exposure [12]. To consider how lower levels of acceleration might be tolerated for long periods, it is relevant to examine research on the human response to vibration.
Low-magnitude vibrations are known to have the capacity to cause harm to human tissues if applied for long periods [22]. Acknowledging this, international standards have been established to quantify exposure in the workplace (ISO 2631-1:1997) [23], and European occupational limits have been developed (EU directive 2002/44/EEC) [24]. While these standards consider the effects of vibrations on musculoskeletal tissues, research has also identified negative effects of exposure on brain function from driving [25,26], agricultural machinery use [27,28] and high-speed marine craft travel [29].
Using industry standards to quantify vibration exposure during sport participation, research has identified that levels in many sports far exceed the recommended industry daily limits [30,31]. Unfortunately, currently these standards are not weighted to have relevance to brain tissue [5], apply only to set postures (seated or lying), and are measured at the vibration/body interface [32]. This limits their application to quantifying potentially harmful levels in sports [30]. Instead, novel metrics have been developed (predominately in pilot studies with small numbers of participants) to quantify lower level repeated non-impact head kinematics that occur during participation in sport (for example, in rodeo riding [33], gymnastics [34], stock car racing [35], and rugby [36]). Jockeys are likely to be subjected to regular head accelerations due to the periodicity of the horses’ gait as well as unexpected perturbations due to unpredictable horse behaviour.
The physiological effects of exposure to low-level repeated head acceleration are not clear, which means that the brain functions most likely to be influenced are not known [37]. Balance, visual function, cognition, and dexterity have all been considered as functions that might be affected [5,6]. For example, levels of head kinematics from soccer heading have been linked to a change in visual function [38]. Hurst et al. examined changes in executive function after mountain biking, finding a significant decline in performance on the Stroop but not TMT test [39]. These findings suggest that a variety of domains of brain function need to be included in any test battery [37].
This pilot study aimed to quantify the head kinematics experienced by professional flat jockeys and identify if any measurable change in executive function, manual dexterity, or visual function occurs after riding out in a morning.

2. Materials and Methods

2.1. Participants

Four professional flat jockeys, two male and two female (age range 24–32 years) who had held a full racing license for at least 5 years, took part in the study. Their experience ranged from apprentice (3 lb claim) to full professional. All had to be over 18 years old and had no diagnosed neurological or psychological disorders, no history of medically diagnosed concussion in the past 6 months, and no history of substance abuse. All rode out 5 or 6 days per week. Ethical approval was granted by the University of Exeter Sport and Health Sciences ethics committee (ID number 516887). Each participant gave written informed consent at least 48 h before commencement of the study.

2.2. Study Design

This study used a longitudinal observational descriptive design. The study included an equal number of male and female participants.

Procedure

The study considered the typical workload and racing season for a jockey in the UK (Figure 1). A two-week data collection period was scheduled at three time points over a year, corresponding to late season (August 2022), pre-season (March 2023), and early season (June 2023). The same four jockeys were contacted to participate at each time point and four test days were scheduled in the two-week period.
The same examiner (15 years’ experience working with professional jockeys and highly experienced physiotherapist, Master of Science student) attended the yard where a jockey was due to ride (at around 6 a.m.) and conducted all testing. Due to the long hours and weight-making demands of horse racing as a sport, jockeys often train and compete in a fatigued and dehydrated state [40]. To account for this, a well-being questionnaire (Appendix A) was used to rank hydration, fatigue, and mood using a self-reported Likert scale of 0 to 10.
A short battery of tests of reaction time, executive function, visual function, and manual dexterity was conducted immediately prior to riding (pre-exposure), with the jockey seated at a table in a quiet room. The test time was restricted to 15/20 min to limit disruption in a busy professional racing yard. Shortened, computerised versions of tests commonly used in comparable research, Trail Making Test B (TMTB), Stroop test, and choice reaction time were run in PsychoPy (https://www.psychopy.org (accessed on 11 November 2023)) [41] using an HP EliteBook 830 G7 Notebook PC. Each recorded test was preceded by a short practice trial.
An RAF Ruler (Product Number: 537800, Good-lite, Elgin, IL, USA) was used to measure subjective near point convergence (NPC) based on the vertical line target and near point accommodation (NPA) using the word target (Font size 10). The cheek rest was placed on the infra orbit with the ruler angled 45 degrees down and the target moved from 35 cm at a rate of approximately 1 to 2 cm per second. The distance of the target from the face was noted after verbal confirmation of visual disturbance by the participant. To allow for a fatiguing effect (noted to be prevalent following concussion [42]), both tests were repeated 5 times and the average was recorded.
Manual dexterity was measured using the grooved pegboard test (Model 32025, Lafayette Instrument, Loughborough, Leicester, UK), which involved inserting shaped pins into shaped holes oriented at different angles. The time taken to fill all holes with pins (for dominant and non-dominant hands) was recorded in seconds by the examiner using a stopwatch.
Following the testing, a Vicon Blue Trident IMU Model V2 (Vicon, Oxford, UK; 1125 Hz) was attached via double-sided tape to the mastoid process behind the jockey’s right ear (Figure 2). The unit was connected via Bluetooth to record once the jockey had mounted and disconnected at the end of each ride.
Within 15 min of the morning’s riding being completed, the same test battery was repeated (post exposure). For each ride on that morning, variables that had previously been noted to influence horse and rider kinematics (age of horse, activity performed, and main surface for the ride) [43,44] were noted.

2.3. Data Processing

2.3.1. Head Kinematics

Data from the low g accelerometer and gyroscope of the IMU were processed using custom-written MATLAB code (version 9.13, R2022b, Natick, MA, USA: The MathWorks Inc.; 2022). Raw data were filtered using a 4th order low pass Butterworth filter with a previously determined cut-off frequency of 30 Hz (see Supplementary Materials, Figures S1 and S2). Linear acceleration data were converted to g and rotational velocity from degrees per second to radians per second in the x-, y-, and z-axes. Rotational velocity was differentiated using a 5-point stencil to give rotational acceleration in rad/s2. Resultant linear acceleration, rotational velocity, and rotational acceleration were calculated from the 3 axes using Pythagoras’ theorem. To calculate the duration of an acceleration in milliseconds (linear and rotational), the limits of an acceleration time curve (‘trough to trough’) were measured. Because the IMU axes were not aligned to any primary axis, gravity could not be removed from the calculations.
A cumulative metric was calculated using an internal MATLAB function, ‘Find Peaks’, to identify the number and magnitude of all individual accelerations in both linear and rotational filtered data. No specific criteria were set (such as threshold, duration, or magnitude, as per international standards for calculating mechanical vibration-containing shocks (ISO 2635-5: 1997 [22]) so that all peaks could be analysed. The peaks, termed head acceleration counts (HACs), were assigned to a ‘bin’ corresponding to their magnitude. Linear accelerations were sorted in 0.2 g bins incrementally up to 10 g and rotational accelerations were sorted in 50 rad/s2 bins incrementally to 2000 rad/s2. The number of HACs above those of daily living (linear > 3 g and rotational > 400 rad/s2) was analysed to quantify the levels above daily living to which the jockeys were subjected (see Supplementary Materials, Figure S3). As the length of each ride varied, a comparable measure, HACs above daily living levels per minute, was also calculated.
The peak and mean resultant linear and rotational metrics (linear acceleration (g), rotational velocity (rad/s), rotational acceleration (rad/s2), and acceleration duration (ms)) and the cumulative metrics (linear and rotational HACs) were calculated individually for each ride in a morning and then averaged for each morning in the study.

2.3.2. Cognitive

The TMTB was scored based on the overall time to complete it and the average of four trials was recorded. The Stroop test was scored based on the time to complete 30 trials under two conditions (15 congruent, 15 incongruent) and a combined time. The average reaction time for each of the three conditions was also recorded. The choice reaction time was scored based on the overall time to complete 18 trials and average reaction time per trial. For the choice reaction time and Stroop tests, errors were noted, and a measure of speed/error was calculated as follows: total time + (2 × mean time per word) × number of uncorrected errors [45]. The grooved pegboard test was timed using a stopwatch and NPC and NPA were recorded in cm.

2.4. Data Analysis

Descriptive statistics, mean and standard deviation, were used to report the average head kinematics for the rides performed on each day of the study. The average daily head kinematics for each individual were calculated overall and at each of the three time points.
Differences between cognitive outcome measures pre and post riding were examined using SPSS (IBM SPSS for Windows, Version 28.0 Armonk, NY IBM Corp., Armonk, NY, USA), and descriptive statistics were calculated (mean difference (MD), standard deviation, 95% confidence interval, and effect size (Hedge’s correction)). Hedge’s correction values of 0.2, 0.5, and 0.8 were considered to interpret the observed effect size as small, medium, or large, respectively [46]. The results at the three time points were compared descriptively.

3. Results

The same four jockeys were contacted at each data collection time point, with all four participants completing the test protocol at the first test point. In the second, three jockeys completed the protocol, and for the third, two jockeys (both female) completed the protocol. This gave a total of 35 days where data were collected, 15 days in August (one jockey only completed 3 of the 4 test days), 12 days in March, and 8 days in June. Data were collected in 8 different professional racing yards and the 35 mornings included 139 individual rides (number per day ranged between 2 to 8 rides). A morning’s riding was on average 145 min on horseback (range 50 to 244 min). The activities recorded included walk, trot, canter, and gallop on different surfaces (sand, carpet fibre, grass, and woodchip) on racehorses aged from 2 to 9 years.

3.1. Head Kinematics

The overall average peak and mean head kinematic values measured for a morning’s riding are summarised in Table 1. The peak metrics recorded on different days varied and the mean values were significantly lower, which gives a limited understanding of cumulative exposure to head accelerations.
For the 35 days included in this study, the average number of linear HACs above daily living levels that a jockey experienced on a morning’s riding out was 739 (Table 2). The average number of linear acceleration counts (LACs) above daily values per minute was almost 5 (range per day less than 1 per minute, to over 12). The average number of rotational acceleration counts (RACs) above daily living levels was 1013 and, on average, a jockey experienced 7.42 RACs per minute (range per day 1.41 to 16.86). For every hour of riding, a jockey experienced an average of 300 linear accelerations and 445 rotational accelerations above the levels expected during normal daily living activities.

3.1.1. Variables That Affect Head Kinematic Levels

Individual Differences

Comparing peak and average levels measured for each jockey, there was large individual variation in head kinematics (Table 3). While average MRLA values were similar for all jockeys (1.02 g), the highest PRLA value experienced ranged from 6.14 to 9.65 g (a 57% difference), and the average PRLA ranged from 5.35 g to 6.71 g (a 25% difference). The variation in levels of rotation experienced was even greater, with the highest PRRV ranging from 11.33 to 24.43 rad/s and PRRA between 1655.92 and 3562.54 rad/s2 (115% difference). The average PRRV differed from 9 to 11.8 rad/s (31% difference) and PRRA from 1300 to 1636 rad/s2 (25% difference), and the average MRRV differed between 0.67 to 1.03 rad/s, (54% difference) and MRRA from 65 to 102.3 rad/s2 (57% difference). There was also a wide range of the acceleration duration measured, with a 28% variation in the longest PLAD, average PLAD, and MLAD. While there was a 33% difference in the longest PRAD experienced, the average RAD was between 729 and 866 ms (18% difference), and MRAD varied between 76.8 and 99.8 ms (29% difference).
The peak and average cumulative metrics also showed large variations between jockeys (Table 3). The average LACs above daily living levels ranged from 448.25 to 1148 (156% difference), and the average LACs above daily levels per minute ranged from 3.58 to 6.20 per minute (73.18% difference). The average RACs above daily living levels ranged from 515 to 1201 (133% difference), while RACs above 400 rad/s2 per minute varied from 3.39 to 9.05 (167% difference). While two jockeys (1 and 4) experienced far higher rotational counts per minute than linear (approximately double), the other two (2 and 3) had similar exposure to both.

Variation Through the Year

For all jockeys that completed more than one data collection period, the length of riding time was longest in March (average 48% longer than August), while it was longer in June than in August (average 16%) but shorter than in March (average 21% shorter) (Table 4). While the mean values for all metrics were similar at each time point, the average peak values were higher in March (on average between 13 and 46% higher than in August). At this time, the variability between different days of riding was also highest (higher standard deviations), and the duration of acceleration (linear and rotational) was longer. In June, the peak values were generally higher than in August but less than in March. Acceleration durations in June were generally shorter than in both August and March.
For all jockeys, the average levels of HACs and HACs above daily living levels (linear and rotational) were higher in March than in August, while in June the linear counts were lower than in August but similar to those in March and the rotational counts varied. The LAC > 3 g per minute showed large variations between jockeys, but taking an average, the levels were similar in March and June (5.50 and 5.44) but lower in August (4.37). While the RAC > 400 rad/s2 was generally higher in March than in August, the counts per minute showed large variations between individual jockeys. The highest number of RAC > 400 per minute was measured in June (average 10.43 per minute) (76% higher than in March (5.9 per minute) and 50% higher than in August (6.92 per minute)).
The heat map of linear acceleration counts (Figure 3a) gave an indication of how both the magnitude and number of linear head accelerations was higher in March than in August. In June, the difference between the two jockeys who completed testing was notable. The rotational acceleration heat map (Figure 3b) showed that individual days gave very different levels of exposure to rotational head accelerations in each time period. Again, the peak and overall counts were higher in March than in August, while they were similar in June and March.

Other Variables

Individual rides were compared to consider factors such as age of horse, surface of ride, and sex of jockey (Appendix B). While low numbers prevented any statistical comparison, it was noted that rides with younger horses and on a grass surface had comparatively higher head kinematics. Comparing sex of the jockey on individual rides, the cumulative metric (LAC > 3 g and RAC > 400 rad/s2) was higher for female jockeys.

3.2. Cognitive Function After Riding

From the pre- and post-riding cognitive test battery conducted on each of the 35 days in this study, the differences in outcome measures were compared and the results are summarised in Table 5. For TMTB, Stroop, simple and choice reaction times, the mean differences in pre- and post-test outcome measures showed that performance was generally slightly slower in the post test; however, this varied, and the effect sizes were small (less than 0.30). There was an improvement in performance on the grooved pegboard test, which became quicker—dominant hand (MD = 1.31 s, 95% CI −0.85 to 3.49 s, Hedge’s correction 0.20) and non-dominant hand (MD = 2.75 s, 95% CI 0.85 to 4.64 s, Hedge’s correction 0.50).
A difference in visual function was observed after riding out, and the measurements were receded in both NPC (MD = 1.63 cm, 95% CI 1.16 to 2.11 cm, Hedge’s correction 1.15) and NPA (MD = 1.85 cm, 95% CI 1.31 to 2.39 cm, Hedge’s correction 1.14).

Variation in Cognitive Results Through the Year

The differences in outcome measures for the pre- and post-riding cognitive tests were compared at each of the three time points. Performance on most of the tests was worse (slower or receded) following the daily exposure in time point two (March). NPC and NPA were more receded after riding at all three time points. Performance on the grooved pegboard test (non-dominant hand) was the only test that was better (quicker) post riding at all three time points.

4. Discussion

The aim of this pilot study is to quantify the head kinematics that professional flat jockeys experience while riding out at timepoints over one year. It also seeks to identify if there is any measurable change in executive function, manual dexterity, or visual function after riding. The levels of linear and angular head acceleration measured were lower than those reported in contact sport but higher than those experienced during daily living and comparable to other non-contact exposure (Table 6). Of the cognitive test battery, only visual function was worse after riding.

4.1. Head Kinematics

4.1.1. Linear Acceleration

The metrics for linear acceleration were in keeping with Quintana et al.’s study of head kinematics in horse racing [19] (Table 6). An average PRLA of 5.82 ± 1.08 g was slightly lower than value measured during competitive riding (6.18 ± 4.12 g) but higher than that on a racing simulator (2.44 ± 0.67 g) [19]. The values are higher than those measured by Legg et al. for a similar activity, track riding (3.46 ± 0.98 g) [20]. This may be because both the surface (polytrack) and activity (canter) measured were far more controlled than the range of activities (walk, trot, canter, and gallop) and surfaces that were seen in this study. Compared to activities of daily living, the highest PRLA value of 9.65 g fell within the range quoted in Miller’s systematic review (range 0.32–13.8 g); however, the average PRLA of 5.8 g was higher than the average quoted in Miller’s study (3.8 g; [12]). This indicates that riding out subjects a jockey to several hours of head accelerations of a higher magnitude than occur during normal daily activities.
The average PRLA was comparable to that in some other activities that have measured accelerations transmitted through the body, such as gymnastics (6.7 g; [34]) and rollercoaster rides (8 g; [47]). During downhill mountain biking, much higher accelerations have been measured (18.1 g; [48]). Surprisingly, stock car racing reports a lower value (4.13 g [35]); however, in computing this value, a moving point average to account for the car’s movement was subtracted from the measurement [35]. As expected, the values in this study were lower than those recorded using an in-ear accelerometer during rodeo riding (15.7 g for bareback and 6.1 g for bull riding) [33]. However, the number of head linear accelerations recorded during rodeo riding was low (238 in total for 18 recorded rides) and the exposure time short (less than 10 min) [33].
The cumulative metric revealed that the jockeys experienced an average of 300 LACs above daily living levels per hour of riding. This metric varied from 0.92 to 12.32 HACs per minute on different days, highlighting its sensitivity to different variables. These findings provide the first quantification of exposure to HACs for jockeys. Despite the PRLA recorded being below levels of immediate concern for concussion (quoted as above 29.3 g; [9]), the repetitive, cumulative stress from riding might have the potential to cause cognitive changes, as noted in other activities [28,39] and with vibrations [4], although only a change in visual function was noted in this study.

4.1.2. Rotational Velocity and Acceleration

The average value for PRRV when riding was 10.37 ± 3.23 rad/s, which again fell within the range measured for race riding of 11.76 ± 13.1 rad/s reported by Quintana et al. [19] (Table 6). The highest peak rotational values were almost double those recorded during daily activities, with the highest PRRV in this study of 24.43 rad/s compared to 12.8 rad/s in daily living [12], and PRRA in this study of 3562.54 rad/s2 compared to 1375 rad/s2 [12]. The average peak rotational values in this study of 10.37 rad/s and 1495 rad/s2 were also higher than those reported in daily living (PRRV 5 rad/s and PRRA 287 rad/s2 [12]) and much greater than those in daily activities that happen repeatedly (85 rad/s2) [12]. The levels measured suggest that riding exposes jockeys to a much higher magnitude of rotational accelerations than would be expected during normal daily activities. The significance of these results is unclear at present.
Riding appears to cause a higher rotational component of head kinematics than some other activities. This may be related to the location of the accelerometer, as rotational values are influenced by accelerometer location more than linear values [49]. The average rotational values in this study were higher than those reported in gymnastics (8 rad/s and 190 rad/s2 [34]), and stock car racing (2.05 rad/s [35]); however, both studies used a mouthpiece to collect accelerometer data. The values were lower than those in downhill mountain biking (1495 rad/s2 compared to 8566.8 rad/s2 [48]), which also used an accelerometer attached behind the ear to collect data. In rodeo riding, an in-ear accelerometer measured comparable levels of rotational acceleration during bull riding (1577.8 rad/s2), while bareback riding had higher levels (2129.4 rad/s2) [33]. The different methods of collecting accelerometer data make comparisons difficult. The cumulative metric, RAC, revealed that jockeys experienced an average of 445 rotational accelerations above daily living values per hour of riding, with exposure varying from 1.41 to 16.86 counts per minute for a morning of riding.
While the peak rotational values measured fell below the concussive threshold of 6000 rad/s2 [50], research has found brain strain patterns demonstrated with levels below those measured in this study (150–350 rad/s [51]) and angular deceleration (299–370 rad/s2 [52]). Recreating the head kinematics experienced on rollercoaster rides with two male participants, Kuo et al. suggested that the rotational values (9.9 rad/s and 290 rad/s2) measured resulted in moderate brain strain rates and peak displacements comparable to mild sport impacts (heading a football), despite being below concussive thresholds [47]. In the current study, the rotational velocity values were similar to those in rollercoaster rides, and the rotational acceleration values were higher, suggesting that moderate levels of brain strain may occur during riding. These comparably higher levels of rotation are of concern as research has demonstrated that rotational accelerations correlate to brain strain, making them the primary mechanism for diffuse brain injury [53,54].

4.1.3. Acceleration Duration

The acceleration duration measured in impact sports may be short as data collection is limited to a pre-set time window triggered by an impact event [55] and head injury criterion calculations used to predict injury limit the acceleration time curve to a 5 to 15 ms window [9]. In non-impact scenarios, Miller et al. calculated a rotational pulse duration for daily activities of 104.9 ms [12]. In the current study, the rotational pulse duration peak was 813.33 ms and the mean was 89.42 ms. Peak acceleration durations (linear and rotational) measured in downhill mountain biking (17.2 ms; [48]) and football headers (25 ms [56]) were lower than the current study. While in gymnastics, the average peak duration of acceleration was 177 ms, and it was noted that head contact durations were shorter while the accelerations measured during skills with no head contact could be up to 2.7 s [34]. This suggests that while of lower magnitude, non-contact head accelerations have longer duration [34].
With sporting impacts, the maximum principal strain at a level for risk of brain injury and high risk of concussion is quoted as 2500 rad/s2 for impacts of 10–15 ms [57]. The current study measured longer duration and higher peak acceleration than this; however, magnitude and duration are not linked, limiting our understanding of how potentially harmful this might be. The brain can tolerate higher magnitude for short duration, while lower magnitude for longer duration is potentially more damaging [8]. Therefore, future research should link acceleration duration to magnitude to clarify the exact nature of kinematics experienced while horse riding.

4.2. Cognition

This study used a battery of tests to consider if any change in cognitive function can be measured after riding. Computerized tests of executive function (TMTB and Stroop), and choice reaction time showed only small differences between pre- and post-riding testing. Cognitive deterioration after heading in football [58,59,60] and mixed results following downhill mountain biking (Stroop test declined, but not Trail Making Test A or B [39]) have been noted; however, these activities involve higher magnitude head kinematic levels. Other research has reported an improvement or no change in executive function after sub-concussive head accelerations [7,61], and systematic reviews report mixed results [6,14,62]. A recent systematic review considering cognitive function following exposure to whole-body vibration found similar conflicting findings [5].
Many factors that are known to affect performance in cognitive tests might influence our findings, including time of day [63,64], exercise [65,66], and hydration [67,68]. To understand the influence of exercise on cognitive testing, a control group has been included when comparing heading exposure [59] and contact with non-contact athletes [7]. An improvement in cognitive performance post exercise was seen in both groups, but it was lower and did not show longitudinal improvement in those exposed to head impacts. These studies suggest that a lack of expected improvement in executive function following exercise, rather than a decline in performance, might be a relevant finding. To account for this, future studies could consider including a control exercise group (with lower head kinematics) for comparison. Advanced imaging techniques have been used to identify both structural [57,69,70] and functional [58], brain changes due to sub-concussive impacts, and their use in combination with standard tests may be more sensitive to the subtle changes expected with lower-level head kinematics [71].

Visual Function

Both NPC and NPA were receded in all jockeys following riding. A receded NPC has been noted after participation in pole vaulting [72], football [73,74], and athletics [7]. NPC measurements are not impacted by exercise and have high levels of within- and between-day reliability [75,76]. While a small but significant change in testing 12 h apart has been noted [77], this should not have influenced the results as the tests in this study were conducted a maximum of 5 h apart. Research suggests that, during rotational acceleration, the highest areas of strain are found in the midbrain, an area important for oculomotor function, memory, consciousness, and autonomic function [78]. While the linear metrics in this study were low, the rotational values were relatively high compared to other non-contact sports and daily living activities, and significant changes in oculomotor function, as evidenced by the receded NPC and NPA, were measured. While few studies have measured NPC longitudinally, Zonner et al. followed football players through a season and found that a receded NPC (compared to pre-season) was positively associated with higher sub-concussive cumulative load. The NPC became significantly worse over time until mid-season, when it began to gradually normalize back to pre-season base levels [74]. The authors noted that this apparent adaptive effect warranted further investigation to understand the underlying pathophysiology [74]. Variability in NPC and NPA was also noted in this study, with values being receded furthest in March when head kinematics were highest. The study size limited any conclusions being drawn, but these findings suggest that larger scale research is warranted to further investigate this link and apparent adaptive effect.

4.3. Variation

The head kinematics measured showed large individual variations between jockeys. While the low number of participants prevented any in-depth analysis, this may be due to factors such as age, sex related differences in neck strength and spinal biomechanics, or experience (Table 3; [79,80,81]).
Variations in levels of head kinematic metrics over the course of the season were identified. The drop out of jockeys over the course of the study made direct comparison of the time points difficult and individual variations will influence the levels measured. However, for all jockeys that completed more than one data collection time point, at the start of the season, the riding time was longer and peak linear and rotational metrics were higher. At this time, horses are being prepared for the upcoming turf season and the increased intensity and volume of riding, coupled with keener and potentially more unpredictable horses, might have contributed to the higher values observed. The cumulative metrics also revealed higher levels of HACs (linear and rotational) at the start of the season, although counts per minute varied. This seasonal variation highlights the importance of considering the time of year when designing future studies.
Studying the effect of low-level head impacts in rodents, Lavender et al. (2020) found that brain changes were not noted in the equivalent of one year of exposure but not after the equivalent of five years [82]. A cognitive decline over a 5-year period has been noted in professional jockeys, which was not related to medically diagnosed concussion [18]. In this study, a variation in performance was noted over the duration of the study. Repeated testing over several seasons might clarify if this indicates a gradual decline that could be linked to continued prolonged exposure to head kinematics (above those in daily living activities) from riding, particularly important in a sport where there is no ‘off season’ to allow for recovery.

4.4. Future Research Lines

To facilitate research on a much larger scale, miniaturised helmet-mounted accelerometers, validated against other methods of measuring head kinematics, could be utilised. This would also allow measurement of the competitive environment, enabling the full day of exposure to riding to be quantified. These studies could build on previous work in the equestrian field that has considered how the surface, experience, and age of the horse influence rider motion. In addition, the unique setting of horse racing, where men and women train and compete together under the same rules, provides a valuable opportunity to explore sex-based differences in head kinematics. Larger scale studies could also access online self-administered cognitive testing. This would allow the effects of fatigue, mood, and hydration to be linked to cognitive test results.

4.5. Limitations

The major limitation is the pilot study nature of this work, including the low number of jockeys and drop out due to the demands of professional sport. This limits our ability to draw conclusions that are generalisable to professional jockeys and to fully understand the inter-individual differences.
Some aspects of the data analysis may have introduced error, as data were not transformed to the head centre of gravity. This is unlikely to affect linear readings but may have added error to rotational values [12]. While skin-mounted devices have been criticised for measurement error due to skin artifacts, this is minimal at lower acceleration levels when mounted over bony landmarks like the mastoid process, making it accurate for the head kinematics experienced in this study [83].

5. Conclusions

The aim of this pilot study was to measure the head kinematics experienced by jockeys while training racehorses and identify if any cognitive change can be detected after riding. In keeping with previous research on riding and other non-impact sports, the magnitude of the head accelerations measured was relatively low. However, the duration of these accelerations was longer than that observed in other impact and non-impact sports. Linking magnitude to duration of acceleration events in future research will clarify if this magnitude presents a potential for higher brain strain.
To expand further than peak and mean kinematics, a novel metric was used to give a measure of the level of head accelerations, above normal daily living levels, that jockeys experience in a period of time. This metric appears to be sensitive to different rides and extraneous variables (time of year, level of experience, age of horse, surface of activity, and sex of jockey). These variables may be considered by future larger scale research in this field, with the aim of improving the understanding of head kinematics during riding.
No deterioration in executive function and manual dexterity was measured after riding, but visual function was adversely affected. This deterioration in visual function (receded NPC and NPA) might indicate that, while at a low level, the repeated head kinematics experienced have some effect on the brain and warrant further investigation.
This work presents initial insights into the head kinematics experienced by jockeys while riding out in the morning and provides a foundation for future research in this field.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/vibration7040060/s1, Figure S1: Example of power spectrum graph for the linear data measured during one ride; Figure S2: Linear resultant data 1 unfiltered, each line represents a different low pass cut-off value—15, 20, 25, and 30 Hz. The black line represents the raw unfiltered data; Figure S3: Schematic of the cut-off values calculated for linear and rotational accelerations during sensor trials and daily living activities.

Author Contributions

Conceptualization, E.E., B.B., J.H. and G.K.R.W.; methodology, E.E., J.H. and G.K.R.W.; software, R.B., E.E. and G.K.R.W.; validation, E.E., R.B. and G.K.R.W.; formal analysis, E.E., R.B., T.P.H. and G.K.R.W.; investigation, E.E.; resources, G.K.R.W.; data curation, E.E.; writing—original draft preparation, E.E.; writing—review and editing, B.B., T.P.H., J.H., R.B. and G.K.R.W.; supervision, B.B. and G.K.R.W.; funding acquisition, B.B. and G.K.R.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Racing Foundation number 323/375, which supported the completion of this research.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki, and approved by the Sport and Health Science Ethics Committee of the University of Exeter (ID number 516887 and date of approval 6 July 2022).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

The raw data that support the findings of this study are not openly available due to reasons of confidentiality. Upon reasonable request, individual de-identified participant data can be made available by the corresponding author due to privacy restrictions.

Acknowledgments

This study was supported by the National Institute for Health and Care Research Exeter Biomedical Research Centre. The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Appendix A

Table A1. Well-being questionnaire—completed on the data collection days at each of the three time periods.
Table A1. Well-being questionnaire—completed on the data collection days at each of the three time periods.
Data Collection Period:
Participant ID:Date:
Any falls (past month)
Any recent injuries (past month)
Any medically diagnosed concussion (recent)
Any undiagnosed concussion
Any new medication
Other (travel, bans, etc)
Day 1
Date:
Weight today:
For the following 3 categories tick the number that best describes your current status12345678910
Hydration (1 = dehydrated; 10 = fully hydrated)
Fatigue (1 = exhausted; 10 = well rested)
Mood (1 = poor mood; 10 = excellent mood)
Any injury/falls past 24 h:
Day 2
Date:
Weight today:
For the following 3 categories tick the number that best describes your current status12345678910
Hydration (1 = dehydrated; 10 = fully hydrated)
Fatigue (1 = exhausted; 10 = well rested)
Mood (1 = poor mood; 10 = excellent mood)
Any injury/falls past 24 h:
Day 3
Date:
Weight today:
For the following 3 categories tick the number that best describes your current status12345678910
Hydration (1 = dehydrated; 10 = fully hydrated)
Fatigue (1 = exhausted; 10 = well rested)
Mood (1 = poor mood; 10 = excellent mood)
Any injury/falls past 24 h:
Day 4
Date:
Weight today:
For the following 3 categories tick the number that best describes your current status12345678910
Hydration (1 = dehydrated; 10 = fully hydrated)
Fatigue (1 = exhausted; 10 = well rested)
Mood (1 = poor mood; 10 = excellent mood)
Any injury/falls past 24 h:

Appendix B

Table A2. Effects of different variables on head kinematics for individual rides.
Table A2. Effects of different variables on head kinematics for individual rides.
MetricAge HorseSurfaceSex of Jockey
Under 5Over 5WoodchipCarpet FibreSandGrassMaleFemale
PRLA (g)4.904.834.844.994.874.915.024.88
MRLA (g)1.021.021.021.021.021.021.021.02
PRRV (rad/s)8.517.278.598.188.308.638.528.49
MRRV (rad/s)0.870.830.890.840.870.820.850.87
PRRA (rad/s2)12241099123411601198128411801209
MRRA (rad/s2)96.1983.0299.4585.2695.8586.5085.9796.61
LAC > 3 g292.5142.1153.6176.2190.8177.5172.9186.9
LAC > 3 g/min3.811.983.353.263.882.493.213.78
RAC > 400 rad/s2313.5247.1335.9356.9306.5412.7245.5305.8
RAC > 400 rad/s2/min10.208.309.679.2210.4011.836.709.90
Key: J = jockey; PRLA = peak resultant linear acceleration; MRLA = mean resultant linear acceleration; PRRV = peak resultant rotational velocity; MRRV = mean resultant rotational velocity; PRRA = peak resultant rotational acceleration; MRRA = mean resultant rotational acceleration; LAC = linear acceleration count; RAC = rotational acceleration count.

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Figure 1. Schematic of the typical workload in a year and a typical week during the season for a UK professional flat jockey.
Figure 1. Schematic of the typical workload in a year and a typical week during the season for a UK professional flat jockey.
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Figure 2. Position of the inertial measurement unit attached on the mastoid process behind a jockey’s right ear.
Figure 2. Position of the inertial measurement unit attached on the mastoid process behind a jockey’s right ear.
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Figure 3. Heat maps of average daily exposure to head accelerations at the three time points, yellow asterisks (*) mark the peak values measured on those days. (a) Linear head acceleration counts above 3 g where the x-axis is the acceleration in g and the y-axis is each day of the data collection; (b) Rotational head acceleration counts above 400 rad/s, where the x-axis is rotational acceleration in rad/s2 and the y-axis is each day of the data collection.
Figure 3. Heat maps of average daily exposure to head accelerations at the three time points, yellow asterisks (*) mark the peak values measured on those days. (a) Linear head acceleration counts above 3 g where the x-axis is the acceleration in g and the y-axis is each day of the data collection; (b) Rotational head acceleration counts above 400 rad/s, where the x-axis is rotational acceleration in rad/s2 and the y-axis is each day of the data collection.
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Table 1. Overall mean (±standard deviation) for peak and mean head kinematics from a morning’s riding out (number of days = 35).
Table 1. Overall mean (±standard deviation) for peak and mean head kinematics from a morning’s riding out (number of days = 35).
CMean ± SDMaximumMinimum
PRLA (g)5.82 ± 1.089.654.35
MRLA (g)1.02 ± 0.011.041.01
PRRV (rad/s)10.43 ± 3.2324.433.21
MRRV (rad/s)0.85 ± 0.151.130.64
PRRA (rad/s2)1495.00 ± 532.753562.54829.02
MRRA (rad/s2)86.58 ± 15.54124.2160.47
PLAD (ms)575.59 ± 62.68737.8453.33
MLAD (ms)127.04 ± 17.22155.8391.13
PRAD (ms)813.34 ± 160.891184.90496.89
MRAD (ms)89.42 ± 19.74127.4650.24
Key: SD = standard deviation; PRLA = peak resultant linear acceleration; MRLA = mean resultant linear acceleration; PRRV = peak resultant rotational velocity; MRRV = mean resultant rotational velocity; PRRA = peak resultant rotational acceleration; MRRA = mean resultant rotational acceleration; PLAD = peak linear acceleration duration; MLAD = mean linear acceleration duration; PRAD = peak rotational acceleration duration; MRAD = mean rotational acceleration duration.
Table 2. Overall mean (±standard deviation) for linear and rotational head acceleration counts experienced during a morning’s riding out (number of days = 35).
Table 2. Overall mean (±standard deviation) for linear and rotational head acceleration counts experienced during a morning’s riding out (number of days = 35).
Cumulative MetricMean ± SDMaximumMinimum
LAC26,830.29 ± 11,067.9851,021.008976.00
LAC > 3 g739.00 ± 586.732385.0088.00
LAC > 3 g min4.99 ± 3.1912.320.92
RAC73,071.46 ± 34,844.49187,585.0019,188.00
RAC > 400 rad/s21013.80 ± 547.572638.00168.00
RAC > 400 rad/s2/min7.42 ± 3.5516.861.41
Key: SD = standard deviation, LAC = linear acceleration count, RAC = rotational acceleration count.
Table 3. Comparison of the overall peak and mean ± standard deviation for head kinematic values measured for individual jockeys.
Table 3. Comparison of the overall peak and mean ± standard deviation for head kinematic values measured for individual jockeys.
MetricOverall Peak ValueMean ± SD
J 1
(Female)		J 2
(Female)		J 3
(Male)		J 4
(Male)		J 1
(n = 12)		J 2
(n = 12)		J 3
(n = 3)		J 4
(n = 8)
PRLA (g)9.656.146.578.125.75 ± 1.355.35 ± 0.455.56 ± 0.916.71 ± 0.96
MRLA (g)1.031.031.021.021.03 ± 0.011.02 ± 0.001.02 ± 0.001.02 ± 0.01
PRRV (rad/s)24.4311.3313.1314.7911.85 ± 4.299.02 ± 1.469.99 ± 3.7010.33 ± 2.79
MRRV (rad/s)1.120.880.690.821.03 ± 0.100.79 ± 0.070.67 ± 0.030.75 ± 0.06
PRRA (rad/s2)35631656171528881636 ± 6961313 ± 2381300 ± 4461631 ± 582
MRRA (rad/s2)124.293.5266.8189.87102.3 ± 12.9080.99 ± 7.7965.10 ± 1.5380.40 ± 6.74
PLAD (ms)720.9737.8559.1613.3613.1 ± 37.57577.4 ± 73.49543.1 ± 21.16528.8 ± 53.65
MLAD (ms)155.8140.41367.0120.1143.0 ± 11.47121.3 ± 15.49129.5 ± 7.09110.7 ± 6.42
PRAD (ms)941.31185974.2889.8839.0 ± 98.02830.4 ± 239.56866.4 ± 107.12729.5 ± 79.31
MRAD (ms)127.5123.697.9989.8499.81 ± 16.1186.43 ± 25.7393.18 ± 4.3476.89 ± 73.71
LAC28,38951,02135,76643,98418,822 ± 648033,857 ± 10,54224,402 ± 11,28229,214 ± 10,697
LAC > 3 g998238510381517448.3 ± 261.71148 ± 726.9609.6 ± 403.4609.9 ± 479.0
LAC > 3 g/min12.3210.577.626.644.78 ± 3.486.20 ± 3.594.76 ± 2.933.58 ± 1.67
RAC70,642264,33887,260187,58551,137 ± 14,67996,894 ± 35,48255,465 ± 29,14176,842 ± 37,289
RAC > 400 rad/s220392638883.02134934.0 ± 441.11094 ± 609.2515.0 ± 357.91201 ± 601.8
RAC > 400 rad/s2/min16.8610.804.1515.239.05 ± 3.356.01 ± 2.673.39 ± 0.968.61 ± 3.97
Key: J = jockey; PRLA = peak resultant linear acceleration; MRLA = mean resultant linear acceleration; PRRV = peak resultant rotational velocity; MRRV = mean resultant rotational velocity; PRRA = peak resultant rotational acceleration; MRRA = mean resultant rotational acceleration; PLAD = peak linear acceleration duration; MLAD = mean linear acceleration duration; PRAD = peak rotational acceleration duration; MRAD = mean rotational acceleration duration; LAC = linear acceleration count; RAC = rotational acceleration count.
Table 4. The average head kinematic values for each jockey measured at the three time points of the study.
Table 4. The average head kinematic values for each jockey measured at the three time points of the study.
MetricTime Period One (August ’22)Time Period Two (March ’23)Time Period Three (June ’23)
J 1J 2J 3J 4MeanJ 1J 2J 3MeanJ 1J 2Mean
Time (min)71.44171.1139.7104.2121.6137.9202.0198.8179.6105.7177.2141.4
PRLA (g)5.824.935.566.275.656.415.667.146.405.035.465.25
MRLA (g)1.021.021.021.021.021.031.021.021.021.021.021.02
PRRV (rad/s)10.948.729.998.169.4514.769.1512.5112.149.849.209.52
MRRV (rad/s)1.070.770.670.720.811.030.830.780.880.990.780.89
PRRA (rad/s2)124111411300123812302000133720251787166814621565
MRRA (rad/s2)102.280.9965.1079.3281.90101.382.2381.4788.34103.470.7787.08
PLAD (ms)601.6587.6543.1484.9554.3642.2619.8572.6611.5595.6524.9560.2
MLAD (ms)135.5126.8129.5112.4126.0151.2133.5109.0131.2141.8103.6122.7
PRAD (ms)712.9879.6866.3749.8802.1914.7989.8709.1871.2889.3621.8755.6
MRAD (ms)86.7190.1293.1880.1487.38116.7112.873.66101.096.0656.3576.21
LAC12,77430,86824,40220,61022,16325,73231,95037,81831,83417,96038,75328,356
LAC > 3 g553.5372.5609.6235.8442.8625.31423.5984.01010.9166.01648.5907.3
LAC > 3 g/min8.292.194.762.244.374.477.114.915.501.589.295.44
RAC40,72282,91990,75247,31965,42859,20172,912106,36679,49353,488134,85294,170
RAC > 400 rad/s2664.8720.0515.01108.0751.9907.0925.01293.01041.71229.01636.31432.6
RAC > 400 rad/s2/min9.454.213.3910.636.926.494.586.645.9011.629.2410.43
Key: J = jockey; PRLA = peak resultant linear acceleration; MRLA = mean resultant linear acceleration; PRRV = peak resultant rotational velocity; MRRV = mean resultant rotational velocity; PRRA = peak resultant rotational acceleration; MRRA = mean resultant rotational acceleration; PLAD = peak linear acceleration duration; MLAD = mean linear acceleration duration; PRAD = peak rotational acceleration duration; MRAD = mean rotational acceleration duration; LAC = linear acceleration count; RAC = rotational acceleration count.
Table 5. Mean and standard deviation of each outcome measure in the cognitive test battery from all 35 days of testing with mean difference, 95% confidence interval, and effect size.
Table 5. Mean and standard deviation of each outcome measure in the cognitive test battery from all 35 days of testing with mean difference, 95% confidence interval, and effect size.
Cognitive Test BatteryPre-TestPost-TestMD95% CIEffect
n = 35MeanSDMeanSDLowerUpperHedges
TMTB (s)speed/error81.4617.8083.6013.442.14−1.425.690.20
mean20.374.4520.893.360.53−0.361.410.20
Stroop Speed/Error (s)combined21.612.9522.125.660.50−1.502.500.08
congruent10.261.2711.003.100.74−0.341.810.23
incongruent11.452.9211.063.04−0.39−1.680.89−0.10
Stroop Reaction Time (s)combined0.670.090.690.150.20−0.040.800.12
congruent0.640.080.690.160.050.010.100.30
incongruent0.700.140.700.160.00−0.080.080.01
Choice Reaction Time (s)speed/error13.702.9613.573.54−0.12−1.651.41−0.03
reaction time0.670.110.680.130.01−0.050.060.05
Grooved Pegboard (s)dominant57.045.3355.724.63−1.31−3.490.85−0.20
non dominant63.645.8060.895.64−2.75−4.65−0.85−0.50
RAF Ruler (cm)NPC11.742.6913.373.631.631.162.111.15
NPA11.762.5213.613.481.851.312.391.14
Key: n = number of days tested; speed/error calculation = Total time + (2 × mean time per word) × number of uncorrected errors; NPC = near point convergence; NPA = near point accommodation; SD = standard deviation, MD = mean difference, CI = confidence interval, Hedges’ = Hedges’ correction.
Table 6. Peak and mean (±standard deviation) head kinematic values measured in the current study with values from comparable research of non-impact head kinematics.
Table 6. Peak and mean (±standard deviation) head kinematic values measured in the current study with values from comparable research of non-impact head kinematics.
MetricCurrent StudyQuintana et al. [19]Mathers et al. [33]Kuo et al. [47]Miller et al. [12]
Overall PeakOverall Mean ± SDRace RidingSimulated RidingBull RidingBare RidingRollercoasterDaily Living
PRLA (g)9.655.82 ± 1.086.18 ± 4.122.44 ± 0.6715.76.183.8
MRLA (g)1.041.02 ± 0.011.15 ± 0.081.02 ± 0.08
PRRV (rad/s)24.4310.37 ± 3.2311.76 ± 13.104.88 ± 1.8033.2129.95
MRRV (rad/s)1.120.85 ± 0.150.99 ± 0.210.53 ± 0.15
PRRA (rad/s2)3562.541495 ± 532.75 2129.41577.8290287
MRRA (rad/s2)124.2186.58 ± 15.54
Key: SD = standard deviation; PRLA = peak resultant linear acceleration; MRLA = mean resultant linear acceleration; PRRV = peak resultant rotational velocity; MRRV = mean resultant rotational velocity; PRRA = peak resultant rotational acceleration; MRRA = mean resultant rotational acceleration.
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Edwards, E.; Bond, B.; Holsgrove, T.P.; Hill, J.; Baker, R.; Williams, G.K.R. Stirred Not Shaken: A Longitudinal Pilot Study of Head Kinematics and Cognitive Changes in Horseracing. Vibration 2024, 7, 1171-1189. https://doi.org/10.3390/vibration7040060

AMA Style

Edwards E, Bond B, Holsgrove TP, Hill J, Baker R, Williams GKR. Stirred Not Shaken: A Longitudinal Pilot Study of Head Kinematics and Cognitive Changes in Horseracing. Vibration. 2024; 7(4):1171-1189. https://doi.org/10.3390/vibration7040060

Chicago/Turabian Style

Edwards, Emma, Bert Bond, Timothy P. Holsgrove, Jerry Hill, Ryan Baker, and Genevieve K. R. Williams. 2024. "Stirred Not Shaken: A Longitudinal Pilot Study of Head Kinematics and Cognitive Changes in Horseracing" Vibration 7, no. 4: 1171-1189. https://doi.org/10.3390/vibration7040060

APA Style

Edwards, E., Bond, B., Holsgrove, T. P., Hill, J., Baker, R., & Williams, G. K. R. (2024). Stirred Not Shaken: A Longitudinal Pilot Study of Head Kinematics and Cognitive Changes in Horseracing. Vibration, 7(4), 1171-1189. https://doi.org/10.3390/vibration7040060

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