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The study examined whether the performance characteristics of male university field hockey players differed when the match format was 2 × 35 min halves compared to 2 × 2 × 17.5 min quarters. Thirty-five male university field hockey players (age 21.2 ± 3.0 years, height 1.81 ± 0.07 m, body mass 75.1 ± 8.9 kg), competing at national level in the UK, were monitored over 52 matches played across the 2018–2019 (2 × 35 min halves) and 2019–2020 (2 × 2 × 17.5 min quarters) seasons using 15 Hz Global Positioning System units and heart rate monitors. Total distance, high-speed running distance (≥15.5 km·h−1), accelerations (≥2 m·s−1), decelerations (≤−2 m·s−1), average heart rate and percentage of time spent at &gt, 85% of maximum heart rate were recorded during both match formats. Two-level random intercept hierarchal models (Match—level 1, Player—level 2) suggested that the change in format from 2 × 35 min halves (2018–2019 season) to 2 × 2 × 17.5 min quarters (2019–2020 season) resulted in a reduction in total distance and high-speed running distance completed during a match (by 221 m and 120 m, respectively, both p &lt, 0.001). As no significant cross-level interactions were observed (between season and half), the change from 35 min halves to 17.5 min quarters did not attenuate the reduced physical performance evident during the second half of matches (total distance: −235 m less in second half, high-speed running distance: −70 m less in second half, both p &lt, 0.001). Overall, the findings suggest that the change in match format did alter the performance characteristics of male university field hockey players, but the quarter format actually reduced the total distance and high-speed running distance completed during matches, and did not attenuate the reduction in performance seen during the second half of matches.

Mechanical analysis at the whole human body level typically assumes limbs are rigid bodies with fixed inertial parameters, however, as the human body consists mainly of deformable soft tissue, this is not the case. The aim of this study was to investigate changes in the inertial parameters of the lower limb during landing and stamping tasks using high frequency three-dimensional motion analysis. Seven males performed active and passive drop landings from 30 and 45 cm and a stamp onto a force plate. A sixteen-camera 750 Hz Vicon system recorded markers for standard rigid body analysis using inverse kinematics in Visual 3D and 7 × 8 and 7 × 9 marker arrays on the shank and thigh. Frame by frame segment volumes from marker arrays were calculated as a collection of tetrahedra using the Delaunay triangulation method in 3D and further inertial parameters were calculated using the method of Tonon (2004). Distance between the centres of mass (COM) of the rigid and soft tissues changed during impact in a structured manner indicative of a damped oscillation. Group mean amplitudes for COM motion of the soft tissues relative to the rigid body of up to 1.4 cm, and changes of up to 17% in moment of inertia of the soft tissue about the rigid body COM were found. This study has shown that meaningful changes in inertial parameters can be observed and quantified during even moderate impacts. Further examination of the effects these could have on movement dynamics and energetics seems pertinent.

Despite being an essential consideration when deciding rule changes, injury prevention strategies, and athlete development models, there is little epidemiological data of U18 field hockey player injuries–something explicitly referred to in the 2015 International Olympic Committee’s Consensus Statement on Youth Athlete Development. The aim of this study was to quantify incidence and characteristics of injuries in elite youth field hockey players during a major international tournament. Standardized reporting forms detailing time, location on pitch, mechanism and anatomical location of injury were completed for new musculoskeletal conditions resulting in a time stoppage by the umpire and where a player was noticeably affected by an injury for up to 20 s regardless of time stoppage. Injury incidence was 1.35 and 2.20 injuries/match or 53 and 86 injuries per 1000 player match hours for boys (B) and girls (G) respectively; girls were over three times more likely to have a minor injury. Most injuries were contusions due to being hit by the ball or stick (B: 12, G: 27), with high numbers of injuries to the torso (B: 8) and head/face (G: 7). Injuries during the penalty corner (B: 3, G: 4) were to the lower limb and hand, and boys were less likely to wear facial protection (B: 65.9%, G: 86.4%). Results form an essential initial dataset of injuries in U18 field hockey players. Current reporting protocols under-report injuries and must be addressed by the international governing body. The high number of head/face injuries, particularly in females, requires further investigation.

PURPOSE: The aim of this study was to investigate the effect of altering preferred running speed by ±20% on kinetic asymmetry. METHODS: Three-dimensional motion analysis and force data were acquired from 15 healthy males (age: 27 ± 4.6 years, height: 1.81 ± 0.09 m, mass: 80.4 ± 12.4 kg) during their preferred running speed, and at ±20% of this speed. 3T magnetic resonance images were used to measure Achilles tendon cross-sectional area and moment arm, for use in calculation of tendon stress. Kinetic and tendon stress asymmetry were subsequently calculated in each condition using the symmetry index. RESULTS: Across all joints and conditions, average asymmetry of peak moments was between ±6% but higher individual values were observed; there was no effect of speed on magnitude of asymmetry. Ground contact times, vertical ground reaction forces and support and ankle moments (maximum absolute asymmetry: 9%) were more symmetrical than hip and knee moments (up to 18%). Individual joint contribution to support moment and positive work were similar in both limbs, and ankle and hip compensatory interactions were observed with alterations in running speed. Achilles tendon stress increased with increased running speed, with higher stress in the preferred limb; asymmetry in tendon stress was not related to asymmetry in vertical ground reaction forces. CONCLUSION: Results show small effects of altering running speed on kinetic asymmetry, but responses are individual-specific with interactions occurring between joints to maintain overall movement symmetry. Further research is needed to understand the mechanical and neuromuscular mechanisms underpinning these compensations.

peer-reviewed ???????????????????????????????????????????????????? The fixed position of force plates has led researchers to pursue alternative methods of determining centre of pressure (CoP) location. To date, errors reported using alternative methods to the force plate during dynamic tasks have been high. The aim of this study was to investigate the accuracy of a motion analysis marker-based system to determine CoP during a two-legged hopping task. Five markers were attached to the left and right feet of eight healthy adults (5 females, 3 males, age: 25.0??2.8 years, height: 1.75??0.07 m, mass: 71.3??11.3 kg). Multivariate forward stepwise and forced entry linear regression was used with data from five participants to determine CoP position during quiet standing and hopping at various frequencies. Maximum standard error of the estimate of CoP position was 12 mm in the anteroposterior direction and 8 mm in the mediolateral. Cross-validation was performed using the remaining 3 participants. Maximum root mean square difference between the force plate and marker method was 14 mm for mediolateral CoP and 20 mm for anteroposterior CoP during 1.5 Hz hopping. Differences reduced to a maximum of 7 mm (mediolateral) and 14 mm (anteroposterior) for the other frequencies. The smallest difference in calculated sagittal plane ankle moment and timing of maximum moment was during 3.0 Hz hopping, and largest at 1.5 Hz. Results indicate the marker-based method of determining CoP may be a suitable alternative to a force plate to determine CoP position during a two-legged hopping task at frequencies greater than 1.5 Hz. ACCEPTED peer-reviewed

Most healthy humans move symmetrically at gross limb level but large kinetic and kinematic asymmetries have been observed at joint level during locomotion. The aim of this study was to assess muscle function asymmetries in healthy, active adults using an adapted force sledge apparatus which isolates the plantarflexors during a stretch-shortening cycle (SSC) task. Peak force, rate of force development and SSC function of preferred and non-preferred limbs were assessed in 21 healthy, active individuals using the adapted sledge and three-dimensional motion analysis. Between-limb differences and relationships were determined using paired t-tests/Wilcoxon Signed-rank test, Cohen's dz, absolute symmetry index and Pearson's r/Spearman's rho. Significant differences with moderate effect size (ES) were observed in peak force (ES: 0.66), rate of peak force development (ES: 0.78), rate of force development in the first 50 ms (ES: 0.76), flight time (ES: 0.64) and SSC function (0.68), with no difference in contact time or duration of eccentric loading. A small ES (0.56) was observed in rate of force development in the first 30 ms. The upper range of asymmetry observed (up to 44.6%) was larger than previously reported for healthy individuals, indicating compensations occur at proximal joints during locomotion to ensure symmetrical movement.

Objective: Muscle volume (MV) analysis from magnetic resonance imaging (MRI) is time-intensive, and limited measurement reliability data are available. This study investigated a method to reduce lower limb MV analysis time demands, established reliability of these measurements, and applied the findings to quantify muscle size and symmetry in healthy adult males. Approach: Bilateral MRI images were acquired from 15 healthy males (age: 26.5 ±4.6 years, height: 1.81 ±0.09 m, body mass: 80.4 ±12.4 kg) for the entire lower limb. In two participants, the individual gluteals, quadriceps, hamstrings, and triceps surae were manually outlined every 5 mm and MV calculated using 5, 10, 15, 20, 25, and 30 mm distances between images to determine an appropriate distance for reducing analysis time. For all 15 participants, 35 muscles in each limb were manually outlined every 15 mm for use in MV calculations. Reliability of muscle cross-sectional area (CSA) measurements was determined within- and between-sessions and MV measurement reliability determined between-sessions. Between-limb symmetry was calculated using symmetry indices. Main results: A 15 mm inter-slice distance was appropriate for measuring MV (mean difference compared to reference method: 0.7 ±0.7%). Between-session measurement reliability was good for MV (Typical Error preferred kicking limb (TEP): 1.2%, nonpreferred kicking limb (TENP): 0.8%) and CSA (TEP: 3.4 ±2.9%, TENP: 3.2 ±1.9%) although CSA typical error was larger with increased between-session time (TEP: 4.1 ±3.1%, TENP: 4.7 ±4.0%). Between-limb differences in MV were small (mean symmetry index: 0.4 ±4.1%). Absolute differences in individual MV were larger (mean: 12.6 ±2.6%), but representing muscles as functional anatomical groups showed smaller absolute between-limb differences (mean: 4.7 ±1.8%). Significance: MV analysis time demand can be reduced by increasing the distance between analysed MRI slices, although participant height, muscle length and shape require consideration. Minimal between-limb muscle size differences have been reported in adult males.