The effects of artificial surface temperature on mechanical properties and player kinematics during landing and acceleration

Background: Artificial turf is considered a feasible global alternative to natural turf by many sports governing bodies. Consequently, its ability to provide a safe and consistent playing surface regardless of climate becomes essential. The aims of this study were to determine the effects of artificial surface temperature on:(1) mechanical properties of the turf and(2) the kinematics of a turf-sport related movement.Methods: Two identical artificial turf pitches were tested: one with a cold surface temperature(1.8°C–2.4°C) and one with a warm surface temperature(14.5°C–15.2°C). Mechanical testing was performed to measure the surface properties. Four amateur soccer players performed a hurdle jump to sprint acceleration movement, with data(contact time, step length and hip, knee and ankle kinematics) collected using CODASport(200 Hz).Results: The temperature difference had a significant influence on the mechanical properties of the artificial turf, including force absorption,energy restitution, rotational resistance, and the height where the head injury criterion was met. Both step length(p = 0.008) and contact time(p = 0.002) of the initial step after the landing were significantly longer on the warm surface. In addition, significant range of motion and joint angular velocity differences were found.Conclusion: These findings highlight different demands placed on players due to the surface temperature and suggest a need for coaches,practitioners, and sports governing bodies to be aware of these differences.

The Influence of Biological Maturity on Dynamic Force-Time Variables and Vaulting Performance in Young Female Gymnasts

Purpose This cross-sectional study investigated dynamic force-time variables and vaulting performance in young female gymnasts of different maturity status.Methods 120 gymnasts aged 5-14 years were sub-divided into maturity groupings using percent of predicted adult height(%PAH)attained.Participants performed three jumping protocols,the squat jump(SJ),countermovement jump(CMJ)and drop jump(DJ),before completing straight jump vaults that were recorded using two-dimensional video.Results Jumping performance improved with biological maturity evidenced by the most mature gymnasts’producing sig-nificantly more absolute force(P<0.05;all d>0.78),impulse(P<0.05;all d>0.75)and power(P<0.05;all d>0.91)than the least mature group,resulting in the greater jump heights(P<0.05;all d>0.70).While,no significant differences were observed in relative peak force across multiple tests,measures of relative peak power did significantly increase with maturity.Based upon regression analyses,maturation was found to influence vertical take-off velocity during vaulting,explaining 41%of the variance in each jumping protocol.Across all tests,the DJ was found to have the highest predictive ability of vaulting vertical take-off velocity,explaining 55%of the total variance.Conclusion Biological maturation impacts jump height and underpinning mechanical variables in young female gymnasts.Vaulting vertical take-off velocity appears to be influenced by maturation and various dynamic force-time variables,par-ticularly those during DJ,which had the highest explained total variance.

Utility of Kinetic and Kinematic Jumping and Landing Variables as Predictors of Injury Risk: A Systematic Review

Purpose Jump-landing assessments provide a means to quantify an individual’s ability to attenuate ground reaction forces,generate lower limb explosive power and maintain joint alignment.In order to identify risk factors that can be targeted through appropriate training interventions,it is necessary to establish which(scalar)objective kinetic,kinematic,and performance measures are most associated with lower-extremity injury.Methods Online searches of MEDLINE,SCOPUS,EBSCOHost,SPORTDiscus and PubMed databases were completed for all articles published before March 2020 in accordance with PRISMA guidelines.Results 40 articles investigating nine jump-landing assessments were included in this review.The 79%of studies using drop jump(n=14)observed an association with future injury,while only 8%of countermovement jump studies(n=13)observed an association with injury risk.The 57%of studies using unilateral assessments found associations with risk of injury(n=14).Studies using performance measures(jump height/distance)as outcome measure were only associated with injury risk in 30%of cases.However,those using kinetic and/or kinematic analyses(knee abduction moment,knee valgus angle,knee separation distance,peak ground reaction force)found associations with injury in 89%of studies.Conclusion The landing element of jump-landing assessments appears to be superior for identifying individuals at greater risk of injury;likely due to a closer representation of the injury mechanism.Consequently,jump-landing assessments that involve attenuation of impact forces such as the drop jump appear most suited for this purpose but should involve assessment of frontal plane knee motion and ground reaction forces.

Is it Possible to Protect the Adolescent Brain with Internal Mechanisms from Repetitive Head Impacts:Results from a PhaseⅡSingle Cohort,Longitudinal,Self-Control Study

Purpose To quantify the effects of an externally worn collar device for mitigating the influence of repetitive head impacts on alterations to diffusion tensor imaging(DTI)metrics of white matter.Methods Fifteen female high-school soccer athletes(age:14.00-16.98 yrs)completed pre-and post-season DTI over two consecutive years,including measures of diffusivity,changes in which may be associated with brain dysfunction.The collar was worn during year 1(Yr1)but not during year 2(Yr2).Athlete exposures(AEs)and head impact exposure were recorded over the competitive seasons.Results There were no significant differences in AEs or head impact exposures between Yr1 and Yr2(P>0.05).In Yr2,there was significant pre-to post-season mean diffusivity and/or axial diffusivity reduction in multiple WM regions(cor-rected P<0.05).Pre-to post-season mean diffusivity,axial diffusivity,and radial diffusivity decreases were 3.04%±2.53%,2.97%±2.19%,and 3.37%±3.34%,respectively,significantly greater than pre-to post-season changes in Yr1(mean dif-fusivity:-0.31%±1.78%,P=0.0014;axial diffusivity:-0.02%±2.25%,P=0.0014;radial diffusivity:-0.63%±2.10%,P=0.0030).Conclusions Mild bilateral compression to athletes'internal jugular vein through collar application may have increased intracranial blood volume and spatially redistributed head-impact-derived brain energy absorption.However,future research is needed to elucidate the potential clinical significance of WM changes of various degrees.Clinical trails registration NCT03014492.