Mechanical behaviour of natural turf sports pitches across a season

A study assessing the mechanical behaviour of six natural turf pitches of varying sporting level and surface construction was undertaken over a period of 10?months, spanning a sporting season (August 2010 to May 2011). Penetration resistance and shear resistance were measured with the GoingStick^?, impact hardness and surface energy absorption were measured with the 2.25?kg Clegg Impact Soil Tester and the Dynamic Surface Tester device, respectively. The two sand rootzone pitches were more resistant to deformation and less variable in their impact behaviour (impact hardness and energy absorption) through the season than the native soil pitches containing greater proportions of silt and clay. Greater consistency was shown for penetration resistance and shear resistance on one of the sand rootzone pitches, with the other behaving similar to the native soil pitches for these parameters. The sand rootzone surfaces exhibited greater (P?<?0.05) impact hardness than the native soil pitches in the winter period of the season (November to mid-March) compared to the beginning or end periods of the season, where data were statistically similar (P?>?0.05). The greater consistency of sand rootzone surfaces should be considered for the effect it may have on player and team performance, and injury potential. Analysis of data against Performance Quality Standard benchmarks indicated that all data on the sand rootzones exceeded preferred values for impact hardness, indicating these ranges may be obsolete for the modern elite natural turf surface.     

Spatial characterisation of natural and third-generation artificial turf football pitches

In contrast to the situation with early artificial turf pitches, little information has previously been published on the characterisation of third-generation artificial surfaces. The spatial variation of ball rebound resilience and rotational resistance were measured here under dry conditions, late in the season, for two natural turf football pitches and a recently laid third-generation artificial turf pitch. Data for the natural turf pitches show a wider variation with position on the pitch than for the artificial pitch. The latter surface showed remarkable consistency in both quantities measured. Surprisingly, all ball rebound resilience data and some of the rotational resistance values were found to lie outside current FIFA specifications, possibly due to the level of wear in natural turf at this stage of the season. For the artificial turf, the deterioration in properties over a period of 6 months is significant and suggests more frequent testing is needed. Taking data from various pitch positions, the two measured quantities were shown for the first time, as far as we are aware, to be inversely related for both natural turf pitches. This correlation may be largely attributed to differences in the extent of grass cover and/or soil compaction. For artificial turf, the lack of variation in measured quantities with pitch position precluded the determination of any correlation.     

A kinematic analysis of the spine during rugby scrummaging on natural and synthetic turfs

Artificial surfaces are now an established alternative to grass (natural) surfaces in rugby union. Little is known, however, about their potential to reduce injury. This study characterises the spinal kinematics of rugby union hookers during scrummaging on third-generation synthetic (3G) and natural pitches. The spine was sectioned into five segments, with inertial sensors providing three-dimensional kinematic data sampled at 40 Hz/sensor. Twenty-two adult, male community club and university-level hookers were recruited. An equal number were analysed whilst scrummaging on natural or synthetic turf. Players scrummaging on synthetic turf demonstrated less angular velocity in the lower thoracic spine for right and left lateral bending and right rotation. The general reduction in the range of motion and velocities, extrapolated over a prolonged playing career, may mean that the synthetic turf could result in fewer degenerative injuries. It should be noted, however, that this conclusion considers only the scrummaging scenario.     

Hardness measurement of natural and hybrid turf soccer fields

Understanding the surface hardness of soccer fields is essential to evaluate the risk of injury and also its influence on the playing behavior of soccer players. In this context, newly developed hybrid turf systems have to be tested for their surface hardness with regard to the increased risk of injury on hard sports surfaces. The hardness of a soccer field can be quantitatively measured using an apparatus with a cylindrical weight that is dropped from a defined height. Since this procedure was first used for road construction, there are few studies investigating its use on sports grounds. This has led to inconsistencies in methodology and the absence of evaluation guidelines for classifying the hardness of soccer fields. This paper considers how turf systems (natural turf and hybrid turf) differ in their hardness and how this method can be used for different soccer turf systems. Natural turf systems, stitched turf systems, hybrid turf-bearing layer systems and woven mat systems were investigated. The assessment results from a comparative representation of hardness values of different soccer fields. By comparison, natural turf systems were found to be the softest, while woven mat systems were the hardest. Furthermore, the parameters that might affect the hardness were investigated. The influence of the measured soil parameters decreases with an increasing number of measurements per measuring point. Turf system-specific correlations make it possible to reduce the amount of measurement effort.     

The playing performance of county cricket pitches

The surface on to which a bowler projects a ball in the game of cricket is made up of hard packed soil with sparse grass cover. This natural turf pitch is of fundamental importance to the play of the game and the quality of the surface is a prime concern of players, officials, commentators and spectators alike. A programme of research has been undertaken to identify the factors that lead to the construction of high quality cricket pitches. This work employed the technology of highspeed video analysis to monitor the performance of first class cricket pitches during county matches. A system for measuring the impact of a cricket ball on a pitch was developed, and over 3000 ball impacts analysed. This analysis enabled pitches to be characterized in terms of pace, bounce and consistency. Soil properties for the monitored pitches were identified and correlations were drawn between pitch performance and soil composition.     

Quasi-static mechanical behaviour of soils used for natural turf sports surfaces and stud force prediction

The quasi-static testing of soils used in natural turf pitches yields key parameters in soil modelling, including elastic moduli, Poisson’s ratio and Mohr–Coulomb parameters for shearing resistance and cohesion in soil. The bulk strength of a Sand soil used in the construction of elite sports surfaces was found to increase initially and then decrease with increasing water content due to apparent cohesion effects. For a Clay Loam soil, more common in recreational facilities, shear strength decreased with water content. Reducing density resulted in a reduction of shear strength and elastic moduli in both soils due to reduced packing of particles reducing particle–particle contact surface area. The effect of roots on the shear strength of a Sand soil was not significant but reduced elastic moduli significantly. Horizontal forces measured during running and turning in a biomechanics laboratory were in good agreement with forces predicted using a simple quasi-static soil model for coarse-grained (Sand) soils although this was not the case with the Clay Loam soil.     

Injuries in Australian school-level rugby union

There is a high incidence of injuries in rugby union due to the physical nature of the game. In youth rugby union, there are large variations in injury rates reported. Our study investigated the rates of injuries in school-level rugby union players in Australia using the consensus statement for rugby union injuries. Injury surveillance was conducted on 480 rugby players from 1 school in Queensland, Australia. Injury data were collected using paper-based injury recording forms during the 8-week rugby season using a “medical-attention” injury definition. In total, 76 players sustained one or more injuries, with a total of 80 injuries recorded. The overall injury rate was 31.8 injuries/1000 match player hours (95% CI, 25.4–39.4). Concussion had an incidence rate of 6.0/1000 match player hours (95% CI, 3.5–9.6). The incidence of upper limb and lower limb injuries were 9.1 and 9.9/1000 match player hours, respectively (95% CI, 5.9–13.5 and 6.6–14.5). The older age divisions had higher injury rates and most injuries occurred while tackling or being tackled. The injury rates observed in this sample of Australian school rugby union players provides direction for future studies to enable informed decisions relating to development of injury prevention programmes at this level of rugby.     

Dynamic behaviour of soils used for natural turf sports surfaces

The modulus and damping properties of soils in compression are a function of soil type, water content, stress history and loading rate. To model human–surface interaction with natural turf sports surfaces, stiffness and damping properties must be determined at dynamic loading rates. Two contrasting soil types, a Sand and a Clay Loam, commonly used in sports surfaces were loaded uniaxially to 2 kN at loading rates between 0.6 and 6 kN s⁻¹ in modified dynamic soil testing apparatus. Soils were compacted prior to loading but initial cycles resulted in viscoplastic deformation, with strain accumulation with repeated cycles of loading. Ultimately a resilient, viscoelastic steady-state equilibrium with loading was established. Resilient modulus and damping ratio varied with soil type, water content, stress history and increased significantly with loading rate. The resilient modulus of the Sand soil, typical of modern free-draining sand construction natural turf sports surfaces, was significantly greater than that of a Clay Loam soil more characteristic of traditional natural turf surfaces; reducing water content caused an increase in modulus and a decrease in damping ratio in the Clay Loam soil. Determination of these properties provides initial data for the modelling natural turf surface behaviour in terms of both ball and human interactions, with further research required to determine the effect of both grass roots and leaves on mechanical behaviour.     

Human perceptions of artificial surfaces for field hockey

Measuring the performance of a sports surface is typically derived from a series of field and laboratory tests that assess the playing properties under simulated game conditions. However, from a player’s perspective their own comfort and confidence in the surface and its playing characteristics are equally if not more important. To date no comparative study to measure playing preference tests has been made. The aim of this research was to develop a suitable method for eliciting player perceptions of field hockey pitches and determine the key themes that players consider when assessing field hockey pitches. To elicit meaningful unbiased human perceptions of a playing surface, an individual subjective analysis was carried out, using interviews and inductive analysis of the recorded player statements. A qualitative analysis of elite hockey players (n = 22) was performed to obtain their perceptions immediately after a competitive match. The significant surface characteristics that emerged as part of an inductive analysis of their responses were grouped together and formed five general themes or dimensions: player performance, playing environment, pitch properties, ball interaction and player interaction. Each dimension was formed from a hierarchy of sub-themes. During the analysis, relationships between the dimensions were identified and a structured relationship model was produced to highlight each relationship. Players’ responses suggested that they perceived differences between pitches and that the majority of players considered a ‘hard’ pitch with a ‘low’ ball bounce facilitating a ‘fast’ game speed was desirable. However, further research is required to understand the relative importance of each theme and to develop appropriate measurement strategies to quantify the relevant engineering properties of pitch materials.     

Skin friction related behaviour of artificial turf systems

The occurrence of skin friction related injuries is an issue for artificial turf sports pitches and remains a barrier to their acceptance. The purpose of this study was to evaluate the current industry standard Securisport® Sports Surface Tester that measures skin surface related frictional behaviour of artificial turf. Little research has been published about the device and its efficacy, despite its widespread use as a standard FIFA test instrument. To achieve a range of frictional behaviours, several “third generation” (3G) carpet and infill combinations were investigated; friction time profiles throughout the Securisport rotations were assessed in combination with independent measurements of skin roughness before and after friction testing via 3D surface scanning. The results indicated that carpets without infill had greatest friction (coefficients of friction 0.97–1.20) while those completely filled with sand or rubber had similar and lower values independent of carpet type (coefficient of friction (COF) ≈0.57). Surface roughness of a silicone skin (s-skin) decreased after friction testing, with the largest change on sand infilled surfaces, indicating an “abrasive” polishing effect. The combined data show that the s-skin is damaged in a surface-specific manner, thus the Securisport COF values appear to be a poor measure of the potential for skin abrasion. It is proposed that the change in s-skin roughness improves assessment of the potential for skin damage when players slide on artificial turf.     

Kinetic and kinematic analysis of stamping impacts during simulated rucking in rugby union

Laceration injuries account for up to 23% of injuries in rugby union. They are frequently caused by studded footwear as a result of a player stamping onto another player during the ruck. Little is known about the kinetics and kinematics of rugby stamping impacts; current test methods assessing laceration injury risk of stud designs therefore lack informed test parameters. In this study, twelve participants stamped on an anthropomorphic test device in a one-on-one simulated ruck setting. Velocity and inclination angle of the foot prior to impact was determined from high-speed video footage. Total stamping force and individual stud force were measured using pressure sensors. Mean foot inbound velocity was 4.3 m ? s^?1 (range 2.1–6.3 m ? s^?1). Mean peak total force was 1246 N and mean peak stud force was 214 N. The total mean effective mass during stamping was 6.6 kg (range: 1.6–13.5 kg) and stud effective mass was 1.2 kg (range: 0.5–2.9 kg). These results provide representative test parameters for mechanical test devices designed to assess laceration injury risk of studded footwear for rugby union.     

Caution using data from triaxial accelerometers housed in player tracking units during running

Usage of accelerometers within player tracking devices in sport to quantify load, vertical ground reaction force (vGRF) or energy expenditure is contrary to placement guidelines. This study aimed to determine whether trunk-mounted accelerometers were a valid and reliable method to estimate thoracic segment or centre of gravity (COG) acceleration or vGRF, and the whether the elasticised harness contributes to the overestimation of acceleration. Ten male amateur rugby players performed five linear running tasks per lower limb at three speeds, twice, each with a different player tracking unit. Three-dimensional data were recorded and triaxial accelerometers were attached lateral to the device on the harness and skin and both shanks. Accelerometers demonstrated poor reliability (ICC:0.0–0.67), high variability (CV%:14–33%) and change in mean (41–160%), and were not valid to estimate vertical acceleration of the COG and thoracic segment nor vGRF. Caution is advised when utilising trunk-mounted triaxial accelerometer data as it is not a valid or reliable means to estimate peak vertical acceleration for its thoracic location nor whole-body COG acceleration or vGRF during running. To improve player tracking instrument validity and reliability, a new attachment method and/or harness material(s), that reduce or eliminate extraneous acceleration during running, are urgently required.     

Automatic detection of collisions in elite level rugby union using a wearable sensing device

Elite rugby union teams currently employ the latest technology to monitor and evaluate the physical demands of training and games on their players. Tackling has been shown to be the most common cause of injury in rugby union, yet current player monitoring technology does not effectively evaluate player tackling measurements. Currently, to evaluate measurements specific to player tackles, a time-consuming manual analysis of player sensor data and video footage is required. The purpose of this work is to investigate tackle modeling techniques which can be utilised to automatically detect player tackles and collisions using sensing technology already being used by elite international and club level rugby union teams. This paper discusses issues relevant to automatic tackle analysis, describes a technique to detect tackles using sensing data and validates the technique by comparing automatically detected collisions to manually labeled collisions using data from elite club and international level players. The results of the validation show that the system is able to consistently identify collisions with very few false positives and false negatives, achieving a recall and precision rating of 0.933 and 0.958, respectively. The aim is that the automatically detected tackles can provide coaching, medical and strength and conditioning staff with objective tackle-specific measurements, in real time, which can be used in injury prevention and rehabilitation strategies.     

The influence of gravimetric moisture content on studded shoe–surface interactions in soccer

It is desirable for the studs of a soccer shoe to penetrate the sport surface and provide the player with sufficient traction when accelerating. Mechanical tests are often used to measure the traction of shoe–surface combinations. Mechanical testing offers a repeatable measure of shoe–surface traction, eliminating the inherent uncertainties that exist when human participant testing is employed, and are hence used to directly compare the performance of shoe–surface combinations. However, the influence specific surface characteristics has on traction is often overlooked. Examining the influence of surface characteristics on mechanical test results improves the understanding of the traction mechanisms at the shoe–surface interface. This allows footwear developers to make informed decisions on the design of studded outsoles. The aim of this paper is to understand the effect gravimetric moisture content has on the tribological mechanisms at play during stud–surface interaction. This study investigates the relationships between: the gravimetric moisture content of a natural sand-based soccer surface; surface stiffness measured via a bespoke impact test device; and surface traction measured via a bespoke mechanical test device. Regression analysis revealed that surface stiffness decreases linearly with increased gravimetric moisture content (p = 0.04). Traction was found to initially increase and then decrease with gravimetric moisture content. It was observed that: a surface of low moisture content provides low stud penetration and therefore reduced traction; a surface of high moisture content provides high stud penetration but also reduced traction due to a lubricating effect; and surfaces with moisture content in between the two extremes provide increased traction. In this study a standard commercially available stud was used and other studs may provide slightly different results. The results provide insight into the traction mechanisms at the stud–surface interface which are described in the paper. The variation between traction measurements shows the influence gravimetric moisture content will have on player performance. This highlights the requirement to understand surface conditions prior to making comparative shoe–surface traction studies and the importance of using a studded outsole that is appropriate to the surface condition during play.     

Effect of turf on the cutting movement of female football players

PurposeThe globalisation of artificial turf and the increase in player participation has driven the need to examine injury risk in the sport of football. The purpose of this study was to investigate the surface–player interaction in female football players between natural and artificial turf.MethodsEight university level female football players performed an unanticipated cutting manoeuvre at an angle of 30° and 60°, on a regulation natural grass pitch (NT) and a 3G artificial turf pitch (AT). An automated active maker system (CodaSport CXS System, 200 Hz) quantified 3D joint angles at the ankle and knee during the early deceleration phase of the cutting, defined from foot strike to weight acceptance at 20% of the stance phase. Differences were statistically examined using a two-way (cutting angle, surface) ANOVA, with an α level of p < 0.05 and Cohen's d effect size reported.ResultsA trend was observed on the AT, with a reduction in knee valgus and internal rotation, suggesting a reduced risk of knee injury. This findings highlight that AT is no worse than NT and may have the potential to reduce the risk of knee injury. The ankle joint during foot strike showed large effects for an increase dorsiflexion and inversion on AT. A large effect for an increase during weight acceptance was observed for ankle inversion and external rotation on AT.ConclusionThese findings provide some support for the use of AT in female football, with no evidence to suggests that there is an increased risk of injury when performing on an artificial turf. The ankle response was less clear and further research is warranted. This initial study provides a platform for more detailed analysis, and highlights the importance of exploring the biomechanical changes in performance and injury risk with the introduction of AT.     

Discriminant analysis of the physiques of schoolboy rugby players,hurlers and non‐team members

The subjects were 31 successful schoolboy rugby players and 25 successful schoolboy hurlers; 34 non‐team members acted as controls. Thirty‐one anthropometric measurements were taken on each subject: height, weight, sitting height, five skeletal lengths, six skeletal diameters, 13 muscle circumferences and four skinfolds. The non‐players were significantly smaller than both the rugby players and the hurlers in weight, biacromial diameter, bideltoid, neck, chest, flexed arm, upper and lower thigh and calf circumferences. The non‐players were significantly smaller than the rugby players in arm length, femur diameter and waist, hip and relaxed arm circumferences. The non‐players were significantly smaller than the hurlers in femur length, biiliac and ankle diameters. There were no statistically significant differences between the rugby players and hurlers. Discriminant analysis produced a function containing terms for height, weight, fat free weight, humerus diameter and neck, bideltoid, forearm and calf circumferences which correctly assigned 83 (92%) of the subjects to ‘player’ and ‘non‐player’ categories. When the function was applied to the 15 members of the rugby team of a different school, 14 were placed in the ‘player’ category and one subject was given a borderline classification. It is concluded that there were differences in physique between the team members and non‐members and that the techniques used in the study were effective in quantifying them.     

Body mass changes during training in elite rugby union: Is a single test of hydration indices reliable?

There is limited research studying fluid and electrolyte balance in rugby union players, and a paucity of information regarding the test–retest reliability. This study describes the fluid balance of elite rugby union players across multiple squads and the reliability of fluid balance measures between two equivalent training sessions. Sixty-one elite rugby players completed a single fluid balance testing session during a game simulation training session. A subsample of 21 players completed a second fluid balance testing session during an equivalent training session. Players were weighed in minimal clothing before and after each training session. Each player was provided with their own drinks which were weighed before and after each training session. More players gained body weight (9 (14.8%)) during training than lost greater than 2% of their initial body mass (1 (1.6%)). Pre-training body mass and rate of fluid loss were significantly associated (r?=?0.318, p?=?.013). There was a significant correlation between rate of fluid loss in sessions 1 (1.74?±?0.32?L?h^?1) and 2 (1.10?±?0.31?L.?h^?1), (r?=?0.470, p?=?.032). This could be useful for nutritionists working with rugby squads to identify players with high sweat losses.     

A novel comparison between standard and new testing procedures to assess shock absorbency of third generation artificial turfs

This study aims to re-examine to what extent the testing procedure of the Artificial Athlete Berlin (DIN18032) is a valid evaluation method to assess the shock absorbency of third generation artificial turf (3-g turf) and to establish a new testing procedure, which precisely reflects the acute load by human sports action. The DIN test was conducted for 3-g turfs with different infill component. The baseline of the load of acute human sports action was obtained from the ground reaction force underneath the standard type of 3-g turf sample during landing from a 55-cm height with minimal shock attenuation. For reproducing the force similar to such a hard landing, a testing rig was developed and the same 3-g turf samples were tested. The DIN test failed to distinguish most types of 3-g turf and was found to be inappropriate to evaluate the shock absorbency of the 3-g turf mainly due to bouncing actions of the test foot on measured samples. In contrast, the newly developed testing rig succeeded in illustrating the differences of shock attenuation properties among most types of 3-g turfs in a high loading condition. In terms of players’ safety, the necessity of high loading test using an alternative testing procedure was highlighted.