1. Introduction: history and development of sports surfaces 2. Surface Classification, Function, Construction and Maintenance 3. Mechanical testing and characterisation of sports surfaces 4. Sports Surfaces, Biomechanics and Injury 5. Sports Surfaces and Performance 6. Mechanical Aspects of Shoe-surface Interaction 7. Human-Shoe-Surface Interaction 8. Natural Turf Sports Surfaces 9. The Future of Sports Surfaces

Mechanical behaviour of natural turf sports pitches is commonly assessed using the Clegg Impact Soil Tester and the studded disc apparatus under benchmark frameworks. Using the studded disc is time consuming and laborious, which restricts the frequency at which data on surfaces can be collected. To address this, the GoingStick® was evaluated for use as a surface assessment tool. The device was originally developed for testing horseracing tracks, and quantifies both the penetration resistance and shear resistance of the turf surface. Data were collected on three sports pitches (rugby union and football) of varying sporting level and soil texture over two seasons of sport. A laboratory experiment was also conducted assessing data from the GoingStick and the Clegg Impact Soil Tester for four soil treatments. The first season data highlighted that the maximum measurable value was too low on the device, owing to sports pitches being harder than race tracks. This issue was also found for the harder soil treatments in the laboratory study. The development of a new sports pitch calibration resolved this issue for the second season, where the entire range of resistance was successfully measured. Linear relationships were evident between penetration resistance measured with the GoingStick and impact hardness measured with the third drop of the 2.25 kg Clegg Impact Soil Tester (r2 = 0.75), and between shear resistance measured with the GoingStick and peak torque resistance measured by the studded disc (r2 = 0.88). The results of the study indicate the potential for the GoingStick to efficiently quantify the mechanical behaviour of natural turf pitches. Further work should aim to determine benchmark ranges for the measured parameters and incorporate the device within decision-support frameworks for surface management.

Reducing external injury risk factors associated with the boot-surface interaction is important in reducing the incidence and severity of foot and ankle injury. A review of prospective football (soccer) injury epidemiology studies determined that the incidence of noncontact ankle sprain injury is relatively high. Research on the impact of cleat shape and configuration and boot design on the boot-surface interaction is providing new understanding of the impact on player biomechanics and injury risk but is not keeping pace with commercial advances in boot design and innovation in natural and synthetic turf surface technology.

The mechanical behaviour of three sports pitches was spatially analysed using geostatistical techniques (variograms and interpolation), at three times across a season of sport. Data were collected from over 100 locations across the pitches. Pure nugget variograms were evident for penetration resistance and shear resistance measured with the GoingStick, surface energy absorption measured with the dynamic surface tester (DST) device, and soil water content. Descriptive statistics and interpolated surface maps of the data confirmed that the surfaces exhibited random variation in their mechanical properties and did not support previous research suggesting that behaviour varies in central areas of the pitch. Temporal variation on the pitches was shown to be similar in magnitude to detected spatial variation. Impact hardness quantified with the CIST was the only mechanical property that exhibited spatially dependent data, and this was attributed to the stress history applied by the first two drops of the device. Temporal and spatial variation of properties was generally smaller on a sand rootzone pitch, in comparison to two native soil pitches. Consideration should be given to the effect that spatial variability of sports pitches may have on player performance or injury risks throughout the sporting season: DST data suggest that the impact attenuation athletes would receive when running on the surface would vary on a small spatial scale. The methodology was considered robust for use in future spatial analysis.

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.

A new laboratory-scale simulator was developed to investigate the compaction of a clay loam soil during repeated passes of a 600mm diameter×500mm wide smooth steel wheeled roller in alternate directions with a mass increasing sequentially from 260 to 1250kgm−1. Soil displacement in the vertical plane parallel to rolling was quantified using automated image analysis of videos of a 5×5 array of 5mm diameter markers inserted at depths between 15 and 135mm in the soil. Mean applied stress increased with roller mass but decreased as soil water content increased due to reduced soil bearing capacity which increased roller-soil contact area. Mean profile soil dry bulk density increased as roller mass increased and as soil water content increased. Analysis of marker displacement determined that soil displacement and therefore density change decreased with depth. Analysing the movement of markers in a vertical cross-section throughout a complete pass of the roller, allowed investigation of the vertical recovery of the soil after loading, and the complex fore-and-aft displacement of the marker as the roller passes. An un-replicated investigation of the same clay loam soil with an established perennial ryegrass sward indicated that plant roots reinforce soil and reduce horizontal soil displacement. Optimum water content for rolling in this clay loam soil is above the Proctor optimum water content for compaction due to the additional effect of horizontal soil displacement. The methodology and results not only have implications for the compaction of soils in this specific amenity context of cricket, but also in wider applications to the compaction of soils in agricultural systems.

Integrated biomechanical and engineering assessments were used to determine how humans responded to variations in turf during running and turning. Ground reaction force (AMTI, 960 Hz) and kinematic data (Vicon Peak Motus, 120 Hz) were collected from eight participants during running (3.83 m/s) and turning (10 trials per condition) on three natural turf surfaces in the laboratory. Surface hardness (Clegg hammer) and shear strength (cruciform shear vane) were measured before and after participant testing. Peak loading rate during running was significantly higher (p < .05) on the least hard surface (sandy; 101.48 BW/s ± 23.3) compared with clay (84.67 BW/s ± 22.9). There were no significant differences in running kinematics. Compared with the "medium" condition, fifth MTP impact velocities during turning were significantly (RM-ANOVA, p < .05) lower on clay (resultant: 2.30 m/s [± 0.68] compared with 2.64 m/s [± 0.70]), which was significantly (p < .05) harder "after" and had the greatest shear strength both "before" and "after" participant testing. This unique finding suggests that further study of foot impact velocities are important to increase understanding of overuse injury mechanisms.

The response of natural turf surfaces to loading changes with the force and loading rate applied. Quantification of surface behaviour to athlete loading is complicated by the lack of devices that replicate forces, stresses and loading rates of athletes that can be specifically used on natural turf. To address this issue, a vertical dynamic impact testing device, the DST, was developed. The DST consists of a compressed air-driven ram that vertically impacts a studded test foot on to the surface using data from biomechanical studies. The vertical dynamic stress of athlete foot strike during running is replicated, using peak force and mean boot contact area data. The ram pressure is adjustable to allow variation of the stress applied upon impact, potentially replicating a range of athlete–surface interactions. Initial laboratory testing indicated that the device was sensitive to changes in soil condition due to variations in impact data. Total penetration time and distance, and surface energy absorption were all significantly greater in prepared ‘soft’ soil treatments ( p < 0.05). The loading rate in the first 50 ms after impact was significantly greater in the ‘hardest’ soil treatment ( p < 0.05). Future research work will determine in situ behaviour of actual playing surfaces, compare device loading rates to those of athletes, and assess surfaces to a range of stresses.

The majority of outdoor sports surfaces are natural turf and they remain the elite-level standard for a number of sports. A natural turf surface is susceptible to environmental and physical stress and has a limited resistance to wear. A number of technological advances have increased the quality and durability of natural turf surfaces including: sand rootzones; drainage; irrigation; agrochemicals; turfgrass breeding; turf reinforcement; supplementary lighting; ventilation; and advanced stadium architecture. These advances have resulted in an increase in resource consumption and where resources are restricted natural turf viability, performance, and safety is limited. This paper examines these challenges and others facing natural turf by reviewing the state of the art and signposting future research required to ensure performance, safety, and sustainability from natural turf surfaces. More development is required for lower-cost technologies for recreational-level facilities. Synthetic turf surfaces can be used to reduce the intensity of use of natural turf but sustainable natural turf construction and management must focus on resource consumption reduction and resilience to climate change for the continued provision of high performance, safe surfaces for sport. Furthermore, greater user-awareness of resource consumption and the consequences of reduced consumption are important for adoption in the future of more sustainable practices.

Sports facilities have been shown to have a positive impact on local biodiversity, quality of life, and the economy. Their impact on global carbon balances is less clearly understood. Increased concentrations of atmospheric carbon dioxide (CO 2 ) have been linked with global climate change. Currently there is a debate as to whether amenity turf is a net source or a net sink for atmospheric CO 2 . The turf grass of a natural sports pitch will sequester carbon through photosynthesis, but there are numerous emission sources associated with the management of turf which release CO 2 into the atmosphere. These include the engines used to power mechanized operations such as mowing and spraying, the application of agrochemicals, including fertilizers, and the disposal of waste. In order to determine whether a real-world example of a sports facility was a source or sink of carbon a mechanistic mass balance model was developed. Analysis indicated that the areas of the golf course that received the most management attention were a net source of carbon emissions. The magnitude of these releases was significantly different on an equal-area basis ( p < 0.01). The net carbon budget for turf grass areas across the whole golf course accounting for the sequestration by the turfgrass was −33.01 MgC/year. The mature trees that formed an integral part of the landscape of the modelled course had a significant impact on the net carbon balance, resulting in overall net sequestration of −177.3 MgC/year for the whole golf course, equivalent to −1.93 MgC/ha/year. The variability in the size, shape, and vegetation composition of different golf courses has a considerable impact on their net carbon balance, and the resultant environmental impact of sports facilities must be assessed on an individual basis.

An estimated 32,000 golf courses worldwide (approximately 25,600 km2), provide ecosystem goods and services and support an industry contributing over $124 billion globally. Golf courses can impact positively on local biodiversity however their role in the global carbon cycle is not clearly understood. To explore this relationship, the balance between plant–soil system sequestration and greenhouse gas emissions from turf management on golf courses was modelled. Input data were derived from published studies of emissions from agriculture and turfgrass management. Two UK case studies of golf course type were used, a Links course (coastal, medium intensity management, within coastal dune grasses) and a Parkland course (inland, high intensity management, within woodland).Playing surfaces of both golf courses were marginal net sources of greenhouse gas emissions due to maintenance (Links −2.2 ± 0.4 Mg CO2e ha(−1) y(−1); Parkland − 2.0 ± 0.4 Mg CO2e ha(−1) y(−1)). A significant proportion of emissions were from the use of nitrogen fertiliser, especially on tees and greens such that 3% of the golf course area contributed 16% of total greenhouse gas emissions. The area of trees on a golf course was important in determining whole-course emission balance. On the Parkland course, emissions from maintenance were offset by sequestration from turfgrass, and trees which comprised 48% of total area, resulting in a net balance of −5.4 ± 0.9 Mg CO2e ha(−1) y(−1). On the Links course, the proportion of trees was much lower (2%) and sequestration from links grassland resulted in a net balance of −1.6 ± 0.3 Mg CO2e ha(−1) y(−1). Recommendations for golf course management and design include the reduction of nitrogen fertiliser, improved operational efficiency when mowing, the inclusion of appropriate tree-planting and the scaling of component areas to maximise golf course sequestration capacity. The findings are transferrable to the management and design of urban parks and gardens, which range between fairways and greens in intensity of management.

The effect of three grass leaf height treatments (50 mm, 25 mm, < 1 mm) of two sports field rootzones (clay loam, sand) was assessed under controlled conditions using the 0.5 kg and 2.25 kg Clegg Impact Soil Testers (CIST) and the Dynamic Surface Tester (DST) device. Results were dependent upon the test device, impact energy, and drop number of the impact. The presence of grass was shown to be more important than specific grass heights in regulating impact behaviour, with no differences detected between 50 mm and 25 mm treatments. Peak deceleration was reduced (P < 0.05) by the presence of grass (50 mm and 25 mm treatments) for drop one, but not drop three of the 0.5 kg CIST missile, indicating grass leaves absorb some impact energy on lower energy single impacts but not when leaves are flattened under repeated loading. There was no difference in peak deceleration of the higher energy 2.25 kg CIST among leaf treatments for first drop, but was significantly lower (P < 0.05) for third drop on the < 1 mm treatment where the soil exhibited greater (P < 0.05) plastic displacement. Surface loading rate and energy absorption did not differ across treatments under athlete-specific impact stresses measured with the DST, suggesting grass leaves may not affect athlete impacts. Greater consideration is required for future impact testing to assess surfaces to specific impacts that occur in game situations through the use of appropriate test devices.

The effect of infill quantity and contamination on the performance of second generation sand-filled synthetic turf sports surfaces was investigated in a laboratory study. Three 1 m2 test surfaces were constructed by placing synthetic turf over a stone–tar-macadam–rubber shockpad sub-base. Ball rebound, ball roll, surface rebound hardness and rotational resistance of a dimpled rubber sole were measured for a range of infill quantities (0–35 kg/m2) and infill contamination concentrations (0, 10 and 20%). Increasing infill quantity increased hardness, reduced ball rebound and reduced rotational resistance linearly (p < 0.01). Ball deceleration increased up to 10 kg/m2 after which there was no further significant increase in the range tested. An optimum infill quantity of 25–30 kg/m2, based on performance characteristics and the length of fibre above the infill, was identified for the synthetic turf surface tested. Increasing contamination also increased ball deceleration and reduced infiltration rate and kept surfaces wetter for longer during drying (p < 0.001), resulting in conditions suitable for moss and algae formation. Maintenance, including regular brushing and monitoring of infill quantity, is required to ensure even distribution of the correct quantity of infill and the minimization of infill contamination in all infilled synthetic turf 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.

In cricket, where a hard leather ball is bounced on to a natural turf, clay soil pitch between the 'bowler' and the 'batsman' at speeds of 20 to 160 km h(-1), the ball-surface interaction is critical. This interaction is a function of the mechanics of the surface, which in turn are affected by soil packing (bulk density) and moisture content in the critical top 100 mm of the profile. To achieve the required mechanical properties of the pitch, the surface is consolidated with a smooth wheeled, steel roller at optimum moisture for compaction. This paper describes initial results from laboratory scale tests using an apparatus designed to investigate the effect of key design and operating variables for the roller (mass, roller diameter, forward speed) and environmental factors (soil type, moisture content, grass) on surface consolidation with depth through the facilitate profile.

The performance of a sports surface is quantified for a number of reasons and by a range of methods. Four categories of surface performance testing are proposed: category 1, to determine compliance with minimum standards; category 2, to assess the overall quality of surfaces across different tiers of sport; category 3, to inform management intervention (construction and maintenance); category 4, to inform research into sports surface engineering, equipment development, the biomechanics of sports performance, and sports injury. The majority of testing in the UK falls into category 1, particularly for synthetic surfaces. Performance quality standards (PQSs) are a system for the quantification of natural turf surface performance and are suitable for category 1 testing but in this study the suitability of the PQS approach for category 2 and category 3 testing was considered in the objective statistical analysis of data from football (soccer) and cricket in the UK. Analysis determined that a PQS is suitable for category 2 testing but that a weighting system for individual components should be developed. Development of a system of decision support based upon PQS data will enable PQS systems to be used for category 3 approaches, although a coherent decision support system is not currently available. The limitation of this type of testing for category 4 was also considered.

Important health and social benefits can be gained from participation in sports and exercise. Appropriate surface provision that aids sports participation, cannot be met by artificial surfaces alone - it requires natural turf surfaces to be utilised. Considerable improvement in the durability of natural turf surfaces and thus, a greater understanding of the human-natural sports surface interaction is required. Ground reaction force data have been used to help quantify how human participants respond to changes in natural turf properties during running and turning. A kinematic analysis would further this understanding. This EPSRC/UK funded study analyses kinematic response to variations in natural turf during running. Three different rootzone conditions (clay, sandy and rootzone) were constructed in portable plastic trays (0.60 m x 0.40 m x 0.08 m) and turfed with ryegrass. Trays were positioned in the laboratory on non-slip matting (6 mm thick) to form a continuous runway. Three-dimensional kinematic data (Vicon Peak, automatic, opto-electronic system 120 Hz) were collected for nine subjects wearing football boots (studded natural turf design) during running (3.83m.s(-1)). Group mean data for initial and peak ankle and knee angles and peak joint angular velocities were statistically compared using an analysis of variance with repeated measures (ANOVA R.M, p<0.05). Mechanical measures of surface hardness (Clegg Hammer) and shear were taken before and after subject testing and assessed using a paired t-test (p<0.05). Moisture content was also assessed. Kinematic data were found to be representative of typical running values presented in the literature. While mechanical measures revealed that natural turf conditions were not identical, changes in surface did not yield any significant kinematic differences. The consistent production of ankle and knee joint kinematics with changes in mechanical surface properties could suggest that humans prefer to maintain similar geometries when running on a variety of natural turf surfaces. Alternatively, the mechanical properties of the natural turf conditions may not have been sufficiently different to elicit changes in human response during running.

It is well documented that health and social benefits can be attained through participation in sport and exercise. Participation, particularly in sports, benefits from appropriate surface provisions that are safe, affordable and high quality preferably across the recreational to elite continuum. Investment, construction and research into artificial sports surfaces have increased to meet this provision. However, not all sports (e.g. golf, rugby and cricket) are suited to training and match play on artificial turf without compromising some playing characteristics of the games. Therefore, full sport surface provision cannot be met without the use of natural turf surfaces, which also have an important role as green spaces in the built environment. Furthermore, a significant number of people participate in outdoor sport on natural turf pitches, although this is a declining trend as the number of synthetic turf surfaces increases. Despite natural turf being a common playing surface for popular sports such as soccer,rugby and cricket, few biomechanical studies have been performed using natural turf conditions. It is proposed that if natural turf surfaces are to help meet the provision of sports surfaces, advancement in the construction and sustainability of natural turf surface design is required. The design of a natural turf surface should also be informed by knowledge of surface related overuse injury risk factors.