Measurement. Biomechanics

Biomechanics focuses on the study of the athlete's movements during physical exercise (Amadio, 1997). This field has applications in a variety of sports, from those with high physical interaction between the player and the playing surface, such as football and rugby, to others with less interaction, such as golf.

Biomechanical assessment is a growing practice due to its numerous benefits for athlete safety. Through a detailed analysis of the movements and forces involved, patterns that could predispose to injury can be identified and corrected.

From the perspective of sports surface maintenance, biomechanics is characterised by the measurement of several key parameters. These include slip resistance, shock absorption and surface deformation under load. Measuring and adjusting these parameters appropriately not only improves athlete performance, but also contributes to the longevity of sports facilities and the reduction of accidents.

Shock Absorption, Energy Restitution and Vertical Displacement

The evaluation of parameters such as shock absorption, vertical deformation and energy restitution is fundamental to understand the relationship between fatigue and possible injuries of players in sports practice. This assessment is especially relevant in sports with high athlete-surface interaction, such as football and rugby. These assessments are performed using standardised instrumentation, as detailed below, and are carried out using the triple A trial.

Triple A

• Shock AbsorptionThis parameter measures the amount of energy that the surface can absorb upon impact of a mass. It is expressed in relative terms, with concrete absorbing 0% (the most damaging surface) and silica sand absorbing 100% (the softest surface). Absorption values above 50% are considered safe for athletes. The ability of a surface to absorb impact is crucial to reduce the load on joints and soft tissues, thus reducing the risk of repetitive impact injuries.

• Energy RestitutionThis indicator reflects the energetic interaction between the surface and the athlete. Stiffer surfaces return more energy, which may make them feel "hard" but generate less fatigue. Concrete gives back 100% of the energy in the hardness testwhereas sand returns 0%, which makes playing on sand much more tiring. High energy restitution can benefit performance by allowing more explosive movements, but it can also increase the risk of injury if not managed properly.

• Vertical DeformationThe surface's ability to deform, measured in millimetres, helps to assess its elasticity. Values between 4 and 11 mm are considered suitable for sports use. Adequate vertical deformation helps to disperse impact forces.

Alternative instrumentation

In addition to standardised instrumentation such as Triple A, there is the option of using rapid testing devices such as the FieldTester. This portable and easy-to-use instrument performs the same measurements with high reproducibility on all types of surfaces, both natural and artificial. It can also measure the hardness of the surface, functioning as a Clegg's hammer. The ability to make quick and accurate measurements in the field allows for constant monitoring and immediate adjustments to maintain optimal field conditions.

Correlation and Consequences

Energy restitution and shock absorption are inversely correlated: as energy restitution increases, shock absorption decreases. Maintaining these parameters within optimal ranges is crucial to prevent injuries such as plantar fasciitis or low back injuries, which can result from inadequate surfaces. Lack of adequate shock absorption can lead to a higher incidence of repetitive stress injuries, while inadequate energy restitution can negatively affect the athlete's performance and comfort.

Tensile or Rotational Strength

Many knee and ankle injuries occur due to the acceleration, stopping and changes of direction that athletes perform during their activity. These movements involve significant stresses that are transmitted to the lower extremities, with rotational forces being particularly dangerous. To assess the ability of the turf to pull on the player's cleats, various devices are used to measure the maximum torque required to rotate a simile of a cleated boot, loaded with a specific weight on the turf.

These devices measure torque, which is the amount of rotational force that the turf can resist before allowing the cue to rotate. The unit of measurement for traction on a pitch is the Newton metre (Nm). Optimum traction ranges between 25 and 50 Nm when using approved instrumentation, thus ensuring a balance between sufficient grip and reduced risk of injury.

The standardised instrumentation for measuring traction has a higher sensitivity, repeatability and accuracy compared to other quick-use kits. These devices advanced technology provides more accurate and reliable measurements, which is crucial for effectively assessing and maintaining field conditions.

Maintaining turf traction within optimal ranges is essential to prevent injury in athletes. Insufficient traction can lead to slipping and loss of balance, while excessive traction can cause the foot to become trapped in the turf, increasing the risk of twisting and serious joint injuries.

HIC - CLE Impact Test

The Head Injury Criteria (HIC) is an index used to assess the likelihood of head injury as a result of impact or violent deceleration of the head on sports surfaces. This index is a standard in the sports equipment industry and is used to predict potential head injuries, contributing to the safety of athletes.

HIC assessment

The HIC tester is the instrument used to determine the critical drop height at which significant damage can occur. This device consists of a standardised artificial head integrating a triaxial sensor, which is dropped from different heights. The triaxial sensor measures accelerations in three axes, providing accurate data on the impact received.

• Critical fall heightDuring the tests, the artificial head is dropped from various heights and the sensor registers the impact forces. A fall is considered critical when the sensor registers a value of 1000 HIC or an acceleration of 200g. These thresholds indicate a high probability of brain damage, which is crucial for assessing and improving the safety of sports surfaces.

The HIC index is essential for the design and maintenance of safe sports surfaces. HIC testing helps to identify high-risk areas on playing fields, allowing improvements to be made in surface design and materials used to reduce the likelihood of serious injury.

The use of the HIC tester and compliance with HIC standards ensures that sports surfaces are assessed and maintained according to best safety practices. This not only protects athletes, but also reduces legal liability for sports facility operators.