Energy restitution is the performance counterpart to force reduction. Where force reduction measures how much impact energy a surface absorbs, energy restitution measures how much of that absorbed energy the surface returns to the athlete as elastic rebound. Together, the two metrics define the complete energy exchange between athlete and surface, how much protection the surface provides and how much energy it gives back to support athletic movement.

A surface with high energy restitution returns more energy to the athlete on every step, push-off, and change of direction, reducing the metabolic cost of movement and delaying fatigue accumulation over the course of a training session or match. A surface with low energy restitution absorbs energy without returning it, increasing the muscular work required for every movement and accelerating fatigue. Understanding energy restitution, how it interacts with force reduction, and what drives it over a field’s lifecycle is essential for specifying a surface that supports elite athletic performance from kickoff to final whistle.

What Energy Restitution Measures

Energy restitution measures the percentage of impact energy that a surface returns to the athlete after absorption. It is expressed as a percentage, an energy restitution of 35% means the surface returned 35% of the absorbed impact energy as elastic rebound. The remaining energy was dissipated as heat or permanent deformation within the surface system.

Energy restitution is the elastic component of surface response. A surface that absorbs energy and returns it efficiently behaves like a spring, storing energy during compression and releasing it during rebound. A surface that absorbs energy without returning it behaves like a damper, dissipating energy as heat and providing no elastic contribution to athletic movement.

How Energy Restitution Is Tested

Energy restitution is measured using a standardized drop test apparatus defined by EN 15301-2 and FIFA Quality Program protocols. A missile of defined mass is dropped from a specified height onto the surface. The rebound height of the missile is measured and compared to the drop height. The ratio of rebound height to drop height,  expressed as a percentage, represents energy restitution.

Energy restitution testing is performed by ISO 17025-accredited independent laboratories alongside force reduction, g-max, HIC, rotational resistance, and vertical deformation. Act Global publishes energy restitution results from Firefly Sports Testing, Labosport, and Sports Labs.

Energy Restitution Thresholds by Standard

FIFA Quality Program

• Acceptable range: 20–50% for FIFA Quality
• Acceptable range: 25–50% for FIFA Quality Pro
• FIFA’s thresholds define both a minimum and maximum energy restitution. A surface below the minimum returns too little energy, increasing fatigue and reducing athletic performance. A surface above 50% returns too much energy, creating an overly bouncy, unpredictable surface that affects ball behavior and traction consistency.

EN 15301-2

EN 15301-2 is the European standard test method for energy restitution on synthetic turf surfaces. It defines the test protocol and apparatus. Acceptable value ranges are defined by the governing body or specification applying the test.

The Relationship Between Energy Restitution and Force Reduction

Energy restitution and force reduction are complementary metrics that together define the complete energy exchange profile of a surface. Understanding their relationship is essential for system-level specification.

The Energy Balance

Every unit of impact energy that reaches the surface is either absorbed by the system, returned to the athlete as elastic rebound, or dissipated as heat. Force reduction captures the absorption side — how much energy the surface took in. Energy restitution captures the return side — how much of that absorbed energy came back. A surface with 65% force reduction and 35% energy restitution absorbed 65% of the impact energy and returned approximately 35% of what it absorbed.

Balancing Protection and Performance

The design challenge in synthetic turf systems is balancing force reduction and energy restitution to optimize both safety and performance simultaneously. A surface optimized purely for force reduction, maximum energy absorption — would dissipate most impact energy as heat, providing excellent impact protection but poor energy return and high fatigue accumulation. A surface optimized purely for energy restitution, maximum elastic return — would provide excellent energy return but poor impact attenuation and high Gmax values. The FIFA thresholds for both metrics define the range within which this balance is achieved for competitive athletic use.

How Energy Restitution Affects Athletic Performance

Metabolic Cost of Movement

Every step on a surface with low energy restitution requires more muscular work than the equivalent step on a surface with higher energy restitution, because the athlete must generate all forward propulsion from muscular effort alone, with no elastic contribution from the surface. Over the course of a 90-minute match, the cumulative difference in metabolic cost between a surface at the lower end of the energy restitution range and one at the upper end is measurable in player performance data.

Fatigue Accumulation

Research on player-surface interaction consistently identifies surface energy return as a contributor to fatigue accumulation over the course of athletic activity. Players on surfaces with appropriate energy restitution report lower perceived exertion and lower fatigue scores at full-time than players on surfaces with lower energy restitution values — independent of other surface metrics.

Explosive Movement

Energy restitution affects explosive athletic movements, sprinting, jumping, and rapid change of direction, more significantly than steady-state running. In movements where the elastic energy storage and return cycle of the surface contributes meaningfully to propulsion, a surface with higher energy restitution within the acceptable range provides a measurable performance advantage.

What Drives Energy Restitution Over Time

Infill Compaction

Infill elastic properties are the primary driver of energy restitution in synthetic turf systems. As infill compacts under repeated use, its elastic capacity decreases — energy restitution values fall. Crumb rubber infill generally provides higher energy restitution than sand or organic alternatives due to its inherent elasticity. As rubber compacts, that elasticity decreases. High-traffic zones experience faster elastic capacity decline than low-traffic areas.

Shock Pad Elastic Properties

Shock pads contribute to energy restitution through their elastic properties, the capacity to store and return energy under compression. As shock pad materials experience compression set over their service life, their elastic contribution to energy restitution decreases. Shock pad elastic performance should be verified through testing at fiber replacement.

Temperature

Temperature significantly affects the elastic properties of infill materials, particularly crumb rubber. At low temperatures, rubber becomes less elastic and energy restitution decreases. At high temperatures, rubber becomes more elastic and energy restitution increases. Temperature effects on energy restitution are more pronounced than on other surface metrics and should be considered when interpreting test results conducted at different ambient temperatures.

Energy Restitution and Lifecycle Management

Energy restitution requires the same lifecycle monitoring approach as all other synthetic turf safety and performance metrics. Industry best practice includes:

• Annual independent energy restitution testing by an ISO 17025-accredited laboratory
• Zone-by-zone measurement to identify localized elastic capacity decline in high-traffic areas
• Infill depth measurement and top-up to maintain elastic energy absorption and return capacity
• Shock pad elastic performance verification at fiber replacement
• Temperature recording at time of testing for accurate result interpretation

Act Global Perspective

Act Global specifies energy restitution as a system-level design target across all sports turf systems. Infill type, infill depth, shock pad specification, and fiber system are selected in combination to achieve and maintain energy restitution values within FIFA Quality thresholds throughout the field’s service life, balancing energy return for athletic performance against force reduction for impact protection.

Energy restitution data for Act Global systems is published exclusively from ISO 17025-accredited independent laboratories, Firefly Sports Testing, Labosport, and Sports Labs. Every published test report includes energy restitution alongside force reduction, g-max , HIC, rotational resistance, and vertical deformation, because no single metric characterizes surface safety and performance in isolation.

Act Global’s infill specifications account for the elastic properties of each infill material and how those properties change over the field’s service life. Maintenance guidelines include infill depth monitoring and top-up schedules designed to maintain energy restitution within acceptable ranges as infill compacts, not just to restore force reduction and g-max values.

Frequently Asked Questions

What is a good energy restitution value for a synthetic turf field?

For most synthetic turf athletic applications, energy restitution values in the 30–45% range represent a well-performing surface, returning enough energy to support athletic performance while remaining within FIFA’s maximum of 50%. Values at the lower end of the FIFA range (20–25%) indicate a surface that absorbs more energy than it returns, which increases fatigue accumulation over the course of a match. Values approaching or exceeding 50% indicate a surface that may feel overly bouncy and affect ball behavior and traction consistency.

How does energy restitution relate to force reduction?

Force reduction and energy restitution are complementary metrics that together define the complete energy exchange profile of a surface. Force reduction measures how much impact energy the surface absorbs. Energy restitution measures how much of that absorbed energy the surface returns. A surface with high force reduction and high energy restitution absorbs impact effectively and returns energy efficiently, the optimal combination for both safety and performance. Both metrics should be independently specified and tested.

Does infill type significantly affect energy restitution?

Yes, infill elastic properties are the primary driver of energy restitution in synthetic turf systems. Crumb rubber infill generally provides higher energy restitution than sand or organic alternatives due to its inherent elasticity. Cork and other organic infill materials provide moderate energy restitution. Sand provides minimal elastic return. Infill selection directly determines the energy restitution profile of the system, and how that profile changes over the field’s service life as infill compacts.

Does temperature affect energy restitution test results?

Yes significantly, more so than other surface metrics. Crumb rubber elasticity decreases at low temperatures and increases at high temperatures, producing measurably different energy restitution values on the same field tested in different seasonal conditions. Independent test reports should always include ambient and surface temperature at time of testing. Results from tests conducted at significantly different temperatures should not be directly compared without accounting for temperature effects.

Should energy restitution be included in synthetic turf procurement specifications?

Yes. A complete synthetic turf procurement specification should include energy restitution thresholds alongside force reduction, g-max , HIC, rotational resistance, and vertical deformation. Energy restitution is the metric most directly linked to athletic performance and fatigue, specifying only safety metrics without addressing performance metrics produces an incomplete characterization of the surface. FIFA Quality thresholds of 20–50% for FIFA Quality and 25–50% for FIFA Quality Pro represent current best practice for competitive athletic surface specification.

Related Resources

• What Makes Synthetic Turf Safe? A Science-Based Definition
• Gmax Explained – Surface Hardness and Impact Attenuation
• HIC Explained – Head Injury Criterion in Synthetic Turf 
• Rotational Resistance Explained – Traction and Lower-Extremity Injury Risk
• Vertical Deformation Explained – Surface Stability and Foot Support
• Force Reduction Explained – What It Measures and Why It Matters
• Act Global Test Report Center

The content in this article reflects Act Global’s interpretation of publicly available independent test data, EN standards, FIFA Quality Program documentation, and peer-reviewed research on synthetic turf surface performance and player-surface interaction. It is provided for educational purposes only and does not constitute medical, legal, or engineering advice. Energy restitution thresholds cited reflect published standards as of the date of this article,  refer to the relevant governing body for current certification requirements. Refer to original sources and accredited testing laboratories for complete methodology and findings.

Force reduction is one of the most practically significant safety metrics in synthetic turf, and one of the least frequently explained in plain terms. It appears in FIFA certification requirements, ASTM standards, and independent test reports as a percentage value, yet few field owners or specifiers can articulate what that percentage represents or why it matters for athlete safety.

Force reduction measures how much of the impact energy from a fall or collision a surface absorbs before transmitting it to the athlete. A surface with high force reduction absorbs more energy, protecting the athlete from peak impact forces. A surface with low force reduction transmits more energy,exposing the athlete to higher peak forces on every impact. Understanding force reduction, how it relates to g-max, and what drives it over a field’s lifecycle is essential for anyone responsible for specifying or managing a synthetic turf athletic surface.

What Force Reduction Measures

Force reduction measures the percentage of impact energy that a surface absorbs during a standardized impact event. It is expressed as a percentage — a force reduction of 60% means the surface absorbed 60% of the impact energy and transmitted 40% to the athlete or test apparatus.

Force reduction and g-max measure related but distinct aspects of the same impact event. g-max captures the peak deceleration force transmitted, the worst single moment of the impact. Force reduction captures the overall energy absorption capacity of the surface across the full impact event. A surface can have an acceptable g-max while having lower-than-optimal force reduction, meaning the peak force was within threshold but the surface absorbed less total energy than a higher-performing surface would.

How Force Reduction Is Tested

Force reduction is measured using the same standardized drop test apparatus as g-max, defined by EN 14808 for synthetic turf surfaces and FIFA Quality Program protocols. A missile of defined mass is dropped from a specified height onto the surface. The force transmitted through the surface is measured and compared to the force that would be transmitted onto a rigid reference surface. The percentage difference represents force reduction.

Force reduction testing is performed by ISO 17025-accredited independent laboratories. Act Global publishes force reduction results from Firefly Sports Testing, Labosport, and Sports Labs.

Force Reduction Thresholds by Standard

FIFA Quality Program

• Acceptable range: 60–70% for FIFA Quality
• Acceptable range: 55–70% for FIFA Quality Pro
• FIFA’s thresholds define both a minimum and maximum force reduction. A surface below the minimum absorbs too little energy — transmitting excessive force to athletes. A surface above 70% absorbs too much energy — creating an overly soft surface that affects ball behavior, traction consistency, and athletic performance.

EN 14808

EN 14808 is the European standard test method for force reduction on synthetic turf surfaces. It defines the test protocol and apparatus. Acceptable value ranges are defined by the governing body or specification applying the test.

ASTM Standards

ASTM F1936 references shock attenuation, the equivalent concept to force reduction in North American standards. The relationship between force reduction and g-max means that fields meeting FIFA force reduction thresholds generally also meet ASTM g-max requirements, though both should be independently verified.

How Force Reduction Relates to g-max and HIC

Force reduction, g-max , and HIC are all derived from impact testing and all measure aspects of how a surface manages impact energy. Understanding the relationship between them is important for complete surface safety specification.

Force Reduction vs. g-max

g-max measures the peak deceleration force, the single highest point on the impact curve. Force reduction measures how much total energy the surface absorbed across the full impact event. A surface with good force reduction generally produces lower g-max values, because a surface that absorbs more energy transmits less peak force. However, the relationship is not perfectly linear, surface design affects how energy is absorbed and at what rate, which means g-max and force reduction should both be specified and tested independently.

Force Reduction vs. HIC

HIC integrates the deceleration curve over time, capturing both magnitude and duration of the impact. Force reduction captures total energy absorption. A surface with high force reduction that absorbs energy gradually over a longer duration will generally produce lower HIC values than a surface that absorbs the same total energy in a shorter, sharper event. Again, both metrics should be independently measured, not inferred from each other.

What Drives Force Reduction Over Time

Infill Compaction

Infill is the primary contributor to force reduction in synthetic turf systems. As infill compacts under repeated use, its capacity to absorb impact energy decreases, force reduction values fall toward and potentially below minimum acceptable thresholds. High-traffic zones experience faster compaction and earlier force reduction decline than low-traffic areas.

Shock Pad Degradation

Shock pads contribute significantly to force reduction by providing a dedicated energy-absorbing layer beneath the turf carpet. As shock pad materials experience compression set over their service life, their energy absorption capacity decreases, reducing force reduction independently of infill condition. Shock pad contribution to force reduction should be verified through testing at fiber replacement to determine whether pad replacement is warranted.

Fiber and Backing Condition

Fiber density and backing system contribute to force reduction by distributing impact load before it reaches the infill and shock pad. Severely degraded fiber systems,flattened, thinned, or split fibers, reduce this distribution effect and increase the load transmitted directly to the infill layer.

Force Reduction and Lifecycle Management

Force reduction requires the same lifecycle monitoring approach as g-max , HIC, rotational resistance, and vertical deformation. Industry best practice includes:

• Annual independent force reduction testing by an ISO 17025-accredited laboratory
• Zone-by-zone measurement to identify localized energy absorption decline in high-traffic areas
• Infill depth measurement and top-up to maintain energy absorption capacity
• Shock pad inspection and performance verification at fiber replacement

A field that passes force reduction thresholds at installation cannot be assumed to maintain those values without active lifecycle management and periodic independent retesting.

Act Global Perspective

Act Global specifies force reduction as a system-level design target across all sports turf systems. Fiber density, infill type, infill depth, shock pad specification, and backing system are selected in combination to achieve and maintain force reduction values within FIFA Quality thresholds throughout the field’s service life, not just at installation.

Force reduction data for Act Global systems is published exclusively from ISO 17025-accredited independent laboratories, Firefly Sports Testing, Labosport, and Sports Labs. Every published test report includes force reduction alongside g-max , HIC, rotational resistance, and vertical deformation, because complete surface safety characterization requires all five metrics, not a selective subset.

Act Global’s shock pad specifications are selected based on system-level force reduction targets, not pad thickness alone. Shock pad performance is verified through independent testing at installation and should be reassessed at fiber replacement to determine whether the pad has maintained its energy absorption capacity over its service life.

Frequently Asked Questions

What is a good force reduction value for a synthetic turf field?

For most synthetic turf athletic applications, force reduction values in the 62–68% range represent a well-performing surface, absorbing enough energy to protect athletes from peak impact forces while remaining firm enough for consistent ball behavior and traction. FIFA Quality standards require 60–70%. Values at the lower end of the range indicate a firmer surface with less energy absorption capacity. Values at the upper end indicate a softer surface that may affect ball bounce and traction consistency.

How does force reduction differ from g-max ?

g-max measures the single peak deceleration force transmitted during an impact event. Force reduction measures the total percentage of impact energy the surface absorbed across the full event. Both metrics are derived from the same drop test and both characterize impact safety — but from different angles. A surface with acceptable Gmax can still have suboptimal force reduction, which is why both should be independently specified and tested.

Does a shock pad significantly affect force reduction?

Yes, shock pads are specifically designed to contribute to force reduction by providing a dedicated energy-absorbing layer beneath the turf carpet. A properly specified shock pad can contribute 10–20% or more to total system force reduction depending on material type and thickness. However, shock pad contribution decreases as the pad experiences compression set over its service life. Force reduction testing at fiber replacement is the only reliable way to determine whether the shock pad has maintained its performance.

Can force reduction be improved on an existing field?

Yes, depending on the cause of decline. If force reduction has fallen due to infill compaction, professional infill decompaction and top-up can restore energy absorption capacity. If the shock pad has experienced significant compression set, pad replacement may be required. Independent testing before and after any remediation confirms whether the intervention was effective and whether force reduction values have been restored to acceptable ranges.

Should force reduction be included in synthetic turf procurement specifications?

Yes. Any synthetic turf procurement specification that references only g-max is incomplete. Including force reduction thresholds, at minimum, the FIFA Quality range of 60–70%, provides a more complete characterization of surface energy absorption capacity.

Specifiers and facility managers who include force reduction alongside g-max , HIC, rotational resistance, and vertical deformation in their procurement documents are applying current best practice in synthetic turf safety specification.

Related Resources

• What Makes Synthetic Turf Safe? A Science-Based Definition
• Gmax Explained — Surface Hardness and Impact Attenuation 
• HIC Explained — Head Injury Criterion in Synthetic Turf
• Rotational Resistance Explained — Traction and Lower-Extremity Injury Risk 
• Vertical Deformation Explained — Surface Stability and Foot Support 
• Act Global Test Report Center 

The content in this article reflects Act Global’s interpretation of publicly available independent test data, ASTM standards, FIFA Quality Program documentation, and peer-reviewed research on synthetic turf surface safety and impact attenuation. It is provided for educational purposes only and does not constitute medical, legal, or engineering advice. Force reduction thresholds cited reflect published standards as of the date of this article, refer to the relevant governing body for current certification requirements. Refer to original sources and accredited testing laboratories for complete methodology and findings.

Vertical deformation is the synthetic turf metric that defines how a surface responds to the vertical load of an athlete’s foot. It measures how far the surface compresses under weight, and that compression determines foot stability, energy expenditure, fatigue accumulation, and biomechanical efficiency across the duration of athletic activity.

Unlike Gmax and HIC, which address impact attenuation from falls, vertical deformation addresses the continuous loading that occurs with every step, plant, and push-off during normal athletic movement. A surface that deforms too much under load creates instability and increases muscular fatigue. A surface that deforms too little feels rigid and unforgiving, increasing joint loading and reducing comfort over the course of a full match or practice session.

What Vertical Deformation Measures

Vertical deformation measures the distance, expressed in millimeters, that a synthetic turf surface depresses under a standardized vertical load applied through a defined foot form. It quantifies the compliance of the surface system under the type of loading that occurs continuously during athletic activity, standing, walking, running, planting, and pushing off.

A surface with high vertical deformation compresses significantly under load, creating a soft, unstable feel underfoot. A surface with low vertical deformation compresses minimally, creating a firm, rigid feel. The acceptable range for athletic use balances surface compliance for comfort and energy return against stability for predictable foot support.

How Vertical Deformation Is Tested

Vertical deformation is measured using a standardized test apparatus defined by EN 12235 and FIFA Quality Program protocols. A weighted foot form is applied to the surface under a defined static load. The apparatus measures the vertical displacement of the surface under that load, the distance the surface compresses from its unloaded position.

Testing is performed by ISO 17025-accredited independent laboratories. Act Global publishes vertical deformation results from Firefly Sports Testing, Labosport, and Sports Labs exclusively.

Vertical Deformation Thresholds by Standard

FIFA Quality Program

• Acceptable range: 4–11mm
• FIFA’s threshold applies to both FIFA Quality and FIFA Quality Pro certification levels. Values below 4mm indicate a surface that is too rigid for comfortable athletic use at the FIFA standard. Values above 11mm indicate excessive compliance that compromises foot stability and ball behavior.

EN 12235

• EN 12235 is the European standard test method for vertical deformation of synthetic turf surfaces. It defines the test protocol and apparatus but does not independently specify acceptable value ranges — those are defined by the governing body or specification applying the test.

How Vertical Deformation Affects Athletic Performance

Foot Stability

A surface that deforms excessively under load creates an unstable base for athletic movement. When the surface compresses unevenly or unpredictably under the foot, the ankle and knee must compensate with increased muscular activation to maintain balance and control. Over the course of a training session or match, this compensation accumulates as fatigue — reducing performance and increasing injury risk in later stages of activity.

Energy Return

Every surface deformation represents energy absorbed from the athlete’s movement. Some of that energy is returned to the athlete as elastic rebound, energy restitution, and some is dissipated as heat. A surface with appropriate vertical deformation absorbs enough energy to cushion joint loading while returning enough to support efficient athletic movement. A surface that deforms excessively absorbs too much energy and returns too little, increasing the metabolic cost of movement.

Fatigue Accumulation

Research on player-surface interaction consistently identifies surface stiffness, of which vertical deformation is the primary metric, as a contributor to muscular fatigue accumulation over the course of athletic activity. Players on surfaces with appropriate vertical deformation report lower perceived exertion and lower fatigue scores at full-time than players on surfaces at the extremes of the acceptable range.

Ball Behavior

Vertical deformation affects ball bounce and roll consistency. Surfaces that deform excessively absorb ball energy on bounce, producing lower, less consistent bounces than natural grass benchmarks. Surfaces with appropriate vertical deformation produce ball behavior closer to natural grass, which is the reference standard for FIFA and World Rugby field certification.

What Drives Vertical Deformation Over Time

Infill Compaction

Infill depth and compaction are the primary drivers of vertical deformation. As infill compacts under repeated use, the surface becomes progressively stiffer, vertical deformation decreases toward and potentially below the minimum acceptable threshold. High-traffic zones develop lower vertical deformation faster than low-traffic areas, creating zone-by-zone variability across the field.

Shock Pad Compression Set

Shock pads contribute to vertical deformation by adding a compressible layer beneath the turf carpet. Over time, shock pad materials can experience compression set — a permanent reduction in thickness from repeated loading. A shock pad that has experienced significant compression set contributes less to vertical deformation and may need replacement before the turf carpet reaches end of life.

Fiber Flattening

Fiber orientation affects how the surface responds to vertical load. Upright fibers contribute to vertical deformation by providing a compressible fiber layer above the infill. Flattened fibers contribute less, effectively reducing the compliance of the surface system independent of infill or shock pad condition.

Vertical Deformation and Lifecycle Management

Vertical deformation requires the same lifecycle monitoring discipline as g-max, HIC, and rotational resistance. Industry best practice includes:

• Testing vertical deformation at installation and annually throughout the field’s service life
• Zone-by-zone measurement to identify localized stiffness development in high-traffic areas
• Infill depth measurement and top-up when depth falls below specification
• Shock pad inspection at fiber replacement to assess compression set and determine whether pad replacement is warranted

Act Global Perspective

Act Global specifies vertical deformation as a system-level design target across all sports turf systems. Fiber density, infill type, infill depth, shock pad specification, and backing system are selected in combination to achieve and maintain vertical deformation values within the FIFA Quality range of 4–11mm throughout the field’s service life, not just at installation.

Vertical deformation data for Act Global systems is published exclusively from ISO 17025-accredited independent laboratories, Firefly Sports Testing, Labosport, and Sports Labs. Every published test report includes vertical deformation alongside Gmax, HIC, and rotational resistance, because no single metric characterizes surface safety and performance in isolation.

Act Global’s maintenance guidelines include infill depth monitoring and top-up schedules specifically designed to prevent vertical deformation from falling below minimum thresholds as infill compacts over time. Field owners receive zone-by-zone maintenance recommendations based on anticipated traffic patterns, not a single field-average maintenance schedule.

Frequently Asked Questions

What is the ideal vertical deformation value for a synthetic turf field?

For most synthetic turf athletic applications, vertical deformation values in the 6–9mm range represent a well-performing surface, compliant enough for comfort and energy return, firm enough for stable foot support. FIFA Quality standards require 4–11mm. Values at the lower end of the range feel firmer and are more common on heavily used fields with compacted infill. Values at the upper end feel softer and are more common on newer installations or fields with deeper infill.

How does vertical deformation differ from g-max?

g-max measures peak deceleration force during a high-energy impact event, a fall or collision. Vertical deformation measures surface compliance under the continuous, lower-energy loading of normal athletic movement, walking, running, and planting. Both metrics are necessary to characterize surface safety and performance completely. A field can have acceptable g-max and still have problematic vertical deformation — or vice versa.

Does a shock pad always improve vertical deformation?

A properly specified shock pad contributes to vertical deformation by adding a compressible layer beneath the turf carpet. However, shock pad contribution depends on material type, density, and current condition. A shock pad that has experienced significant compression set over its service life may contribute minimally to vertical deformation. Shock pad performance should be verified through independent testing, not assumed based on installation specifications alone.

How often should vertical deformation be tested?

Annual independent testing is industry best practice for vertical deformation, consistent with g-max and HIC testing cycles. Fields with heavy use, above 1,000 hours per year, should consider biannual measurement. Zone-by-zone measurement is strongly recommended to identify localized stiffness development in high-traffic areas before values fall below the minimum acceptable threshold.

Can vertical deformation be restored on an existing field?

Yes, in most cases where the cause is infill compaction or depth loss. Professional infill decompaction, redistribution, and top-up can restore vertical deformation values to acceptable ranges. If the shock pad has experienced significant compression set, pad replacement may be required, typically at the time of fiber replacement. Independent testing before and after any remediation confirms whether the intervention was effective.

Related Resources

• What Makes Synthetic Turf Safe? A Science-Based Definition 
• Gmax Explained — Surface Hardness and Impact Attenuation
• HIC Explained — Head Injury Criterion in Synthetic Turf
• Rotational Resistance Explained — Traction and Lower-Extremity Injury Risk 
• Act Global Test Report Center