Documentation:FIB book/Biomechanics of Gymnastics Landings on Mats

Introduction

Gymnastics is an activity where athletes rely on padded flooring to reduce the likelihood of injury due to landing. Unfortunately, landings still make up 70% of all Injuries in gymnastics making it the highest risk part of the sport. Gymnasts can typically be expected to undergo upwards of 200 landings per week while training. With landings being high-energy events, gymnasts can at times have to absorb forces 14 times their body weight. Within the sport, their bodies undergo repetitive impact loading which can cause overuse and repetitive strain injuries in addition to bony and ligament injuries. One study looked at the epidemiology of competitive collegiate female athlete injuries and found that injuries are predominantly made up of lower extremity injuries such as sprains, strains, and overuse Injuries.

The severity of injury is also a major concern especially considering the long-term impacts on healthcare systems and the injured individual. Of injuries to the lower extremities 39% were classified as severe or recurrent requiring at least a few days to recover. The impacts to the athletes can be substantial and potentially career-ending depending on the severity of the injury. There are also major costs to the healthcare systems that treat these injuries. Improving the safety of landing mats will benefit both the well-being of athletes and the cost on society and health care resources.  

There is therefore a need to continue researching and finding ways to reduce the number of injuries and injury severity. There are currently many approaches to making landings safer. Most researched is the pad material and hardness. Softer pad materials decrease the forces transferred to the gymnast by increasing impact time compared to harder surfaces. There is also ongoing research into different simulations and modeling to create an accurate representation of internal loading within the lower extremities. It is important to note that due to the gymnasts’ abilities and activity being performed there can be a wide range of variation within the landing characteristics.

Summary

In gymnastics, the landing is a unique high-risk event. During the landing, the immense energy of an impact must be dissipated either by the musculoskeletal system or the landing mat. However, to execute a flawless landing, an athlete must land with no steps and minimal lower joint flexion, in order to receive full points. Thus, as athletes cannot change their landing technique to minimize impact loads, the landing mat must be wholly responsible in reducing impact loading and ensuring the safety of the athletes.

To investigate how landing mats accomplish this task, research on the loading of the musculoskeletal system corresponding injury risks mechanisms during landing and how mats can reduce these risks of injury have been conducted. One study covers the epidemiology of competitive collegiate female athlete injuries and found that injuries are predominantly made up of lower extremity injuries such as sprains, strains, and overuse Injuries. Out of all female gymnastics injuries, 54% were comprised of injuries to the knees, lower leg, ankle, and foot. Research has found that out of all injuries in gymnastics, close to 35% are due to contact with surfaces including mats making it the single highest mechanism of injury closely followed by overuse at 30%.

In most injuries in the lower extremities, 61% are classified as no time loss, meaning the individual could return to activity within a day. 13% of injuries were classified as severe with 7% requiring surgery, and 19% were classified as recurrent injuries. It is important to note that knee injuries comprised the smallest rate of occurrence. However, 21% required surgery most commonly for tears of the anterior cruciate ligament (ACL). To properly understand injury patterns and severity, extensive research and data acquisition methods have been researched.

Methods and Data Acquisition

To gain a better understanding of landing mat properties and their overall impact during landing, numerous considerations and methods have been implemented over the years. While the research topic and data collection methods may vary between studies, elements such as acquiring anthropometric measurements and relevant medical history of the athlete(s), performing impact analysis in different conditions, and analyzing injury/data post-testing are common amongst all studies. An understanding of landing mat composition and properties, and landing surfaces to mimic an athlete's footprint is also commonly found.

Computational and experimental methods along with their overall setup can vary drastically between studies. The use of high-speed video cameras is typically used in conjunction with force plates, pressure-sensitive mats, and accelerometers to measure the body positions, angles, and impact forces generated during a gymnast’s landing. This is important in determining the impact on the gymnast's body and identifying thresholds beyond which risk of injury increases. One study even incorporates specialized insoles containing sensors to measure the reaction forces between the mat and the gymnasts’ feet. Two insoles were used, one in the front and one in the rear of the foot allowing for better insight as to how the feet interact with the surface during landing. Generally, to aid in determining the actual position and motion of the individual, markers are placed on key anatomical landmarks on the body such as the ankles, knees, and limbs to serve as reference points to capture the motion in 3D space.

Figure 1: Marker placement to define the shank-foot model

Figure 2: Sample landing pad and marker placement

To simulate scenarios where high-level injuries are likely occur, a commonly used method is the ‘drop test’. A mass is dropped from a controlled height on to a sensor impregnated pad while the data is obtained from onboard accelerometer(s). In one study, the size of the landing pad was selected based on the width of the athlete’s feet inline with their hips. The mass of the impactor, however, was selected based on several tests in which the final vertical force, impulse, and rate of force production matched the same data of a 72 kg male gymnast performing a competition style landing from a height of 1.56 m.

More recently, computer modeling has become a valuable tool for understanding the biomechanics of gymnasts during different landing scenarios which allows for the evaluation of the risk of injury with more variables to work with. Modern computer models serve as powerful tools to help researchers devise and validate strategies in mitigating risk of injury to gymnasts and gauge a better understanding as to how the properties of landing mats can directly or indirectly affect the athlete. A sample of a multi-degree of freedom model is shown in Figure 3 along with modeling considerations to better represent a human body.

Results

The results of computer modeling have shown the three main joints that participate in energy dissipation during landing on to a mat. These are the knees, the ankle joints, and the hip itself. During landings, flexion in each joint results in energy dissipation due to muscle resistance to the impact. This reduces the peak joint reaction forces which also increase the risk of injury. Impact forces can be visualized as travelling up the lower limbs from the feet and decreasing at each joint as they flex, resisting the impact motion. Thus, the ankle joints along with the foot and lower leg experience the largest impact force as they are closest to the impact. Additionally, due to relatively low limb flexion the ankle joint does nearly zero work in reducing impact loads, putting the

Figure 3: “The seven-segment planar simulation model with damped springs representing the elastic properties of the landing mat and the gymnast.”

lower leg at the most at risk of injury. Contrastingly, the knee joints flex the most dissipating the most energy, followed by the hips, significantly decreasing joint reaction forces and reducing injury risk. Shown in Figures 4 and 5, are the reaction forces experienced and corresponding work done by each respective joint during a landing.

These values corresponded the epidemiolocal results presented by Kerr et al, with lower leg injuries comprising 72% of all lower extremity injuries followed by 17% knee injuries and 11% hip and upper leg injuries. The results of this research indicate that a reduction in impact loading from ground reaction forces experienced the foot, ankle and lower leg must be accomplished to reduce injury risk. However, due to ankle flexion being very limited, the only way to reduce these forces is to adjust mat properties.

The standard artistic gymnastics mat is composed of multilayered polymer foam covered by a PVC layer. By varying material composition, three key deterministic properties can be changed, mat stiffness, dampness, deformation area, and surface friction. The first three properties determine the important properties of impact absorbance and ensure athlete safety. Mat stiffness is referred to as the rigidity of the landing pad itself. Stiffer mats provide less cushioning during impact and can lead to increased ankle loads and a higher risk of injury. Gymnasts require a balance between both support and cushioning to absorb the forces generated during landing. Adjusting mat stiffness can play a major role on the impact of biomechanics of landings which makes it a critical aspect in injury prevention. The dampening of the landing mats pertains to their ability to effectively absorb and dissipate the energy upon impact. The kinetic energy of the landing will ideally be dispersed more effectively reducing the overall force of impact on joints and muscles. The deformation area is the extent in which the mat deforms and changes shape during the landing. A larger deformation tends to reduce the load on the athlete’s joints and muscles as there is a higher energy dissipation caused by the increase in deformation surface area. Surface friction, though not found to have a direct impact during landing, has shown a significant increase of loads on the internal loads of the ankle.

Figure 4: Joint Reaction Forces During a Gymnastics Landing

Figure 5: Work Down By Joints During Gymnastics Landing

Problems and Controversies

The main controversy in this space is the disconnect between the biomechanics research in this space and the International Gymnastic Federation (FIG) standards for mats and landing form. FIG is the worldwide governing body for gymnastics, the standards set by FIG determine the composition and properties of all mats used in gymnastics competitions around the globe. The root of this issue is the mat standards outlined by FIG were created out of necessity to ensure the uniformity of competition mats rather than to guarantee that the mats are as effective as possible at preventing injury. There are many shortcomings in FIG’s work to create mat standards. First, standards for mats are determined using rigid body drop tests to determine the mat properties of shock absorption, deflection, and resilience. This method of standardization neglects to consider how these mat properties affect the loading of the lower limbs of a gymnast during landing and how the properties could be further optimized to minimize the risk of injury.  The next problem in this space is the relationship between performance and safety. Standard judging criteria requires gymnasts to land with a single impact and no additional steps and to limit joint flexion or else incur deductions. However, satisfying these requirements greatly increases internal loading of the lower limbs and risk of injury. As the standardized mats are not optimized to minimize this risk of injury, for a solution to take place the mat properties must be changed and/or the judging criteria. Despite clear pathways forward to decrease injury risk, FIG is reluctant to make the necessary changes, this is due to the high costs for gyms to retrofit mats worldwide and the judging value placed on completing more difficult skills that are inherently more dangerous.

Future Research

It is clear from the current research and competitive nature of the competition that a new approach for reducing injuries to the lower extremities must come from professional gymnastics organizations, namely FIG. As the current judging standards prevent techniques which could reduce forces endure by athletes during their routines, this leads to a competitive environment where athletes are forced to risk injury to maximize performance. Further areas of research should be tailored to mitigating the forces either by changing mat materials and surfaces or by looking at external aids that athletes could wear to further reduce the risk of injury. One area of research could be to look at electro variable materials to use in foam pads potentially in combination with a sensor array to determine impact velocity and vary the mats stiffness accordingly. There are current limitations in the existing materials that demonstrate these properties, most notably being the activation time and stiffness variation. Another hurdle in researching and implementing this approach would be creating or updating the current standards around mats. By further researching biomechanics of injury to the lower extremities during landing depending on mat properties, concrete steps to make mat standards safer could be proposed to FIG to encourage them to make these changes. Development of a low-cost impactor that better represents the forces applied to mats during landing and the creation of new standards of mat performance to accompany the new impactor will further improve the safety of mats. The research could also be used to enforce a change in FIG judging standards for landings by proposing a clear path to allow the athletes to change their landing technique to decrease the large forces experienced by the lower extremities during landings.