Determining impact intensities in contact sports

Most sports Personal Protective Equipment (PPE) consist of varying levels of foam – more foam equals more protection. This has led to bulky, cumbersome PPE which restricts user movement. However, before existing PPE can be modified, their performance must be assessed and a baseline for necessary protection must be explicitly determined. This is a major limitation since current techniques for assessing PPE performance and impact intensity measurements from sport have used surrogate anvils and impactors which were not validated for the sports-related impact they tried to replicate. Through a series of independent studies, a better understanding of human impact response in sporting impacts was sought. This included investigating methods for improving the measurement of impact intensities in sports and the assessment of PPE performance. Human impact response revealed that tensed muscle led to a significant increase in impact force but was associated with less perceived discomfort. At low impact intensities common to sport, the increased local stiffness helped to dissipate impact energy and reduce soft tissue compression. As previous anvils omitted this soft tissue response, modifications were made to a martial arts dummy, BOBXL, to increase its biofidelity. This anvil was validated using in vivo kicks and an impact force – impact velocity relationship. Using this validated anvil, existing methods of assessing PPE performance were evaluated. Current methods were found to create artificially comparable levels of force but did so by using an incorrect effective mass and impact velocity. In all tests, PPE performance was found to depend on weight providing evidence of the ‘more protection, more foam’ concept. As it is impractical to use in vivo kicks to assess PPE performance, kick kinematics were investigated to assess its variability in terms of the impact force – impact velocity relationship and its accuracy. This aided in the development of a mechanical kicking robot which could more properly assess PPE performance. This research was applied to the design of form-fitting, impact-mitigating sports PPE with the capability for integrated technology. Proposed amendments to the current methods of assessing PPE will help to develop better testing and better performing PPE in the future

Utilising human performance criteria and computer simulation to design a martial arts kicking robot with increased biofidelity

The rules and regulations of Taekwondo stipulate how the sport must be played and the necessary personal protective equipment. As such, personal protective equipment performance under controlled rigid drop-tests is also outlined. Unfortunately, these impacts do not replicate human loading effectively, making conclusions about their performance unknown. However, it may be possible to use human kinematic data to improve the biofidelity of current impactors, including a current single-segment martial arts kicking robot. Five martial artists performed a series of roundhouse kicks while reflective markers on the kicking leg and pelvis were used to track hip, knee, ankle and foot positions. Using specific single-segment martial arts kicking robot robot parameters, computer simulation was used to model a singlesegment martial arts kicking robot performance (1-SM) and to form a multi-segment, multi-joint model to match human kinematic data (3-SM). The 3-SM was found to produce similar kinematics to human performance while reducing the overall effective mass at impact, motor torque and stress concentration magnitudes in the leg when compared to the 1-SM. This study suggested that human performances could be used to improve current mechanical testing techniques without introducing much complexity to improve the external validity of protective equipment evaluation testing

Spatial and temporal analysis of surface hardness across a third-generation artificial turf pitch over a year

Despite the potentially negative effects on play performance and safety, little is currently known about the spatial and temporal variability in the properties of artificial turf pitches. The primary purpose of this study was to quantify the spatial and temporal variations in surface hardness across a 5-year-old third-generation artificial turf pitch over full year cycle. The secondary purpose was to investigate the key variables that contributed to these variations in surface hardness using a correlation approach. Surface hardness (2.25 kg Clegg impact hammer, average of drops 2-5), ground temperature and infill depth were measured at 91 locations across the third-generation artificial turf pitch in 13-monthly test sessions from August 2011 to August 2012 inclusive. For each month, rainfall in the 24 h prior to testing and pitch usage statistics were also obtained. Shockpad thickness was obtained from measurements taken when the carpet was replaced in 2007. Spatial and temporal variations were assessed using robust statistical measures while Spearman correlation was used to assess the contributions of the secondary variables to surface hardness variability. The results indicated that spatial variation in surface hardness exceeded temporal variation; the former demonstrated a median absolute deviation of 12 6 1 G across the pitch in any test session while the median absolute deviation for the latter was only 4 6 2 G across the 13 test sessions. Spatial variation in surface hardness was moderately correlated with shockpad thickness and weakly correlated with infill depth (both negative). These results reinforce the importance of monitoring spatial and temporal variations in play performance variables for third-generation surfaces as well as providing support for the role of maintenance in minimising the spatial variation

In vivo determination of the effect of shoulder pads on tackling forces in rugby

Tackling in rugby is now a major cause of injury. The use of rugby shoulder pads is intended to reduce injury from front-on tackles, though the pad’s ability to reduce injury has not been examined. This paper strives to present a novel method, using Tekscan sensors, for measuring in vivo impact intensities during an actual front-on tackle in order to assess the effectiveness of rugby shoulder padding in reducing peak force during impact. It was hypothesised that padding would not significantly reduce peak impact force. Rugby pads were instrumented with thin film force sensors to measure impact intensities during tackles with and without pads. Sensors were statically calibrated then dynamically calibrated using force plate data. Results showed that the pad significantly reduced peak impact force by up to 35% when impacted with an object and by 40% overall for all tackles. The hypothesis that the shoulder pad could not significantly reduce peak force at impact was rejected since the pad reduced peak force by 41% in tackles with a run-up and 40% overall for all tackles. However, this reduction in force was localised directly above the acromioclavicular joint, while forces in the surrounding areas were not reduced

Muscle tension increases impact force but decreases energy absorption and pain during visco-elastic impacts to human thighs

Despite uncertainty of its exact role, muscle tension has shown an ability to alter human biomechanical response and may have the ability to reduce impact injury severity. The aim of this study was to examine the effects of muscle tension on human impact response in terms of force and energy absorbed and the subjects' perceptions of pain. Seven male martial artists had a 3.9 kg medicine ball dropped vertically from seven different heights, 1.0-1.6 m in equal increments, onto their right thigh. Subjects were instructed to either relax or tense the quadriceps via knee extension (≥60% MVC) prior to each impact. F-scan pressure insoles sampling at 500 Hz recorded impact force and video was recorded at 1000 Hz to determine energy loss from the medicine ball during impact. Across all impacts force was 11% higher, energy absorption was 15% lower and time to peak force was 11% lower whilst perceived impact intensity was significantly lower when tensed. Whether muscle is tensed or not had a significant and meaningful effect on perceived discomfort. However, it did not relate to impact force between conditions and so tensing may alter localised injury risk during human on human type impacts