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Shivam Bhan, Iris Levine and Andrew C. Laing

The biomechanical effectiveness of safety floors has never been assessed during sideways falls with human volunteers. Furthermore, the influence of body mass index (BMI) and gender on the protective capacity of safety floors is unknown. The purpose of this study was to test whether safety floors provide greater impact attenuation compared with traditional flooring, and whether BMI and gender modify their impact attenuation properties. Thirty participants (7 men and 7 women of low BMI; 7 men and 9 women of high BMI) underwent lateral pelvis release trials on 2 common floors and 4 safety floors. As a group, the safety floors reduced peak force (by up to 11.7%), and increased the time to peak force (by up to 25.5%) compared with a traditional institutional grade floor. Force attenuation was significantly higher for the low BMI group, and for males. Force attenuation was greatest for the low BMI males, averaging 26.5% (SD = 3.0) across the safety floors. These findings demonstrate an overall protective effect of safety floors during lateral falls on the pelvis, but also suggest augmented benefits for frail older adults (often with low body mass) who are at an increased risk of hip fracture.

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Janet S. Dufek, John A. Mercer, Kaori Teramoto, Brent C. Mangus and Julia A. Freedman

Context:

Impact is known to cause injury during running, while variability is thought to promote healthy performance.

Objective:

Quantify contributions of the lower extremity and back and the variability of impact generation among (1) prepubescent girls (Grp 1), (2) normally menstruating women (Grp 2), and (3) postmenopausal women (Grp 3) to address possible lifespan changes during running.

Design:

A mixed model experiment.

Setting:

Biomechanics Laboratory.

Participants:

31 healthy females owing membership to Grp1, Grp 2, or Grp 3.

Intervention:

Participants ran on a treadmill at their preferred speed (45 s) and at a speed 10% faster (45 s) while instrumented with uniaxial accelerometers.

Main Outcome Measures:

Lower extremity attenuation, back attenuation and variability of peak impact acceleration values.

Results:

Lower extremity attenuation and variability were greatest for Grp 1 while impact variability was least for Grp 2.

Conclusion:

Lifespan phases appear to affect impact attenuation strategies and variability of impact during running for females.

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Songning Zhang, Kurt Clowers, Charles Kohstall and Yeon-Joo Yu

The purpose of this study was to examine effects of shoe midsole densities and mechanical demands (landing heights) on impact shock attenuation and lower extremity biomechanics during a landing activity. Nine healthy male college athletes performed 5 trials of step-off landing in each of 9 test conditions, i.e., a combination of landings in shoes of 3 midsole densities (soft, normal, hard) from each of 3 landing potential energy (PE) levels (low, median, high). Ground reaction forces (GRF), accelerations (ACC) of the tibia and forehead, and sagittal kinematic data were sampled simultaneously. A 3 × 3 two-way (surface × height) repeated-measures analysis of variance (ANOVA) was performed on selected kinematic, ACC, and GRF variables; a 3 × 3 × 3 three-way (surface × height × joint) ANOVA was performed on variables related to eccentric muscular work. The GRF results showed that the forefoot peak GRF in the normal and hard midsoles was significantly greater than the soft midsole at the low and median PEs. Rearfoot peak GRF was significantly greater for the hard midsole than for the soft and normal midsoles at the median and high PEs, respectively. The peak head and tibia peak ACC were also attenuated in similar fashion. Kinematic variables did not vary significantly across different midsoles, nor did energy absorbed through lower extremity extensors in response to the increased shoe stiffness. Knee joint extensors were shown to be dominant in attenuating the forefoot impact force across the landing heights. The results showed limited evidence of impact-attenuating benefits of the soft midsole in the basketball shoes.

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John Strickland and Grant Bevill

limited information regarding the relationship between mask design features and impact attenuation, it was not explicitly designed for this purpose. For example, the authors observed a wide range of peak angular acceleration values across fielder’s masks for high-speed chin impacts. However, there are

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Arnel Aguinaldo and Andrew Mahar

This study evaluated the effects of running shoes—with two types of cushioning column systems—on impact force patterns during running. Kinematic and ground reaction force data were collected from 10 normal participants wearing shoes with the following cushions: 4-column multicellular urethane elastomer (Shoe 1), 4-column thermoplastic polyester elastomer (Shoe 2), and 1-unit EVA foam (Shoe 3). Participants exhibited significantly lower impact force (p = .02) and loading rate (p = .005) with Shoe 2 (1.84 ± 0.24 BW; 45.6 ± 11.6 BW/s) compared to Shoe 1 (1.94 ± 0.18 BW; 57.9 ± 12.1 BW/s). Both cushioning column shoes showed impact force characteristics similar to those of a top-model running shoe (Shoe 3), and improved cushioning performance over shoes previously tested in similar conditions. Alterations in impact force patterns induced by lower limb alignment and running speed were negligible since participants did not differ in ankle position, knee position, or speed during all shod running trials. Ankle plantarflexion, however, was higher for barefoot running, indicating an apparent midfoot strike. Mechanical testing of each shoe during physiologic, cyclic loading demonstrated that Shoe 3 had the greatest stiffness, followed by Shoe 2 and Shoe 1. Shoe 1 was the least stiff of the two shoes with cushioning column systems, yet it displayed a significantly higher impact loading rate during running, possibly due to rearfoot motion alterations induced by the stiffer shoe. This study showed that even in similar shoe types, impact force and loading rate values could vary significantly with midsole cushion constructions. The findings of this study suggest that using these newer running shoes may be effective for runners who want optimal cushioning during running.

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Carl G. Mattacola, Carolina Quintana, Jed Crots, Kimberly I. Tumlin and Stephanie Bonin

standards for a wide range of products, including equestrian helmets. ASTM F1163 is the standard specification for protective headgear in equestrian activities. It includes impact-attenuation performance criteria that require a helmet to be impacted at 6 and 5 m/s against a flat anvil and a hazard anvil

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Adam C. Clansey, Mark J. Lake, Eric S. Wallace, Tom Feehally and Michael Hanlon

The purpose of this study was to investigate the effects of prolonged high-intensity running on impact accelerations in trained runners. Thirteen male distance runners completed two 20-minute treadmill runs at speeds corresponding to 95% of onset of blood lactate accumulation. Leg and head accelerations were collected for 20 s every fourth minute. Rating of perceived exertion (RPE) scores were recorded during the third and last minute of each run. RPE responses increased (P < .001) from the start (11.8 ± 0.9, moderate intensity) of the first run to the end (17.7 ± 1.5, very hard) of the second run. Runners maintained their leg impact acceleration, impact attenuation, stride length, and stride frequency characteristics with prolonged run duration. However, a small (0.11–0.14g) but significant increase (P < .001) in head impact accelerations were observed at the end of both first and second runs. It was concluded that trained runners are able to control leg impact accelerations during sustained high-intensity running. Alongside the substantial increases in perceived exertion levels, running mechanics and frequency domain impact attenuation levels remained constant. This suggests that the present trained runners are able to cope from a mechanical perspective despite an increased physiological demand.

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Peter L. Davidson, Suzanne J. Wilson, David J. Chalmers, Barry D. Wilson, David Eager and Andrew S. McIntosh

The amount of energy dissipated away from or returned to a child falling onto a surface will influence fracture risk but is not considered in current standards for playground impact-attenuating surfaces. A two-mass rheological computer simulation was used to model energy flow within the wrist and surface during hand impact with playground surfaces, and the potential of this approach to provide insights into such impacts and predict injury risk examined. Acceleration data collected on-site from typical playground surfaces and previously obtained data from children performing an exercise involving freefalling with a fully extended arm provided input. The model identified differences in energy flow properties between playground surfaces and two potentially harmful surface characteristics: more energy was absorbed by (work done on) the wrist during both impact and rebound on rubber surfaces than on bark, and rubber surfaces started to rebound (return energy to the wrist) while the upper limb was still moving downward. Energy flow analysis thus provides information on playground surface characteristics and the impact process, and has the potential to identify fracture risks, inform the development of safer impact-attenuating surfaces, and contribute to development of new energy-based arm fracture injury criteria and tests for use in conjunction with current methods.

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Jean-Philippe Dionne, Ismail El Maach, Ahmed Shalabi and Aris Makris

The objective of the present paper is to investigate the overall impact performance of various riot helmets in a comparative study. The National Institute of Justice (NIJ-0104.02) and the Canadian Standards Association (CSA-Z611-02) standards regulate the use of riot helmets in North America. Both sets of standards have a number of requirements for impact performance. Impact tests carried out with the use of a drop tower apparatus compliant with NIJ test protocols demonstrated large differences in impact attenuation level among the helmets from six manufacturers in terms of frontal and lateral impacts to the shell, and face-shield deflection. For instance, the impact energy yielding a head form acceleration of 300 g’s was measured for each helmet for frontal impacts on the helmet shell. Values ranging from 69 J up to 171 J were obtained. The energy levels of typical crowd-control threats, e.g., baton blows and projectiles, were quantified and compared with the impact energy values used in the standards. It is observed that the NIJ face-shield deflection requirement is low as compared to actual riot threats, whereas the CSA requirements are more in line with these threats. A novel method was devised to objectively assign a global impact performance score to each helmet. This method takes into account the frontal and lateral impacts to the shell as well as the face-shield deflection tests. It is based on the directional origin of the threat and the geometry of the helmets (frontal percentage area of the visor). From these global performance scores, it is possible to obtain a ranking of the various riot helmets used in the present comparative study. Based on the analysis of the global scores, it was found that appropriate protection of the face (through an impact resistant visor) is the key feature for a helmet that will be used in riot environments.

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Joshua M. Thomas and Timothy R. Derrick

The purpose of this research was to determine the effects of step uncertainty on shock attenuation and knee/subtalar synchrony. Uncertainty was manipulated by decreasing the intensity of light and introducing bumps to the running surface. Twelve experienced distance runners ran at their chosen pace on a treadmill with two surfaces (smooth and irregular) and three light intensities (light, medium, dark). Knee angle, subtalar angle, leg impacts, and head impacts were recorded at 1,000 Hz. Heart rate was also monitored. Injury potential was assessed by evaluating the impacts and asynchronous activity between the knee and subtalar joint. Stride length was not influenced by either source of uncertainty. Heart rate increased with the intensity of light on the smooth running surface but decreased with the intensity of light on the irregular surface. The knee was more flexed at heel contact during the irregular surface conditions but was not affected by the intensity of light. This decreased the effective mass of the impact and allowed greater peak leg accelerations and greater impact attenuation during irregular surface running. There was a decrease in the rearfoot angle at contact on the irregular surface that approached significance (p = 0.056). Knee/subtalar asynchrony increased with the intensity of light on the smooth surface but decreased on the irregular surface. It appears that participants used the knee joint to adapt to the irregular surface and thus accommodate changes in the terrain. The subtalar joint may have become more stable during irregular surface running to minimize the chance of inversion sprains. The effects of intensity of light were small and generally mediated the irregular surface effects. Overall, these adaptations likely reduced the potential for injury during irregular surface running but may have been detrimental to performance.