Edward C. Frederick

Systematic ankle stabilization and the effect on performance

Stabilization of the ankle joint is used as a deterrent to injury, however, insufficient or excessive ankle control can cause negative effects. This study determined the effects of systematic changes in ankle and subtalar joint stabilization on performance through an obstacle course. Data were collected on six subjects as they completed two test procedures. Ankle range of motion in the sagittal and frontal planes was determined using a modified Inman apparatus. Completion time through an obstacle course, set up on a basketball court, was used as a measure of performance. High-top basketball shoes were constructed with pockets which allowed strips of plastic (stiffeners) to be positioned just anterior and posterior to the medial and lateral malleoli. Four shoe conditions were used including the shoe with no stiffeners. Significant differences (P less than 0.05) in eversion, flexion, and inversion were found between the shoe conditions. A general trend of decreased range of motion with increased restriction was observed. Significant differences (P less than 0.05) in performance were found between the shoe conditions, with a general trend of increased times with increased restriction. These results indicate that systematic changes in the range of motion of the ankle and subtalar joints can measurably affect performance.

Effects of unknown footwear midsole thickness on running kinematics within the initial six minutes of running

Introduction: Research on minimal footwear hasn’t utilised runners who habitually wear typical training footwear and therefore what adjustments to running patterns are made and how quickly they occur is unknown. Purpose: The purposes of this study were: 1) to investigate how kinematic patterns are adjusted while running barefoot and in footwear with systematic changes in shock attenuating material; and 2) to determine the time it takes for adjustments to occur when little is known about the footwear condition before running commences. Methods: Ten male heel-toe runners performed treadmill runs of 6 minutes in thin, medium, and thick footwear and barefoot. Participants ran immediately after putting shoes on to limit information about each footwear condition. Standard kinematics and acceleration signals were captured. Repeated measures analysis of variance (ANOVA) was utilised (p < 0.05) to determine differences across footwear conditions and time. Results: The foot was flatter at touchdown (due to a more vertical leg segment and more plantar flexion), the knee had reduced excursion, and stance times, eversion and tibial rotation excursions were greater in the thin footwear or when barefoot. Several variables were adjusted from the initial steps to later in the run. Acceleration standard deviations had more variability during initial steps than immediately following. Discussion: Many kinematic adjustments agreed with previous works though participants did not adopt a midfoot or forefoot strike pattern. Experimental design and participant knowledge and experiences may be contributing to discrepancies in footstrike patterns. Runners sensitive to eversion and tibial internal rotation should use caution when barefoot or in minimal footwear. Finally, the greatest kinematic changes occurred within the first six to eight steps, however more subtle changes continued throughout the six minute run.

Midsole thickness affects running patterns in habitual rearfoot strikers during a sustained run.

The purpose of this study was to: (1) investigate how kinematic patterns are adjusted while running in footwear with THIN, MEDIUM, and THICK midsole thicknesses and (2) determine if these patterns are adjusted over time during a sustained run in footwear of different thicknesses. Ten male heel-toe runners performed treadmill runs in specially constructed footwear (THIN, MEDIUM, and THICK midsoles) on separate days. Standard lower extremity kinematics and acceleration at the tibia and head were captured. Time epochs were created using data from every 5 minutes of the run. Repeated-measures ANOVA was used (P < .05) to determine differences across footwear and time. At touchdown, kinematics were similar for the THIN and MEDIUM conditions distal to the knee, whereas only the THIN condition was isolated above the knee. No runners displayed midfoot or forefoot strike patterns in any condition. Peak accelerations were slightly increased with THIN and MEDIUM footwear as was eversion, as well as tibial and thigh internal rotation. It appears that participants may have been anticipating, very early in their run, a suitable kinematic pattern based on both the length of the run and the footwear condition.

Forefoot bending stiffness of cleated American football shoes

In American football, hyper-dorsiflexion of the first metatarsophalangeal (1 MTP) joint is the predominant mechanism of 1 MTP sprains (turf toe). The risk of acute 1 MTP sprain has been found to increase as 1 MTP angle increases. The bending resistance of the shoe dictates the proportion of an externally applied load that can be passed into the shoe (i.e., not through the 1 MTP joint) and thus influences the magnitude of flexion imparted to the 1 MTP joint. This study quantified the forefoot bending resistance of a range of cleated American football shoes. A total of 21 pairs of size 12 shoes were dynamically tested over flexion angles from 30° to 90°. Bending stiffness ranged from 0.10 to 0.35 Nm/deg, while peak torque ranged from 5.1 to 16.6 Nm. The relationship between torque and flexion angle was nearly linear for all of the shoes tested and the peak torque values were substantially lower than 1 MTP joint moments that have been measured in the human foot during athletic activities. These results suggest that an opportunity exists to better balance athletic performance and acute 1 MTP joint injury risk by incorporating non-linearity into the torque-angle characteristic of football cleats, such that the proportion of external load borne by the shoe increases at flexion angles above 60°.

High impact forces in skateboarding landings affected by landing outcome

Purpose. Despite concerns elicited by the injury-rate statistics for skateboarding, the literature has been silent on biomechanical factors that might be causing or exacerbating these injuries. To help fill this void, we sought to describe the kinetic characteristics of landing from a rail slide, one of the more high-risk, albeit common, maneuvers practiced by skateboarders. Methods. Twelve top-amateur or professional skateboarders (BW = 688 ± 89 N) performed rail slide maneuvers down a steep handrail before landing on a force plate. We recorded ground reaction force (GRF) data whether the subjects landed successfully (L) on their skateboards, or, bailed-out (BO), i.e. landed on their feet. Results. Vertical GRF (VGRF) during L had an initial peak, due to skateboard contact, immediately followed by a set of impact peaks (mean = 7.98 ± 1.32 (SD) BW) representing landing on the board. BO showed a VGRF impact peak rising to a significantly higher (P < 0.05) mean of 12.09 ± 2.63 BW. Conclusions. These data suggest that the skateboard provides significant shock attenuation. However, because BO landings are frequent, the relatively high peak ground reaction forces are a cause for concern. Given the musculoskeletal immaturity of typical skateboarders, clinicians should be aware of these high impact forces, and footwear manufacturers should explore ways to reduce peak pressures, and high impact and shear forces in the heel, forefoot, and toe box.

Quantifying the forefoot bending stiffness of cleated American football shoes using the Football American Shoe Tester (FAST)

In American football, hyper-dorsiflexion of the first metatarsophalangeal (first MTP) joint is the predominant mechanism of first MTP joint sprains (turf toe). The risk of acute first MTP joint sprain has been found to increase as first MTP joint angle increases. The bending resistance of the shoe dictates the proportion of an externally applied load that can be passed into the shoe (i.e. not through the first MTP joint) and thus may influence the magnitude of flexion imparted to the first MTP joint and hence the risk of injury. The current study introduces the Football American Shoe Tester (FAST), a flexion apparatus designed to measure the bending resistance of American football shoes at angles of forefoot dorsiflexion from 15° to 75°. The FAST was used to quantify the forefoot bending behaviour of a range of American football shoes. Thirty different models of US size 12 shoes were tested. Linearized bending stiffness ranged from 0.27 to 0.8 Nm/deg, while peak torque ranged from 11.8 to 25.5 N m. The testing revealed characteristic differences in torque-angle response across shoe models and quantified the extent of shoe stiffening at angles of dorsiflexion beyond those studied in the past.

Initial foot contact and related kinematics affect impact loading rate in running

ABSTRACT This study assessed kinematic differences between different foot strike patterns and their relationship with peak vertical instantaneous loading rate (VILR) of the ground reaction force (GRF). Fifty-two runners ran at 3.2 m · s−1 while we recorded GRF and lower limb kinematics and determined foot strike pattern: Typical or Atypical rearfoot strike (RFS), midfoot strike (MFS) of forefoot strike (FFS). Typical RFS had longer contact times and a lower leg stiffness than Atypical RFS and MFS. Typical RFS showed a dorsiflexed ankle (7.2 ± 3.5°) and positive foot angle (20.4 ± 4.8°) at initial contact while MFS showed a plantar flexed ankle (−10.4 ± 6.3°) and more horizontal foot (1.6 ± 3.1°). Atypical RFS showed a plantar flexed ankle (−3.1 ± 4.4°) and a small foot angle (7.0 ± 5.1°) at initial contact and had the highest VILR. For the RFS (Typical and Atypical RFS), foot angle at initial contact showed the highest correlation with VILR (r = −0.68). The observed higher VILR in Atypical RFS could be related to both ankle and foot kinematics and global running style that indicate a limited use of known kinematic impact absorbing “strategies” such as initial ankle dorsiflexion in MFS or initial ankle plantar flexion in Typical RFS.

Quantifying the physical and functional characteristics of footwear

One hundred and twenty male and female subjects (39.5 13.5 years, 1.75 0.10 m, 70.1 11.8 kg) were analysed at a running speed of 3.5 m/s. Subjects were running barefoot on 2 cm thick ethylene-vinyl acetate (EVA) mats (55 shore C durometer) and in a neutral running shoe (Brooks Glycerin, Brooks Sports Inc., Bothell, WA, USA) on the regular lab ground. GRFs and FMs were captured using a piezo-type force platform (1250 Hz, 0.9 m x 0.6 m, Kistler AG, Winterthur, Switzerland). FM curves were time and amplitude normalised to the stance phase and to body mass, respectively. Intraand inter-subject variability were determined by calculating the average standard deviation of distinct FM stance phase values for 5 trials provided per subject / condition and for 120 mean values per condition, respectively. Time normalised subject mean values of the running shoe condition were used in a cluster analysis (distance measure: squared Euclidean distance; cluster extraction: Ward algorithm) to identify possible patterns inside the FM dataset. Free moments were expressed as reaction moments. Results

Measuring the shock attenuation properties of skateboarding shoes

Introduction Impact forces on the feet in skateboarding can be much higher than in more traditional sports. In a typical two-footed, bail-out landing, skateboarders experienced impact forces averaging 8282 +/1913 N (Determan et al., 2004). These large forces help explain why a large proportion of injuries (50%) affect the lower extremity in skaters (Forsman and Eriksson, 2001). The most common method for testing the shock attenuating properties of athletic footwear is ASTM F1614, which specifies impact energy of 5.0 ± 0.5 J. However, our research on the kinetics of landings in skateboarding (Determan, et al. (2004)), allows us to estimate that the impact energy generated by skateboarders can be as high as 40 to 50 J. To better understand the real world shock attenuation properties of skateboarding shoes, we set out to develop a more realistic and representative impact testing method.

Apparatus for measuring the forefoot bending stiffness of cleated American football shoes

Among the three GRF cushioning variables, maximum LR is recommended for evaluating heel cushioning performance, as suggested by its better agreement with mechanical impact scores. Tibial acceleration seems to be effective in differentiating shoe of varying mechanical heel impact scores during higher loading intensity. Further investigation on mechanical impact score with different loading intensities should be done to help footwear manufacturer in the design of cushioning evaluation protocol. Forefoot and rearfoot loading biomechanics should be better differentiated to explore the underlying shock attenuation mechanism of different shoe-subject interfaces and in different force intensities.