Heel Impact Research Articles

The ‘heel impact’ force peak during running is neither ‘heel’ nor ‘impact’ and does not quantify shoe cushioning effects

It has been common practice in studies of running shoe cushioning to use the magnitude of the initial transient peak (Fz1) of the vertical ground reaction force (Fz(t)), as an index of heel impact severity. Frequently, the results of such studies have been inconsistent with impact attenuation theory, in vitro impact test results and other load measures. This paper concludes that such use of Fz1 as a measure of heel impact load is not valid. Fz(t) and in shoe-pressure distributions were recorded while 20 male subjects ran at 4.0 ± 0.2 m/s on a laboratory runway in three footwear conditions representing the approximate range of commercially available running shoes and a minimal, uncushioned control shoe. Pressure data were used to identify spatial (heel and distal foot) components of Fz(t) and spectral analysis was used to distinguish high and low frequency components. Consistent with previous reports, cushioned shoes attenuated Fz1 magnitude by less than 10% and the most compliant shoe produced significantly higher force peaks than shoes with stiffer cushioning. Analysis of the spatial and frequency components of Fz(t) revealed that Fz1 is a composite that includes high frequency (heel impact) loads but that low frequency force components originating both in the heel and distal forefoot contribute about half its magnitude. In contrast to Fz1, cushioned shoes attenuated the high frequency (impact) force component by 35%, and effects across shoe conditions were consistent with both theory and in vitro impact test results. Thus Fz1 is neither uniquely defined by heel impact, nor a reliable indicator of impact magnitude. It can be shown that the artifactual effects of cushioning on Fz1 magnitude are derived from the superimposition of low frequency (non-impact) and non-heel load components.

B35 有限要素解析によるゴルフクラブ特性がスピン軸を考慮したボールの反発に及ぼす影響(ボール特性)

The objective of this study was to construct a finite element (FE) model which can accurately simulate the rebound behaviour of a ball including a spin axis for a golf impact, and to investigate the effect of a position of centre of gravity (CoG) of a clubhead on the ball rebound, by conducting an FE analysis on a ball colliding with a simplified club. The club was constructed by holding the simplified clubhead in a locking ring fitted onto a steel shaft. The club model with linear elasticity was constructed. A ball model with hyperelasticity and viscoelasticity was constructed using solid elements. Impact experiments were also conducted to devise a method for calculating a spin rate and axis using a rotation matrix and to also confirm the accuracy of the FE model. The simulated results closely matched the experimental results. The ball rebound was analysed using the constructed model by varying positions of the height and depth of the CoG. The rebound angle and backspin tended to be depended on the height of the CoG and the variation seemed to be influenced by the tangential force of the impact face. In the toe and heel impact cases, the deviation angle and sidespin tended to increase with the depth of the CoG and a component of impact force, which led to a generation of the sidespin, was identified from the relationship between the variation of the sidespin and positions of the depth of the CoG.

Tibialis anterior muscle fatigue leads to changes in tibial axial acceleration after impact when ankle dorsiflexion angles are visually controlled

Heel impact forces may lead to injury as they travel through the human musculoskeletal system. Previous work on the effect that localized muscle fatigue has on the tibial response (shank axial acceleration) to impact was limited because ankle angle was not controlled. The purpose of this study was to compare the tibial response when the tibialis anterior was fatigued and when not fatigued, while participants controlled dorsiflexion angles at impact using visual feedback. Twenty participants (10 male, 10 female; M ± SD = 21.8 ± 2.9 years) were strapped supine to a human pendulum apparatus, and instrumented with a low mass accelerometer (affixed medial to the tibial tuberosity). Participant dorsiflexion angle range was recorded by an electro-goniometer, and divided into four angle ranges so tibial response variables (peak tibial acceleration, time to peak acceleration, acceleration slope) could be compared when fatigued and not fatigued. Peak tibial acceleration and acceleration slopes decreased, and time to peak acceleration increased following fatigue, when comparing values across the same dorsiflexion ranges. Dorsiflexion angle alone did not account for differences in tibial response during localized leg muscle fatigue; supporting prior work and suggesting that the muscle and ankle joint become less stiff when fatigued, thereby increasing the lower extremity attenuation capability to heel impacts.

Systematically modified crash-pad reduces impact shock in running shoes

The purpose of this study was to compare the effect of (a) crash-pad thickness and (b) midsole height at the heel to reduce heel impact load during running. Twenty male runners performed heel-toe runs in four different shoe conditions. While three shoe conditions had systematic changes in crash-pad thickness without changing general heel height, a fourth shoe condition differed only in overall heel height. Kinetic and kinematic running variables were quantified by using a force platform and an electrogoniometer. Data were collected for five valid running trials at a constant running speed of 3.5 ± 0.1 m s−1. Kolmogorov–Smirnov tests, a one-way repeated measures ANOVA (P < 0.05) as well as effect sizes (η 2) were calculated for all variables. The findings of this study showed that (a) increasing crash-pad thickness resulted in reduced impact variables without influencing traditional rearfoot motion variables. Furthermore, reduced heel height (b) is influencing predominantly rearfoot stability. Consequently, crash-pad modification can be used to improve cushioning properties without influences on rearfoot stability. Furthermore, crash-pad modification allows reducing shoe weight while maintaining cushioning properties.

63789 SOME ASPECTS OF HEEL STRIKE IMPACT DYNAMICS IN THE STABILITY OF BIPEDAL LOCOMOTION(Biomechanics)

Heel impact contributes to the stability of bipedal locomotion: the change of trajectory induced at heel strike has a stabilizing effect, and the phase-space volume contraction to which heel strike contributes is a necessary condition for stability. For a given passive walker, there is a slope limit to obtain stable limit cycles. However, this limit can be surpassed if extra dissipation is introduced. This stabilizing mechanism can be used or be present in bipedal locomotion. In this paper, it is proposed that heel strike can be accommodated to absorb more or less energy, and then that it is used as a regulation or control mechanism in bipedal locomotion. From a biomechanical point of view, dissipation through heel impact is the most efficient way to lose energy, any other way requires an active participation of muscles. This signifies the importance of the proposed regulation mechanism. In this work, some of the control possibilities of heel impact are briefly analyzed related to the energetics in order to claim its role and importance as a control mechanism in bipedal locomotion. This study can be valuable in several areas, for example, in control, prosthetics, shoe design, and generally in further understanding of bipedal locomotion.

Acceleration Thresholds of Vertical Floor Vibrations According to Human Perception Levels in Korea

Vertical floor vibrations in residential buildings are typically induced by the movements of jumping and walking of occupants, which often annoy other occupants. To help control such floor vibrations, several criteria have been developed mostly based on human perception tests. The objective of this study is to propose acceleration thresholds of appropriate vertical floor vibration due to heel impacts and walking activities. Four different perception levels are considered appropriate criteria for Korean residential buildings; imperceptible, slightly perceptible, distinctly perceptible, and strongly perceptible. Shaking table tests were conducted simulating heel impact induced- and walking induced-vertical vibrations for various combinations of frequencies, damping ratios and acceleration amplitudes. Twenty Korean test subjects were used. It is observed that test subjects are more sensitive to walking-induced vibrations than those induced by heel impacts having the same peak accelerations. This study also shows that the acceleration thresholds proposed as a result of this study using Korean testing subjects are lower than those proposed by other researchers in different countries.

Estimation of anterior cruciate ligament tension from inverse dynamics data and electromyography in females during drop landing

Background Recent human performance studies have shown that various kinematic and kinetic parameters may be implicated in non-contact anterior cruciate ligament (ACL) injury during landing and cutting. In this paper, a phenomenological sagittal plane model was used to estimate the ACL tension during drop landing from the net knee moments and forces, obtained from inverse dynamics and electromyography. Methods Model parameters were determined with data from anatomical and ACL loading studies of cadaveric specimens. The model was used to process averaged data from 60 cm drop landing trials of sixteen healthy females. Findings ACL loading during drop landing occurred during the between toe and heel impact with a peak tension of 0.15 body weight. The factors that contributed to ACL tension were the patellar tendon force and the tibial slope in combination with the joint axial loads. Factors responsible for reducing ACL tension were hamstring and ground reaction forces. Interpretation Sagittal plane results largely confirmed a previous forward dynamics study of landing. The knee appeared to be largely stabilized against abduction moments due to the large axial loads present during drop landing for typical landing trials. Rotational moments were small in drop landing and contributed little to ACL tension. Estimates from this model can be used in human performance studies to determine the relative amount of ACL tension produced in different landing scenarios.

Redesigning Figure Skating Boots To Reduce Impact Forces

Figure skating has evolved into a highly specialized and athletic sport with difficult triple and quadruple jumps increasingly becoming the primary focus. Skaters are spending more time practicing jumps and overuse injury rates show an associated increase. The current rigid leather skating boot severely restricts ankle motion, reducing the body's ability to absorb damaging landing stresses. Modifying the current skating boot by introducing an ankle articulation may help reduce peak transient forces during landing. PURPOSE The purpose of this study was to test the ability of an articulated skating boot to attenuate ground reaction forces during landing. It was hypothesized that articulated figure skates would reduce peak forces as well as loading rates when compared to traditional boots. METHODS Prototype articulated boots were manufactured by Jackson Ultima Skates inc. Nine US Figure Skating juvenile-level or higher figure skaters from the surrounding area were tested in off-ice simulated jump landings from a 30cm platform onto a force plate. Kinetic and kinematic data were collected and analyzed from skaters wearing standard skating boots and, after a brief training period, wearing articulated boots. A repeated measures ANOVA was used to determine significant differences (alpha=.05) in ground reaction forces, loading rates, and several kinematic variables. RESULTS Peak heel impact forces and loading rates decreased significantly in the articulated boot. Ankle plantarflexion and boot/ice angles at impact increased while the total jointfiexion at impact decreased. There were no statistical changes in toe impact force, jump height, and hip and knee angles at impact. CONCLUSIONS The majority of skaters used the increased range of motion in the articulated skates to effectively reduce landing forces and loading rates. However, a few showed very little change between conditions, even with increased ankle plantarflexion and boot/ice angles at toe contact. In some skaters, the ankle musculature was apparently not utilized to stiffen the ankle during the impact phase. The findings suggest that some skaters attempt to utilize the ankle, while others do not, and that some retraining may be necessary to decrease landing forces.

On the influence of soft tissue coverage in the determination of bone kinematics using skin markers

Accurate measurement of underlying bone positions is important for the understanding of normal movement and function, as well as for addressing clinical musculoskeletal or post-injury problems. Non-invasive measurement techniques are limited by the analysis technique and movement of peripheral soft tissues that can introduce significant measurement errors in reproducing the kinematics of the underlying bones when using external skin markers. Reflective markers, skeletally mounted to the right hind limb of three Merino-mix sheep were measured simultaneously with markers attached to the skin of each segment, during repetitions of gait trials. The movement of the skin markers relative to the underlying bone positions was then assessed using the Point Cluster Technique (PCT), raw averaging and the Optimal Common Shape Technique (OCST), a new approach presented in this manuscript. Errors in the position of the proximal joint centre, predicted from the corresponding skin markers, were shown to be phasic and strongly associated with the amount soft tissue coverage, averaging 8.5 mm for the femur, 2.8 for the tibia and 2.0 for the metatarsus. Although the results show a better prediction of bone kinematics associated with the Optimal Common Shape Technique, these errors were large for all three assessment techniques and much greater than the differences between the various techniques. Whilst individual markers moved up to 4 mm from the optimal marker set configuration, average peak errors of up to 16, 5 and 3 mm (hip, knee and tibio-metatarsal joints respectively) were observed, suggesting that a large amount of kinematic noise is produced from the synchronous shifting of marker sets, potentially as a result of underlying muscle firing and the inertial effects of heel impact. Current techniques are therefore limited in their ability to determine the kinematics of underlying bones based on skin markers, particularly in segments with more pronounced soft tissue coverage.

Compensatory adjustments in lower extremity kinematics in response to a reduced cushioning of the impact interface in heel–toe running

The response of heel-toe runners to changes in cushioning of the impact interface was investigated. Ground reaction force and sagittal plane kinematic data were collected for six heel-toe runners performing barefoot running trials on a conventional asphalt surface and an asphalt surface with additional cushioning. Statistical analysis indicated that similar peak impact force values were maintained when running on the two surfaces (p 0.1). In addition, individual subjects demonstrated reductions in heel velocity and increases in knee flexion immediately prior to ground contact. The observed reduction in ankle dorsiflexion at impact, resulting in a flatter foot at ground contact, supports previous suggestions that this is a strategy to reduce local plantar pressure loads. The additional use of adjustments in heel velocity and initial knee flexion highlights the ability of some subjects to adopt compensatory measures to reduce peak impact loading. However, some subjects appear unable to make these adjustments, resulting in higher impact loading on the less cushioned surface for these subjects. This study provides experimental evidence to support the theoretical potential of heel impact velocity and initial knee flexion to influence impact loading in running.

Floor serviceability under dynamic loading

Some structures such as floors and tall buildings that meet the code design criteria exhibit unacceptable vibrations relative to the human user. In particular, occupants of long-span floors constructed with open-web joists and light-weight concrete are likely to experience perceptible or annoying vibrations due to normal human activity that is characterized by impact, such as walking, dancing, running, and jumping. Thus, it is important that a serviceability criterion based on human response be used at the design stage to avoid costly problems after the floor is constructed and put into service. Note that human response to vibration is a function of the human body characteristics, the intensity and type of the loading, and the characteristics of the structure such as its frequency, stiffness, mass, and damping. In this paper, a serviceability criterion based on the humanload-structure system is presented. This criterion is the value of the absorbed power (rate of energy dissipation) through the human body as represented by a biomechanical model. The absorbed power levels for the thresholds of perception and annoyance were determined and compared with available human comfort curves. The close agreement demonstrates that absorbed power is a good measure of human response to vibration. To demonstrate the usefulness of absorbed power, floor serviceability was assessed due to walking, heel impact, and dancing. Also, the serviceability of forty-one floors was evaluated using absorbed power and compared to the reported subjective assessments. Absorbed power values correctly predicted the serviceability of thirty-nine of the floors. Furthermore, design curves were produced to assist the engineer in designing serviceable floors.

Rearfoot Kinematics during Initial Takeoff of Elite High Jumpers: Estimation of Spatial Position and Orientation of Subtalar Axis

As the spatial position and orientation of the subtalar ankle axis documented in biomechanical literature has mainly been estimated in unloaded conditions, it was hypothesized that high loads on the subtalar joint during very dynamic movements may force the respective axis away from its normal anatomical location. Therefore, high jump takeoffs of two elite athletes were selected to estimate and analyze the kinematic behavior of the subtalar axis during initial takeoff. The subtalar motion of the calcaneus was reconstructed using 3-D high-speed cinematography and a three-segment ankle model expressing subtalar pronation as the movement of the calcaneus around the talus. Results revealed that the subtalar axis moved away from its initial orientation and position at first heel impact, respectively more horizontally and laterally. The pronational angular displacement and velocity were calculated for all jumps and reached maximal values close to 30°, respectively 2000°/s. They compared surprisingly well with values obtained from frontal plane projections as used in a conventional cinematographical approach. But values corresponding to a subtalar axis fitting conventional anatomical descriptions showed consistently larger discrepancies, up to 10° for pronational displacement and close to 600°/s for pronational velocity. Finally, a comparison with results obtained from helical or screw axes produced nearly identical findings, suggesting good validity of the analytical techniques applied in this study for the 3-D reconstruction of the subtalar axis.

Biomechanics of the heel pad for type 2 diabetic patients

Objectives. To quantify the dynamic behavior of the heel pad in type 2 diabetic patients and age-matched healthy individuals using mathematical modeling. Background. No single parameter can fully describe the heel-pad biomechanical properties during the loading–unloading process. Design. A descriptive study using pseudoelastic modeling was conducted to simulate the heel-pad stress–strain relationship in the loaded and unloaded states. Transmission electron microscope was used to examine six heel specimens taken from amputated legs in diabetic and non-diabetic patients. Methods. Energy dissipation ratio, loading curvature, and unloading curvature were calculated from the stress–strain curve-fits. Differences in ultrastructure between the heel pad of healthy subjects and those with diabetes were described. Results. The diabetic patients had a significantly higher mean energy dissipation ratio (mean 36.1% (SD, 8.7%) vs mean 27.9% (SD, 6.1%); P<0.001) and mean unloaded curvatures (mean 11.8 (SD, 5.1) vs mean 8.46 (SD, 2.6); P<0.001) than those of the control group. The collagen fibrils in diabetic heel samples were ruptured with unclear striation and uneven distribution. Conclusions. The curvature parameters may explain the poor rebound phenomenon resulting in the high impact energy in diabetic heel pads. Breakdown in collagen fibrils may be responsible for this observation. Relevance These findings can be integrated into the fabrication of orthotics that dissipate excessive heel impact energy and protect against injury.

The Influence of High Heeled Shoes on Kinematics, Kinetics, and Muscle EMG of Normal Female Gait

The purpose of this investigation was to determine whether a graded response in gait kinematics, kinetics, and EMG occurs as shoe heel height increases. Four different shoes, including one flat shoe and three shoes with high heels, were tested in this investigation. The average heel heights of the four shoes were 1.4 cm, 3.7 cm, 5.4 cm, and 8.5 cm. Kinematics, kinetics, and muscle EMG were measured during the stance phase of gait on 13 healthy female subjects while wearing each of these 4 shoes. Systematic increases in the active vertical, propulsive, and braking forces were found as shoe height increased. Ankle and knee flexion and soleus and rectus femoris activity showed a graded response as heel height increased. One surprising result was the behavior of the maximal vertical impact force peak and the maximal loading rate during heel impact. The vertical impact force peaks and the maximal vertical loading rates were highest for the shoe with 3.7 cm heel height and lowest for the flat shoe and the shoe with heel height of 8.5 cm.

Mechanical Modeling of Tibial Axial Accelerations Following Impulsive Heel Impact

A fourth order mass/spring/damper (MSD) mechanical model with linear coefficients was used to estimate axial tibial accelerations following impulsive heel impacts. A generic heel pad with constant stiffness was modeled to improve the temporal characteristics of the model. Subjects (n= 14) dropped (~5 cm) onto a force platform (3 trials), landing on the right heel pad with leg fully extended at the knee. A uni-axial accelerometer was mounted over the skin on the anterior aspect of the medial tibial condyle inferior to the tibial plateau using a Velcro™ strap (normal preload ~45 N). Model coefficients for stiffness (k1, k2) and damping (c1, c2) were varied systematically until the minimum difference in peak tibial acceleration (%PTAmin) plus maximum rate of tibial acceleration (%RTAmax) between the estimated and measured curves was achieved for each trial. Model responses to mean subject and mean group model coefficients were also determined. Subject PTA and RTA magnitudes were reproduced well by the model (%PTAmin= 1.4 ± 1.0 %, %RTAmin= 2.2 ± 2.7%). Model estimates of PTA were fairly repeatable for a given subject despite generally high variability in the model coefficients, for subjects and for the group (coefficients of variation: CVk1= 57; CVk2= 59; CVc1= 48; CVc2= 85). Differences in estimated parameters increased progressively when subject and group mean coefficients (%PTAsub= 8.4 ± 6.3%, %RTAsub= 18.9 ± 18.6%, and %PTAgrp= 19.9 ± 15.2 %, %RTAgrp= 30.2 ± 30.2%, respectively) were utilized, suggesting that trial specific calibration of coefficients for each subject is required. Additional model refinement seems warranted in order to account for the large intra-subject variability in coefficients.

Comparison of Heel Strike Accelerations While Walking on Carpet, Tile, and a Motorized Treadmill

The objective of this study was to investigate the validity of utilizing treadmills in human gait studies--to investigate the correlation between heel strike data obtained while walking on a treadmill to that obtained while walking on carpet and vinyl tile. The impact data were recorded using accelerometers located in the heels of tennis and casual buck shoes. Seven male subjects were tested while walking at a normal pace on the carpeted and tiled floors and then on the treadmill at that pace. Additional gait velocities were also tested on the treadmill to study the effect of velocity on heel impact. A correlation was found between heel strike accelerations on the treadmill and the ones on the tile for both shoe types. No correlation was found for the carpet. Heel strike peak accelerations increased linearly with increasing velocity on the treadmill. Results indicate that a motorized treadmill can be utilized in gait studies as long as several factors are kept in mind: the material characteristics of the shoe, the subject's stride length, the hardness of heel impact of the subject, the subject's own walking speed, and whether the subject uses a treadmill regularly.

Anatomy and Biomechanics of the First Ray

The medial longitudinal arch serves as the chief load-bearing structure in the foot1–3 and is dependent on the kinematics of the first ray for optimal support during gait.4 The first ray is a single foot segment consisting of the first metatarsal and first cuneiform bones.5 Pronation of the subtalar joint lowers the first ray to the ground in early stance5 and dissipates the shock of heel impact.3 As body weight moves forward, the mechanics of supination stabilize the medial arch, preparing the foot for the propulsive phase of gait. The dichotomous actions of weight acceptance and weight-bearing stability required of the first ray underscore the importance for clinicians who treat the foot to understand the biomechanics of the first ray. The importance of the first ray to the mechanics of the foot is, in part, because of the metatarsocuneiform joint's location, which intersects the transverse and medial longitudinal arches.6 A curved beam and a truss (Fig. 1) are frequently used when modeling the medial arch.7–10 Beams are designed to withstand bending under an applied force. A truss is a triangular framework with 2 rigid supports connected together at its base. Because the ends of the foot are not secure at the beginning of stance, the foot functions like a beam. As the weight of the body transfers forward, the calcaneus and the heads of the metatarsals are pressed to the ground, with the arch functioning as a truss. Truss-and-beam mechanics of the foot rely on the first ray to function as the pillar for the medial arch. The first ray, therefore, is a critical element in controlling the structural integrity of the foot.4 Figure 1. During early stance (A), the medial longitudinal arch functions like a curved beam to support …

Significance of mat and shoe softness during prolonged work in upright position: based on measurements of low back muscle EMG, foot volume changes, discomfort and ground force reactions

The aim of the investigation was to study the significance of mat and shoe softness during prolonged work in an upright position based on some physiological, biomechanical and comfort measurements related to the lower extremities and the low back. Eight healthy female volunteers performed 2 h of simulated standing and 2 h of standing/walking work tasks in the laboratory using four combinations of soft shoes, clogs, soft mat and concrete. Thus, each subject performed a total of eight 2 h work tests. The following parameters were measured pre-experimentally and one or more times during 2 h: total foot volume, vascular volume and interstitial volume of the left foot, EMG from the lumbar paraspinals, movement of centre of gravity (only during standing), biomechanical heel impact (only during standing/walking), perceived discomfort in lumbar back, legs and feet, whole body oxygen uptake, arterial blood pressure and heart rate. Using soft shoes rather than clogs during standing/walking work implies approximately a halving of the foot oedema formation and the heel impact. The effects due to the introduction of the soft mat are negligible. The local circulatory responses in the feet and the EMG-signs of paravertebral muscle fatigue are larger during standing compared to standing/walking work. The two investigated work types in this study differ regarding exposures as well as responses. Thus, it is recommended to shift between these postures and seated work during the working hours to improve job exposures.

In-shoe heel pressure distribution and impact ground reaction force during running

In-shoe heel pressure distribution and impact ground reaction force during running

Effect of shoe cushioning on the development of reticulocytosis in distance runners.

We studied erythropoietic activity in relation to the rearfoot cushioning of shoes worn by 14 male runners before, during, and the morning after a 17-day period of increased training mileage. The percentage of reticulocytes in the red blood cell count (normal, less than 0.8%) served as the marker for erythropoietic activity. Each runner was assigned to either a firm-sole group (7) or a soft-sole group (7) according to the heel impact attenuation character (Peak g) of his shoes. Peak g was 18% greater in the firm-sole group (P less than 0.001). Otherwise, the groups were similar in physical characteristics, training mileage, and running ability. All subjects ran a total of 430 km, a distance that averaged 79% higher than their regular training distance for a 17-day period. Resting blood samples were obtained at baseline and on three mornings (Days 11, 13, and Day 18, which followed the completion of the increased training period). No significant differences were found between the groups in red blood cell count, hematocrit, or total hemoglobin, haptoglobin, plasma-free hemoglobin, and serum ferritin levels. The groups did not differ in percent reticulocytes at baseline (0.2% firm-sole versus 0.2% soft-sole), on Day 11 after running 280 km (0.8% firm-sole versus 0.8% soft-sole), or on Day 13 after 48 hours of rest (1.3% firm-sole versus 1.0% soft-sole). However, on Day 18 after running 430 km, reticulocyte counts were 29% higher (P less than 0.05) in firm-sole than soft-sole (2.2% versus 1.7%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)