Hard Shoe Research Articles

Soft-tissue vibration and damping response to footwear changes across a wide range of anthropometrics in running.

Different factors were shown to alter the vibration characteristics of soft-tissue compartments during running. Changing pre-heel strike muscle activation or changing footwear conditions represents two possibilities to influence the vibration response via frequency shift or altered damping. Associated with the study of muscle pre-tuning is the difficulty in quantifying clean experimental data for the acceleration of soft-tissue compartments and muscle activities in heterogeneous populations. The purpose of this study was to determine the vibration and pre-tuning response to footwear across a wide range of participants during running and establish and describe groups formed according to the damping coefficient. 32 subjects were used for further analysis. The subjects ran at a self-selected speed (5 min) on a treadmill in two different shoes (soft & hard), while soft-tissue accelerations and muscle activation at the gastrocnemius medialis were quantified. Damping coefficients, total muscle intensity and dominant vibration frequencies were determined. Anthropometrics and skinfold measurements of the lower limbs were obtained. According to the damping coefficient response to the footwear intervention, three groups were formed, with most runners (n = 20) showing less damping in the hard shoe. Total muscle intensity, anthropometrics, and dominant vibration frequency across footwear were not different for these three groups. Most runners (84.4%) used the strategy of adjusting the damping coefficients significantly when switching footwear. Despite damping being the preferred adjustment to changes in footwear, muscle pre-tuning might not be the only mechanism to influence damping as previously suggested. Future studies should focus on the subject-specific composition of soft-tissue compartments to elucidate their contribution to vibrations.

Characteristics of Eight Irish Dance LandingsConsiderations for Training and Overuse Injury Prevention.

Irish dance has evolved in aesthetics that lead to greater physical demands on dancers' bodies. Irish dancers must land from difficult moves without letting their knees bend or heels touch the ground, causing large forces to be absorbed by the body. The majority of injuries incurred by Irish dancers are due to overuse (79.6%). The purpose of this study was to determine loads on the body of female Irish dancers, including peak force, rise rate of force, and impulse, in eight common Irish hard shoe and soft shoe dance movements. It was hypothesized that these movements would produce different ground reac- tion force (GRF) characteristics. Sixteen female Irish dancers were recruited from the three highest competitive levels. Each performed a warm-up, reviewed the eight movements, and then performed each movement three times on a force plate, four in soft shoes and four in hard shoes. Ground reaction forces were measured using a three-dimensional force plate recording at 1,000 Hz. Peak force, rise rate, and vertical impulse were calculated. Peak forces normalized by each dancer's body weight for each of these variables were significantly different between move- ments and shoe types [F(15, 15)= 65.4, p < 0.01; F(15, 15) = 65.0, p < 0.01; and F(15, 15) = 67.4, p < 0.01, respectively]. The variable years of experience was not correlated with peak force, rise rate, or impulse (p > 0.40). It is concluded that there was a large range in GRF characteristics among the eight movements studied. Understanding the force of each dance step will allow instructors to develop training routines that help dancers adapt gradually to the high forces experienced in Irish dance training and competitions, thereby limiting the potential for overuse injuries.

Music to Our Ears: Are Dancers at Risk for High Sound Level Exposure?

Enduring exposure to high sound pressure levels (SPLs) can lead to noise-induced hearing loss (NIHL). In the performing arts population, NIHL has been studied primarily in the context of sound exposure experienced by musicians and less so by dancers. This research aimed to identify sound exposure that dancers may experience in some dance classes. Decibel levels were recorded in 12 dance classes (6 ballet, 4 modern, and 1 soft and 1 hard shoe Irish dance) at 8 different studios using the NIOSH SLM app on an iOS smartphone with external microphone. A minimum of five recordings of each class was measured, each collected on a different day, yielding a total of 114 measurements. Results showed that 20.2% of all recordings exceeded the recommended NIOSH sound exposure limits of both 100% projected daily dose and 85 LAeq. Analysis between styles of dance demonstrated significantly lower LAeq (p≤0.05) in soft shoe Irish dance compared to ballet (p=0.023), modern (p=0.035), and Irish hard shoe dance (p=0.009). Irish soft shoe dance demonstrated minimal to no risk of high sound exposure. Conversely, 53.25% of ballet, 90.9% of Irish hard shoe dance, and 68.24% of modern recordings exhibited minimal to moderate risk of high sound exposure. Furthermore, we found wide ranges of projected daily noise doses within classes taught by the same teacher. It is recommended that multiple recordings of dance environments be obtained, as a single sound recording may not accurately represent potential exposure. These findings indicate that dancers of Irish hard shoe, modern, and ballet may benefit from noise intervention such as audiometric testing, noise controls, and hearing protection.

Effect of shoe cushioning on landing impact forces and spatiotemporal parameters during running: results from a randomized trial including 800+ recreational runners

In a recent randomized trial including 800+ recreational runners, injury risk was lower in those who received the Soft shoe version compared to those using the Hard version (Hazard ratio = 1.52; 95% Confidence Interval = 1.07–2.16). Here, we investigated the effect of shoe cushioning on ground reaction forces (GRF) and spatiotemporal parameters in the same cohort, with a special focus on Vertical Impact Peak Force (VIPF) and Vertical Instantaneous Loading Rate (VILR). Healthy runners (n = 848) randomly received one of two shoe prototypes that differed only in their cushioning properties (Global stiffness: 61 ± 3 and 95 ± 6 N/mm in the Soft and Hard versions, respectively). Participants were tested on an instrumented treadmill at their preferred running speed. GRF data was recorded over 2 min. VIPF was higher in the Soft shoe group compared to the Hard shoe group (1.53 ± 0.21 vs. 1.44 ± 0.23 BW, respectively; p < 0.001). However, the proportion of steps with detectable VIPF was lower in the Soft shoe group (84 vs. 97%, respectively; p < 0.001) and Time to VIPF was longer (46.9 ± 8.5 vs. 43.4 ± 7.4 milliseconds, respectively; p < 0.001). No significant differences were observed for VILR (60.1 ± 13.8 vs. 58.9 ± 15.6 BW/s for Soft and Hard shoe group, respectively; p = 0.070) or any other kinetic variable. These results show that the beneficial effect of greater shoe cushioning on injury risk in the present cohort is not associated with attenuated VIPF and VILR. These GRF metrics may be inappropriate markers of the shoe cushioning-injury risk relationship, while delayed VIPF and the proportion of steps displaying a VIPF could be more relevant. Trial registration: ClinicalTrials.gov identifier: NCT03115437..

Characteristics Of Eight Irish Dance Landings: Implications For Overuse Injury And Training

The aesthetics in Irish dance have evolved to create greater physical demands on dancer’s bodies. Irish dancers must land from difficult movements without letting their knees bend or heels touch the ground, causing large forces to be absorbed by the body. The majority of injuries incurred by Irish dancers are due to overuse (79.6%). PURPOSE: The purpose of this study was to determine loads on the body in female Irish dancers, including peak force, rise rate of force, and impulse in selected Irish hard shoe and soft shoe dance movements. It was hypothesized that the 8 movements would produce different GRF characteristics. METHODS: Sixteen female Irish dancers were recruited from the three highest competitive levels. Each performed a warm-up, reviewed 8 common Irish dance movements, and then performed each movement three times upon a force plate. Of the 8 movements, 4 were performed in soft shoes and 4 were performed in hard shoes. Ground reaction forces (GRFs) were measured using a three-dimensional force plate recording at 1000 Hz. Peak force, rise rate, and vertical impulse were calculated. GRFs were normalized by each dancer’s body weight. RESULTS: Peak forces, rise rates, and impulses were significantly different across movements (F = 65.4, p < 0.01; F = 65.0, p < 0.01; and F = 67.4, p < 0.01 respectively). The movement with the highest peak force was the stomp. The movement with the highest rise rate was the double-toe. The movement with the highest impulse was the leap. The skip had the lowest values for all GRFs measured. Individual peak forces ranged from 0.67-9.86 times body weight. Individual rise rates ranged from 10-147 body weights per second. Individual impulses ranged from −0.12 to 0.32 body weight seconds. Years of experience was not correlated with peak force, rise rate, or impulse (p > 0.40). CONCLUSIONS: There is a large range in GRF characteristics created by Irish dancers. Dance movements that have high average peak forces may be associated with higher risk of overuse injury. Irish dancers should use appropriate training methods to strengthen the tissues at greatest risk of overuse injury.

Physiological Demands of Hard Shoe and Soft Shoe Irish Dancing: A Pilot Study

MP. Trebour, MM. Cutten, TG. Coffey, LQ. Jimenez, JP. Morrison. Longwood University, Farmville, VA 23909 PURPOSE: Irish Step Dance is a form of dance characterized by maintaining an upright posture and primarily moving the lower extremities with two different shoe styles. Soft shoe (SS) dance requires light and delicate movements, while hard shoe (HS) dance requires forceful and powerful movements. Irish dance competition pieces can last 30-60 seconds and performance pieces can last 10 minutes. The purpose of this study was to characterize the cardiorespiratory demands of female recreational Irish dancers. METHODS: Seven female dancers (35.8±9.6 y; 166.6±7.5 cm; 79.1±13.1 kg) volunteered for HR monitoring during three separate 45 min classes (n=16 measurements). Classes consisted of a mixture of HS and SS dancing. Three female dancers (28.0±13.9 y; 168.7±1.2 cm; 76.5±15.2 kg) volunteered for VO2 testing. Dancers completed a three minute reel and treble reel dances while wearing soft and hard shoes. Steady-state data were analyzed from the last 30 sec of the three minute dance test. The order of testing was randomized and the same piece of music was used for all dances. RESULTS: The mean HR for a class session was 128±14 bpm (69.7±9.3 %HRmax). The mean maximal HR achieved in class was 184±10 bpm (93.9±8.7 %HRmax). There was no significant (p<0.05) difference in VO2 (HS 23.33±7.51 ml/kg/min; SS 23.57±6.17 ml/kg/min), R-value (HS 1.31±0.05; SS 1.31±0.12), HR (HS 184.7±8.7 bpm; SS 185.0±2.0 bpm), or %HRmax (HS 96.3±3.2 %HRmax; SS 94.5±3.7 %HRmax) for HS and SS dance. CONCLUSIONS: The class data suggest that Irish dance classes are a moderate intensity activity with vigorous intensity intervals. Hard shoe and soft shoe Irish dance are physiologically demanding aerobic activities with anaerobic contribution. Despite differences in dance style these data suggest that there is no difference between the metabolic demands of HS and SS Irish dancing.

Shoe cushioning affects lower extremity joint contact forces during running

This study evaluated the effect of running shoes with differing midsole cushioning on ankle, knee and hip contact forces during running. Joint contact forces were estimated in 40 recreational runners (28 female, 12 male) while running over ground in three shoe conditions. Shoes differed only in midsole cushioning (45, 57 and 70 Asker C). Three-dimensional kinetics and kinematics were collected during running and input to a musculoskeletal model to estimate internal axial forces at the ankle, knee and hip. Multivariate ANOVA suggested that more cushioned shoes, relative to less cushioned shoes, reduced peak joint contact forces (p < 0.01) and load rates (p < 0.01). Ankle joint contact force and load rate were reduced with increased cushioning (p < 0.01) with moderate to large effects observed between pairwise comparisons (p ≤ 0.01–0.05, dz=0.41–1.35). Cushioning effects were also observed for knee joint contact force (p = 0.03) and loading rate (p < 0.01) with load reduction only seen when comparing the soft and hard shoes (p ≤ 0.05, dz=0.41–0.44). Midsole cushioning had less of an effect on hip contact force (p = 0.31) although hip contact force loading rate was influenced by midsole cushioning (p < 0.01) with lower rates observed for soft versus medium and hard shoe comparisons (p ≤ 0.01, dz=0.41–0.62). These results suggest that increasing shoe cushioning properties ∼10–20% may benefit individuals susceptible to high loads at the ankle, and to a lesser extent knee and hip, during running.

Effect of body mass and midsole hardness on kinetic and perceptual variables during basketball landing manoeuvres

This study investigated the effects of body mass and shoe midsole hardness on kinetic and perceptual variables during the performance of three basketball movements: (1) the first and landing steps of layup, (2) shot-blocking landing and (3) drop landing. Thirty male basketball players, assigned into “heavy” (n = 15, mass 82.7 ± 4.3 kg) or “light” (n = 15, mass 63.1 ± 2.8 kg) groups, performed five trials of each movement in three identical shoes of varying midsole hardness (soft, medium, hard). Vertical ground reaction force (VGRF) during landing was sampled using multiple wooden-top force plates. Perceptual responses on five variables (forefoot cushioning, rearfoot cushioning, forefoot stability, rearfoot stability and overall comfort) were rated after each movement condition using a 150-mm Visual Analogue Scale (VAS). A mixed factorial analysis of variance (ANOVA) (Body Mass × Shoe) was applied to all kinetic and perceptual variables. During the first step of the layup, the loading rate associated with rearfoot contact was 40.7% higher in the “heavy” than “light” groups (P = .014) and 12.4% higher in hard compared with soft shoes (P = .011). Forefoot peak VGRF in a soft shoe was higher (P = .011) than in a hard shoe during shot-block landing. Both “heavy” and “light” groups preferred softer to harder shoes. Overall, body mass had little effect on kinetic or perceptual variables.

The Effects of Different Shoes on Plantar Forces in Irish Dance

The purpose of this study was to compare the effects of different footwear on plantar loading in Irish dance. Participants were 12 open class dancers (the highest level) who were actively engaged in Irish dance competition. Subjects had a mean of 9.2 ± 2.1 years of experience in Irish dance. All dancers completed one bar of a set phrase in each of three shoes: Irish dance soft shoe, hard shoe, and a dance trainer. The order in which the shoes were tested was counterbalanced with a Latin square design. The variables compared were maximum force, maximum pressure, and impulse. Data were collected at 100 Hz using a Pedar insole pressure sensor system. Values were analyzed for the whole foot, forefoot, and rearfoot. Significant differences between shoe types were observed in impulse (p < 0.01) and maximum pressure (p < 0.01), with the trainer exhibiting lower values than the other shoes. Differences were also found between shoes in loading on regions of the foot (p < 0.01), with forefoot values highest in the soft shoe. The footwear choice had a significant effect on the measured kinetics of the dancers. The trainer displayed significantly lower values for kinetics than did the soft shoe. Thus, it may be a safer (less injurious) choice for daily training.

Every Treatment Plan Has Its Consequences

HISTORY: A 24 yo male tri-athlete presents 5 days after an injury while playing ping-pong. The athlete jumped to celebrate a point and landed on the lateral portion of his left foot inverting and twisting it at which point he heard and felt a "pop." Thirty minutes later he still had excruciating pain at the base of his 5th metatarsal and presented to the immediate care center where he was diagnosed with a fracture, and was placed in a posterior splint, given crutches, and told to follow up. At clinic, he had been non-weight-bearing for 4 days and kept his left leg immobilized in a posterior splint. In the past two days he noticed dorsolateral foot numbness following several bouts of intermittent left calf cramping lasting several minutes which was not relieved by massage. Today he notes left foot and ankle joint swelling, stiffness, and weakness. He denied using tobacco, drugs or alternative medicines. PHYSICAL EXAMINATION: General: Muscular, healthy appearing, well tempered male in no acute distress. Left foot: Tender, 5th metatarsal, yellow-brown discoloration, unable to weight-bear due to pain. Left ankle: Erythema, 1+ swelling, slight discoloration, full ROM. Left Calf: Tender to palpation medially, increased calf pain with dorsiflexion. Negative Thompson test. Left knee: normal. Right Foot/Ankle/Calf/Knee: normal findings. Neurological: Numbness/tingling in his left foot post calf cramps, but otherwise no abnormalities. Skin: No petechiae, swelling, erythema, and discoloration only in locations noted earlier DIFFERENTIAL DIAGNOSIS: 5th metatarsal Jones-Type fracture 5th metatarsal stress fracture, lateral ankle sprain Calf pain due to inactivity/immobilization with posterior splint, Deep venous thrombosis, as complication of immobilization Calf strain due to injury TEST AND RESULTS: X-RAY: Foot films consistent with Jones-type fracture. No evidence of stress fracture. Doppler Ultrasound Left lower extremity (LLE): an acute venous thrombus in the LLE Peroneal Vein. FINAL WORKING DIAGNOSIS: 1. Fifth Metatarsal Jones Type Fracture on Left Foot- metaphyseal area 2. Acute DVT LLE in the Peroneal Vein TREATMENT AND OUTCOMES: Placed in a hard shoe with crutches Aspirin 325mg 2x/day Scheduled for a f/u US with Vascular Radiology in 5days.

Influence of Running Shoe Midsole Composition and Custom Foot Orthotic Intervention on Lower Extremity Dynamics during Running

The purpose of this study was to analyze the influence of varying running shoe midsole composition on lower extremity dynamics with and without a custom foot orthotic intervention. Three-dimensional dynamics were collected on 12 female runners who had completed 6 weeks of custom foot orthotic therapy. Participants completed running trials in 3 running shoe midsole conditions-with and without a custom foot orthotic intervention. Results from the current study revealed that only maximum rearfoot eversion velocity was influenced by the midsole durometer of the shoe. Maximum rearfoot eversion velocity was significantly decreased for the hard shoe compared with the soft shoe. However, the orthotic intervention in the footwear led to significant decreases in several dynamic variables. The results suggest that the major component influencing the rearfoot dynamics was the orthotic device and not the shoe composition. In addition, data suggest that the foot orthoses appear to compensate for the lesser shoe stability enabling it to function in a way similar to that of a shoe of greater stability.

The effect of muscle stiffness and damping on simulated impact force peaks during running

It has been frequently reported that vertical impact force peaks during running change only minimally when changing the midsole hardness of running shoes. However, the underlying mechanism for these experimental observations is not well understood. An athlete has various possibilities to influence external and internal forces during ground contact (e.g. landing velocity, geometrical alignment, muscle tuning, etc.). The purpose of this study was to discuss one possible strategy to influence external impact forces acting on the athlete's body during running, the strategy to change muscle activity (muscle tuning). The human body was modeled as a simplified mass–spring–damper system. The model included masses of the upper and the lower bodies with each part of the body represented by a rigid and a non-rigid wobbling mass. The influence of mechanical properties of the human body on the vertical impact force peak was examined by varying the spring constants and damping coefficients of the spring–damper units that connected the various masses. Two types of shoe soles were modeled using a non-linear force deformation model with two sets of parameters based on the force–deformation curves of pendulum impact experiments. The simulated results showed that the regulation of the mechanical coupling of rigid and wobbling masses of the human body had an influence on the magnitude of the vertical impact force, but not on its loading rate. It was possible to produce the same impact force peaks altering specific mechanical properties of the system for a soft and a hard shoe sole. This regulation can be achieved through changes of joint angles, changes in joint angular velocities and/or changes in muscle activation levels in the lower extremity. Therefore, it has been concluded that changes in muscle activity (muscle tuning) can be used as a possible strategy to affect vertical impact force peaks during running.

Passive regulation of impact forces in heel-toe running

Objective. the purpose of this study was to determine whether passive mechanisms can account for impact force regulation with changing shoe hardness. Design. A three-dimensional musculoskeletal model of the lower extremity was developed to simulate impact in running with two different shoe hardnesses. Background. Considerable research has focused on developing shoe cushioning to reduce impact forces. However, only minimal changes in peak external impact force have been observed with changes in shoe hardness. It is hypothesized that passive mechanisms can regulate impact forces with changing shoe hardness, without changing muscle activities. Methods. Initial kinematic inputs for the simulations were measured from nine male subjects performing heel-toe running. Simulations were performed with initial conditions and muscle stimulation patterns held constant while shoe hardness was varied between a hard and a soft condition. Results. There was no significant difference between the soft and hard shoe peak impact forces. Peak rates of loading were greater for the hard shoe than the soft shoe. Muscle forces changed with shoe conditions. For some muscles (including the tibialis anterior) the forces were greater for the hard shoe, whereas for other muscles (including the peroneus) forces were greater for the soft shoe condition. Conclusions. Peak impact forces with changing shoe conditions can be regulated by passive mechanical changes without changing muscle activities or kinematics before touchdown.

The influence of a small insert, in the footbed of a shoe, upon plantar pressure distribution

INTRODUCTION:: A recent development in plantar pressure distribution research, has been the study of the effects of sensory input on pressure distribution. It has been suggested that proprioceptive and exteroceptive information received from the plantar surface of the foot plays an important role in adapting to high pressures in shoes. Robbins and Gouw (1991) suggested that surface irregularities should be added to the insoles of running shoes to gain correct sensory input. Hayda et al. (1994) found that placing a pad proximal to the metatarsal heads produced significant reductions in forefoot plantar pressures around the first and second metatarsal heads. A development by Villeneuve (1993), 'La Posteropodle', utilized a small insert to maintain postural equilibrium, by stimulating the mechanoreceptors in the plantar surface of the foot. The aim of this study was to measure changes in plantar pressure distribution using a small circular insert. METHODS:: Ten non-pathological male subjects were tested whilst walking, after one day of wearing a pair of oxfords (hard) and running shoes (soft), containing an insert of 4 mm in height placed on a 0.8 mm EVA insole. The foot was split into five sections: (1) midfoot, (2) first metatarsal head, (3) 2nd and 3rd metatarsal heads, (4) 4th and 5th metatarsal heads, (5) the phalanges. A PEDAR system (Novel GmbH) was used to collect in-shoe plantar pressure data, with data collections at the beginning and end of a working day. Subjects were tested under two conditions: (1) the insert 5 mm proximal to the metatarsal heads, between the 2nd and 3rd heads, (2) a control, with no insert. RESULTS:: Preliminary results indicate that whilst wearing a hard shoe the insert had the effect of shifting peak pressures from the first metatarsal head, to the area of the second and third metatarsal heads. Peak pressures were found to be lower with the insert present. This has not yet been tested for significance. With the running shoe there appeared to be no significant differences between conditions with and without the insert. There were also no differences between the beginning and end of the day, for both shoe types. DISCUSSION:: From the results it appears that the insert is successful in both shifting peak pressures from the medial to the lateral forefoot, whilst reducing peak pressures simultaneously. This was only evident in the hard shoe condition however, suggesting that the footbed of the running shoe was perhaps too soft to allow the insert to influence sensory input sufficiently. These findings indicate that there may be implications for the use of small orthotics. Further study is required, however, to fully substantiate this hypothesis.

The Effect of Varying Midsole Hardness on impact Forces and Foot Motion during Foot Contact in Running

The purpose of this study was to investigate the influence of midsole hardness on both impact forces and rearfoot motion. Seven trained male long-distance runners were assessed with a Kistler force plate and with high-speed video, while running at 4.5 ± 0.1 m · s"1 with soft and hard shoe soles (EVA; soft shore Asker C40; hard shore Asker C65). The results showed smaller initial vertical impact peaks, occurring with a higher loading rate, and a significantly larger and faster initial eversion when subjects ran with hard shoes. Support is given to the concept that a more pronounced initial eversion offers an additional deceleration mechanism (Stacoff, Denoth, Kaelin, &amp; Stuessi, 1988) also increasing the eccentric loading of the inverting muscles. On the other hand, during midstance soft shoe soles were found to produce a larger maximum eversion and pronation, also imposing an increased load on the same muscles. So, a good running shoe should be focused on a balance between reducing impact forces and reducing overpronation.

Lateral stability in sideward cutting movements

Objective. the purpose of this study was to determine whether passive mechanisms can account for impact force regulation with changing shoe hardness.Design. A three-dimensional musculoskeletal model of the lower extremity was developed to simulate impact in running with two different shoe hardnesses.Background. Considerable research has focused on developing shoe cushioning to reduce impact forces. However, only minimal changes in peak external impact force have been observed with changes in shoe hardness. It is hypothesized that passive mechanisms can regulate impact forces with changing shoe hardness, without changing muscle activities.Methods. Initial kinematic inputs for the simulations were measured from nine male subjects performing heel-toe running. Simulations were performed with initial conditions and muscle stimulation patterns held constant while shoe hardness was varied between a hard and a soft condition.Results. There was no significant difference between the soft and hard shoe peak impact forces. Peak rates of loading were greater for the hard shoe than the soft shoe. Muscle forces changed with shoe conditions. For some muscles (including the tibialis anterior) the forces were greater for the hard shoe, whereas for other muscles (including the peroneus) forces were greater for the soft shoe condition.Conclusions. Peak impact forces with changing shoe conditions can be regulated by passive mechanical changes without changing muscle activities or kinematics before touchdown.

Cushioning versus stability

Cushioning and stability are still key words for functionally constructed sport shoes. The goal of this investigation is to present and discuss the possibilities and limits of these shoe properties. Here, stability is not regarded as rigidity (like in a ski boot), but as a "dynamic stability" in the sense of functionality which supports the foot under load in such a manner that no unphysiological movements are provoked. Cushioning (in physics terminology: "damping") is defined to reduce and eliminate (kinetic) energy. When considering the impact peak in running, this peak can be reduced by using hard shoe soles with large heel flares. However, by doing that, large levers are introduced which produce an increased distance to decelerate the touchdown. This is basically the opposite of dynamic stability. Current shoe sole materials (homogeneous/isotropic) improve the "cushioning" but enhance the instability. New ways of shoe construction using more sophisticated anisotropic materials may lead out of this dichotomy.

Deformation characteristics of the heel region of the shod foot during a simulated heel strike: the effect of varying midsole hardness.

Impact tests using a pendulum were performed on the shod heel region of nine subjects. Both soft- and hard-soled shoes were used. The deformations involved were calculated from the registered decelerations during impact. Thus, load-deformation cycles were recorded for various impact velocities. In contrast to in vivo force-platform recordings, peak loadings for the soft- and hard-soled conditions differed significantly (614 +/- 29 N vs 864 +/- 49 N, respectively), thus challenging the evidence for compensation at the level of the heel pad. Moreover, computation of the compression of the heel pad in the shoe showed an unexpected inverse relationship between shoe midsole hardness and degree of heel pad compression: the harder the midsole, the smaller the compression (soft shoe 7.6 +/- 0.9 mm; hard shoe 6.7 +/- 0.9 mm). This can be explained by assuming a loading rate dependent stiffness of the heel pad in the shod condition (stiffness in N.m-1 = 51.25x (loading rate in N.s-1)0.76; R2 = 0.90), determined by the visco-elastic nature of the heel pad and the spatial confinement of the heel counter of the shoe.