Characterizing the effective stiffness of the pelvis during sideways falls on the hip

The force applied to the proximal femur during a fall, and thus hip fracture risk, is dependent on the effective stiffness of the body during impact. Accurate estimates of pelvis stiffness are required to predict fracture risk in a fall. However, the dynamic force–deflection properties of the human pelvis have never been measured in-vivo. Our objectives were to (1) measure the force–deflection properties of the pelvis during lateral impact to the hip, and (2) determine whether the accuracy of a mass-spring model of impact in predicting peak force depends on the characterization of non-linearities in stiffness. We used a sling and electromagnet to release the participant’s pelvis from heights up to 5 cm, simulating low-severity sideways falls. We measured applied loads with a force plate, and pelvis deformation with a motion capture system. In the 5 cm trials peak force averaged 1004 (SD 115) N and peak deflection averaged 26.3 (5.1) mm. We observed minimal non-linearities in pelvic force–deflection properties characterized by an 8% increase in the coefficient of determination for non-linear compared to linear regression equations fit to the data. Our model consistently overestimated peak force (by 49%) when using a non-linear stiffness equation, while a piece-wise non-linear fit (non-linear for low forces, linear for loads exceeding 300 N) predicted peak force to within 1% at our highest drop height. This study has important implications for mathematical and physical models of falls, including mechanical systems that assess the biomechanical effectiveness of protective devices aimed at reducing hip fracture risk.     

Effect of pelvis impact angle on stresses at the femoral neck during falls

Improved understanding is required of how the mechanics of the fall affect hip fracture risk. We used a hip impact simulator to determine how peak stresses at the femoral neck were affected by pelvis impact angle, hip abductor muscle force, and use of a wearable hip protector.We simulated falls from standing (2 m/s impact velocity) involving initial hip abductor muscle forces of 700 or 300 N. Trials were acquired for impact to the lateral aspect of the greater trochanter, and impact to the pelvis rotated 5°, 10° and 15° anteriorly (positive) or posteriorly (negative). Measures were acquired with and without a commercially available hip protector. During trials, we measured three-dimensional forces with a load cell at the femoral neck, and derived peak compressive and tensile stresses.Peak compressive stress increased 37% (5.91 versus 4.31 MPa; p < 0.0005) and peak tensile stress increased 209% (2.31 versus 0.75 MPa; p < 0.0005) when the pelvis impact angle changed from 15° anterior to −15° posterior. For lateral impacts, the peak tensile and compressive stresses averaged 73% and 8% lower, respectively, in the 700 N than 300 N muscle force condition, but the effect was reversed for anteriolateral or posteriolateral impacts. The attenuation in peak compressive stress from the hip protector was greatest for posteriolateral impacts (−15 to −5°; 36–41%), and least for anteriolateral (+15°; 10%).These results clarify the effects on hip fracture risk during a fall of pelvis impact angle and muscle forces, and should inform the design of improved hip protectors.     

Can martial arts techniques reduce fall severity? An in vivo study of femoral loading configurations in sideways falls

Sideways falls onto the hip are a major cause of femoral fractures in the elderly. Martial arts (MA) fall techniques decrease hip impact forces in sideways falls. The femoral fracture risk, however, also depends on the femoral loading configuration (direction and point of application of the force). The purpose of this study was to determine the effect of fall techniques, landing surface and fall height on the impact force and the loading configuration in sideways falls. Twelve experienced judokas performed sideways MA and Block ('natural') falls on a force plate, both with and without a judo mat on top. Kinematic and force data were analysed to determine the hip impact force and the loading configuration. In falls from a kneeling position, the MA technique reduced the impact force by 27%, but did not change the loading configuration. The use of the mat did not change the loading configuration. Falling from a standing changed the force direction. In all conditions, the point of application was distal and posterior to the greater trochanter, but it was less distal and more posterior in falls from standing than from kneeling position. The present decrease in hip impact force with an unchanged loading configuration indicates the potential protective effect of the MA technique on the femoral fracture risk. The change in loading configuration with an increased fall height warrant further studies to examine the effect of MA techniques on fall severity under more natural fall circumstances.     

Pelvis and femur geometry: Relationships with impact characteristics during sideways falls on the hip

While metrics of pelvis and femur geometry have been demonstrated to influence hip fracture risk, attempts at linking geometry to underlying mechanisms have focused on fracture strength. We investigated the potential effects of femur and pelvis geometry on applied loads during lateral falls on the hip. Fifteen female volunteers underwent DXA imaging to characterize two pelvis and six femur geometric features. Additionally, participants completed low-energy sideways falls on the hip; peak impact force and pressure, contact area, and moment of force applied to the proximal femur were extracted. No geometric feature was significantly associated with peak impact force. Peak moment of force was significantly associated with femur moment arm (p = 0.005). Peak pressure was positively correlated with pelvis width and femur moment arm (p < 0.05), while contact area was negatively correlated with metrics of pelvis width and femur neck length (p < 0.05). This is the first study to link experimental measures of impact loads during sideways falls with image-based skeletal geometry from human volunteers. The results suggest that while skeletal geometry has limited effects on overall peak impact force during sideways falls, it does influence how impact loads are distributed at the skin surface, in addition to the bending moment applied to the proximal femur. These findings have implications for the design of protective interventions (e.g. wearable hip protectors), and for models of fall-related lateral impacts that could incorporate the relationships between skeletal geometry, external load magnitude/distribution, and tissue-level femur loads.     

Effect of pre-impact movement strategies on the impact forces resulting from a lateral fall

Approximately 90% of hip fractures in older adults result from falls, mostly from landing on or near the hip. A three-dimensional, 11-segment, forward dynamic biomechanical model was developed to investigate whether segment movement strategies prior to impact can affect the impact forces resulting from a lateral fall. Four different pre-impact movement strategies, with and without using the ipsilateral arm to break the fall, were implemented using paired actuators representing the agonist and antagonist muscles acting about each joint. Proportional-derivative feedback controller controlled joint angles and velocities so as to minimize risk of fracture at any of the impact sites. It was hypothesized that (a) the use of active knee, hip and arm joint torques during the pre-contact phase affects neither the whole body kinetic energy at impact nor the peak impact forces on the knee, hip or shoulder and (b) muscle strength and reaction time do not substantially affect peak impact forces. The results demonstrate that, compared with falling laterally as a rigid body, an arrest strategy that combines flexion of the lower extremities, ground contact with the side of the lower leg along with an axial rotation to progressively present the posterolateral aspects of the thigh, pelvis and then torso, can reduce the peak hip impact force by up to 56%. A 30% decline in muscle strength did not markedly affect the effectiveness of that fall strategy. However, a 300-ms delay in implementing the movement strategy inevitably caused hip impact forces consistent with fracture unless the arm was used to break the fall prior to the hip impact.     

The influence of muscle activation on impact dynamics during lateral falls on the hip

Muscle activation has been demonstrated to influence impact dynamics during scenarios including running, automotive impacts, and head impacts. This study investigated the effects of targeted muscle activation magnitude on impact dynamics during low energy falls on the hip with human volunteers. Fifteen university-aged participants (eight females, seven males) underwent 12 lateral pelvis release trials. Half of the trials were muscle-‘relaxed’; in the remaining ‘contracted’ trials participants isometrically contracted their gluteus medius to 20–30% of maximal voluntary contraction before the drop was initiated onto a force plate. Peak force applied to the femur-pelvis complex averaged 9.3% higher in contracted compared to relaxed trials (F = 6.798, p = .022). Muscle activation effects were greater for females, resulting in (on average) an 18.5% increase in effective pelvic stiffness (F = 5.838, p = .046) and a 23.4% decrease in time-to-peak-force (F = 5.109, p = .042). In the relaxed trials, muscle activation naturally increased during the impact event, reaching levels of 12.8, 7.5, 11.1, and 19.1% MVC at the time of peak force for the gluteus medias, vastus lateralis, erector spinae, and external oblique, respectively. These findings demonstrated that contraction of trunk and hip musculature increased peak impact force across sexes. In females, increases in the magnitude and rate of loading were accompanied (and likely driven) by increases in system stiffness. Accordingly, incorporating muscle activation contributions into biomechanical models that investigate loading dynamics in the femur and/or pelvis during lateral impacts may improve estimate accuracy.     

Energy absorption during impact on the proximal femur is affected by body mass index and flooring surface

Impact mechanics theory suggests that peak loads should decrease with increase in system energy absorption. In light of the reduced hip fracture risk for persons with high body mass index (BMI) and for falls on soft surfaces, the purpose of this study was to characterize the effects of participant BMI, gender, and flooring surface on system energy absorption during lateral falls on the hip with human volunteers. Twenty university-aged participants completed the study with five men and five women in both low BMI (<22.5 kg/m²) and high BMI (>27.5 kg/m²) groups. Participants underwent lateral pelvis release experiments from a height of 5 cm onto two common floors and four safety floors mounted on a force plate. A motion-capture system measured pelvic deflection. The energy absorbed during the initial compressive phase of impact was calculated as the area under the force–deflection curve. System energy absorption was (on average) 3-fold greater for high compared to low BMI participants, but no effects of gender were observed. Even after normalizing for body mass, high BMI participants absorbed 1.8-fold more energy per unit mass. Additionally, three of four safety floors demonstrated significantly increased energy absorption compared to a baseline resilient-rolled-sheeting system (% increases ranging from 20.7 to 28.3). Peak system deflection was larger for high BMI persons and for impacts on several safety floors. This study indicates that energy absorption may be a common mechanism underlying the reduced risk of hip fracture for persons with high BMI and for those who fall on soft surfaces.     

Effect of upper and lower extremity control strategies on predicted injury risk during simulated forward falls: a study in healthy young adults

Fall-related wrist fractures are common at any age. We used a seven-link, sagittally symmetric, biomechanical model to test the hypothesis that systematically alterations in the configuration of the body during a forward fall from standing height can significantly influence the impact force on the wrists. Movement of each joint was accomplished by a pair of agonist and antagonist joint muscle torque actuators with assigned torque-angle, torque-velocity, and neuromuscular latency properties. Proportional-derivative joint controllers were used to achieve desired target body segment configurations in the pre- andor postground contact phases of the fall. Outcome measures included wrist impact forces and whole-body kinetic energy at impact in the best, and worst, case impact injury risk scenarios. The results showed that peak wrist impact force ranged from less than 1 kN to more than 2.5 kN, reflecting a fourfold difference in whole-body kinetic energy at impact (from less than 40 J to more than 160 J) over the range of precontact hip and knee joint angles used at impact. A reduction in the whole-body kinetic energy at impact was primarily associated with increasing negative work associated with hip flexion. Altering upper extremity configuration prior to impact significantly reduced the peak wrist impact force by up to 58% (from 919 N to 2212 N). Increased peak wrist impact forces associated greater shoulder flexion and less elbow flexion. Increasing postcontact arm retraction can reduce the peak wrist impact force by 28% (from 1491 N to 1078 N), but postcontact hip and knee rotations had a relatively small effect on the peak wrist impact force (8% reduction; from 1411 N to 1303 N). In summary, the choice of the joint control strategy during a forward fall can significantly affect the risk of wrist injury. The most effective strategy was to increase the negative work during hip flexion in order to dissipate kinetic energy thereby reducing the loss in potential energy prior to first impact. Extended hip or elbow configurations should be avoided in order to reduce forearm impact forces.     

The relation between hip impact velocity and hip impact force differs between sideways fall techniques.

Fall techniques that reduce fall severity may decrease the risk of hip fractures. A fundamental variable for fall severity is impact force, but impact velocity is also used. The purpose of the study was to determine whether impact velocity is valid to determine differences in fall severity between different techniques. Five young adults with martial arts (MA) experience performed sideways falls from kneeling height using three techniques: Block with arm (Block) and MA techniques with and without use of the arm to break the fall. In addition, one subject also performed MA falls from standing height. Linear regression analysis showed a moderate relation between hip impact velocity and force, which was depended on technique. In falls with comparable impact velocities, forces in MA falls were lower than forces in Block falls. Hence, differences in impact force could not be predicted by velocity. In conclusion, hip impact velocity may be useful to make an approximate prediction of impact force within fall techniques. However, to determine differences between techniques it was not always a valid predictor. When direct impact force measurements are not possible, methods combining impact velocity with energy estimates before and after impact might be more valid.     

Bone mineral density correlates with fracture load in experimental side impacts of the pelvis

Pelvic fractures resulting from automotive side impacts are associated with high mortality and morbidity, as well as substantial economic costs. Previous experimental studies have produced varying results regarding the tolerance of the pelvis to lateral force and compression. While bone mineral density (BMD) has been shown to correlate with fracture loads in the proximal femur, no such correlation has been established for the pelvis. Presently, we studied the relationships between total hip BMD and impact response parameters in lateral impacts of twelve isolated human pelves. The results indicated that total hip BMD significantly correlated with fracture force, Fmax, and maximum ring compression, Cmax, of the fractured pelves. These findings are evidence that BMD may be useful in assessing the risk of pelvic fracture in automotive side impacts. Poor correlation was observed between total hip BMD and maximum viscous response, (VC)max, energy at fracture, Epeak, and time to fracture, tpeak. Mean Fmax and calculated tolerances for Cmax and (VC)max were lower than those established in previous studies using full cadavers, likely a result of our removal of soft tissues from the pelves prior to impact.     

Could martial arts fall training be safe for persons with osteoporosis?: a feasibility study

Background

Osteoporosis is a well-established risk factor for fall-related hip fractures. Training fall arrest strategies, such as martial arts (MA) fall techniques, might be useful to prevent hip fractures in persons with osteoporosis, provided that the training itself is safe. This study was conducted to determine whether MA fall training would be safe for persons with osteoporosis extrapolated from the data of young adults and using stringent safety criteria.

Methods

Young adults performed sideways and forward MA falls from a kneeling position on both a judo mat and a mattress as well as from a standing position on a mattress. Hip impact forces and kinematic data were collected. For each condition, the highest hip impact force was compared with two safety criteria based on the femoral fracture load and the use of a hip protector.

Results

The highest hip impact force during the various fall conditions ranged between 1426 N and 3132 N. Sideways falls from a kneeling and standing position met the safety criteria if performed on the mattress (max 1426 N and 2012 N, respectively) but not if the falls from a kneeling position were performed on the judo mat (max 2219 N). Forward falls only met the safety criteria if performed from a kneeling position on the mattress (max 2006 N). Hence, forward falls from kneeling position on a judo mat (max 2474 N) and forward falls from standing position on the mattress (max 3132 N) did not meet both safety criteria.

Conclusions

Based on the data of young adults and safety criteria, the MA fall training was expected to be safe for persons with osteoporosis if appropriate safety measures are taken: during the training persons with osteoporosis should wear hip protectors that could attenuate the maximum hip impact force by at least 65%, perform the fall exercises on a thick mattress, and avoid forward fall exercises from a standing position. Hence, a modified MA fall training might be useful to reduce hip fracture risk in persons with osteoporosis.

     

Estimating severity of sideways fall using a generic multi linear regression model based on kinematic input variables

Many research groups have studied fall impact mechanics to understand how fall severity can be reduced to prevent hip fractures. Yet, direct impact force measurements with force plates are restricted to a very limited repertoire of experimental falls. The purpose of this study was to develop a generic model for estimating hip impact forces (i.e. fall severity) in in vivo sideways falls without the use of force plates.Twelve experienced judokas performed sideways Martial Arts (MA) and Block (‘natural’) falls on a force plate, both with and without a mat on top. Data were analyzed to determine the hip impact force and to derive 11 selected (subject-specific and kinematic) variables. Falls from kneeling height were used to perform a stepwise regression procedure to assess the effects of these input variables and build the model.The final model includes four input variables, involving one subject-specific measure and three kinematic variables: maximum upper body deceleration, body mass, shoulder angle at the instant of ‘maximum impact’ and maximum hip deceleration. The results showed that estimated and measured hip impact forces were linearly related (explained variances ranging from 46 to 63%). Hip impact forces of MA falls onto the mat from a standing position (3650 ± 916 N) estimated by the final model were comparable with measured values (3698 ± 689 N), even though these data were not used for training the model. In conclusion, a generic linear regression model was developed that enables the assessment of fall severity through kinematic measures of sideways falls, without using force plates.     

Active responses decrease impact forces at the hip and shoulder in falls to the side.

Active responses, such as using the arm to break the fall, may be an effective means of decreasing likelihood of injury in a fall and may help explain why only a small percentage of falls result in a fracture. We quantified the impact force at the hip and shoulder in falls to the side from a kneeling position under three conditions: (1) attempting to break the fall by using an arm; (2) falling with the body relaxed; and (3) falling with the body tensed. Subjects fell from a kneeling position onto a force platform array covered with foam padding and impact force data were recorded. The ground reaction force-time curve was generally bimodal due to sequential impacts of the hip and shoulder. Impact forces at the hip and shoulder were 12 and 16% less for the slap condition (p < 0.05) than for the tensed condition. The impact forces for the relaxed and tensed conditions were not significantly different, although impact forces tended to be less in the relaxed condition. We concluded that active responses reduce the impact forces experienced at the hip and shoulder in falls to the side. Decreased effectiveness of protective responses, due to increases in reaction time and decreases in strength with age, may help explain why so many hip fractures occur in the elderly but so few occur in younger people.     

Reducing hip fracture risk during sideways falls: evidence in young adults of the protective effects of impact to the hands and stepping

Hip fracture is rare in young adults, despite evidence that the energy available in a fall is sufficient to fracture the young proximal femur. This might be explained by protective responses that allow young individuals to avoid hip impact during sideways falls. To test this hypothesis, we conducted experiments with 44 individuals (31 women and 13 men) aged 19-26 years, who were instructed to try to maintain balance after a sudden unpredictable sideways translation was applied to the platform they stood upon. While the surface adjacent to the platform was formed of gymnasium mats, we provided no information on surface compliance, or the direction and speed of the perturbation. Ninety percent of participants fell and impacted the pelvis, and 98% of those cases involved direct impact to the hip region. Impact occurred to the hand in 98% of falls, and preceded impact to the pelvis by 50 ms on average (SD=40, range=-12-175 ms). The impact velocity of the pelvis decreased 3.6% for every 10 ms increase in the interval between hand and pelvis impact, and was reduced by 22% on average by stepping prior to impact. Our results suggest that the lack of hip fractures in young adults cannot be explained by avoidance of hip impact during sideways falls. Rather, it probably relates to use of the hands and stepping, and by simply possessing sufficient bone strength to withstand the direct blow to the greater trochanter that tends to accompany sideways falls.     

Reflex stiffness of man''s anti-gravity muscles during kneebends while carrying extra weights

The effective lumped stiffness and damping ratio of the human leg system was determined from measurements of parallel and antiparallel-mode oscillations while standing on a linear spring. Knee flexion angle was held fixed in each trial, and varied systematically from 0° to 75°. At each knee angle, subjects carried weights up to twice body weight on their shoulders to determine the effect of increasing muscle force. For small knee flexion angles (θ ≤ 30°), reflex stiffness was independent of muscle force, but rose slightly with muscle force for large flexions. The damping ratio was calculated to be 0.34, showing the underdamped character often reported for skeletomotor feflex mechanisms. Leg stiffness measured in this way is consistent with measurements taken during human running.     

Disturbance type and gait speed affect fall direction and impact location

Since falling to the side and impacting on or near the hip increase hip fracture risk, we examined the fall direction and pelvis impact location resulting from four disturbances (faint, slip, step down, trip) at three gait speeds (fast, normal, slow) in 14 young adults instructed not to attempt recovery. We hypothesized that certain disturbances such as faints and slips and slow walking speed were more likely to result in an impact on the hip. For each trial, the fall direction, impact location and pelvis impact velocity were measured. The results showed that both disturbance type and gait speed significantly affected fall direction and impact location (analysis of covariance with repeated measures, p< or =0.0001) with a significant interaction (p<0.05). Trips and steps down usually resulted in forward falls, with frontal impacts regardless of gait speed. At fast gait speed, slips and faints also usually resulted in forward falls, with frontal impacts. As gait speed decreased, however, slips usually resulted in sideways or backward falls, with impact on the hip or buttocks, and faints resulted in a greater number of sideways falls, with impact near the hip. Therefore, compared to other disturbances and gait speeds, slipping or fainting while walking slowly was more likely to result in an impact on the hip, suggesting a greater risk for hip fracture. Furthermore, 56% of the impact velocities generated were within one standard deviation of the estimate of the mean impact velocity needed to fracture an elderly femur.     

A single-spring model predicts the majority of variance in impact force during a fall onto the outstretched hand

The objective of this study was to validate a single-spring model in predicting measured impact forces during an outstretched arm falling scenario. Using an integrated force plate, impact forces were assessed from 10 young adults (5 males; 5 females), falling from planted knees onto outstretched arms, from a random order of drop heights: 3, 5, 7, 10, 15, 20, and 25 cm. A single-spring model incorporating body mass, drop height plus the estimated linear stiffness of the upper extremity (hand, wrist and arm) was used to predict impact force on the hand. We used an analysis of variance linearity test to test the validity of using a linear stiffness coefficient in the model. We used linear regression to assess variance (R²) in experimental impact force predicted by the single-spring model. We derived optimum linear stiffness coefficients for male, female and sex-combined. Our results indicated that the association between experimental and predicted impact forces was linear (P < 0.05). Explain variance in experimental impact force was R² = 0.82 for sex-combined, R² = 0.88 for males and R² = 0.84 for females. Optimum stiffness coefficients were 7436 N/m for sex-combined, 8989 N/m for males and 4527 N/m for females. In conclusion, a linear spring coefficient used in the single-spring model proved valid for predicting impact forces from fall heights up to 25 cm. Results also suggest the use of sex-specific spring coefficients when estimating impact force using the single-spring model. This model may improve impact force to bone strength ratios (factor-of-risk) and prediction of forearm and wrist fracture.     

Martial arts fall techniques decrease the impact forces at the hip during sideways falling

Falls to the side and those with impact on the hip are risky for hip fractures in the elderly. A previous study has indicated that martial arts (MA) fall techniques can reduce hip impact force, but the underlying mechanism is unknown. Furthermore, the high impact forces at the hand used to break the fall have raised concerns because of the risk for wrist fractures. The purpose of the study was to get insight into the role of hand impact, impact velocity, and trunk orientation in the reduction of hip impact force in MA techniques. Six experienced judokas performed sideways falls from kneeling height using three fall techniques: block with arm technique (control), MA technique with use of the arm to break the fall (MA-a), and MA technique without use of the arm (MA-na). The results showed that the MA-a and MA-na technique reduced the impact force by 27.5% and 30%, respectively. Impact velocity was significantly reduced in the MA falls. Trunk orientation was significantly less vertical in the MA-a falls. No significant differences were found between the MA techniques. It was concluded that the reduction in hip impact force was associated with a lower impact velocity and less vertical trunk orientation. Rolling after impact, which is characteristic for MA falls, is likely to contribute to the reduction of impact forces, as well. Using the arm to break the fall was not essential for the MA technique to reduce hip impact force. These findings provided support for the incorporation of MA fall techniques in fall prevention programs for elderly.     

Protective movements during sideways falls from standing height

To examine the effect of protective movements during sideways falls from standing height (i.e., from the standing position), a two-step study was performed. In the first step, 80 young male and female volunteers freely fell onto a sport-mat. All falls were recorded on videotape, and replayed to analyze movements in response to the falls. Several protective movements were observed; forward flexion and lateral flexion were observed with a particularly high frequency. In the second step, impact velocities of the head and hip were measured by a three-dimensional motion analyzer regarding three types of falls: stiff falls, forward flexion falls and lateral flexion falls. Both types of flexion reduced impact velocities of the head, but not those of the hip. The reduction of the impact velocity on the head correlated with the lowering of the height of the head from the floor.     

The Penn State Safety Floor: Part II--Reduction of fall-related peak impact forces on the femur.

The goal of this study was to develop and validate a finite element model (FEM) for use in the design of a flooring system that would provide a stable walking surface during normal locomotion but would also deform elastically under higher loads, such as those resulting from falls. The new flooring system is designed to reduce the peak force on the femoral neck during a lateral fall onto the hip. The new flooring system is passive in nature and exhibits two distinct stiffnesses. During normal activities, the floor remains essentially rigid. Upon impact, the floor collapses and becomes significantly softer. The flooring system consists of a multitude of columns supporting a continuous walking surface. The columns were designed to remain stiff up to a specific load and, after exceeding this load, to deform elastically. The flooring returns to its original shape after impact. Part I of this study presented finite element and experimental results demonstrating that the floor deflection during normal walking remained less than 2 mm. To facilitate the floor's development further, a nonlinear finite element model simulating the transient-impact response of a human hip against various floor configurations was developed. Nonlinearities included in the finite element models were: changing topology of deformable-body-to-deformable-body contact, snap-through buckling, soft tissue stiffness and damping, and large deformations. Experimental models developed for validating the finite element model included an anthropomorphic hip, an impact delivery mechanism, a data collection system, and four hand-fabricated floor tiles. The finite element model discussed in this study is shown to capture experimentally observed trends in peak femoral neck force reduction as a function of flooring design parameters. This study also indicates that a floor can be designed that deflects minimally during walking and reduces the peak force on the femoral neck during a fall-related impact by 15.2 percent.