Impulsive forces during walking and their clinical implications

Biomechanical Tradeoffs in Foot Function From Variations in Shoe Design

There is debate and confusion over how to evaluate the biomechanical effects of running shoe design. Here, we use an evolutionary perspective to analyze how key design features of running shoes alter the evolved biomechanics of the foot, creating a range of tradeoffs in force production and transmission that may affect performance and vulnerability to injury.

Association of tibial acceleration during walking to pain and impact loading in adults with knee osteoarthritis

BACKGROUND

Higher impact loading during walking is implicated in the pathogenesis of knee osteoarthritis. Accelerometry enables the measurement of peak tibial acceleration outside the laboratory. We characterized the relations of peak tibial acceleration to knee pain and impact loading during walking in adults with knee osteoarthritis.

METHODS

Adults with knee osteoarthritis reported knee pain then walked at a self-selected speed on an instrumented treadmill for 3 min with an ankle-worn inertial measurement unit. Ground reaction forces and tibial acceleration data were sampled for 1 min. Vertical impact peaks, and average and peak instantaneous load rates were determined and averaged across 10 steps. Peak tibial acceleration was extracted for all steps and averaged. Pearson's correlations and multiple linear regression analyses assessed the relation of peak tibial acceleration to pain and impact loading metrics, independently and after controlling for gait speed and pain.

FINDINGS

Higher peak tibial acceleration was associated with worse knee pain (r = 0.39; p = 0.01), and higher vertical average (r = 0.40; p = 0.01) and instantaneous (r = 0.46; p = 0.004) load rates. After adjusting for gait speed and pain, peak tibial acceleration was a significant predictor of vertical average (R2 = 0.33; p = 0.003) and instantaneous (R2 = 0.28; p = 0.02) load rates, but not strongly associated with vertical impact peak.

INTERPRETATIONS

Peak tibial acceleration during walking is associated with knee pain and vertical load rates in those with knee osteoarthritis. Clinicians can easily access measures of peak tibial acceleration with wearable sensors equipped with accelerometers. Future work should determine the feasibility of improving patient outcomes by using peak tibial acceleration to inform clinical management.

Modulating Energy Among Foot-Ankle Complex With an Unpowered Exoskeleton Improves Human Walking Economy

Over the course of both evolution and development, the human musculoskeletal system has been well shaped for the cushion function of the foot during foot-strike and the impulsive function of the ankle joint during push-off. Nevertheless, an efficient energy interaction between foot structure and ankle joint is still lacking in the human body itself, which may limit the further potential of economical walking. Here we showed the metabolic expenditure of walking can be lessened by an unpowered exoskeleton robot that modulates energy among the foot-ankle complex towards a more effective direction. The unpowered exoskeleton recycles negative mechanical energy of the foot that is normally dissipated in heel-strike, retains the stored energy before mid-stance, and then transfers the energy to the ankle joint to assist the push-off. The modulation process of the exoskeleton consumes no input energy, yet reduces the metabolic cost of walking by 8.19 ± 0.96 % (mean ± s.e.m) for healthy subjects. The electromyography measurements demonstrate the activities of target ankle plantarflexors decreased significantly without added effort for the antagonistic muscle, suggesting the exoskeleton enhanced the subjects' energy efficiency of the foot-ankle complex in a natural manner. Furthermore, the exoskeleton also provides cushion assistance for walking, which leads to significantly decreased activity of the quadriceps muscle during heel-strike. Rather than strengthening the functions of existing biological structures, developing the complementary energy loop that does not exist in the human body itself also shows its potential for gait assistance.

Walking Speed Alters Barefoot Gait Coordination and Variability

Using the dynamic system approach, we examined the pattern and variability of inter-joint coordination in barefoot and shod walking in 20 women at three speeds: SLOW, FAST, and comfortable walking speed (CWS). We found that barefoot and shod walking used different coordination strategies to cope with increasing walking speed. As walking speed increased, ankle-knee coordination patterns between shod and barefoot became less different (p < 0.00001), and ankle-hip coordination patterns became more different (p < 0.001). Compared to shod, barefoot walking had significantly lower coordination variability in mid stance of knee-hip at CWS and FAST and late swing of ankle-hip at SLOW and CWS with medium effect (effect size 0.61-0.74). Future research should investigate the connection between the decreased coordination variability and joint tissue stress to understand the impact of barefoot walking on the lower extremity joints.

The menisci are not shock absorbers: A biomechanical and comparative perspective

The lateral and medial menisci are fibrocartilaginous structures in the knee that play a crucial role in normal knee biomechanics. However, one commonly cited role of the menisci is that they function as "shock absorbers." Here we provide a critique of this notion, drawing upon a review of comparative anatomical and biomechanical data from humans and other tetrapods. We first review those commonly, and often exclusively, cited studies in support of a shock absorption function and show that evidence for a shock absorptive function is dubious. We then review the evolutionary and comparative evidence to show that (1) the human menisci are unremarkable in morphology compared with most other tetrapods, and (2) "shock" during locomotion is uncommon, with humans standing out as one of the only tetrapods that regularly experiences high levels of shock during locomotion. A shock-absorption function does not explain the origin of menisci, nor are human menisci specialized in any way that would explain a unique shock-absorbing function during human gait. Finally, we show that (3) the material properties of menisci are distinctly poorly suited for energy dissipation and that (4) estimations of meniscal energy absorption based on published data are negligible, both in their absolute amount and in comparison to other well-accepted structures which mitigate shock during locomotion. The menisci are evolutionarily ancient structures crucial for joint congruity, load distribution, and stress reduction, among a number of other functions. However, the menisci are not meaningful shock absorbers, neither in tetrapods broadly, nor in humans.

Effects of prolonged load carriage on angular jerk of frontal and sagittal knee motion

BACKGROUND

During training, service members routinely walk with heavy body borne loads for long periods of time. These loads alter knee biomechanics and may produce jerky knee motions that reportedly increase joint loading and risk of musculoskeletal injury. Yet, it is unknown if service members use jerky knee motions during prolong walking with body borne load.

RESEARCH QUESTION

To quantify the effects of body borne load and duration of walking on the jerkiness of sagittal and frontal plane knee motion.

METHODS

Eighteen participants had angular jerk of knee motion quantified while they walked (1.3 m/s) for 60-min with three body borne loads (0, 15, and 30 kg). Peak and cost of angular jerk for sagittal and frontal plane knee motion was quantified and submitted to a repeated measures linear model to test the main effects and interaction of load (0, 15, and 30 kg) and time (0, 15, 30, 45, and 60 min).

RESULTS

Body borne load increased peak and cost of angular jerk for sagittal plane knee motion up to 35 % and 110 %, respectively, and frontal plane knee motion up to 20 % and 51 %, respectively (all p<0.001), while jerk cost of frontal plane knee motion (p=0.001) increased 31 % after walking 45 min.

SIGNIFICANCE

Body borne load produced large (between 20 % and 110 %), incremental increases in angular jerk for both sagittal and frontal plane knee motion; whereas, duration of walking led to a 31 % increase in jerkiness of frontal plane knee motion. Service members who often walking for long periods of time with heavy body borne loads may have greater risk of developing musculoskeletal injury and disease due to large increases in jerky knee motions.

Form in the context of function: Fundamentals of an energy effective striding walk, the role of the plantigrade foot and its expected size

What morphological and functional factors allow for the unique and characteristic upright striding walk of the hominin lineage? Predictive models of locomotion that arise from considering mechanisms of energy loss indicate that collision-like losses at the transition between stance limbs are important determinants of bipedal gait. Theoretical predictions argue that these collisional losses can be reduced by having "functional extra legs" which are physically the heel and the toe part of a single anatomical foot. The ideal spacing for these "functional legs" are up to a quarter of a stride length, depending on the model employed. We evaluate the foot in the context of the dynamics of a bipedal system and compare predictions of optimal foot size against empirical data from modern humans, the Laetoli footprint trackways, and chimpanzees walking bipedally. The dynamics-based modeling approach provides substantial insight into how, and why, walking works as it does, even though current models are too simple to make predictions at a level adequate to anticipate specific morphology except at the most general level.

Can Directed Compliant Running Reduce the Magnitude of Variables Associated With the Development of Running Injuries?

Ó Catháin, CP, Richter, C, and Moran, K. Can directed compliant running reduce the magnitude of variables associated with the development of running injuries? J Strength Cond Res XX(X): 000-000, 2020-Running is one of the most popular modes of activity worldwide and provides numerous health benefits. However, impact forces associated with the foot contacting the ground have been implicated in the development of running related injuries. As such, previous studies have used various methods to alter running to reduce the magnitude of these impact forces. However, it is unclear what kinematic changes facilitate this reduced loading or how loading further up the body changes. In this study, verbal direction was used to teach subjects to run with a more compliant running technique. Kinetic and kinematics characteristics of each subjects "normal" running technique and new "compliant technique" were measured in a fatigued and unfatigued state. Energy expenditure of each running style was also measured. Verbally directed compliant running significantly decreased (17%) vertical ground reaction force impact peaks, sacral (41%) and head (28%) impact accelerations, and increased energy expenditure (21%), in comparison with normal running. Findings suggest that verbally directed compliant running may reduce the magnitude of variables associated with the development of running injuries.

Effects of varus knee alignment on gait biomechanics and lower limb muscle activity in boys: A cross sectional study

BACKGROUND

There is evidence that frontal plane lower limb malalignment (e.g., genu varus) is a risk factor for knee osteoarthritis development. However, only scarce information is available on gait biomechanics and muscle activity in boys with genu varus.

RESEARCH QUESTION

To examine the effects of knee varus alignment on lower limb kinematics, kinetics and muscular activity during walking at self-selected speed in boys with genu varus versus healthy age-matched controls.

METHODS

Thirty-six boys were enrolled in this study and divided into a group of boys with genu varus (n = 18; age: 11.66 ± 1.64 years) and healthy controls (n = 18; age: 11.44 ± 1.78 years). Three-dimensional kinematics, ground reaction forces, loading rates, impulses and free moments of both limbs were recorded during five walking trials at self-selected speed. Surface electromyography was recorded for rectus femoris and vastus lateralis/medialis muscles.

RESULTS

No significant between-group differences were found for gait speed. Participants in the genu varus group versus controls showed larger peak knee flexion (p = 0.030; d = 0.77), peak knee adduction (p < 0.001; d = 1.63), and peak ankle eversion angles (p < 0.001; d = 2.06). Significantly higher peak ground reaction forces were found at heel contact (vertical [p = 0.002; d = 1.16] and posterior [p < 0.001; d = 1.63] components) and at push off (vertical [p = 0.010; d = 0.93] and anterior [p < 0.001; d = 1.34] components) for genu varus versus controls. Peak medial ground reaction force (p = 0.032; d = 0.76), vertical loading rate (p < 0.001; d = 1.52), anterior-posterior impulse (p = 0.011; d = 0.92), and peak negative free moment (p = 0.030; d = 0.77) were significantly higher in genu varus. Finally, time to reach peak forces was significantly shorter in genu varus boys compared with healthy controls (p < 0.01; d = 0.73-1.60). The genu varus group showed higher activities in vastus lateralis (p < 0.001; d = 1.82) and vastus medialis (p = 0.013; d = 0.90) during the loading phase of walking.

SIGNIFICANCE

Our study revealed genu varus specific gait characteristics and muscle activities. Greater knee adduction angle in genu varus boys may increase the load on the medial compartment of the knee joint. The observed characteristics in lower limb biomechanics and muscle activity could play a role in the early development of knee osteoarthritis in genu varus boys.

Ground reaction force metrics are not strongly correlated with tibial bone load when running across speeds and slopes: Implications for science, sport and wearable tech

INTRODUCTION

Tibial stress fractures are a common overuse injury resulting from the accumulation of bone microdamage due to repeated loading. Researchers and wearable device developers have sought to understand or predict stress fracture risks, and other injury risks, by monitoring the ground reaction force (GRF, the force between the foot and ground), or GRF correlates (e.g., tibial shock) captured via wearable sensors. Increases in GRF metrics are typically assumed to reflect increases in loading on internal biological structures (e.g., bones). The purpose of this study was to evaluate this assumption for running by testing if increases in GRF metrics were strongly correlated with increases in tibial compression force over a range of speeds and slopes.

METHODS

Ten healthy individuals performed running trials while we collected GRFs and kinematics. We assessed if commonly-used vertical GRF metrics (impact peak, loading rate, active peak, impulse) were strongly correlated with tibial load metrics (peak force, impulse).

RESULTS

On average, increases in GRF metrics were not strongly correlated with increases in tibial load metrics. For instance, correlating GRF impact peak and loading rate with peak tibial load resulted in r = -0.29±0.37 and r = -0.20±0.35 (inter-subject mean and standard deviation), respectively. We observed high inter-subject variability in correlations, though most coefficients were negligible, weak or moderate. Seventy-six of the 80 subject-specific correlation coefficients computed indicated that higher GRF metrics were not strongly correlated with higher tibial forces.

CONCLUSIONS

These results demonstrate that commonly-used GRF metrics can mislead our understanding of loading on internal structures, such as the tibia. Increases in GRF metrics should not be assumed to be an indicator of increases in tibial bone load or overuse injury risk during running. This has important implications for sports, wearable devices, and research on running-related injuries, affecting >50 scientific publications per year from 2015-2017.

Lower extremity joint stiffness during walking distinguishes children with and without autism

How children with Autism Spectrum Disorder (ASD) and peers with typical development (TD) modulate lower extremity stiffness during walking could identify a mechanism for gait differences between groups. We quantified differences in lower extremity joint stiffness and linear impulses, along the vertical and anterior/posterior axes during over-ground walking in children with ASD compared to age- and gender-matched children with TD. Nine age- and gender-matched pairs of children, aged 5-12 years, completed the current study. Joint stiffness and linear impulses were computed in four sub-phases of stance: loading response, mid-stance, terminal stance, and pre-swing. The Model Statistic technique (α = 0.05) was used to test for statistical significance between the matched-pairs for each variable and sub-phase. Furthermore, dependent t-tests (α = 0.05) were utilized, at the group level, to determine whether significant differences existed between sub-phases. Results indicate that children with ASD may exhibit greater stiffness in pre-swing, and thus, produce inefficient propulsive forces during walking. We attribute these differences to sensory processing dysfunction previously observed in children with ASD.

A systematic review of shock-attenuating componentry for lower limb amputees

BACKGROUND

Shock-attenuating pylons are commonly fitted to prostheses in order to compensate for the anatomical and biomechanical shock-absorbing features of the lower limb removed upon amputation. However, studies concerning their shock-attenuating capacity are highly variable and, to date, have not yet been reviewed, making them difficult to interpret and apply in clinical practice.

OBJECTIVES

To synthesise and appraise the available literature examining the effectiveness of shock-attenuating pylons in attenuating shock upon limb loading compared to rigid pylons among lower limb amputees.

STUDY DESIGN

Systematic review.

METHODS

A comprehensive search of seven databases was conducted using search terms concerning amputation level, shock-attenuating and rigid pylons as well as measures of shock attenuation. All studies yielded were screened against established inclusion and exclusion criteria before eligible articles were appraised using the Quality Assessment Standard for Crossover Studies adapted from the Cochrane handbook.

RESULTS

Nine articles were eligible for inclusion. While there was a trend among studies to indicate only a limited positive effect of shock-attenuating pylons in attenuating transient impact forces, limitations to the study designs, namely, in sampling, poor reporting of methodological details and heterogeneity of outcomes made conclusive interpretation of results difficult.

CONCLUSION

While the current body of literature does not reconcile with claims made by manufacturers of shock-attenuating pylons, it is insufficient to conclusively determine how effective shock-attenuating pylons are, in comparison with conventional rigid pylons, in attenuating transient impact forces among lower limb amputees. Higher quality research is required to better guide decisions regarding prescription of shock-attenuating componentry in clinical practice. Clinical relevance When delivered well, research can provide clinicians with objective and reliable data that can be applied in their practice to guide prescription of componentry. However, methodological limitations to research may compromise the reliability of findings, thereby producing potentially misleading outcomes. These limitations must be recognised and appreciated such that findings may be interpreted accurately and applied appropriately.

The effects of a simulated occupational kneeling exposure on squat mechanics and knee joint load during gait

Occupational kneeling is associated with an increased risk for tibiofemoral knee osteoarthritis. Forces on the knee in the kneeling posture, as well as the greater incidence of meniscus tears among workers, likely contribute to the increased risk. We hypothesise that an additional mechanism may contribute - altered neuromuscular control due to prolonged high knee flexion. Forty participants (20 male, 20 female) completed an evaluation of gait and squatting before, immediately following, and 30 min following a 30 min simulated occupational kneeling exposure. An increase in the peak external knee adduction moment and a delay in vastus medialis activation onset during walking were observed post-kneeling, as well as increased frontal plane knee motion during squatting. This was the first investigation to find changes in high flexion transitions as a result of kneeling. Greater frontal plane knee motion may increase the risk for meniscal tears, and subsequently, knee osteoarthritis. Practitioner Summary: A 30 min simulated occupational kneeling exposure resulted in small but significant gait changes. The greatest effect was on frontal plane knee movement during squatting, which is especially relevant to occupations requiring frequent kneeling/squatting. This increased motion may indicate an increased risk of injury, which supports a link to knee osteoarthritis.

Association between increase in vertical ground reaction force loading rate and pain level in women with patellofemoral pain after a patellofemoral joint loading protocol

BACKGROUND

The etiology of patellofemoral pain (PFP) is thought to be the result of increased patellofemoral joint (PFJ) load and aberrant lower extremity mechanics, including altered vertical ground reaction forces (VGRF). However, few studies have investigated the association between an increase in pain and VGRF loading rates in the context of PFP. Thus, this study aimed to investigate the immediate effects of PFJ loading on pain and VGRF loading rate, and to see if there is a link between modification of both pain and VGRF loading rate during stair negotiation.

METHODS

Thirty-four women with PFP underwent VGRF analysis during stair negotiation under two conditions: with (condition 2) and without (condition 1) being previously submitted to a PFJ loading protocol in order to or not to exacerbate their knee pain, respectively.

RESULTS

The VGRF loading rates were significantly higher in condition 2 (Mean ± standard deviation (SD)=4.0±0.6N/s) compared to condition 1 (Mean±SD=3.6±0.5N/s) during stair ascent and during stair descent (Mean±SD: condition 1=6.3±1.1N/s; condition 2=7.0±1.4N/s). In addition, VGRF loading rates were higher during stair descent compared to stair ascent in both conditions. There were significant correlations between the increase in pain and VGRF loading rate during both tasks.

CONCLUSION

There seemed to be an important relation between the increase in pain and VGRF loading rates in women with PFP. Based on these findings, interventions aimed at reducing VGRF loading rates are important in the context of PFP.

A three-year prospective comparative gait study between patients with ankle arthrodesis and arthroplasty

BACKGROUND

End-stage ankle arthritis is a debilitating condition that often requires surgical intervention after failed conservative treatments. Ankle arthrodesis is a common surgical option, especially for younger and highly active patients; however, ankle arthroplasty has become increasingly popular as advancements in implant design improve device longevity. The longitudinal differences in biomechanical outcomes between these surgical treatments remain indistinct, likely due to the challenges associated with objective study of a heterogeneous population.

METHODS

Patients scheduled for arthroplasty (n = 27) and arthrodesis (n = 20) were recruited to participate in this three-year prospective study. Postoperative functional outcomes were compared at distinct annual time increments using measures of gait analysis, average daily step count and survey score.

FINDINGS

Both surgical groups presented reduced pain, improved survey scores, and increased walking speed at the first-year postoperative session, which were generally consistent across the three-year follow-up. Arthrodesis patients walked with decreased sagittal ankle RoM, increased sagittal hip RoM, increased step length, and increased transient force at heel strike, postoperatively. Arthroplasty patients increased ankle RoM and cadence, with no changes in hip RoM, step length or heel strike transient force.

INTERPRETATION

Most postoperative changes were detected at the first-year follow-up session and maintained across the three-year time period. Despite generally favorable outcomes associated with both surgeries, several underlying postoperative biomechanical differences were detected, which may have long-term functional consequences. Furthermore, neither technique was able to completely restore gait biomechanics to the levels of the contralateral unaffected limb, leaving potential for the development of improved surgical and rehabilitative treatments.

Heel impact forces during barefoot versus minimally shod walking among Tarahumara subsistence farmers and urban Americans

Despite substantial recent interest in walking barefoot and in minimal footwear, little is known about potential differences in walking biomechanics when unshod versus minimally shod. To test the hypothesis that heel impact forces are similar during barefoot and minimally shod walking, we analysed ground reaction forces recorded in both conditions with a pedography platform among indigenous subsistence farmers, the Tarahumara of Mexico, who habitually wear minimal sandals, as well as among urban Americans wearing commercially available minimal sandals. Among both the Tarahumara (n = 35) and Americans (n = 30), impact peaks generated in sandals had significantly (p < 0.05) higher force magnitudes, slower loading rates and larger vertical impulses than during barefoot walking. These kinetic differences were partly due to individuals' significantly greater effective mass when walking in sandals. Our results indicate that, in general, people tread more lightly when walking barefoot than in minimal footwear. Further research is needed to test if the variations in impact peaks generated by walking barefoot or in minimal shoes have consequences for musculoskeletal health.

How does the canine paw pad attenuate ground impacts? A multi-layer cushion system

Macroscopic mechanical properties of digitigrade paw pads, such as non-linear elastic and variable stiffness, have been investigated in previous studies; however, little is known about the micro-scale structural characteristics of digitigrade paw pads, or the relationship between these characteristics and the exceptional cushioning of the pads. The digitigrade paw pad consists of a multi-layered structure, which is mainly comprised of a stratified epithelium layer, a dermis layer and a subcutaneous layer. The stratified epithelium layer and dermal papillae constitute the epidermis layer. Finite element analyses were carried out and showed that the epidermis layer effectively attenuated the ground impact across impact velocities of 0.05–0.4 m/s, and that the von Mises stresses were uniformly distributed in this layer. The dermis layer encompassing the subcutaneous layer can be viewed as a hydrostatic system, which can store, release and dissipate impact energy. All three layers in the paw pad work as a whole to meet the biomechanical requirements of animal locomotion. These findings provide insights into the biomechanical functioning of digitigrade paw pads and could be used to facilitate bio-inspired, ground-contacting component development for robots and machines, as well as contribute to footwear design.

Summary: This study examines the micro-scale structural characteristics of the digitigrade paw pad and analyses how these structures work together to further clarify the paw pad cushioning mechanism.

Vibration transmission of the spine during walking is different between the lumbar and thoracic regions in older adults

Background

fractures occur more commonly in the thoracic than in the lumbar spine. Physical activity complemented with pharmacological interventions has been advocated as a preventive measure for osteoporosis. However, walking has been shown to produce only a small improvement in spinal bone mineral density. The characteristics of vibration transmission during walking at the lumbar and thoracic spines may be different, and this may help explain the relative incidence of fractures in the two spine regions.

Objective

to determine how mechanical vibration is transmitted in the lumbar and thoracic spines in older adults with and without osteoporosis.

Methods

16 young healthy adults, 19 older adults without osteoporosis and 41 adults with osteoporosis were recruited. Inertial sensors were attached to the skin over the lumbar and thoracic spines for recording the vibration transmitted during level walking. Vibration characteristics were compared across lumbar and thoracic spines and across groups.

Results

the lumbar spine generally amplified the vibration transmitted during walking, whereas the thoracic spine exhibited a much smaller amplification effect, except at the lowest frequency. The magnitude of vibration was generally reduced in the older spines. Osteoporosis had minimal effects on vibration transmission.

Conclusions

the larger amplification of vibration in the lumbar spine may explain the lower incidence of vertebral fractures in this region when compared to the thoracic spine. Ageing alters the transmission of vibration in the spine while osteoporosis has minimal effects. Future research should determine the characteristics of vibration transmitted through the thoracic spine during other physical activities.

Impact loading following quadriceps strength training in individuals with medial knee osteoarthritis and varus alignment

BACKGROUND

Greater impact loading at initial contact is postulated to play a role in the progression of osteoarthritis. Quadriceps weakness is common in individuals with knee osteoarthritis and may contribute to high impact loading. The purpose of this study was to examine the effects of quadriceps strengthening on impact loading parameters.

METHODS

Data from 97 individuals with knee osteoarthritis who participated in a randomized clinical trial examining effects of a 12-week quadriceps strengthening program was used to conduct this secondary exploratory analysis. Participants completed a three-dimensional gait assessment within 10% of 1.0m/s from which maximum rate of loading (Body Weight/second), average rate of loading (Body Weight/second), and peak vertical ground reaction force during early stance (Body Weight) were determined. Peak isometric quadriceps strength (Nm/kg) was also assessed.

FINDINGS

There was a significant increase in quadriceps strength in the training group (mean change (95%CI): 0.35(0.25, 0.045) Nm/kg, P=0.01) with no change in the control group (mean change (95%CI): 0.03(-0.39, 0.45) Nm/kg, P>0.05). There were no changes in impact loading variables. With data from both groups combined, changes in quadriceps strength explained 3% of variance in the change in maximum rate of loading. Change in quadriceps strength was not predictive of the change in peak vertical ground reaction force or average rate of loading.

INTERPRETATIONS

While change in strength was predictive of change in maximal loading rate, this explained only a small proportion of the variance. Future research examining the role parameters such as neuromuscular control play in impact loading are warranted.

Loading rates during walking in adolescents with type II osteonecrosis secondary to pelvic osteotomy

Although Pemberton osteotomy has shown a high success rate even in older children, the occurrence of osteonecrosis (ON) remains one of the most severe complications, leading to premature osteoarthritis. Patients with type II ON are characterized by a valgus deformity of the proximal femur with altered musculoskeletal conditions, affecting the ability to attenuate or sustain the impulsive loading from the ground reaction force. It remains unclear whether these conditions also predispose these patients to harmful impulsive loadings. This study aimed to bridge the gap by measuring the loading rates in the lower limbs during level walking in adolescents who were treated during their infancy for unilateral developmental dysplasia of the hip by a pelvic osteotomy, with or without having developed type II ON. Patients with type II ON were found to display increased loading rates, not only at both the affected and unaffected hip, but also at other joints of the affected limb during level walking when compared to patients without ON changes (p < 0.05). These results suggest that patients with type II ON may be at a higher risk of developing premature hip osteoarthritis that is closely related to abnormal loading rates during gait. It is suggested that regular monitoring of joint loading rates in patients with type II ON is necessary for early identification of damaging loadings, and that early intervention aimed at reducing these loadings should be considered. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2199-2206, 2016.

Influence of heel design in an orthopedic shoe on ground reaction forces during walking

BACKGROUND

One of the treatments prescribed for musculoskeletal patients is orthopedic shoe. The use of an orthopedic shoe is thought to produce a more typical ground reactive force pattern.

OBJECTIVES

This study was designed to determine the influence of three heel designs of an orthopedic shoe on the ground reaction forces during walking in healthy subjects.

STUDY DESIGN

Quasi-experimental.

METHOD

In total, 30 healthy adults (12 males, 18 females) walked at a self-selected pace for six trials in each of the three shoe conditions having three different heels which included the following: standard heel, beveled heel, and positive posterior heel flare. For each trial, ground reaction force parameters were recorded using a force plate.

RESULTS

Repeated measures analysis of variance indicated that the impact force was significantly reduced for the positive posterior heel flare condition by 8% and 13% compared with standard and beveled heels, respectively (p < 0.001). The first peak of vertical force showed a significant reduction in the beveled heel by 5% and 4% compared with the standard heel and the positive posterior heel flare, respectively (p < 0.001). Loading rate was significantly reduced in the beveled heel and the positive posterior heel flare conditions (p < 0.05).

CONCLUSION

Positive posterior heel flare reduced impact force due to its geometry flexibility, while a beveled heel reduced first peak of vertical force. The findings of this study show that the shape of the heel therefore has the potential to modify impact loads during walking.

CLINICAL RELEVANCE

This study provides new evidence that by changing shape in the heel of orthopedic shoe impact loads are reduced during walking. Thus, these findings indicate that use of heel design may be beneficial for various musculoskeletal disorders, including key public health problems.

Effect of unilateral and bilateral use of laterally wedged insoles with arch supports on impact loading in medial knee osteoarthritis

BACKGROUND

Increased impact loading is implicated in knee osteoarthritis development and progression.

OBJECTIVES

This study examined the impact ground reaction force (GRF) peak, its loading rate, its relative timing to stance phase timing, and walking speed during unilateral and bilateral use of laterally wedged insoles with arch supports.

STUDY DESIGN

Within-subject design.

METHODS

Thirty-three female patients with medial knee osteoarthritis were examined with (unilateral 6° and 11°, and bilateral 0°, 6°, and 11°) and without insole use.

RESULTS

Repeated measures MANOVA revealed that the impact force increased significantly in bilateral 11° versus unilateral 6° and without-insole conditions. The loading rate decreased significantly in unilateral 11° versus bilateral 6° insoles. The relative timing increased significantly in each of bilateral 6°, bilateral 11°, and unilateral 11° versus bilateral 0° insoles and in each of bilateral 11° and unilateral 11° versus without-insole condition. There were significant positive correlations between the walking speed and each of the force and loading rate. The Chi-square test revealed insignificant association between the insole condition and the presence of impact forces.

CONCLUSION

Unilateral 11° insoles are capable of reducing impact loading possibly through increasing foot pronation. Walking slowly is another possible strategy to reduce loading.

CLINICAL RELEVANCE

Unilaterally applied 11° laterally wedged insoles are capable of reducing and delaying the initial impact ground reaction forces and reducing their loading rates during walking in patients with medial knee osteoarthritis, thus reducing osteoarthritis progression. Walking slowly could also be used as a strategy to reduce impact loading.

Shock attenuation properties at heel strike: Implications for the clinical management of the cavus foot

BACKGROUND

This study explored the relationship between foot types and corresponding variations in shock attenuating properties of the heel.

METHODS

Thirty matched participants were assigned to 3 groups: pronated, neutral, and supinated. A low-mass accelerometer was mounted to the calcaneus of the right leg of each participant.

RESULTS

Acceleration at heel strike for supinators was significantly higher than that in individuals with pronated and neutrally aligned feet. No significant difference was found in mean and maximum acceleration at heel strike between pronators and neutrals.

CONCLUSION

Cavus feet undergo significantly higher mean and maximum acceleration forces than neutrally aligned and pronated feet.

Does flip-flop style footwear modify ankle biomechanics and foot loading patterns?

BACKGROUND

Flip-flops are an item of footwear, which are rubber and loosely secured across the dorsal fore-foot. These are popular in warm climates; however are widely criticised for being detrimental to foot health and potentially modifying walking gait. Contemporary alternatives exist including FitFlop, which has a wider strap positioned closer to the ankle and a thicker, ergonomic, multi-density midsole. Therefore the current study investigated gait modifications when wearing flip-flop style footwear compared to barefoot walking. Additionally walking in a flip-flop was compared to that FitFlop alternative.

METHODS

Testing was undertaken on 40 participants (20 male and 20 female, mean ± 1 SD age 35.2 ± 10.2 years, B.M.I 24.8 ± 4.7 kg.m(-2)). Kinematic, kinetic and electromyographic gait parameters were collected while participants walked through a 3D capture volume over a force plate with the lower limbs defined using retro-reflective markers. Ankle angle in swing, frontal plane motion in stance and force loading rates at initial contact were compared. Statistical analysis utilised ANOVA to compare differences between experimental conditions.

RESULTS

The flip-flop footwear conditions altered gait parameters when compared to barefoot. Maximum ankle dorsiflexion in swing was greater in the flip-flop (7.6 ± 2.6°, p = 0.004) and FitFlop (8.5 ± 3.4°, p < 0.001) than barefoot (6.7 ± 2.6°). Significantly higher tibialis anterior activation was measured in terminal swing in FitFlop (32.6%, p < 0.001) and flip-flop (31.2%, p < 0.001) compared to barefoot. A faster heel velocity toward the floor was evident in the FitFlop (-.326 ± .068 m.s(-1), p < 0.001) and flip-flop (-.342 ± .074 m.s(-1), p < 0.001) compared to barefoot (-.170 ± .065 m.s(-1)). The FitFlop reduced frontal plane ankle peak eversion during stance (-3.5 ± 2.2°) compared to walking in the flip-flop (-4.4 ± 1.9°, p = 0.008) and barefoot (-4.3 ± 2.1°, p = 0.032). The FitFlop more effectively attenuated impact compared to the flip-flop, reducing the maximal instantaneous loading rate by 19% (p < 0.001).

CONCLUSIONS

Modifications to the sagittal plane ankle angle, frontal plane motion and characteristics of initial contact observed in barefoot walking occur in flip-flop footwear. The FitFlop may reduce risks traditionally associated with flip-flop footwear by reducing loading rate at heel strike and frontal plane motion at the ankle during stance.

Locomotor patterns in cerebellar ataxia

Several studies have demonstrated how cerebellar ataxia (CA) affects gait, resulting in deficits in multijoint coordination and stability. Nevertheless, how lesions of cerebellum influence the locomotor muscle pattern generation is still unclear. To better understand the effects of CA on locomotor output, here we investigated the idiosyncratic features of the spatiotemporal structure of leg muscle activity and impairments in the biomechanics of CA gait. To this end, we recorded the electromyographic (EMG) activity of 12 unilateral lower limb muscles and analyzed kinematic and kinetic parameters of 19 ataxic patients and 20 age-matched healthy subjects during overground walking. Neuromuscular control of gait in CA was characterized by a considerable widening of EMG bursts and significant temporal shifts in the center of activity due to overall enhanced muscle activation between late swing and mid-stance. Patients also demonstrated significant changes in the intersegmental coordination, an abnormal transient in the vertical ground reaction force and instability of limb loading at heel strike. The observed abnormalities in EMG patterns and foot loading correlated with the severity of pathology [International Cooperative Ataxia Rating Scale (ICARS), a clinical ataxia scale] and the changes in the biomechanical output. The findings provide new insights into the physiological role of cerebellum in optimizing the duration of muscle activity bursts and the control of appropriate foot loading during locomotion.

The effects of load carriage and muscle fatigue on lower-extremity joint mechanics

Military personnel are commonly afflicted by lower-extremity overuse injuries. Load carriage and muscular fatigue are major stressors during military basic training.

PURPOSE

To examine effects of load carriage and muscular fatigue on lower-extremity joint mechanics during walking.

METHOD

Eighteen men performed the following tasks: unloaded walking, walking with a 32-kg load, fatigued walking with a 32-kg load, and fatigued walking. After the second walking task, muscle fatigue was elicited through a fatiguing protocol consisting of metered step-ups and heel raises with a 16-kg load. Each walking task was performed at 1.67 m x s(-1) for 5 min. Walking movement was tracked by a VICON motion capture system at 120 Hz. Ground reaction forces were collected by a tandem force instrumented treadmill (AMTI) at 2,400 Hz. Lower-extremity joint mechanics were calculated in Visual 3D.

RESULTS

There was no interaction between load carriage and fatigue on lower-extremity joint mechanics (p > .05). Both load carriage and fatigue led to pronounced alterations of lower-extremity joint mechanics (p < .05). Load carriage resulted in increases of pelvis anterior tilt, hip and knee flexion at heel contact, and increases of hip, knee, and ankle joint moments and powers during weight acceptance. Muscle fatigue led to decreases of ankle dorsiflexion at heel contact, dorsiflexor moment, and joint power at weight acceptance. In addition, muscle fatigue increased demand for hip extensor moment and power at weight acceptance.

CONCLUSION

Statistically significant changes in lower-extremity joint mechanics during loaded and fatigued walking may expose military personnel to increased risk for overuse injuries.

Size-related changes in foot impact mechanics in hoofed mammals

Foot-ground impact is mechanically challenging for all animals, but how do large animals mitigate increased mass during foot impact? We hypothesized that impact force amplitude scales according to isometry in animals of increasing size through allometric scaling of related impact parameters. To test this, we measured limb kinetics and kinematics in 11 species of hoofed mammals ranging from 18-3157 kg body mass. We found impact force amplitude to be maintained proportional to size in hoofed mammals, but that other features of foot impact exhibit differential scaling patterns depending on the limb; forelimb parameters typically exhibit higher intercepts with lower scaling exponents than hind limb parameters. Our explorations of the size-related consequences of foot impact advance understanding of how body size influences limb morphology and function, foot design and locomotor behaviour.

Influence of barefoot, barefoot inspired and conventional shoes on tibial accelerations and loading kinetics during running in natural rearfoot strikers

Running barefoot and in footwear designed to mimic barefoot locomotion, has received considerable attention in footwear research. This study examined the differences in impact force and tibial acceleration parameters. Ten male participants completed 10 trials when running barefoot, in vibram five-fingers and in conventional footwear at three locomotion velocities: walk, jog and run (1.25, 3.5 and 5.0 m/s, respectively). Impact force and tibial acceleration parameters were synchronously obtained and contrasted between footwear and velocities using 3 (footwear) x 3 (velocity) repeated measures ANOVA's. Significant main effects were obtained for both footwear and velocity which suggest that barefoot running at higher velocities is associated with increases in impact loading magnitude. This leads to the conclusion that barefoot locomotion may be associated with increased risk of injury regardless of running velocity and that more specifically running barefoot at higher velocities should be undertaken with caution.

The 'impact' of force filtering cut-off frequency on the peak knee abduction moment during landing: artefact or 'artifiction'?

BACKGROUND

Joint moments computed using inverse dynamic techniques are important estimators of net joint loads. Joints moments computed from marker position and ground reaction force data filtered using different cut-off frequencies may capture changes in moment magnitudes at a single joint that exceed normal physiological response. Peak external knee abduction moment (KAM) generated during landing (ie, the drop vertical jump, DVJ) predicts anterior cruciate ligament injury risk using marker and force data filtered at different cut-off frequencies. The purpose of the current investigation was to determine the effects of using the same low cut-off frequencies versus different cut-off frequencies on joint moment magnitudes to evaluate if artificial smoothing attenuates actual resultant joint loads related to injury risk.

METHODS

Twenty-two female, high school volleyball players performed three maximum DVJs in a laboratory setting. The average peak KAM was computed for each knee using marker and force data filtered with the same low cut-off frequencies and different cut-off frequencies.

RESULTS

Peak KAMs were significantly larger using different cut-off frequencies. The order of athletes ranked based on the magnitude of their peak KAMs did not significantly change across all filtering cut-off frequencies.

CONCLUSIONS

The magnitude of peak KAM may differ when the same low or different higher cut-off frequencies are used to filter marker and ground reaction forces (GRF) data collected using standard motion capture equipment. It is not clear to what extent the decrease in peak KAM reported when the same low cut-off frequencies were used was solely due to attenuation of the GRF signal.

Loading rate patterns in scoliotic children during gait: the impact of the schoolbag carriage and the importance of its position

PURPOSE

Concerns have been raised regarding the effects of schoolbag carriage on adolescent schoolchildren and particularly those with a pre-existing spinal deformity. The purpose of this study was to determine the effect of school backpack loads in scoliotic and healthy school-age children during walking, in terms of peak vertical ground reaction forces and loading rates. We hypothesized that walking with a loaded backpack would have a greater effect on gait kinetics of scoliotic compared to healthy.

METHODS

Eight children with idiopathic scoliosis and eight healthy children were assessed. Kinetic data were collected using two AMTI OR6-7 force-plates, while the subjects walked freely along a 6-m walkway under three walking conditions: (1) without a schoolbag, (2) carrying a schoolbag bilaterally (over both shoulders-symmetrical load) and (3) carrying a schoolbag unilaterally (over each shoulder-asymmetrical load). Kinetic data were collected and four parameters were calculated; peak ground reaction force at the first maximum force peak (F1), time needed to reach F1 (T1), loading rate of F1 (LRF1) and total contact time (T2).

RESULTS

We found no significant differences between the scoliotic and healthy children for any of the kinetic variables examined. In addition, the position of the bag did not seem to have any effect on loading rate.

CONCLUSIONS

The results of this study indicate that in terms of kinetic parameters during normal gait, the schoolbag load (symmetrical or asymmetrical) does not have a different effect on children with mild adolescent idiopathic scoliosis compared to normal controls.

THE EFFECTS OF PEDAL RATES ON PEDAL REACTION FORCES DURING ELLIPTICAL EXERCISE

Despite the growing popularity in recent years of elliptical exercise (EE), little is known regarding the loadings applied to the body during EE. Since overloading to the body may lead to early fatigue of the muscles and increase the incidence of overuse injuries, such information is necessary for safe use of the elliptical trainer (ET) as a fitness tool. The current study aimed to determine the typical patterns and loading rates of the measured pedal reaction forces (PRF), and to quantify their differences from those during level walking, and the effects of pedaling rate. Fifteen male adults performed level walking and EE while 3D marker data, right PRFs and ground reaction forces (GRF) were measured. The parameters of the ET were set for two different pedal rates: 50 rpm and 70 rpm. For each pedal rate, the parameters were set to match the variables measured during level walking, with a mean step length of 55% leg length and no workload. During early stance the vertical PRF was smaller than the GRF, while the medial and posterior PRF were greater. PRFs also occurred during swing. Loading rates around heelstrike during EE were all smaller than those during walking. The medial, anterior and posterior PRF, as well as the medial and vertial loading rates increased with increasing pedal rates. The basic force patterns of EE and the effects of pedal rate were established in order to determine the true potential for such instrumentation in locomotion analysis. The results will be helpful for future related studies.

The impact of stochastic resonance electrical stimulation and knee sleeve on impulsive loading and muscle co-contraction during gait in knee osteoarthritis

BACKGROUND

Increased impulsive loading and muscle co-contraction during gait have been observed in individuals with knee osteoarthritis. Proprioceptive deficits in this population may contribute to these effects. Proprioception has been shown to improve with the combination of stochastic resonance electrical stimulation and a knee sleeve in knee osteoarthritis. Our goal was to determine whether stochastic resonance stimulation combined with a knee sleeve would decrease impulsive loading rates and muscle co-contraction during gait in knee osteoarthritis.

METHODS

Gait kinetics, kinematics and muscle activity were assessed during walking in subjects with knee osteoarthritis during three different conditions: no stochastic resonance/no sleeve (control), stochastic resonance at 75% threshold/sleeve, and no stochastic resonance/sleeve. Loading rates were calculated from the ground reaction force. Muscle co-contraction was calculated from the ratio of vastus lateralis to lateral hamstring activity. Differences between conditions were assessed using a repeated measures analysis of variance (P<0.05).

FINDINGS

The 75% threshold/sleeve and sleeve only conditions resulted in increased knee flexion at contact and reduced loading rates compared to the control condition (P<0.05). However, these measures did not significantly differ between the 75% threshold/sleeve and sleeve only conditions. Muscle co-contraction was found to decrease with the 75% threshold/sleeve condition compared to the other conditions.

INTERPRETATION

Increased knee flexion and decreased loading rates may be a result of proprioceptive improvements resulting from the sleeve or sleeve/stimulation combination. The stochastic resonance stimulation did not demonstrate an ability to enhance the effects of the sleeve with the exception of reductions in muscle co-contraction.

Human walking isn't all hard work: evidence of soft tissue contributions to energy dissipation and return

The muscles and tendons of the lower extremity are generally considered the dominant producers of positive and negative work during gait. However, soft-tissue deformations not captured by joint rotations might also dissipate, store and even return substantial energy to the body. A key locomotion event is the collision of the leg with the ground, which deforms soft tissues appreciably in running. Significant deformation might also result from the impulsive ground collision in walking. In a study of normal human walking (N=10; 0.7-2.0 m s(-1) speeds), we show indirect evidence for both negative and positive work performed by soft tissue, consistent with a damped elastic collision and rebound. We used the difference between measured joint work and another quantity - the work performed on the body center of mass - to indicate possible work performed by soft tissue. At 1.25 m s(-1), we estimated that soft tissue performs approximately 7.5 J of negative work per collision. This constitutes approximately 60% of the total negative collision work and 31% of the total negative work per stride. The amount of soft tissue work during collision increases sharply with speed. Each collision is followed by 4 J of soft tissue rebound that is also not captured by joint work measures. Soft tissue deformation may save muscles the effort of actively dissipating energy, and soft tissue elastic rebound could save up to 14% of the total positive work per stride. Soft tissues not only cushion impacts but also appear to perform substantial work.

Different knee joint loading patterns in ACL deficient copers and non-copers during walking

PURPOSE

Rupture of the anterior cruciate ligament (ACL) causes changes in the walking pattern. ACL deficient subjects classified as copers and non-copers have been observed to adopt different post-injury walking patterns. How these different patterns affect the knee compression and shear forces is unresolved. Thus, the aim of the present study was to investigate how different walking patterns observed between copers, non-copers, and controls affect the knee compression and shear forces during walking.

METHODS

Three-dimensional gait analyses were performed in copers (n = 9), non-copers (n = 10), and control subjects (n =19). The net knee joint moment, knee joint reaction forces, and the sagittal knee joint angle were input parameters to a biomechanical model that assessed the knee compression and shear forces.

RESULTS

The results showed that the non-copers walked with significantly reduced knee compression and shear forces than the controls. The overall knee compression force pattern was similar between the copers and controls, although this variable was significantly increased at heel strike in the copers compared to both non-copers and controls. The peak shear force was significantly dependent on the peak knee extensor moment. This covariance was significantly different between groups meaning that at a given knee extensor moment the shear force was significantly reduced in the copers compared to controls.

CONCLUSION

The different knee joint loading patterns observed between non-copers and copers reflected the different walking strategies adopted by these groups, which may have implications for the knee joint stability. The strategy adopted by the copers may resemble an effective way to stabilize the knee joint during walking after an ACL rupture and that the knee kinematics may play a key role for this strategy. It is clinically relevant to investigate if gait retraining would enable non-copers to walk as copers and thereby improve their knee joint stability.

Walking for fitness: is it enough to maintain both heart and bone health?

Exercising at levels of whole body accelerations exceeding 3.6 g has been shown to have positive effects on cardiovascular fitness, bone density and balance. This pilot research project evaluated the whole body accelerations and cardiovascular challenge provided by selected walks in the Canberra region of Australia to determine if walks could be ranked according to potential level of impact on both cardiovascular fitness and bone health. Nine participants, who described themselves as walking at least 3 km, three times per week, wore a data logging device recording heart rate, acceleration and GPS position while walking three outdoor tracks: (1) the running track of an athletics stadium; (2) on a hill climb path through bushland; and (3) on a route through suburban streets. There was a significant difference (P < 0.05) for heart rate, distribution of whole body accelerations and average walking speed between track 2 and tracks 1 and 3. There was a significant difference for heart rate, distribution of whole body accelerations and average walking speed between the walks. The running track and the suburban walk provide a moderate exercise challenge, with the hill climb walk providing progressively greater vertical height challenge, resulting in an increased cardiovascular exercise challenge. No participant effectively exceeded the threshold for achieving a positive impact on bone density (100 or more accelerations/day >3.6 g) on track 1, and only two of the nine participants intermittently achieved this threshold on tracks 2 and 3.

Design and Validation of a Knee Brace With Feedback to Reduce the Rate of Loading

The repetitive nature of walking can lead to repetitive stress and associated complications due to the rate of loading (ROL) experienced by the body at the initial contact of the foot with the ground. An individual’s gait kinematics at initial contact has been suggested to give rise to the ROL, and a repetitive, high ROL may lead to several disorders, including osteoarthritis. We present the design, development, and validation of a knee brace that provides feedback to the user during gait. The feedback consists of an auditory signal when the specific parameters of knee angle or tibial acceleration 50 ms prior to contact are exceeded. Nine women were recruited for the gait analysis, and the gait characteristics with and without the brace and feedback are analyzed. Our results indicate that using a knee brace with feedback can effectively change the gait kinematics used during walking, leading to a reduced ROL experienced at initial contact. Using a knee brace with feedback is a novel approach to gait retraining. Al-though the kinetics of how the subjects change in gait pattern is unknown, the reduced ROL experienced is significant and warrants further investigation.

Development and evaluation of a tool for the assessment of footwear characteristics

BACKGROUND

Footwear characteristics have been linked to falls in older adults and children, and the development of many musculoskeletal conditions. Due to the relationship between footwear and pathology, health professionals have a responsibility to consider footwear characteristics in the etiology and treatment of various patient presentations. In order for health professionals and researchers to accurately and efficiently critique an individual's footwear, a valid and reliable footwear assessment tool is required. The aim of this study was to develop a simple, efficient, and reliable footwear assessment tool potentially suitable for use in a range of patient populations.

METHODS

Consideration of previously published tools, other footwear related literature, and clinical considerations of three therapists were used to assist in the development of the tool. The tool was developed to cover fit, general features, general structure, motion control properties, cushioning, and wear patterns. A total of 15 participants (who provided two pairs of shoes each) were recruited, and assessment using the scale was completed on two separate occasions (separated by 1 - 3 weeks) by a physiotherapist and a podiatrist on each participant's dominant foot. Intra-rater and inter-rater reliability were evaluated using intra-class correlation coefficients (ICCs) (model 2, 1) and the 95% limits of agreement (95% LOAs) for continuous items, and percentage agreement and kappa (kappa) statistics for categorical items.

RESULTS

All categorical items demonstrated high percentage agreement statistic for intra-rater (83 - 100%) and inter-rater (83 - 100%) comparisons. With the exception of last shape and objective measures used to categorise the adequacy of length, excellent intra-rater (ICC = 0.91 - 1.00) and inter-rater reliability (ICC = 0.90 - 1.00) was indicated for continuous items in the tool, including the motion control properties scale (0.91 - 0.95).

CONCLUSION

A comprehensive footwear assessment tool with good face validity has been developed to assist future research and clinical footwear assessment. Generally good reliability amongst all items indicates that the tool can be used with confidence in research and clinical settings. Further research is now required to determine the clinical validity of each item in various patient populations.

Hitting a support surface at unexpected height during walking induces loading transients

The impact phase during walking is sometimes characterised by an early loading peak, termed 'transient', followed by a brief decline in the force profile, termed 'unloading phase'. It was hypothesized that transients occur more frequently when subjects are unaware of the landing condition, and that the unloading phase represents a yield of the leg. This was tested experimentally by introducing an unexpectedly lowered or level support surface height during walking. Furthermore, associations between the unloading phase and type of foot placement, load-rate, kinesiology and centre of pressure were investigated. The transient occurred more frequently when subjects were unaware of the surface height. The amplitude of unloading was higher in flatfooted (combined), as compared to heel and toe landings. The percentage of combined landings, as well as the amplitude and duration of unloading were highest in the first unexpected level trials (UL1) and gradually decreased in the subsequent level trials, when subjects adapted to the situation. Following the UL1 unloading phase, the foot roll-off was halted, the ipsilateral knee flexed, the onset of the contralateral swing phase was delayed, and the double support phase increased. The unloading amplitude correlated significantly with the load-rate and knee flexion. It is concluded that an unexpected surface height frequently induces an early stance transient that is followed by an unloading phase, flexion response and halt in foot roll-off. These characteristics deserve further study in the context of the frequent falls induced by uneven surfaces during walking.

Asymmetric knee loading at heel contact during walking in patients with unilateral knee replacement

Increased load on the knee joint by excessive levels of impact forces during initial contact has been suggested to lead to knee osteoarthritis (OA). Asymmetric loading after knee replacement may also relate to the development of OA in the contralateral limb, therefore this study investigated the heel strike transient vertical force and subsequent lower extremity kinematic, kinetic and spatio-temporal parameters during level walking between the operated and the contralateral limbs in patients 12 months following unilateral knee replacement. A six camera motion analysis system with a force plate was used to investigate the differences between limbs in the heel strike transient vertical GRF and its relative timing, and hip, knee and ankle angles and moments at initial contact, as well as spatio-temporal parameters during the stance phase of walking in 19 subjects with unilateral knee replacement. Paired t tests showed a significant difference in the contralateral limb relative to the operated limb in the heel strike transient magnitude (p=0.03), hip moment (p=0.01), knee moment (p=0.02) and ankle moment (p=0.03). No significant differences were found for the joint angles at heel contact or the spatio-temporal parameters (p>0.05). The heel strike transient magnitude was lower for the operated limb with no differences in the spatio-temporal parameters or the joint angles at initial contact between the limbs. Differences in the hip, knee and ankle moments were also found indicating an asymmetric loading of the impact force at initial contact on the lower extremity. The current findings may indicate an asymmetric loading on the knee joint and therefore may be clinically relevant in patients undergoing unilateral knee replacement.

Influence of pain and gender on impact loading during walking: a randomised trial

BACKGROUND

Knee joint osteoarthritis is painful and with an overweight of female incidence. The cardinal symptom is pain, which causes compensatory gait changes, and gender differences in pain sensitivity exist. Impact loadings at heel strike during walking are suspected as a co-factor in development of knee osteoarthritis. Thus the purpose of this study was to investigate the influence of experimental muscle pain and gender on generation and attenuation of impact loading during walking.

METHODS

Ten healthy males and 10 healthy females were recruited. Impact loadings during walking were measured using force platforms and accelerometers attached to the tibia and sacrum. Impact ground reaction force peaks and loading rates, and peak accelerations were used to quantify impact loadings. Attenuation was quantified by means of a transfer function between the tibial and sacral accelerometer signals, and the relative peak acceleration reduction. Knee joint kinematics were collected using a three-dimensional movement analysis system. The study was a cross-over study and data were collected before, during, and after experimental vastus medialis pain and a control situation.

FINDINGS

Experimental muscle pain did not affect generation or attenuation of impact loading in either gender. While the impact loading magnitude was similar across genders, lower loading rates and more efficient attenuation were observed in females.

INTERPRETATION

It is concluded that generation and attenuation of impact loadings during walking are independent of quadriceps pain in both genders. The present study does not provide any evidence of the tested variables to address the gender differences in loading rates and attenuation.