Impulsive forces during walking and their clinical implications

Effect of a shock-absorbing pylon on transmission of heel strike forces during the gait of people with unilateral trans-tibial amputations: a pilot study

The primary objective was to test the hypothesis that walking with a shock-absorbing pylon (SAP) decreases the peak magnitude and frequency content of the heel-strike-initiated shock wave transmitted to the stump. The secondary hypotheses were that walking with a SAP decreases the heel-strike transient force between the ground and the foot and increases function as measured by walking velocity and subjective assessments. Seven people with unilateral trans-tibial amputations walked at self-selected speeds without and with a SAP. As the primary outcome measure, accelerometers were used mounted proximally and distally along the prosthetic pylon to measure the transmitted shock wave. Secondary measures included ground reaction forces from a force plate, a ten-minute walking test to determine walking speed and a questionnaire to evaluate gait function and subjective preference. The SAP provided no significant shock absorption as indicated by either the mean peak proximal accelerations of 3.19 g and 2.82 g (p = 0.28) without and with the SAP respectively or the mean difference between the peak proximal and distal accelerometers, 0.16 g and 0.19 g (p = 0.58). No significant change in the frequency content was found. Variances were high. There were no significant differences noted in the secondary measures. Although this study failed to identify any statistically significant effects due to the SAP, the magnitude and variance of the data will permit an accurate estimation of the appropriate sample size for future studies required to determine the efficacy of SAPs.

Joint Loading in the Lower Extremities during Elliptical Exercise

PURPOSE

To determine the joint loading during elliptical exercise (EE) by a detailed three-dimensional dynamic analysis, and to compare the results with those during level walking.

METHODS

Fifteen male adults performed level walking and EE while 3D kinematic data, right pedal reaction forces (PRF), and ground reaction forces (GRF) were measured. Pedal rate (cadence) and step length during EE without workload were set according to those measured during level walking for each subject. The motion of the body's center of mass, lower-limb-joint angles and moments were obtained.

RESULTS

Pedal rates and step lengths were 52.20 rpm (SD=2.34) and 50.56 cm (SD=2.14), respectively. During early stance the vertical PRF was smaller than the GRF, and the medial and posterior shear components were greater. PRF also occurred during swing. Loading rates around heelstrike during EE were all smaller than those during walking. During EE, the peak flexion angles of the hip, knee and ankle were greater. Peak hip flexor and knee extensor moments were also greater, whereas peak ankle plantarflexor moments and all abductor moments were smaller.

CONCLUSIONS

Different lower-limb kinematics and kinetics were found between EE and level walking. Smaller vertical PRF and loading rates during EE were achieved at the expense of greater hip flexor and knee extensor moments. Use of the elliptical trainer for athletic and rehabilitative training would have to consider users' joint function and muscle strength, especially at the knee, to avoid injuries.

A force plate study of avian gait

OBJECTIVE

To test the force plate as a gait analysis system for broilers and to determine how the ground reaction force (GRF) patterns change in these birds with growth and administration of analgesia.

MATERIALS AND METHODS

Thirty-three male Ross 308 chicks were raised on either an ad libitum or restricted-feeding regime, and subsequently treated with carprofen or a placebo. Vertical, craniocaudal and mediolateral GRFs were measured as the birds walked across a standard force plate.

RESULTS

The data were easy to collect, and peak vertical forces of an equivalent percentage of bodyweight as seen in human walking were identified. Mediolateral forces were 2-3 times greater than those demonstrated in other species. GRF patterns showed significant changes during growth, but analgesia did not have a significant effect on the speed of walking, or GRF patterns.

CONCLUSIONS AND CLINICAL RELEVANCE

The force plate is a suitable research tool for recording GRFs from avian bipeds. The large mediolateral forces identify a particularly inefficient aspect of avian gait; however, the role of pain remains to be determined.

Impulse-forces during walking are not increased in patients with knee osteoarthritis

BACKGROUND

Impulsive forces in the knee joint have been suspected to be a co-factor in the development and progression of knee osteoarthritis. We thus evaluated the impulsive sagittal ground reaction forces (iGRF), shock waves and lower extremity joint kinematics at heel strike during walking in knee osteoarthritis (OA) patients and compared them to those in healthy subjects.

SUBJECTS AND METHODS

We studied 9 OA patients and 10 healthy subjects using three-dimensional gait analyses concentrated on the heel strike. Impulse GRF (iGRF) was measured together with peak accelerations (PA) at the tibial tuberosity and sacrum. Sagittal lower extremity joint angles at heel strike were extracted from the gait analyses. As OA is painful and pain might alter movement strategies, the patient group was also evaluated following pain relief by intraarticular lidocaine injections.

RESULTS

The two groups showed similar iGRF, similar tibial and sacral PA, and similar joint angles at heel strike. Following pain relief, the OA patients struck the ground with more extended hip and knee joints and lower tibial PA compared to the painful condition. Although such changes occurred after pain relief, all parameters were within their normal ranges.

INTERPRETATION

OA patients and healthy subjects show similar impulse-forces and joint kinematics at heel strike. Following pain relief in the patient group, changes in tibial PA and in hip and knee joint angles were observed but these were still within the normal range. Our findings make us question the hypothesis that impulse-forces generated at heel strike during walking contribute to progression of OA.

Modelling the effect of prosthetic feet and shoes on the heel-ground contact force in amputee gait

Gait laboratory measurements have been widely used to explore footwear and prosthetic effects on intact and amputee gait in spite of the confounding effects of adaptation, acclimation and inherent variability of human subjects. To facilitate understanding of the variables that affect impact forces that arise from heel-ground contact during amputee walking, a lumped parameter model is proposed to simulate the movement of the human body, prosthetic components and footwear during the period immediately following initial contact. Non-linear viscoelastic properties of prosthetic feet have a proportional relationship to both the magnitude of the impact peak and the rate of increase in the ground reaction force (GRF) immediately following initial contact. Footwear, in spite of a larger capacity to dissipate impact energy than a prosthetic foot alone, can actually amplify the magnitude of the impact peak. These results suggest limitations in the ability of conventional prosthetic feet and footwear to attenuate transmission of potential tissue-damaging forces.

Handling of impact forces in inverse dynamics

In the standard inverse dynamic method, joint moments are assessed from ground reaction force data and position data, where segmental accelerations are calculated by numerical differentiation of position data after low-pass filtering. This method falls short in analyzing the impact phase, e.g. landing after a jump, by underestimating the contribution of the segmental accelerations to the joint moment assessment. This study tried to improve the inverse dynamics method for the assessment of knee moment by evaluating different cutoff frequencies in low-pass filtering of position data on the calculation of knee moment. Next to this, the effect of an inclusion of direct measurement of segmental acceleration using accelerometers to the inverse dynamics was evaluated. Evidence was obtained that during impact, the contribution of the ground reaction force to the sagittal knee moment was neutralized by the moments generated by very high segmental accelerations. Because the accelerometer-based method did not result in the expected improvement of the knee moment assessment during activities with high impacts, it is proposed to filter the ground reaction force with the same cutoff frequency as the calculated accelerations. When this precaution is not taken, the impact peaks in the moments can be considered as artifacts. On the basis of these findings, we recommend in the search to biomechanical explanations of chronic overuse injuries, like jumper's knee, not to consider the relation with impact peak force and impact peak moment.

Mechanical energy and effective foot mass during impact loading of walking and running

The human heel pad is considered an important structure for attenuation of the transient force caused by heel-strike. Although the mechanical properties of heel pads are relatively well understood, the mechanical energy (Etot) absorbed by the heel pad during the impact phase has never been documented directly because data on the effective foot mass (Meff) was previously unavailable during normal forward locomotion. In this study, we use the impulse-momentum method (IMM) for calculating Meff from moving subjects. Mass-spring-damper models were developed to evaluate errors and to examine the effects of pad property, upper body mass, and effective leg spring on Meff. We simultaneously collected ground reaction forces, pad deformation, and lower limb kinematics during impact phase of barefoot walking, running, and crouched walking. The latter was included to examine the effect of knee angle on Meff. The magnitude of Meff as a percentage of body mass (M(B)) varies with knee angle at impact and significantly differs among gaits: 6.3%M(B) in walking, 5.3%M(B) in running, and 3.7%M(B) in crouched walking. Our modeling results suggested that Meff is insensitive to heel pad resilience and effective leg stiffness. At the instant prior to heel strike, Etot ranges from 0.24 to 3.99 J. The combination of video and forceplate data used in this study allows analyses of Etot and Etot as a function of heel-strike kinematics during normal locomotion. Relationship between Meff and knee angle provides insights into how changes in posture moderate impact transients at different gaits.

The damping properties of the venous plexus of the heel region of the foot during simulated heelstrike

The damping mechanisms that are operational in the heel pad during the impact phase of locomotion have the important function to protect the musculo-skeletal system from injuries. How this is achieved is still not fully understood, as is for instance illustrated by the 'heel pad paradox', the observation that in vivo and in vitro experiments yielded widely different results. This paradox could so far only partially be explained. In the light of this paradox, and a previous study by our group, we conjectured that the venous plexus might contribute as a hydraulic shock absorber to the damping properties of the heel pad. To investigate this hypothesis in vivo, heel pads of 11 volunteers were subjected to pendulum impact tests, using velocities of 0.2, 0.4, and 0.6 m/s, and three physiologically different, consecutive conditions: (i) a relatively empty venous plexus, (ii) a congested venous plexus, and (iii) a decongested venous plexus. At congestion, the maximum impact force decreased slightly but significantly by 2.6% at 0.2 m/s and 1.8% at 0.4 m/s. This effect was no longer found at 0.6 m/s. Although these effects are rather small, they confirm the fundamental hypothesis that the venous plexus contributes to the damping properties of the heel pad during walking. It is likely that some underestimation of the effect has occurred.

Frequency-Domain Analysis Detects Previously Unidentified Changes in Ground Reaction Force with Visually Guided Foot Placement

Studies investigating the effect of targeting on gait have focused on the analysis of ground reaction force (GRF) within the time domain. Analysis within the frequency domain may be a more sensitive method for evaluating variations in GRF. The aim of the present study was to investigate the effect of visual targeting on GRF analyzed within the frequency domain. A within-subject repeated-measures design was used to measure the mediolateral, vertical, and antero-posterior components of the GRF of 11 healthy volunteers while walking at their own pace over a paper-covered walkway. A 30 × 24-cm target area was superimposed over a hidden Kistler force plate mounted at the midpoint of the walkway. GRF were recorded with and without the target and were analyzed within the frequency domain. Although visually guided foot placement has previously been undetected by traditional time-domain measures, targeting was found to significantly increase the frequency content of both the mediolateral (t10= -4.07,p <0.05) and antero-posterior (t10= -2.52,p <0.05) components of GRF. Consequently, it appears that frequency analysis is a more sensitive analytic technique for evaluating GRF. These findings have methodological implications for research in which GRF is used to characterize and assess anomalies in gait patterns.

Evaluation of ground reaction forces produced by chickens walking on a force plate

OBJECTIVE

To evaluate the use of a force plate as a method for objective gait analysis in adult poultry, to characterize ground reaction forces (GRFs) produced in adult chickens during normal walking, and to assess the variability of GRFs.

ANIMALS

18 clinically normal 5-month-old Brown Leghorn hens.

PROCEDURE

Vertical, craniocaudal, and mediolateral GRFs were measured as hens walked across a standard force plate embedded in the middle of a runway.

RESULTS

All GRFs were significantly affected by speed, and variability was high. With increasing speed, overall stance time decreased, but the percentage of stance time spent in braking or propulsion remained approximately equal. There was an overall increase in maximum propulsion force, which was produced at a greater rate over a shorter time; thus, propulsion integral decreased. Maximum braking forces and braking integrals were variable, but the rate at which the forces were generated increased. Mediolateral forces were 2 to 3 times greater in hens than values that have been reported for other species.

CONCLUSIONS AND CLINICAL RELEVANCE

A standard force plate can be used to objectively measure GRFs in walking adult hens; however, the large variation in the data suggests that the technique in its current form would be of limited clinical use. Overall, vertical and craniocaudal forces had similar characteristics to those of other species, whereas mediolateral forces were found to be much greater in chickens than for other species.

Fatigue-induced changes in decline running

OBJECTIVE

Study the relation between muscle fatigue during eccentric muscle contractions and kinematics of the legs in downhill running.

DESIGN

Decline running on a treadmill was used to acquire data on shock accelerations, muscle activity and kinematics, for comparison with level running.

BACKGROUND

In downhill running, local muscle fatigue is the cause of morphological muscle damage which leads to reduced attenuation of shock accelerations.

METHODS

Fourteen subjects ran on a treadmill above level-running anaerobic threshold speed for 30 min, in level and -4 degrees decline running. The following were monitored: metabolic fatigue by means of respiratory parameters; muscle fatigue of the quadriceps by means of elevation in myoelectric activity; and kinematic parameters including knee and ankle angles and hip vertical excursion by means of computerized videography. Data on shock transmission reported in previous studies were also used.

RESULTS

Quadriceps fatigue develops in parallel to an increasing vertical excursion of the hip in the stance phase of running, enabled by larger dorsi flexion of the ankle rather than by increased flexion of the knee.

CONCLUSIONS

The decrease in shock attenuation can be attributed to quadriceps muscle fatigue in parallel to increased vertical excursion of the hips.

Analysis of ground reaction forces by means of wavelet transform

OBJECTIVE

To identify details of clinical relevance in ground reaction forces by means of wavelet transform.

DESIGN

A retrospective analysis of gait tests performed by total knee replacement patients and a control population has been performed.

METHODS

The ground reaction forces have been processed by means of wavelet transform. Results of the wavelet analysis are represented, in a time-frequency plane, by tiles. These are coloured in different grey levels associated to the values of a suitable energy function of the expansion coefficients, resulting from the wavelet transform.

RESULTS

The high frequency tiles revealed the presence of irregularities with clinical significance in the first part of the stance phase. These transients in ground reaction forces are described in a quantitative manner allowing to monitor their evolution during the patient observation time. The heel strike transient has been identified by the tile representation of the vertical component of ground reaction forces and confirmed by its correlation with corresponding irregularities in the other components.

CONCLUSIONS

The tile representation allows to detect and to quantify details not easily perceivable by the examiner through traditional techniques. The wavelet transform seems particularly appealing for clinical applications such as outcome assessment or treatment evaluation and can assist in the definition of normative models of ground reaction forces. The effectiveness of the procedure suggest to try to automate it.

RELEVANCE

The tile representation allows to identify and to keep the records of ground reaction forces clinically significant details, such as heel strike transient.

Determining the protective function of sports footwear

To reduce the risk of injury associated with foot-ground interaction during sporting activities, there is a need for adequate assessment of the protective function of sports footwear. The present objectives are to review the typical biomechanical approaches used to identify protection offered by sports footwear during dynamic activities and to outline some of the recent methodological approaches aimed at improving this characterization. Attention is focused on biomechanical techniques that have been shown to best differentiate safety features of footwear. It was determined that subject tests would be used in combination with standard mechanical techniques to evaluate footwear protection. Impact attenuation characteristics of footwear during sporting activities were most distinguished by analysis of tibial shock signals in the frequency and joint time-frequency domains. It has been argued that lateral stability and traction properties of footwear are better assessed using game-like manoeuvres of subjects on the actual sporting surface. Furthermore, the ability of such tests to discriminate between shoes has been improved through methods aimed at reducing or accounting for variability in individual execution of dynamic manoeuvres. Advances in tools allowing measurement of dynamic foot function inside the shoe also aid our assessment of shoe protective performance. In combination, these newer approaches should provide more information for the design of safer sports footwear.

Relationship between quadriceps strength and rate of loading during gait in women

One function of skeletal muscle is to serve as the body's shock absorbers and thus dampen rates of loading during activity. The aim of this cross-sectional study was to determine the significance of muscle strength on rates of loading during gait. Thirty-seven women (mean age: 34.5 +/- 8.2 years) were solicited by advertisement and placed into one of two groups-strength-trained or sedentary-on the basis of training history. They walked (10 trials) over a 10-m walkway at a controlled speed of 1.22-1.35 m/s while the rate of loading was sampled with a 1,000-Hz force platform. Quadriceps and hamstring strength was measured at 90 degrees/s with an isokinetic dynamometer. Statistical analyses (p < 0.05) included descriptive statistics and unpaired t tests for comparison between groups. The women in the sedentary group weighed more and had significantly less concentric and eccentric strength of the quadriceps and hamstrings relative to body weight than did those in the strength-trained group. In addition, they demonstrated significantly higher rates of loading (2.21 +/- 0.15 compared with 1.75 +/- 0.08%wt/ms) than those in the strength-trained group.

Generation and attenuation of transient impulsive forces beneath the foot: a review

At the end of the swing phase of gait, the moving foot generates a transient force, due to the exchange of momentum as it contacts the ground. This review article examines the transient, which is known as the heelstrike in walking and the footstrike in running. The resulting 'shock wave', which passes up the limb, may produce damage, leading to degenerative joint disease and a variety of other pathologies. Protection against transient forces is provided by limb positioning at initial contact, by the anatomical heel pad, by materials used in shoe construction and by the use of viscoelastic shoe inserts.

Shock Transmission and Fatigue in Human Running

The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO2pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike–induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.

An investigation into the relation between step height and ground reaction forces in step exercise: a pilot study

The aim of this study was to investigate the effect that changing step height had on ground reaction force. Using a randomised crossover design, 12 volunteers with no previous experience of step aerobics were recruited to perform at three different step heights: 6, 8 and 10 inches. Subjects performed a basic step at a cadence of 120 beats/min and performed three one minute trials during which ground reaction force was measured. Measurement of peak impact force, time to achieve peak impact, and total time of foot contact was made, and impulse of the force was calculated. Statistically significant differences were found to exist for peak impact force between the 6 and 8 inch and 6 and 10 inch, but not between the 8 and 10 inch conditions. No significant differences were found in any other parameters. The study supports the present advice that participants should use low step heights, and possible mechanisms of injury are discussed.

Influences of inversion/eversion of the foot upon impact loading during locomotion

Pronation of the foot is believed to be one of the mechanisms used during locomotion to attenuate the loading experienced by the body at ground contact. The purpose of this study was to quantify the changes in loading induced by modifications to the normal pronation of the foot during walking and running. Impact loading in 10 subjects was determined using ground reaction force and tibial acceleration. The results indicated that impact loading was increased when normal pronation was prevented during running. However, there was no reduction in impact loading when normal pronation was exaggerated. RELEVANCE: Orthotic corrections are commonly prescribed to control excessive foot pronation in patients who experience knee pain. The findings of the present paper demonstrate that pronation modifications can affect the magnitude of the impact experienced by the body during locomotion. It was also found that the loading responses to pronation modifications were not consistent between walking and running. Thus care should be exercised when orthotics that will be used for both walking and running are prescribed. Furthermore, patients should be informed that their orthotics may be activity specific.

The redundant nature of locomotor optimization laws

A sagittal-plane model of the lower limb, which considered the possibility of antagonistic and synergistic muscle action and took account of the load-bearing roles of the cruciate ligaments, was applied to a dynamic analysis of level walking. It was hypothesized that: (1) the simple, one-sided constraints that intra-articular contact forces must be compressive and muscle and ligament forces tensile substantially reduce the redundancy of the load-transmitting structures of the lower limb, (2) many previously proposed optimization laws for muscle selection yield equivalent results, when they are applied to a finite set of admissible limiting solutions, and (3) the aforementioned optimization laws, when applied to a finite set of admissible limiting solutions, do not adequately predict the co-contraction of antagonistic muscles during gait. The problem of indeterminacy was resolved by considering all possible limiting solutions of the system unknowns on the dynamic equations. Although 498 limiting solutions of nine unknowns could arise at each sampled point on the gait cycle, the aforementioned one-sided constraints ruled out the large majority of them. It was shown that of the 498 possible, the minimum number of simultaneous admissible solutions for any subject was as few as three and the maximum number was only 18. The Principles of minimal total muscle force, squared muscle force, muscle stress, intra-articular contact force and instantaneous muscle power predicted remarkably similar patterns of muscle activity over the gait cycle. Of the six tested performance criteria, the Principle of minimal total ligament force was the least successful in terms of selecting solutions that closely matched the EMG patterns. This result implied that the muscles do not always act to protect the knee ligaments during gait. Finally, each of the above minimum principles failed to predict any antagonistic quadriceps-hamstrings action at the knee and hip around the event of heelstrike, although such activity was indicated by electromyography.

Relationship between foot placement and mediolateral ground reaction forces during running

This study investigated the relationship between foot placement relative to midline and mediolateral ground reaction forces during running. Data from 40 runners seen over a period of 2 years in a running injury clinic were analysed. A linear regression analysis revealed no significant relationship between foot placement and peak mediolateral values. Significance was found between foot placement and impulse, indicating that as the foot became more crossed over the lateral contribution to the total impulse increased (and vice versa). However, only 15% of the total variance in this model was accounted for. Despite these weak findings, subjects in the extreme range of foot placement (both wide-base and cross-over) appeared to exhibit stronger influences on mediolateral impulses. Therefore in the second phase of this study a symptom-free runner was tested while running with a 5-cm cross-over and wide-base gait, along with a neutral gait pattern. In the cross-over gait the contribution of the lateral impulse to the total impulse was 97%. Similar findings were noted with the medial contribution in the wide-based gait. Finally, the cross-over gait resembled the mediolateral force pattern observed during a 45-degree cut to the right (but exhibited lesser magnitudes), while the wide-base gait was similar to a cut to the left.

Cushioning properties of footwear during walking: accelerometer and force platform measurements

Repetitive impact loadings of the musculoskeletal system have been linked to the development of osteoarthritis and low back pain. An important function of footwear is to attenuate foot-ground impacts. The purpose of this study was to measure the effects of footwear types upon the impact ground reaction forces and the transient stress waves transmitted up the lower limb. The results have shown that both transient stress waves and ground reaction forces are affected by footwear during walking. Furthermore, with harder midsoles footwear, higher shock was transmitted to the lower extremities. This paper confirms the importance of using footwear to cushion the impact generated at heelstrike during walking. It also reveals that both shock and force measurements are required to evaluate and prescribe footwear to patients suffering from impact-related chronic diseases.

Long term comparison of some shock attenuating insoles

The effect of one years general use on the performance of four shock attenuating insoles is reported. Testing was carried out using the JP Biomechanics Shock Meter on twelve volunteers on a timed oval course at eight intervals during the year. The results show that two of the insoles perform well (Viscolas and PPT) although deterioration does occur after 6-9 months use; the other two insoles (Plastazote and Gait Aid) perform poorly. It is suggested that manufacturers provide some information to the user or supplier regarding the effective life of their products.

Influence of gait parameters on the loading of the lower limb

The ground reaction force which acts on the foot during normal walking consists of the sum of two components: the support of the weight of the body and the acceleration of the body. The relationships between the initial loading rate of the lower limb (ignoring the contribution of the heelstrike transient) and the general gait parameters--cadence, stride length, and velocity--have been examined. Plots of the resultant ground reaction force were used to calculate the loading rate of the limb. A sample of 13 normal male subjects, aged from 18 to 63 years, walked at five different self-selected speeds. Velocity showed the highest correlation with loading rate (r = 0.95) and stride length the lowest (r = 0.85). The relationship between cadence and loading rate was non-linear.