Heydar Sadeghi

Symmetry and limb dominance in able-bodied gait: a review

As one of the most universal of all human activities, gait in the able-bodied has received considerable attention, but many aspects still need to be clarified. Symmetry or asymmetry in the actions of the lower extremities during walking and the possible effect of laterality on gait are two prevalent and controversial issues. The purpose of this study was to review the work done over the last few decades in demonstrating: (a) whether or not the lower limbs behave symmetrically during able-bodied gait; and (b) how limb dominance affects the symmetrical or asymmetrical behavior of the lower extremities. The literature reviewed shows that gait symmetry has often been assumed, to simplify data collection and analysis. In contrast, asymmetrical behavior of the lower limbs during able-bodied ambulation was addressed in numerous investigations and was found to reflect natural functional differences between the lower extremities. These functional differences were probably related to the contribution of each limb in carrying out the tasks of propulsion and control during able-bodied walking. In current debates on gait symmetry in able-bodied subjects, laterality has been cited as an explanation for the existence of functional differences between the lower extremities, although a number of studies do not support the hypothesis of a relationship between gait symmetry and laterality. Further investigation is needed to demonstrate functional gait asymmetry and its relationship to laterality, taking into consideration the biomechanical aspects of gait.

Relations Between Standing Stability and Body Posture Parameters in Adolescent Idiopathic Scoliosis

Study Design. A retrospective study of standing imbalance and body posture in 71 able-bodied girls and subjects with adolescent idiopathic scoliosis was conducted. Objective. To test the hypothesis that postural parameters are related to standing stability parameters. Summary of Background Data. Spinal deformity not only modifies the shape of the trunk, but also changes the relations between body segments affecting posture in scoliotic children. These postural adaptations to the scoliotic curve progression could be linked in part to increased body sway in upright standing. This has not yet been related to specific postural parameters involving the head, trunk, and pelvis in nontreated idiopathic scoliosis. Methods. The head, trunk, and pelvis orientations of each subject were measured by a Flock of Bird system. An AMTI force platform was used to assess quiet standing stability and to monitor the position and displacement of the center of pressure (COP). The center of mass (COM) excursion was estimated from a biomechanical model using force plate information only. Analyses of variance (ANOVAS) were performed to determine the statistical differences between the scoliotic and nonscoliotic subjects, and backward stepwise multiple regression analyses were performed to identify any correlation between measures of quiet standing stability and body postural parameters Results. The scoliotic group was characterized by a decrease in standing stability. There was an increase in the sway areas measured by the variations of the COP and COM. From the backward stepwise multiple regression analysis, it appears that for the able-bodied girls, the body posture parameters were correlated only with the mean anteroposterior center of pressure (COPAP) position. For the scoliotic group, the sway areas and the mean position of the centers of pressure and the COPAP–COMAP were correlated significantly with body posture parameters. The higher COP–COM differences for the scoliotic group were attributed to a greater neuromuscular demand to maintain standing balance. The coefficients of correlation of the multiple regression analyses ranged from 0.64 to 0.85 for the nonscoliotic group and from 0.55 to 0.72 for the scoliotic group. Conclusions. The use of backward stepwise multiple correlations highlighted the interaction between several body parameters and their relation to standing stability in both able-bodied girls and scoliotic subjects. The scoliotic group displayed a much larger number of correlations between standing stability and body posture parameters than the nonscoliotic group. Standing imbalance was related to altered body posture parameters measured in the frontal and horizontal planes only. Although the correlation coefficients were relatively high, factors other than body posture parameters appeared related to standing imbalance in adolescent idiopathic scoliosis. These findings support the concept of either a primary or a secondary dysfunction in the postural regulation system of scoliotic subjects.

Functional gait asymmetry in able-bodied subjects

Abstract Symmetry is assumed in unilateral gait studies or when pooling right and left limb data. The purpose of this study was to identify which muscle powers and associated mechanical energies were related to the support and propulsion functions using Principal Component Analysis (PCA). Nineteen able-bodied male subjects participated in this study. They were all right-hand and leg dominant. Simultaneous bilateral three-dimensional data were collected from an eight-camera video system and two force plates. The PCA method was used to reduce and categorize the peak muscle powers and mechanical energies calculated at the hip, knee and ankle in each plane. Students t-test for paired data was applied to determine significant differences between the identified gait parameters. The limb which had a propulsion function was characterized by a strong third hip power at push off. Most of the parameters identified by the PCA were associated with the hip, and were mainly in the sagittal plane. These parameters were concentrated during push-off. There was a secondary support function which occurred during midstance. For the limb having a supporting function, most of its activities were associated with the knee, and were spread throughout the stance phase.

Local or global asymmetry in gait of people without impairments

Using two consecutive gait cycles, simultaneous and bilateral kinetic gait data, the main objectives of this study were (a) to identify the main functional roles of ankle, knee and hip extensors/flexors, and (b) to determine whether the action taken by these muscle groups appears to be symmetric or not. Gait of our able-bodied subjects appears to be asymmetric with significant differences noted between each two corresponding peak muscle moment values. Using principal component analysis (PCA) as a curve structure detection method, task discrepancies were recognized when comparisons were made between each two corresponding representative moment curves at each joint (local asymmetry). Muscle moment behaved symmetrically when the right limb representative curve was compared to its corresponding principal component (PC) at the contralateral limb. Gait of able-bodied subjects appears to be symmetric, while control and propulsion were recognized as two major roles of the extensors and flexors (global gait asymmetry). Symmetrical behavior of the lower limbs should be considered a consequence of local asymmetry which indicates different levels of within and between muscle activities developed at each joint during gait cycles.

Muscle power compensatory mechanisms in below-knee amputee gait

Sadeghi H, Allard P, Duhaime M: Muscle power compensatory mechanisms in below-knee amputee gait. Am J Phys Med Rehabil 2001;80:25–32. Objective This three-dimensional and bilateral gait study on five below-knee amputees was undertaken to demonstrate the following: (1) how hip muscle powers can compensate for the lack of ankle function on the amputated side; and (2) how these compensatory mechanisms can influence muscle power activities in the sound limb. Design Gait data were assessed by an eight-camera high-speed video system synchronized to two force plates. The three-dimensional mechanical muscle powers were calculated at the joints of the lower limbs. Significant differences between each limb were determined using the Student’s t test for paired data with P < 0.05. Results In the absence of ankle plantar flexor power, hip extensors and flexors as well as hip external rotators became the major power generators, whereas hip abductors and adductors and knee extensors muscle powers became the main source of absorption. For the sound limb, increased hip extensor activity was observed, accompanied by less hip abduction-adduction activity. Conclusions Perturbations in below-knee amputee gait affected the hip muscle powers on the amputated side in all three planes, although the hip frontal plane balance was modified in the sound limb.

Functional roles of ankle and hip sagittal muscle moments in able-bodied gait.

OBJECTIVE The main objectives of this study on able-bodied gait were (a) to identify the main functions of the ankle and hip muscle moments and their contribution to support and propulsion tasks, and (b) to illustrate the interaction between the ankle and hip moment activities. DESIGN Twenty young, able-bodied male subjects walked along a 13 m path at a freely chosen speed. BACKGROUND Functional contributions of the ankle and hip muscles and their interactions in achieving support and propulsion tasks during gait are still subject to controversy. METHODS Principal component analysis was applied as a curve structure detection method to identify the main functional characteristics of the ankle and hip muscle moments. The first two principal components which contained over 70% and 85%, respectively, of the information in the ankle and hip moment curves revealed their functional tasks. Ankle versus hip moment plots was used to illustrate the interactions between muscles acting at the hip and ankle in the sagittal plane. Correlation coefficient and covariance calculations quantified the interaction between the ankle and hip moments. RESULTS The first principal component revealed that the main role of the ankle and hip is to keep the body from collapsing. The second principal component is associated with the functional contribution of both ankle plantarflexors and hip flexors during the propulsion phase (50-60% of the gait cycle). High coordination (r=0.82) between the ankle and hip moments was observed. CONCLUSION Maintaining body support against gravity was identified as the first functional task of the ankle plantarflexors and hip extensors, while contribution to propulsion was recognised as the second major role for the ankle plantarflexors and hip flexors. RELEVANCE Identifying the main roles of the muscles acting at the hip and ankle during able-bodied walking provides better insight into how pathological gait should be evaluated.

Reduction of gait data variability using curve registration

Timing in peak gait values shifts slightly between gait trials. When averaged, the standard deviation (S.D.) in gait data may increase due to this inter-trial variability unless normalization is carried out beforehand. The objective of this study was to determine how curve registration, an alignment technique, can reduce inter-subject variability in gait data without perturbing the curve characteristics. Twenty young, healthy men participated in this study each providing a single gait trial. Gait was assessed by means of a four-camera high-speed video system synchronized to a force plate. A rigid body three-segment model was used in an inverse dynamic approach to calculate three-dimensional muscle powers at the hip, knee and ankle. Curve registration was applied to each of the 20 gait trials to align the peak powers. The mean registered peak powers increased by an average of 0.10 +/- 0.13 W/kg with the highest increases in the sagittal plane at push-off. After performing curve registration, the RMS values decreased by 13.6% and the greatest reduction occurred at the hip and knee, both in the sagittal plane. No important discontinuities were reported in the first and second derivatives of the unregistered and registered curves. Curve registration did not have much effect on the harmonic content. This would be an appropriate technique for application prior to any statistical analysis using able-bodied gait patterns.

Effect of trunk inclination on lower limb joint and lumbar moments in able men during the stance phase of gait

BACKGROUND Though the effect of imposed trunk posture affects walking patterns little is known about the effect of natural orientation of the trunk on gait. The objectives of this study are to test if the lower limb joint and thoraco-lumbar moments are similar in subjects who maintain an average natural forward or backward trunk inclination during gait and verify if the lower limbs are equally affected. METHODS Twenty-five young men were divided according to their natural backward or forward trunk inclination during level walking. Ankle, knee, hip and thoraco-lumbar moments were calculated by an inverse dynamic approach for the two limbs. A two-way ANOVA was performed on peak lower limb moments. A one-way ANOVA was performed on thoraco-lumbar peak moments. FINDINGS There was a main effect for both trunk inclinations and lower limb sides but no interaction. For the forward leaners, the duration of hip extension moment was longer (P<0.001) while the hip flexion moment was 1.3 times smaller (P<0.001). Differences between the lower limb sides were noted in all joints but at push-off of the stance phase only. The two thoraco-lumbar extension moments were, respectively, 1.4 times higher for the forward leaners while the two flexion moments were approximately 1.4 times higher for the backward leaners. INTERPRETATIONS The backward leaners propel themselves with a strong hip flexor activity at push-off while the forward leaners use their hip muscles throughout stance. These results support the idea that trunk inclinations and moment variations are associated with the type of walking patterns.

Principal component analysis of the power developed in the flexion/extension muscles of the hip in able-bodied gait.

This study was undertaken to demonstrate how principal component analysis (PCA) can be used: (a) to detect the main functional structure of actions taken by hip extensors and flexors during two consecutive gait cycles of able-bodied subjects, and (b) to determine whether or not symmetrical behaviour exists between right and left hip muscle power activity. Twenty young, healthy male subjects walked along a 13 m path at a freely-chosen speed. Applying curve structure detection methods such as PCA to walking patterns can provide insight into the functional tasks accomplished by the lower limbs of able-bodied and disabled subjects. PCA was applied as a classification and curve structure detection method to hip sagittal muscle power calculated for the right and left lower limbs. Over 70% of the information provided by the first four principal components (PCs) was chosen for further biomechanical interpretation. PC1 for both right and left sides mainly described the action taken by the hip extensors/flexors corresponding to the vertical component of ground force on the respective limbs during mid-stance. Propulsion and limb preparation were identified as the second and third tasks attributed to right hip muscle power, while between limb co-ordination was recognised as the second and third functional tasks of the left hip extensors/flexors. Balance was identified as the fourth main functional contribution of the hip extensors/flexors at the right limb while for the left limb, these muscles were mainly responsible for preparing the limb to enter into new gait cycle. PCA was able to identify the four main functional contributions of hip sagittal muscle power during able-bodied gait. PCA was also able to examine the existence of functional asymmetry in gait by highlighting different task priorities at the hip level for the right and left lower limbs.

Main functional roles of knee flexors/extensors in able-bodied gait using principal component analysis (I).

This study was undertaken to demonstrate how principal component analysis (PCA) can be used to detect the main functional structure of actions taken by knee flexors/extensors during able-bodied gait. PCA was applied as a classification and curve structure detection method for knee sagittal muscle moment developed during walking of 20 young, healthy male subjects. Over 90% of the information provided by the first three principal components (PCs) was chosen for further biomechanical interpretation. PCA was able to identify the three main functional contributions of knee sagittal muscle moment during able-bodied gait, namely control balance, foot clearance/limb preparation and shock absorption.