Importance of lumbar instability in the study of associations between muscle morphology, pain, and disability in chronic low back pain.

OBJECTIVE: The purpose of this study was to (1) evaluate the relationship between lumbar extensor muscle morphology, with pain and disability in patients with chronic low back pain (CLBP) and (2) compare these relationships in subgroup of CLBP with and without lumbar structural segmental instability. DESIGN AND METHODS: This cross-sectional study included 183 patients with CLBP. Standing lateral lumbar flexion/extension radiographs were used to assess lumbar structural segmental instability. Lumbar multifidus (MF), erector spinae (ES), and psoas major (PM) morphology were determined from axial magnetic resonance imaging. Associations between lumbar muscle morphologies and patient pain and disability were evaluated in two groups with and without lumbar instability. RESULTS: Patients' disability was negatively associated with PM total cross-sectional area (beta = -22.82, 95%CI = -37.05 to -8.59) and functional cross-sectional area (beta = -23.45, 95%CI = -37.81 to -9.09). MF morphology was negatively associated with disability in the lumbar instability group. Pain intensity was only associated to PM total cross-sectional area (Beta = -3.33, 95%CI = -6.43 to -2.24) and functional cross-sectional area (Beta = -3.22, 95%CI = -6.40 to -0.05) only in the lumbar instability group. CONCLUSION: PM atrophy was associated with greater disability and pain in CLBP, but MF atrophy was associated with greater disability in CLBP patients with lumbar structural segmental instability.

Effect of non-elastic taping on vertical stiffness of healthy athletes during a basketball jump shot.

BACKGROUND: Basketball is a high-risk team sport for lower extremity injuries, with ankle sprains being the most common injury. Non-elastic tape is widely used in injury prevention and quick return to play after ankle sprains, but its impact on stiffness, particularly global stiffness, has not been thoroughly investigated. OBJECTIVES: The aim of this study was to investigate the effects of non-elastic ankle taping on vertical stiffness, among basketball players during the jump shot tasks; and to assess the reliability of accelerometers to evaluate vertical stiffness. DESIGN: Single group, repeated measures study. PARTICIPANTS: Thirty healthy semi-professional basketball players (15 males and 15 females) participated in the study. INTERVENTIONS: Vertical stiffness was compared among three conditions: 1) without taping, 2) while the non-elastic tape was applied to their ankles, and 3) after running while taped. Vertical stiffness was calculated from acceleration data using a mass-spring model. RESULTS: The result of a one-way repeated measures ANOVA showed that vertical stiffness was not significantly different between the three conditions (P = 0.162). Within-day and between-day reliability for average measurements were found to be high or very high. CONCLUSION: The findings showed that the vertical stiffness is unaffected by non-elastic taping. Therefore, while non-elastic tape can limit ankle range of motion, it may not have an impact on vertical stiffness, a global parameter which reflects the musculoskeletal performance. On the other hand, the high reliability of the stiffness variable supports the use of an accelerometer as a small portable instrument for outdoor sports measurements.

Variability of Postural Coordination in Dual-Task Paradigm.

Postural control is influenced by cognition. In most studies, variability of motor output has been considered regardless of variability in patterns of joint coordination. Uncontrolled manifold framework has been applied to decompose the joint's variance in two components. The first component leaves position of the center of mass in anterior-posterior direction (CoMAP) unchanged (VUCM) while the second component is in charge of variations of CoM (VORT). In this study, 30 healthy young volunteers were recruited. The experimental protocol consisted of three random conditions: quiet standing on a narrow wooden block without a cognitive task (NB), quiet standing on a narrow wooden block with an easy cognitive task (NBE), and quiet standing on a narrow wooden block with a difficult cognitive task (NBD). Results showed that CoMAP sway in NB condition was higher than both NBE and NBD conditions (p = .001). VORT in NB condition was higher than NBE and NBD conditions (p = .003). VORT in NB condition was higher than NBE and NBD conditions (p = .003). VUCM was unchanged in all conditions (p = 1.00) and synergy index in NB condition was smaller than NBE and NBD conditions (p = .006). These results showed that postural synergies increased under dual-task conditions.

Coordination of the Lower Limbs of Soccer Players after Anterior Cruciate Ligament Reconstruction with Allograft and Autograft during Landing.

Objectives: Quantitative biomechanical tests, along with physical assessment, may be useful to understand kinematics associated with graft types in anterior cruciate ligament surgery, particularly in individuals aiming for a safe return to sport. Methods: Sixty male soccer players in three groups participated in this study. Three equal groups of healthy, auto transplanted and allotransplanted participants, matched for age, gender, activity level and functional status, landed with one foot on a force plate. Their kinematic information was recorded by the motion analyzer and used to describe coordination the variability by measuring coupling angles using vector coding. Results: The coordination variability of the allograft group in the surgical limb was significantly greater than that of the healthy group at least 9 months after the reconstructive surgery of the ACL and at the stage of return to sports, (F (6, 35) = 2.79, p = 0.025; Wilk's Λ = 0.676, partial η2 = 0.32). The coordination pattern in the surgical and healthy limbs of the surgical groups also differed from that of the healthy people, which was more pronounced in the allograft group, (F (6, 35) = 2.61, p = 0.034; Wilk's Λ = 0.690, partial η2 = 0.31). Conclusion: These results show that the allograft group has a different coordination variability at return to sport than the healthy group, so they may need more time for excessive training and competition.

Evaluation of orofacial force-related measures using a novel measuring device: explanation of associations with speech rate in dysarthria.

BACKGROUND: The aim of this study was to examine the potential associations between orofacial force-related measures and speech rate in matched groups of 23 adults with dysarthria, and 69 healthy adults. RESEARCH DESIGN AND METHODS: A novel piezoresistive sensor-based device was utilized to obtain the orofacial maximum forces (OMFs) and rate of force development (RFD) measures. The study computed alternating motion rates (AMRs), sequential motion rates (SMRs), and articulation rate (AR) for all participants. The analysis included between-group comparisons and correlation analyses. The study also examined the reliability of the OMFs and RFD measures. RESULTS: Individuals with dysarthria exhibited significantly slower speech rates (approximately 41.89% to 56.53% slower) compared to the control group. Except for a few exceptions in the jaw, the dysarthria group demonstrated significantly lower OMFs and RFD measures. The correlation analysis revealed that OMFs were weakly to moderately correlated (r = .488-.674) and RFD measures were very weak to moderately correlated (r = .047-.578) with speech rate measures. CONCLUSIONS: The findings suggest that reduced OMFs and RFD measures may contribute to the slowed speech rate observed in adults with dysarthria. The study also highlights that OMFs are significantly more reliable (day-to-day) than RFD measures.

Assessment of the effects of white cane variables on step symmetry of blind individuals.

BACKGROUND: Step symmetry is an important feature of human gait and is often regarded as a key index of healthy individuals' walking. This study evaluated the effects of height, white cane technique, and cane tip on symmetrical gait in blind individuals. MATERIALS AND METHODS: Twenty blind and ten sighted subjects, aged 15-38 years, participated in this study. The harmonic ratio (HR) and improved HR (iHR) were measured by trunk accelerometer as gait symmetry index in three axes: anteroposterior (AP), vertical, and mediolateral of the body. These parameters were measured in the sighted group in open-eye conditions and in the blind group in five experimental conditions with different two heights (standard and long), two tips (pencil and roller), and two techniques (two-point touch and constant contact) of white cane when they walked in the 6-m path. RESULTS: There was a significant difference between HR and iHR of the blind and sighted group, which indicates a significant reduction of symmetry loss in the blind group. Among the five different conditions studied in the group of blind people, an increase was observed in the HR and the iHR on the AP axis during the application of a standard cane with a roller tip, which indicated an increase in symmetry. CONCLUSION: Based on the results, a long cane with a pencil tip and a standard cane with a roller tip in the constant contact technique can increase step symmetry.

The Effect of Mental and Muscular Fatigue on the Accuracy and Kinematics of Dart Throwing.

In this study, we analyzed the effect of mental and muscular fatigue on the accuracy and kinematics of dart throwing. For this purpose, 28 young adults (19 females and 9 males) aged 25-35 years, without any regular experience in dart throwing, participated in this study. We evaluated their dart throwing skills in mental fatigue, muscular fatigue, and non-fatigue conditions. To induce mental fatigue, we used the Stroop task for 70 minutes and a simulated dart throwing exercise with an elastic band. In all three conditions, we collected accuracy data, based on the score of the dart on the board and the kinematic properties with a motion capture device. For analyzing the data and testing the research hypotheses, we employed ANOVA analyses with repeated measures after examining the normality of data distributions using skewness and kurtosis. We observed a significant decrease in the accuracy of dart throwing following mental fatigue (p = 0.027) and muscular fatigue (p = 0.001) compared to non-fatigue and following muscular fatigue compared to mental fatigue (p = 0.001). In the kinematic results, we observed a significant difference in the mean velocity of the elbow between different experimental conditions (p = 0.001). This variable decreased due to muscular fatigue, compared to the other two conditions. On the other hand, there was no significant difference among the three experimental conditions for the variables of elbow range of motion, shoulder range of motion, and mean velocity of the shoulder joint. These findings affirm mental and muscular fatigue effects on dart throwing and provide further detail regarding the specific aspects of these effects on dart throwing skills or other fine motor activities.

Single subject analysis of individual responses to prosthetic modifications based on passive dynamic walking model.

BACKGROUND: Group statistical analysis may mask individual differences in response to interaction with rehabilitative devices such as prostheses. This study sets out to evaluate the effect of asymmetric prosthesis using a single subject methodology on individuals with unilateral transfemoral amputation. METHODS: Acceleration data of 17 participants with unilateral transfemoral amputation were collected using a triaxial accelerometer attached at the L3 level of the spine during level ground walking under four prosthesis conditions: 1) no added mass; 2) the knee joint relocated downwards by 18% of the total shank length, shank mass decreased by 68%, thigh mass increased by 7%; 3) the knee joint relocated downwards by 37% of the total shank length, shank mass decreased by 68%, thigh mass increased by 7%, and 4) thigh mass increased 17%, shank mass decreased by 38%. Step length, step time, step length variability, step time variability and Floquet multiplier were statistically assessed. FINDINGS: The single subject analysis highlighted that under prosthetic modifications, intact limb step length was increased and prosthetic step length was deceased in most participants (n > 9). No significant changes were observed in Floquet multiplier (n > 14), step length (n > 6) and step time variability (n > 9) across all conditions. INTERPRETATION: Single subject analysis showed that in response to the immediate effect of asymmetric prosthesis, increase in the intact limb step length and decrease in the prosthetic limb step length emerged as a dominant strategy for most participants. Regarding Floquet multiplier, step length, and step time variability, our prosthetic modifications did not produce the anticipated effects.

Does the Extension Torque Control Differ between Injured and Uninjured Knees of ACL-Deficient Individuals?

Background: Knee extension torque control decreases after anterior cruciate ligament (ACL) rupture. There is a controversy in neuromuscular control changes on the uninvolved side. We intended to evaluate the steadiness and accuracy of quadriceps muscle control in the healthy and deficient sides of people with acute ACL rupture. Methods: In this cross-sectional study, thirteen men with ACL rupture (age: 27.8±7.0, body mass index (BMI): 24.7±2.25: 24.7, days from injury: 48.1±21.3) participated in the study. We measured quadriceps force control, which is quantitatively assessed by the standard deviation (SD) of joint torque for a predefined submaximal target. The accuracy of muscular control or performance of quadriceps is commonly quantified by the root mean square of error (RMSE) was also measured. A two-way analysis of variance was conducted to assess SD and RMSE of two levels of quadriceps contraction (30% of muscle voluntary contraction (MVC), 50% of MVC) across both healthy and deficient knees. Results: There was a significant main effect for SD and RMSE of MVC percentage (p<0.001). SD of quadriceps torque in 50% of MVC (1.44 ± 0.13) was higher than 30% of MVC (0.88 ± 0.1). In contrast, there was no significant main effect for SD and RMSE of knee condition. Conclusion: After unilateral ACL rupture, the neuromuscular system becomes defected and quadriceps muscle control is then reduced in the healthy side. Therefore, the healthy side is also vulnerable to ligamentous damage. Besides, with the increasing intensity of physical activities, neuromuscular control decreases and the risk of re-injury rises.

Relationship between the morphology and composition of the lumbar paraspinal and psoas muscles and lumbar intervertebral motion in chronic low-back pain: An exploratory study.

Muscles of the lumbar spine play an important role in controlling segmental intervertebral motion. This study aimed to evaluate the association between lumbar intervertebral motion and changes in lumbar morphology/composition in people with chronic low-back pain (CLBP). A sample of 183 patients with CLBP participated in this cross-sectional study. Participants underwent lumbar flexion-extension X-rays to determine vertebral motion (translational and/or rotational motion) of lumbar levels (L1-L2 to L5-S1) and lumbar spine magnetic resonance imaging to quantify total and functional cross-sectional areas (CSAs) and asymmetry of the multifidus (MF), lumbar erector spinae (LES), and psoas muscles. The relationship between morphology/composition of the muscles and lumbar intervertebral motion was investigated. Smaller total and functional CSAs of the MF and greater CSAs of the LES muscle were observed in participants with greater intervertebral motion. Muscle asymmetry was observed at different lumbar vertebral levels. The greatest amount of translational intervertebral motion was observed at the L3-L4 level, while the greatest amount of rotational translation occurred at the L4-L5. Associations were observed between the morphology of the paraspinal muscles at the vertebral levels adjacent to the L3-L4 level and the increased intervertebral motion at this level. Relationships between measures of muscle morphology/composition and increased segmental vertebral motion were observed. The results may provide a plausible biological reason for the effectiveness of rehabilitating deficient paraspinal muscles in a subset of people with CLBP.

Combining clinical exams can better predict lumbar spine radiographic instability.

BACKGROUND/OBJECTIVES: Several clinical tests have been proposed to diagnose lumbar instability, but their accuracy is still in question. The primary purpose of this study was to evaluate the diagnostic accuracy of the clinical lumbar instability tests. The secondary goal was to design a model to detect lumbar instability. DESIGN: A prospective diagnostic cross-sectional study. METHOD: A sample of 202 patients with chronic low back pain were participated in the study. Five lumbar instability tests including Aberrant movement, Passive lumbar extension, Prone segmental instability, H and I and pheasant tests were compared to flexion/extension radiography as the gold standard for diagnosing lumbar instability using two by two tables. Multiple Logistic Regression analysis was applied to develop a model using demographic information as well as the patients' pain intensity, disability level, lumbar lordosis and the clinical tests. RESULTS: Among the five examined tests, Prone segmental instability, H and I and pheasant tests showed very small likelihood ratios and diagnostic odd's ratio. The largest values were for H and I test with the positive likelihood ratio of 1.28 (95% CI: 0.72 to 2.29) and diagnostic odd's ratio of 1.37 (95% CI: 0.66 to 2.83); the diagnostic accuracy measures were smaller for the other studied clinical tests. The model was developed using weight (t = 1.15, p = 0.03) and lumbar lordosis (t = 3.04, p = 0.00) (which showed a significant relationship with lumbar instability) and prone segmental instability test. The final model has the positive likelihood ratio of 2.07 (95% CI: 1.41 to 3.05) and diagnostic odd's ratio of 3.77 (95% CI: 2.03 to 7.01). CONCLUSION: Each individual test had very small to no power in discriminating patients with lumbar instability. The developed model just slightly improved the accuracy of radiological instability detection.

Trunk Dynamic Stability Assessment for Individuals With and Without Nonspecific Low Back Pain During Repetitive Movement.

OBJECTIVE: This study aimed to employ nonlinear dynamic approaches to assess trunk dynamic stability with speed, symmetry, and load during repetitive flexion-extension (FE) movements for individuals with and without nonspecific low back pain (NSLBP). BACKGROUND: Repetitive trunk FE movement is a typical work-related LBP risk factor contingent on speed, symmetry, and load. Improper settings/adjustments of these control parameters could undermine the dynamic stability of the trunk, hence leading to low back injuries. The underlying stability mechanisms and associated control impairments during such dynamic movements remain elusive. METHOD: Thirty-eight male volunteers (19 healthy, 19 NSLBP) enrolled in the current study. All participants performed repetitive trunk FE movements at high/low speeds, in symmetric/asymmetric directions, with/without a wearable loaded vest. Trunk instantaneous rotation angle was computed for each trial to be assessed in terms of local and orbital stability, using maximum finite-time Lyapunov exponents (LyEs) and Floquet multipliers (FMs), respectively. RESULTS: Both groups demonstrated equivalent competency in terms of trunk control and stability, suggesting functional adaptation strategies may be used by the NSLBP group. Wearing the loaded vest magnified the effects of trunk control impairment for the NSLBP group. The combined presence of high-speed and symmetrical FE movements was associated with least trunk local stability. CONCLUSION: Nonlinear dynamic techniques, particularly LyE, are potentially effective for assessing trunk dynamic stability dysfunction for individuals with NSLBP during various activities. APPLICATION: This work can be applied toward the development of quantitative personalized spinal evaluation tools with a wide range of potential occupational and clinical applications.

Alteration of lumbar muscle morphology and composition in relation to low back pain: a systematic review and meta-analysis.

BACKGROUND CONTEXT: Previous studies have proposed that there is a relationship between low back pain (LBP) and morphology and composition of paraspinal muscles. However, results have been conflicting, especially regarding fatty infiltration of muscles. PURPOSE: The primary goal of this study was to review and analyze results from imaging studies which investigated morphological and composition changes in the multifidus, erector spinae and psoas major muscles in people with LBP. STUDY DESIGN/SETTING: Systematic review with meta-analysis. PATIENT SAMPLE: A patient sample was not required OUTCOME MEASURES: This review did not have outcome measures. METHODS: PubMed, Scopus, Web of Sciences, EMBASE and ProQuest were searched for eligible studies up to 31st July 2020 (all languages). A systematic search of electronic databases was conducted to identify studies investigating the association between the morphology and fat content of lumbar muscles in people with LBP compared with a (no LBP) control group. 13,795 articles were identified. Based on the screening for inclusion/ exclusion, 25 were included. The quality of the studies was evaluated using the Newcastle-Ottawa Scale. From the 25 articles, 20 were included in the meta-analysis. RESULTS: Results showed that the total cross-sectional area of the multifidus was smaller in people with LBP (Standardized mean difference, SMD = -0.24, 95% CI = -0.5 to 0.03). Combined SMDs showed a medium effect of LBP on increasing multifidus muscle fat infiltration (SMD = 0.61, 95% CI = 0.30 to 0.91). There were no LBP related differences identified in the morphology or composition of the lumbar erector spine and psoas major muscles. CONCLUSIONS: People with LBP were found to have somewhat smaller multifidus muscles with a significant amount of intramuscular fat infiltration. Varying sample size, age and BMI of participants, quality of studies and the procedures used to measure fat infiltration are possible reasons for inconsistencies in results of previous studies.

Revisiting the lumbosacral orthosis from the perspective of dynamical systems theory: a preliminary randomized clinical trial on patients with chronic low back pain.

BACKGROUND: The prevalent method for investigating the effect of therapeutic interventions on walking in the individuals with chronic low back pain (CLBP) is component-level approach in which all measurements focus on the spine component alone. However, this approach cannot disclose information about the overall function of the movement system such as complex walking patterns, which, in turn, reveal the underlying movement control. OBJECTIVES: To compare the effect of 3-week wearing of lumbosacral orthosis (LSO) along with routine physical therapy with routine physical therapy alone on walking complexity in the individuals with nonspecific CLBP on the basis of the systems approach. STUDY DESIGN: Preliminary randomized clinical trial. METHODS: Twenty-four subjects were randomly allocated to two groups. The control group received the routine physical therapy for 3 weeks. The intervention group received the same program plus an LSO. Nonlinear analysis was used to quantify walking complexity, as behavior of the entire movement system, before and after the intervention and at 1-month follow-up. RESULTS: An average of 496 strides during ten minutes of walking was used for analysis. There was no significant difference (p > 0.05) in degree of walking complexity between two groups during all evaluation periods. CONCLUSIONS: The administered orthotic intervention did not alter walking complexity. This suggests that therapeutic goal of current LSOs, which is not based on the systems approach, cannot recover the emergent behavior of the movement system. This may be a potential source of controversies. CLINICAL RELEVANCE: To achieve an effective treatment, orthotists should focus on the individuals themselves, not only on their CLBP symptoms. Although the component-level approach aims to decrease the symptoms, the systems approach focuses on the whole context that fosters LBP symptoms.

Ground reaction force complexity in hallux valgus.

BACKGROUND: Investigating the complexity of movement systems can be insightful in clinical decision making. The study conducted to evaluate whether complexity of ground reaction force is affected by hallux valgus grades and footwear or foot side conditions. METHODS: A sample of 120 females including 30 participants in each group of healthy and mild, moderate, and severe hallux valgus were recruited in this case-control study. Hallux valgus grades were assessed using Manchester scale. Ground reaction force were measured in bare foot and shod conditions for both feet and weighted permutation entropy was used to calculate the complexity. Nonparametric tests were employed for statistical inference. FINDINGS: The first important result was that hallux valgus caused loss of complexity of ground reaction force with a medium to large effect size. However, we did not find any difference between three grades of hallux valgus entropy. The second finding was that entropy of healthy group decreased from barefoot to shod condition with a large effect size and the third finding was that ground reaction force entropy were similar in both feet. INTERPRETATION: The findings are aligned with the theory that loss of complexity appears when the biological systems become functionally impaired. As soon as hallux valgus initiates, all potential risks related to the reduction of complexity appear. So, we suggest to administer conservative treatments in the early stages of hallux valgus. The study outcomes can be used for evaluation of foot function, classification of the foot types, or footwear selection.

Foot structural factors and ground reaction force in hallux valgus grades.

BACKGROUND: Little attention has been paid to foot structural factors and ground reaction force in hallux valgus. Investigating the structural factors in detail and determining their biomechanical effects can help to better manage hallux valgus. METHODS: In this case-control study, 120 females, 90 hallux valgus and 30 healthy, were recruited. Hallux valgus grades (mild, moderate, severe), first metatarsal mobility, foot pronation, hallux rotation, and pain were assessed by clinical tests. Ground reaction forces were measured in barefoot and shod conditions for both feet and analyzed using mixed within-between MANOVA. The association between structural factors and pain with force was analyzed using Spearman correlation coefficient. RESULTS: The frequency of foot structural factors and pain severity were reported in hallux valgus grades. A significant difference was seen in the force values between groups (P<0.001). Bonferroni post hoc test indicated that the mean of the first peak for the severe group was significantly higher than the mild group (P=0.013) and the mean of second peak for the moderate group was higher than that of the healthy group (P=0.009). The force values were affected by wearing shoe (P<0.001) but not by foot side (P=0.086). There was a medium, positive correlation between the hallux rotation and force in the moderate group (r=0.39, P=0.03) and also between the pronation and force in the severe group (r=0.36, P=0.04). CONCLUSION: Foot structural factors, pain, and force were different in each hallux valgus grads. Similar force in both feet, and increased force by wearing shoe were seen. The relationship between the pronation and hallux rotation with force revealed the importance of these factors from the biomechanical viewpoint.

Gait initiation and lateral wedge insole for individuals with early knee osteoarthritis.

BACKGROUND: People with knee osteoarthritis are at higher risk of postural deficits and locomotor adaptations which could be manifested in transient tasks like gait initiation. To better understand the effect of early knee osteoarthritis on gait initiation, we measured the gait initiation in two groups of early knee osteoarthritis and healthy age-matched controls and assessed the effect of lateral wedge insole in knee osteoarthritis group. METHODS: Twenty-one individuals with early knee osteoarthritis, mean (SD) age = 53.1 (7.4, years), and 19 age- and sex-matched asymptomatic healthy individuals, mean (SD) age = 47.5 (11.2, years), participated. Centre of pressure trajectories were used to quantify the two phases of gait initiation in barefoot condition: anticipatory postural adjustment, and locomotor phase. The immediate and four-week effect of lateral wedge insole and shod condition were also compared for individuals in knee osteoarthritis group. FINDINGS: Longer duration of anticipatory postural adjustment phase (P = 0.046), locomotor phase (P = 0.049), and total duration of gait initiation (P = 0.035) with lower length and velocity of the center of pressure trajectories in anticipatory postural adjustment phase (P = 0.002, and 0.008, respectively) were observed in knee osteoarthritis group compared to controls. Lateral wedge insole could increase the length and velocity of the centre of pressure in locomotor phase compared to barefoot condition (P = 0.001, and 0.002, respectively). INTERPRETATION: Our study outlined that people with early knee osteoarthritis adopt different gait initiation strategies mainly in postural preparation phase. The potential effect of lateral wedge insole was shown with better performance of the locomotor phase. CLINICAL TRIAL REGISTRY NUMBER: IRCT2016060628310N1.

Fatigue effects on the viscoelastic behavior of men and women in a landing task: a Mass-Spring-Damper modeling approach.

The aim of this study was to compare the fatigue effect on the viscoelastic behavior of the musculoskeletal system between the two sexes in a landing task. Stiffness and shock absorption capacity were studied from ground reaction force data using a mass-spring-damper model. A parametric simulation was also performed to demonstrate the effect of different values of model parameters on the vertical ground reaction force. Following fatigue, the shock absorption capacity reduced in men. According to the parametric simulation, this reduction can result in lower rate of force development which may make men less susceptible to impact injuries than women.

Experimental study of prosthesis modifications based on passive dynamic walking model: A limit cycle stability analysis.

The aim of the current study was to examine the effect of asymmetric prosthesis derived from the passive dynamic walking (PDW) concept on dynamic stability and symmetry in unilateral transfemoral amputees. Seventeen transfemoral amputees were asked to walk on 77.8 m in preferred speed under four conditions: 1) no added mass, 2) the knee joint relocated downwards by 18% of the total shank length, shank mass decreased by 68%, thigh mass increased by 7%, 3) the knee joint relocated downwards by 37% of the total shank length, shank mass decreased by 68%, thigh mass increased by 7% and 4) thigh mass increased 17%, shank mass decreased by 38%. Trunk accelerations were recorded by a triaxle accelerometer, attached at the L3 level of spine. For each condition, stability (orbital and local), intra-limb step length and step time variability, step length and step time symmetry, were estimated from the vertical acceleration. Our findings showed no significant change in the orbital stability (P = 0.627) and the local stability (P = 0.748). In addition, no significant difference was found in the step length symmetry (P = 0.891), intra-limb step length variability (P > 0.234), the step time symmetry (P = 0.960) and intra-limb step time variability (P > 0.847) with the new prosthetic configurations. Our empirical findings indicate that contrary to the modeling predictions, manipulating physical parameters does not improve gait pattern in terms of stability, variability and symmetry in transfemoral amputees. It suggests that proposed modifications based on PDW cannot be directly applied to real human conditions without further elaborations.