Calculating individual and total muscular translational stiffness: a knee example.

Research suggests that the knee joint may be dependent on an individual muscle's translational stiffness (KT) of the surrounding musculature to prevent or compensate for ligament tearing. Our primary goal was to develop an equation that calculates KT. We successfully derived such an equation that requires as input: a muscle's coordinates, force, and stiffness acting along its line of action. This equation can also be used to estimate the total joint muscular KT, in three orthogonal axes (AP: anterior-posterior; SI: superior-inferior; ML: medial-lateral), by summating individual muscle KT contributions for each axis. We then compared the estimates of our equation, using a commonly used knee model as input, to experimental data. Our total muscular KT predictions (44.0 N/mm), along the anterior/posterior axis (AP), matched the experimental data (52.2 N/mm) and was well within the expected variability (22.6 N/mm). We then estimated the total and individual muscular KT in two postures (0 deg and 90 deg of knee flexion), with muscles mathematically set to full activation. For both postures, total muscular KT was greatest along the SI-axis. The extensors provided the greatest KT for each posture and axis. Finally, we performed a sensitivity analysis to explore the influence of each input on the equation. It was found that pennation angle had the largest effect on SI KT, while muscle line of action coordinates largely influenced AP and ML muscular KT. This equation can be easily embedded within biomechanical models to calculate the individual and total muscular KT for any joint.

Reliability and validity of spinal coordination patterns during treadmill walking in persons with thoracic spine pain--a preliminary study.

BACKGROUND: Persons with low back pain fail to show the same transition as healthy individuals from in-phase to anti-phase rotation of the thorax and pelvis as walking speed increases. The purpose of this study was to determine if the relative phase of the thorax and pelvis during walking was a reliable (within day test-retest) and valid measure for persons with thoracic pain. METHODS: The time series motion of the spine over C7, T8 and sacrum were measured at five treadmill walking speeds (0.67, 0.89, 1.12, 1.34, 1.56 m/s) in 19 persons with thoracic spine pain and 19 healthy control subjects. After a 20 minute rest, all tests were repeated. The average relative phases of the transverse plane rotation between C7-T8, C7-sacrum and T8-sacrum during a one-minute walk were calculated. The standard error of measurement (SEM) and the intra-class correlation coefficient (ICC) were used to estimate test-retest reliability. Three-way repeated measures analyses of variance were performed to determine the influence of group, walking speed and session on the relative phases. RESULTS: The minimum transverse plane motion amplitudes, across all participants and speeds, for the C7-T8, C7-sacrum, and T8-sacrum were 2.9, 5.1 and 2.8 degrees, respectively. The C7-T8 relative phase changed little with speed. The C7-sacrum and T8-sacrum relative phases showed increases as subjects walked faster, but both groups had similar patterns of change. Only the C7-T8 relative phase at 0.67 and 0.89 m/s exhibited good reliability (ICC > 0.80, SEM 4.2-5.7, no significant time effects) for both groups. The C7-T8 and T8-sacrum relative phases demonstrated significant group by speed effects. CONCLUSIONS: The C7-T8 relative phase showed reasonable reliability and some discrimination between groups, but changes in response to walking speed were small. The T8-sacrum relative phase showed some discriminative ability, but reliability was not adequate.

Physical activity level is associated with the O2 cost of walking in cerebral palsy.

PURPOSE: To determine, in children and adolescents with cerebral palsy (CP), the relationship between physical activity level (PAL) and i) oxygen cost of walking, and ii) peak VO2. METHODS: In 11 subjects (10.6-16.3 yr) with mild CP, PAL, the ratio of total energy expenditure to resting energy expenditure, was determined from 3 d of heart rate (HR) monitoring (field), with individual HR-VO2 calibrations done in the lab. The oxygen cost of walking was measured during three 3-min walks on a treadmill at 60, 75, and 90% of each subject's fastest treadmill walking speed (FWS). Subjects also performed a maximal treadmill exercise test. Alpha was set at 0.05. RESULTS: One subject was an outlier and eliminated from all simple linear regression analyses. For the remaining 10 subjects, PAL (1.37+/-0.18) was related (r=-0.70 to -0.84) to net VO2 at 60 and 75% FWS (13.1+/-4.1 and 16.2+/-4.2 mL.kg.min), net VO2.m, averaged across the three speeds (0.32+/-0.23 mL.kg.m), and percent peak VO2 at all three speeds (54.5+/-21.5, 63.5+/-20.9, and 75.5+/-15.1%). PAL was not significantly related to net VO2 at 90% FWS (20.8+/-5.3 mL.kg.min) or to peak VO2 (34.0+/-9.2 mL.kg.min). CONCLUSION: For this population, those with low PAL may also have a high oxygen cost of walking. These individuals' PAL was not related to their peak VO2. Further research is required to determine whether interventions that decrease the oxygen cost of walking also affect PAL and whether changes in PAL affect the oxygen cost of walking.

Women with fibromyalgia walk with an altered muscle synergy.

Most individuals can use different movement and muscle recruitment patterns to perform a stated task but often only one pattern is selected which optimizes an unknown global objective given the individual's neuromusculoskeletal characteristics. Patients with fibromyalgia syndrome (FS), characterized by their chronic pain, reduced physical work capacity and muscular fatigue, could exhibit a different control signature compared to asymptomatic control volunteers (CV). To test this proposal, 22 women with FS, and 11 CV, were assessed in a gait analysis laboratory. Each subject walked repeatedly at self-selected slow, comfortable, and fast walking speeds. The gait analysis provided, for each walk, each subject's stride time, length, and velocity, and ground reaction force, and lower extremity joint kinematics, moments and powers. The data were then anthropometrically scaled and velocity normalized to reduce the influence of subject mass, leg length, and walking speed on the measured gait outcomes. Similarities and differences in the two groups' scaled and normalized gait patterns were then determined. Results show that FS and CV walk with externally similar stride lengths, times, and velocities, and joint angles and ground reaction forces but they use internally different muscle recruitment patterns. Specifically, FS preferentially power gait using their hip flexors instead of their ankle plantarflexors. Interestingly, CV use a similar muscle fatiguing recruitment pattern to walk fast which parallels the common complaint of fatigue reported by FS walking at comfortable speed.

Influence of treadmill design on rearfoot pronation during gait at different speeds.

Understanding the dynamic function of the rearfoot is necessary for recognizing and treating several types of mechanical foot dysfunction. Although the motion of the rearfoot is often measured during treadmill locomotion, the effect of different types of treadmills on the motion of the foot is unclear. In this study, the kinematics of the right subtalar joint in 24 volunteers walking at three speeds on two motorized treadmills were examined. The two treadmills (a wide width and a soft surface versus a narrow width and a hard surface) were selected to maximize motion differences. Maximal change in angular position (positive: supination; negative: pronation) about each volunteer's subtalar joint axis was estimated during three gait phases: weight acceptance, midstance, and push-off. A factorial, repeated-measures analysis of variance determined that the treadmill design had a significant effect on subtalar joint position (F = 5.423; P = .029), albeit with moderate power (0.61). Descriptively, collapsed over all speeds, the subject's feet on the narrow/hard compared with the wide/soft treadmill showed more pronation (0.44 degrees ), less pronation (0.46 degrees ), and more supination (1.44 degrees ) during weight acceptance, midstance, and push-off, respectively. We conclude that treadmill design can affect an individual's rearfoot kinematics.

Relationship between pain and vertebral motion in chronic low-back pain subjects.

OBJECTIVES: To investigate the relationship between intervertebral motion, intravertebral deformation and pain in chronic low-back pain patients. DESIGN: This study measured vertebral motion of the lumbar spine and associated pain in a select group of chronic low-back pain patients as they performed a standard battery of motions in all planes. BACKGROUND: Numerous studies have demonstrated that individuals with low-back pain have impaired spinal motion, yet few studies have examined the specific relationship between pain and motion parameters. Although it is accepted that the pain in mechanical low-back patients is due to specific spinal motions, no studies have related specific motions to pain measures. METHODS: Percutaneous intra-pedicle screws were placed into the right and left L4 (or L5) and S1 segments of nine chronic low-back pain patients. The external fixator frame was removed following the clinical external fixation test. The 3D locations of the pedicle screws and the level of pain were recorded as the subjects performed a battery of motions. The relationship between the pain and motion parameters was assessed using linear discriminant analysis and neural network models. RESULTS: The neural network model showed a strong relationship between observed and predicted pain (R(2)=0.997). The discriminant analysis showed a weak relationship (R(2)=0.5). CONCLUSIONS: Vertebral motion parameters are strongly predictive of pain in this select group of chronic low-back pain patients. The nature of the relationship is nonlinear and involves interactions; neural networks are able to effectively describe these relationships. RELEVANCE: Specific patterns of intervertebral motion and intravertebral deformation result in pain in chronic low-back pain patients. This substantiates the mechanical back pain aetiology.

Relationship between the subtalar joint inclination angle and the location of lower-extremity injuries.

This study hypothesized that individuals who have a history of knee pain during repetitive weightbearing activities have a higher subtalar joint inclination angle than those with a history of foot pain. Study participants were selected on the basis of results of a written questionnaire that asked about the site and cause of injury and pain frequency and intensity. Pain items were graded on a 7-point Likert scale. Subjects were mainly young (18 to 32 years of age), healthy university students who had a history of knee pain (knee group) or foot pain (foot group) during weightbearing activity. Both foot and lower-leg kinematic data were used to estimate the magnitude of each participant's subtalar joint inclination angle. These data were obtained while participants performed a series of open- and closed-kinetic-chain motions. The subtalar joint inclination angle was significantly greater for the knee group than for the foot group. The results of this study support the hypothesis that a higher subtalar joint inclination angle may predispose an individual to knee pain, and a lower subtalar joint inclination angle to foot pain.

The Current Perception Threshold Test Differentiates Categories of Mechanical Neck Disorder.

Study Design Cross-sectional discriminative analysis. Objective To determine whether current perception threshold (CPT) can differentiate between categories of patients with mechanical neck disorders (MNDs). Background Neck pain is the third most common musculoskeletal disorder, affecting a third of all adults each year. It can present as neck pain without musculoskeletal signs; neck pain with musculoskeletal signs but no neurological signs; neck pain with neurological signs. CPT testing can assess altered sensory perception that may reflect neurological changes. Methods Patients with MNDs (n=106) were classified into 3 groups based on a standardized musculoskeletal examination process performed by an experienced physiotherapist blinded to CPT scores. The 3 groups were defined as: MND-I, neck pain without musculoskeletal signs (n=60); MND-II, neck pain with musculoskeletal signs (n=29); MND-III, neck pain with neurological signs (n=17). A rapid protocol of CPT testing was performed at 3 frequencies (5, 250, 2000 Hz), using 3 dermatomal locations on the hand. A 1-way ANOVA with post hoc comparison and effect sizes were calculated to compare the mean CPT score between the groups. A binary logistic regression model was used to predict probability of higher CPT in MND-III and used to create a receiver operating characteristic (ROC) curve. Results Mean CPT differed significantly across the 3 MND groups (MND-I, 9.7; MND-II, 10.6; and MND-III, 11.8; P < .001, η2 = .6). Post hoc comparisons indicated differences between MND-I and MND-II (P = .05) and between MND-II and MND-III (P = .01), that were large effect sizes (MND I versus II, d = 1 and MND II versus III, d = 2.2). CPT testing was able to distinguish between MND II and III when a threshold value of greater than 11 was used to indicate MND-III. The predicted probability of abnormal CPT in MND-III had an estimated 73% sensitivity and 81% specificity; the odds ratio was 11.5 (P =.001) for the differentiation capacity of CPT between MND-II and III with a cut-off of 11. The area under the ROC curve (AUC) was .84 (95% CI =.72 to .96, P < .001). Conclusions CPT testing has moderate discriminatory accuracy, specificity, and sensitivity for classification of MND categories into neck pain with or without neurological signs. J Orthop Sports Phys Ther, Epub 10 May 2014. doi:10.2519/jospt.2014.5691.

The current perception threshold test differentiates categories of mechanical neck disorder.

STUDY DESIGN: Cross-sectional discriminative analysis. OBJECTIVE: To determine whether current perception threshold (CPT) can differentiate between categories of patients with mechanical neck disorders (MNDs). BACKGROUND: Neck pain is the third most common musculoskeletal disorder and affects a third of all adults each year. It can present as neck pain without musculoskeletal signs, neck pain with musculoskeletal signs but no neurological signs, or neck pain with neurological signs. CPT testing can assess altered sensory perception that may reflect neurological changes. METHODS: Patients with MNDs (n = 106) were classified into 3 groups, based on a standardized musculoskeletal examination process performed by an experienced physiotherapist who was blinded to CPT scores. The 3 groups were defined as neck pain without musculoskeletal signs (MND I) (n = 60), neck pain with musculoskeletal signs (MND II) (n = 29), and neck pain with neurological signs (MND III) (n = 17). A rapid protocol of CPT testing was performed at 3 frequencies (5, 250, and 2000 Hz), using 3 dermatomal locations on the hand. A 1-way analysis of variance with post hoc comparison and effect sizes was calculated to compare the mean CPT scores between the groups. A binary logistic-regression model was used to predict probability of higher CPT in MND III and to create a receiver-operating-characteristic curve. RESULTS: Mean CPT differed significantly across the 3 MND groups (MND I, 9.7; MND II, 10.6; and MND III, 11.8; P<.001; η(2) = 0.6). Post hoc comparisons indicated differences between MND I and MND II (P = .05) and between MND II and MND III (P = .01) that had large effect sizes (MND I versus II, d = 1 and MND II versus III, d = 2.2). CPT testing was able to distinguish between MND II and III when a threshold value of greater than 11 was used to indicate MND III. The predicted probability of abnormal CPT in MND III had an estimated 73% sensitivity and 81% specificity; the odds ratio was 11.5 (P = .001) for the differentiation capacity of CPT between MND II and III, with a cutoff of 11. The area under the receiver-operating-characteristic curve was 0.84 (95% confidence interval: 0.72, 0.96; P<.001). CONCLUSION: CPT testing has moderate discriminatory accuracy, specificity, and sensitivity for classification of MND categories into neck pain with or without neurological signs. J Orthop Sports Phys Ther 2014;44(7):532-540. Epub 10 May 2014. doi:10.2519/jospt.2014.4691.

On the derivation of a tensor to calculate six degree-of-freedom, musculotendon joint stiffness: implications for stability and impedance analyses.

Major joints, such as the knee, shoulder, and spine, can buckle along the translational degrees-of-freedom (DoF), causing injury to ligaments and other passive tissues. Despite this, stability and impedance analyses have focused primarily on the rotational DoF. As such, mathematical models quantifying musculotendon translational stiffnesses remain limited and, to our knowledge, there are no published works that explicitly describes the interactions between DoF. Using an energy approach, we derived a six DoF stiffness tensor and provided the necessary equations needed to quantify the musculotendon stiffness of any joint. Using a knee model, we then compared the derived stiffness tensor against two commonly used measures: one that excludes translational DoF and another that excludes interactions between DoF. We found that both of these measures had large over-estimations of stiffness, particularly for the rotational DoF, compared to our derived tensor. These findings indicate that previous analyses may have found rotational DoF to be stable when they were unstable.

The development of rhythm regularity, neuromuscular strategies, and movement smoothness during repetitive reaching in typically developing children.

INTRODUCTION: This study examined the development of paced coordinated reaching characterized by the successful entrainment of the movement to an external pacer, synchronous muscle activations and movement smoothness. METHODS: Thirty children, 5-10 years of age, and ten adults were instructed to repeatedly reach for and move an object from a lower shelf to an upper shelf in time to a metronome. Surface electromyography data were recorded. Amplitude and cross-correlations were calculated on three muscle pairs crossing the shoulder and elbow. A motion capture system captured the space curve accelerations of hand, forearm and upper arm segments to quantify movement smoothness. RESULTS: The 5-6 year old children showed the greatest amount of temporal variability, followed by 7-10 year olds and then the adults. Correlations between muscle pairs stabilizing the shoulder girdle were higher in each group as compared to the other two muscle pairs but the correlations for all pairs were consistently higher for adults. Movement smoothness for children 9-10 years of age was closer to an adult-like pattern with respect to control of the upper arm, but the hand segment had the greatest variability across groups. CONCLUSIONS: The increased temporal variability and decreased movement smoothness of the hand and forearm segments suggest that control of more distal musculature may be more difficult in children. The neuromuscular strategies adopted by adults were more optimal than those adopted by children as reflected by smoother and more consistent reaching.

Motion in response to the hypnotic suggestion of arm rigidity: a window on underlying mechanisms.

Among hypnotized subjects passing a challenge suggestion of arm rigidity, how might patterns of motor activity (strategies) contribute to the illusion that the elbow cannot be bent? Kinematic analyses of upper limb and trunk were performed. Nonhypnotized subjects carefully enacted a set of prescribed strategies typifying responses possibly adopted by a hypnotized subject. Profile analysis showed striking heterogeneity of response in hypnotic subjects. Half of participants showed no perceivable strategy consistent with the hypothesis that subjects hallucinate the suggestion and so do not engage the motor periphery. Equally common were subtle oscillations or trembling of the arm implying that motion resembling difficulty in bending was initiated. This can be misperceived as unintentional and thus evidence of inability to bend. The lack of a motor strategy is more consistent with dissociated-control theory, whereas the trembling response is more consistent with social-cognitive and dissociated-experience theories.

Exploring children's movement characteristics during virtual reality video game play.

There is increasing interest in the use of commercially-available virtual reality video gaming systems within pediatric rehabilitation, yet little is known about the movement characteristics of game play. This study describes quantity and quality of movement during Nintendo Wii and Wii Fit game play, explores differences in these movement characteristics between games and between novice and experienced players, and investigates whether motivation to succeed at the game impacts movement characteristics. Thirty-eight children (aged 7-12) with and without previous game experience played Wii (boxing and tennis) and Wii Fit (ski slalom and soccer heading) games. Force plate data provided center of pressure displacement (quantity) and processed pelvis motion indicated smoothness of pelvic movement (quality). Children rated their motivation to succeed at each game. Movement quantity and quality differed between games (p<.001). Children with previous experience playing Wii Fit games demonstrated greater movement quantity during Wii Fit game play (p<.001); quality of movement did not differ between groups. Motivation to succeed did not influence the relationship between experience and outcomes. Findings enhance clinical understanding of this technology and inform the development of research questions to explore its potential to improve movement skills in children with motor impairments.

Habitual physical activity levels are associated with biomechanical walking economy in children with cerebral palsy.

OBJECTIVE: To evaluate in children and adolescents with cerebral palsy the relationship between habitual physical activity and biomechanical treadmill walking economy and whether treadmill belt speed or walking time affect economy. DESIGN: Physical activity was measured in 11 subjects (10.6-16.3 yrs) with mild cerebral palsy using a triaxial accelerometer. To determine biomechanical walking economy, subjects' stride lengths and vertical sacral excursions were measured during each minute of three 3-min walks on a treadmill (at 60%, 75%, and 90% of individually determined fastest treadmill walking speed). RESULTS: Biomechanical walking economy at 60%, 75%, and 90% of (their) fastest speed each explained about half of the intersubject variance in daily physical activity (movement counts). A similar relationship was found between these biomechanical walking economy variables and movement counts at or above the 80th and 90th percentile (total minutes per day, number of 5-min bouts per day). Walking economy was 23.9% higher when subjects walked at 90% than when they walked at 60% of their fastest walking speed. No other speed-related effects on economy were found, nor did time affect economy. CONCLUSIONS: Within this population, those with high biomechanical treadmill walking economy are the more habitually physically active. Treadmill belt speed, but not walking time, affects biomechanical walking economy.