Natural control of limb motion is continuous and progressively adaptive to individual intent. While intuitive interfaces have the potential to rely on the neuromuscular input by the user for continuous adaptation, continuous volitional control of assistive devices that can generalize across various tasks has not been addressed. In this study, we propose a method to use spatiotemporal ultrasound features of the rectus femoris and vastus intermedius muscles of able-bodied individuals for task-invariant learning of continuous knee kinematics during steady-state and transient ambulation. The task-invariant learning paradigm was statistically evaluated against a task-specific paradigm for the steady-state (1) level-walk, (2) incline, (3) decline, (4) stair ascent, and (5) stair descent ambulation tasks. The transitions between steady-state stair ambulation and level-ground walking were also investigated. It was observed that the continuous knee kinematics can be learned using a task-invariant learning paradigm with statistically comparable accuracy to a task-specific paradigm. Statistical analysis further revealed that incorporating the temporal ultrasound features significantly improves the accuracy of continuous estimations (p < 0.05). The average root mean square errors (RMSEs) of knee angle and angular velocity estimation were 7.06° and 53.1°/sec, respectively, for the task-invariant learning compared to 6.00° and 51.8°/sec for the task-specific models. High accuracy of continuous task-invariant paradigms overcome the barrier of task-specific control schemes and motivate the implementation of direct volitional control of lower-limb assistive devices using ultrasound sensing, which may eventually enhance the intuitiveness and functionality of these devices towards a "free form" control approach.
Clinically, the five-times STS task (FTSTS) is used to assess balance and muscle efficiency in the lower extremities of various populations. However, the changes that occur in body mechanics with greater repetitions and the effects of dual tasking while performing FTSTS are currently unknown. PURPOSE: To determine the effects of dual tasking and multiple repetitions on the FTSTS task in healthy, young adults. METHODS:10 healthy adults (age 24 (4.1) years) stood up and sat down five times fast without (SingleTask) and with a concurrent cognitive task of counting backwards by 3 (DualTask). Time to complete FTSTS was measured. Impulse (Ns/BW), peak force (N/BW), and power (Nm/BW.s) were calculated using ground reaction forces. A 2-way ANOVA and paired samples t-test were conducted. RESULTS: Participants took significantly longer to complete FTSTS during DualTask (8.16[1.77]s) vs. SingleTask (7.38[1.08]; p=.05). Concentric impulse significantly increased from 0.55 (0.02) during SingleTask to 0.59 (0.03) during DualTask (p=.022). Power significantly decreased from 0.99 (0.04) during SingleTask to 0.92 (0.05) during DualTask (p=.017). FTSTS concentric, and eccentric impulse significantly increased from 1st to 5th repetition respectively: 0.56 (0.03) to 0.59 (0.03; p=.005), 0.49 (0.03) to 0.56 (0.04; p=.013). Also, standing peak force significantly decreased from 1st repetition (1.39[0.03]) to 5th repetition (1.34[0.03]; p=.004). The mean peak force standing decreased more from 1st to 5th repetition under SingleTask (1.39[0.04] to 1.32[0.03]) compared to DualTask (1.39[0.03] to 1.35[0.03]; p=.044). CONCLUSION: Force characteristics are altered by both dual tasking and number of repetitions during the FTSTS task in healthy, young adults.
Healthy articular cartilage supports load bearing and frictional properties unmatched among biological tissues and man-made bearing materials. Balancing fluid exudation and recovery under loaded and articulated conditions is essential to the tissue’s biological and mechanical longevity. Our prior tribological investigations, which leveraged the convergent stationary contact area (cSCA) configuration, revealed that sliding alone can modulate cartilage interstitial fluid pressurization and the recovery and maintenance of lubrication under load through a mechanism termed ‘tribological rehydration.’ Our recent comparative assessment of tribological rehydration revealed remarkably consistent sliding speed-dependent fluid recovery and lubrication behaviors across femoral condyle cartilage from five mammalian species (equine/horse, bovine/cow, porcine/pig, ovine/sheep, and caprine/goat). In the present study, we identified and characterized key predictive relationships among tissue properties, sliding-induced tribological rehydration, and the modulation/recovery of lubrication within healthy articular cartilage. Using correlational analysis, we linked observed speed-dependent tribological rehydration behaviors to cartilage’s geometry and biphasic properties (tensile and compressive moduli, permeability). Together, these findings demonstrate that easily measurable tissue characteristics (e.g., bulk tissue material properties, compressive strain magnitude, and strain rates) can be used to predict cartilage’s rehydration and lubricating abilities, and ultimately its function in vivo.
Conflicting evidence exists regarding the presence of aberrant gait biomechanics more than one-year following anterior cruciate ligament reconstruction (ACLR). Overground walking may not elucidate differences in those further removed from surgery due to the unexacting nature of the task. Quadriceps dysfunction is common post-ACLR and contributes to aberrant gait biomechanics, thus downhill walking may exacerbate differences as this task places greater demands on the quadriceps. Purpose: To compare gait biomechanics between individuals with ACLR and healthy controls during level and downhill walking conditions. Methods: 24 individuals more than 1-year removed from ACLR and 24 healthy controls completed both level and downhill (10 degree grade) gait biomechanics assessments on an instrumented split-belt treadmill at their preferred walking speed. Peak variables were evaluated over the first 50% of stance including the vertical ground reaction force, internal knee extension and abduction moments and knee flexion angle. Moments were normalized to %body weight*height (%BW*Ht) and vGRF was normalized to %body weight. Dependent variables were compared across groups and conditions via two-way repeated measures ANCOVAs controlling for gait speed. Results: There were no significant condition*group interaction effects nor group main effects for any outcomes. However, there were significant condition increases in knee extension moment (P=0.020) and knee flexion angle (P=0.018) from level to downhill. Conclusions: Downhill walking necessitates larger knee extension moments and knee flexion angle compared to level gait. Our results suggest that changes in gait biomechanics between level and downhill conditions do not differ between individuals with ACLR >1 year post-reconstruction and controls.
No reliable calibration method has yet been developed for scanning probe friction measurements. As a result, the tribology basic science literature sits on a foundation of uncalibrated measurements that may or may not be comparable across studies. This paper aims to resolve this critical problem. Essentially, we adapt a mature and widely accepted technology, the pre-calibrated reference lever, as a means to store forces from a traceable calibration standard of fixed range (e.g. microbalance) and scale them to accommodate the load ranges (normal and lateral) of an arbitrary scanning probe. This paper presents the theory, demonstrates a simple prototype device and method of use, and validates the approach along several independent lines of analysis. As the results demonstrate, the generalized reference lever method is simple, reliable, and traceable. The concept, approach, and validation will be especially easy to grasp and implement by those who are practiced with the reference lever method of normal force calibration.
In this work, a 3D lower limb musculoskeletal model and simulation of multiple sclerosis disease is presented. The Model was developed using the Musculoskeletal Modeling Software (MSMS), MSMS has the advantage that the model can be exported directly to Simulink allowing us to generate Functional Electrical Stimulation (FES) and evaluate different injuries. From the simulations, is possible to obtain the joint range of motion, joint torque, muscle-tendon length, force and moment arm, this is important not only to perform biomechanical analysis but also to design exoskeleton robots for rehabilitation and to generate reference trajectories for control purposes. In order to validate the results, a study case of a normal and pathological gait is presented, then, the results are compared with the literature and with real data obtained from a low cost, and a professional gait capture system.
The objective of this study was to investigate the effect of induced stress on the performance of each task during high cognitive load situations(HCLS). We hypothesized that induced stress leads to performance decrements during HCLS.
In this study, the HCLS included standing while completing a secondary task(wire maze). The wire maze was composed of a metal wire path(maze) and a single ring, held in one hand that was moved over the maze without contacting the maze itself. Stress was induced through a loud buzzer when the ring contacted the maze. Participants were asked to randomly stand 1)quietly, or while completing the wire maze 2)with or 3)without the buzzer. Trials were three-minute long.
A sample of 18 healthy young participants, (24.76±3.56 years) were randomly recruited.
Perceived stress was obtained after each trial. Regularity of ground-reaction-force (GRF) in anterior-posterior and medial-lateral directions as well as wire maze error (ring-to-path contact) were calculated as primary and secondary task performance.
GRF was more irregular during quietly standing compared to HCLS with and without the buzzer in both the AP and ML directions(p=0.02, p=0.001, respectively in anterior-posterior,η^2=0.28)&(p=0.004, p<0.0001, respectively in medial-lateral, η^2=0.39). Perceived stress was significantly lower during quietly standing compared to HCLS with(p=0.001, η^2=0.45) and without buzzer(p=0.007) conditions. Overall, the hypothesis was supported partially; during the most stressful HCLS, the high level of perceived stress coincided with less wire maze errors(P<0.0001, d= 0.72).
Identifying the strategies underlying task prioritization can help clinicians design appropriate interventions to challenge patients appropriately to improve performance during HCLS.
Biomechanical studies have tried to assess the impact of the surgical approach on gait characteristics and recovery after total hip arthroplasty (THA). Some studies which used discrete analyses have shown that some surgical approaches provide better hip joint function after one year post-surgery, but several studies did not find any differences. The goal of this study was to compare hip biomechanics during gait using statistical parametric mapping (SPM) in patients who underwent THA with either a lateral (LAT), anterior (ANT), or posterior (POS) approach. Forty-five patients underwent unilateral THA with either a LAT, ANT, or approach, and were compared with 15 healthy controls (CTRL). All patients underwent biomechanical gait analysis approximately 9 months following surgery. Hip biomechanics were compared between groups throughout the entire gait cycle using a One-Way ANOVA SPM. Alpha was set to 0.05 and Bonferroni post hoc comparisons were completed. The POS group had a significantly lower hip flexion moment just prior to toe-off compared to the ANT and CTRL groups. The ANT group had significantly lower hip abduction moment for most of the stance phase compared to the LAT and CTRL groups. The POS group had a significantly lower hip abduction moment compared to the LAT and CTRL groups. These findings tend to contradict existing literature. Future studies should complete both pre- and post-operative assessments with a larger cohort in each group, as well as standardize the implants as much as possible to determine if observed differences are due to the approach and no other factors.
Injury could lead to impaired postural stability which is commonly assessed during return-to-sport rehabilitation. The Dynamic Postural Stability Index (DPSI) estimates variability in tri-axial ground reaction forces. DPSI is higher in injured runners and predicts performance in soccer players. DPSI has also been related to ankle range of motion (ROM) and strength in military personnel. PURPOSE: To explore relationship between previous injury, ankle ROM and strength with DPSI in collegiate runners. METHODS: Twenty-seven Division I collegiate cross country athletes (19.8±1.3 years) participated. Athletes jumped over a hurdle on to an AMTI force plate and landed on a single leg for DPSI estimation. Three trials were performed bilaterally. Ankle ROM was assessed via active dorsiflexion and gastrocnemius length measurement. Ankle and hip strength were measured using a handheld dynamometer. An independent samples t-test was used to compare DPSI between injured (IG – those injured in the past 3 years) and uninjured (UG) groups. Pearson’s correlation coefficients were determined between DPSI and other variables. RESULTS: No significant difference was found for DPSI on left (IG: 0.30±0.03 vs. UG: 0.32±0.04) and right (IG: 0.30± 0.03 vs. UG: 0.31±0.03) sides. There was a significant moderate negative correlation between dorsiflexion ROM and DPSI (right side r= -0.605, p= 0.001; left side r= -0.452, p= 0.001). There were no correlations between strength and DPSI except for right inversion strength and right DPSI (r= 0.446, p=0.020). CONCLUSION: DPSI seems to be influenced to a greater extent by ankle dorsiflexion than strength or previous injury in a collegiate runners.
Accurate measurements of tendon mechanics are necessary for biomechanists when trying to identify injury risk factors, optimise athletic performance and develop musculoskeletal models. Measuring Achilles tendon (AT) mechanics dynamically is now possible by combining motion capture and ultrasound (US). The aim of this study was to quantify sources of error when measuring AT length using motion capture and US, and establish their effect on calculated strain values. Errors in AT insertion tracking and data synchronisation caused differences in AT length and moment arm of 5.3 ± 1.1 mm and 11.2 ± 0.9 mm, respectively; this decreased calculated AT peak strain from 11.6 ± 3.5% to 5.4 ± 2.5%. These differences could significantly impact a researcher‘s interpretation of the effects of footwear, technique, and specific kinematics on AT loading.