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• Voluntary muscle fatigue increases the effort perceived to contract the fatigued muscles. • We observed the opposite following muscle fatigue induced with neuromuscular electrical stimulation. • The perceived effort to contract the fatigued muscles decreased during subsequent voluntary contractions. • The effects of fatigue on the sense of effort depend on the nature of the muscle fatigue induced. • Fatiguing electrical stimulation seems to decrease activation in the cortical structures integrating effort signals. As voluntary muscle fatigue increases, the perception of the effort required to produce a particular level of force also increases. This occurs because we produce greater neural outputs from the brain to compensate for the fatigue-induced loss of force. Muscle fatigue can also be generated following bouts of neuromuscular electrical stimulation (NMES), a technique widely used for rehabilitation and training purposes. Yet the effects of NMES-induced fatigue on the perception of effort have never been tested. In this study, we thus evaluated how electrically evoked fatigue would affect the sense of effort. For this purpose, we used two psychophysical tasks intended to assess effort perception: (i) a bilateral matching task in which subjects were asked to contract the elbow flexors of their reference and indicator arms with similar amounts of effort and (ii) a unilateral matching task in which they produced controlled levels of isometric force with their indicator arm and rated their perceived effort using the Borg CR10 scale. These tasks were performed before and after the biceps brachii of the indicator arm was submitted to a fatiguing NMES program that generated maximal force losses of 10–15%. Contrary to voluntary muscle fatigue, the sense of effort decreased post-NMES in both tasks despite increased neural outputs to the elbow flexors of the fatigued indicator arm. This shows that the relationship between motor command magnitude and effort perception was completely modified by NMES. It is proposed that NMES alters the sensory structures responsible for effort signal integration. [ABSTRACT FROM AUTHOR]

• Three sEMG-based features are introduced to assess damping ability and interpret activation patterns in lower-limb muscles of ACLR athletes. • Power spectrum's median frequency to study recruitment patterns of muscular units. • Muscles' relative frequency to study equivalent damping and equivalent stiffness. • Pseudo-Wigner-Ville distribution to evaluate muscles' ability to damp the energy. The main goal of the athletes who undergo anterior cruciate ligament reconstruction (ACLR) surgery is a successful return-to-sport. At this stage, identifying muscular deficits becomes important. Hence, in this study, three discriminative features based on surface electromyographic signals (sEMG) acquired in a dynamic protocol are introduced to assess the damping ability and interpret activation patterns in lower-limb muscles of ACLR athletes. The features include the median frequency of the power spectrum density (PSD), the relative percentage of the equivalent damping or equivalent stiffness derived from the median frequency, and the energy of the signals in the time–frequency plane of the pseudo-Wigner-Ville distribution (PWVD). To evaluate the features, 11 healthy and 11 ACLR athletes (6 months post-reconstruction surgery) were recruited to acquire the sEMG signals from the medial and the lateral parts of the hamstrings, quadriceps, and gastrocnemius muscles in pre- and post-fatigue single-leg landings. A significant damping deficiency is observed in the hamstring muscles of ACLR athletes by evaluating the proposed features. This deficiency indicates that more attention should be paid to this muscle of ACLR athletes in pre-return-to-sport rehabilitations. The quality of electromyography-based pre-return-to-sport assessments on ACLR subjects depends on the sEMG acquisition protocol, as well as the type and nature of the extracted features. Hence, combinatorial application of both energy-based features (derived from the PWVD) and power-based features (derived from the PSD) could facilitate the assessment process by providing additional biomechanical information regarding the behavior of the muscles surrounding the knee. [ABSTRACT FROM AUTHOR]

Abstract: Background and purpose: The ability to ascend and descend a flight of stairs is considered as one of the best predictors of free-living activity and is correlated with domestic extrinsic activity in hemiparetic patients. However, the relationship between timed-stair performance and clinical and biomechanical parameters has never been studied this population. The aim of this study was to determine if performance on the Timed Up and Down Stairs (TUDS) test was related to clinical variables (maximal gait speed, strength and spasticity) and to biomechanical gait parameters (spatio-temporal, kinematic and kinetic gait parameters) in hemiparetic patients. Methods: Sixty hemiparetic patients performed the TUDS test, underwent 3D gait-analysis and a clinical assessment. Pearson's correlations and two stepwise multiple linear regression analyses were carried out to identify the parameters which were the most highly correlated with TUDS test performance among the clinical variables and gait parameters on the paretic side. Results: Maximal walking speed on the 10-m walk test and strength of the ankle dorsiflexors were the clinical variables that were the most related to TUDS test performance (63% of variance explained). The percentage of single support phase on the paretic side was the biomechanical gait parameter which was the most related to TUDS test performance (58% of variance explained). Conclusion: The results of this study identified three parameters which predicted the performance to ascend and descend a flight of stairs as fast as possible in hemiparetic patients. Rehabilitation programs which aim to improve stair performance and independence in daily life activities should focus on these three parameters. [Copyright &y& Elsevier]

• An algorithm to improve kinematics accuracy in markerless gait analysis is presented. • This algorithm refines AI-driven skeletons in a subject-specific geometric manner. • It preserves skeleton links' length during walking, using intra-frame modelization. • It benefits from gait phases information in between-frames adjustments. • It smooths lower limb joints' trajectory in between-frames adjustments. Despite the advancements in developing markerless gait analysis systems, they still demonstrate lower accuracy compared to gold-standard systems. Hence, in this research, a novel approach is presented to improve the lower limb kinematics accuracy in markerless gait analysis. This approach refines the 3D lower-limb skeletons obtained by AI-based pose estimation algorithms in a subject-specific geometric manner, preserves skeleton links' length, benefits from gait phases information that adds biomechanical awareness to the algorithm, and utilizes an embedded trajectory smoothing. Validation of the proposed method shows that it reduces 12.6–43.5 % of root mean square error (RMSE) and significantly improves kinematic curves' similarity to the gold-standard ones. Results also prove the feasibility of more accurate lower limb kinematics calculation using a single (2.02–7.57° RMSE) or dual RGB-D camera (1.66–7.25° RMSE). Development of such algorithms could result in requirement of fewer cameras that deliver comparable or even superior measurement accuracy compared to multi-camera approaches. [ABSTRACT FROM AUTHOR]

Abstract: Vibration applied to the Achilles tendon is well known to induce in freely standing subjects a backward body displacement and in restrained subjects an illusory forward body tilt. The purpose of the present experiment was to evaluate the effect of Achilles tendon vibration (90Hz) on postural orientation in subjects free of equilibrium constraints. Subjects (n =12) were strapped on a backboard that could be rotated in the antero-posterior direction with the axis of rotation at the level of the ankles. They stood on a rigid horizontal floor with the soles of their feet parallel to the ground. They were initially positioned 7° backward or forward or vertical and were required to adjust their body (the backboard) to the vertical orientation via a joystick. Firstly, results showed that in response to Achilles tendon vibration, subjects adjusted their body backward compared to the condition without vibration. This backward body adjustment likely cancel the appearance of an illusory forward body tilt. It was also observed that the vibratory stimulus applied to the Achilles tendon elicited in restrained standing subjects an increased EMG activity in both the gastrocnemius lateralis and the soleus muscles. Secondly, this vibration effect was more pronounced when passive displacement during the adjustment phase was congruent with the simulated elongation of calf muscles. These results indicated that the perception of body orientation is coherent with the postural response classically observed in freely standing subjects although the relationship between these two responses remains to be elucidated. [Copyright &y& Elsevier]

The 6-min walk test (6MWT) is a useful tool for clinicians and researchers to estimate gait performance and fatigue affecting functional mobility. A modified 6MWT administered on a treadmill (TM) can be an efficient, space-saving alternative to perform the 6MWT. The aim of this study was to investigate if a 6MWT on a self-paced (SP) TM produced similar results compared to an overground (OG) 6MWT among healthy participants with the hypothesis that users would demonstrate similar gait parameters. The second aim was to assess the reliability of SP TM sessions with the hypothesis that gait parameters would be reliable. Twelve healthy young adults performed one OG 6MWT and two SP TM 6MWTs, with the TM tests performed on two different testing days. The OG 6MWTs were conducted along a 20 m corridor with a portable optometric system. The SP TM 6MWTs were performed using a dual-belt instrumented TM with speed controlled by feedback from a LIDAR sensor. In the OG condition, participants walked 664.8 m ± 48.9 m when the standard method was used to calculate distance and 721.3 m ± 56.2 m with an average-speed-based estimation of distance, which corrects for U-turns. For the SP TM 6MWT, they covered 729.4 m ± 45.8 m in the first session and 727.4 m ± 56.0 m in the second session. Gait parameters showed good to excellent within- and between-day reliability on the adaptive TM. Gait parameters were similar between modalities. A significant difference in the 6MWT distance was found between modalities. This is attributable to the U-turns, because a comparison between TM 6MWT distance and the average-speed-based estimation of the distance for the OG modality showed no significant difference. However, this system produced similar spatiotemporal gait parameters among participants compared to OG. [ABSTRACT FROM AUTHOR]

The excitability of some neural circuits involved in walking and affected in individuals with chronic stroke can be modulated during and/or immediately after anodal transcranial direct current stimulation (a-tDCS). This study was designed to investigate the effects of a-tDCS during and immediately after application on leg muscle activity during gait, and on spatiotemporal and kinematic gait parameters in patients with chronic stroke. This study was randomized, sham-controlled and double-blinded with a cross-over design and included 24 individuals with chronic stroke. Each participant underwent one 30-minute session each of effective a-tDCS at 2 mA and sham tDCS. In both sessions, the anode was placed over the leg motor cortex of the affected hemisphere and the cathode over the contralateral orbit. Six gait trials were performed before, during and immediately after each effective/sham tDCS session. Electromyographic activity of leg muscles, as well as spatiotemporal (e.g. gait speed) and kinematic (e.g. peak knee flexion and ankle dorsiflexion in the swing phase of gait) gait parameters were recorded. Genotyping for the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism was undertaken since this gene may influence motor skill learning and the effects of tDCS. No significant effects of a-tDCS on gait parameters were found either for the total group or for the Val66Met (N = 10) and Val66Val (N = 14) subgroups. A single session of a-tDCS delivered to the leg motor cortex did not immediately improve gait parameters in individuals with chronic stroke, regardless of their BDNF genotype. [ABSTRACT FROM AUTHOR]

The emergence of RGB-D cameras and the development of pose estimation algorithms offer opportunities in biomechanics. However, some challenges still remain when using them for gait analysis, including noise which leads to misidentification of gait events and inaccuracy. Therefore, we present a novel kinematic-geometric model for spatio-temporal gait analysis, based on ankles' trajectory in the frontal plane and distance-to-camera data (depth). Our approach consists of three main steps: identification of the gait pattern and modeling via parameterized curves, development of a fitting algorithm, and computation of locomotive indices. The proposed fitting algorithm applies on both ankles' depth data simultaneously, by minimizing through numerical optimization some geometric and biomechanical error functions. For validation, 15 subjects were asked to walk inside the walkway of the OptoGait, while the OptoGait and an RGB-D camera (Microsoft Azure Kinect) were both recording. Then, the spatio-temporal parameters of both feet were computed using the OptoGait and the proposed model. Validation results show that the proposed model yields good to excellent absolute statistical agreement (0.86 ≤ R c ≤ 0.99). Our kinematic-geometric model offers several benefits: (1) It relies only on the ankles' depth trajectory both for gait events extraction and spatio-temporal parameters' calculation; (2) it is usable with any kind of RGB-D camera or even with 3D marker-based motion analysis systems in absence of toes' and heels' markers; and (3) it enables improving the results by denoising and smoothing the ankles' depth trajectory. Hence, the proposed kinematic-geometric model facilitates the development of portable markerless systems for accurate gait analysis. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: The aim of this study was to assess the effects of neuromuscular fatigue on stretch reflex-related torque and electromyographic activity of spastic knee extensor muscles in hemiplegic patients. The second aim was to characterize the time course of quadriceps muscle fatigue during repetitive concentric contractions. Methods: Eighteen patients performed passive, isometric and concentric isokinetic evaluations before and after a fatigue protocol using an isokinetic dynamometer. Voluntary strength and spasticity were evaluated following the simultaneous recording of torque and electromyographic activity of rectus femoris (RF), vastus lateralis (VL) and biceps femoris (BF). Results: Isometric knee extension torque and the root mean square (RMS) value of VL decreased in the fatigued state. During the fatigue protocol, the normalized peak torque decreased whereas the RMS of RF and BF increased between the first five and last five contractions. There was a linear decrease in the neuromuscular efficiency-repetitions relationships for RF and VL. The peak resistive torque and the normalized RMS of RF and VL during passive stretching movements were not modified by the fatigue protocol for any stretch velocity. Discussion: This study showed that localized quadriceps muscle fatigue caused a decrease in voluntary strength which did not modify spasticity intensity. Changes in the distribution of muscle fiber type, with a greater number of slow fibers on the paretic side, may explain why the stretch reflex was not affected by fatigue. [Copyright &y& Elsevier]

Highlights: [•] This study assessed for the first time the gait pattern of adults with CP. [•] It showed that five different gait patterns can be identified. [•] Each gait pattern identified was related to specific kinematic parameters. [•] These specific kinematic parameters can be easily checked in clinical practice. [•] Results may permit to follow changes throughout growth, aging or after treatments. [ABSTRACT FROM AUTHOR]

Abstract: High upper extremity (U/E) demands are required when manual wheelchair users (MWUs) with spinal cord injury (SCI) ascend curbs; this may contribute to the risk of developing U/E musculoskeletal impairments. The aim of this study was to compare movement strategies (kinematics), mechanical loads (kinetics) and muscular demand (EMG) at the non-dominant U/E among 15 MWUs with SCI when ascending curbs of 4cm (3 trials), 8cm (3 trials) and 12cm high (3 trials) from a starting line set 3m before the curb. Biomechanical data was collected during three trials for each height. The curb ascent task was divided into three adjustment phases: caster pop, rear-wheel ascent and post-ascent. The greatest effort was generated by the shoulder flexors and internal rotators as well as the elbow flexors. A significant difference (p <0.0167) between the curb heights was found for most outcome measures studied: movement excursion, net joint moments and muscular utilization ratio (MUR) of the main muscles increased with the higher curb heights, mainly around the shoulder joint. These results provide insight that aside from adhering to a highly structured training method for wheelchair curb ascent, rehabilitation professionals need to propose task-specific strength training programs based on the demands documented in this study and continue to advocate for physically accessible environments. [Copyright &y& Elsevier]

• Adherence to the self-rehabilitation program targeting arm function was excellent. • Motor task quality and speed only improved in the self-rehabilitation group. • Improvement of WMFT time was clinically relevant in the self-rehabilitation group. • The difference between both groups was not statistically significant. Botulinum toxin injection (BTI) reduces muscle hyperactivity, but its effect on active upper-limb function is limited. Intensive rehabilitation could optimize the effects; however, outpatient post-stroke rehabilitation is usually not intensive. One solution could be self-rehabilitation. The aim of this randomized controlled trial was to determine the effect of a self-rehabilitation program combined with BTI on upper-limb function in individuals with chronic hemiparesis. In total, 33 outpatients were randomly allocated to receive BTI + self-rehabilitation (R group: n = 17) or BTI alone (C group: n = 16). Outcomes evaluated just before the BTI and 4 weeks later included the Wolf Motor Function Test (WMFT time: primary outcome), Action Research Arm Test, fatigue and quality of life. Change in WMFT did not differ between groups at 4 weeks (WMFT time: −14% for R group, −4% for C group. WFMT score: +12% for R group, 0% in C group). WFMT time and score improved significantly in the R group only (−14%, P = 0.01, and +12%, P = 0.02). In addition, the proportion of patients with improved WMFT time and score was higher in the R than C group (R group: 71% improved score, 77% improved time; C group: 43% improved score, 50% improved time). Also, passive range of shoulder flexion (P = 0.03) and wrist extension (P = 0.01) improved only in the R group. No other variables changed significantly. Compliance was excellent; average daily training time was greater than that prescribed. The addition of a self-rehabilitation program to BTI did not significantly improve functional outcomes more than BTI alone; however, movement quality and speed improved only in the self-rehabilitation group. Participants in the self-rehabilitation group trained more than they were asked to, which suggests that they found the program worthwhile. These clinically relevant findings justify larger-scale studies of the effects of self-rehabilitation to enhance the effects of BTI. Clinical trial: NCT02699762. [ABSTRACT FROM AUTHOR]