Electromyography of Extrinsic and Intrinsic Ear Muscles in Healthy Probands and Patients with Unilateral Postparalytic Facial Synkinesis

There are currently no data on the electromyography (EMG) of all intrinsic and extrinsic ear muscles. The aim of this work was to develop a standardized protocol for a reliable surface EMG examination of all nine ear muscles in twelve healthy participants. The protocol was then applied in seven patients with unilateral postparalytic facial synkinesis. Based on anatomic preparations of all ear muscles on two cadavers, hot spots for the needle EMG of each individual muscle were defined. Needle and surface EMG were performed in one healthy participant; facial movements could be defined for the reliable activation of individual ear muscles’ surface EMG. In healthy participants, most tasks led to the activation of several ear muscles without any side difference. The greatest EMG activity was seen when smiling. Ipsilateral and contralateral gaze were the only movements resulting in very distinct activation of the transversus auriculae and obliquus auriculae muscles. In patients with facial synkinesis, ear muscles’ EMG activation was stronger on the postparalytic compared to the contralateral side for most tasks. Additionally, synkinetic activation was verifiable in the ear muscles. The surface EMG of all ear muscles is reliably feasible during distinct facial tasks, and ear muscle EMG enriches facial electrodiagnostics.

Basic locomotor muscle synergies used in land walking are finely tuned during underwater walking

Underwater walking is one of the most common hydrotherapeutic exercises. Therefore, understanding muscular control during underwater walking is important for optimizing training regimens. The effects of the water environment on walking are mainly related to the hydrostatic and hydrodynamic theories of buoyancy and drag force. To date, muscular control during underwater walking has been investigated at the individual muscle level. However, it is recognized that the human nervous system modularly controls multiple muscles through muscle synergies, which are sets of muscles that work together. We found that the same set of muscle synergies was shared between the two walking tasks. However, some task-dependent modulation was found in the activation combination across muscles and temporal activation patterns of the muscle synergies. The results suggest that the human nervous system modulates activation of lower-limb muscles during water walking by finely tuning basic locomotor muscle synergies that are used during land walking to meet the biomechanical requirements for walking in the water environment.

Wearables-Only Analysis of Muscle and Joint Mechanics: An EMG-Driven Approach

Complex sensor arrays prohibit practical deployment of existing wearables-based algorithms for free-living analysis of muscle and joint mechanics. Machine learning techniques have been proposed as a potential solution, however, they are less interpretable and generalizable when compared to physics-based techniques. Herein, we propose a hybrid method utilizing inertial sensor- and electromyography (EMG)-driven simulation of muscle contraction to characterize knee joint and muscle mechanics during walking gait. Machine learning is used only to map a subset of measured muscle excitations to a full set thereby reducing the number of required sensors. We demonstrate the utility of the approach for estimating net knee flexion moment (KFM) as well as individual muscle moment and work during the stance phase of gait across nine unimpaired subjects. Across all subjects, KFM was estimated with 0.91 %BW·H RMSE and strong correlations (r = 0.87) compared to ground truth inverse dynamics analysis. Estimates of individual muscle moments were strongly correlated (r = 0.81-0.99) with a reference EMG-driven technique using optical motion capture and a full set of electrodes as were estimates of muscle work (r = 0.88-0.99). Implementation of the proposed technique in the current work included instrumenting only three muscles with surface electrodes (lateral and medial gastrocnemius and vastus medialis) and both the thigh and shank segments with inertial sensors. These sensor locations permit instrumentation of a knee brace/sleeve facilitating a practically deployable mechanism for monitoring muscle and joint mechanics with performance comparable to the current state-of-the-art.

The relationship between myonuclear number and protein synthesis in individual rat skeletal muscle fibre

Skeletal muscle cell has numerous nucleus within a cell. The nucleus has been considered as the central organelle for muscle protein synthesis. However, it is unclear whether myonuclear number associate with the MPS capacity within the individual muscle fibre. Therefore, the purpose of the present study was to reveal the relationship between myonuclear number per unit muscle fibre length and MPS under basal and conditions of elevated MPS by high-intensity muscle contraction (HiMC) using in vivo nascent protein labelling technique (SUnSET) in rodent. As the result, myonuclear number positively correlate to the MPS in individual muscle fibre at the basal condition. Similarly, ribosomal protein S6 (rpS6) content, which is a rough estimate of ribosome content, was positively correlated with MPS. However, myonuclear number was not associated with rpS6 content. In contrast to the basal condition, where MPS was increased by acute HiMC, no correlation was observed between myonuclear number and MPS, but the association between rpS6 and MPS was maintained. Importantly, these observations indicate that the number of nuclei in individual myofibers is related only to the MPS at rest. However, the ribosome content in individual fibres is related to the MPS of individual myofibers both at rest and in the elevated MPS, due to HiMC.

Selective Atrophy of the Vastus Medialis: Does It Exist in Women With Nontraumatic Patellofemoral Pain?

Background: A commonly cited theory related to the pathomechanics of patellofemoral pain (PFP) states that atrophy of the vastus medialis (VM) muscle leads to lateral tracking of the patella. However, isolated atrophy of the VM or atrophy of the quadriceps muscle group as a whole, has not been consistently reported in this population. Purpose: To compare individual and total quadriceps muscle volumes between women with nontraumatic PFP and women without PFP as measured on magnetic resonance imaging scans. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 52 women with nontraumatic PFP and 64 women without PFP between the ages of 18 and 45 years participated. Magnetic resonance imaging scans of the thigh were obtained from the anterior inferior iliac spine to the tibial plateau. Individual quadriceps muscle cross-sectional area measurements were obtained from each image, and muscle volumes for the VM, vastus lateralis, vastus intermedius, and rectus femoris were calculated. Muscle volume measurements were expressed in absolute values and normalized to body mass. Separate 2-way mixed-factorial analysis of variance (group × muscle) were used to compare absolute and normalized individual muscle volumes between groups. Independent t tests were used to compare absolute and normalized total quadriceps volumes between groups. Results: There was no difference in absolute and normalized individual muscle volumes between individuals with and those without PFP. Additionally, absolute and normalized total muscle volumes did not differ between groups. Conclusion: Our findings do not support the concept of preferential atrophy of the VM or generalized quadriceps atrophy in women with nontraumatic PFP.

Revealing the unique features of each individual's muscle activation signatures

There is growing evidence that each individual has unique movement patterns, or signatures. The exact origin of these movement signatures, however, remains unknown. We developed an approach that can identify individual muscle activation signatures during two locomotor tasks (walking and pedalling). A linear support vector machine was used to classify 78 participants based on their electromyographic (EMG) patterns measured on eight lower limb muscles. To provide insight into decision-making by the machine learning classification model, a layer-wise relevance propagation (LRP) approach was implemented. This enabled the model predictions to be decomposed into relevance scores for each individual input value. In other words, it provided information regarding which features of the time-varying EMG profiles were unique to each individual. Through extensive testing, we have shown that the LRP results, and by extent the activation signatures, are highly consistent between conditions and across days. In addition, they are minimally influenced by the dataset used to train the model. Additionally, we proposed a method for visualizing each individual's muscle activation signature, which has several potential clinical and scientific applications. This is the first study to provide conclusive evidence of the existence of individual muscle activation signatures.

A device for prosthesis length correction

In some cases, the parameters of the stump may undergo changes while walking on the prosthesis of the thigh or lower leg. The volume of the stump can change rapidly with certain pathologies (vascular diseases, multiple cicatricial changes), while a temporary increase in volume can occur in case of, for example, overload. In other cases, the parameters change gradually and, as a rule, downward. The result of a change in their volume is a change in the distance of the greater trochanterfloor, which leads to temporary or permanent overload of individual muscle groups when walking, a change in gait, and the formation of secondary changes from the various structures of the musculoskeletal system. The use of an insert in the carrier module in the form of a prosthesis length corrector allows to improve the quality of the rehabilitation and life of the disabled person and also avoids a significant number of secondary complications.