Simultaneous Contraction Research Articles

Sensory-motor circuit is a therapeutic target for dystonia musculorum mice, a model of hereditary sensory and autonomic neuropathy 6.

Mutations in Dystonin (DST), which encodes cytoskeletal linker proteins, cause hereditary sensory and autonomic neuropathy 6 (HSAN-VI) in humans and the dystonia musculorum (dt) phenotype in mice; however, the neuronal circuit underlying the HSAN-VI and dt phenotype is unresolved. dt mice exhibit dystonic movements accompanied by the simultaneous contraction of agonist and antagonist muscles and postnatal lethality. Here, we identified the sensory-motor circuit as a major causative neural circuit using a gene trap system that enables neural circuit-selective inactivation and restoration of Dst by Cre-mediated recombination. Sensory neuron-selective Dst deletion led to motor impairment, degeneration of proprioceptive sensory neurons, and disruption of the sensory-motor circuit. Restoration of Dst expression in sensory neurons using Cre driver mice or a single postnatal injection of Cre-expressing adeno-associated virus ameliorated sensory degeneration and improved abnormal movements. These findings demonstrate that the sensory-motor circuit is involved in the movement disorders in dt mice and that the sensory circuit is a therapeutic target for HSAN-VI.

Anconeus and pronation: a palpatory and ultrasonographic study

PurposeDepending on its axis, pronation varies from the radius rotation around the steady ulna to the reciprocal adduction of the radius and abduction of the ulna. While there is no question that pronator teres is a central pronation agonist, anconeus’s role is not settled. The current investigation comparing palpation and ultrasonography in these two muscles during pronation along the axis capitulum-second digit evolved from a serendipitous finding in a clinical anatomy seminar.MethodsSingle-hand palpation and two-transducer ultrasonography over anconeus and pronator teres were used on ten normal subjects to investigate their contraction during pronation around the capitulum-second digit axis. These studies were done independently and blind to the results of the other. The statistical analysis between palpation and ultrasonography was performed with Cohen’s kappa coefficient and the χ2 test.ResultsOn palpation, on resisted full pronation, anconeus contracted in 8/10 subjects and pronator teres in 10/10 subjects. Without resistance, the corresponding ratios were 5/10 and 9/10. On two-transducer ultrasonography, the comparable ratios were 7/10 and 10/10, and 3/10 and 10/10. A fair concordance (Cohen’s kappa = 0.21) between palpation and ultrasonography in detecting the simultaneous status of anconeus and pronator teres during resisted full pronation. Anatomic dissection illustrated the elements involved.ConclusionsPlain palpation confirmed by ultrasonography showed the simultaneous contraction of anconeus and pronator teres during resisted pronation in most of the studied subjects. The study suggests that palpation can be helpful in directly studying muscle activity during movement.

Poststroke Spasticity: Pathophysiology and Management An Accurate Evaluation of Spasticity

Stroke is a major contributor to long-term impairment and disability, affecting up to one-third of survivors and almost half of patients showing neurological deficit at six months. Spasticity affects approximately 25% of individuals within two weeks of a stroke and increases to 44% in patients who have had a second stroke. Severe or incapacitating spasticity affects 15% of post-stroke individuals. Poststroke spasticity is also linked to additional signs and symptoms of the upper motor neuron syndrome, such as simultaneous contraction of agonist and antagonist muscles, weakness of the muscles, and a lack of coordination. Spasticity arises due to aberrant neuroplasticity that develops after a stroke and there is currently no specific intervention method designed to address and correct this abnormal plasticity that takes place during the acute phase. Just before implementing any measures to deal with spasticity, it is crucial to evaluate the influence on the quality of life and level of severity. Several grading scales are used to measure spasticity such as the MAS and modified Tardieu scale.There are various therapeutic approaches that may be categorized into three main classes: physical, pharmaceutical, and surgical. Each class has a distinct purpose and is used at the appropriate moment to reduce the level of spasticity and improve the patient's health. Physiotherapy serves as a base of improving the patient's condition and facilitating the development of brain networks. The objective of post stroke spasticity management must include not only the reduction of muscle hypertonia, but also the evaluation of how post stroke influences functionality and overall mental health. Improper treatment or non-compliance may result in increased pain, joint contraction, and further disability. The goal is to assist the patient in achieving the best possible quality of life. Keywords: Pathophysiology of Post-Stroke Spasticity; Management of Post-Stroke Spasticity; Evaluation of Post-Stroke Spasticity

Advanced nerve regeneration enabled by neural conformal electronic stimulators enhancing mitochondrial transport

Addressing peripheral nerve defects remains a significant challenge in regenerative neurobiology. Autografts emerged as the gold-standard management, however, are hindered by limited availability and potential neuroma formation. Numerous recent studies report the potential of wireless electronic system for nerve defects repair. Unfortunately, few has met clinical needs for inadequate electrode precision, poor nerve entrapment and insufficient bioactivity of the matrix material. Herein, we present an advanced wireless electrical nerve stimulator, based on water-responsive self-curling silk membrane with excellent bioabsorbable and biocompatible properties. We constructed a unique bilayer structure with an oriented pre-stretched inner layer and a general silk membrane as outer layer. After wetting, the simultaneous contraction of inner layer and expansion of outer layer achieved controllable super-contraction from 2D flat surface to 3D structural reconfiguration. It enables shape-adaptive wrapping to cover around nerves, overcomes the technical obstacle of preparing electrodes on the inner wall of the conduit, and prevents electrode breakage caused by material expansion in water. The use of fork capacitor-like metal interface increases the contact points between the metal and the regenerating nerve, solving the challenge of inefficient and rough electrical stimulation methods in the past. Newly developed electronic stimulator is effective in restoring 10 mm rat sciatic nerve defects comparable to autologous grafts. The underlying mechanism involves that electric stimulation enhances anterograde mitochondrial transport to match energy demands. This newly introduced device thereby demonstrated the potential as a viable and efficacious alternative to autografts for enhancing peripheral nerve repair and functional recovery.

Effect of Pressure on the Conformational Landscape of Human γD-Crystallin from Replica Exchange Molecular Dynamics Simulations.

Human γD-crystallin belongs to a crucial family of proteins known as crystallins located in the fiber cells of the human lens. Since crystallins do not undergo any turnover after birth, they need to possess remarkable thermodynamic stability. However, their sporadic misfolding and aggregation, triggered by environmental perturbations or genetic mutations, constitute the molecular basis of cataracts, which is the primary cause of blindness in the globe according to the World Health Organization. Here, we investigate the impact of high pressure on the conformational landscape of wild-type HγD-crystallin using replica exchange molecular dynamics simulations augmented with principal component analysis. We find pressure to have a modest impact on global measures of protein stability, such as root-mean-square displacement and radius of gyration. Upon projecting our trajectories along the first two principal components from principal component analysis, however, we observe the emergence of distinct free energy basins at high pressures. By screening local order parameters previously shown or hypothesized as markers of HγD-crystallin stability, we establish correlations between a tyrosine-tyrosine aromatic contact within the N-terminal domain and the protein's end-to-end distance with projections along the first and second principal components, respectively. Furthermore, we observe the simultaneous contraction of the hydrophobic core and its intrusion by water molecules. This exploration sheds light on the intricate responses of HγD-crystallin to elevated pressures, offering insights into potential mechanisms underlying its stability and susceptibility to environmental perturbations, crucial for understanding cataract formation.

Belt electrode tetanus muscle stimulation reduces denervation-induced atrophy of rat multiple skeletal muscle groups

Belt electrode-skeletal muscle electrical stimulation (B-SES) involves the use of belt-shaped electrodes to contract multiple muscle groups simultaneously. Twitch contractions have been demonstrated to protect against denervation-induced muscle atrophy in rats, possibly through mitochondrial biosynthesis. This study examined whether inducing tetanus contractions with B-SES suppresses muscle atrophy and identified the underlying molecular mechanisms. We evaluated the effects of acute (60 Hz, 5 min) and chronic (60 Hz, 5 min, every alternate day for one week) B-SES on the tibialis anterior (TA) and gastrocnemius (GAS) muscles in Sprague–Dawley rats using belt electrodes attached to both ankle joints. After acute stimulation, a significant decrease in the glycogen content was observed in the left and right TA and GAS, suggesting that B-SES causes simultaneous contractions in multiple muscle groups. B-SES enhanced p70S6K phosphorylation, an indicator of the mechanistic target of rapamycin complex 1 activity. During chronic stimulations, rats were divided into control (CONT), denervation-induced atrophy (DEN), and DEN + electrically stimulated with B-SES (DEN + ES) groups. After seven days of treatment, the wet weight (n = 8–11 for each group) and muscle fiber cross-sectional area (CSA, n = 6 for each group) of the TA and GAS muscles were reduced in the DEN and DEN + ES groups compared with that in the CON group. The DEN + ES group showed significantly higher muscle weight and CSA than those in the DEN group. Although RNA-seq and pathway analysis suggested that mitochondrial biogenesis is a critical event in this phenomenon, mitochondrial content showed no difference. In contrast, ribosomal RNA 28S and 18S (n = 6) levels in the DEN + ES group were higher than those in the DEN group, even though RNA-seq showed that the ribosome biogenesis pathway was reduced by electrical stimulation. The mRNA levels of the muscle proteolytic molecules atrogin-1 and MuRF1 were significantly higher in DEN than those in CONT. However, they were more suppressed in DEN + ES than those in DEN. In conclusion, tetanic electrical stimulation of both ankles using belt electrodes effectively reduced denervation-induced atrophy in multiple muscle groups. Furthermore, ribosomal biosynthesis plays a vital role in this phenomenon.

Unexpected softening of a fibrous matrix by contracting inclusions

Cells respond to the stiffness of their surrounding environment, but quantifying the stiffness of a fibrous matrix at the scale of a cell is complicated, due to the effects of nonlinearity and complex force transmission pathways resulting from randomness in fiber density and connections. While it is known that forces produced by individual contractile cells can stiffen the matrix, it remains unclear how simultaneous contraction of multiple cells in a fibrous matrix alters the stiffness at the scale of a cell. Here, we used computational modeling and experiments to quantify the stiffness of a random fibrous matrix embedded with multiple contracting inclusions, which mimicked the contractile forces of a cell. The results showed that when the matrix was free to contract as a result of the forces produced by the inclusions, the matrix softened rather than stiffened, which was surprising given that the contracting inclusions applied tensile forces to the matrix. Using the computational model, we identified that the underlying cause of the softening was that the majority of the fibers were under a local state of axial compression, causing buckling. We verified that this buckling-induced matrix softening was sufficient for cells to sense and respond by altering their morphology and force generation. Our findings reveal that the localized forces induced by cells do not always stiffen the matrix; rather, softening can occur in instances wherein the matrix can contract in response to the cell-generated forces. This study opens up new possibilities to investigate whether cell-induced softening contributes to maintenance of homeostatic conditions or progression of disease. Statement of significanceMechanical interactions between cells and the surrounding matrix strongly influence cellular functions. Cell-induced forces can alter matrix properties, and much prior literature in this area focused on the influence of individual contracting cells. Cells in tissues are rarely solitary; rather, they are interspersed with neighboring cells throughout the matrix. As a result, the mechanics are complicated, leaving it unclear how the multiple contracting cells affect matrix stiffness. Here, we show that multiple contracting inclusions within a fibrous matrix can cause softening that in turn affects cell sensing and response. Our findings provide new directions to determine impacts of cell-induced softening on maintenance of tissue or progression of disease.

Dysphagia associated with esophageal wall thickening in patients with nonspecific high-resolution manometry findings: Understanding motility beyond the Chicago classification version 4.0.

Previous studies have demonstrated that 50% of patients with normal high-resolution manometry (HRM) findings or ineffective esophageal motility (IEM) may have abnormal functional luminal imaging probe (FLIP) results. However, the specific HRM findings associated with abnormal FLIP results are unknown. Herein, we investigated the relationship between nonspecific manometry findings and abnormal FLIP results. We retrospectively analyzed 684 patients who underwent HRM at a tertiary care center in Seoul, Korea, based on the Chicago Classification version 4.0 protocol. Among the 684 patients, 398 had normal HRM findings or IEM. Of these 398 patients, eight showed esophageal wall thickening on endoscopic ultrasonography or computed tomography; however, no abnormalities were seen during esophagogastroduodenoscopy. Among these eight patients, seven showed repetitive simultaneous contractions (RSCs) in at least one of the two positions: 61% (±29%) in 10 swallows in the supine position and 51% (±30%) in five swallows in the upright position. Four patients who underwent FLIP had a significantly decreased esophagogastric junction distensibility index (1.0 ± 0.5 at 60 mL). Two of these patients underwent per-oral endoscopic myotomy (POEM) due to a lack of response to medication. Esophageal muscle biopsy revealed hypertrophic muscle with marginal eosinophil infiltration. A subset of patients (2%) with normal HRM findings or IEM and RSCs experienced dysphagia associated with poor distensibility of the thickened esophageal wall. FLIP assessment or combined HRM and impedance protocols may help better define these patients who may respond well to POEM.

Acute and chronic effect of resistance training on pelvic floor muscle morphology and function in older women: a clinical trial

We aimed to evaluate the effects of resistance training with and without pelvic floor muscle (PFM) contraction on pelvic floor morphology and muscle function in older women. Seventeen older women without pelvic floor disorders participated in this clinical feasibility trial. The women were divided into three groups: resistance training without PFM contraction (RT); resistance training with simultaneous PFM contraction (RT+PFMC); and control. Maximum voluntary contraction (MVC) and the endurance of PFM contraction were measured by perineometer, and bladder neck angle and Hiatal area by translabial ultrasound. As an acute effect, MVC increased in the RT group (effect size r = −0.51). After 12 weeks, worsening was observed in the duration of contraction in RT (effect size r = −0.55) and RT+PFMC (effect size r = −0.52). Bladder neck angle improved in the RT+PFMC group (effect size r = −0.51). Resistance training acutely improves MVC and chronically worsens the duration of contraction. Resistance training with simultaneous PFM contraction improves the bladder neck angle after 12 weeks.

INFLUENCE OF ESOPHAGEAL MOTILITY IMPAIRMENT ON UPPER AND LOWER ESOPHAGEAL SPHINCTER PRESSURE IN CHAGAS DISEASE.

Chagas disease causes digestive anatomic and functional changes, including the loss of the myenteric plexus and abnormal esophageal radiologic and manometric findings. To evaluate the association of abnormal esophageal radiologic findings, cardiac changes, distal esophageal contractions, and complaints of dysphagia and constipation in upper (UES) and lower (LES) esophageal sphincter basal pressure in Chagas disease patients. The study evaluated 99 patients with Chagas disease and 40 asymptomatic normal volunteers. The patients had normal esophageal radiologic examination (n=61) or esophageal retention without an increase in esophageal diameter (n=38). UES and LES pressure was measured with the rapid pull-through method in a 4-channel water-perfused round catheter. Before manometry, the patients were asked about dysphagia and constipation and submitted to electrocardiography and chest radiography. The amplitude of esophageal distal contraction decreased from controls to chagasic patients with esophageal retention. The proportion of failed and simultaneous contractions increased in patients with abnormal radiologic examination (P<0.01). There were no significant differences in UES and LES pressure between the groups. UES pressure was similar between Chagas disease patients with cardiomegaly (n=27, 126.5±62.7 mmHg) and those without it (n=72, 144.2±51.6 mmHg, P=0.26). Patients with constipation had lower LES pressure (n=23, 34.7±20.3 mmHg) than those without it (n=76, 42.9±20.5 mmHg, P<0.03). Chagas disease patients with absent or mild esophageal radiologic involvement had no significant changes in UES and LES basal pressure. Constipation complaints are associated with decreased LES basal pressure.

Auxetic piezoelectric effect in heterostructures

Inherent symmetry breaking at the interface has been fundamental to a myriad of physical effects and functionalities, such as efficient spin–charge interconversion, exotic magnetic structures and an emergent bulk photovoltaic effect. It has recently been demonstrated that interface asymmetry can induce sizable piezoelectric effects in heterostructures, even those consisting of centrosymmetric semiconductors, which provides flexibility to develop and optimize electromechanical coupling phenomena. Here, by targeted engineering of the interface symmetry, we achieve piezoelectric phenomena behaving as the electrical analogue of the negative Poisson’s ratio. This effect, termed the auxetic piezoelectric effect, exhibits the same sign for the longitudinal (d33) and transverse (d31, d32) piezoelectric coefficients, enabling a simultaneous contraction or expansion in all directions under an external electrical stimulus. The signs of the transverse coefficients can be further tuned via in-plane symmetry anisotropy. The effects exist in a wide range of material systems and exhibit substantial coefficients, indicating potential implications for all-semiconductor actuator, sensor and filter applications.

Event segmentation structures temporal experience: Simultaneous dilation and contraction in rhythmic reproductions.

We experience the world in terms of both (continuous) time and (discrete) events, but time seems especially primitive-since we cannot perceive events without an underlying temporal medium. It is all the more intriguing, then, to discover that event segmentation can itself influence how we perceive the passage of time. We demonstrated this using a novel "rhythmic reproduction" task, in which people listened to irregular sequences of musical tones, and then immediately reproduced those rhythmic patterns from memory. Each sequence contained a single salient (and entirely task-irrelevant) perceptual event boundary, but the temporal placement of that boundary varied across multiple trials in which people reproduced the same underlying rhythmic pattern. Reproductions were systematically influenced by event boundaries in two complementary ways: tones immediately following event boundaries were delayed (being effectively played "too late" in the reproductions), while tones immediately preceding event boundaries were sped up (being effectively played "too early"). This demonstrates how event segmentation influences time perception in subtle and nonuniform ways that go beyond global temporal distortions-with dilation across events, but contraction within events. Events structure temporal experience, facilitating a give-and-take between the subjective expansion and contraction of time. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Decreased bladder contraction interval induced by periaqueductal grey stimulation is reversed by subthalamic stimulation in a Parkinson’s disease model rat

The medial prefrontal cortex (mPFC) regulates bladder contractions via the periaqueductal grey (PAG). Subthalamic nucleus deep brain stimulation (STN-DBS) modulates urinary afferent information from PAG in Parkinson’s disease (PD). We do not know how STN-DBS modulates the activities of mPFC induced by PAG stimulation. We aim to clarify how STN-DBS modulates the neuronal activity of mPFC induced by PAG stimulation and its effects on bladder contraction Experiments were conducted under urethane anesthesia in normal (n = 9) and 6-hydroxydopamine hemi-lesioned PD rats (n = 7). Left-sided PAG stimulation and STN-DBS were applied with simultaneous bladder contraction monitoring. Local field potential (LFP) recording and collection of extracellular fluid in the mPFC were performed before stimulation, during PAG stimulation, during PAG+STN stimulation, and after stimulation. The bladder inter-contraction intervals significantly decreased with PAG stimulation with a concomitant decrease in mPFC LFP power in PD rats. Adding STN stimulation to PAG stimulation significantly increased the bladder inter-contraction intervals with a concomitant increase in mPFC LFP power in PD rats. Several mPFC catecholamine levels were modulated by PAG or PAG+STN stimulation in PD rats. The present study revealed that STN-DBS modulate the activities of mPFC induced by PAG, thereby leading to normalization of bladder contraction.

Real-time ultrasound evaluation of CORE muscle activity in a simultaneous contraction in subjects with non-specific low back pain and without low-back pain. Protocol of an observational case-control study.

Non-specific low back pain represents 90-95% of all cases of low back pain and it has a prevalence of 18% in the adult population, assuming a great socioeconomic impact. The main objective of this observational case-control study study is to evaluate if there are differences in the simultaneous contraction of the core muscles between nonspecific low back pain and healthy subjects. This study will be carried out in the Physiotherapy department of the University of Alcalá. Eighty-two participants <18 years old, will be recruited, paired with NSLBP (n = 41) and healthy (n = 41). The main outcome will be the onset muscle contraction of lateral abdominal wall (internal oblique, external oblique and transversus abdominis), pelvic floor, lumbar multifidus and respiratory diafragm. The maneuvers that the subjects will perform will be abdominal drawing in maneouver, contralateral arm lift, valsalva, and voluntary pelvic floor contraction in sitting and standing. As a secondary objective, to analyze the amount of contraction of each muscle group and the capacity of the diaphragms to be excreted in both groups of subjects. Finally, to relate pain and disability.

Effects of breathing methods on patients with chronic back pain during plank exercise

Objective: The purpose of this study is to provide an exercise method for effective trunk stabilization by analyzing the thickness of the abdominal muscles, low back pain, and lumbar spine dysfunction by applying the simultaneous contraction of the plank exercise and the maximal expiratory method to patients with chronic back pain. Method: The number of subjects was 20 in total, 10 in the experimental group and 10 in the control group. The control group applied a plank exercise program, and the experimental group was provided with a plank exercise program in parallel with maximal exhalation. The exercise time was about 10 minutes. It was conducted 5 times a week for a total of 2 weeks. In both groups, the thickness of the abdominis muscle, pain level(NRS), and Korean-osweatry disability index(K-ODI) level were evaluated before and after the intervention. Results: All subjects who participated in the exercise program showed a common result: low back pain and low back pain disability index, and increased abdominal muscle thickness. In the case of the experimental group, there were more significant changes in the thickness of the abdominal muscles, the degree of low back pain, and the degree of low back pain disability index compared to the control group(p&lt;.05). However, there was no significant difference between the two groups. Conclusion: It is considered that plank exercise accompanied by maximum exhalation will be an effective plank exercise method to reduce low back pain and low back pain disability index by activating deep abdominal muscles.

Simultaneous Ring Contraction and Expansion Reaction: Electrosynthesis of Heterocycle-Fused Fulleroids and Photovoltaic Application.

Simultaneous electrochemical ring contraction and expansion reactions remain unexplored to date. Herein, the reductive electrosynthesis of heterocycle-fused fulleroids from fullerotetrahydropyridazines and electrophiles in the presence of a trace amount of oxygen has been achieved with concurrent ring contraction and ring expansion. When trifluoroacetic acid and alkyl bromides are employed as electrophiles, heterocycle-fused fulleroids with a 1,1,2,6-configuration are regioselectively formed. In contrast, heterocycle-fused fulleroids with a 1,1,4,6-configuration are regioselectively produced as two separable stereoisomers if phthaloyl chloride is used as the electrophile. The reaction proceeds through multiple steps of electroreduction, heterocycle ring-opening, oxygen oxidation, heterocycle contraction, fullerene cage expansion, and nucleophilic addition. The structures of these fulleroids have been determined by spectroscopic data and single-crystal X-ray diffraction analyses. The observed high regioselectivities have been rationalized by theoretical calculations.Representative fulleroids have been applied in organic solar cells as the third component and exhibit good performance.

Simultaneous Ring Contraction and Expansion Reaction: Electrosynthesis of Heterocycle‐Fused Fulleroids and Photovoltaic Application

AbstractSimultaneous electrochemical ring contraction and expansion reactions remain unexplored to date. Herein, the reductive electrosynthesis of heterocycle‐fused fulleroids from fullerotetrahydropyridazines and electrophiles in the presence of a trace amount of oxygen has been achieved with concurrent ring contraction and ring expansion. When trifluoroacetic acid and alkyl bromides are employed as electrophiles, heterocycle‐fused fulleroids with a 1,1,2,6‐configuration are regioselectively formed. In contrast, heterocycle‐fused fulleroids with a 1,1,4,6‐configuration are regioselectively produced as two separable stereoisomers if phthaloyl chloride is used as the electrophile. The reaction proceeds through multiple steps of electroreduction, heterocycle ring‐opening, oxygen oxidation, heterocycle contraction, fullerene cage expansion, and nucleophilic addition. The structures of these fulleroids have been determined by spectroscopic data and single‐crystal X‐ray diffraction analyses. The observed high regioselectivities have been rationalized by theoretical calculations. Representative fulleroids have been applied in organic solar cells as the third component and exhibit good performance.

Protocolo de tratamiento de la disfunción del tracto urinario inferior en la esclerosis múltiple y trastornos relacionados

Lower urinary tract dysfunction (LUTD) affects between a third and the majority of patients with multiple sclerosis, its prevalence increasing with the duration of the disease and causing a great impact on quality of life. LUTD is classified into filling symptoms, voiding symptoms, or mixed symptoms. The scenario of simultaneous contraction of the detrusor and bladder sphincter is called bladder detrusor sphincter dyssynergia and requires periodic ultrasound and renal function monitoring, due to the risk of kidney impairment caused by a retrograde increase in pressure. Filling symptoms are treated with hygienic-dietary measures, antimuscarinics, mirabegron, desmopressin, botulinum toxin or neuromodulation. Symptoms of voiding (postvoid residue greater than 100mL) are treated with intermittent self-catheterization or, less commonly, indwelling bladder or suprapubic catheterization.

Bilateral Force Deficit in Proximal Effectors Versus Distal Effectors in Lower Extremities

ABSTRACT Purpose: Bilateral force deficit occurs when the maximal generated force during simultaneous bilateral muscle contractions is lower than the sum of forces generated unilaterally. Neural inhibition is stated as the main source for bilateral force deficit. Based on differences in bilateral neural organization, there might be a pronounced neural inhibition for proximal compared to distal effectors. The aim of the present experiment was to evaluate potential differences in bilateral force deficit in proximal compared to distal effectors in lower extremities. Methods: Fifteen young adults performed single-joint maximal voluntary contractions in isometric dorsiflexion of ankle (distal) and knee (proximal) extension unilaterally and bilaterally. Results: Results showed a significant absolute bilateral force deficit for both proximal (123.46 ± 59.51 N) and distal effectors (33.00 ± 35.60 N). Interestingly, the relative bilateral force deficit for knee extension was significantly larger compared to dorsiflexion of ankle, 19.98 ± 10.04% and 10.27 ± 9.57%, respectively. Our results indicate a significantly higher bilateral force deficit for proximal effectors compared to distal effectors. Conclusion: Plausible explanations are related to neuroanatomical and neurophysiological differences between proximal effectors and distal effectors where proximal muscles have a higher potential for bilateral communication compared to distal muscles. In addition, higher forces produced with proximal effectors could cause a higher perceived exertion and cause a more pronounced bilateral force deficit to proximal effectors.

Increased hip adductor activation during sit-to-stand improves muscle activation timing and rising-up mechanics in individuals with hemiparesis

Long sit-to-stand (STS) time has been identified as a feature of impaired functional mobility. The changes in biomechanics of STS performance with simultaneous hip adductor contraction have not been studied, which may limit indications for use of hip adductor activation during STS training. Ten individuals with hemiplegia (mean age 61.8years, injury time 29.8±15.2months) performed the STS with and without squeezing a ball between two legs. The joint moments, ground reaction force (GRF), chair reaction force and movement durations and temporal index of electromyography were calculated from the control condition for comparison with those from the ball squeezing condition. Under the squeeze condition, reduced peak vertical GRF during the ascension phase with increased loading rate was observed in the nonparetic limb, and the peak knee extensor moment occurred earlier in the paretic. Earlier activation of tibialis anterior and gluteus maximus, and gluteus medius were found in squeeze STS. Squeezing a ball between limbs during STS increased the contraction timing of tibialis anterior, gluteus maximus, gluteus medius, and soleus as well as a more symmetric rising mechanics encourage the use of squeezing a ball between limbs during STS for individuals with hemiparesis.