Agonist Contraction Research Articles

A COMPARATIVE STUDY ON THE IMMEDIATE EFFECTIVENESS OF MULLIGAN BENT LEG RAISE TECHNIQUE VS PNF HOLD-RELAX WITH AGONIST CONTRACTION IN IMPROVING HAMSTRING RANGE OF MOTION AND MUSCLE PERFORMANCE: A LITERATURE REVIEW.

Background: Hamstring tightness is a common issue that can hinder athletic performance and increase the risk of injury. Effective interventions are needed to enhance hamstring range of motion (ROM) and muscle performance. This study aims to compare two manual therapy techniques: the Mulligan Bent Leg Raise technique and the PNF Hold-Relax with Agonist Contraction technique. Objective: The primary objective is to compare the immediate effects of these two techniques on hamstring ROM and muscle performance. Secondary objectives include evaluating participants’ perceived comfort during the interventions and exploring the practical application of both techniques in clinical settings. Methods: A review of literature, focusing on randomized controlled trials involving participants aged 18–35 years, was conducted. Participants were divided into two groups: one receiving the Mulligan Bent Leg Raise technique and the other undergoing PNF Hold-Relax with Agonist Contraction. Pre- and post-intervention measurements of hamstring ROM and muscle performance were collected. Immediate effects were recorded and analyzed to compare outcomes between the two techniques. Results: Preliminary results indicate significant immediate improvements in hamstring flexibility and muscle performance for both techniques. Literature supports the effectiveness of both the Mulligan and PNF techniques in enhancing hamstring function. Conclusion: Evidence suggests that both the Mulligan Bent Leg Raise and PNF Hold-Relax with Agonist Contraction techniques effectively improve hamstring flexibility and muscle performance. Implications: This study provides valuable insights for physiotherapy practice, equipping clinicians with evidence-based strategies to address hamstring tightness and dysfunction. By integrating these techniques, physiotherapists can achieve rapid improvements and enhance overall treatment outcomes.

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.

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

Effects of Sub-Occipital Muscle Inhibition with and Without Hold Relax Agonist Contraction of Hamstrings on Pain, Disability and Craniovertebral Angle in Neck Pain Patients with Hamstring Tightness

Background: Neck pain is a prevalent musculoskeletal disorder with significant impacts on individuals' daily functioning and quality of life. The Superficial Backline (SBL) concept suggests that muscles and fascial structures are interconnected, implying that addressing muscle tightness in one area can influence distant regions. This study explored the effects of sub-occipital muscle inhibition (SMI) with and without hold-relax agonist contraction (HR-AC) of the hamstrings on pain, disability, and craniovertebral angle in patients with neck pain and hamstring tightness. Objective: To determine the efficacy of SMI with and without HR-AC on pain relief, neck disability, and craniovertebral angle in patients suffering from neck pain and hamstring tightness. Methods: This randomized controlled trial included 34 participants aged 20-40 years with neck pain (NPRS ≥ 5) and hamstring tightness (≥ 30° extension lag). Participants were randomly assigned to two groups: Group A (SMI without HR-AC) and Group B (SMI with HR-AC). Interventions were administered three times per week for two weeks. Pain, craniovertebral angle, and neck disability were assessed using the Numeric Pain Rating Scale (NPRS), Bubble Inclinometer, Image J software, and Neck Disability Index (NDI). Data were collected at baseline and post-treatment. Statistical analysis was performed using SPSS version 25, with paired and independent t-tests used to compare outcomes within and between groups. Results: Significant reductions in NPRS scores were observed in both groups: Group A (mean pre-treatment: 6.25 ± 0.85, post-treatment: 3.18 ± 0.98) and Group B (mean pre-treatment: 6.40 ± 0.986, post-treatment: 2.133 ± 0.743). Craniovertebral angle improved significantly in both groups: Group A (mean pre-treatment: 41.25° ± 3.51, post-treatment: 45.48° ± 2.94) and Group B (mean pre-treatment: 40.99° ± 2.70, post-treatment: 49.02° ± 2.868). NDI scores also showed marked improvement: Group A (mean pre-treatment: 32.96 ± 3.04, post-treatment: 15.38 ± 3.39) and Group B (mean pre-treatment: 33.03 ± 2.89, post-treatment: 11.25 ± 3.27). Group B demonstrated more significant improvements in all measured outcomes compared to Group A (p < 0.05). Conclusion: Both interventions, SMI without HR-AC and SMI with HR-AC, significantly reduced pain, improved craniovertebral angle, and decreased neck disability. However, the combination of SMI with HR-AC was more effective, highlighting the importance of addressing both ends of the myofascial chain in managing neck pain and hamstring tightness.

A COMPARATIVE ANALYSIS OF VARIOUS PROPRIOCEPTIVE NEUROMUSCULAR FACILITATION (PNF) TECHNIQUES ON MUSCLE FLEXIBILITY AMONG EXTENDED SITTING POSTURE INDIVIDUALS

Purpose: The purpose of this research is to compare the effectiveness of different Proprioceptive Neuromuscular Facilitation (PNF) stretching techniques for hamstring muscle tightness, and to find out the best PNF technique for improving hamstring flexibility. Methods: In this quasi-experimental designed study, 30 university students who were between 18-25 years-old, sitting >6 hours per day, and had a Active Knee Extension Test (AKET) >20º were recruited with convenience sampling and equally allocated into Group A, B and C, non-randomly. Hold-Relax (HR), Agonist Contraction (AC) and Contract-Relax-Antagonist-Contract (CRAC) stretching techniques were given respectively, 3 sessions/week, for three weeks. Results: Paired t-test showed significant effect of each technique compared between pre-test value and post-test value of AKET measurements of Hold-relax (HR), AC and CRAC groups (p

Comparative Effects of Hold Relax with Agonist Contraction and Active Release Therapy on Pain, Functional Disability, and Sleep Quality in Piriformis Syndrome

Background: Piriformis syndrome is characterized by pain, numbness, and tingling from the hip down to the leg. It develops from a variety of contributing factors. Objective: The objective of this study was to compare the effects of active release therapy (ART) and hold relax with agonist contraction (HRAC) on pain, functional disability, and sleep quality in patients with piriformis syndrome. Material and Methods: This study was conducted from March 2022 to November 2022. A total of 82 participants of both genders, 25 to 55 years of age, diagnosed with piriformis syndrome were involved in the study. Those with a history of fracture of the pelvis or hip, disc disease, or postural deformity were excluded. Participants were assigned into two groups; HRAC and ART with routine physical therapy. Outcome measures were pain, functional disability, and sleep quality measured by the Numeric Pain Rating Scale, Roland Morris Disability Questionnaire, and Chronic Pain Sleep Inventory respectively. Assessment was made at baseline, at the end of 1st and 2nd week. Mann-Whitney Test was used for between-group analysis and Friedman’s ANOVA was computed for within-group differences. Results: Between-groups analysis showed a statistically significant difference in pain score (P ≤ 0.05), but no significant difference was found between both techniques regarding functional disability and sleep quality (P ≥ 0.05). However, the within-group analysis showed statistically significant results in all outcome measures (P<0.05). Conclusion: ART was more effective in decreasing pain. Whereas, both techniques had equal effects in enhancing sleep quality and reducing functional disability among patients with piriformis syndrome.

The orderly recruitment of motor units may be modified when a muscle is acting as an antagonist.

Despite the perceived importance of antagonist muscle activity, it is unknown if motor unit (MU) behavior at recruitment differs when a muscle acts as an antagonist versus agonist. Fourteen healthy participants performed ramped, isometric elbow flexor or extensor contractions to 50% or 100% maximal voluntary contraction (MVC) torque. Surface and fine-wire intramuscular electromyographic (EMG) recordings were sampled from biceps and triceps brachii. During agonist contractions, low-threshold MUs (recruited at <10% MVC torque) were sampled in all participants, with a total of 107 and 90 for biceps and triceps brachii, respectively. For ramped MVCs, antagonist surface EMG coactivation (% amplitude during agonist MVC) was 8.3 ± 6.6% for biceps and 15.2 ± 7.3% for triceps brachii. However, antagonist single MU activity was recorded from only four participants, with only one of these individuals having antagonist MUs recorded from both muscles. All antagonist MUs were successfully detected during agonist contractions, but many (∼40%) had a recruitment threshold >10% MVC torque. For MUs recorded during both agonist and antagonist contractions, discharge rate at recruitment was seemingly lower for antagonist than agonist contractions. Coexistence of typical levels of surface EMG-derived coactivation with scant antagonist MU recordings suggests that coactivation in these muscles is primarily the result of cross talk. Based on the limited antagonist MU data detected, MUs recruited early during an agonist contraction are not necessarily among those first recruited during an antagonist contraction. These findings highlight the possibility of a modification of orderly recruitment when a motoneuron pool is acting as an antagonist.NEW & NOTEWORTHY Modest levels of coactivation are widely considered essential for appropriate motor control; however, minimal attention has been given to recruitment patterns of motor units (MUs) from antagonist muscles. Despite the successful recording of many low-threshold MUs during agonist contractions, we recorded no antagonist MUs in most participants. Of the units recorded, only ∼60% matched those recruited at <10% of maximal torque when the muscle acted as an agonist, which suggests a modified recruitment order for antagonist MUs.

Inter-muscle differences in modulation of motor evoked potentials and posterior root-muscle reflexes evoked from lower-limb muscles during agonist and antagonist muscle contractions

Voluntary contraction facilitates corticospinal and spinal reflex circuit excitabilities of the contracted muscle and inhibits spinal reflex circuit excitability of the antagonist. It has been suggested that modulation of spinal reflex circuit excitability in agonist and antagonist muscles during voluntary contraction differs among lower-limb muscles. However, whether the effects of voluntary contraction on the excitabilities of corticospinal and spinal reflex circuits depend on the tested muscles remains unknown. The purpose of this study was to examine inter-muscle differences in modulation of the corticospinal and spinal reflex circuit excitabilities of multiple lower-limb muscles during voluntary contraction. Eleven young males performed isometric plantar-flexion, dorsi-flexion, knee extension, and flexion at low torque levels. Motor evoked potentials (MEPs) and posterior root-muscle reflexes from seven lower-leg and thigh muscles were evoked by transcranial magnetic stimulation and transcutaneous spinal cord stimulation, respectively, at rest and during weak voluntary contractions. MEP and posterior root-muscle reflex amplitudes of agonists were significantly increased as agonist torque level increased, except for the reflex of the tibialis anterior. MEP amplitudes of antagonists were significantly increased in relation to the agonist torque level, but those of the rectus femoris were slightly depressed during knee flexion. Regarding the posterior root-muscle reflex of the antagonists, the amplitudes of triceps surae and the hamstrings were significantly decreased, but those of the quadriceps femoris were significantly increased as the agonist torque level increased. These results demonstrate that modulation of corticospinal and spinal reflex circuit excitabilities during agonist and antagonist muscle contractions differed among lower-limb muscles.

Scalp electroencephalograms over ipsilateral sensorimotor cortex reflect contraction patterns of unilateral finger muscles

A variety of neural substrates are implicated in the initiation, coordination, and stabilization of voluntary movements underpinned by adaptive contraction and relaxation of agonist and antagonist muscles. To achieve such flexible and purposeful control of the human body, brain systems exhibit extensive modulation during the transition from resting state to motor execution and to maintain proper joint impedance. However, the neural structures contributing to such sensorimotor control under unconstrained and naturalistic conditions are not fully characterized. To elucidate which brain regions are implicated in generating and coordinating voluntary movements, we employed a physiologically inspired, two-stage method to decode relaxation and three patterns of contraction in unilateral finger muscles (i.e., extension, flexion, and co-contraction) from high-density scalp electroencephalograms (EEG). The decoder consisted of two parts employed in series. The first discriminated between relaxation and contraction. If the EEG data were discriminated as contraction, the second stage then discriminated among the three contraction patterns. Despite the difficulty in dissociating detailed contraction patterns of muscles within a limb from scalp EEG signals, the decoder performance was higher than chance-level by 2-fold in the four-class classification. Moreover, weighted features in the trained decoders revealed EEG features differentially contributing to decoding performance. During the first stage, consistent with previous reports, weighted features were localized around sensorimotor cortex (SM1) contralateral to the activated fingers, while those during the second stage were localized around ipsilateral SM1. The loci of these weighted features suggested that the coordination of unilateral finger muscles induced different signaling patterns in ipsilateral SM1 contributing to motor control. Weighted EEG features enabled a deeper understanding of human sensorimotor processing as well as of a more naturalistic control of brain-computer interfaces.

Reaching exercise for chronic paretic upper extremity after stroke using a novel rehabilitation robot with arm-weight support and concomitant electrical stimulation and vibration: before-and-after feasibility trial

BackgroundOur group developed a rehabilitation robot to assist with repetitive, active reaching movement of a paretic upper extremity. The robot is equipped with a servo motor-controlled arm-weight support and works in conjunction with neuromuscular electrical stimulation and vibratory stimulation to facilitate agonist-muscle contraction. In this before-and-after pilot study, we assessed the feasibility of applying the robot to improve motor control and function of the hemiparetic upper extremity in patients who suffered chronic stroke.MethodsWe enrolled 6 patients with chronic stroke and hemiparesis who, while sitting and without assistance, could reach 10 cm both sagitally and vertically (from a starting position located 10 cm forward from the patient’s navel level) with the affected upper extremity. The patients were assigned to receive reaching exercise intervention with the robot (Yaskawa Electric Co., Ltd. Fukuoka, Japan) for 2 weeks at 15 min/day in addition to regular occupational therapy for 40 min/day. Outcomes assessed before and after 2 weeks of intervention included the upper extremity component of the Fugl-Meyer Assessment (UE-FMA), the Action Research Arm Test (ARAT), and, during reaching movement, kinematic analysis.ResultsNone of the patients experienced adverse events. The mean score of UE-FMA increased from 44.8 [SD 14.4] to 48.0 [SD 14.4] (p = 0.026, r = 0.91), and both the shoulder–elbow and wrist–hand scores increased after 2-week intervention. An increase was also observed in ARAT score, from mean 29.8 [SD 16.3] to 36.2 [SD 18.1] (p = 0.042, r = 0.83). Kinematic analysis during the reaching movement revealed a significant increase in active range of motion (AROM) at the elbow, and movement time tended to decrease. Furthermore, trajectory length for the wrist (“hand path”) and the acromion (“trunk compensatory movement”) showed a decreasing trend.ConclusionsThis robot-assisted modality is feasible and our preliminary findings suggest it improved motor control and motor function of the hemiparetic upper extremity in patients with chronic stroke. Training with this robot might induce greater AROM for the elbow and decrease compensatory trunk movement, thus contributing to movement efficacy and efficiency.Trial registration UMIN Clinical Trial Registry, as UMIN000018132, on June 30, 2015. https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000020398

COMPARACIÓN DE TÉCNICAS DE ENTRENAMIENTO DE FLEXIBILIDAD (FNP) CON Y SIN ELECTROESTIMULACIÓN

The objective of this study was to analyze the effect of the Contract-Relax Agonist Contract stretching technique with (CRAC+EE) and without (CRAC) electrostimulation on the improvement and retention of active movement range (AROM) and passive (PROM) of hip in flexion, in dominant lower extremity. 34 university students were assigned to three groups: control, CRAC+EE and CRAC. AROM and PROM were evaluated before, once completed and after 2 weeks of completion the training. The training lasted 4 weeks, with 3 sessions per week.The ANOVA showed a very significant increase in AROM (p&lt;0.001 and p&lt;0.005) and PROM (p&lt;0.001 and p&lt;0.01) in both experimental groups respectively. In the retention, higher values are maintained with respect to the pre-test measurement. In conclusion, the application of CRAC++EE and CRAC improved AROM and PROM, being also effective in the retention of two types of range of motion.

Effect of electrical stimulation of antagonist muscles for voluntary motor drive

Voluntary motor drive is an important central command that descends via the corticospinal tract to initiate muscle contraction. When electrical stimulation (ES) is applied to an antagonist or agonist muscle, it changes the agonist muscle’s representative motor cortex and thus its voluntary motor drive. In this study, we used a reaction time task to compare the effects of weak and strong ES of the antagonist or agonist muscle during the premotor period of a wrist extension. We recorded motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) that was applied to the extensor carpi radialis (ECR; agonist) and flexor carpi radialis (FCR; antagonist). When stronger ES intensities were applied to the antagonist, the MEP control ratio in the ECR significantly increased during the premotor time. Furthermore, the MEP control ratio with stronger antagonist ES intensity was significantly larger than that in the agonist for the same ES intensity. In the FCR, the MEP control ratio was also significantly greater at the strong ES intensity than at the weak ES intensity. Furthermore, the MEP control ratio in the antagonist with a strong ES intensity was significantly larger than that in the agonist with the same ES intensity. These results suggest that agonist corticomotor excitability might be enhanced by ES of the antagonist, which in turn strongly activates the descending motor system in the preparation of agonist contraction.

Trastornos del movimiento. Etiopatogenia. Clasificación. Síndromes coreicos y distonía

Semiology of movement disorders is varied. They are classified by movement type and syndrome. Parkinsonism is the most prominent hypokinetic syndrome; while among hypokinetic highlight dystonia, myoclonus, tic and chorea. The etiology is diverse, predominating pathophysiologically the dysfunction of basal ganglia and its cortical connections.Abnormal contraction of agonist and antagonist muscles takes place in dystonia, causing abnormal postures. Dystonias are classified according to the area of the body that is affected, clinical characteristics and etiology. More than twenty loci, previously named DYT loci, haven been identified in genetic dystonia.Chorea describes involuntary, purposeless and irregular movements. Several causes can lead to choreic movements, for example genetically determined diseases. Huntington's disease is an autosomal-dominant disease caused by a pathological triplet repeat expansion in HTT gene. It is a neurodegenerative disorder co-existing with multiple movement disorders (chorea, dystonia and parkinsonism).Primary and genetically determined dystonia as well as Huntington's disease and other primary chorea, are treated symptomatically.

A study to compare efficacy of hold-relax and agonist contraction of proprioceptive neuromuscular facilitation technique on hamstring muscle flexibility in healthy female-An interventional study

Background: There are mainly 2 types of stretching technique: active and passive techniques.1 PNF uses the concept of muscle relaxation being fundamental to elongation of muscle tissue. There are three stretching techniques included in PNF: Hold-Relax (HR), Agonist Contraction (AC), Hold-Relax with Agonist Contraction (HR-AC). The purpose of this study to compare efficacy of Hold-Relax and Agonist Contraction of PNF technique on hamstring muscle flexibility in healthy females. Objective: To compare the effect of Hold-Relax (HR) with Agonist Contraction (AC) of PNF technique on hamstrings muscle’s flexibility in healthy female individuals. Method: Study design is an interventional study and sample population taken was normal healthy female individuals from college area with sample size of 30. Simple random sampling method (lottery method) was used. 30 subjects having hamstrings muscle tightness which is examined by measurement of Active Knee Extension angle and Perceived level of hamstring muscle score scale. Subjects received following treatments: group A was taken Hold and Relax stretching with 30 seconds hold for 3 times per set and 1 set per day. Group B was taken agonist contraction stretching with 30 seconds hold for 3 times per set and 1 set per day. In both technique therapy was given for 5days/week, 1set/day and 3 times for each set. 5 sessions were given. Outcome Measures: 1. Active Knee Extension angle 2. Perceived level of hamstring tightness score scale Results: Results showed improvement in hamstring muscle flexibility in group A (t = -7.94, p- <0.05) and group B (t= -4.75, p<0.05) but more significant improvement seen in subjects of group A (p- <0.05). Conclusion: Result of present study showed that Hold & Relax technique is more effective in increasing flexibility of hamstring muscle compared to Agonist Contraction technique.

Comparison of Joint Mobilization with Manual Stretching Exercises in the Treatment of Hallux Valgus

The purpose of this study was to evaluate the effect of joint mobilization and manual stretching exercises in patients with hallux valgus. Twenty-three participants were divided into two groups; joint mobilization (n=11) and manual stretching exercises (n=12). The subjects participated in the experiment for 15minutes, three times a week, four weeks. The joint mobilization (Grade III, Maitland) was performed to experimental group for a minute and then rested for 10 seconds for each set. The manual stretching was performed to control group with three exercise session (preparatory and finishing exercises, agonist contraction exercises, agonist contraction and hold-relax exercises). In the results of the study, intragroup comparison of the deformity angles (DA) was shown to decrease from 15.18° to 13.09° in the joint mobilization group (p .05). The current study suggests that JM and MSE are effective in decreasing the DA in patients with hallux valgus.

The center of pressure and ankle muscle co-contraction in response to anterior-posterior perturbations.

Though both contraction of agonist muscles and co-contraction of antagonistic muscle pairs across the ankle joint are essential to postural stability, they are perceived to operate independently of each other, In an antagonistic setup, agonist muscles contract generating moment about the joint, while antagonist muscles contract generating stiffness across the joint. While both work together in maintaining robustness in the face of external perturbations, contractions of agonist muscles and co-contractions of antagonistic muscle pairs across the ankle joint play different roles in responding to and adapting to external perturbations. To determine their respective roles, we exposed participants to repeated perturbations in both large and small magnitudes. The center of pressure (COP) and a co-contraction index (CCI) were used to quantify the activation of agonist muscles and antagonistic muscle pairs across the ankle joint. Our results found that participants generated moment of a large magnitude across the ankle joint—a large deviation in the COP curve—in response to perturbations of a large magnitude (p <0.05), whereas the same participants generated higher stiffness about the ankle—a larger value in CCI—in response to perturbations of a small magnitude (p <0.05). These results indicate that participants use different postural strategies pertaining to circumstances. Further, the moment across the ankle decreased with repetitions of the same perturbation (p <0.05), and CCI tended to remain unchanged even in response to a different perturbation following repetition of the same perturbation (p <0.05). These findings suggest that ankle muscle contraction and co-contraction play different roles in regaining and maintaining postural stability. This study demonstrates that ankle moment and stiffness are not correlated in response to external perturbations.

Changes in Myosin Heavy Chain Isoforms Along the Length of Orbital Fibers in Rabbit Extraocular Muscle.

Extraocular muscles express 10 myosin heavy chain (MyHC) isoforms that cater for a wide range of contractile speeds. We aim to characterize the variations in MyHC expression along the length of singly (SIFs) and multiply innervated fibers (MIFs) in the orbital layer of rabbit superior rectus muscle. Monospecific antibodies to nine MyHCs, including an anti-slow-tonic antibody characterized here were used to immunohistochemically map variations in MyHC distribution in serial sections along the muscle's full length. The fastest MyHC, EO, is expressed at the endplate zone (EPZ) of SIFs, flanked proximally and distally by segments expressing the slower 2A, with or without embryonic MyHC. MIFs with constant diameter express α-cardiac MyHC at the EPZ, flanked by segments co-expressing α-cardiac/embryonic and possibly slow-tonic MyHCs. MIFs with varying diameter also express α-cardiac MyHC at the EPZ in their thin, central region, flanked by thin segments co-expressing α-cardiac/embryonic MyHCs, with long proximal and distal extensions of larger diameter that co-express embryonic/slow-tonic and α-cardiac or β/slow MyHCs. Orbital fiber types express multiple MyHCs, with faster ones in SIFs, slower ones in MIFs, but all have fast EPZs and slower end segments. We hypothesize that these unique MyHC distributions enable these fibers to relax in two kinetically distinct phases while acting in an antagonistic manner during a saccade: the fast phases facilitate acceleration of eyeball rotation during agonist contraction, while the slow phases help its deceleration toward the visual target, thereby linearizing the saccade. These properties also facilitate pulley movements to implement Listing's law.

Muscle co-contraction in elderly people change due to postural stability during single-leg standing

BackgroundMuscle co-contraction is the simultaneous contraction of agonist and antagonist muscles crossing a joint, and it increases with age. This study primarily aimed to clarify the difference in the effect of a light fingertip contact to stationary surface on postural sway and muscle co-contraction during single-leg standing (SLS) between young and elderly groups; the secondary aim was to reveal the quantitative difference in the muscle co-contraction of the ankle joint among the three different support structure conditions in the elderly group.MethodsThis study included eight young adults (age 23.4 ± 2.6 years) and nine community dwelling older adults (age 74.7 ± 3.4 years). The task was SLS under the following conditions: (1) no supporting structure, FR; (2) light index fingertip contact to a stationary supporting structure (to touch in force < 1 N), LT; and (3) dependence on a supporting structure for stabilization as desired, DO. Center of pressure (COP) variables [root-mean-square distance (RDIST), total excursion (TOTEX), mean velocity (MVELO), and standard deviation area (AREA-SD)] and the co-contraction index (CI) between the tibialis anterior and soleus were measured using surface electromyography.ResultsWith regard to the effect of the light fingertip contact to stationary surface, in the young group, TOTEX, MVELO, AREA-SD, and CI during SLS were smaller under the LT condition than under the FR condition. However, in the elderly group, only AREA-SD and CI were smaller under the LT condition than under the FR condition. No significant difference was observed in COP variables and CI under the DO condition between the young and elderly groups.ConclusionBoth young and elderly groups could decrease muscle co-contraction using the light fingertip contact. On the other hand, in the elderly group, COP variables showed a limited effect from the light fingertip contact; only the “sway” domain measure (AREA-SD). Both young and elderly groups showed the smallest CI under the DO condition. Therefore, the elderly group could decrease muscle co-contraction of the ankle joint depending on postural stability.

Slow Intermuscular Oscillations are Associated with Cocontraction Steadiness.

Voluntary muscle contraction often involves low-frequency correlated neural oscillations across muscles, which may degrade steady cocontraction between antagonistic muscles with distinct levels of activation per each muscle (unbalanced cocontraction). The purposes of the study were 1) to determine whether there is an association between the low-frequency correlated EMG oscillations and the performance of steady unbalanced cocontraction across individuals and 2) to determine whether a bout of out-of-phase cocontraction practice reduces the in-phase low-frequency correlated neural oscillations and improves the performance of steady unbalanced cocontraction. Healthy young adults were divided into three intervention groups: cocontraction, contraction, and control. All participants were tested for unbalanced steady cocontractions with antagonistic muscles about the elbow joint before and after a bout of intervention with the visual feedback of surface EMG. During the intervention period, the cocontraction group practiced an out-of-phase cocontraction, whereas the contraction group practiced agonist contractions. Mean squared error and variance of EMG amplitude were positively correlated with low-frequency EMG coherence <3 Hz across subjects, which became more prevalent after the intervention period. There was no specific effect of the cocontraction intervention on these variables. These findings suggest that individuals with less low-frequency correlated neural oscillations tend to perform steady cocontraction more skillfully, and the low-frequency correlated oscillations may not be acutely modulated by one bout of out-of-phase cocontraction practice.

Prophylactic stretching does not reduce cramp susceptibility.

Some clinicians advocate stretching to prevent muscle cramps. It is unknown whether static or proprioceptive neuromuscular facilitation (PNF) stretching increases cramp threshold frequency (TFc ), a quantitative measure of cramp susceptibility. Fifteen individuals completed this randomized, counterbalanced, cross-over study. We measured passive hallux range of motion (ROM) and then performed 3 minutes of either static stretching, PNF stretching (hold-relax-with agonist contraction), or no stretching. ROM was reassessed and TFc was measured. PNF stretching increased hallux extension (pre-PNF 81 ± 11°, post-PNF 90 ± 10°; P < 0.05) but not hallux flexion (pre-PNF 40 ± 7°, post-PNF 40 ± 7°; P > 0.05). Static stretching increased hallux extension (pre-static 80 ± 11°, post-static 88 ± 9°; P < 0.05) but not hallux flexion (pre-static 38 ± 9°, post-static 39 ± 8°; P > 0.05). No ROM changes occurred with no stretching (P > 0.05). TFc was unaffected by stretching (no stretching 18 ± 7 Hz, PNF 16 ± 4 Hz, static 16 ± 5 Hz; P = 0.37). Static and PNF stretching increased hallux extension, but neither increased TFc . Acute stretching may not prevent muscle cramping. Muscle Nerve 57: 473-477, 2018.