Average Electromyographic Activity Research Articles

Assessing the Sensitivity of the Ratio Method in Identifying the Flexion-Relaxation Phenomenon in People With Non-specific Low Back Pain and Healthy People

Background and Aims There are different methods for quantifying the flexion-relaxation phenomenon (FRP). However, there is little standardization for them. This study aimes to evaluate the sensitivity of the ratio method in identifying the FRP in people with non-specific low back pain (LBP) and healthy people. Methods In this study,10 patients with nonspecific LBP and 10 healthy people participated voluntarily. They performed a trunk flexion with a straight knee. Each trunk flexion was done in four modes: (1) standing in the starting position, (2) trunk flexion at a fixed speed (using a metronome), (3) full flexion, and (4) trunk extension to the standing position. Each mode took 5 seconds and was performed 3 times. Then, the FRP was investigated using the ratio method as well as the visual inspection method. Results The sensitivity of all ratios in identifying the FRP in healthy people was 100%, except for the third ratio (the root mean square of EMG activity in a standing position divided by the root mean square in flexion mode), which was 60%. In the LBP group, the sensitivity of the first ratio was 70%; for the second ratio, it was 80%; for the third ratio, 40%; for the fourth ratio, 50%; for the fifth mode (the root mean square in extension mode divided by the root mean square in full flexion mode), 40%; and for the sixth mode, 50%. Conclusion All ratios (except for the second ratio) are valid for identifying the FRP in healthy people, but caution should be taken in using the ratio method for people with LBP; only the second ratio (maximum EMG activity in the extension mode divided by the average EMG activity in the full flexion mode) should be used for these individuals.

The Influence of Transcranial Alternating Current Stimulation on Fatigue Resistance.

Previous research has shown that some forms of non-invasive brain stimulation can increase fatigue resistance. The purpose of this study is to determine the influence of transcranial alternating current stimulation (tACS) on the time to task failure (TTF) of a precision grip task. The study utilized a randomized, double-blind, SHAM-controlled, within-subjects design. Twenty-six young adults completed two experimental sessions (tACS and SHAM) with a 7-day washout period between sessions. Each session involved a fatiguing isometric contraction of the right hand with a precision grip with either a tACS or SHAM stimulation applied to the primary motor cortex (M1) simultaneously. For the fatiguing contraction, the participants matched an isometric target force of 20% of the maximum voluntary contraction (MVC) force until task failure. Pre- and post-MVCs were performed to quantify the force decline due to fatigue. Accordingly, the dependent variables were the TTF and MVC force decline as well as the average EMG activity, force error, and standard deviation (SD) of force during the fatiguing contractions. The results indicate that there were no significant differences in any of the dependent variables between the tACS and SHAM conditions (p value range: 0.256-0.820). These findings suggest that tACS does not increase the TTF during fatiguing contractions in young adults.

The relative activation of pelvic floor muscles during selected yoga poses

BackgroundIndividuals with pelvic floor muscle (PFM) dysfunction can benefit from core stabilization exercises. Yoga is a popular activity that can generate moderate to high trunk activity and has been shown to benefit this patient population. No data exist regarding PFM activity during yoga. Determining PFM activity will provide important information for developing an evidence-based exercise program. ObjectivesTo determine the relative activation of the PFM during select yoga poses. Study designCross-sectional design. MethodsPerianal surface EMG sensors were used to capture levator ani (LA) activation. Peak activity of a maximum voluntary isometric contraction (MVIC) represented 100% activity. For testing, subjects held the following poses for 30 s: locust; modified side plank; side angle; and hands-clasped front plank. The average EMG activity, expressed as a 100% percent of the MVIC (%MVIC), from 5 to 25 s of each pose was analyzed. ResultsSubjects generated the most activity (63.5 %MVIC) during the locust. Side angle (35.3 %MVIC) required greater activity than the side (29.1 %MVIC) and front planks (26.3 %MVIC). Locust activity was significantly greater (P < 0.001) than all poses; side angle activity was significantly greater (P < 0.01) than the front and side planks. ConclusionLA activation during locust was very high and sufficient for strength gains. LA activation during side angle, front plank, and side plank would be best for improving endurance and/or neuromuscular control of the PFM. Findings from this study showed differing levels of PFM activation across yoga poses that may benefit patients with pathology associated with PFM dysfunction.

Flexor-Pronator Mass Training Exercises Selectively Activate Forearm Musculature.

The flexor-pronator mass of the forearm contributes dynamic stability to the medial elbow. Training this muscle group is essential for overhead athletes, however, there is lack of evidence supporting use of training exercises. The purpose of this study was to measure the extent of EMG activity of the flexor pronator musculature during two distinct forearm strengthening exercises using resistance bands. It was hypothesized that two exercises would elicit at least moderate level of muscle activity, but the activation would be different in the pronator versus the flexor muscles. 10 healthy subjects (all males, age 36±12 years) were included. Surface EMG activity was measured on three muscles of the dominant-side forearm: flexor carpi ulnaris (FCP), flexor digitorum superficialis (FDS), and pronator teres (PT). After measurement of maximal voluntary contraction (MVC) for each muscle, subjects performed wrist ulnar deviation and forearm pronation exercises using elastic band resistance. Resistance was set to elicit moderate exertion (5/10 on the Borg CR10 scale). Order of exercise was randomized and three repetitions of each exercise were performed. Mean peak EMG activity in each muscle across repetitions during the eccentric phase of each exercise was calculated and expressed as a percentage of MVC. Moderate level of activity was defined as 21% of MVC or higher. Peak normalized EMG activity in each muscle was compared using two-way (exercise x muscle) repeated-measures ANOVA with post-hoc pairwise comparisons if a significant interaction was found. There was an exercise by muscle interaction effect (p<0.001). The ulnar deviation exercise selectively activated FCU (40.3%) versus FDS (19.5%, p=0.009) and PT (21.5%, p=0.022). Conversely, the pronation exercise selectively activated FDS (63.8%, p=0.002) and PT (73.0%, p=0.001) versus FDS (27.4%). The ulnar deviation and pronation exercises using elastic band resistance studied targeted and activated the flexor-pronator mass musculature. The ulnar deviation and pronation exercises using elastic band resistance are practical and effective means of training the flexor-pronator mass. These exercises can be readily prescribed to athletes and patients as part of their arm care program.

Differences in Thigh Muscle Activation Between Standing and Landing Exercises for Knee Injury Prevention and Rehabilitation.

In injury prevention or rehabilitation programs, exercises that facilitate enhanced hamstring activity may be beneficial when aiming to enhance knee joint stability during movements in sports with higher risk of acute knee injury. Information about neuromuscular activation of the hamstring muscles in commonly used exercises may improve exercise selection and progression in programs for knee injury prevention or rehabilitation. To investigate (1) how balance devices with progressing degrees of instability influence the activity of muscles controlling the knee joint in typical balance exercises with different demands on postural control, and (2) if any between-sex differences exist. Cross-sectional study. Twenty habitually active healthy adults (11 males) participated in this cross-sectional study. Single-leg stance, single-leg squat and single-leg landing were performed on the floor and two different balance devices imposing various levels of challenge to postural control. Three-dimensional motion analysis was used to obtain hip and knee joint angles, and as primary outcomes, and peak normalized EMG activity from the hamstrings and quadriceps muscles was measured for comparison between exercises. The more challenging in terms of maintaining stable balance the devices were, the higher hamstring muscle activity levels were observed. There was a clear progression across balance devices from single-leg stance to single-leg squat and further to single-leg landing displaying increasing hamstring activity levels. The change in medial hamstring activity across all devices when changing from single-leg squat to single-leg landing was significantly higher for the female participants than for the males reaching a higher level of activity. The muscle activity of the hamstrings and quadriceps increased when the motor task was more dynamic. Specifically, single-leg landings were effective in increasing the hamstring muscle activity over the single-leg stance to single-leg squat exercises, and muscle activity was significantly increased with the most unstable device. Increases in hamstring muscle activation was greater in female subjects than males with increasing instability of the balance devices. Not registered. 3.

Band Pull-Apart Exercise: Effects of Movement Direction and Hand Position on Shoulder Muscle Activity.

Background/PurposeThe Elastic band pull-apart exercise is commonly used in rehabilitation. It involves pulling an elastic resistance band with both hands in horizontal abduction or diagonal arm movements. The extent of muscle activation during this exercise is unknown. The purpose of this study was to measure the electromyographic (EMG) activity of shoulder-girdle muscles during the pull-apart exercise using resistance bands and to determine the effects of arm position and movement direction on shoulder-girdle muscle activity.Materials/MethodsSurface EMG activity was measured on the infraspinatus, upper trapezius, middle trapezius, lower trapezius and posterior deltoid of the dominant shoulder. After measurement of maximal voluntary contraction (MVC) for each muscle, subjects performed the band pull-apart exercise in three hand positions (palm up, neutral, palm down) and three movement directions (diagonal up, horizontal, diagonal down). Elastic band resistance was chosen to elicit moderate exertion (5/10 on the Borg CR10 scale). The order of the exercises was randomized and three repetitions of each exercise were performed. Mean peak EMG activity in each muscle across the repetitions was calculated and expressed as a percentage of MVC. Peak normalized EMG activity in each muscle was compared in two-way (hand position x direction) repeated-measures ANOVA.ResultsData were collected from 10 healthy subjects (all males, age 36±12 years). Peak muscle activity ranged from 15.3% to 72.6% of MVC across muscles and exercise conditions. There was a significant main effect of hand position for the infraspinatus and lower trapezius, where muscle activity was highest with the palm up hand position (p < 0.001), and for the upper trapezius and posterior deltoid, where muscle activity was highest with the palm down position (p-value range < 0.001-0.004). There was a significant main effect of movement direction, where the diagonal up direction demonstrated the highest muscle activity for the infraspinatus, upper trapezius, lower trapezius, and posterior deltoid (p-value range < 0.001-0.02).ConclusionAltering hand position and movement direction during performance of an elastic band pull-apart exercise can affect magnitudes of shoulder-girdle muscle activity. Clinicians may alter a patient’s hand position and movement direction while performing the band pull-apart exercise in order to increase muscle activity in target muscles or diminish muscle activity in other muscles.Level of Evidence2b

Assessment of changes in muscle activity using electromyography in patients undergoing orthognathic surgery

The aim of the present clinical trial study is to evaluate the effect of double jaw orthognathic surgery (OGS) on electromyographic activity of the masseter, anterior temporal, digastric, and sternocleidomastoid muscles in skeletal Class III patients. This prospective study included 10 patients who underwent Lefort 1 osteotomy of the maxilla and genioplasty of the mandible to correct skeletal dental class III malocclusion and presurgical and postsurgical EMG data were analyzed and compared. The participants underwent bilateral surface electromyography activity evaluation with a focus on the masseter, anterior temporalis, digastric and sternocleidomastoid muscles. Recordings were made each during 3 jaw positions: clench, resting and swallowing positions. The pre-surgical EMG data were compared with the post-surgical EMG data taken after 1 month to evaluate any changes in muscle activity. A significant increase in the average EMG activity after an orthognathic corrective surgery was observed. There were no significant postoperative changes in the EMG potentials of the anterior temporalis and masseter bilateral balance in the pre-op and post-op clench positions. Significant muscle posturing was observed in the post-op resting position with bilateral masseter, sternocleidomastoid, and right temporalis values&gt;2mcv with mandible and rest.

Electromyography Activity of Vastus Medialis Obliquus and Vastus Lateralis Muscles During Lower Limb Proprioceptive Neuromuscular Facilitation Patterns in Individuals with and without Patellofemoral Pain Syndrome.

Exercise therapy to strengthen quadriceps muscle is recommended in rehabilitation program for people with patellofemoral pain syndrome (PFPS). This study aimed to investigate the electromyography (EMG) activity of vastus medialis obliquus (VMO), vastus lateralis (VL) and VMO/VL ratio during PNF in individuals with and without PFPS. 26 persons with PFPS and 26 healthy subjects participated to study. All subjects performed PNF patterns (Flexion-Adduction-External Rotation (D1FL), Extension-Adduction-External Rotation (D2EX), D1FL+ load, D2EX+ load) and straight leg raise (SLR). The normalized EMG activity of VMO, VL and VMO/VL ratio were measured and analyzed using repeated measure ANOVA. There were significant main effects of group and exercises for the both VMO and VL (p<0.05). It was found that except SLR and D2EX, in the other motions PFPS group had lower VMO activity compared to healthy group (p<0.05). For VL except SLR, in the other motions PFPS group had lower VL activity too (p<0.05). The PNF patterns activated VMO more than SLR, however it was not significant (p>0.05). Also; there weren't any significant difference between the two groups in VMO/VL activation ratios. Also, performing the PNF patterns with load increased VMO and VL muscles activity significantly (p<0.05). It also found that in PFPS group the VMO/VL ratio values in PNF patterns were significantly more than SLR and the highest VMO/VL ratio value (0.96) was found during D2EX. The PNF patterns due to provide optimal VMO/VL ratio value than SLR and proper balance between these two muscles can be recommended in rehabilitation of individuals with PFPS.

Dynamic Control of Upper Limb Stretch Reflex in Wrestlers.

ABSTRACTPurposeThe objective of this study was to clarify the characteristics of the upper limb stretch reflex in wrestlers.MethodsTen wrestlers and 11 control subjects participated in the study. The experiment was divided into two sessions. In the extension perturbation session, participants either relaxed or flexed the elbow when they felt a perturbation (abrupt elbow extension induced by a dynamometer). This was done 30 times by each subject for both sessions. In the flexion perturbation session, participants also relaxed or extended the elbow when they felt a perturbation (abrupt elbow flexion). During the tasks, the stretch reflex was monitored by recording the surface EMG activities of the right biceps and triceps brachii. The EMG reflex components were divided into three periods based on the time after the perturbation (M1, 20–50 ms; M2, 50–80 ms; and M3, 80–100 ms). The averaged background EMG activity just before the disturbance was subtracted from the EMG activity in each period. The resultant value was integrated to obtain reflex magnitudes of M1 to M3.ResultsFor the triceps brachii, in the relaxation task, the wrestler group showed a significantly smaller value for M2 than did the control group. In the extension task, the wrestler group showed a significantly larger value for M3 than did the control group. There was no difference in M1 between the two groups. For the biceps brachii, there was no significant difference between any reflex components.ConclusionsOur results suggest that high-level wrestlers have specific characteristics of the long-latency stretch reflex in the triceps brachii that are modulated in a situation-specific manner.

Exploring the Interaction Between Head-Supported Mass, Posture, and Visual Stress on Neck Muscle Activation.

Assess neck muscle activity for varying interactions between helmet, posture, and visual stress in a simulated "helo-hunch" posture. Military aviators frequently report neck pain (NP). Risk factors for NP include head-supported mass, awkward postures, and mental workload. Interactions between these factors could induce constant low-level muscle activation during helicopter flight and better explain instances of NP. Interactions between physical loading (helmet doffed/donned), posture (symmetric/asymmetric), and visual stress (low/high contrast) were studied through neck muscle electromyography (EMG), head kinematics, subjective discomfort, perceived workload, and task performance. Subjects (n = 16) performed eight 30-min test conditions (varied physical loading, posture, and visual stress) while performing a simple task in a simulated "helo-hunch" seating environment. Conditions with a helmet donned had fewer EMG median frequency cycles (which infer motor unit rotation for rest/recovery, where more cycles are better) in the left cervical extensor and left sternocleidomastoid. Asymmetric posture (to the right) resulted in higher normalized EMG activity in the right cervical extensor and left sternocleidomastoid and resulted in less lateral bending compared with neutral across all conditions. Conditions with high visual stress also resulted in fewer EMG cycles in the right cervical extensor. A complex interaction exists between the physical load of the helmet, postural stress from awkward postures, and visual stress within a simulated "helo-hunch" seating environment. These results provide insight into how visual factors influence biomechanical loading. Such insights may assist future studies in designing short-term administrative controls and long-term engineering controls.

Effect of Using an 8-Figure Shoulder Brace on Posture and Muscle Activities during the Performance of Dental Hygiene Procedures.

The incidence of work-related musculoskeletal disorders (MSDs) among dental workers has been increasing. Many ergonomic devices and accessories have been introduced. The aim of this study was to investigate the effects of an 8-figure shoulder brace on posture-related muscle activities in dental hygiene practitioners during scaling procedures. In this study, 33 participants (age: 21.9 ± 2.1 years, height: 162.0 ± 6.0 cm, weight: 55.8 ± 9.0 kg, body mass index: 21.2 ± 2.4 kg/m2) performed the scaling procedure with and without the 8-figure shoulder brace in a randomized order. The normalized electromyography activity in the amplitude probability distribution function and joint angles (cervical, thoracic, lumbar, and shoulder joints) were simultaneously recorded during scaling. A paired t test was used to compare the differences in muscle kinematics, with the alpha level set at 0.05. The dental hygienists who wore the 8-figure shoulder brace during scaling showed thoracic and lumbar extension, improved sitting postures, and reduced shoulder joint abduction. However, we also observed an unintended increase in internal rotation. Use of the 8-figure shoulder brace could prevent work-related MSDs in lumbar and thoracic regions by reducing the effort exerted by the upper trapezius and deltoid muscles, despite the increased muscular effort of the cervical erector spinae.

Optimal activation ratio of the scapular muscles in closed kinetic chain shoulder exercises: A systematic review.

Muscle synergies contribute to scapular position during arm movement. The trapezius and serratus anterior (SA) muscles are the main stabilizers and are therefore the main target muscles of therapeutic exercises. To systematically review the current literature investigating the optimal activation ratio of the scapular muscles during a range of closed kinetic chain exercises. A systematic review search was conducted to identify studies reporting shoulder electromyography (EMG) activity during rehabilitation exercises in healthy participants. The search was conducted in PubMed, Cochrane Library, MEDLINE, CINAHL, Scopus, SPORTDiscus, and ScienceDirect. The included studies reported closed kinetic chain exercises and the muscle activity as a percentage of maximum voluntary isometric contraction (%MVIC) or muscle ratios of the lower trapezius (LT), middle trapezius (MT), and SA with respect to the upper trapezius (UT). Muscle ratios were classified as optimal if they were equal to or lower than 0.6, and the adapted Newcastle-Ottawa Scale (NOS) was used to evaluate the methodological quality of the selected studies. Twenty-nine studies were included in this review; 7 main exercises and 30 variations of these were reported. The average electromyographic activity of the concentric and eccentric phase was considered. Half Push Up, Push Up Plus, and Scap Protraction exercises showed optimal SA activity (UT/SA < 0.6), while Press Up, Half Push Up, and One Hand Plank exercises showed optimal LT activity (UT/LT < 0.6). According to the NOS, 15 studies were classified as moderate methodological quality. The exercises in higher positions (e.g. exercises with the trunk closest to the vertical line) or unstable surfaces tend to favor UT activity over the MT, LT and SA. The exercises including scapular retraction showed optimal UT/MT and UT/LT ratios, while those including scapular protraction showed optimal UT/SA ratios. This will assist therapists in the correct selection of exercises for shoulder rehabilitation.

Virtual Reality Balance Games Provide Little Muscular Challenge to Prevent Muscle Weakness in Healthy Older Adults.

Objective: Muscle weakness is an important risk factor for falls in older adults. Intensity and duration of muscle activity are important determinants of exercise effectiveness in combating muscle weakness. The aim of this article was to assess the intensity and duration of muscle activity in virtual reality (VR) balance games. Materials and Methods: Thirty young and 30 healthy older adults played seven different VR balance games. Muscle activity of the vastus lateralis, vastus medialis, soleus, and gluteus medius was obtained using surface electromyography (EMG). The processed EMG signals were divided into 200-ms blocks, after which each block was categorized by its average normalized EMG activity, that is, >80%, 60%-80%, 40%-60%, or <40% of maximum voluntary contraction (MVC). We calculated the total number of blocks in each category to score intensity, as well as the maximal number of consecutive 200-ms blocks (MCBs) >40% MVC, to identify prolonged muscle activity. Results: Muscle activity during game play was mostly <40% MVC and prolonged activation was lacking. Only the games that included more dynamic movements showed activation blocks of higher intensity and resulted in more MCBs. Conclusion: Our method allowed us to analyze the overall muscle activity and the distribution of activity over a trial. Although the activation levels during these VR games were low in general, we identified game elements that could potentially provide a strength training stimulus. Future research should aim to implement these elements, such that the intensity, prolonged activity, and rest are optimized to sufficiently challenge lower limb muscles in VR training.

The effect of surface electromyography biofeedback on the activity of extensor and dorsiflexor muscles in elderly adults: a randomized trial

Surface electromyography-biofeedback (sEMG-B) is a technique employed for the rehabilitation of patients with neurological pathologies, such as stroke-derived hemiplegia; however, little is known about its effectiveness in the rehabilitation of the extension and flexion of several muscular groups in elderly patients after a stroke. Therefore, this research was focused on determining the effectiveness of sEMG-B in the muscles responsible for the extension of the hand and the dorsiflexion of the foot in post-stroke elderly subjects. Forty subjects with stroke-derived hemiplegia were randomly divided into intervention or control groups. The intervention consisted of 12 sEMG-B sessions. The control group underwent 12 weeks (24 sessions) of conventional physiotherapy. Muscle activity test and functionality (Barthel index) were determined. Attending to the results obtained, the intervention group showed a higher increase in the average EMG activity of the extensor muscle of the hand and in the dorsal flexion of the foot than the control group (p < 0.001 in both cases), which was associated with an increase in the patients’ Barthel index score (p = 0.006); In addition, Fugl-Meyer test revealed higher effectiveness in the lower limb (p = 0.007). Thus, the sEMG-B seems to be more effective than conventional physiotherapy, and the use of this technology may be essential for improving muscular disorders in elderly patients with physical disabilities resulting from a stroke.

Aminophylline increases parasternal muscle action in awake canines

The traditional theophylline bronchodilator, aminophylline, is still widely used, especially in the treatment of COPD. The effects of aminophylline on ventilation and action of the costal diaphragm have been previously defined, but other respiratory muscles – notably the chest wall, are not well determined. Therefore, we investigated the effects of aminophylline on the Parasternal intercostal, a key obligatory inspiratory muscle, examining muscle length, shortening and EMG. We studied 11 awake canines, chronically implanted with sonomicrometer crystals and fine-wire EMG electrodes in the parasternal muscle. Ventilatory parameters, muscle length (shortening), and moving average muscle EMG activity, were measured at baseline and with aminophylline, during resting and hypercapnic stimulated breathing. Experiments were carried out prior to administration of aminophylline (baseline), and 1.5 h after loading and ongoing infusion. Minute ventilation, tidal volume and respiratory frequency all increased significantly with aminophylline, both during resting breathing and at equivalent levels of hypercapnic stimulated breathing. Parasternal baseline muscle length was entirely unchanged with aminophylline. Parasternal shortening increased significantly with aminophylline while corresponding parasternal EMG activity remained constant, consistent with increased contractility. Thus, in awake, intact mammals, aminophylline, in the usual therapeutic range, elicits increased ventilation and increased contractility of all primary inspiratory respiratory muscles, including both chest wall and diaphragm.

Adults' facial reaction to affective facial expressions of children and adults

Facial mimicry, the unconscious imitation of others' affective facial expressions, serves as an important basis for interpersonal communication. Although there are many studies dealing with this phenomenon regarding the interaction between adults, only few experiments have explored facial mimicry in response to affective facial expressions of children. In the following study affect-prototypical video clips of children's and adults' faces were presented to 44 adults while the activity of corrugator supercilii and zygomaticus muscles was electromyographically measured. A discrete mimic reaction was detected in response to each basic affect (fear, disgust, happiness, sadness, surprise and anger). The activity of corrugator supercilii muscle was significantly lower when affective facial expressions of children were presented in contrast to those of adults. In addition, negative correlations between alexithymia and the averaged facial EMG activity were detected.

Influence of intentional breath-holding on trunk muscle activity and kinematics during patient transfer

We investigated the effects of intentional breath-holding also known as a valsalava maneuver on the kinematics of the lumbar spine, pelvis, hips, and knees, as well as electromyographic (EMG) activity of the trunk muscle during patient transfer with and without knee flexion. The kinematics of the lumbar spine, pelvis, hip, and knee were recorded using a synchronized 3-D motion capture system. Surface EMG was used to assess the activity of the external oblique (EO), internal oblique (IO), erector spinae (ES), and rectus femoris (RF). There was a significant difference in the peak angle of the lumbar spine (η2 = 0.644–0.600), pelvis (η2 = 0.514–0.294), hips (η2 = 0.897–0.746), and knees (η2 = 0.977–0.870), as well as in normalized EMG activity of the EO (η2 = 0.543–0.501), IO (η2 = 0.619–0.460), ES (η2 = 0.567–0.195), and RF (η2 = 0.607–0.144) (except for the RF in the lowering phase, p = 0.10), between the different types of patient transfer, in both the lifting and lowering phases (p < 0.001). These findings suggest that intentional breath-holding during patient transfer contributes to decreased lumbar flexion and ES activity, thus potentially preventing low back injury. However, individuals with a history of heart and cardiovascular disease are advised to avoid the valsalava maneuver.

Trunk muscle activation pattern in parkinsonian camptocormia as revealed with surface electromyography

IntroductionCamptocormia is frequently seen in Parkinson's disease (PD) and multiple system atrophy. It is characterized by a pathological forward bending of the trunk during standing, often combined with a lateral trunk deviation. The etiology of camptocormia in PD is still unknown. Muscle MRI studies show abnormalities mainly of the erector spinae confirmed by muscle biopsies. Quantitative electromyographic examination of trunk muscle activity is missing. MethodsVentral (rectus and obliquus externus abdominis) and dorsal (iliocostalis lumborum, longissimus, multifidus) trunk muscles and the rectus femoris were recorded bilaterally with surface electromyography in standing PD patients with camptocormia (n = 10) and matched healthy controls (n = 10) who mimicked the patients' posture. EMG amplitudes were compared quantitatively. In controls, the relation between varying degrees of trunk flexion and EMG was established systematically. ResultsIncreasing forward trunk flexion was associated with increasing back muscle activity in controls, while abdominal muscle activity was negligible. During anterolateral trunk flexion, back muscle activity increased particularly on the contralateral side. The patients showed a similar pattern. However, normalized EMG activity of their trunk extensors was significantly higher than in controls, often reaching half-maximal amplitudes. Their rectus femoris and oblique abdominal muscles were overactive, but to a lesser extent. ConclusionsPD patients with camptocormia must use the functional reserve of their lumbar trunk muscles to counteract gravity. We interpret this as a weakness of the paravertebral muscles. Compared to the other examined muscles the paravertebral muscles are most affected. The increased EMG activity of the rectus femoris warrants further research.

S60 Clinical neurophysiology in movement disorders: Myoclonus

Myoclonus can be defined as abnormal short jerks caused by bursts of muscular activity or brief periods of inhibition. Myoclonus can be classified depending on their origin and pathophysiologic mechanism in cortical, cortical-subcortical, subcortical (including spinal) and peripheral myoclonus. From a topographic point of view, myoclonus can be generalized, segmentary or focal. Myoclonus can be spontaneous, induced by action, or induced by an external stimulus (reflex). Clinical Neurophysiology is a key step in this diagnostic process. The battery of tests that can be performed in the study of myoclonus include EEG, somatosensory evoked potentials (SSEPs), multi-muscle surface EMG and back-averaging of the EEG signal using the EMG as trigger. If reflex myoclonus is suspected, it might be necessary to average EMG activity using the triggering stimulus in order to demonstrate the reflex mechanism. EEG and back-averaging are useful in the study of cortical myoclonus. Epileptiform activity preceding the muscle jerks can be sometimes observed in the EEG, while the back-averaging should show a cortical spike preceding the jerk with a latency compatible with cortico-spinal conduction times. EEG can also provide specific information about the etiology of the myoclonus (suggesting a metabolic encephalopathy or a myoclonic epilepsy, for instance). High amplitude (giant) SSEPs can be observed in many patents with cortical myoclonus, and their presence is highly suggestive of a cortical origin. In some of them, a reflex response (enhanced C reflex) can be detected (and recorded) during the SSEPs. Surface EMG from different muscles gives valuable information about the duration and spatial spread of the myoclonus. Additionally, the timing and pattern of activation of the different muscles may also be useful to determine the origin (for instance, in reticular or propriospinal myoclonus).

Manifestations of Hysteresis in EMG Activity of Muscles of the Human Upper Limb in Generation of Cyclic Isometric Efforts

Manifestations of muscle hysteresis were examined in seven subjects who generated cyclic isometric efforts by their upper limb in a two-joint mode. Force moments in generation of voluntary efforts with respect to the shoulder and elbow joints were measured, and averaged EMG activity was recorded from eight shoulder and shoulder girdle muscles at five different fixed positions of the upper limb. Hysteresis loops for EMG activity under conditions of two opposite directions of circulation of the isometric effort vectors (clockwise and counterclockwise) were compared. Significant disagreements between segments of increase (“advance”) or decrease (“retardation”) in the EMG amplitude with respect to zero values of the respective force movements were found. Directions of parametric hysteresis loops for EMG activity could be different both for a certain muscle against the background of different configurations of the upper limb links and for different subjects. It is supposed that there is no definite standard strategy for taking into account hysteresis effects in the control of motor phenomena; the CNS selects such specific individual strategy, which demonstrates its validity in the course of formation of the motor experience of an individual