Intramuscular pressure and electromyography in the supraspinatus muscle at shoulder abduction

In ergonomic and biomechanic research, estimations of shoulder muscle load and evaluation of different measuring techniques are important. Intramuscular pressure (IMP), using the microcapillary infusion technique and bipolar intramuscular electromyography (EMG), was recorded from the same part of the supraspinatus muscle. In 12 subjects, IMP and EMG were recorded at shoulder abduction angles of 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 135 degrees with no or a 1- or 2-kg hand load in each position. The shoulder torque was calculated for each test position. A correlation was found for both mean IMP and mean EMG versus shoulder torque if the position with extreme muscle shortening (135 degrees abduction) was excluded. IMP was high (greater than 50 mmHg) in almost all test situations. In seven other subjects, isometric force in abduction was correlated with IMP and EMG. Both methods showed an equally good correlation with external shoulder force, IMP gives as good an estimation of relative muscle force as EMG, but any comparison between EMG and IMP must be done at the same muscle length.     

Electromyography of superficial cervical muscles with exertion in the sagittal, coronal and oblique planes

The purpose of the current study was twofold: (1) to determine the isometric force and electromyographic (EMG) relationship of the sternocleidomastoid, splenii and trapezii muscles bilaterally in graded and maximal exertions in the sagittal, coronal and oblique planes. and (2) to develop regression equations to predict force based on the EMG scores. A newly designed and validated cervical isometric strength testing device was used to measure the cervical muscle isometric strength and force/EMG relationship in cervical flexion, extension, bilateral lateral flexion, bilateral anterolateral flexion, and bilateral posterolateral extension, all beginning with an upright seated neutral posture. A group of 40 healthy subjects were asked to exert their cervical motions in the directions of interest, while the force output and EMG from the sternocleidomastoids, splenii, and trapezii were sampled bilaterally at 1 kHz. ANOVA, correlation, and regression analyses were carried out. The force and EMG scores were significantly different between the directions of effort (P<0.01). All regressions were significant (P<0.01). All subjects registered the highest forces in pure extension and the lowest in pure flexion, showing a gradual decrease from the posterior to anterior direction. There was a modest correlation between EMG of the investigated muscles and force (r=0.15-0.76, P<0.01). EMG output was, for example, approximately 66% higher in flexion than in extension (while force output was roughly 30% less in flexion than extension) - thus relatively more muscle activity was required in flexion than extension to generate a given force. The intermediate positions (i.e. anterolateral flexion) revealed force/EMG ratio scores that were intermediate in relation to the force/EMG ratios for pure flexion and pure extension. The cervical muscle strength and cervical muscle EMG are therefore dependent on the direction of effort.     

The application of an external wrist extension force reduces electromyographic activity of wrist extensor muscles during gripping

STUDY DESIGN: Experimental repeated-measures study. OBJECTIVE: To investigate the effect of different extension forces applied to the palm of the hand on electromyographic (EMG) activity of the wrist extensor muscles during hand gripping. BACKGROUND: Lateral epicondylitis is usually caused by repetitive wrist extension that leads to an overuse injury. The current theory is that the process of lateral epicondylitis begins with an overuse injury that leads to microtearing of the extensor carpi radialis brevis muscle and occasionally the extensor digitorum communis muscle. Use of an external wrist extension force might reduce muscle activity during gripping. METHODS: Muscle activity was measured using surface EMG while subjects gripped at an intensity of 10%, 20%, and 30% of the maximum voluntary contraction force without, and with, an applied external wrist extension force of 1%, 2%, and 3% of maximum voluntary contraction. RESULTS: Applying an extension force to the palm of the hand reduced EMG activity of the extensor muscles at the same strength generation during hand gripping. The muscles with the most significant reduction in EMG level, the extensor carpi radialis brevis and extensor digitorum communis, are those muscles that are most often involved with lateral epicondylitis. CONCLUSIONS: This study shows that an external extension force reduces EMG activity of the wrist extensor muscles during gripping in healthy volunteers. As the extension force increased, a greater reduction in muscle activity was noted.     

Effect of wrist hand splints on grip, pinch, manual dexterity, and muscle activation in children with spastic hemiplegia: a preliminary study.

The effect of wrist/hand orthoses on force production, dexterity, and upper extremity muscle recruitment was investigated in children with and without cerebral palsy (CP) to determine if splint design affects 1) hand function and 2) muscle activation. Ten children with hemiplegic CP used hands with spasticity (n=10) and five age-matched control children used dominant and nondominant hands (n=10) in three splint conditions (no, dynamic, static) during grip, pinch, and peg-board tests while electromyography (EMG) recorded muscle activation. Children with spasticity increased their grip (p=0.008) and dexterity (p=0.02) when wearing dynamic splints and pinch (p=0.04) with no splints. All children had significantly less wrist EMG activity during grip with static splints; only children with CP had greater compensatory shoulder activation. Preliminary findings suggest that dynamic splints increased function of children with CP while static splints decreased muscle activation at wrist and increased compensatory shoulder muscle recruitment.     

Hand grip increases shoulder muscle activity: An EMG analysis with static handcontractions in 9 subjects

We examined 4 shoulder muscles-the supraspina-tus, infraspinatus, the middle portion of the deltoid and the descending part of the trapezius-with electromyography (EMG) in abducted and flexed arm positions, in 9 healthy subjects. the subjects were asked to produce a static handgrip force of 30% and 50% of maximal voluntary contraction (MVC) in 8 different arm positions. in all positions, the subjects held a dynamometer in the hand. the myoelectric activity in the shoulder muscles with only the dynamometer in the hand was compared to the EMG activity when static contractions were added. There was an association between static handgrip and shoulder muscle activity, as revealed by EMG. the EMG activity increased in the supraspinatus muscle in humeral flexion from and above 60° and in 120° abduction. in the infraspinatus muscle, the changes were less; a significant increase, however, was noticed in flexion. in the deltoid muscle there was a tendency towards increased activity in positions lower than 90°, in the higher arm positions, the activity decreased. There was no significant alteration regarding the EMG activity of the trapezius.

Our findings imply that high static handgrip force, particularly in elevated arm positions, increases the load on some shoulder muscles. the stabilizing muscles (the rotator cuff) were more influenced than the motor muscles by hand activity. Handgrip activity is important to evaluate while assessing shoulder load in manual work and in clinical evaluations of patients with shoulder pain.     

Intramuscular pressure, tissue oxygenation and EMG fatigue measured during isometric fatigue-inducing contraction of the multifidus muscle

Simultaneous measurement of intramuscular pressure (IMP), tissue oxygen partial pressure (pO₂) and EMG fatigue parameters in the multifidus muscle during a fatigue-inducing sustained muscular contraction. The study investigated the following hypotheses: (1) Increases in IMP result in tissue hypoxia; (2) Tissue hypoxia is responsible for loss of function in the musculature. The nutrient supply to muscle during muscle contraction is still not fully understood. It is assumed that muscle contraction causes increased tissue pressure resulting in compromised perfusion and tissue hypoxia. This tissue hypoxia, in turn, leads to muscle fatigue and therefore to loss of function. To the authors knowledge, no study has addressed IMP, pO₂ and EMG fatigue parameters in the same muscle to gain a deeper sight into muscle perfusion during contraction. As back muscles need to have a constant muscular tension to maintain trunk stability during stance and locomotion, muscle fatigue due to prolonged contraction-induced hypoxia could be an explanation for low back pain. Sixteen healthy subjects performed an isometric muscular contraction exercise at 60% of maximum force until the point of localized muscular fatigue. During this exercise, the individual changes of IMP, pO₂ and the median frequency (MF) of the surface EMG signal of the multifidus muscle were recorded simultaneously. In 12 subjects with a documented increase in intramuscular pressure, only five showed a decrease in tissue oxygen partial pressure, while this parameter remained unchanged in six other subjects and even increased in one. A fall in tissue pO₂ was associated with a drop in MF in only five subjects, while there was no correlation between these parameters in the other 11 subjects. To summarize, an increase in IMP correlated with a decrease in pO₂ and a drop in MF in only five out of 16 subjects. High intramuscular pressure values are not always associated with a hypoxia in muscle tissue. Tissue hypoxia is not automatically associated with a median frequency shift in the EMG signals power spectrum.C. Dehner and E. Hartwig contributed to this work equally. The experiments comply with the current laws of Germany and were performed inclusive of ethics approval     

Muscle oxygenation and intramuscular pressure related to posture and load in back muscles

Background contextThere is little information about the simultaneous changes of intramuscular pressure (IMP) and oxygen saturation (StO₂) of the paraspinal muscle under various conditions of posture and load.PurposeTo measure simultaneously and compare IMP and StO₂ across a range of static trunk postures commonly observed during normal work tasks.Study designA prospective study using a repeated-measure design in clinical setting.Patient sampleSixteen healthy young men with no history of back pain.Outcome measuresSimultaneous measurements of IMP by a flexible slit catheter and StO₂ by near infrared spectroscopy of the multifidus muscle were performed.MethodsThe two measures were taken in six static posture tasks: standing upright and bending forward with and without load (20 kg), bending backward and during a sustained isometric contraction (ie, Sorensen test). To compare the influence of the tasks on IMP and StO₂ variables, a one-way variance analysis with repeated measures was used. Spearman's rank correlation coefficient (rho) was determined between the two variables for each posture task.ResultsWe observed only a moderate but significant correlation between IMP and StO₂ values in upright standing and a trend in bending forward positions with load (p<.05). IMP increased in the bending backward position and showed the greatest increase during the Sorensen test. StO₂ decreased significantly during the Sorensen test, in the bending forward position with and without load bearing but did not in bending backward.ConclusionThe simultaneous recording of IMP and StO₂ of the multifidus muscle allows a deeper insight of physiological events during various trunk postures. In the mutifidus muscle, there is no evident linear relationship between IMP and StO₂ values in various static postures of the trunk in young males. This preliminary study shows that IMP may play a role on StO₂ only in some circumstances, such as a prolonged endurance test or in a bending forward position with a significant load bearing.     

Intramuscular pressure in the supraspinatus muscle

Shoulder pain correlated to manual labour is an increasing problem. The etiology is multifactorial and often unclear. High local muscle load and muscle ischemia in the supraspinatus muscle is present in elevated arm positions, as shown in several electromyographic studies. The purpose of this study was to evaluate intramuscular pressure (IMP) as a way to describe local muscle load in the supraspinatus muscle. Measurements were made in 15 arm positions, and with hand loads of 0, 1, or 2 kg weight, in 12 shoulders. The IMP was recorded with microcapillary infusion technique. The method was found to be suitable in recording IMP at rest and during exercise. High intramuscular pressures, i.e., above 50 mm Hg (6.7 kPa), were seen in moderate humeral abduction. The IMP increased further in abduction up to 90 degrees, where mean IMP was 122 mm Hg (16.2 kPa). Added hand load increased intramuscular pressure in all positions except in shoulder flexion of 135 degrees. The study thus demonstrated that intramuscular pressure offers important information about the load on the supraspinatus muscle in different positions of the arm. The results indicate that fatigue and shoulder pain related to elevated arm positions may be caused by muscle ischemia induced by the high intramuscular pressure present in these positions.     

Effects of the forearm support band on wrist extensor muscle fatigue

STUDY DESIGN: A crossover experimental design with repeated measures. OBJECTIVE: To determine whether the forearm support band alters wrist extensor muscle fatigue. BACKGROUND: Fatigue of the wrist extensor muscles is thought to be a contributing factor in the development of lateral epicondylitis. The forearm support band is purported to reduce or prevent symptoms of lateral epicondylitis but the mechanism of action is unknown. METHODS AND MEASURES: Fifty unimpaired subjects (36 men, 14 women; mean age = 29 +/- 6 years) were tested with and without a forearm support band before and after a fatiguing bout of exercise. Peak wrist extension isometric force, peak isometric grip force, and median power spectral frequency for wrist extensor electromyographic activity were measured before and after exercise and with and without the forearm support band. A 2 x 2 repeated measures multivariate analysis of variance was used to analyze the data, followed by univariate analysis of variance and Tukey's multiple comparison tests. RESULTS: Peak wrist extension isometric force, peak grip isometric force, and median power spectral frequency were all reduced after exercise. However, there was a significant reduction in peak grip isometric force and peak wrist extension isometric force values for the with-forearm support band condition (grip force 28%, wrist extension force 26%) compared to the without-forearm support band condition (grip force 18%, wrist extension force 15%). CONCLUSIONS: Wearing the forearm support band increased the rate of fatigue in unimpaired individuals. Our findings do not support the premise that wearing the forearm support band reduces muscle fatigue in the wrist extensors.     

Evaluation of motor blockade by isometric force measurement and electromyographic recording during epidural anaesthesia – a methodological study

Methods for assessing motor blockade by means of isometric force measurements and surface electromyographic (EMG) recordings in the lower extremities and abdominal wall were evaluated in 30 volunteers. The coefficients of variation were 10% for force measurements and 14% and 20% for average rectified EMG (RIEMG) recordings over the quadriceps muscle and abdominal muscles, respectively, and 8% overall for TURNS (the number of changes in the sign of the direction of the EMG signal). Seven of the 30 volunteers received epidural anaesthesia with 20 ml of mepivacaine 2% with adrenaline. The mean maximal cephalad analgesic level was T9. At that abdominal segment, RIEMG showed a reduction of 50% and TURNS of 20%. Isometric force and RIEMG recorded simultaneously in the quadriceps muscles during epidural anaesthesia displayed a linear relationship with a correlation coefficient of 0.91. TURNS was insensitive to force variations above 60% of maximum voluntary contraction. During the regression phase, 90% of both the initial force and RIEMG value was noted 180 min after the epidural injection. It is concluded that recording of RIEMG is a good method for quantitative assessment of motor blockade during epidural anaesthesia.     

EMG to torque relationship in rectus abdominis muscle. Results with repeated testing

Rectus abdominis muscles of young healthy female volunteers were studied to determine both the maximum strength in isometric flexion and the relation between the surface electromyogram (RMS EMG) and torque. Both the upper and lower portions of the abdominal muscle were studied during graded increase and decrease of torque. Repeated testing was performed over 6 weeks. The form of the relation between torque and EMG was better described by a quadratic than by a linear regression relationship, but with considerable variability about the best-fit line. The torque-increasing and torque-decreasing parts of each test were different and were analyzed separately. After 6 weeks of repeated testing, maximum voluntary isometric flexion torque increased 16.8% (P less than 0.01). There was a decrease in the ratio of electromyographic activity to torque production, which was statistically significant in the torque-increasing recordings. These changes in maximum torque and in the EMG-torque relation were attributed to learning through a test-retest effect, rather than to a true change in muscle characteristics. These findings, which show changes in normal subjects undergoing repeated testing, do not support the reliability of isometric strength measurements, or measurements based on RMS EMG recordings, for quantifying abdominal muscle function in patients with back pain, or those undergoing strengthening exercises.     

Phasic relationships of the extrinsic muscles of the normal hand

The objective of this investigation was to improve the interpretation of dynamic electromyogram studies of upper extremity musculature by providing normal reference data. Fine wire electrodes recorded electromyogram data from the extrinsic forearm and hand muscles of 10 normal adults. Simultaneous wrist and finger motions were recorded by goniometers with the electromyogram data. Subjects performed hand opening and closing while actively maintaining selected elbow, forearm, and wrist positions. Phasic muscle activity was identified in each position for individual subjects. Normal adult subjects use gravity and tenodesis effects in addition to active muscle contraction to achieve motor goals. Individual subjects used different muscles to accomplish the same motor task, but each subject was remarkably consistent in muscle assignment. These findings suggest that individuals employ "motor planning strategies" in hand function.     

A dynamic extensor brace reduces electromyographic activity of wrist extensor muscles in patients with lateral epicondylalgia

STUDY DESIGN: Semiexperimental study. OBJECTIVE: To investigate the effect of an external wrist extension force on extensor muscle activity during hand gripping in patients with lateral epicondylalgia. BACKGROUND: Lateral epicondylalgia or "tennis elbow" is a common, often disabling ailment affecting millions of people. An optimal treatment strategy remains to be identified. The use of an external wrist extension force may reduce the extensor muscle activity during gripping in these patients. METHODS: Muscle activity of the extensor carpi radialis brevis (ECRB), extensor digitorum communis (EDC), and extensor carpi radialis longus (ECRL) was measured using surface EMG. Subjects gripped at an intensity of 10%, 20%, and 30% of the maximum voluntary contraction (MVC) force with and without the dynamic extensor brace and with and without an applied external wrist extension force of 1%, 2%, and 3% of MVC. RESULTS: At all levels of MVC gripping, the EMG signal of the ECRB and EDC were significantly lower for gripping with than without brace. An extension force of 3% of the MVC force significantly reduced the EMG signal of all muscles in almost all measurement conditions. CONCLUSIONS: The results of this study indicate that the dynamic extensor brace as well as the external extension force significantly reduced the EMG signal of the wrist extensor muscles during gripping in patients with lateral epicondylalgia. Based on these results, the dynamic extensor brace could be a promising new intervention for lateral epicondylalgia.     

The effects of lumbosacral orthoses on spine stability: What changes in EMG can be expected?

Antagonistic trunk muscle activity is normally required to stabilize the spine. A lumbosacral orthosis (LSO) might reduce the need for this antagonistic activity by providing passive stiffness to the trunk and increasing spine stability. The maximum reduction in trunk muscle EMG and in the resultant spine compression force due to the LSO was estimated using a biomechanical model. The lumbar spine stability was first quantified for the average trunk muscle EMG recorded from 11 male subjects performing various isometric trunk exertion tasks. Subsequently, the spine-stiffening effects of the LSO were implemented in the model and trunk muscle forces were reduced iteratively until the original level of spine stability without the LSO was achieved. The upper bound estimates of the reduction in trunk muscle EMG due to LSO ranged from 0.6% to 14.1% of the maximum voluntary activation depending on the task and the muscle. The resultant spine compression force averaged across all tasks decreased by only 355 N. A much larger variance of the experimental data precluded the detection of these effects at statistically significant levels. However, the small effects size does not necessarily exclude the possibility of functional benefits of slightly reducing muscle activity in patients with low back pain.     

A supination splint worn distal to the elbow: a radiographic, electromyographic, and retrospective report.

The purposes of this study were to 1) describe a dynamic supination splint that does not cross the humeroulnar and humeroradial joints, allowing flexion and extension of the elbow; 2) provide retrospective data on effectiveness of this splint in patients with limited supination; and 3) provide data from radiography and electromyography (EMG) that document this splint's ability to provide a passive supination force. Eleven subjects treated for various elbow and/or wrist fractures leading to losses of forearm supination significantly increased their passive range of motion (PROM) from 34.0 degrees at the initial visit to 82.3 degrees at discharge and active range of motion (AROM) from 27.0 degrees to 72.3 degrees. Radiographic images of the radius and ulna were identical in maximal voluntary supination and resting in the splint. Surface EMG was used to measure supinator muscle activity at rest, passively supinated while wearing the splint, and during a maximal isometric supination effort (without splint). Average supinator EMG activity was 7.9 mV at rest, 7.8 mV in the splint, and 68.0 mV with maximal isometric contraction. Results indicate the supination splint is clinically effective in increasing supination PROM. EMG data and radiographs indicate that the splint passively positions the forearm in supination even though the proximal margin of the splint does not cross the elbow.     

Asymmetry of paraspinal EMG-time characteristics in idiopathic scoliosis

The purpose of this study was to investigate the activation pattern of the paraspinal muscles in scoliotic and normal subjects. Force-time and electromyography (EMG)-time curves of paraspinal muscles were recorded during maximal isometric trunk extensions in 15 girls with adolescent idiopathic scoliosis (AIS) and in 14 healthy girls with structurally normal spines. The isometric force-time curves as well as the maximal integrated electromyography (IEMG) activities that were recorded from both sides of the thoracic and lumbar spine did not show any significant differences between the two subject groups. However, in the subjects with AIS, the IEMG activities recorded at the onset and during the early (submaximal) phases of muscle contraction were significantly higher in the left lumbar muscles compared with the right side. The observed intensity-specific EMG asymmetry in the present scoliotic subjects may be attributed to the imbalanced neural input associated with AIS that may also have pathogenetic importance in the etiology of idiopathic scoliosis.     

Motor blockade and EMG recordings in epidural anaesthesia. A comparison between mepivacaine 2%, bupivacaine 0.5 % and etidocaine 1.5%

In a double-blind study young volunteers randomly received 20 ml of mepivacaine 2%, bupivacaine 0.5% or etidocaine 1.5% epidurally, all solutions with adrenaline. The mean cephalad spread of pin-prick analgesia was equal (T10) in the groups, but the duration was longest for bupivacaine and etidocaine. The motor blockade of the rectus abdominis muscles was assessed quantitatively by rectified integrated electromyographic recordings (RIEMG) and as number of turns in EMG recordings [changes in the direction (rise/fall) of the EMG; TURNS] from three different segmental levels, T7, T9 and T11. The motor blockade of the quadriceps muscles was estimated by EMG recordings simultaneously with muscle force measurements at maximal isometric knee extension. Motor blockade was also evaluated by the Bromage scale. There was good correlation (correlation coefficient 0.91) between RIEMG values and muscle force in knee extension during epidural anaesthesia. TURNS showed a non-linear relationship to isometric force during epidural anaesthesia and added no further information. At the lower parts of the abdomen (T11), etidocaine gave more profound and longer motor blockade than mepivacaine. For quadriceps muscle function, motor blockade was almost complete with all three local anaesthetics; the duration of maximum motor blockade was short (45-60 min) for mepivacaine, but about 5 h with etidocaine. At the time when the Bromage scale indicated complete regression of motor blockade, the muscle force of knee extension was only 30% and the quadriceps RIEMG 35% of control values and 1-3 h remained until the time of mobilization.(ABSTRACT TRUNCATED AT 250 WORDS)