A guide for use and interpretation of kinesiologic electromyographic data.

Physical therapists are among the most common users of electromyography as a method for understanding function and dysfunction of the neuromuscular system. However, there is no collection of references or a source that provides an overview or synthesis of information that serves to guide either the user or the consumer of electromyography and the data derived. Thus, the purpose of this article is to present a guide, accompanied by an inclusive reference list, for the use and interpretation of kinesiologic electromyographic data. The guide is divided into 4 major sections: collecting, managing, normalizing, and analyzing kinesiologic electromyographic data. In the first of these sections, the issues affecting data collection with both indwelling and surface electrodes are discussed. In the second section, data management through alternative forms of data processing is addressed. In the third section, various reasons and procedures for data normalization are discussed. The last section reviews qualitative descriptors once used as the only means of analyzing data, then focuses on more quantitative procedures that predominate today. The guide is intended as a tool for students, educators, clinicians, and beginning researchers who use and interpret kinesiologic electromyographic data. Modifications will likely be needed as alternative forms of collecting, managing, normalizing, and analyzing electromyographic data are proposed, used in various settings, and reported in the literature.

Electromyographic analysis of selected lower extremity musculature in normal subjects during ambulation with and without a Protonics knee brace.

Often, braces are an integral part of treatment programs for patients with pathology of the knee joint. Little evidence exists, however, as to the effect of braces on muscle function. The purpose of this investigation was to compare electromyography (EMG) from six lower extremity muscles during level walking without the Protonics knee brace and with the brace at eight resistance settings. Surface electrodes were placed on one lower extremity of 19 subjects (ages = 21-57) to evaluate EMG activity during ambulation with and without the knee brace. Data were normalized to maximum voluntary contractions and averaged across cycles. There was a significant increase in muscle activity of the rectus femoris, vastus medialis, and vastus lateralis muscles when the brace resisted knee extension and was set at the level of 9. Significantly higher EMG levels also occurred in the vastus lateralis and vastus medialis with the extension module set at level 6 when compared with the no brace trial and resistance levels set at 6 and 2 with the flexion module. In this normal population, there was an increase in activity of selected muscles when the brace was set at the highest resistance settings. These data serve as a guide for clinicians when considering incorporation of a brace of this type into patient management.

Reliability of lower extremity girth measurements after anterior cruciate ligament reconstruction.

The purpose of this study was to determine the intra- and inter-rater reliability of lower extremity girth measurements in patients recovering from anterior cruciate ligament (ACL) reconstructive surgery. Nine subjects, within several months of their surgery, volunteered. Circumferential measurements were taken of the involved and uninvolved legs at the following locations: 15 cm inferior to the joint line; 5, 10 and 15 cm superior to the joint line; at the joint line; and at mid-thigh. All subjects were supine with the knee in extension whilst a specially designed device, formulated to make circumferential measurements at locations around the knee, was applied to the extremity. Three physical therapists each repeated all measurements on two occasions, in random order, during the same test session. Intra-tester intraclass correlation (ICCs) calculated showed high coefficients (0.82-1.0) for both the involved and uninvolved sides for all locations of the measurement. Inter-tester ICCs ranged from 0.72 to 0.97. The measurements established sufficiently high reliability to justify their use both within and between examiners for subjects recovering from surgery of the ACL.

Influence of examiner experience and gender on interrater reliability of KT-1000 arthrometer measurements.

BACKGROUND AND PURPOSE: Measurements of the integrity of knee ligaments are used to diagnose injuries as well as to document the state of recovery. Many factors, such as gender and experience of the examiner, are capable of influencing the reliability of such measurements. The purpose of this study was to determine the effects on interrater reliability of measurements obtained using the KT-1000 arthrometer of experience, gender, and leg tested. SUBJECTS: Two experienced examiners (1 male, 1 female) and two inexperienced examiners (1 male, 1 female) tested 22 subjects with unilateral anterior cruciate ligament (ACL) pathology. METHODS: The leg with an ACL injury and the uninjured leg of each subject were evaluated by all four examiners within one test session using 67-N, 89-N, maximum manual, and active anterior drawer tests. RESULTS: Greater anterior displacement values were found in the legs with ACL injury than in the uninjured legs. Reliability estimates, as assessed by intraclass correlation coefficients (2,k) and measurement error (SEM), suggest that therapist experience may be a more important factor influencing reliability than gender. CONCLUSION AND DISCUSSION: Given the magnitude of the errors obtained for tests routinely conducted in the clinic using the KT-1000 arthrometer, we recommend that repeated measurements should be taken by the same examiners whenever possible. [Ballantyne BT, French AK, Heimsoth SL, et al. Influence of examiner experience and gender on interrater reliability of KT-1000 arthrometer measurements.

A study of various normalization procedures for within day electromyographic data.

Normalization of electromyographic (EMG) data has been described in the scientific literature as crucial for comparisons between subjects and between muscles. The reference value used in the normalization equation has, however, varied across reports. Comparison between studies could be facilitated by use of a common value. We propose the best way to select the common value is through a reliability approach. Accordingly, the purpose of this study was to identify which of three EMG normalization values provided the most reproducible data set. The gastrocnemius EMG results from 20 normal persons and 20 individuals with anterior cruciate deficiency who were participating in a larger study were normalized to a maximum voluntary isometric contraction (MVIC) EMG, peak dynamic EMG, and mean dynamic EMG. Values were then subjected to evaluation using four statistical measures: inter and intrasubject coefficients of variation (CV), variance ratio (VR), and intraclass correlation coefficient (ICC). The CV measures, while not being reflective of reliability were included for comprehensive consideration in view of other literature. The intersubject CV which measures group variability and the intrasubject CV which measures precision were lower for the dynamic conditions, however, the VR and ICC suggested reproducibility was best with EMG from the MVIC. Given that other studies have advocated normalizing EMG by taking data from the dynamic event, reconsideration may be warranted if high reproducibility is desired. Interpretations of the findings given the population, muscle and condition studied are discussed.

Electromyographic activity of selected shoulder muscles in commonly used therapeutic exercises.

BACKGROUND AND PURPOSE: The purpose of this study was to evaluate and compare the muscle activity of the supraspinatus, infraspinatus, teres minor, and lower trapezius muscles during commonly prescribed therapeutic exercises in subjects with and without shoulder pathology. SUBJECTS: Twenty healthy subjects (9 male, 11 female) and 20 subjects with recurrent unilateral shoulder pain and weakness (14 male, 6 female), aged 18 to 40 years (mean = 28, SD = 5.8), participated in this study. METHODS: Subjects performed each of the following exercises using a hand-held weight: prone lateral (external) rotation, sidelying lateral rotation, and arm elevation in the scapular plane. Indwelling fine-wire electrodes recorded electromyographic (EMG) activity during each exercise. The EMG activity in five phases of concentric contraction of each exercise was averaged and divided into three equal time intervals. Mean EMG values normalized to maximal activity for the entire phase of concentric contraction and for each of the three intervals were used in subsequent analyses. RESULTS: Two-way repeated-measures analyses of variance (ANOVAs) revealed between-group differences only in the prone lateral rotation exercise. Compared with subjects without shoulder pathology, subjects with shoulder pain showed significantly greater EMG activity in the infraspinatus muscle and less activity in the supraspinatus muscle during this exercise. CONCLUSION AND DISCUSSION: These results suggest that the pattern of muscle activation during specific shoulder movements in patients with shoulder pain may be related to pathology. Future studies are needed to determine whether an imbalance in neuromuscular control is a factor contributing directly to shoulder dysfunction or whether such an imbalance is secondary to some pathology.

Motor unit recruitment in human medial gastrocnemius muscle during combined knee flexion and plantarflexion isometric contractions.

Previous work on multifunctional muscle has suggested that motor unit recruitment during a combined force task is the result of an interactive effect of weighted inputs acting simultaneously on the motoneuron pool. The present study shows that a similar effect describes motor unit activation in a two-joint muscle as forces are combined at both proximal and distal attachments. The recruitment thresholds of single motor units in medial gastrocnemius muscle were determined during combined knee flexion and plantarflexion isometric contractions. Slow isometric ramp contractions in knee flexion were produced while maintaining various background levels of plantarflexion force. The combination of knee flexion and plantarflexion forces at which a motor unit initially discharged was used to characterize recruitment as represented by the slope of the regression line fit to the individual data points. Each subject completed two experiments; one at each of two knee joint angles, with the ankle joint fixed at 90 degrees. The effect of knee angle was assessed by comparing the slopes of the regression lines that characterized motor unit recruitment at each knee angle. Motor units in medial gastrocnemius were recruited when the linear sum of the forces exerted in plantarflexion and knee flexion exceeded a certain threshold of combined force. Specifically, the apparent force threshold of recruitment in knee flexion decreased as the level of force maintained in plantarflexion increased. Further, evidence is provided indicating that the linear relationship describing recruitment in two-joint muscle is dependent upon joint angle.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in postural responses preceding rapid self-paced and reaction time arm movements.

The electromyographic responses in postural (thigh and trunk) and primary agonist (shoulder) muscles were examined in standing young and older adults prior to rapid self-paced (SP) and simple reaction time (RT) arm flexion movements. In contrast to younger subjects, older adults demonstrated significantly lower frequencies of trials for self-paced movements in which thigh muscle responses preceded the activation of the shoulder muscle. Furthermore, younger adults showed more frequent early lower limb postural responses for SP versus RT movements, whereas older subjects retained comparable frequencies between task conditions. Overall, a significantly shorter intermuscular timing interval between leg and arm muscle onsets was also found for the older group.

Reliability of performance measurements obtained using the stability testing and rehabilitation station (STARStation).

The purpose of this study was to determine within- and between-day reliability of measurements of nondisabled subjects for the variables of force and velocity when a balance board (STARStation) was positioned at heights of 4.5 and 7.5 cm from the supporting surface. Twenty-four nondisabled subjects each completed six trials of board rotation at a self-selected velocity. Each trial consisted of 10 revolutions in a clockwise direction. Measurements were repeated within the same day for a second board position, and all tests were completed again on a second day. Descriptive statistics were computed for force and velocity, and intraclass correlation coefficients (ICCs) were calculated. Data were submitted to analyses of variance and follow-up tests. Results showed slight differences between the first three and last three trials. Intraclass correlation coefficients for within-subject reliability for the independent variable day ranged from .72 to .81, and ICCs for within-day reliability for the independent variable trial ranged from .46 to .81. Clinicians using such protocols should be aware of differences within and between days and recognize that measurements will be influenced by the number of trials completed.

Modeling physical therapy clinical research centers.

Because the establishment of physical therapy clinical research centers (PTCRCs) has been of interest to the profession, this project was undertaken to (1) assess the available resources, (2) complete a systems analysis, and (3) apply the results of a Delphi survey to the resulting clinical research center models. The methodology included several techniques. First, a questionnaire that addressed the status and elements of organization of PTCRCs was distributed to 118 academic institutions and 22 other facilities. A systems analysis of clinical research centers supported by various institutes at the National Institutes of Health was then completed. A Delphi procedure was also used to query a panel of physical therapy researchers regarding the components of a PTCRC. Site visits were conducted at three facilities to assess the possibility of those facilities becoming PTCRCs. From the data derived via these methods, models for PTCRCs were developed. Results showed that as many as 40 facilities reported the capability of becoming a PTCRC, but the data also showed that only four sites had extensively contributed by means of publication in peer-reviewed journals. The Delphi survey produced a number of items regarding characteristics and foci on which consensus was reached. Considering all the data, several models for PTCRCs were developed. Allowance for diversity in the structure and focus of PTCRCs appears to be a critical factor if the development of PTCRCs is to be encouraged.

Electromyographic activity of selected leg musculature in subjects with normal and chronically sprained ankles performing on a BAPS board.

The purpose of this study was to evaluate the magnitude and temporal features of tibialis anterior, peroneus longus, and gastrocnemius muscle activity during exercises performed on a Biomechanical Ankle Platform System (BAPS) board by subjects with normal and chronically sprained ankles. Fourteen participants in each of the two groups rotated the platform in both clockwise and counterclockwise directions at self-selected velocities. Trials were completed with both medium- and large-sized hemispheres under the platform while electromyographic surface recordings were made from the three muscles of interest. Electromyographic values, normalized within individuals as a percentage of maximal voluntary isometric contraction (MVIC), ranged from 20% to 80% of MVIC. An analysis of variance for the average myoelectric signals from all three muscles revealed no differences between the two groups. Effects of direction and hemisphere size were shown for all muscles. The large hemisphere produced significantly greater average activity and a more pronounced effect on the tibialis anterior muscle. The data provide information on the level of muscle activity required for conditions used in this study and may assist the physical therapist with making judgments about the use of this device in rehabilitation programs.

A comparison of motor unit behaviour in young and aged subjects.

We evaluated motor unit behaviour in young and aged subjects during ramped tension development and release to 10% maximum voluntary contraction requiring 10 seconds to complete. Six young and six elderly adults performed isometric abductor digiti minimi muscle contractions while motor units were recorded with implanted fine wire electrodes. Computer interactive programs yielded interspike interval (ISI) data for 16 units from the young and for 15 units from the aged subjects. Mean ISIs for young were 88.4 ms for shortening and 96.5 ms for lengthening contractions. Units from the aged had ISIs of 110.5 ms and 117.1 ms for shortening and lengthening contractions. Some evidence for between-group differences in firing pattern during ascending and descending ramps was also found.

The effect of muscle length on motor unit discharge characteristics in human tibialis anterior muscle.

Muscle length influences the contractile properties of muscle in that when muscle is lengthened the relaxation phase of the muscle twitch is prolonged and when muscle is shortened, the relaxation phase is shorter in duration. As a result, the force exerted by active motor units varies with muscle length during voluntary contractions. To determine if motoneuron spike trains were adjusted to accommodate for changes in the contractile properties imposed by shortened and lengthened muscle, motor unit action potentials were recorded from the tibialis anterior muscle at different muscle lengths. Twenty subjects performed isometric ramp contractions at ankle angles of 20 degrees dorsiflexion, neutral between dorsiflexion and plantar flexion, and 30 degrees plantar flexion, which put the tibialis anterior muscle in a shortened, neutral, or lengthened condition, respectively. During isometric contractions where torque increased at 5% MVC/s, motor unit discharge rate at recruitment was greater in shortened muscle than in lengthened muscle (P less than 0.05). Brief initial interspike intervals (less than 40 ms) occurred more frequently in shortened muscle than in either neutral length or lengthened muscle. During steady contractions, motor unit discharge rate was greater per unit torque (N.m) in shortened muscle than in neutral length or lengthened muscle (P less than 0.05). These findings indicate that muscle length does influence the discharge pattern of motor unit spike trains during isometric ramp contractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Electromyographic analysis of hip abductor musculature in healthy right-handed persons.

The right hip abductor (HA) musculature has been reported to demonstrate stretch weakness attributable to chronic elongation imposed by standing posture common to right-handed healthy individuals. Research has shown side-specific differences in maximal isometric torque-hip abduction angle curves for the HA muscles in a similar population. The purposes of this study were to assess isometric hip abduction torque in a sample of 40 healthy right-handed persons and to compare side differences in the HA muscles' neural drive index across a wide range of hip abduction angles. The neural drive index was defined as the magnitude of the normalized surface electromyographic activity divided by the absolute magnitude of a submaximal (20% of maximal) isometric HA muscle torque. Data were collected while subjects were positioned supine with trunk and pelvis stabilized. Statistical analysis of the data did not support earlier research on right HA muscle stretch-weakness; however, trends in the data suggest the need for further research. We also discuss the functional role of the passive noncontractile elements of the HA musculature.

Comparison of maximal isometric hip abductor muscle torques between hip sides.

A posturally induced "stretch weakness" of the right hip abductor muscles has been reported in many healthy right-handed persons in the literature. The purpose of this study was to test for differences in the maximal isometric hip abduction torque produced between hip sides across multiple hip abduction angles. The torques were measured on 40 healthy right-handed individuals using a specialized torque-testing table at hip abduction angles of -10, 0, 10, 20, 30, and 40 degrees. Statistical analysis of the results did not demonstrate a specific "weakness" of the right hip abductor muscles at the hip angle used to clinically test them. The results, however, did demonstrate statistically significant differences in the torque-hip angle slopes across hip sides. We hypothesized that these slope differences may result from muscle adaptation to lengths imposed by standing posture. We discuss how manual muscle testing procedures may bias the likelihood of encountering stretch weakness in muscles that are habitually maintained at near-maximal elongation.

Electromyographic analysis of knee exercises in healthy subjects and in patients with knee pathologies.

Little information exists about the intensity of contraction required from knee and hip musculature during common therapeutic exercises used for patient populations. This study, therefore, was designed to compare electromyographic data obtained from the vastus medialis, rectus femoris, gluteus medius, and biceps femoris muscles during maximally resisted straight-leg-raising (SLR) exercises with EMG data obtained from the same muscles during quadriceps femoris muscle setting (QS) exercises in healthy subjects and in patients with knee pathologies. Of the 30 participants in the study, 16 had a history of knee injury or surgery. All participants performed randomly ordered trials of the SLR and QS exercises while the EMG data were recorded from surface electrodes and normalized to values derived from maximal effort isometric contraction trials. An analysis of variance demonstrated significantly greater activity (p less than .05) of the vastus medialis, biceps femoris, and gluteus medius muscles during QS exercises than during SLR exercises. The rectus femoris muscle was significantly more active (p less than .05) during SLR exercises than during QS exercises. The study demonstrated remarkably different degrees of muscle activation between the SLR and QS exercises, indicating that the exercise selected will affect the therapeutic intention.

Postural adjustments preceding rapid arm movements in parkinsonian subjects.

The electromyographic (EMG) responses in postural (thigh and trunk) and agonist (shoulder) muscles were examined in standing parkinsonian subjects and healthy controls prior to visual reaction time and self-paced rapid arm flexion movements. Recruitment of postural muscles typically preceded arm displacement in normals, but was less frequent, of shorter duration, and characterized by multiple EMG bursts which extended to the agonist in parkinsonians. Moreover, parallel delays in EMG recruitment times relative to the visual signal for both postural and agonist muscles were observed in akinetic patients. These abnormalities suggest that the basal ganglia may serve a preparatory motor function, by linking synergistic muscles through a common selection process.