Reliability of EMG measurements for trunk muscles during maximal and sub-maximal voluntary isometric contractions in healthy controls and CLBP patients.

The purpose of this study was to compare the reliability of trunk muscle activity measured by means of surface electromyography (EMG) during maximal and sub-maximal voluntary isometric contractions (MVC/sub-MVC) over repeated trials within-day and between-days in healthy controls and patients with chronic low back pain (CLBP). Eleven volunteers (six controls and five CLBP patients) were assessed twice with a 1-week interval. Surface EMG signals were recorded bilaterally from six trunk muscles. Intra-class correlation coefficients (ICC) and standard error of measurement as a percentage of the grand mean (%SEM) were calculated. MVC and sub-MVC showed excellent within-day reliability in both healthy controls and CLBP patients (ICC mean 0.91; range 0.75-0.98; %SEM mean 4%; range 1-12%). Sub-MVC for both groups between-days showed excellent reliability (ICC mean 0.88; range 0.78-0.97; %SEM mean 7%; range 3-11%). The between-days MVC for both groups showed trends towards lower levels of reliability (ICC mean 0.70; range 0.19-0.99; %SEM mean 17%; range 4-36%) when compared to sub-MVC. Findings of the study provide evidence that sub-MVC are preferable for amplitude normalisation when assessing EMG signals of trunk muscles between-days.     

Influence of the intensity of a conditioning contraction on the subsequent twitch torque and maximal voluntary concentric torque

This study aimed to clarify the influence of the intensity of a conditioning contraction on subsequent isometric twitch and maximal voluntary concentric torques. Subjects (n=12men) performed voluntary isometric plantar flexion for six seconds as a conditioning contraction, at intensities of 40%, 60%, 80% and 100% of a maximal voluntary isometric contraction (MVIC). Before and immediately after the conditioning contraction, isometric twitch and maximal voluntary concentric (180°/s) plantar flexion torques were determined. Surface electromyograms were recorded from the triceps surae muscles and M-wave amplitudes and root-mean-square values of the electromyographic signals (RMS(EMG)) were calculated. The isometric twitch torque increased significantly after conditioning contraction at all intensities (P<0.05), whereas maximal voluntary concentric torque increased significantly only at 80% and 100% MVIC conditions (P<0.05). It is concluded that during a six second conditioning contraction, the effect of the intensity of a conditioning contraction on subsequent torque development is different between an isometric twitch and maximal voluntary concentric contractions, with the latter being less affected.     

Reliability of lower limb electromyography during overground walking: A comparison of maximal- and sub-maximal normalisation techniques

The purpose of this study was to determine the reliability of investigating electromyography (EMG) of selected leg muscles during walking. Tibialis posterior and peroneus longus EMG activity were recorded via intramuscular electrodes. Tibialis anterior and medial gastrocnemius EMG activity were recorded with surface electrodes. Twenty-eight young adults attended two test-sessions approximately 15 days apart. Relative and absolute measures of reliability were calculated for EMG timing and amplitude parameters during specific phases of the gait cycle. Maximum contractions and sub-maximal contractions were obtained via maximum isometric voluntary contractions and a very fast walking speed, respectively. Time of peak EMG amplitude for all muscles displayed relatively narrow limits of random error. However, reliability of peak and root mean square amplitude parameters for tibialis posterior and peroneus longus displayed unacceptably wide limits of random error, regardless of the normalisation reference technique. Whilst some amplitude parameters for tibialis anterior and medial gastrocnemius displayed good to excellent relative reliability, the corresponding values for absolute error were generally large.Timing and amplitude EMG parameters for all muscles displayed low to moderate coefficient of variation within each test session (range: 7–25%). Overall, between-participant variability was minimised with sub-maximal normalisation values. These results demonstrate that re-application of electrodes results in large random error between sessions, particularly with tibialis posterior and peroneus longus. Researchers planning studies of these muscles with a repeated-test design (e.g. to evaluate the effect of an intervention) must consider whether this level of error is acceptable.     

Test–retest reliability of cardinal plane isokinetic hip torque and EMG

The objective of the present study was to establish test–retest reliability of isokinetic hip torque and prime mover electromyogram (EMG) through the three cardinal planes of motion. Thirteen healthy young adults participated in two experimental sessions, separated by approximately one week. During each session, isokinetic hip torque was evaluated on the Biodex Isokinetic Dynamometer at a velocity of 60 deg/s. Subjects performed three maximal-effort concentric and eccentric contractions, separately, for right and left hip abduction/adduction, flexion/extension, and internal/external rotation. Surface EMGs were sampled from the gluteus maximus, gluteus medius, adductor, medial and lateral hamstring, and rectus femoris muscles during all contractions. Intraclass correlation coefficients (ICC – 2,1) and standard errors of measurement (SEM) were calculated for peak torque for each movement direction and contraction mode, while ICCs were only computed for the EMG data. Motions that demonstrated high torque reliability included concentric hip abduction (right and left), flexion (right and left), extension (right) and internal rotation (right and left), and eccentric hip abduction (left), adduction (left), flexion (right), and extension (right and left) (ICC range = 0.81–0.91). Motions with moderate torque reliability included concentric hip adduction (right), extension (left), internal rotation (left), and external rotation (right), and eccentric hip abduction and adduction (right), flexion (left), internal rotation (right and left), and external rotation (right and left) (ICC range = 0.49–0.79). The majority of the EMG sampled muscles (n = 12 and n = 11 for concentric and eccentric contractions, respectively) demonstrated high reliability (ICC = 0.81–0.95). Instances of low, or unacceptable, EMG reliability values occurred for the medial hamstring muscle of the left leg (both contraction modes) and the adductor muscle of the right leg during eccentric internal rotation. The major finding revealed high and moderate levels of between-day reliability of isokinetic hip peak torque and prime mover EMG. It is recommended that the day-to-day variability estimates concomitant with acceptable levels of reliability be considered when attempting to objectify intervention effects on hip muscle performance.     

Active recovery has a positive and acute effect on recovery from fatigue induced by repeated maximal voluntary contractions of the plantar flexors

This study investigated the acute effect of active recovery (AR) following fatigue induced by 80 three-second maximal voluntary isometric plantar flexion contractions (MVICs) in 12 young men. AR consisted of a total of 180 voluntary isometric ramp contractions of the plantar flexors (0.75-s contraction/relaxation) targeting 10% of MVIC torque. MVIC torque, voluntary activation and root mean square values of electromyographic signals for the triceps surae normalized by each peak-to-peak amplitude of compound motor action potential were determined before, and immediately, 10, 20 and 30 min after the fatiguing task. Evoked torques were similarly assessed except for immediately after it. The AR and passive recovery were randomly performed on two days by each participant between 5 min and 10 min after the fatiguing task. For all the parameters other than MVIC torque, there was no significant difference between the conditions at any time point. MVIC torque decreased significantly immediately after the fatiguing task regardless of condition (P < 0.05), and the corresponding decrease in MVIC torque recovered 30 min after the fatiguing task only in AR (P < 0.05). These results suggest an acute positive effect of AR on recovery of neuromuscular function and/or contractile properties after fatigue.     

Gluteus medius: An intramuscular EMG investigation of anterior,middle and posterior segments during gait

Previous electromyographic (EMG) studies of gluteus medius (GMed) have not accurately quantified the function of the three proposed structurally and functionally unique segments (anterior, middle and posterior). Therefore this study used anatomically verified locations for intramuscular electrode recordings in three segments of GMed to determine whether the segments are functionally independent. Bipolar fine wire electrodes were inserted into each segment of GMed in 15 healthy individuals. Participants completed a series of four walking trials, followed by maximum voluntary isometric contractions (MVICs) in five different positions. Temporal and amplitude variables for each segment were compared across the gait cycle using ANOVA. The relative contributions of each segment to the MVIC trials were compared with non-parametric tests. All segments showed a biphasic response during the stance phase of gait. There were no differences in amplitude variables (% MVIC) between segments, but the anterior segment had a later peak during both the first and second bursts. For the MVIC trials, there were significant differences in amplitude between segments in four of the five test positions. These data indicate that GMed is composed of three functionally independent segments. This study contributes to the theoretical understanding of the role of GMed.     

Reproducibility of surface EMG variables and peak torque during three sets of ten dynamic contractions.

The interpretation of the electromyogram (EMG) of dynamic contractions might be difficult because the movement per se introduces additional factors that could affect its characteristics. There is a lack of studies concerning the reproducibility of surface EMG registrations during dynamic contractions. The aim was to investigate the during-the-day reproducibility (using intra-class correlation; ICC) of the peak torque (PT) and the EMG variables (without removing the electrodes) of dynamic contractions. Ten healthy subjects performed three sets of 10 dynamic maximum right-knee extensions with a one-hour interval in between, using an isokinetic dynamometer and the PT was determined. EMG signals were recorded from the right vastus lateralis, rectus femoris and vastus medialis muscles using surface electrodes and the mean frequency of the power spectrum (MNF [Hz]) and the signal amplitude (RMS [microV]), were computed. The ability to relax in-between the maximum extensions was calculated as a ratio of the RMS during the passive flexion phase and the RMS during the active extension phase of each contraction cycle: the signal amplitude ratio (SAR). Both PT (ICC = 0.99) and RMS (ICC = 0.83-0.98) had good reproducibility. The reproducibility of MNF was good for all muscles when the mean of contraction nos.: 1-10 was used. Vastus lateralis had the highest ICC among the three muscles. The reproducibility of SAR was generally poor (ICC < 0.60). The present study showed good reproducibility for common EMG variables (MNF and RMS) obtained during maximum isokinetic contractions.     

A new technique for the selective recording of extensor carpi radialis longus and brevis EMG.

Tennis Elbow or Lateral Epicondylalgia is manifested by pain over the region of the lateral epicondyle of the humerus, related to use of the wrist extensor muscles. Extensor carpi radialis longus (ECRL) and brevis (ECRB) have been implicated in the dysfunction associated with Lateral Epicondylalgia. For muscles in the human forearm, particularly those in close proximity, selective recordings are nearly impossible without the use of fine wire, indwelling electrodes. These can be inserted in precise locations and have small recording areas. Standard electromyography texts indicate, however, that the activity of ECRL and ECRB cannot be distinguished, even with intramuscular electrodes. We present a new technique for determining the most appropriate sites at which to insert intramuscular electrodes for selective recordings of ECRB and ECRL. The location of ECRB and ECRL was measured on 10 cadaver specimens, 5 right arms and 5 left arms. The distance from the muscle origin to (1) insertion, (2) largest portion of the muscle belly, (3) most proximal fibres and (4) most distal fibres were measured and expressed relative to forearm length. The mean distance and 95% confidence interval was calculated for each of the four measures. These data indicated a significant separation of the belly of each muscle along the length of the forearm. These relative distances were used to mark electrode insertion points on three volunteers. Fine wire electrodes were used to record the electromyogram in three participants. Each participant was required to perform isometric contractions to produce (1) wrist extension torque, (2) radial deviation torque, (3) elbow flexion torque and (4) finger extension. The electromyographic recordings show clear differentiation of ECRB and ECRL with the relative activation patterns reflecting the underlying anatomical organisation of the two muscles. This technique provides an important objective method that can be used in conjunction with manual muscle testing to provide a means of ensuring accurate intramuscular electromyographic recording from these two muscles.     

Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction

Objective: the purpose of this study was to compare vastus medialis obliquus (VMO) and vastus lateralis (VL) activity while performing a mini-squat with and without isometric hip adduction.

Design and setting: a repeated measures within subjects design was used. Subjects performed two sets of three repetitions of a traditional mini-squat and a mini-squat with concurrent hip adduction (squeeze).

Subjects: 20 recreationally active subjects (10 men, 10 women AGE=28.10±5.91 years, HEIGHT=170.94±11.03 cm, MASS=72.32±16.66 kg) with no history of patellofemoral pain (PFP), quadriceps injury, or other knee injury participated in the study.

Measurements: the EMG signal of the VMO and VL was recorded bilaterally during both exercises. EMG data were normalized to the maximal voluntary isometric contraction (MVIC) of the quadriceps produced during seated, isometric knee extension.

Results: results of repeated measures ANOVA's revealed that the squeeze squat produced significantly greater VMO and VL activity than the traditional squat (p=0.02). For both the traditional and squeeze squats, intrasession reliability from the first to the second set was calculated using intraclass correlation coefficient (ICC) formula (3:1) bilaterally for both the VMO and the VL. All ICC values were greater than 0.9.

Conclusion: combining isometric hip adduction with a mini-squat exercise significantly increases the activity of the quadriceps. Performing mini-squats with isometric hip adduction will be beneficial to patellofemoral patients as they increase quadriceps activity, however, based on our data we cannot conclude that this exercise preferentially recruits the VMO. Further research is needed to determine the exact mechanism by which quadriceps function is altered.     

Knee angle-dependent oxygen consumption during isometric contractions of the knee extensors determined with near-infrared spectroscopy.

Fatigue resistance of knee extensor muscles is higher during voluntary isometric contractions at short compared with longer muscle lengths. In the present study we hypothesized that this would be due to lower energy consumption at short muscle lengths. Ten healthy male subjects performed isometric contractions with the knee extensor muscles at a 30, 60, and 90 degrees knee angle (full extension = 0 degrees ). At each angle, muscle oxygen consumption (m.VO2) of the rectus femoris, vastus lateralis, and vastus medialis muscle was obtained with near-infrared spectroscopy. m.VO2 was measured during maximal isometric contractions and during contractions at 10, 30, and 50% of maximal torque capacity. During all contractions, blood flow to the muscle was occluded with a pressure cuff (450 mmHg). m.VO2 significantly (P < 0.05) increased with torque and at all torque levels, and for each of the three muscles. m.VO2 was significantly lower at 30 degrees compared with 60 degrees and 90 degrees and m.VO2 was similar (P > 0.05) at 60 degrees and 90 degrees . Across all torque levels, average (+/- SD) m.VO2 at the 30 degrees angle for vastus medialis, rectus femoris, and vastus lateralis, respectively, was 70.0 +/- 10.4, 72.2 +/- 12.7, and 75.9 +/- 8.0% of the average m.VO2 obtained for each torque at 60 and 90 degrees . In conclusion, oxygen consumption of the knee extensors was significantly lower during isometric contractions at the 30 degrees than at the 60 degrees and 90 degrees knee angle, which probably contributes to the previously reported longer duration of sustained isometric contractions at relatively short muscle lengths.     

Technical report: Reliability and validity of the iSAM 9000 isokinetic dynamometer

This study assessed the mechanical reliability and validity of the INRTEK iSAM 9000 isokinetic dynamometer, and compared the obtained torque values of the prototype device with those from a traditional device. Sixty volunteers (40 men and 20 women) were tested at 60 degrees per second for shoulder, knee, and trunk flexion, and extension on both the Cybex 6000 and a new isokinetic dynamometer (iSAM 9000). Intraclass correlation coefficients (ICC) and standard errors of measurement (SEM) revealed a high level of reproducibility and precision in the device's torque measurements (ICC range = 0.94-0.98; SEM range = 5.2-29.7). Pearson r values revealed very high relationships between the two instruments (set 1: r = 0.84-0.93; set 2: r = 0.87-0.93; P < 0.05). Significantly higher peak torque for both sets of left and right knee flexion and extension, right shoulder extension and trunk extension was found for the iSAM 9000 compared to the Cybex 6000 (P < 0.05). The strong ICCs and small SEMs support the device's mechanical reliability and validity. The high correlation coefficients between the prototype dynamometer and the Cybex 6000 support the new device's validity in the measurement of isokinetic torque. The findings of this study will be used to refine the next generation of the INRTEK isokinetic device with respect to test protocols and the reliability of measuring human muscle performance.     

Reliability of surface EMG during sustained contractions of the quadriceps.

The purpose of this study was to determine test-retest reliability for median frequency (MDF) and amplitude of surface EMG during sustained fatiguing contractions of the quadriceps. Twenty-two healthy subjects (11 males and 11 females) were tested on two days held one week apart. Surface EMG was recorded from rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) during sustained isometric contractions at 80% and 20% of maximal voluntary contraction (MVC) held to exhaustion. Quadriceps fatigue was described using four measures for both MDF and amplitude of EMG: initial, final, normalized final and slope. For both MDF and amplitude, the initial, final and normalized EMG showed moderate to high reliability for all three muscle groups at both contraction levels (ICC=0.59-0.88 for MDF; ICC=0.58-0.99 for amplitude). Slope of MDF and amplitude was associated with a large degree of variability and low ICCs for the 80% but not the 20% MVC. MDF and amplitude of EMG during sustained contractions of the quadriceps are reproducible; normalized final values of MDF and amplitude show better reliability than slope.     

A comparison of surface and fine wire EMG recordings of gluteus medius during selected maximum isometric voluntary contractions of the hip

Electromyographic (EMG) studies into gluteus medius (GMed) typically involve surface EMG electrodes. Previous comparisons of surface and fine wire electrode recordings in other muscles during high load isometric tasks suggest that recordings between electrodes are comparable when the muscle is contracting at a high intensity, however, surface electrodes record additional activity when the muscle is contracting at a low intensity. The purpose of this study was to compare surface and fine wire recordings of GMed at high and low intensities of muscle contractions, under high load conditions (maximum voluntary isometric contractions, MVICs). Mann–Whitney U tests compared median electrode recordings during three MVIC hip actions; abduction, internal rotation and external rotation, in nine healthy adults. There were no significant differences between electrode recordings in positions that evoked a high intensity contraction (internal rotation and abduction, fine wire activity >77% MVIC; effect size, ES < 0.42; p > 0.277). During external rotation, the intensity of muscle activity was low (4.2% MVIC), and surface electrodes recorded additional myoelectric activity (ES = 0.67, p = 0.002). At low levels of muscle activity during high load isometric tasks, the use of surface electrodes may result in additional myoelectric recordings of GMed, potentially reflective of cross-talk from surrounding muscles.     

Obtaining maximum muscle excitation for normalizing shoulder electromyography in dynamic contractions

Muscle specific maximal voluntary isometric contractions (MVIC) are commonly used to elicit reference amplitudes to normalize electromyographic signals (EMG). It has been questioned whether this is appropriate for normalizing EMG from dynamic contractions. This study compares EMG amplitude when shoulder muscle activity from dynamic contractions is normalized to isometric and isokinetic maximal excitation as well as a hybrid approach currently used in our laboratory. Anterior, middle and posterior deltoid, upper and lower trapezius, pectoralis major, latissimus dorsi and infraspinatus were monitored during (1) manually resisted MVICs, and (2) maximum voluntary dynamic concentric contractions (MVDC) on an isokinetic dynamometer. Dynamic contractions were performed (a) at 30°/s about the longitudinal, frontal and sagittal axes of the shoulder, and (b) during manual bi-rotation of a tilted wheel at 120°/s. EMG from the wheel task was normalized to the maximum excitation from (i) the muscle specific MVIC, (ii) from any MVIC (MVIC_ALL), (iii) for any MVDC, (iv) from any exertion (maximum experimental excitation, MEE). Mean EMG from the wheel task was up to 45% greater when normalized to muscle specific isometric contractions (method i) than when normalized to MEE (method iv). Seventy-five percent of MEE’s occurred during MVDCs. This study presents an 20 useful and effective process for obtaining the greatest excitation from the shoulder muscles when normalizing dynamic efforts.     

Discharge properties of motor units during steady isometric contractions performed with the dorsiflexor muscles

The purpose of this study was to record the discharge characteristics of tibialis anterior motor units over a range of target forces and to import these data, along with previously reported observations, into a computational model to compare experimental and simulated measures of torque variability during isometric contractions with the dorsiflexor muscles. The discharge characteristics of 44 motor units were quantified during brief isometric contractions at torques that ranged from recruitment threshold to an average of 22 ± 14.4% maximal voluntary contraction (MVC) torque above recruitment threshold. The minimal [range: 5.8-19.8 pulses per second (pps)] and peak (range: 8.6-37.5 pps) discharge rates of motor units were positively related to the recruitment threshold torque (R(2) ≥ 0.266; P < 0.001). The coefficient of variation for interspike interval at recruitment was positively associated with recruitment threshold torque (R(2) = 0.443; P < 0.001) and either decreased exponentially or remained constant as target torque increased above recruitment threshold torque. The variability in the simulated torque did not differ from the experimental values once the recruitment range was set to ～85% MVC torque, and the association between motor twitch contraction times and peak twitch torque was defined as a weak linear association (R(2) = 0.096; P < 0.001). These results indicate that the steadiness of isometric contractions performed with the dorsiflexor muscle depended more on the distributions of mechanical properties than discharge properties across the population of motor units in the tibialis anterior.     

Electromyographic normalization procedures for determining exercise intensity of closed chain exercises for strengthening the quadriceps femoris muscles

The purpose of this study was to compare the electromyographic (EMG) amplitudes of the quadriceps femoris (QF) muscles during a maximum voluntary isometric contraction (MVIC) to submaximal and maximal dynamic concentric contractions during active exercises. A secondary purpose was to provide information about the type of contraction that may be most appropriate for normalization of EMG data if one wants to determine if a lower extremity closed chain exercise is of sufficient intensity to produce a strengthening response for the QF muscles. Sixty-eight young healthy volunteers (39 female, 29 male) with no lower extremity pain or injury participated in the study. Surface electrodes recorded EMG amplitudes from the vastus medialis obliquus (VMO), rectus femoris (RF), and vastus lateralis (VL) muscles during 5 different isometric and dynamic concentric exercises. The last 27 subjects performed an additional 4 exercises from which a second data set could be analyzed. Maximum isokinetic knee extension and moderate to maximum closed chain exercises activated the QF significantly more than a MVIC. A 40-cm. lateral step-up exercise produced EMG amplitudes of the QF muscles of similar magnitude as the maximum isokinetic knee extension exercises and would be an exercise that could be considered for strengthening the QF muscles. Most published EMG studies of exercises for the QF have been performed by comparing EMG amplitudes during dynamic exercises to a MVIC. This procedure can lead one to overestimate the value of a dynamic exercise for strengthening the QF muscles. We suggest that when studying the efficacy of a dynamic closed chain exercise for strengthening the QF muscles, the exercise be normalized to a dynamic maximum muscle contraction such as that obtained with knee extension during isokinetic testing.     

EMG of upper trapezius − Electrode sites and association with clavicular kinematics

The upper trapezius (UT) has been widely studied and related to alterations in clavicular kinematics in subject with shoulder disorders. However, the most common electrode site used to capture UT EMG is between C7 and the acromion, placing the electrodes over the acromial fibers rather than clavicular ones. Therefore, this study aimed to investigate the relationship between clavicular movements (elevation and retraction) and UT EMG recorded from three electrode sites (traditional electrode positioning and two different sites proposed for clavicular fibers evaluation). Furthermore, the position associated with the highest EMG during maximal isometric voluntary contractions (MVIC), for each electrode site, was determined for normalization purposes. EMG was simultaneously captured in the three electrode sites of 20 healthy subjects, during MVIC at five different positions and during shoulder elevation and abduction in scapular plane. Clavicular kinematics was recorded using an electromagnetic tracking system during the dynamic contractions. Shoulder abduction with head rotation and lateral flexion elicited the highest EMG amplitude on the three electrode sites and was used to normalize the signals. A cross-correlation analysis showed high correlations between all electrode sites and clavicular movements. However, the traditional electrode site seems to record more informative signals in healthy subjects.     

The relation between spectral changes of the myoelectric signal and the intramuscular pressure of human skeletal muscle

The purpose of the present study was to investigate if the intramuscular pressure generated during an isometric muscle contraction is important for the appearance of EMG spectral changes accompanying localized muscular fatigue. The EMG and intramuscular pressure of the left biceps brachii in eight volunteers were recorded during standardized isometric contractions by means of intramuscular wire electrodes and infusion catheters, respectively. Spectral changes were elicited by a submaximal contraction and the intramuscular pressure at which the induced spectral changes were able to recover was determined. It was found that significant recovery was possible only if the intramuscular pressure dropped below a level of about 2.7 kPa (20 mm Hg). It is concluded that the intramuscular pressure during a sustained isometric contraction is relevant for the generation of fatigue induced spectral changes, and that measurement of the intramuscular pressure makes possible predetermination of whether or not an isometric muscle contraction is liable to result in localized muscular fatigue.     

Reliability of EMG power-spectrum and amplitude of the semitendinosus and biceps femoris muscles during ramp isometric contractions

Appropriate reliability is a necessary condition for the use of surface EMG for evaluation of hamstring muscle function in cases of knee joint pathologies or ligament injuries. The aim of the study was to investigate the test-retest reliability of power spectrum and amplitude of surface electromyographic (EMG) measurements of semitendinosus (ST) and biceps femoris (BF) during ramp isometric contractions. Eleven males performed maximum isometric contractions (MVC) of the knee flexors in two sessions, a week apart with simultaneous recording of surface EMG of the BF and ST. Intra class correlation (ICC) and standard error measurements (SEM) were applied to assess test-retest reliability of the averaged EMG (aEMG) and the median frequency (MF) over 10 levels of force, from 0% to 100% of the maximum. The ICC values ranged from 0.38 to 0.96 for the aEMG with SEM values reaching 11.37% of MVC. For the MF, the ICCs ranged from 0.44 to 0.98 (SEM range 4.49–18.19 Hz). In our set up, ramp contractions can be used to examine hamstring EMG patterns with acceptable reliability.     

Between-session reliability of opto-electronic motion capture in measuring sagittal posture and 3-D ranges of motion of the thoracolumbar spine

This study evaluated between-session reliability of opto-electronic motion capture to measure trunk posture and three-dimensional ranges of motion (ROM). Nineteen healthy participants aged 24–74 years underwent spine curvature, pelvic tilt and trunk ROM measurements on two separate occasions. Rigid four-marker clusters were attached to the skin overlying seven spinous processes, plus single markers on pelvis landmarks. Rigid body rotations of spine marker clusters were calculated to determine neutral posture and ROM in flexion, extension, total lateral bending (left-right) and total axial rotation (left-right). Segmental spine ROM values were in line with previous reports using opto-electronic motion capture. Intraclass correlation coefficients (ICC) and standard error of measurement (SEM) were calculated as measures of between-session reliability and measurement error, respectively. Retroreflective markers showed fair to excellent between-session reliability to measure thoracic kyphosis, lumbar lordosis, and pelvic tilt (ICC = 0.82, 0.63, and 0.54, respectively). Thoracic and lumbar segments showed highest reliabilities in total axial rotation (ICC = 0.78) and flexion-extension (ICC = 0.77–0.79) ROM, respectively. Pelvic segment showed highest ICC values in flexion (ICC = 0.78) and total axial rotation (ICC = 0.81) trials. Furthermore, it was estimated that four or fewer repeated trials would provide good reliability for key ROM outcomes, including lumbar flexion, thoracic and lumbar lateral bending, and thoracic axial rotation. This demonstration of reliability is a necessary precursor to quantifying spine kinematics in clinical studies, including assessing changes due to clinical treatment or disease progression.