Detection algorithm for single motor unit firing in surface EMG of the trapezius muscle.

BACKGROUND: Work-related musculoskeletal disorders (MSD) of the neck and the shoulders are a growing problem in society. An interesting pattern of spontaneous muscle activity, the firing of a single motor unit, in the trapezius muscle is observed during a laboratory study in a rest state or a state with a mental load. OBJECTIVE: In this study, we report on the finding of the single motor unit firing and we present a detection algorithm to localize these single motor unit firings. METHODS: A spike train detection algorithm, using a nonlinear energy operator and correlation, is presented to detect burst of highly correlated, high energetic spike-like segments. RESULTS: This single motor unit was visible in 65% of the test subjects on one or both trapezius muscles although there was no change in posture of the test subjects. All the segments in the data that were determined as single motor unit firings were detected by the algorithm. DISCUSSION: The physiological meaning of this firing pattern is a very low and subconscious contraction of the muscle. A long-term contraction could lead to the exhaustion of the muscle fibers, thus resulting in musculoskeletal disorders. The detection algorithm is able to localize this phenomenon in a sEMG measurement. The ability of detecting these firings is helpful in the research of its origin. CONCLUSION: The detection algorithm can be used to gain insight in the physiological origin of this phenomenon. In addition, the algorithm can also be used in a biofeedback system to warn the user for this undesired contraction to prevent MSD.

Aberrant pelvis and hip kinematics impair hip loading before and after total hip replacement.

Musculoskeletal loading is an important factor affecting the development of osteoarthritis, bone remodelling and primary fixation of total hip replacement (THR). In this study, we analyzed the relation between muscular force, gait kinematics and kinetics and hip loading in 20 patients before and six weeks after THR. Hip contact forces were calculated from gait analysis data using musculoskeletal modelling, inverse dynamics and static optimization. We found aberrant pelvis and hip kinematics and kinetics before and six weeks after surgery, confirming previous findings in literature. Furthermore, we found a decrease in the total contact force and its vertical component. These changes result in a decrease of the associated inclination angles of the total hip contact force in the sagittal and transverse planes, changing the orientation towards more vertical implant loading after THR. These changes in hip loading were related to observed gait kinematics and kinetics. Most importantly, excessive pelvic obliquity and associated hip adduction related to impaired implant loading. We concluded, therefore, that physical therapy in the early post-operative phase should primarily focus on stretching of anterior and medial structures and strengthening of hip flexors and abductors to achieve normalization of the hip and pelvis kinematics and consequently normalize hip loading.

Subject-specific hip geometry and hip joint centre location affects calculated contact forces at the hip during gait.

Hip loading affects the development of hip osteoarthritis, bone remodelling and osseointegration of implants. In this study, we analyzed the effect of subject-specific modelling of hip geometry and hip joint centre (HJC) location on the quantification of hip joint moments, muscle moments and hip contact forces during gait, using musculoskeletal modelling, inverse dynamic analysis and static optimization. For 10 subjects, hip joint moments, muscle moments and hip loading in terms of magnitude and orientation were quantified using three different model types, each including a different amount of subject-specific detail: (1) a generic scaled musculoskeletal model, (2) a generic scaled musculoskeletal model with subject-specific hip geometry (femoral anteversion, neck-length and neck-shaft angle) and (3) a generic scaled musculoskeletal model with subject-specific hip geometry including HJC location. Subject-specific geometry and HJC location were derived from CT. Significant differences were found between the three model types in HJC location, hip flexion-extension moment and inclination angle of the total contact force in the frontal plane. No model agreement was found between the three model types for the calculation of contact forces in terms of magnitude and orientations, and muscle moments. Therefore, we suggest that personalized models with individualized hip joint geometry and HJC location should be used for the quantification of hip loading. For biomechanical analyses aiming to understand modified hip joint loading, and planning hip surgery in patients with osteoarthritis, the amount of subject-specific detail, related to bone geometry and joint centre location in the musculoskeletal models used, needs to be considered.

Subject-specific hip geometry affects predicted hip joint contact forces during gait.

Hip loading affects bone remodeling and implant fixation. In this study, we have analyzed the effect of subject-specific modeling of hip geometry on muscle activation patterns and hip contact forces during gait, using musculoskeletal modeling, inverse dynamic analysis and static optimization. We first used sensitivity analysis to analyze the effect of isolated changes in femoral neck-length (NL) and neck-shaft angle (NSA) on calculated muscle activations and hip contact force during the stance phase of gait. A deformable generic musculoskeletal model was adjusted incrementally to adopt a physiological range of NL and NSA. In a second similar analysis, we adjusted hip geometry to the measurements from digitized radiographs of 20 subjects with primary hip osteoarthrosis. Finally, we studied the effect of hip abductor weakness on muscle activation patterns and hip contact force. This analysis showed that differences in NL (41-74 mm) and NSA (113-140 degrees ) affect the muscle activation of the hip abductors during stance phase and hence hip contact force by up to three times body weight. In conclusion, the results from both the sensitivity and subject-specific analysis showed that at the moment of peak contact force, altered NSA has only a minor effect on the loading configuration of the hip. Increased NL, however, results in an increase of the three hip contact-force components and a reduced vertical loading. The results of these analyses are essential to understand modified hip joint loading, and for planning hip surgery for patients with osteoarthrosis.

Muscular effort in multiple sclerosis patients during powered wheelchair manoeuvres.

BACKGROUND: This study applied EMG analysis methods to identify muscle group activity profiles and potential overload risks in powered wheelchair use. METHODS: We quantified muscle effort and fatigue using EMG analysis methods during powered wheelchair manoeuvres by 10 multiple sclerosis patients. Video recordings of the different sub-tasks were related to information on surface EMG amplitude (rectified EMG) and spectral information (Median frequency) from M. trapezius, M. deltoideus (pars medius), M. deltoideus (pars anterior), M. pectoralis, M. biceps, M. triceps, wrist extensors and flexors, using Joint Analysis of EMG Spectrum and Amplitude (JASA analysis). FINDINGS: Task durations and subjective data indicated that tasks requiring finer motor control took longer and were perceived as more difficult. Kinesiological functions of all muscle groups identified forward steering to be associated with activation of M. deltoideus (pars anterior), M. pectoralis, M. trapezius and M. deltoideus (pars medius); backwards steering with predominant activation of M. deltoideus (pars medius), M. biceps brachii and wrist flexors; left steering with maximal activation of M. biceps and wrist flexors, and right steering with maximal activation of M. triceps and wrist extensors. These profiles were confirmed in analysis of the functional tasks. JASA analysis documented muscle fatigue in the wrist extensors, whereas increased activation was found in M. trapezius, M. deltoideus (pars anterior) and wrist flexors. INTERPRETATION: EMG based kinesiological analysis gives insight in muscle activity and fatigue during powered wheelchair manoeuvres.

A new method for semiautomatic analysis of surface EMG in patients with oral parafunctions.

Sleep-related phenomena or disorders, including snoring and tooth grinding, can be investigated using polysomnography. This method, however, generates large amounts of synchronically recorded data that are often analyzed visually with subjective interpretation. The purpose of this study was to minimize the need for subjective evaluation by developing a computer program for analysis of EMG data linked with polysomnographic recordings in a standardized and semi-automatic way. The selected algorithm differs from the Root Mean Square (RMS) method by being based on the theory of "differentiated EMG" (DIFEMG), which relies on two principles. The first says that the activation of a larger number of motor units results in a greater force production. The second principle says that the force production will continue for some time after the muscle is no longer stimulated. After a visual check for artifacts in the basic EMG recordings, the computer program is used to analyze the corrected basic EMG signal. The results were that both methods yield identical results as far as the detected number of events is concerned. There is, however, a significant difference when the duration of the events is considered, because the start and end of an event can be more accurately determined with the new method presented here. The computer program described will make comparison of data from different studies easier.

In vivo precision of quantitative shoulder cartilage measurements, and changes after spinal cord injury.

Recent advances in MRI have enabled the quantitative assessment of articular cartilage morphology in human joints. In this study, we tested the hypothesis that the precision of quantitative shoulder cartilage measurements is sufficient to detect changes between and within patients, and that shoulder cartilage thickness in paraplegic patients increases due to increased loading. We imaged the shoulders of seven healthy volunteers four times using a coronal 3D, fat-suppressed, gradient-echo sequence. The humeral head cartilage in seven paraplegic patients was evaluated soon after injury and 1 year post injury. A precision of 4.5% (root mean square (RMS) average coefficient of variation (CV) %) was found for shoulder cartilage thickness measurements in the humeral head. Whereas a significant decrease of cartilage thickness (-11%, P < 0.05) was observed in the knee, there was no significant change in articular cartilage thickness in the shoulder (-1.1%). Our data show, for the first time, that articular cartilage of the humeral head can be quantified with acceptable precision in vivo. It was demonstrated that, in contrast to the knee, the articular cartilage morphology of the humeral head changes very little (i.e., there is no significant increase or decrease in thickness) after spinal cord injury (SCI).

Validation of the wavelet spectral estimation technique in biceps brachii and brachioradialis fatigue assessment during prolonged low-level static and dynamic contractions.

An experiment was carried out to investigate the myoelectrical manifestations of fatigue of the Biceps Brachii and Brachioradialis muscles in low-level (15% MVC) prolonged isometric and dynamic contractions. The range of the joint angle was 70-110 degrees and the mean speed of flexion and extension was about 33.33 degrees /s (1.2 s for 40 degrees ). The use of Wavelet transform (IMNF) in weakly stationary dynamic SEMG signals was validated in comparison with the Fourier transform (MPF). The development of fatigue and its myoelectrical manifestations (increase in RMS and decrease in mean frequency) in dynamic contractions show no deviations from what is found in literature for both spectral estimation techniques. The benefit of Wavelets is its future use in non-stationary conditions. Lower IMNF slopes in dynamic compared to isometric contractions for Biceps Brachii might be an indication that wavelets reflect more the changes in muscle fiber propagation velocity. The results of the use of Wavelet transform in detecting frequency modulations in different movement phases of the dynamic tests show that in the eccentric phase a systematic shift towards lower frequencies occurs. It also reveals the great possibilities of phase separation using Wavelets with high resolution and low interaction.

Longitudinal analysis of cartilage atrophy in the knees of patients with spinal cord injury.

OBJECTIVE: A previous cross-sectional study indicated that the morphology of patellar and tibial cartilage is subject to change after spinal cord injury (SCI). The aim of this study was to perform a longitudinal analysis of cartilage atrophy in all knee compartments, including the femoral condyles, in SCI patients over 12 months. METHODS: The right knees of 9 patients with complete, traumatic SCI were examined shortly after the injury (mean +/- SD 9 +/- 4 weeks) and at 6 and 12 months postinjury. Three-dimensional morphology of the patellar, tibial, and femoral cartilage (mean and maximum thickness, volume, and surface area) was determined from coronal and transversal magnetic resonance images (fat-suppressed gradient-echo sequences) using validated postprocessing techniques. RESULTS: The mean thickness of knee joint cartilage decreased significantly during the first 6 months after injury (range 5-7%; P < 0.05). The mean change at 12 months was 9% in the patella, 11% in the medial tibia, 11% in the medial femoral condyle, 13% in the lateral tibia, and 10% in the lateral femoral condyle (P < 0.05 for all compartments). CONCLUSION: This is the first report of a longitudinal analysis of cartilage atrophy in patients with SCI. These data show that human cartilage atrophies in the absence of normal joint loading and movement after SCI, with a rate of change that is higher than that observed in osteoarthritis (OA). A potential clinical implication is that cartilage thinning after SCI may affect the stress distribution in the joint and render it vulnerable to OA. Future studies should focus on whether specific exercise protocols and rehabilitation programs can prevent cartilage thinning.

Intraoperative sentinel node identification with Technetium-99m-labeled nanocolloid in patients with cancer of the uterine cervix: a feasibility study.

The objective of this study is to determine the feasibility of intraoperative lymphatic mapping in patients with cervical carcinoma. Patients with early-stage cervical cancer, scheduled to undergo a Wertheims radical hysterectomy and pelvic lymphadenectomy, were eligible for the study. Technetium-99-m-labeled nanocolloid was injected intracervically at two locations around the tumor 3-6 hours before the operation. Images were recorded immediately and 2.5 hours later using a gamma camera. During the operation sentinel nodes (SLN) were identified using a handheld or laparoscopic gamma-detection probe (Navigator, Auto-Suture). After resection of the SLNs a standard pelvic (and para-aortic) lymphadenectomy was performed. The results of the histopathology of SLNs and non-SLNs were compared. The procedure was well tolerated by 24 of 25 patients. One or more SLN could be identified in 21 out of 25 patients. In one patient who was preoperatively irradiated, in two patients who had had a cone biopsy, and in one patient without previous interventions, no SLN could be detected. The mean time for identification was 5 minutes. In 16 patients, pathologic examination showed no metastatic disease in both SLNs and non-SLNs, whereas metastases were found in the SLN in five patients (in one case only SLN involved, four cases SLN and respectively 3, 11, 22 and 31 other positive nodes). This study shows that identification of SLNs in cancer of the uterine cervix is feasible with preoperatively administered 99mTc-labeled nanocolloid. To date, no false negative SLNs have been found, but expansion of the study is necessary to determine possible clinical application of this new technique.

Knee cartilage of spinal cord-injured patients displays progressive thinning in the absence of normal joint loading and movement.

OBJECTIVE: Alterations in the morphologic, biochemical, and mechanical properties of cartilage occur after unloading and immobilization in animals. However, the findings have been inconsistent and it is unclear whether such changes also take place in humans. This study tested the hypothesis that progressive thinning of knee joint cartilage is observed after spinal cord injury. METHODS: In this in vivo study, knee cartilage was assessed in patients with complete, traumatic spinal cord injury at 6 (n = 9), 12 (n = 11), and 24 months (n = 6) after injury. Morphologic parameters of the knee cartilage (mean and maximum thickness as well as surface area) were computed from magnetic resonance imaging (MRI) data, and results were compared with those in young, healthy volunteers (n = 9). RESULTS: After 6 months of injury, the mean articular-cartilage thickness was significantly less in the patella and medial tibia (decrease of 10% and 16%, respectively; P < 0.05), but not in the lateral tibia (decrease of 10%), compared with the MRI findings in healthy volunteers. After 12 and 24 months of injury, the differences amounted to a reduction of 21% and 23%, respectively, in the patella, 24% and 25%, respectively, in the medial tibia, and 16% and 19%, respectively, in the lateral tibia. The changes were significant in all 3 surfaces of the spinal cord-injured joint cartilage (P < 0.05-0.01). CONCLUSION: Our data show, for the first time, that progressive thinning (atrophy) of human cartilage occurs in the absence of normal joint loading and movement. This may have important implications for patient management, in particular for spinal cord-injured patients and patients who are immobilized after surgery.

An EMG-based, muscle driven forward simulation of single support phase of gait.

This paper describes the process used to generate lower limb kinematics during single limb stance phase of gait, using musculoskeletal modelling, muscle driven forward simulation and gradient based optimisation techniques (including design of experiment techniques). Initial inputs to the forward simulation process were the normalised quantified muscle activation patterns of 22 muscles, and the initial segmental configuration (both angles and angular velocity) derived from Winter (The biomechanics and motor control of human gait, 1987, University of Waterloo Press, pp. 1-72). Two distinct musculoskeletal models (one including 6 DOF, the other 7 DOF) were defined and a muscle driven forward simulation was implemented.A series of optimisation sequences then were executed to modify the muscle activation patterns and initial segmental configuration, until the system output of the forward simulation approximated the angle data reported by. The accuracy and effectiveness of the analysis sequence proposed and the model response obtained using two distinct musculoskeletal models were verified and analysed with respect to the kinesiology of normal walking.

A method of reconstruction of the muscular force profile from the EMG in the voluntary exercise.

The paper deals with an original approach of reconstructing the muscular force profile, in voluntary exercise of human subjects. Based on the idea that the changes within the activation of the muscle are the most relevant factors in producing the muscular force, we built a dynamic estimator of the force within the isometric dynamic tasks (ACTM), using the surface EMG as an input signal. The exercise involved mainly the Biceps and Brachioradialis muscles, together. The estimated resultant force was built taking into consideration the weighted contribution of the acting muscles. The weights were taken as to match the actual force measured at the wrist within a steady contraction, then used accordingly, during the dynamic exercise. The results show a spectacular improvement over previous attempts. This may open a practical way towards the estimation of the resultant force at the joints.

A study on the low frequency oscillations in the activation of the muscle under sustained isometric task.

We studied the periodicity of a relatively slow oscillation of the muscle activation, via the surface electromyogram (EMG), recorded from the Biceps and Brachioradialis muscles, under an endurance isometric task. The peaks in the Root Mean Square (RMS) of the EMG were assigned as peaks of the muscle activation; the estimate of their periodicity was checked via correlation. 32 subjects participated in different exercises involving isometric isotonic tasks, at 25%, 50% and 75% MVC (maximal voluntary contraction). The activation of the muscle under such an exercise has an overall low frequency periodicity of between 14.29 s and 16.75 s with standard deviations (sd) between 2.97 s and 5.04 s, independent of the intensity of the task and sex. They are larger for the Brachioradialis (mean 15.08-19.6 s/sd 2.59-6.3 s) than for the Biceps (mean 11.96-16.41 s/sd 1.24-4.86 s).

Buttock and back pressure distribution tests on seats of mobile agricultural machinery.

Multidisciplinary effort is usually required in the evaluation of comfort problems in the working environment of mobile agricultural machinery workers. Comfort can be partly assessed from the study of the pressure distribution of the human-seat interface. Four combine foam seats and a new air-based seat were compared with regards to static buttocks and back support pressures. Within and between subject variability and the issue of measurement repeatability were addressed. Significant differences were found in the maximum pressure profiles of the four seating systems with seats 2 and 3 performing better than seat I (seat 4 showed no significant difference when compared to the other seats). There is an almost linear relationship between mean pressure and body mass index. In all cases the air seating system performed better with regards to the static pressure gradients.

Torque variations during repeated passive isokinetic knee movements in persons with multiple sclerosis.

The purposes of this study were to investigate the effect of movement repetitions on resistive torque during passive isokinetic dynamometry of the knee and to determine the role of electromyographic activity in the stretched muscles on the torque measurements. Ten persons with multiple sclerosis and hypertonia of the knee muscles were compared with 10 healthy age- and gender-matched control subjects. During series of 10 flexion and extension movements of the knee at 60, 180 and 300 degrees/s, torque and electromyographic activity in the stretched muscles were registered. The persons with hypertonia presented a significantly larger torque reduction (p < 0.05) than the control subjects in all test conditions except for repeated knee flexion at 300 degrees/s. Electromyographic activity in the stretched muscles was not identified as the only explanatory mechanism for the reduction in hypertonia during the movement repetitions, suggesting that other factors were also involved.

Reliability of torque measurements during passive isokinetic knee movements in healthy subjects.

In the literature, few data are available about the reliability of torque measured during passive isokinetic knee movements. This study investigated the consistency of torque measurements during passive knee movements at 60, 180 and 300 degrees/second in 30 healthy subjects. Intraclass correlation values ranged between 0.78 and 0.92 when the results of two consecutive tests were compared. When retests were performed after repositioning the subjects, intraclass correlation values ranged between 0.43 and 0.87. These findings indicate the necessity for meticulous standardization of the test situation. Series of 10 consecutive movements, specifically repetitions of knee flexion at 180 and 300 degrees/second, indicated that torque measurements during the first two movements were less stable than those following. A concurrent change in electromyographic activity in the rectus femoris muscle suggested that these torque variations resulted from habituation of the stretch reflex.

Torque variations during repeated passive isokinetic movements of the knee in subjects with Parkinson's disease and healthy control subjects.

The purpose of this study was to quantify response variations during isokinetic passive movements of the knee in subjects with Parkinson's disease. Parkinsonian patients demonstrated a greater decrease of resistive torque compared to healthy control subjects, particularly in tests at higher velocities and during knee flexion movements. Responses were influenced by electromyographic activity in stretched and shortened muscle groups and also by mechanical factors. The results indicate that repetition of movements needs to be taken into account when measuring hypertonia in parkinsonian subjects.

Lumbosacral repositioning accuracy in standing posture: a combined electrogoniometric and videographic evaluation.

OBJECTIVE: To provide a new method of measuring repositioning accuracy in the lumbosacral spine in a standing position. DESIGN: A test-retest and parallel-forms reliability testing was performed. BACKGROUND: The contribution of proprioception to lumbar muscle function and to the stability of the lumbar spine is relatively unknown. METHOD: A piezoresistive electrogoniometer attached to the skin over the sacrum and a three-dimensional video analysis system with reflective markers on anatomical landmarks were both employed to measure the repositioning accuracy of pelvic tilting in standing. Eleven subjects without low back pain participated in this study. RESULTS: The overall mean repositioning accuracy was 1.87 degrees. Probability values from repeated measures ANOVA revealed no significant mean absolute error (AE) differences between sessions. Correlation coefficients between electrogoniometer and 3-D video analysis measurements of position sense ranged from 0.84 to 0.97. CONCLUSIONS: The proposed instruments and method are adequate for measuring lumbosacral repositioning accuracy. Healthy subjects are capable of repositioning their pelvis and back precisely. RELEVANCE: A reliable method assessing the lumbosacral repositioning accuracy can add insight into neuromuscular dysfunction as a cause of mechanical low back pain.

Measuring small linear displacements with a three-dimensional video motion analysis system: determining its accuracy and precision.

OBJECTIVES: To determine accuracy, precision, and smallest detectable difference for a three-dimensional (3D) video motion analysis system specifically configured for measuring small and slow displacements within a small measurement volume (0.7 x 0.5 x 0.3 m). DESIGN: Repeated measurements with random sequence of conditions. SETTING: Rehabilitation research laboratory. INTERVENTION: A reference sliding device was used to control cyclic displacements of two reflective markers over 5 calibrated ranges (1, 3, 10, 30, and 60 mm). Nine cycles were performed for each of 9 conditions (3 directions x 3 zones). Four cameras recorded all trials on tapes, which were digitized with a Kinemetrix system. MAIN OUTCOME MEASURES: Change in distance of the moving markers relative to a third static marker was averaged over 50 frames per trial. Mean error, mean absolute error, and intertrial and intratrial standard deviations (SDs) were calculated for each zone and direction. RESULTS: For 810 trials, mean error and absolute error were, respectively, .034 mm and .094 mm. The mean intertrial and intratrial SDs and 99% confidence interval were .047 mm (CI = +/- .121 mm) and .030 mm (CI = +/- .077 mm). The corresponding smallest detectable differences were .171 mm and .109 mm. CONCLUSION: Motion analysis configured for registration within small volumes allows measurement of minuscule displacements with great accuracy and may therefore be suitable for many applications in rehabilitation research other than gait analysis.