Josef Kollmitzer

Reliability of surface electromyographic measurements

OBJECTIVES The aim of the study was to investigate short-term, intermediate-term and long-term reliability of surface electromyographic (EMG) measurements. METHODS Eighteen healthy subjects performed 810 isometric knee extension tests. Reliability for maximum voluntary contraction (MVC) and 50% MVC was assessed with retest intervals of 3 min, 90 min and 6 weeks. Reliability for sustained contractions was assessed with retest intervals of 90 min and 6 weeks. EMG was recorded from the rectus femoris, vastus lateralis and vastus medialis muscles. The root mean square (RMS) and the median frequency (MF) parameters were extracted. At sustained contraction tasks, estimated linear regression values of both parameters were analyzed. Bland-Altman-plots, coefficient of repeatability, Pearsons coefficient of correlation and intra class correlation (ICC) procedures were applied to assess test-retest reliability. RESULTS EMG recordings taken at short-term intervals were generally better reproducible than those of the longer-term intervals. Moreover, 50% MVC EMG recordings demonstrated better reproducibility than 100% MVC measurements, and EMG recorded from the rectus femoris were more constant than that from the vastus lateralis or vastus medialis. The MF parameter recorded from the rectus femoris was the only reliable parameter of EMG fatigue change. CONCLUSION In our set up, EMG measurement is best suited for clinical applications if submaximal MVC measurements are performed and signal is taken from rectus femoris muscle.

Muscle fatigue and fatigue-related biomechanical changes during a cyclic lifting task.

Study Design. Electromyographic and biomechanical methods were utilized to investigate correlations between indexes of localized muscle fatigue and changes in the kinematics and kinetics of motion during a cyclic lifting task. Summary of Background Data. Recent advances in time-frequency analysis procedures for electromyographicic signal processing provide a new way of studying localized muscle fatigue during dynamic contractions. These methods provide a means to investigate fatigue-related functional impairments in patients with low back pain. Objectives. To study the relationship between localized muscle fatigue and the biomechanics of lifting and lowering a weighted box. Fatigue-related changes in the electromyographicic signal of trunk and limb muscles were evaluated and compared to kinematic and kinetic measures in order to determine whether lifting strategy is modified with fatigue. Methods. A total of 14 healthy male subjects (26 ± 5 years) cyclically lifted and lowered a 13 kg box (12 lifts/min) for 4.5 minutes. A 5-second static maximum lifting task was included immediately before and after the cyclic lifting task to measure changes in lifting strength and static electromyographicic fatigue indexes. Electromyographic signals from 14 muscle sites (including paravertebral and limb muscles) were measured. Changes in the electromyographicic Instantaneous Median Frequency, a fatigue index, were computed using time-frequency analysis methods. This index was compared with more standardized measures of fatigue, such as those based on electromyographicic median frequency acquired during a static trunk extension test, subjective fatigue measures, and maximal static lifting strength. Biomechanical measures were gathered using a motion analysis system to study kinematic and kinetic changes during the lifting task. Results. During the cyclic lifting task, the electromyographic Instantaneous Median Frequency significantly decreased over time in the paravertebral muscles, but not in the limb muscles. Paravertebral electromyographicic Instantaneous Median Frequency changes were consistent with self-reports of fatigue as well as decreases in trunk extension strength. The magnitude of muscle-specific changes in electromyographicic Instantaneous Median Frequency was not significantly correlated with electromyographicic median frequency changes from the static trunk extension task. The load of the box relative to the maximal static lifting strength significantly affected the electromyographicic Instantaneous Median Frequency changes of paravertebral back muscles. Significant changes with fatigue during the task were found in the angular displacements at the knee, hip, trunk, and elbow. These biomechanical changes were associated with increased peak torque and forces at the L4–L5 vertebral segment. Conclusions. Our results demonstrate correlation between localized muscle fatigue and biomechanical adaptations that occur during a cyclic lifting task. This new technique may provide researchers and clinicians with a means to investigate fatigue-related effects of repetitive work tasks or assessment procedures that might be useful in improving education, lifting ergonomy, and back school programs. Although both the dynamic and static tasks resulted in spectral shifts in the electromyographicic data, the fact that these methods led to different muscle-specific findings indicates that they should not be considered as equivalent assessment procedures.

EMG fatigue patterns accompanying isometric fatiguing knee-extensions are different in mono- and bi-articular muscles

OBJECTIVES AND METHODS Isometric, fatiguing knee-extensions at 30%, 50% and 70% maximum voluntary contraction (MVC) were performed by 18 healthy human subjects. Surface electromyographic (SEMG) activity was recorded from the mono-articular vastus medialis (VM) and vastus lateralis (VL) muscles, and the bi-articular rectus femoris muscle (RF). To make the bi-articular muscle work under (1) constant and (2) similar working conditions as the two mono-articulars do, the hip was fixed in a flexed position. The root mean square (RMS) SEMG recorded during fatigue was standardized to the respective values of MVC. The mean coefficients of regression of the RMS and median frequency (MF) changes were then analyzed by multivariate analysis of variance. RESULTS The load effect upon the muscle fatigue changes, as measured by increase in RMS EMG, differed between the bi-articular muscle and the two mono-articulars, in that the parameter dropped with maximum load for the bi-articular, whilst it remained stable or even increased for the mono-articulars. This might suggest that the mono- and bi-articular muscles have different roles in fatigue tasks where the bi-articulars function purely as mono-articulars. By contrast, such a clear dichotomy between the bi-articular RF and the two mono-articulars, VM and VL, was lacking for the fatigue parameter of MF. CONCLUSIONS As these findings were confined to the changes in RMS EMG, different neuronal coding mechanisms for the mono- and bi-articular muscles in the central nervous system may be inferred.

The role of the biarticular agonist and cocontracting antagonist pair in isometric muscle fatigue

Isometric knee extensions until exhaustion at 30%, 50%, and 70% of maximum voluntary contraction were performed by 18 healthy subjects. During muscle fatigue, surface electromyographic activity was recorded from the knee‐extensors vastus lateralis, vastus medialis, and rectus femoris, and the coactive antagonistic biceps femoris. The electromyographic parameter median frequency (MF) served as a measure of fatigue. Coefficients of regression of the MF fatigue changes were analyzed statistically. MF fatigue occurred within the coactive biceps femoris and was significantly more pronounced than in the quadriceps. When the MF fatigue shifts of the coactive biceps femoris were compared with each of the three investigated parts of the quadriceps separately, MF fatigue shifts were similar in shape for the biarticular coactive biceps femoris and the biarticular rectus femoris, but differed significantly between the biceps femoris and the two monoarticular muscles, vastus medialis and vastus lateralis. As both the biarticular agonist and coactive antagonist muscles fatigued at a higher rate than the two monoarticular muscles, it seems likely that this biarticular agonist/antagonist pair determines the time to the limit of endurance.

Effects of back extensor strength training versus balance training on postural control.

PURPOSE Aim of this study was to investigate effects of 1) regular back extensor strength training as opposed to balance training, and 2) the influence of the sequence of both training types on postural control, force, and muscle efficiency. METHODS Twenty-six young, healthy subjects were investigated at baseline, 1 month and 2 months later. At each examination, subjects completed a posturographic, balance skill, and isometric maximum voluntary (MVC) back extension testing, including surface electromyographic (SEMG) recordings. After baseline evaluation, subjects were assigned to either daily strength training or balance training. After 1 month, the type of training was exchanged between groups. RESULTS After 1 month, back extensor strengthening led to decreased postural stability on hard surface, whereas there were no change after balance skill training. Analysis of the low- and high-frequency components of the sway signal revealed that strength training increased control efforts as indicated by an increased high-frequency component in order to maintain postural stability and unchanged low-frequency component. Balance skill training, however, increased postural stability as indicated by a decreased low-frequency component. The control effort remained unchanged. After completing either sequence of training, all postural parameters remained unchanged in both groups. Muscular efficiency as measured by SEMG root mean square during a standardized motor skill task revealed improved muscle economy regardless of the type of training. Back extension torque improved in both groups. CONCLUSION To avoid reduction of postural stability in rehabilitation processes, we recommend to include antagonist muscles in a comprehensive strength training regime or balance skill training.

Functional impact of unvarying exercise program in women after menopause.

Low bone mass, functional impairment, low muscle strength, and postural instability are predictors of the risk of fracture in an elderly person. The purpose of this study was to investigate the functional impact of an unvarying long-term exercise program to be carried out at home. The exercises had been shown to delay bone loss in an elderly population. At the Department of Physical Medicine and Rehabilitation, University of Vienna, postmenopausal women who had been stratified into exercise or control groups 5 to 10 yr ago were called in for a follow-up examination. Frequency of training, habits, and pain causing disability in activities of daily living were recorded. Walking velocity, muscle strength, and postural stability were measured. Functional assessment, blood analysis, and x-rays of the spine were performed additionally. One hundred twenty-four women aged 68.3 +/- 6.8 yr (mean +/- SD) underwent a follow-up investigation at the outpatient clinic. After 7.7 +/- 1.1 yr the compliance of the training group was still 36%. Self-chosen gait velocity was slightly higher in the regular exercisers than in the controls. No intergroup differences were found for pain induced disability, muscle strength, body sway, and fracture rate. The pain disability index was significantly associated with corrected self-chosen gait velocity. The results suggest that an unvarying home-based exercise program may support general agility but does not yield enough force to improve muscle strength and postural stability in healthy, nondisabled, postmenopausal women who start exercising at the age of 60 yr. Further studies are needed to define more appropriate exercise programs for a comprehensive improvement of functional outcome in a population at high risk for osteoporosis.

Postural control during lifting

Any voluntary motion of the body causes an internal perturbation of balance. Load transfer during manual material handling may increase these perturbations. This study investigates effects of stance condition on postural control during lifting. Nineteen healthy subjects repeatedly lifted and lowered a load between a desk and a shelf. The base of support was varied between parallel and step stance. Ground reaction force and segmental kinematics were measured. Load transfer during lifting perturbed balance. In parallel stance postural response consisted of axial movements in the sagittal plane. Such strategy was accompanied by increased posterior shear forces after lift-off. Lifting in step stance provided extended support in anterior/posterior direction. The postural control mechanisms in the sagittal plane are less complex as compared to parallel stance. However, lifting in step stance was asymmetrical and thus accompanied by distinct lateral transfer of the body. Lateral shear forces were larger as compared to parallel stance. Both lifting techniques exhibit positive and negative aspects. We cannot recommend either one as being better in terms of postural control.

An investigation of the effectiveness of exercise and manual therapy in treating symptoms of TMJ osteoarthritis.

ABSTRACT The background and purpose of this investigation was to evaluate the use of a treatment protocol which included active and passive jaw movements, manual therapy techniques, correction of body posture, and relaxation techniques for the treatment of temporomandibular joint (TMJ) osteoarthrosis (OA). Twenty consecutive patients suffering from TMJ OA participated in this study. Inclusion criteria: a. pain in the temporomandibular region; b. symptoms lasting at least three months; and c. radiologically proven OA. All patients were assigned to a waiting list, serving as a no treatment control period. Nineteen patients completed the study. No adverse effects occurred. During the control period (mean duration 35 days), the parameters did not change significantly. After treatment (mean duration 46 days) pain, impairment, and incisal edge clearance improved significantly (Wilcoxon test p < 0.001). At follow-up, pain and impairment were further reduced. The number of patients experiencing no pain at rest (80%), chi-square test p = 0.02) and stress (47%), chi-square test p = 0.03), and no impairment (37%), chi-square test p = 0.05) increased significantly. This therapeutic treatment protocol seems to be useful treatment for the symptoms of clinical dysfunction in OA of the TMJ.

Load-dependence of fatigue related changes in tremor around 10 Hz

OBJECTIVES The aim of the study was to investigate the effects of different loads on tremor around 10 Hz during fatiguing contractions. METHODS Eighteen healthy volunteers performed sustained isometric knee extensions at 30%, 50% and 70% maximum voluntary contraction (MVC). During the fatiguing contractions, mechanical recordings were made with a high-resolution force sensor. Tremor-power was calculated for the 6-20 Hz frequency window as a function of time normalized to endurance time. RESULTS Initial tremor power was different between the high and low load tasks. Changes of tremor with contraction time differed between the three tasks, in that tremor of the 30% MVC contraction showed the least decrease throughout the sustained contraction, whilst that of the 50% and 70% MVC showed progressively higher decreases. At failure, all 3 contractions merged to the same tremor level. CONCLUSION Load-dependent, fatigue-related 6-20 Hz tremor changes during sustained submaximum voluntary contractions seem mainly the consequence of recruitment of new units and fatigue-related properties of the high threshold motor units of muscles.

Long-term outcome after treatment of temporomandibular joint osteoarthritis with exercise and manual therapy.

ABSTRACT In a previous study, exercise and manual therapy demonstrated a 90% success rate in patients with osteoarthrosis of the temporomandibular joints in the short-term. The aim of this follow-up study was to assess the long-term effect of these treatment modalities. Seventeen patients were evaluated. All patients suffered from osteoarthrosis of the temporomandibular joints with pain in the temporomandibular joint at baseline and were treated successfully in a prior short-term study. The parameters were pain at rest and at chewing, impairment in daily life, and mouth opening. At follow-up, 11 patients (65%) experienced no pain and 13 patients (76%) had no pain at rest (Fishers Exact Test: p<0.02). Thirteen patients (76%) had a normal incisal edge clearance, and ten patients (59%) felt no impairment due to the disease (Fishers Exact Test: p=0.01). Thirteen patients (76%), who had been treated once successfully, have not needed treatment within the three years after cessation of their therapy. Exercise therapy is an effective tool to treat osteoarthrosis of the temporomandibular joints.