Functional asymmetry is among the multitude of risk factors for low-back pain (LBP), the most common injury under general industrial and agricultural conditions. However, previous studies showed that normal healthy individuals exhibit some functional asymmetry, indicating that not all asymmetry causes LBP. Therefore, the threshold value that is able to discriminate between normal and pathological situations is used as critical information to predict LBP. As a preliminary study to find threshold, the purpose of this study is to quantify the magnitude of bilateral asymmetries of erector spinae muscle forces of a healthy group during sagittally symmetric lifting. Ten healthy male subjects with no history of back pathology participated in this study, which collected motion capture, force data, and electromyography signals from six infrared cameras (MCam2, Vicon), two force platforms (AMTI), and surface EMG (BME Korea). In order to quantify the magnitude of bilateral asymmetry in the trunk muscle forces, we used 3D linked segment and EMG-assisted modeling approaches, both of which were verified based on their recapitulation of previously-proposed models. The results indicated that each muscle force in the lumbar region exhibited asymmetry during the entire lifting process. In particular, the erector spinae muscle forces exhibited an approximate 24% difference between bilateral sites (p<0.05). The results of this study provided data from normal individuals by which to identify pathological situations and predict LBP incidence within general industrial and agricultural conditions.
A number of studies have examined the validity of using spectral parameters, such as median frequency (F med ) and Dimitrov spectral index of muscle fatigue (FI nsm5 ) from the surface EMG signal during dynamic exercise, to assess muscle fatigue. Despite these studies, the ability to accurately predict endurance capacity using these spectral parameters during repetitive dynamic contractions is limited. The main purpose of this study was to examine the potential of using the incremental time, defined as the time when the Dimitrov spectral index increases to a certain value relative to the initial value, to predict the endurance time (T end ), which was determined when the subject became exhausted and could no longer follow the fixed contraction cycle. Ten healthy subjects performed five sets of voluntary isotonic contractions until they could only produce 10% and 20% of their maximal voluntary contraction level (MVC). The T end for all subjects were within the following ranges: 157±62 s at 10% MVC; 75±31 s at 20% MVC. Spectral parameters such as median frequency and Dimitrov spectral index were extracted from every contraction segment and estimated using linear regressive analysis at every contraction. The initial slope of both spectral parameters and the incremental time of the Dimitrov spectral index were compared as a predictor of endurance time. Significant correlations were found: 1) between T end and contraction level (p<0.05) and 2) between T end and the incremental time when the Dimitrov spectral index was above 130% of the increment with respect to the initial value at 20%MVC (p<0.01). In conclusion, the incremental time of the Dimitrov spectral index could be used to describe the changes in the spectral content of the sEMG signal and could be used as a good predictor of endurance time in comparison to the initial slope of the median frequency.
The purpose of this study is to calculate the length and velocity change of gastrocnemius and soleus muscle-tendon complex (MTC) for diagnosis and estimation of the rehabilitation procedure of the patient from non-invasive 3D markers. The previous method measuring the length of MTC has been dependant on the regression equation based on the rotation angle in the sagittal plane. However, in view of the fact that movement analysis is based on the human body having a variety of structure, the measurement using merely rotation angle and regression equation which not based on each subject shank and foot length might not be accurate. In order to overcome these limitations, the length change of MTC is calculated, employing 3D MTC model accompanied with the trajectory data of markers attached anatomical landmarks, each subject measurements and femur condyle radius. Basically, more accurate length change could be acquired through the 3D trajectory data of markers in comparing with 2D data based on the rotation angle. As our study, the difference of the gastrocnemius length change between 3D marker trajectory based method and the method using a 2-D angle was approximately 4% (2cm) at maximum contraction and 1% (0.5cm) at maximum relaxation. Similarly, the difference in terms of the soleus was approximately 0.7% (0.3cm) at maximum contraction and 0.5% (0.2cm) at maximum relaxation.
Minimizing artifacts from skin movement is vital for acquiring more accurate kinematic data in human movement analysis. There are several stages that cause skin movement artifacts and these stages depend on the selection of the reference system, the error reduction method and the coordinate system in clinical gait analysis. Due to residual errors, which are applied to the Euler and Bryant angle methods in each stage, significant cumulative errors are generated in the motion analysis procedure. Thus, there is currently a great deal of research focusing on reducing kinematic errors through error reduction methods and kinematic error estimations in relation to the reference system. However, there have been no studies that have systematically examined the effects of the selected coordinate system on the estimation of kinematic errors, because most of these previous studies have been mainly concerned with the analysis of human movement using only the human models that are provided in the commercial 3D motion capture systems.Therefore, we have estimated the differences between the results of human movement analyses using an absolute coordinate system and a relative coordinate system during a gait, in order to establish which system provides a more accurate kinematic analysis at the ankle joint. Six normal adult subjects with no neurological or orthopedic conditions, lower extremity injuries, or recent history of lower extremity surgery were used in this study. The analysis was conducted at a walking speed of 1.35m/s. For the clinical estimation, we used a cardinal plane based on the segmental reference system and the differences were plotted on the planes. From this analysis, when a relative coordinate system was in the gait analysis, the average kinematic error occurring during the gait was determined to be 13.58mm, which was significantly higher than the error generated with an absolute coordinate system. Therefore, although the relative coordinate system can also be used to calculate the ankle joint center during the clinical gait analysis, the absolute coordinate system should be employed in order to obtain more accurate joint kinematic data. In addition, the results from this study can be used as a basis to select an appropriate coordinate system with regards to the diagnostic accuracy level required for various kinds of gait disorders.
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