EMG activity in neck and back muscles during selected static postures in adult males and females

A systematic review of biomechanical risk factors for the development of work-related musculoskeletal disorders in surgeons of the head and neck

BACKGROUND

Previous studies have shown high rates (47-72%) of self-reported work-related musculoskeletal disorders (WRMDs) in surgeons of the head and neck. Physical requirements in the workplace, individual factors (e.g. poor posture, obesity) and psychosocial factors have been identified as risk factors. Establishing biomechanical risk factors may help prevent further development of WRMDs in this population.

OBJECTIVE

The purpose of this critical review was to source studies that identified the biomechanical risk factors for WRMDs in this surgical sub-specialty.

METHODS

Searches were conducted of Medline, CINAHL, and AMED databases from 1980 until September 2018.

RESULTS

A total of 182 article were identified. Exclusion criteria lead to 163 full-text articles being screened, generating a total of 6 articles for review. The aims of the included studies varied significantly. Surgeons spend the majority of operating time in static, asymmetrical positions. Surgical loupes/headlamps significantly increased cervical spine loading. Articulated surgical arm supports provided optimal ergonomic conditions. Performing surgical operations with the surgeon in standing or sitting had no effect on task performance or demand. Physical fatigue was also measured in both positions.

CONCLUSIONS

A combination of equipment-based and patient/surgeon position-based factors predispose surgeons to biomechanical risk factors. Studies of greater methodological quality are required.

Yoga Posture Recognition and Quantitative Evaluation with Wearable Sensors Based on Two-Stage Classifier and Prior Bayesian Network

Currently, with the satisfaction of people’s material life, sports, like yoga and tai chi, have become essential activities in people’s daily life. For most yoga amateurs, they could only learn yoga by self-study, like mechanically imitating from yoga video. They could not know whether they performed standardly without feedback and guidance. In this paper, we proposed a full-body posture modeling and quantitative evaluation method to recognize and evaluate yoga postures to provide guidance to the learner. Back propagation artificial neural network (BP-ANN) was adopted as the first classifier to divide yoga postures into different categories, and fuzzy C-means (FCM) was utilized as the second classifier to classify the postures in a category. The posture data on each body part was regarded as a multidimensional Gaussian variable to build a Bayesian network. The conditional probability of the Gaussian variable corresponding to each body part relative to the Gaussian variable corresponding to the connected body part was used as criterion to quantitatively evaluate the standard degree of body parts. The angular differences between nonstandard parts and the standard model could be calculated to provide guidance with an easily-accepted language, such as “lift up your left arm”, “straighten your right forearm”. To evaluate our method, a wearable device with 11 inertial measurement units (IMUs) fixed onto the body was designed to measure yoga posture data with quaternion format, and the posture database with a total of 211,643 data frames and 1831 posture instances was collected from 11 subjects. Both the posture recognition test and evaluation test were conducted. In the recognition test, 30% data was randomly picked from the database to train BP-ANN and FCM classifiers, and the recognition accuracy of the remaining 70% data was 95.39%, which is highly competitive with previous posture recognition approaches. In the evaluation test, 30% data were picked randomly from subject three, subject four, and subject six, to train the Bayesian network. The probabilities of nonstandard parts were almost all smaller than 0.3, while the probabilities of standard parts were almost all greater than 0.5, and thus the nonstandard parts of body posture could be effectively separated and picked for guidance. We also tested separately the trainers’ yoga posture performance in the condition of without and with guidance provided by our proposed method. The results showed that with guidance, the joint angle errors significantly decreased.

Neck and trunk representations in the primary motor cortex in rats

[Purpose] The neck and trunk play crucial roles in body movement and are extremely important areas of treatment for physical therapists. However, many aspects of the neural basis of this motor control remain unknown. Therefore, we investigated the distribution and electrophysiological properties of the neck and trunk in the primary motor cortex in rats. [Subjects and Methods] Using intracortical microstimulation, we investigated the somatotopic representation and movements induced by electrical stimulation of the neck and truck areas of the motor cortex in 8 Wistar rats. [Results] We determined that the neck and trunk areas are located separately on the rostral and caudal sides of the motor cortex, respectively. The neck area was significantly larger in size, while the threshold was significantly larger for the trunk area. Stimulation of the neck area with a current higher than the threshold induced movement of the forelimbs, jaw, trunk, and whiskers. However, stimulation of the trunk area did not result in movement in sites other than the trunk. [Conclusion] During movement, the respective activities of the neck and trunk are interdependent. However, due to the separate locations of these areas in the motor cortex, their properties differ greatly.

On the use of EMG-ratios to assess the coordination of back muscles

BACKGROUND

Electromyographic (EMG) amplitude ratios (EMG-ratios) have been proposed to assess back muscle coordination in chronic low back pain patients to avoid the normalization of EMG using maximal contractions. The aim of this study was to test the relevance of this type of EMG analysis.

METHODS

Healthy subjects (44 men and 13 women) and patients with chronic low back pain (57 men) performed three 7s static ramp extension contractions ranging from 0% to 100% of the maximal voluntary contraction while standing in a static dynamometer. A subgroup of 20 healthy men also performed 5s step contractions at 10%, 20%, 40%, 60% and 80% of the maximal voluntary contraction. Finally, to assess reliability, another subgroup (n=20 healthy and 20 men with chronic low back pain) performed the protocol three times, on different days. Surface EMG signals were collected from four pairs of back muscles and subcutaneous tissue thickness was measured at the corresponding electrode sites. EMG amplitude values were computed at each 5% force level from 10% to 80% of the maximal voluntary contraction. Then, EMG-ratios were computed between different electrode sites and averaged bilaterally.

FINDINGS

All EMG-ratios were affected by the force level and the contraction type (ramp vs step contractions). Statistically significant Pearson's correlations (r=-0.38 to -0.57) were obtained between some EMG-ratios and their corresponding subcutaneous tissue thickness ratios. The reliability of the EMG-ratio variables ranged from moderate to excellent (intra-class correlation coefficients between 0.50 and 0.91). Comparisons between 12 men and 13 women and between 24 healthy men and 57 men with chronic low back pain showed that EMG-ratios were sensitive to sex but not to pain status. Multivariate analyses applied on the EMG-ratios identified clusters of subjects but none of the main clinical variables were able to clearly characterize these clusters.

INTERPRETATION

Overall, even though additional research is warranted to further substantiate some important psychometric characteristics of the EMG-ratios as well as their biomechanical and clinical significance, these results support their use for assessing the coordination patterns of back muscles, provided that confounding variables such as the force level, the contraction type, and subcutaneous tissue thickness are accounted for.