Comparing two methods to record maximal voluntary contractions and different electrode positions in recordings of forearm extensor muscle activity: Refining risk assessments for work-related wrist disorders

Consistency between the ACGIH TLV for hand activity and proposed action levels for wrist velocity and forearm muscular load based on objective measurements: an example from the assembly industry

Objectives. This study aimed to investigate the consistency between results of the American Conference for Governmental Occupational Hygienists (ACGIH) threshold limit value (TLV) for hand activity and proposed action levels of objective measurements in risk assessments of work-related musculoskeletal disorders. Methods. Wrist velocities and forearm muscular load were measured for 11 assemblers during one working day. Simultaneously, each assembler's hand activity level (HAL) during three sub-cycles was rated twice on two separate occasions by two experts, using a HAL scale. Arm/hand exertion was also rated by the assemblers themselves using a Borg scale. In total, 66 sub-cycles were assessed and assigned to three exposure categories: A) below ACGIH action limit (AL) (green); B) between AL and TLV (yellow); and C) above TLV (red). The median wrist velocity and the 90th percentile of forearm muscular load obtained from the objective measurements corresponding to the sub-cycles were calculated and assigned to two exposure categories: A) below or C) above the proposed action level. Results. The agreement between ACGIH TLV for hand activity and the proposed action level for wrist velocity was 87%. Conclusions. The proposed action level for wrist velocity is highly consistent with the TLV. Additional studies are needed to confirm the results.

How does the consecutive use of intraoral scanners affect musculoskeletal health? A preliminary clinical study

BACKGROUND

Minimizing muscle strain and reducing the risk of musculoskeletal disorders associated with intraoral scanner (IOS) usage require ergonomic awareness, device selection, and workplace adjustments in dental practice. This preliminary clinical study aimed to simulate intraoral scanning tasks using wired and wireless IOSs and assess muscle activation and fatigue for both types.

MATERIALS AND METHODS

Fourteen participants performed intraoral scanning tasks using wired and wireless IOSs (i700; MEDIT), with weights of 280 g and 328 g, respectively. The same computer system and software conditions were maintained for both groups (N = 14 per IOS group). Electrodes were placed on arm, neck, and shoulder muscles, and maximal voluntary contraction (MVC) was measured. Surface electromyography (EMG) was performed during the simulation, and EMG values were normalized using MVC. The root mean square EMG (%MVC) and muscle fatigue (%) values were calculated. Statistical comparisons were performed using the Mann-Whitney U and Friedman tests, with the Bonferroni adjustment for multiple comparisons (α = 0.05).

RESULTS

Arm (flexor digitorum superficialis) and neck muscles (left sternocleidomastoid and left splenius capitis) showed significantly higher EMG values with wireless IOS (P < 0.05). The neck (left sternocleidomastoid and right levator scapulae) and shoulder muscles (right trapezius descendens) demonstrated significantly higher muscle fatigue with wireless IOS (P < 0.05).

CONCLUSIONS

The consecutive use of heavier wireless IOS may increase the risk of muscle activation and fatigue in certain muscles, which may have clinical implications for dentists in terms of ergonomics and musculoskeletal health.

Machine learning for hand pose classification from phasic and tonic EMG signals during bimanual activities in virtual reality

Myoelectric prostheses have recently shown significant promise for restoring hand function in individuals with upper limb loss or deficiencies, driven by advances in machine learning and increasingly accessible bioelectrical signal acquisition devices. Here, we first introduce and validate a novel experimental paradigm using a virtual reality headset equipped with hand-tracking capabilities to facilitate the recordings of synchronized EMG signals and hand pose estimation. Using both the phasic and tonic EMG components of data acquired through the proposed paradigm, we compare hand gesture classification pipelines based on standard signal processing features, convolutional neural networks, and covariance matrices with Riemannian geometry computed from raw or xDAWN-filtered EMG signals. We demonstrate the performance of the latter for gesture classification using EMG signals. We further hypothesize that introducing physiological knowledge in machine learning models will enhance their performances, leading to better myoelectric prosthesis control. We demonstrate the potential of this approach by using the neurophysiological integration of the "move command" to better separate the phasic and tonic components of the EMG signals, significantly improving the performance of sustained posture recognition. These results pave the way for the development of new cutting-edge machine learning techniques, likely refined by neurophysiology, that will further improve the decoding of real-time natural gestures and, ultimately, the control of myoelectric prostheses.

Correlations between Ratings and Technical Measurements in Hand-Intensive Work

An accurate rating of hand activity and force is essential in risk assessment and for the effective prevention of work-related musculoskeletal disorders. However, it is unclear whether the subjective ratings of workers and observers correlate to corresponding objective technical measures of exposure. Fifty-nine workers were video recorded while performing a hand-intensive work task at their workplace. Self-ratings of hand activity level (HAL) and force (Borg CR10) using the Hand Activity Threshold Limit Value^® were assessed. Four ergonomist observers, in two pairs, also rated the hand activity and force level for each worker from video recordings. Wrist angular velocity was measured using inertial movement units. Muscle activity in the forearm muscles flexor carpi radialis (FCR) and extensor carpi radialis (ECR) was measured with electromyography root mean square values (RMS) and normalized to maximal voluntary electrical activation (MVE). Kendall's tau-b correlations were statistically significant between self-rated hand activity and wrist angular velocity at the 10th, 50th, and 90th percentiles (0.26, 0.31, and 0.23) and for the ratings of observers (0.32, 0.41, and 0.34). Significant correlations for force measures were found only for observer-ratings in five of eight measures (FCR 50th percentile 0.29, time > 10%MVE 0.43, time > 30%MVE 0.44, time < 5% -0.47) and ECR (time > 30%MVE 0.26). The higher magnitude of correlation for observer-ratings suggests that they may be preferred to the self-ratings of workers. When possible, objective technical measures of wrist angular velocity and muscle activity should be preferred to subjective ratings when assessing risks of work-related musculoskeletal disorders.

Effects of cleaning spray use on eyes, airways, and ergonomic load

BACKGROUND

Cleaning workers are exposed to chemicals and high physical workload, commonly resulting in airway problems and pain. In this study the response in the upper airways and the physical workload following airborne and ergonomic exposure of cleaning spray was investigated.

METHODS

A survey was answered by professional cleaning workers to investigate their use of cleaning sprays and the perceived effects on eyes, airways and musculoskeletal pain. A human chamber exposure study was then conducted with 11 professional cleaning workers and 8 non-professional cleaning workers to investigate the airborne exposure, acute effects on eyes and airways, and physical load during cleaning with sprays, foam application and microfiber cloths premoistened with water. All cleaning products used were bleach, chlorine, and ammonia free. The medical assessment included eye and airway parameters, inflammatory markers in blood and nasal lavage, as well as technical recordings of the physical workload.

RESULTS

A high frequency of spray use (77%) was found among the 225 professional cleaning workers that answered the survey. Based on the survey, there was an eight times higher risk (p < 0.001) of self-experienced symptoms (including symptoms in the nose, eyes and throat, coughing or difficulty breathing) when they used sprays compared to when they cleaned with other methods. During the chamber study, when switching from spray to foam, the airborne particle and volatile organic compound (VOC) concentrations showed a decrease by 7 and 2.5 times, respectively. For the whole group, the peak nasal inspiratory flow decreased (-10.9 L/min, p = 0.01) during spray use compared to using only water-premoistened microfiber cloths. These effects were lower during foam use (-4.7 L/min, p = 0.19). The technical recordings showed a high physical workload regardless of cleaning with spray or with water.

CONCLUSION

Switching from a spraying to a foaming nozzle decreases the exposure of both airborne particles and VOCs, and thereby reduces eye and airway effects, and does not increase the ergonomic load. If the use of cleaning products tested in this study, i.e. bleach, chlorine, and ammonia free, cannot be avoided, foam application is preferable to spray application to improve the occupational environment.

Electromyography analysis: Comparison of maximum voluntary contraction exercises for the latissimus dorsi

BACKGROUND: A prerequisite for interpreting electromyography (EMG) data is to normalize them to a maximum voluntary contraction (MVC), expressing them as percentage of the MVC. OBJECTIVE: The objective of this study was to compare different recommended MVC exercises for the latissimus dorsi and identify the exercise that elicits the highest EMG amplitude. METHODS: Fifteen male participants were recruited. Five recommended MVC exercises were investigated, including chest-supported shoulder extension, prone shoulder extension, lat-pull down, abducted shoulder flexion, and internal shoulder rotation. RESULTS: Chest-supported shoulder extension reported the highest mean EMG, which was not significantly different from the mean EMG of prone shoulder extension. Both of these exercises led to significantly greater EMG means than the other exercises. Sixty percent of the participants achieved their highest EMG amplitude with chest-supported shoulder extension and 40% with prone shoulder extension. None of the other exercises elicited the highest EMG amplitude in any of the participants. CONCLUSIONS: Both chest-supported shoulder extension and prone shoulder extension proved to be effective MVC exercises, with the former showing more consistency in eliciting the highest EMG amplitude. If the true MVC is desired, the authors recommend performing both exercises and then using the overall highest EMG amplitude for normalization purposes.

Movement Analysis with Inertial Measurement Unit Sensor After Surgical Treatment for Distal Radius Fractures

Inertial measurement unit (IMU) has recently been used to evaluate a movement of a body segment to provide accurate information of movement's characteristics. IMU systems have been validated to successfully measure joint angle during upper limb range of motion (ROM). The study aimed to retrospectively evaluate, using an IMU, the ROM recovery of the wrist after surgical treatment for distal-radius fractures with Kirschner wire fixation (KWF) or with volar plate fixation (VPF) and screws. To assess pain in the wrist joint, muscle-fatigue (MF), and functional difficulties in activities of daily living, we evaluated the patients through patient-related wrist evaluation questionnaire (PRWE) scale, disability of the arm, shoulder and hand (DASH) scale, Hand Grip Strength (HGS), and surface electromyography (EMG). We used a single IMU composed of three-axis gyroscope, a three-axis accelerometer, and a magnetometer. We calculated the value of ROM as a percentage with respect to the unaffected wrist. We also recorded surface-EMG signals over biceps brachialis, flexor carpi radialis (FCR), extensor carpi radialis (ECR), and pronator teres muscles. Forty patients were recruited for our study. Ulnar deviation (UD) was significantly higher for VPF than for KWF (p = 0.017); supination was significantly higher for VPF than for KWF (p = 0.031). The percentage of decay of the median frequency of FCR of volar plate was significantly higher than KWF. The HGS of KWF was significantly higher than VPF. In literature, there were no significant differences between the two types of treatment at long-term follow-up. Our results demonstrate a superior efficacy of VPF in terms of ROM improvement in UD and supination, but for these patients, muscle fatigue is greater than the KWF group. Based on the data available, VPF is similar to KWF for the treatment of distal radius fractures. The IMU sensor could be used in the future to evaluate ROM after surgery during patient's rehabilitation and to compare the effects with stratified analysis regarding age and fracture type, paralleled with cost-effectiveness analysis.

The effect of two types of maximal voluntary contraction and two electrode positions in field recordings of forearm extensor muscle activity during hotel room cleaning

Purpose. This study aimed to investigate the effects of using hand grip or resisted wrist extension as the reference contraction, and two electrode positions, on field recordings of forearm extensor muscle activity. Materials and methods. Right forearm extensor muscle activity was recorded using two electrode pairs (over the most prominent part (position 2) and proximal to that (position 1)) during one working day in 13 female hotel housekeepers. Each subject performed the two maximal voluntary contractions (MVCs), and the electrical activity obtained during these (maximal voluntary electrical activity (MVE)) was used for normalization. Each set of recordings was analysed twice, once using hand grip as the MVC and once using resisted wrist extension. Results. Resisted wrist extension showed a higher group mean MVE than hand grip. Position 2 had higher correlation between MVE and force during the MVCs. The workload during cleaning was lower when using resisted wrist extension as reference than when using hand grip (24%MVE vs 46%MVE; p = 0.002 at position 2) for the 90th percentile. The workload (99th percentile) was overestimated in two subjects when using hand grip as reference. Conclusions. Problems associated with poorly activated forearm extensors can be overcome by using resisted wrist extension as reference.

Investigation of observational methods assessing workload of static working postures based on surface electromyography

BACKGROUND:

A large number of different methods are available to identify and assess working postures. Although observation-based methods are most commonly used in practise, investigations showed different results regarding validity of such methods.

OBJECTIVE:

To investigate validity of one of the most commonly used observation-based assessment method in ergonomics, the Ovako Working Posture Analysing System (OWAS) and the European standard EN 1005-4 for evaluation of working postures, an experimental laboratory study was conducted.

METHODS:

Muscle activity was measured under combinations of static working postures of trunk inclination and shoulder flexion to compare these measurements and observation-based assessments according to OWAS and EN 1005-4. In order to investigate the magnitude of correspondence between muscle activity and observation-based assessments, Spearman rank correlation coefficients (r_s) were calculated.

RESULTS:

Significant correlations were found between OWAS and muscle activity (range from r_s² = 0.17 r_s² = 0.55). Significant correlations were found between EN 1005-4 and muscle activity (range from r_s² = 0.34 to r_s² = 0.74).

CONCLUSIONS:

Results emphasise a need for further developments of observation-based methods, since the two investigated methods showed a variance of validity ranging from small to large. Such improvements may also form a better basis for the ergonomic improvement of working conditions in practise, which is highly necessary due to a constantly high prevalence of MSDs in the last decades.