Determination of subject-specific muscle fatigue rates under static fatiguing operations

Review and comparison of linear algorithms to quantify muscle fatigue based on sEMG signals

Surface electromyography techniques are widely used in field of motion analysis and ergonomics combining precise muscular activation assessment with low-invasiveness and wearability. The aim of this investigation is to identify the myoelectrical manifestations of fatigue and to compare the effectiveness of sEMG-based quantitative indices for fatigue assessment. The investigated indexes are the ARV and RMS signal amplitudes, the mean frequency, the median frequency, the Dimitrov index, the instantaneous mean frequency and Wavelet distribution-based WIRE51 index. Two different protocols were developed, and the activity of the lateral deltoid and middle trapezius muscles was recorded. The WIRE51 index is found to have the highest sensitivity in the detection of the difference between the repetitions of each exercise for both protocols. Due to the lack of a unified standard for the performance comparison of fatigue indices, a correlation analysis was carried out between the result provided by the indices and the subjective fatigue perception employing the RPE scale.

Behavioral and physiological fatigue-related factors influencing timing and force control learning in pianists

Optimizing the training regimen depending on neuromuscular fatigue is crucial for the well-being of professionals intensively practicing motor skills, such as athletes and musicians, as persistent fatigue can hinder learning and cause neuromuscular injuries. However, accurate assessment of fatigue is challenging because of the dissociation between subjective perception and its impact on motor and cognitive performance. To address this issue, we investigated the interplay between fatigue and learning development in 28 pianists during three hours of auditory-motor training, dividing them into two groups subjected to different resting conditions. Changes in behavior and muscle activity during training were measured to identify potential indicators capable of detecting fatigue before subjective awareness. Our results indicate that motor learning and fatigue development are independent of resting frequency and timing. Learning indices, such as reduction in force and timing errors throughout training, did not differ between the groups. No discernible distinctions emerged in fatigue-related behavioral and physiological indicators between the groups. Regression analysis revealed that several fatigue-related indicators, such as tapping speed variability and electromyogram amplitude per unit force, could explain the learning of timing and force control. Our findings suggest the absence of a universal resting schedule for optimizing auditory-motor learning.

Characterizing exposure to physical risk factors during veterinary surgery with wearable sensors: a pilot study

Occupational ApplicationsVeterinarians provide comprehensive health services for animals, but despite exposure to similar occupational and safety hazards as medical physicians, physical risk factors for these doctors and healthcare teams have not been characterized. In this pilot study, we used wearable sensor technology and showed that veterinary surgeons commonly experience static and demanding postures while performing soft tissue and orthopedic surgeries. Observations showed that muscle activation was highest in the right trapezius. Job factors such as surgical role (attending vs. assisting) and surgical specialty (soft tissue vs. orthopedics) appeared to influence exposure to physical risk factors. These findings suggest a need to consider the unique demands of surgical specialties in order to address the key risk factors impacting injury risks among veterinarians. For example, static postures may be a priority for soft tissue surgeons, while tools that reduce force requirements are more pressing for orthopedic surgeons.Technical AbstractBackground: Although musculoskeletal fatigue, pain, and injuries are commonly reported among surgeons in veterinary medicine, few studies have objectively characterized the exposure to physical risk factors among veterinary surgeons.Purpose: This study aimed to characterize muscle activation and postures of the neck and shoulders during live veterinary surgeries in the soft tissue and orthopedic specialties.Methods: Forty-four ergonomic exposure assessments (exposures) were collected during 26 surgical procedures across five surgeons. Exposures were collected from both soft tissue (n = 23) and orthopedic (n = 21) specialties. Physical risk factors were characterized by: 1) directly measuring muscle activation and posture of the neck and shoulders, using surface electromyography and inertial measurement units, respectively; and 2) collecting self-reported workload, pain, and stiffness.Results: Across the 44 exposures, neck and back symptoms respectively worsened after the surgery in 27% and 14% of the exposures. Veterinary surgeons exhibited neck postures involving a mean of 17° flexion during the surgical procedures. Static postures were common, occurring during 53-80% of the procedures. Compared to soft tissue procedures (e.g., 13.2% MVC in the right trapezius), higher muscle activity was observed during orthopaedic procedures (e.g., 27.6% MVC in the right trapezius).Conclusions: This pilot study showed that physical risk factors (i.e., muscle activity and posture of the neck/shoulder) can be measured using wearable sensors during live veterinary surgeries. The observed risk factors were similar to those documented for medical physicians. Further studies are needed to bring awareness to opportunities for improving workplace ergonomics in veterinary medicine and surgery.

Self-Reported Neck and Back Pain among Supermarket Cashiers in Gaborone, Botswana

OBJECTIVE

Investigate the prevalence, risk factors and impacts of neck and back pain among supermarkets cashiers in Botswana.

MATERIALS AND METHODS

A cross-sectional study was conducted among supermarkets cashiers using self-administered. Data were analysed using χ² and logistic regression models. Statistical significance was assumed at p<0.05.

RESULTS

A total of 174 supermarkets cashiers participated in this study majority of whom were females (72%). The prevalence of lower back pain was 69%, upper back pain 53% and neck pain 37%. Increasing age was associated with neck 95% CI [1.43-5.15] and upper back 95% CI [1.43-3.60] pain. Cashiers working at low work surface and overreaching for items were 19 and 11 times more likely to report neck 95% CI [1.7-255.9] and lower back 95% CI [1.84-62.1] pain, respectively. Almost 6% of cashiers who reported lower back pain reported considering changing jobs due to pain.

CONCLUSIONS

More than two-thirds, half and about two-fifths of supermarket cashiers reported lower back, upper back and neck pain, respectively. Individual and work-related factors were associated with neck and/or back pain. Back and neck pain workers' health and wellbeing, their families, workplace productivity and the health care system. To reduce their prevalence and progression, supermarkets should introduce occupational health and safety talks.

REDUCED PERIPHERAL AND INSPIRATORY MUSCLE ENDURANCE IN PATIENTS WITH LIVER CIRRHOSIS: A CROSS-SECTIONAL STUDY

BACKGROUND

Liver cirrhosis (LC) causes several musculoskeletal changes.

OBJECTIVE

To test the hypothesis that the peripheral and inspiratory muscle endurance are reduced in patients with liver cirrhosis.

METHODS

Twenty-one patients with LC (LC group; 61±14 years) and 18 age-matched subjects (control group; 56±17 years) had accepted to participate in this cross-sectional observational study. To assess peripheral muscle endurance, all volunteers performed a rhythmic handgrip exercise at 45% of their maximum voluntary contraction. A metronome was used to control the contraction-relaxation cycles at 60/min. The inspiratory muscle endurance was assessed using PowerBreath®. Participants underwent inspiratory muscle exercise at 60% of their maximal inspiratory muscle strength. The time until failure characterized the muscle endurance for both handgrip and inspiratory muscle exercises. Additionally, the quality of life of the participants was assessed.

RESULTS

The muscle endurance was lower in the LC group when compared to the control group for both handgrip (67 vs 130 s, P<0.001) and inspiratory muscle exercises (40 vs 114 s, P<0.001). The peripheral muscle endurance was directly correlated with the total quality of life score (r=0.439, P=0.01) and to the following domains: fatigue (r=0.378 e P=0.030), activity (r=0.583, P=0.001), systemic symptoms (r=0.316, P=0.073) and preoccupation (r=0.370, P=0.034). The inspiratory muscle endurance was inversely correlated with the total quality of life score (r=0.573, P=0.001) and the following domains: fatigue (r=0.503, P=0.002), activity (r=0.464, P=0.004), systemic symptoms (r=0.472, P=0.004), abdominal symptoms (r=0.461, P=0.005), emotional function (r=0.387, P=0.02) and preoccupation (r=0.519, P=0.001).

CONCLUSION

Both peripheral and inspiratory muscle endurance were lower in LC patients when compared to the control group.

Effects of handle height and load on the endurance time for simulated demolition tasks

BACKGROUND

Manual demolition tasks are heavy physical demanding tasks which involve forceful exertion of sustained pushing. They result in muscle fatigue which could lead to musculoskeletal disorders. Assessments of maximum endurance time (MET) are essential in understanding the developing of muscle fatigue for these tasks.

OBJECTIVE

The objectives of this study were to determine the effects of handle height and load conditions on the MET, and to establish MET models for the simulated demolition tasks.

METHODS

Twenty three male participants performed simulated demolition tasks under three loads and three handle heights conditions until they could not do so any longer. Their METs and ratings of perceived exertion were recorded and analyzed.

RESULTS

The results showed that both load and handle height were significant (p < 0.0001) factors affecting the MET. Regression models to predict the MET under handle height and load conditions were established. The mean absolute deviations of these models were between 1.91 and 4.84 min.

CONCLUSION

The MET models established may be used to estimate the MET which may be adopted in work/rest arrangement for demolition tasks using a handheld demolition hammer.

Effects of Vertical Lifting Distance on Upper-Body Muscle Fatigue

Manual material handling (MMH) is commonly demanded in the manufacturing industry. Occupational muscle fatigue of the arm, shoulder, and back, which arise from MMH tasks, can cause work absences and low efficiency. The available literature presents the lack of the fatigue comparison between targeted muscles, on the same part or on different parts. The main aim of the present study was to evaluate and compare the fatigue of upper-body muscles during repetitive bending tasks, an experiment involving 12 male subjects has been conducted to simulate material handling during furniture board drilling. The vertical lifting distance was chosen to be the single independent variable, and the three levels were 0, 250, and 500 mm. Surface electromyography (sEMG) was used to measure the muscle fatigue of the biceps brachii, upper trapezius, and multifidus, while the sEMG parameters, including the normalized electromyographic amplitude (Normalized EA) and mean power frequency (MPF), of the target muscles were analyzed. The experimental results reveal that during the manual handling tasks, the biceps brachii was the most relaxed muscle, contributing the least muscle tension, while the multifidus was the most easily fatigued muscle. Furthermore, the EMG MPF fatigue threshold (MPFFT) of multifidus muscle tension was tested to estimate its maximum workload in the long-term muscle contraction. In conclusion, bending angle should be maintained to a small range or bending should even be avoided during material-handling tasks.

Adaptive robot mediated upper limb training using electromyogram-based muscle fatigue indicators

Studies on improving the adaptability of upper limb rehabilitation training do not often consider the implications of muscle fatigue sufficiently. In this study, electromyogram features were used as fatigue indicators in the context of human-robot interaction. They were utilised for auto-adaptation of the task difficulty, which resulted in a prolonged training interaction. The electromyogram data was collected from three gross-muscles of the upper limb in 30 healthy participants. The experiment followed a protocol for increasing the muscle strength by progressive strength training, that was an implementation of a known method in sports science for muscle training, in a new domain of robotic adaptation in muscle training. The study also compared how the participants in three experimental conditions perceived the change in task difficulty levels. One task benefitted from robotic adaptation (Intervention group) where the robot adjusted the task difficulty. The other two tasks were control groups 1 and 2. There was no difficulty adjustment at all in Control 1 group and the difficulty was adjusted manually in Control 2 group. The results indicated that the participants could perform a prolonged progressive strength training exercise with more repetitions with the help of a fatigue-based robotic adaptation, compared to the training interactions, which were based on manual/no adaptation. This study showed that it is possible to alter the level of the challenge using fatigue indicators, and thus, increase the interaction time. The results of the study are expected to be extended to stroke patients in the future by utilising the potential for adapting the training difficulty according to the patient's muscular state, and also to have a large number repetitions in a robot-assisted training environment.

Strength Decrease, Perceived Physical Exertion and Endurance Time for Backpacking Tasks

Manual material handling (MMH) tasks create a burden for workers which could result in musculoskeletal injuries. Assessments of the decrease of muscular strength and the maximum endurance time (MET) for MMH tasks are essential in studying the ergonomic risk of MMH tasks. A backpacking experiment was conducted for measuring the MET for MMH tasks. Human participants carried a load on their back and walked on a treadmill under various load, walking speed, and ramp angle conditions until they coud no longer do so. It was found that the participants were able to walk for approximately 15 min to two hours before they needed to have a pause. Their back and leg strengths declined moderately due to performing the tasks. These tasks resulted in an increase in heart rate and elevated perceived physical exertion. The rating of perceived exertion (RPE)/heart rate ratio in our backpacking tasks was 31% higher than that in the literature, implying the calibration of the RPE may be required for such tasks. A MET model incorporating the f_{MVC_back}, body weight, walking speed, and ramp angle was established. This model may be used to determine the work/rest allowance for backpacking tasks under conditions similar to this study.

Pulling strength, muscular fatigue, and prediction of maximum endurance time for simulated pulling tasks

Truck pulling is one of the common manual materials handling tasks which contribute to musculoskeletal disorders. The maximum endurance time (MET) for two-handed truck pulling tasks has been rarely discussed in the literature. The objectives of this study were to explore the development of muscular fatigue when performing two-handed pulling task and to establish models to predict the MET. A simulated pallet truck pulling experiment was conducted. Sixteen healthy adults including eight females and eight males participated. The participants pulled a handle simulating that of a pallet truck using two hands until they could not pull any longer under two postures. The forces applied for females and males were 139.65 N and 170.03 N, respectively. The maximum voluntary contractions (MVC) of the pulling strength both before and after the simulated pull were measured. After each trial, both the MET and subjective ratings of muscular fatigue on body segments were recorded. The results showed that posture significantly affected MVC of pull both before and after the trial. It was found that foot/shank of the front leg had higher subjective ratings of muscular fatigue than the other body segments. The MET equations employing both power and logarithmic functions were developed to predict the MET of the two-handed pulling tasks. Predictive models established in this study may be used to assess the MET for two-handed pulling tasks.

Experimental validation of a subject-specific maximum endurance time model

This study aimed at experimentally validating a subject-specific maximum endurance time (MET) model. Thirty health participants (15 males and 15 females; Age: mean = 21.5 years, SD = 1.6 years) volunteered to conduct an isometric elbow flexion task until exhaustion. The endurance times of each participant were measured under relative exertion levels ranging from 30% MVC (Maximum Voluntary Contraction) to 70% MVC at 10% intervals. Assessment of the model showed that the intensity-endurance time relationship for each studied individual could be well fitted by the subject-specific MET model (R² > 0.89). The fatigue rates identified from the model fitting were normally distributed (Mean = 0.96 min^-1, SD = 0.29 min^-1). In addition, the fatigue rates of the male group were significantly higher than the female group. The subject-specific MET model can be used to predict the MET for individual workers, and further support physical task design, based on the fatigability data of a targeted worker population. Practitioner Summary: Ergonomists have extensively used MET models in physical fatigue assessment and physical task design. A subject-specific MET model could be used to predict the MET at individual levels, and also to support work design for a target worker population, based on the fatigability data distribution obtained from sampled workers.

Isometric arm strength and subjective rating of upper limb fatigue in two-handed carrying tasks

Sustained carrying could result in muscular fatigue of the upper limb. Ten male and ten female subjects were recruited for measurements of isometric arm strength before and during carrying a load for a period of 4 minutes. Two levels of load of carrying were tested for each of the male and female subjects. Exponential function based predictive equations for the isometric arm strength were established. The mean absolute deviations of these models in predicting the isometric arm strength were in the range of 3.24 to 17.34 N. Regression analyses between the subjective ratings of upper limb fatigue and force change index (FCI) for the carrying were also performed. The results indicated that the subjective rating of muscular fatigue may be estimated by multiplying the FCI with a constant. The FCI may, therefore, be adopted as an index to assess muscular fatigue for two-handed carrying tasks.