The electromyographic (EMG) normalization (often to maximum voluntary isometric contraction MVIC) is used to control for interparticipant and day-to-day variations. Repeated MVIC exertions may be ...inadvisable from participants' safety perspective. This study developed a technique to predict the MVIC EMG from submaximal isometric voluntary contraction EMG. On day 1, 10 participants executed moment exertions of 100%, 60%, 40%, and 20% of the maximum (biceps brachii, rectus femoris, neck flexors, and neck extensors) as the EMG data were collected. On day 2, the participants replicated the joint moment values from day 1 (60%, 40%, and 20%) and also performed MVIC exertions. Using the ratios between the MVIC EMGs and submaximal isometric voluntary contraction EMG data values established on day 1, and the day 2 submaximal isometric voluntary contraction EMG data values, the day 2 MVIC EMGs were predicted. The average absolute percentage error between the predicted and actual MVIC EMG values for day 2 were calculated: biceps brachii, 45%; rectus femoris, 27%; right and left neck flexors, 27% and 33%, respectively; and right and left neck extensors, both 29%. There will be a trade-off between the required accuracy of the MVIC EMG and the risk of injury due to exerting actual MVIC. Thus, using the developed predictive technique may depend on the study circumstances.
As we seek to develop high fidelity human simulation models for ergonomic applications, the characterisation of the variability in human performance is needed. This technical note describes a method ...for generating probability density functions (PDFs) for one performance characteristic: trunk kinematics. A PDF from the Johnson family of distributions is defined by four parameters (γ, ξ, δ and λ) and can represent a variety of distributions. In this study, previously published trunk kinematic data were fit to Johnson distributions and regression equations for each of the four parameters were created as a function of starting lift height. Using regression coefficients and Monte Carlo simulation, PDFs for novel lifting conditions were generated. These predicted PDFs were compared with histograms of empirical data collected from a new group of ten lifters performing lifts in these novel conditions. A Kolmogorov-Smirnov goodness of fit test was performed to assess the quality of the fit. Seven of the predicted distributions of these kinematic variables were found to be a good fit with the novel empirical data.
Sustained non-neutral postures of the head/neck are related to transient neck discomfort and longer-term disorders of the neck. Periodic breaks can help but the ideal length and frequency of breaks ...are yet to be determined. The current study aimed to quantify the effects of three work-rest strategies on fatigue development. Participants maintained a 45-degree neck flexion posture for a total of 60 min and were provided 3 min of rest distributed in different ways throughout the experiment LONG (one, 3-min break), MEDIUM (two, 1.5-min breaks), or SHORT (five, 36-s breaks). Surface electromyography data were collected from the bilateral neck extensors and trapezius. Subjective discomfort/fatigue ratings were also gathered. Results of the analysis of the EMG data revealed that the SHORT condition did not show increased EMG activity, while LONG 21% and MEDIUM 10% did (p < 0.05), providing objective data supporting the guidance of short, frequent breaks to alleviate fatigue.
•Effect of break schedule strategies on neck and shoulder muscle fatigue was assessed.•Participants held a 45° neck flexion for 60 min with 3 min of rest.•Frequent and shorter rest breaks were effective in mitigating the fatigue response.
During scanning, sonographers often assume significant awkward postures which may lead to musculoskeletal pain and disability. Two exoskeletons were tested as an ergonomic intervention by ...sonographers during transthoracic echocardiograms (TTE). Four sonographers each performed TTEs using right- and left-handed scanning techniques, with and without two different passive upper extremity exoskeletons in two two-by-two experimental designs. Posture, muscle activity, and subjective discomfort scores were recorded. Of the two exoskeletons tested, the updated FLEX® design significantly reduced 10th percentile upper trapezius muscle activity during left hand scanning, while the AIRFRAME® did not impact muscle activity across all the muscles of interest. Furthermore, there was a slight decrease in the self-reported discomfort levels in their wrist and hands associated with performing TTE when wearing Exos1 compared to baseline. However, participants experienced issues with comfort, limitations on their range of motion (ROM), and interference with tasks with both exoskeletons. Collectively, the results indicate that the tested exoskeleton designs provide minimal benefit for reducing upper extremity muscle workload during TTE ultrasonography tasks.
•Upper extremity pain is predominant in cardiac sonographers.•Two commercially available exoskeletons provided minimal benefit for shoulder muscles of cardiac sonographers performing TTEs.•Upper extremity exoskeletons for cardiac sonography applications need to be designed with shallow abduction engagement angles.
Sonographers assume awkward postures of the upper extremities and torso while performing scanning tasks. Upper extremity exoskeletons are a potential ergonomic intervention to support sonographers in ...their work. This study examined the effects of a passive upper extremity exoskeleton on objective muscle activity and posture and subjective discomfort of sonographers performing transthoracic echocardiograms (TTE). Four practicing sonographers performed TTE procedures using both the right- and left- handed scanning TECHNIQUES, with and without a passive upper extremity EXOSKELETON (2x2 design). A randomized complete block design was used with participants acting as the blocking variable. At the 50th percentile of normalized muscle activity, the exoskeleton significantly reduced the right upper trapezius (p=0.045), left upper trapezius (p<0.001), and the right medial deltoid (p=0.034) activation. There was also a significant interaction between EXOSKELETON and TECHNIQUE for the right anterior deltoid (p=0.0007) and the left medial deltoid (p=0.006), though simple effects analysis revealed the exoskeleton only reduced muscle activity in left-handed scanning. At every percentile level considered, the exoskeleton tended to reduce muscle activity during left-handed scanning but had little impact on right-handed scanning. Averaged across right and left-handed scanning, the 50th percentile of posture data showed the exoskeleton significantly reduced the vertical angles of the torso (14.5 vs. 21.1 degrees), left arm (15.3 vs. 21.4 degrees), and right arm (24.4 vs. 28.4 degrees) but had no impact on head angle. However, self-reported discomfort and utility did not reflect the results from the objective measures. This study provides data to support the hypotheses that upper extremity exoskeletons have positive impacts on muscle activity and posture in sonography, but the type of work and the interaction between the sonographer and patient must be considered in order for the device to provide the greatest benefit.
Trunk kinematic variables have been used to understand the risk of low back injuries in the workplace. Variability in the trunk kinematics as an individual performs a repetitive lifting task is an ...underexplored area of research. In the current study, it was hypothesized that workplace variables (starting height of lift and load weight) would have an impact on the variance in the kinematic and kinetic variables. Twenty participants performed 60 repetitions of an asymmetric lifting task under four different conditions representing two levels of load weight (5% or 10% of the participant's body weight) and two levels of starting height (80% or 120% of the participant's knee height). The Lumbar Motion Monitor was used to capture trunk kinematic variables from the concentric range of lifting motion while ground reaction forces were collected using a force platform. The primary dependent variables were the variance of kinematic and kinetic variables across these 60 repetitions. The results showed a significant effect of starting height on the variance of sagittal plane trunk kinematics with the lower starting height generating an increased variance (sagittal range of motion increased by 55%, average sagittal velocity increased by 95%, peak sagittal velocity increased by 105%, and peak sagittal acceleration increased by 130%). There was no consistent significant main effect of either independent variable on the variance of the transverse plane kinematics. Additionally, there was no significant effect of load weight on the variance of any trunk kinematic variables tested. In terms of ground reaction forces, it was shown that the starting height of the load had a significant effect on the variance of peak vertical ground reaction force, while the weight of the load had a significant effect on the variance of the peak shear force.
•Workplace parameters can affect the variance of low back kinematics in lifting.•Decreasing the load starting height increased the variance of sagittal kinematics.•Changing the load weight didn't affect lifting kinematics variability significantly.
Relevance to industry: A relationship between trunk kinematics and risk of injury has been previously demonstrated. Investigating the variability of these trunk kinematics parameters in a repetitive lifting task and its relation with workplace parameters can provide an understanding of how changing workplace parameters may affect the risk of low back problems.
Trunk kinematic variables have been used to understand the risk of low back injuries in the workplace. Variability in trunk kinematics has not been explored to the same level. In the current study, ...it was hypothesized that workplace variables (starting height and load weight) would have an impact on the variability in the kinematic variables describing trunk motion. Ten participants performed a repetitive lifting task under four different conditions representing two levels of load weight and starting height. The Lumbar Motion Monitor was used to capture key trunk kinematic variables from the concentric range of lifting motion. The dominant parameter in this experiment was found to be the starting height of the lift which significantly affected the variability of trunk kinematics in sagittal plane. In the transverse plane neither starting height of the load nor the weight of the load were found to influence the variability of trunk kinematics significantly.
This study aimed to describe interruptions experienced by emergency nurses and establish convergence validity of 1 objective workload measure by linking interruption characteristics to objective and ...subjective measures of workload.
Interruptions were captured in real time across 8- or 12-hour shifts using a previously validated Workflow Interruptions Tool (WIT). Data collected on each interruption included type, priority, and location where the interruption occurred. At mid- and end-shift, the Surgery Task Load Index (SURG-TLX) and the Rapid Cognitive Assessment Tool (RCAT) were administered to participating nurses to measure workload subjectively and objectively.
Thirty-eight emergency nurse shifts were observed. A total of 3,229 interruptions were recorded across 372.5 clinical hours and 38 shifts (means M = 85.0 interruptions per shift, standard deviation SD = 34.9; M = 8.7 interruptions per hour, SD = 3.36). The median duration per interruption was 13.0 seconds. A moderate positive association was identified between the number of interruptions experienced during a shift and the increased overall SURG-TLX workload reported at end-shift, r(36) = 0.323, P = 0.048. Also, a moderate positive association was identified between increased reaction times during the RCAT task and increased mental demand experienced at end of shift, r(36) = 0.460, P < 0.001.
This study observed interruptions throughout the entirety of a nursing shift and found that the majority of interruptions caused by the environment were low priority. Targeting interventions to reduce low-priority and environmental interruptions may aid in alleviating the impact of interruptions on clinical staff and patient care. Furthermore, results demonstrate that the frequency of interruptions was perceived to increase the nursing staff workload overall.Unlabelled Box
Ames, IA Cardiac sonographers suffer from high prevalence of work-related upper extremity musculoskeletal pain due to awkward postures and fatigue accumulation. Sonographers can choose either left- ...or right-hand scanning, or alternate between both, however, the impact of each scanning technique on the upper extremity muscles remains unknown. Four ambidextrous cardiac sonographers performed between four to six cardiac scans using left- and right-hand while postural and muscle activity were collected from specific muscles on the upper extremities. A comparison of the posture showed that apart from forearm pitch and 90th percentile upper arm deviation, upper extremity postures between the two scanning techniques did not differ significantly. Furthermore, while right-hand scanning (RHS) appeared to induce slightly higher muscle activity in the deltoids compared to left-hand scanning (LHS), the difference between the two techniques was not significant. We recommend alternating between these two techniques to distribute muscle stress evenly to prevent muscle overuse.
PDF
