Development and Assessment of a Method to Estimate the Value of a Maximum Voluntary Isometric Contraction Electromyogram from Submaximal Electromyographic Data.

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.

Interruptions Experienced by Emergency Nurses: Implications for Subjective and Objective Measures of Workload.

INTRODUCTION: 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. METHODS: 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. RESULTS: 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. DISCUSSION: 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.

Effects of break scheduling strategies on subjective and objective measures of neck and shoulder muscle fatigue in asymptomatic adults performing a standing task requiring static neck flexion.

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.