Koenig, Jordyn

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 90 th 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.

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.