Mirka, Gary A.

The neck muscle fatigue and subjective discomfort due to neck postural exposure was evaluated. Ten male participants were asked to hold one of the two static neck postural exposures for 30 minutes (one condition per day): 1) Neck flexion (N-45) where head and neck were flexed 45º relative to trunk while the participant was standing upright, and 2) Trunk flexion (T-45) where head and neck were not flexed relative to trunk, but trunk was flexed 45º. Surface electromyography was used to collect muscle activity of neck extensors. T-45 caused higher fatigue in neck extensor muscles (p=0.0229) and higher neck subjective discomfort (p=0.0088) compared to N-45, but the long-term effects of these two conditions are not clear because of the difference in the role of passive tissues. We recommend that work assessment tools consider both measures of neck postural exposure (neck flexion and trunk flexion) in their assessment tools.

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.

The use of lead vest/aprons in interventional medicine has been identified in self-report surveys as a contributing factor to the development of occupational low back pain. Controlled studies (both laboratory and field) that have explored this association have not provided a conclusive link. This review explores the knowledge and gaps surrounding the use of lead vest/apron and low back pain development.