Exploring the relationship between neck flexion and neck problems in occupational populations: a systematic review of the literature.

A systematic review was conducted to evaluate the relationship between occupational neck flexion angles and neck problems. The synthesised findings were used to answer three research questions: (1) Is there a positive/negative relationship between neck flexion and neck problems? (2) What is the appropriate angular threshold for neck flexion as a risk factor for neck problems? (3) What are the gaps in our current knowledge? A review of 21 papers revealed (1) a consistent positive correlation between neck flexion and neck problems, and (2) a neck flexion angle of 20° as the most evidence-based (not necessarily the best) cut-off angle separating high- and low-risk neck flexion postures. Future research should focus on the (1) continuous collection of three-dimensional neck postures through longitudinal studies to quantify cumulative exposures of neck postures, and (2) development of standard descriptions of 'neck problems' and 'neck flexion' to facilitate the development of a dose-response relationship. Practitioner summary: Practitioners depend on thresholds for evaluating neck postural exposure using work assessment tools; however, the scientific basis for this is unclear. This systematic review investigated the angular threshold for neck flexion and found 20° of neck flexion with the greatest evidence-based support as the threshold for high-risk neck postural exposure.

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.

The effects of repetitive bouts of a fatiguing exertion (with breaks) on the slope of EMG measures of localized muscle fatigue.

Decreases in the median frequency of the power spectrum and increases in amplitude measures of an electromyographic signal have been used to assess localized muscle fatigue. How these responses are affected by repetitive bouts of exertions - separated by rest breaks - is not well understood. It was hypothesized that repetitive bouts of a fatiguing, isometric exertion, separated by periods of rest, would have cumulative effects (across bouts) on the slope of these EMG-based variables, with an expectation of a steeper rate of decline in the median frequency and a steeper rate of increase in amplitude measures in subsequent bouts. To test these hypotheses, 24 participants performed four bouts of an isometric (15% MVC) elbow flexion exertion. Each exertion lasted for four minutes and then a 15-minute break was provided between bouts. Surface electromyography was used to capture the activity of the biceps brachii at twenty-second intervals during the exertions. The median frequency and average rectified value were calculated, as were the slopes of these variables within each of the four-minute bouts. Contrary to the original hypotheses, the results showed that there were no statistically significant differences in the slopes of these EMG-based measures across bouts. One direction for future work is to explore different combinations of work-rest durations to refine this response while another may be to explore alternate EMG-based measures of muscular fatigue that may be more sensitive to this cumulative effect.

Effect of surgical radiation personal protective equipment on EMG-based measures of back and shoulder muscle fatigue: A laboratory study of novices.

Interventional radiologists are at increased risk for musculoskeletal discomfort/disorders and this has been linked to the use of radiation personal protective equipment (rPPE). This study examined the effects of rPPE on the development of fatigue of the erector spinae and trapezius muscles. Surface electromyography (EMG) was used to capture muscle activity, and both time domain (average rectified value) and frequency domain (median frequency) measures were considered in the assessment of localized muscle fatigue. Sixteen participants performed a simulated surgical procedure requiring intermittent 30° flexed static trunk posture with and without rPPE on separate days. The results showed that the rPPE condition demonstrated significantly greater (p < 0.05) downward shift in median frequency in the left lumbar erector spinae and left lower thoracic erector spinae consistent with task-induced localized muscle fatigue. Ergonomic intervention strategies are discussed.