Electromyographical Assessments of Recommended Neck and Trunk Positions for Dental Hygienists

Abstract

Purpose: Dental professionals are recommended to limit neck and trunk flexion to within 20° of a neutral (0°) body posture, however empirical support for the recommendations is lacking. The purpose of this study was to determine whether there are differences in muscle workload between a range of neck and trunk postures in a population of dental hygiene students. 
Methods: Fifteen first semester senior dental hygiene students with no history of neck and trunk injury volunteered to participate. Surface electromyography was used to record muscle activity from two neck extensors muscles, cervical erector spinae (CES) and upper trapezius (UT), and two trunk extensor muscles, thoracic erector spinae (TES) and iliocostalis lumboruni (IL). Participants performed ten conditions, including five neck flexion angles (0°, 10°, 20°, 30°, 40°) and five trunk flexion angles (0°,10°, 20°, 30°, 40°). For each trial, posture was checked with a goniometer and maintained for 20s. Muscle activity for each muscle was normalized to the individual’s maximum voluntary isometric contraction (MVIC). 
Results: Activity of the CES was significantly lower in the neutral position than all flexed neck positions. Activation of the UT increased with neck flexion but required 30° of flexion to differ significantly from the neutral position. Activity of the TES required 20° of trunk flexion to differ significantly from neutral and IL activity in the neutral position was significantly lower than all other trunk flexion conditions. 
Conclusion: Even small amounts of neck or trunk flexion (10°), within the recommended range (≤ 20°), can significantly increase the workload for some muscles in an oral health care provider.