Original ResearchThe Effects of Forward Head Posture on Neck Extensor Muscle Thickness: An Ultrasonographic Study
Introduction
One of the predisposing factors that cause occupational neck pain is irregular head and neck posture.1 Forward head posture (FHP) is one of the most common deviations from normal cervical posture2 and may lead to an increase in gravitational load and mechanical stress to cervical facet joints, altered neck extensor muscles activity, and length of cervical muscles.3, 4, 5, 6 Forward head posture is defined as leaning the head and the upper cervical spine anterior to the plumb line that passes the lateral malleolus in sagittal view.7 It is expected that FHP should be typically accompanied by shortening of neck extensor muscles and lengthening of neck ventral muscles.4 This length alteration could secondarily decrease neck muscles’ tension during daily or work-related activities. Each muscle induces the largest tension in only an optimal resting length.8 If a muscle passes its own optimal length by getting either lengthened or shortened, the tension produced by the muscle can be reduced. As such, it is expected that neck extensor muscles produce altered tension in individuals with FHP compared with individuals with normal head posture (NHP). Forward head posture is recognized as a risk factor for neck pain; therefore, studying neck muscle function and strength in individuals with FHP may reduce the incidence of neck pain.
Ultrasonographic studies on neck muscles have revealed that there is a correlation between thickness and strength of neck muscles.9, 10, 11, 12, 13, 14, 15 In other words, reduced muscle thickness probably implies muscle weakness. Although such morphologic and physiologic changes have been reported in patients with neck pain,10, 14, 16, 17, 18 there are limited studies on neck muscles in FHP. Evidence in the literature supports that poor postural orientation could predispose people to the risk of neck pain.5, 6 One of the most common postural deviations associated with suboccipital trigger points, headache, and neck pain is FHP.19 This signals the need for a study to investigate neck extensor muscles and their strength in individuals with FHP compared with individuals with NHP. Thus, the present study was carried out to compare the thickness and strength of neck extensor muscles in individuals with FHP compared with individuals with NHP. The study also examined the possible relationship between the strength of neck extensor muscles and the degree of FHP. As such, the following hypotheses were formulated: (1) Neck extensor muscles could produce less tension during maximum voluntary isometric contraction (MVIC) in individuals with FHP compared with individuals with NHP; (2) Neck extensor muscles have less thickness in individuals with FHP compared with individuals with NHP; (3) Neck extensor muscles have altered thickness changes during an isometric neck extension task in individuals with FHP compared with individuals with NHP. Moreover, it was hypothesized that there is a direct relationship between the amount of forward head inclination and neck extensor muscle strength.
Section snippets
Participants
Twenty college students with FHP (11 females, 9 males; mean age 21.85 ± 2.87 years) and 20 students with NHP (11 females, 9 males; mean age 21.30 ± 2.36 years) participated in this case-control study. The experimental setup is described in Figure 1. The sample size was estimated based on the following formula assuming ∝= 0.05 and β = 0.2. Based on the pilot study, the mean difference and standard deviation for the muscle thickness changes were expected to be 0.2 and 0.2, respectively.
Participants’ Demographic Data
The Shapiro-Wilk test revealed normal distribution of all data. Therefore, parametric statistical tests were carried out to analyze the data. Participant demographic data, including age, weight, height, and body mass index, are presented in Table 1.
Reliability Study
The evaluated ICC and SEM varied from 0.82 to 0.94 and 0.11 to 0.69 for muscle thickness measurements. The ICC and SEM for neck extensor muscle strength were 0.94 and 0.19, respectively.
Muscle Strength
Participants with FHP showed statistically lower neck extensor
Neck Extensor Muscle Strength
The results of the present study indicate that participants with FHP demonstrated a significant reduction in neck extensor MVIC compared with those with NHP. Given that the length tension relationship of neck extensor muscles changes in FHP, it could produce a lower amount of extensor force compared with NHP. This finding is in line with the findings of a study by Lee et al in which less electromyographic activity of some neck extensor muscles was reported in individuals with FHP compared with
Conclusions
The findings of this study indicate that FHP weakens the neck extensor muscles. Within these muscles, semispinalis capitis has less participation in an isometric neck extension task in FHP compared with NHP. Moreover, the strength of the neck extensor muscles is associated with the severity of FHP. However, no morphometric changes in terms of thickness were observed in any of the neck extensor muscles in participants with FHP at the state of rest.
Funding Sources and Conflicts of Interest
No funding sources or conflicts of interest were reported for this study.
Contributorship Information
Concept development (provided idea for the research): L.R., N.K.
Design (planned the methods to generate the results): L.R., N.K.
Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): L.R., N.K., S.J.
Data collection/processing (responsible for experiments, patient management, organization, or reporting data): F.G., R.B.
Analysis/interpretation (responsible for statistical analysis, evaluation, and presentation of the results): L.R., F.G., N.K.
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