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Kawasaki Journal of Medical Welfare
 Vol.27 No.2
 February 2022
Published by
The Kawasaki Medical Welfare Society
288 Matsushima, Kurashiki, 701-0193, Japan


Title page

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ISHIDA, Hiroshi

SUEHIRO, Tadanobu

15
Kawasaki Journal of Medical Welfare Vol. 28,  No. 1,  2022 15-20
＊1 Department of Physical Therapist, Faculty of Rehabilitation
    Kawasaki University of Medical Welfare, 288 Matsushima, Kurashiki, 701-0193, Japan
    E-Mail: ishida@mw.kawasaki-m.ac.jp
＊2 Department of Rehabilitation, Faculty of Health Science and Technology
    Kawasaki University of Medical Welfare
Original Paper
Associations between Forward Head Posture and 
Cervical Extensor Muscle Thickness in 
Asymptomatic Subjects
Hiroshi ISHIDA＊1 and Tadanobu SUEHIRO＊2
(Accepted May 16, 2022)
Key words: head, neck, posture, muscle thickness, ultrasound imaging
Abstract
　This study aimed to clarify the association between forward head posture and cervical extensor 
muscle thickness in asymptomatic subjects; hence, 35 asymptomatic men were recruited for the 
study. The forward head posture was assessed by measuring the neck-to-horizontal, head-to-
horizontal, and neck-to-head angles using a right sagittal view image. The thickness of the right 
upper trapezius, splenius capitis, semispinalis capitis, and deep cervical extensor (semispinalis 
cervicis, multifidus) muscles were measured using ultrasonography. The relationships between 
the three angles and the cervical extensor muscle thickness were evaluated using Spearman’s 
correlation coefficient. A significant negative correlation was observed between the upper trapezius 
muscle thickness and neck-to-head angle. An increase in the upper trapezius muscle thickness was 
observed with a decrease in the neck-to-head angle. The results indicated that inhibition of the 
upper trapezius muscle activity should be considered to correct severe head protrusion with neck 
extension during sitting.
1. Introduction
　The most prevalent risk factor for neck pain is sustained awkward posture1). The forward head posture 
is not recommended during prolonged sitting conditions, especially in front of computers2). In a typical case 
of forward head posture, anterior translation of the head occurs because of lower cervical flexion with an 
increase in upper cervical extension3). Neck and head postures are assessed by measuring the neck-to-
horizontal and head-to-horizontal angles2) (Figure 1). A meta-analysis showed that adults with neck pain 
had a lower neck-to-horizontal angle than that in asymptomatic adults, although, in adolescents and adults 
aged above 50-years, there was no difference in the neck-to-horizontal angle among asymptomatic persons 
and those with neck pain4). In a systematic review, three studies that included adolescents, adults, including 
older adults, and participants with a broad, unmatched age range, respectively, showed no between-group 
differences; the head-to-horizontal angle in the neck pain group was higher than that in the asymptomatic 
group in the study that included only adults4). Not all cases of forward head posture require corrective 
16 Hiroshi Ishida and Tadanobu Suehiro
interventions; however, some individuals with forward head posture experiencing moderate neck pain (non-
specific neck pain or pain resulting from cervical spondylotic radiculopathy) require therapeutic exercises 
(stretching, strengthening, and stability of the neck, thoracic, and shoulder muscles) for correcting the neck-
to-horizontal angle5,6). 
　The abovementioned therapeutic exercises could effectively modify the neck-to-horizontal angle, and 
these exercises might improve neck pain but do not correct the head-to-horizontal angle5,6). All studies 
included in the abovementioned systematic review5) reported strengthening of deep cervical flexors. 
Another study reported that the neck-to-horizontal angle improved after deep cervical extensor training6). 
Morphology studies of cervical muscles in asymptomatic subjects may provide insights into how therapeutic 
exercise affects the forward head posture since neck pain induces muscle volume changes and activates 
cervical muscles7). Ishida et al.8) showed a correlation between the neck-to-horizontal angle and deep cervical 
flexor muscle thickness in asymptomatic adult men. Bokaee et al.9) reported a higher sternocleidomastoid 
muscle thickness in subjects with a decreased neck-to-horizontal angle than that of the control subjects, but 
no increase in thickness of deep cervical flexor muscles was observed in asymptomatic adult women. These 
results support the concept of craniocervical flexor training with an emphasis on the coordinated action of 
the deep and superficial cervical flexor muscles7). Cervical extensor muscles are as important as the flexor 
muscles for controlling the forward head posture7). However, Goodarzi et al.10,11) reported that the thicknesses 
of the cervical extensor muscles (upper trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, 
and multifidus) of the subjects with decreased neck-to-horizontal angles were comparable with that of the 
control subjects. These muscle morphology studies used the neck-to-horizontal angle and not the head-to-
horizontal angle to estimate forward head posture. Therefore, little is known about the relationship between 
the head-to-horizontal angle and cervical extensor muscle thickness. Moreover, to indicate the severity 
of head protrusion with neck extension2), the relative neck-to-head angle (the difference between neck-to-
horizontal and head-to-horizontal angles) should be used for assessing the forward head posture (Figure 1). 
Therefore, in this study, we aimed to clarify the association between forward head posture and cervical 
extensor muscle thickness in asymptomatic subjects. 
Figure 1　Assessment of absolute neck and head angles with forward head posture
The absolute neck and head angles were assessed by measuring the neck-to-horizontal angle between the C7 
spinous process (A), tragus of the ear (B), and horizontal line and the head-to-horizontal angle between the tragus of 
the ear, lateral canthus of the eye (C), and horizontal line, respectively. The relative head angle (neck-to-head) was 
defined as the difference between the neck-to-horizontal and head-to-horizontal angles.
17Forward Head Posture and Muscle Thickness
2. Methods
2.1 Participants
　This study included 35 asymptomatic men. Their age, height, and weight (mean ± standard deviation) 
were 20.5 ± 0.5 years, 172.3 ± 5.2 cm, and 63.3 ± 7.7 kg, respectively. The exclusion criteria were as 
follows: the presence of neck and shoulder pain, presence of radicular pain, history of cervical surgery, 
history of neuromuscular disease, history of neck and shoulder pain in the previous year, or history of any 
specific neck-muscle training in the previous year. 
2.2 Procedure
2.2.1 Forward head posture
　Forward head posture was assessed in a relaxed sitting posture using a digital video camera (FDR-AXP35, 
Sony Co. Ltd., Tokyo, Japan) positioned on a tripod placed 0.8 m away from the participant12). The camera 
lens was at a height that corresponded to the C7 spinous process of the participant12). The assessor imaged 
the right sagittal view with a vertical reference line in the background of the image. The neck-to-horizontal 
angle and the head-to-horizontal angle were measured using ImageJ (US National Institutes of Health, 
Maryland, USA). The neck-to-head angle was calculated as the difference between the neck-to-horizontal 
angle and the head-to-horizontal angle ( °). In recent studies, ImageJ was used frequently to assess head 
and neck posture13,14), and high intra-rater and inter-rater reliabilities were confirmed in the measurement of 
angles during movement15).
2.2.2 Cervical extensor muscle thickness
　B-mode ultrasound imaging of the right cervical extensor muscles was performed for all the subjects 
(Hitachi Noblus, Hitachi Medical Corporation, Tokyo, Japan) with a 7-3 MHz linear probe (L34). The subjects 
were asked to lie down in the prone position on a table with arms flanked on both sides of the body. A 
comfortable position was fixed for the neck and head angle measurements by resting the face in the 
facial opening. The examiner identified the C7 spinous process by palpation. The transducer was placed 
longitudinally and moved laterally to identify the C6-C7 facet joint. From this position, the transducer was 
moved superiorly to identify the C5-C6 facet joint, and the examiner rotated the transducer transversely 
and moved it to identify the lamina at the C5 level (Figure 2). The cervical extensor muscle images were 
obtained twice. The caliper was positioned at 90° relative to the lamina. The measurement was performed 
where the examiner considered the muscular unit to be the thickest16). Inter-rater reliability was found to 
be good for the semispinalis capitis and moderate to poor for deep cervical extensors16). Intra-rater reliability 
was good for the semispinalis capitis and moderate for deep cervical extensors16). The average values of the 
two trials were used for the analysis (mm).
2.3 Statistical analysis
　SPSS Statistics 23.0 (IBM Japan Inc., Tokyo, Japan) was used for the statistical analysis. The relationship 
between the three angles and the cervical extensor muscle thickness was assessed using Spearman’s 
correlation coefficient. The significance level was set at p < 0.05.
3. Results
　The obtained values are listed in Table 1. The correlation coefficients between the three angles and 
cervical extensor muscle thickness are listed in Table 2. A significant negative correlation was observed 
between the upper trapezius muscle thickness and the neck-to-head angle. 
4. Discussion
　In this study, the association between forward head posture and cervical extensor muscle thickness 
18 Hiroshi Ishida and Tadanobu Suehiro
was examined in asymptomatic participants. No significant correlation was observed between the neck-to-
horizontal angle and the cervical extensor muscle thickness. These results are consistent with the findings 
reported by Goodarzi et al.10,11), who measured the neck-to-horizontal angle and cervical extensor muscle 
thickness in asymptomatic subjects. This is the first study to investigate the correlation between the head-
Figure 2　Ultrasonographic measurements of the right cervical extensor muscles
(A) upper trapezius, (B) splenius capitis, (C) semispinalis capitis, and (D) deep cervical extensors (semispinalis 
cervicis, multifidus)
Table 1　Median (first-third quartile) values of obtained data 
Neck-to-horizontal angle (°) 50.0 (45.6-53.4)
Head-to-horizontal angle (°) 16.7 (12.4-20.6)
Neck-to-head angle (°) 34.0 (25.6-39.4)
Cervical extensor thickness
　Upper trapezius (mm) 2.9 (2.4-3.6)
　Splenius capitis (mm) 3.6 (3.0-4.1)
　Semispinalis capitis (mm) 3.8 (3.0-4.5)
　Deep cervical extensors (mm) 16.2 (14.8-17.8)
Table 2　Spearman correlation coefficients of the three angles and cervical extensor muscle thickness 
Neck-to-horizontal Head-to-horizontal Neck-to-head
r p r p r p
Upper trapezius -0.17 0.34 0.27 0.12 -0.35 0.04
Splenius capitis -0.09 0.63 0.14 0.41 -0.23 0.19
Semispinalis capitis -0.08 0.67 0.03 0.85 -0.04 0.83
Deep cervical extensors 0.17 0.33 -0.10 0.57 0.11 0.54
19Forward Head Posture and Muscle Thickness
to-horizontal angle and cervical extensor muscle thickness and to show no significant correlation between 
these factors. However, a significantly negative correlation between the neck-to-head angle and upper 
trapezius muscle thickness was confirmed. The results indicated that inhibition of upper trapezius muscle 
activity should be considered to correct severe head protrusion with neck extension while sitting.
　An increase in the upper trapezius muscle thickness with a decrease in neck-to-head angle was observed 
in the participants. Regarding gravitational movements, the movement demand varies with the neck and 
head angles, and these movements increase with increasing degrees of flexion17). Activation of cervical 
extensor muscles increases with a decrease in neck-to-horizontal angle and/or the head-to-horizontal angle. 
However, in the present study, there was no significant correlation between the neck-to-horizontal and 
head-to-horizontal angles and cervical extensor muscle thickness. There might have been an imbalance 
of neck muscles in asymptomatic participants with increased upper cervical extension. Muscle imbalance 
occurs because hypertrophy or over-recruitment of one group of muscles might be associated with a 
corresponding decrease in size or recruitment of opposing muscles, one of which is the upper crossed 
syndrome18). Alterations in muscle activation include overactivity of suboccipitals, upper trapezius, levator 
scapula, and pectoral muscles, and underactivity of deep cervical flexors, rhomboid, and lower trapezius17). 
In the present study, an increased upper cervical extension angle indicated dysfunction of deep cervical 
flexor muscles, which might induce heightened antagonist muscle activity. Therefore, to correct upper 
cervical hyperextension, stretching exercises of the upper trapezius muscle and strengthening exercises of 
deep cervical muscles are recommended.
　This study has some limitations. First, only asymptomatic adult male participants were recruited. No 
influences of neck pain, sex, and age were detected. Second, muscle activation was not measured in this 
study. Third, we only measured parameters related to cervical extensor muscles at the C5 level. Upper 
cervical muscle activation should be measured to evaluate occipital muscles. Additionally, regarding upper 
crossed syndrome, evaluation of cervical extensors, cervical flexors, and upper trunk muscle thickness 
should be performed. Fourth, to eliminate bias, it is desirable that different examiners record ultrasound 
images, measure muscle thickness, and analyze posture, independently. Finally, the cross-sectional design 
could not detect the cause-effect relationships. Therefore, a longitudinal study is required.　
Ethical considerations
　The Ethics Committee of the Kawasaki University of Medical Welfare approved the protocol (20-004). 
Written informed consent was obtained from each subject prior to participation. There is no conflict of 
interest.
Acknowledgements
　A subset of our findings was presented at the 26th congress of the Japanese Physical Therapy 
Fundamentals.
References
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systematic review. Musculoskeletal Science and Practice, 33, 77-83, 2018.
2. Kang JH, Park RY, Lee SJ, Kim JY, Yoon SR and Jung KI : The effect of the forward head posture on 
postural balance in long time computer based worker. Annals of Rehabilitation Medicine, 6, 98-104, 2012.
3. Neumann DA : Kinesiology of the musculoskeletal system: Foundations for rehabilitation. 2nd ed, 
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4. Mahmoud NF, Hassan KA, Abdelmajeed SF, Moustafa IM and Silva AG : The relationship between 
forward head posture and neck pain: A systematic review and meta-analysis. Current Reviews in 
Musculoskeletal Medicine, 12, 562-577, 2019.
5. Sheikhhoseini R, Shahrbanian S, Sayyadi P and O’Sullivan K : Effectiveness of therapeutic exercise on 
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forward head posture: A systematic review and meta-analysis. Journal of Manipulative and Physiological 
Therapeutics, 41, 530-539, 2018.
6. Suvarnnato T, Puntumetakul R, Uthaikhup S and Boucaut R : Effect of specific deep cervical muscle 
exercises on functional disability, pain intensity, craniovertebral angle, and neck-muscle strength in 
chronic mechanical neck pain: A randomized controlled trial. Journal of Pain Research, 12, 915-925, 2019.
7. O’Leary S, Falla D, Elliott JM and Jull G : Muscle dysfunction in cervical spine pain: implications for 
assessment and management. The Journal of Orthopaedic and Sports Physical Therapy, 39, 324-333, 2009.
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Therapeutics, 41, 34-41, 2018.
12. Falla D, Jull G, Russell T, Vicenzino B and Hodges P : Effect of neck exercise on sitting posture in 
patients with chronic neck pain. Physical Therapy, 87, 408-417, 2007.
13. Hida M, Wada C, Imai R, Kitagawa K, Okamatsu S, Ohnishi T and Kawashima S : Spinal postural 
alignment measurements using markerless digital photography. Journal of Orthopaedic Surgery, 28, 
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Associations between Forward Head Posture and Cervical Extensor Muscle Thickness in Asymptomatic Subjects

川崎医療福祉大学博士（リハビリテーション学）令和3年度doctoral thesi

永田, 裕恒

ナガタ, ヤスユキ

重症心身障害児者に対する環境因子としての座位保持装置及び移乗 補助具についての研究

古賀, 雄二

石田, 実知子

西田, 洋子

若井, 和子

Ａ大学看護系学科における新入生と卒業生の社会人基礎力の比較

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