Postural alignment in static and dynamic conditions in adults with and without forward head posture

Abstract

Objectives

This study aims to compare the spinal alignment in static and dynamic postures between adults with and without forward head posture (FHP).

Patients and methods

Between June 2024 and December 2024 a total of 28 participants were included in the study and divided into two groups: the FHP group (7 males, 7 females; mean age: 24.29 years; range, 20 to 31 years) and the without FHP group (8 males, 6 females; mean age: 23.36; range, 21 to 31 years). To assess FHP, the craniovertebral angle was measured using the MB-ruler software. Spinal alignment was evaluated with a three-dimensional spinal structural analysis system, which provided measures of thoracic kyphotic angle, lumbar lordotic angle, sagittal imbalance, and coronal imbalance in standing posture and during walking at speeds of 3, 5, and 6 km/h.

Results

In static posture, participants with FHP demonstrated significantly greater thoracic kyphotic angle and coronal imbalance compared to those without FHP. During dynamic conditions, the sagittal imbalance at a walking speed of 3 km/h was significantly higher in the FHP group.

Conclusion

The characteristics of spinal alignment in both standing and walking should be taken into account when evaluating and managing adults with FHP.

Postural alignment is traditionally defined in the sagittal plane by a vertical line passing sequentially through the external auditory meatus, acromion, greater trochanter, just anterior to the midline of the knee joint, and anterior to the lateral malleolus. This alignment represents an ideal posture that maintain balance and provides optimal joint stability. Deviation of these anatomical landmarks from the vertical line is generally classified as a deviation from normal postural alignment.^[1] In addition, the normal spinal structure in the sagittal plane is characterized by a sequence of physiological curvatures: a cervical lordosis extending from the C2 odontoid process to T2, a thoracic kyphosis extending from T2 to T12, and a lumbar lordosis from T12 to the lumbosacral angle.^[2] Spinal curvatures outside the physiological range are a major indicator of impaired postural alignment.

Forward head posture (FHP) is one of the most common posture abnormalities in the sagittal plane. FHP is characterized by the anterior displacement of the external auditory meatus relative to the vertical line passing through key anatomical landmarks from the ear to the ankle, resulting in a forward head position.^{[3, 4]} This positional change can increase the load on the joints and affect functional movement. Prolonged FHP can lead to structural changes in the muscles surrounding the head and cervical spine, as well as alterations in spinal alignment.

Forward head posture causes imbalances in the length of cervical muscle-tendon units, including lengthening of the upper cervical flexors and lower cervical extensors, and shortening of the upper cervical extensors and lower cervical flexors.^{[5, 6]} These changes are reflected in a decreased craniovertebral angle (CVA) and an increased cranial rotation angle.^[7]

Previous studies have shown that CVA is negatively correlated with thoracic kyphosis and has a weak correlation with lumbar lordosis. In addition, FHP has been associated with altered balance in the sagittal plane.^{[8, 9, 10]} A study investigating the correlation between the degree of FHP and sagittal imbalance demonstrated that the more severe the FHP, the farther the vertical line drawn from the seventh cervical vertebra (C7) was from the S1, which resulted in greater sagittal imbalance.^[11] These findings suggest that FHP may lead to disproportionate alignment between the upper and lower vertebral segments, thereby compromising overall sagittal plane balance. Although many of these studies have addressed the effects of FHP on spinal alignment in a standing static posture, no studies have reported on the effects of FHP on spinal alignment in dynamic conditions such as gait.

Saad et al.^[12] reported that a decreased CVA leads to postural imbalance, which negatively affects motor performance during walking and jumping. Therefore, they emphasized the importance of considering head posture during gait. In individuals with normal postural alignment, head angle modulation plays a key role in maintaining postural stability during gait.^{[13, 14]} However, the gait-related characteristics of individuals with FHP, in which the head is displaced anteriorly, remain poorly understood. Recently, as the number of FHP adults is increasing and the age of onset is decreasing due to the increase in the use of electronic devices, social interest is increasing.

Although numerous studies have examined FHP, to date, no research has investigated spinal alignment during dynamic activities such as walking in adults with FHP. Therefore, this study aimed to compare spinal alignment in static and dynamic postures between participants with and without FHP. We hypothesized that adults with FHP would exhibit significant differences in sagittal-plane spinal alignment, compared with those without FHP, in both static and dynamic conditions.

PATIENTS AND METHODS

This cross-sectional study was conducted at the Department of Physical Therapy, Catholic University of Pusan between June 2024 and December 2024. A total of 28 valid participants were included in the study and divided into two groups: the FHP group (7 males, 7 females; mean age: 24.29 years; range, 20 to 31 years) and the without FHP group (8 males, 6 females; mean age: 23.36; range, 21 to 31 years). The inclusion criteria were established as follows: (1) participants with a body mass index below 35 kg/m²; (2) a CVA of less than 49° for the FHP group. The exclusion criteria were as follows: (1) a history of cervical surgery or trauma;^[12] (2) musculoskeletal pain treated within the past six months;^[15] (3) neurological disorders involving the cervical spine;^[16] (4) diagnosed scoliosis or kyphosis;^[17] and (5) any systemic condition that could affect treadmill walking.^[16] All participants provided written informed consent after receiving an explanation of the study. The study protocol was approved by the Institutional Review Board of the Catholic University of Pusan Ethics Committee (Date: 12.12.2024, No. 24029). The study was conducted in accordance with the principles of the Declaration of Helsinki.

Sample size calculation

The sample size was calculated using G*Power version 3.1.9.7 (Universität Kiel, Germany) before participant recruitment. Based on a previous study comparing postural balance in adults with and without FHP,^[18] the effect size was set at 1.22. With a statistical power of 0.80 and a significance level of 0.05, at least 12 participants were required for each group (total n=24).^[18] Considering a potential dropout rate of approximately 20%, we recruited 14 participants per group, resulting in a total of 28 participants.

Assessment of forward head posture

The presence of FHP was assessed by measuring the CVA, a widely used and reliable indicator for identifying this postural deviation.^[19] To standardize posture, participants were seated on a chair positioned at a fixed distance from a tripod-mounted smartphone camera (IPhone 12 Pro, Apple Inc.) placed on a level surface. After performing 2-3 cycles of cervical flexion and extension, participants were instructed to gaze at a fixed target on the wall to achieve neutral head position.^{[20, 21]} Reflective markers were attached to the tragus and the spinous process of C7 to serve as anatomical landmarks. The CVA was then calculated using MB-Ruler software (MBruler 5.4, Markus Bader Software Solutions) by measuring the angle between a line connecting the two markers and a horizontal line passing through C7. A smaller CVA indicates a greater degree of FHP.^{[22, 23]}

Three-dimensional spinal analysis

A three-dimensional (3D) spinal analysis device (DiERS formetric III 4D motion, DIERS International GmbH) based on raster stereography and video raster stereography was used to assess spinal alignment in static (upright standing) and dynamic (walking) postures, as shown in Figure 1. Raster stereography is a non-invasive method that rapidly evaluates spinal morphology through surface topography without radiation exposure.^[24] Video raster stereography records movements in real time and is used to measure changes in the body surface during dynamic posture and gait analysis. This measurement device was developed by the Institute for Experimental Biomechanics at the University of Münster, Germany, and has demonstrated high reliability and accuracy compared with radiographic methods.^{[25, 26]} In addition, this device enables objective assessment of spinal structure without the risk of radiation exposure.^[27] Due to its high reproducibility and minimal inter-rater variability, the system is particularly well-suited for longitudinal spinal analysis and follow-up.^[27] This device projects a halogen light source parallel to the back surface of the participant while walking on a treadmill and converts the triangulated image into a three-dimensional motion representation to provide detailed and objective quantitative data.^[28] In addition to the major spinal parameters analyzed in this study, the system can measure various indicators of spinal and pelvic characteristics, such as trunk length, pelvic obliquity, pelvic torsion, pelvic inclination, pelvic rotation, surface rotation, and apical deviation. Overall, the system quantifies a total of 40 parameters, 36 of which have demonstrated high reliability.^[26]

Figure 1.

DiERS formetric III 4D motion device for spinal alignment assessment.

Measurement protocol

For image acquisition, participants removed their tops and lifted their clothing to the mid-pelvic level so that the posterior superior iliac spines (PSIS) was clearly visible. To ensure accurate measurement, reflective stickers were attached to the spinous process of C7 and both PSIS to establish anatomical markers. To prevent interference with the halogen light source, participants removed metal accessories and tied their hair back so that the C7 landmark was fully exposed. Before the measurement, participants stood barefoot in an anatomical position 2 meters away from the halogen light source, aligning their heels with designated lines next to the treadmill rails and ensuring their backs were not facing the camera. They were instructed to take a few deep breaths and then maintain a neutral posture.

Static measurements were performed using the “Static 4D Average” mode. This mode acquired 12 frames over a 6-sec period, and the average of the recorded data was used as the final value. For dynamic assessment, the “Dynamic DIERS 4D Motion” mode was used, to capture 330-335 frames during a 6-sec recording per measurement. Spinal alignment was compared at three treadmill walking speeds: 3 km/h (slow), 5 km/h (average), and 6 km/h (fast), based on the average walking speed of Korean adults (approximately 4.6–5.1 km/h).^[29] All gait tests were performed in a fixed sequence (3 → 5 → 6 km/h). Participants were instructed to walk for at least 1 minute after each speed change to adapt to the treadmill speed.

Outcome parameters

The following spinal alignment parameters were extracted from the 3D raster stereographic data: kyphotic angle, lordotic angle, sagittal imbalance, and coronal imbalance. The kyphotic angle, representing thoracic curvature in the sagittal plane, was calculated as the maximum angle between the line connecting the cervical-thoracic inflection point and the thoraco-lumbar inflection points. The lordotic angle, reflecting lumbar curvature, was defined similarly using the thoraco-lumbar and lumbosacral inflection points. Sagittal imbalance was defined as the anterior-posterior deviation of the spine and quantified by the absolute angle (°) between the vertical plumb line from the spinous process of the C7 and the body’s gravitational centerline. Coronal imbalance represented lateral deviation in the coronal plane and was measured as the absolute horizontal distance (mm) between the vertical line from C7 and the midpoint between the bilateral PSIS.^{[30, 31]}

Statistical analysis

Statistical analysis was performed using IBM SPSS for Windows version 30.0 software (IBM Corp., Armonk, NY, USA). Descriptive data are presented as mean ± standard deviation (SD). The normality of each variable measured in both groups (with and without FHP) was confirmed using the Kolmogorov-Smirnov test. The homogeneity between the two groups was tested using Levene's test. Independent t-tests were used to compare spinal alignment variables between the two groups. A two-way repeated measures ANOVA was used to examine changes in the spinal alignment variables and the interaction effects according to walking speed within and between the groups. Post-hoc comparisons were performed using the Bonferroni method. A p-value of <0.05 was considered statistically significant.

RESULTS

The demographic characteristics of the participants are presented in Table 1. In the static posture, a significant difference was observed in the kyphotic angle between the two groups (p<0.001), whereas the lordotic angle (p=0.115) and sagittal imbalance (p=0.054) exhibited no significant differences. Coronal imbalance was significantly greater in the with FHP group than in the without FHP group, as shown in Table 2 (p<0.001). In the dynamic condition, there were no significant differences in kyphotic angle between the groups at any walking speed (p=0.150, p=0.074, p=0.286). Two-way repeated measures ANOVA revealed no significant main effects of speed or group, and no interaction effects, as shown in Table 3 (p=0.074, p=0.140, p=0.416). Similarly, the lordotic angle did not differ significantly between groups at any speed (p=0.930, p=0.930, p=0.473), and there were no significant main effects or interactions (p=0.635, p=0.854, p=0.294). Sagittal imbalance was significantly different between groups only at 3 km/h (p=0.032), but not at 5 or 6 km/h (p=0.078, p=0.059), and there were no significant main or interaction effects (p=0.066, p=0.866, p=0.975; Table 3). Coronal imbalance exhibited no significant differences between groups at any speed (p=0.482, p=0.384, p=0.842), and no significant main effects or interaction effects were found (p=0.259, p=0.815, p=0.879; Table 3). Post hoc tests confirmed no significant within-group differences across walking speeds for any variable.

TABLE 1. Demographic characteristics of the participants.

-	With FHP (n=14)			Without FHP (n=14)			-
-	n	%	Mean±SD	n	%	Mean±SD	p
Age (year)	-	-	24.29±3.93	-	-	23.36±4.11	0.546
Sex Male Female	- 7 7	- 50 50	-	- 8 6	- 57.1 42.9	-	0.717
Height (cm)	-	-	169.86±8.86	-	-	169.50±8.36	0.913
Weight (kg)	-	-	70.07±14.61	-	-	63.50±12.42	0.211
BMI (kg/m2)	-	-	24.12±3.41	-	-	22.01±3.57	0.122
CVA (˚)	-	-	45.39±2.51	-	-	53.21±2.67	<0.001*

FHP, forward head posture; SD, standard deviations; BMI, body mass index; CVA, craniovertebral angle; p values from independent t-test.

TABLE 2. Comparison of spinal alignment between the groups in static posture.

-	With FHP (n=14)	Without FHP (n=14)	-	-
-	Mean±SD	Mean±SD	t	p
Kyphotic angle (˚)	54.29±3.38	47.64±3.37	–5.208	<0.001*
Lordotic angle (˚)	33.21±10.80	40.57±12.98	1.630	0.115
Sagittal imbalance (˚)	2.71±1.07	2.00±0.78	–2.016	0.054
Coronal imbalance (mm)	5.93±1.86	2.79±0.97	–5.602	<0.001*

FHP, forward head posture; SD, standard deviations; p-values from independent t-test.

TABLE 3. Comparison of spinal alignment between groups at different walking speeds.

-	-	With FHP (n=14)	Without FHP (n=14)	-	-	-	-	-
-	Gait speed (km/h)	Mean±SD	Mean±SD	t	p	-	F	p
Kyphotic angle (˚)	3	49.14±5.42	44.79±9.55	–1.484	0.150	S	2.825	0.074
	5	48.71±4.75	43.50±9.33	–1.864	0.074	G	2.313	0.140
	6	47.07±5.01	43.34±10.55	–1.098	0.286	S×G	0.871	0.416
Lordotic angle (˚)	3	34.57±10.89	34.93±10.51	0.088	0.930	S	0.288	0.635
	5	35.29±11.36	35.64±9.79	0.089	0.930	G	0.034	0.854
	6	36.07±12.31	33.29±7.19	–0.731	0.473	S×G	1.255	0.294
Sagittal imbalance (˚)	3	5.64±1.60	4.36±1.39	–2.269	0.032*	S	2.899	0.066
	5	6.21±2.12	4.79±2.01	–1.832	0.078	G	0.029	0.866
	6	6.64±1.78	5.21±2.04	–1.971	0.059	S×G	0.023	0.975
Coronal imbalance (mm)	3	5.71±3.65	6.64±3.23	0.714	0.482	S	1.389	0.259
	5	7.21±5.82	9.50±7.70	0.886	0.384	G	0.194	0.815
	6	8.07±6.27	8.57±6.87	0.201	0.842	S×G	0.024	0.879

FHP, forward head posture; SD, standard deviations; S, speed; G, group; Angles within a column with different superscripts are significantly different; values from independent t-test.

DISCUSSION

In this study, we compared static and dynamic spinal alignment between adults with and without FHP using a 3D spinal structure analysis system. The main findings were as follows. First, in static posture, participants with FHP exhibited significantly greater thoracic kyphotic angle and coronal imbalance compared with those without FHP. Second, during treadmill walking, thoracic and lumbar angles did not differ significantly between groups at any speed. Third, sagittal imbalance during gait was significantly greater in the with FHP group only at the slow walking speed of 3 km/h. These findings indicate that FHP is associated with altered spinal alignment in standing and subtle instability during slow walking, whereas several static differences may be compensated for under dynamic conditions.

In static posture, the thoracic kyphotic angle was significantly greater in the with FHP group than in the without FHP group. This result aligns with previous studies reporting a negative correlation between the CVA and thoracic kyphotic angle.^{[8, 9]} The kyphotic curvature of the spine helps maintain the center of gravity and absorb vertical loading. In FHP, the forward translation of the head alters spinal alignment, potentially increasing thoracic kyphosis as a compensatory mechanism to realign the body’s center of gravity. Moreover, excessive muscle tension in the cervical and thoracic regions caused by FHP can exacerbate thoracic kyphosis. This increase may represent compensatory musculoskeletal adaptations to FHP.

In contrast, the lordotic angles did not show significant differences between groups in static posture, between the degree of FHP and lumbar lordosis.^{[10, 11]} This may be due to the fact that FHP primarily affects the upper spine, with the lumbar region remaining structurally unaffected. Indeed, lumbar lordosis appears to be more sensitive to intrinsic structural features such as pelvic tilt, vertebral height, intervertebral disc thickness, and the strength and endurance of the surrounding musculature-rather than cephalic positioning.^[32] As participants in the present study were young adults in their 20s and 30s, it is unlikely that FHP had a significant effect on their pelvic or lumbar structure. However, Elabd and Elabd^[33] reported a moderate correlation between FHP and increased lumbar lordosis, which may be attributable to the older age of their participants (40-55 years). The duration of postural abnormality and the presence of low back pain may have influenced their results. In the present study, the average lumbar lordotic angle in the with FHP group was 37.25±11.07°, which falls within the normal range of 32-45° for this device.^{[30, 31]} Future studies should consider stratifying participants by age, severity of FHP based on CVA, and presence of pain or tenderness to further investigate its effect on lumbar curvature.

In terms of spinal imbalance, FHP participants exhibited no significant difference in sagittal imbalance but a significant difference in coronal imbalance. The 3D spinal analysis system defines sagittal imbalance as the anterior-posterior tilt of the spine in the sagittal plane and coronal imbalance as the lateral tilt in the frontal plane. These findings partly contrast with earlier reports suggesting that both sagittal and coronal imbalances affect weight distribution and trunk balance.^{[34, 35]} The finding that only coronal imbalance differed significantly may indicate that FHP-induced postural shifts exert a more pronounced effect on the coronal balance. This is consistent with the findings of Lee,^[36] who reported that FHP affects static balance, and Youssef et al.,^[37] who reported that a decrease in CVA is associated with coronal balance disorders. These results suggest that FHP-related spinal misalignment primarily impairs the body's coronal plane stability during static posture.

Although the importance of posture for normal gait is well established, few studies have examined the characteristics of spinal alignment during gait in individuals with FHP. The 3D spinal analysis system can evaluate spinal alignment during treadmill walking at speeds up to 6 km/h.^{[16, 38]} Michalik et al.^[16] investigated thoracic kyphosis, lumbar lordosis, and sagittal imbalance at multiple walking speeds in healthy adults.

During walking, both groups showed a tendency for thoracic kyphotic angle to decrease as walking speed increased. These observations are similar to previous studies using the same analysis protocols in healthy adults.^[16] However, there were no significant between-group differences in thoracic kyphotic angle at any walking speed, which contrasts with the static posture findings. Shin et al.^[39] reported that as walking speed increases, the joint moments of the knees and hips increase, leading to increased mechanical loading on the lower limbs increases due to higher joint moments at the knee and hip. This increased lower limb load may have offset the effects of FHP on spinal alignment during gait. Similarly, Kim^[40] and colleagues reported increased joint moments with larger step length at higher speeds. These biomechanical adaptations may explain the lack of group differences in thoracic curvature during walking.

While the kyphotic angle decreased with speed, the lordotic angle did not exhibit consistent trends across walking speeds and demonstrated no significant differences between groups, mirroring the static results. This reinforces the idea that the lumbar lordotic angle is less influenced by FHP and may not serve as a reliable indicator of FHP-related postural change.

In particular, sagittal plane imbalance during gait showed a significant difference between the two groups only at a speed of 3 km/h, and the imbalance was greater in the FHP group. This aligns with Rasha et al.,^[11] who reported a positive correlation between FHP severity and sagittal imbalance. Given the increased anterior load and muscular imbalance in FHP,^{[8, 41]} it is plausible that such musculoskeletal alterations contribute to sagittal instability during gait. On the other hand, coronal plane imbalance did not show a significant difference between the two groups at all speeds. These results suggest that while FHP-related coronal imbalance occurs in static posture, dynamic movement may induce compensatory mechanisms.

Our data demonstrate that FHP involves distinct standing alignment shifts and heightened sagittal instability at low walking speeds, emphasizing the clinical importance of dual static and dynamic assessments. These observations suggest the importance of evaluating not only the CVA but also thoracic curvature, coronal balance, and trunk control in addition to CVA. Clinically, exercises that promote thoracic extension, enhance cervicothoracic stability, and restore a neutral head posture using visual feedback can be helpful. Additionally, personalize gait training at slow speeds can help address early imbalance before progressing to faster walking.

The study has several limitations. First, the exclusion of symptomatic patients or the elderly populations may restrict the generalizability of these findings. Second, physical activity levels and occupational habits were not controlled, which may have influenced posture. Third, the small sample size may limit the generalizability of the results. Considering these limitations, future studies requires a well-designed randomized controlled trial using a large sample.

In conclusion, participants with FHP exhibited greater thoracic kyphotic angle and coronal imbalance in static posture, and increased sagittal imbalance during walking. Interestingly, most alignment differences observed in static posture did not persist under dynamic conditions, suggesting the possibility of compensatory adjustments during gait. These results emphasize that both static and dynamic postures should be evaluated during FHP management, with particular attention to dynamic sagittal balance.