Physical Therapy Korea

Lifestyles of contemporary society are often characterized by increased sedentary behaviors, such as prolonged sitting time and insufficient physical activity, as well as irregular sleep patterns. These behaviors concurrently introduce profound health challenges, resulting in degenerative changes in posture, evident across various settings such as educational institutions, workplaces, and residential areas [1,2]. Frequent use of technical equipment is associated with postural deviation, such as computers, smartphones, and tablets, is associated with postural deviation. For instance, forward head posture (FHP), characterized by the forward movement of the head relative to the spine, places significant stress on the neck and upper back muscles, disrupting the biomechanical balance of the body [3]. Furthermore, FHP is a major risk factor for chronic neck pain, highlighting its significant health implications [4].

Biomechanical imbalances induced by FHP frequently require compensatory modifications, including enhancement of thoracic kyphosis and lumbar lordosis. Such adaptations may perturb the normal activation patterns of the spinal muscles [5]. As a result, these compensatory adjustments increase mechanical stress on the vertebrae, which may ultimately lead to various spinal pathologies [6,7]. Notably, the erector spinae muscle group, which is essential for maintaining an upright trunk posture and providing important mechanical leverage for extending the lumbar spine, is severely affected by FHP [1,8]. Empirical studies have consistently linked a weakened erector spinae to lower back pain, emphasizing the need to maintain erector spinae muscle strength and function [9]. This relationship highlights the significance of postural health and its key role in preventing musculoskeletal injuries and improving exercise efficiency.

Given these considerations, the primary objective of this study was to analyze the specific effects of FHP on the erector spinae muscles and, by extension, its systemic implications on overall postural health.

1. Participants

This study included participants residing in Wonju, Gangwon Province, South Korea. According to the G-Power software ver. 3.1 (Kiel University), with a 95% confidence interval, the required sample size was 52. The objective of this study was to probe the biomechanical effects of FHP on musculoskeletal health through a relative analysis of 26 adults diagnosed with FHP and 26 non-FHP groups. Positioned in the same geographic locale, all participants were aged 20–30 years and followed strict criteria to bolster the delicacy and relevance of the findings [3]. FHP, illustrated by the anterior release of the head relative to the chin, is thought to affect the diapason in musculoskeletal diseases. Employing quantifiable pointers, such as the craniovertebral angle (CVA) and the Neck Disability Index (NDI), this dissertation methodically assesses the implicit health ramifications associated with FHP [10]. The eligibility for the FHP group was confined to individuals whose CVA did not exceed 50°.

Comprehensive informed consent was obtained following detailed briefings on the methodology of the study. A prerequisite NDI score ≤ 4 was required to ensure that the participants endured minimum or no neck discomfort originally, excluding those with any history of neck or back surgery [11]. The exclusion criteria comprised individuals diagnosed with psychiatric diseases, habitual musculoskeletal conditions (such as rheumatoid arthritis and osteoarthritis, which might confound the study findings) [12,13], and pregnancy. This trial was approved by the Yonsei University Mirae Campus Institutional Review Board (IRB no. 1041849-202403-BM-061-02).

2. Craniovertebral Angle

CVA was measured by gauging the angle between the spinous process of the seventh cervical vertebra and a horizontal line projected through the tragus, with angles < 50° indicating FHP [14].

In this study, the biomechanical effects of the FHP on musculoskeletal health were systematically assessed using photogrammetry to accurately measure the CVA. Using the advanced imaging capabilities of the iPhone 13 Pro Max primary camera (Apple), the participants were instructed to sequentially adjust their heads from the lowest point achievable to the most comfortable posture while seated in a backless chair. This adjustment sequence was repeated two to three times to ensure the reliability of the collected data.

Throughout this process, the camera was optimally placed 2 m to the side of the participant’s dominant hand, enhancing the precision of the neck and torso angle measurements. The elevation angle of the camera was carefully adjusted to align with the shoulder height of the seated participants. After data acquisition, the images were digitally transferred and extensively analyzed using the Kinovea software (Kinovea) [15].

3. Procedures

For recording, disposable self-adhesive patches with 10 mm conductive Ag/AgCl discs were utilized. Each channel consisted of two recording surfaces spaced 20 mm apart. The ground electrode for each channel comprised an array of three 6 mm dry metal discs situated on the ventral side of the electromyography (EMG) sensor, affixed to the skin with double-sided adhesive tape. The recording electrodes were connected to the ground electrode via a 3-inch shielded lead.

Skin preparation before electrode application was performed with precision, and involved hair removal, dermal abrasion using fine-grit sandpaper, and thorough cleansing with an alcohol swab. This preparation protocol is critical for minimizing signal interference and enhancing electrode conductivity [16]. The electrode placement followed strict criteria, with one set located at the T12 level and the other at the L3 level (Figure 1) of the spine, approximately 2 cm lateral to the spine and directly above the muscle belly. These placements were chosen with strict adherence to the SENIAM project guidelines, a respected source for standardized EMG procedures (http://seniam.org).

Figure 1. Electrode placement for the T12, L3 paraspinal site.

In this study, EMG data and maximum spinal joint range of motion (ROM) assessments were systematically performed. First, the ROM of the trunk extensors was assessed using the Biering-Sørensen test, which is a recognized method for assessing postural stability and muscular endurance [17]. To improve the accuracy of the results, each spinal extension was measured twice and the average of these measurements was calculated.

The collected ROM data were documented in an Excel file 2016 (Microsoft Co.) to facilitate detailed analyses and ensure the integrity of data handling and alignment with the best practices in data management [18]. Following the initial measurements, participants were allowed a 2-minute rest period before proceeding to the next phase of the study, which involved measuring the maximum voluntary isometric contraction (MVIC). This sequence is critical for assessing muscle strength and endurance and provides valuable insights into muscular health and functionality [19].

The MVIC data were collected in line with the established guidelines provided by Noraxon (Noraxon, Inc.). EMG signals were captured using advanced ultra-EMG sensors paired with an ultra-receiver supplied by Noraxon (Noraxon, Inc.). These sensors are distinguished by their high fidelity, with specifications including a sampling rate of 2,000 Hz, an overall gain of 500, a common-mode rejection ratio of > 100 dB, and an input impedance exceeding 100 mΩ [20].

Surface EMG data and maximum lung capacity were measured as follows: hold for 2 seconds, rest for 5 seconds, and repeat these maneuvers 5 times. After completing the initial test, the participants underwent a 2-minute recovery period. Subsequently, an endurance test was performed using the Biering-Sørensen test [17] (Figure 2), which is known for its effectiveness in assessing the isometric endurance of the trunk extensor muscles. The participant laid prone on the test table with the lower body secured at the hips and ankles with sturdy straps. The upper body was extended over the edge of a table on a bench. The participant was asked to raise the upper body to a horizontal position using only the trunk muscles and hold this position for as long as possible. The examiner monitored the endurance duration with a stopwatch until the participant could no longer hold the position, indicating the end of the test. This process was repeated three times with a 2-minute break between sessions. The mean of the medians of three experiments was extracted for statistical analysis.

Figure 2. Biering-Sørensen test.

In conjunction with the evaluation, EMG signals were recorded and analyzed to elucidate the frequency spectrum. Signal processing and recording for the MVIC and Biering-Sørensen endurance tests were conducted using MyoResearch 3.18 software (Noraxon, Inc.) on a laptop computer.

The test was terminated if the participant could not maintain the prescribed position, or experienced discomfort or pain. The principal investigator was present throughout the experimental measurements to manage and minimize any potential risks. If the participant reported fatigue or pain during the measurement, the experiment was stopped immediately. In cases of accidental injury or damage, the participants were immediately transported to the nearest hospital.

4. Data Analysis

To evaluate the characteristics of individuals with normal posture and those with FHP, we performed descriptive statistical analysis. Our aim was to present quantitative information that is easy to understand and interpret. Descriptive statistics were used in this experiment to summarize the endurance times in the non-FHP and FHP groups, reporting the mean, standard deviation, maximum and minimum values. In addition, a Pearson correlation analysis was used to examine the relationship between CVA and spinal extension ROM in the two groups. For the primary EMG analysis, we used independent t-tests to compare the muscle activity and maximum muscle strength between the normal and FHP groups. We chose these tests to compare the means of the two distinct groups and check for significant differences between them. This method suits the analysis of two separate groups of continuous, normally distributed data [21]. All statistical analyses were performed using IBM SPSS ver. 26.0 (IBM Co.). This software supports a broad range of analytical tasks, ranging from manipulating complex data to analyzing detailed datasets.

1. Characteristics of the Study Participants

Twenty-six adults with FHP and 26 non-FHP groups without FHP participated in this study. Among them, 22 were females, and 30 were males. Their average age, weight, and height were 23.40 ± 2.46 years, 68.63 ± 17.69 kg, and 170.94 ± 8.79 cm, respectively. Table 1 presents the characteristics of the participants.

Table 1 . Descriptive statistics for age, weight, and height of the study group.

Variable	FHP	Non-FHP	Total
Age (y)	22.26 ± 2.08	24.53 ± 2.31	23.40 ± 2.46
Weight (kg)	68.65 ± 16.18	68.60 ± 19.41	68.63 ± 17.69
Height (cm)	170.07 ± 8.46	171.80 ± 9.20	170.94 ± 8.79

Values are presented as mean ± standard deviation. FHP, forward head posture..

2. Craniovertebral Angle and Spine Extension Range of Motion

The non-FHP group had higher mean CVA and spine extension ROM compared to the FHP group (Table 2). The FHP group exhibited notably lower CVA and spine extension ROM (Table 3). The significance of the maximum and minimum values is to emphasize that this study also influences extended ROM if there is FHP, rather than only measuring specific muscles.

Table 2 . Descriptive statistics of the CVA and spine extension ROM of the non-FHP study group.

Variable	Mean ± SD	Maximum	Minimum
CVA (°)	51.35 ± 1.15	53.7	50.1
Spine extension ROM (°)	43.50 ± 7.19	60.0	34.0

SD, standard deviation; CVA, craniovertebral angle; ROM, range of motion; FHP, forward head posture..

Table 3 . Descriptive statistics of the CVA and spine extension ROM of the FHP study group.

Variable	Mean ± SD	Maximum	Minimum
CVA (°)	37.09 ± 4.12	45.8	27.6
Spine extension ROM (°)	20.11 ± 7.03	33.0	7.0

SD, standard deviation; CVA, craniovertebral angle; ROM, range of motion; FHP, forward head posture..

3. Endurance Time

The non-FHP group demonstrated significantly longer endurance times than the FHP group (Table 4).

Table 4 . Endurance time in the FHP group and non-FHP group.

Variable	Mean ± SD	Maximum	Minimum
Non-FHP endurance time (s)	92.00 ± 34.66	45.80	52.25
FHP endurance time (s)	31.45 ± 12.40	205.20	9.09

SD, standard deviation; FHP, forward head posture..

The correlation between CVA and spinal extension ROM in the FHP study group was positive and prominent (r = 0.999, p < 0.001) (Figure 3).

Figure 3. Correlation between CVA and spine extension ROM of the FHP study group. CVA, craniovertebral angle; ROM, range of motion; FHP, forward head posture.

The correlation between CVA and spinal extension ROM in the non-FHP study group was positive and prominent (r = 0.997, p < 0.001) (Figure 4).

Figure 4. Correlation between CVA and spine extension ROM of the non-FHP study group. CVA, craniovertebral angle; ROM, range of motion; FHP, forward head posture.

4. Muscle Activity and Endurance

There were significant differences in muscle activity and endurance time between the FHP and non-FHP groups. The activity levels of the thoracic and lumbar erector spinae muscles were significantly higher in the non-FHP group than in the FHP group. Endurance times for these muscles were also significantly longer in the non-FHP group (Table 5).

Table 5 . Maximum voluntary isometric contraction.

Muscle name	Group		p-value	95% CI
	FHP	Non-FHP
Thoracic ES LTuV	131.24 ± 42.75	266.90 ± 56.65	< 0.001*	–163.61 to –107.70
Thoracic ES RTuV	92.69 ± 41.04	205.82 ± 65.25	< 0.001*	–143.49 to –82.76
Lumbar ES LTuV	91.59 ± 29.33	221.07 ± 202.97	0.002	–210.25 to –48.80
Lumbar ES RTuV	86.77 ± 34.72	189.50 ± 60.25	< 0.001*	–130.12 to –75.33

CI, confidence interval; FHP, forward head posture; Thoracic ES LTuV, thoracic erector spinae on the left side; Thoracic ES RTuV, thoracic erector spinae on the right side; Lumbar ES LTuV, lumbar erector spinae on the left side; Lumbar ES RTuV, lumbar erector spinae on the right side. *p < 0.001..

These results showed that CVA, spinal extension ROM, endurance time, and muscle activity were significantly reduced in patients with FHP compared to healthy controls without FHP (Table 6). The strong positive correlation between the CVA and spinal extension ROM in both groups highlights the impact of FHP on these parameters. It has also been demonstrated that the presence or absence of FHP affects the activity level of the erector spinae muscles.

Table 6 . Endurances.

Muscle name	Group		p-value	95% CI
	FHP	Non-FHP
Thoracic ES LTuV (s)	56.68 ± 14.88	129.19 ± 41.61	< 0.001**	55.09 to –89.91
Thoracic ES RTuV (s)	52.48 ± 16.83	144.79 ± 30.41	0.004*	30.85 to 153.76
Lumbar ES LTuV (s)	54.42 ± 19.17	104.90 ± 24.20	< 0.001**	38.31 to 62.63
Lumbar ES RTuV (s)	52.30 ± 17.25	106.29 ± 30.21	< 0.001**	40.28 to 67.69

CI, confidence interval; FHP, forward head posture; Thoracic ES LTuV, thoracic erector spinae on the left side; Thoracic ES RTuV, thoracic erector spinae on the right side; Lumbar ES LTuV, lumbar erector spinae on the left side; Lumbar ES RTuV, lumbar erector spinae on the right side. *p < 0.01, **p < 0.001..

This study examined the biomechanical effects of FHP on erector spinal muscle activity using a comparative analysis of FHP patients and healthy controls. The increased muscle activity observed in patients with FHP is a compensatory mechanism designed to support inconsistent head and neck posture, which is thought to contribute to the increased biomechanical strain. FHP can alleviate biomechanical defects caused by poor posture, thereby maintaining the functional and structural integrity of the musculoskeletal system under increased load. This is consistent with recent findings suggesting that these adaptations may lead to an increased risk of musculoskeletal injury, especially in conditions that require a lot of physical labor [22,23]. Recent literature further supports and extends these findings. FHP can increase the load on the spinal structure and may lead to chronic musculoskeletal diseases [24]. In addition, individuals with FHP have significant changes in the pattern of muscle activation during exercise, which can lead to acute and chronic injury mechanisms [25]. Compensatory strategies employed by patients with FHP affect not only the cervical and thoracic regions, but also extend to the lumbar region [26]. This study confirms the theory that FHP leads to altered activity of the paraspinal muscles through a compensatory mechanism, which may increase the risk of developing musculoskeletal disorders. The findings suggest the need for targeted interventions aimed at correcting FHP to reduce potential injury and improve overall postural health.

In addition, this study deepens the understanding of muscle fatigue associated with FHP. We noted that participants with FHP had increased fatigue in the erector spinae muscles, especially when performing the Biering-Sørensen test. Previous research has shown that the Billing-Sørensen test requires sustained isometric contractions of the back muscles, effectively mimicking conditions that may exacerbate muscle fatigue in people with poor posture [27]. This is particularly important for people with FHP because the altered alignment of the spine places additional biomechanical demands on the erector spine muscles [28]. This stretching acts as a longer lever and increases the risk of fatigue and injury [29].

Additionally, this study explored how changes in the CVA affect the erector spinae muscles and suggests that postural deviations can dynamically alter muscle structure. Future studies should provide a clearer understanding of this relationship. We also investigated how the MVIC of the erector spinae correlated with the CVA, which could reveal more about the biomechanical adjustments required owing to the FHP [30,31].

Our rigorous methods and structured approach to collecting and analyzing data ensured that our findings were reliable. They also highlighted the need to follow the clinical biomechanical research guidelines. This provides essential insights for the development of targeted therapeutic interventions [32].

Understanding the specific muscle changes associated with FHP will allow physical therapists to design more effective treatments. Customized strengthening and stretching exercises designed to correct FHP can reduce compensatory muscle activity and alleviate the associated discomfort. Early detection and treatment are vital for preventing long-term musculoskeletal problems. This underscores the importance of regular posture checks and ergonomic adjustments in daily routines [33].

This study had several limitations. First, young individuals with FHP were recruited, which limits the generalizability of our findings. Second, CVA was measured using digital photographs rather than a more reliable radiological analysis of the head. Third, we did not differentiate between males and females. Finally, as the most important limitation to acknowledge, the spinal muscles are located deeper than the other muscles.

Our detailed study of erector spinae activation in individuals with FHP shows the importance of fixing posture to prevent musculoskeletal disorders. This study provides deeper insights into how FHP affects spinal muscles and highlights the key role of biomechanical health in overall wellness. This lays a strong groundwork for future studies and clinical work by focusing on preventive and corrective strategies for the effects of FHP on muscle function. Future research should investigate the long-term effects and efficacy of different interventions. Such comprehensive analyses are essential for developing effective interventions aimed at mitigating the adverse effects of FHP and promoting healthier postural habits, thereby improving physical health and reducing the likelihood of long-term health complications [34]. Overall, this study contributes greatly to our understanding of muscle function and issues related to posture changes [35].

None.

None to declare.

No potential conflicts of interest relevant to this article are reported.

Conceptualization: FL, YC, CY. Data curation: FL, YC. Formal analysis: FL, YC. Investigation: FL. Methodology: FL, YC, CY. Project administration: FL, IM, CY. Resources: FL. Software: FL. Supervision: FL, IM, CY. Validation: FL, IM, CY. Visualization: FL. Writing - original draft: FL, YC. Writing - review & editing: FL, CY.