Correlation between forward head posture,respiratory functions,and respiratory accessory muscles in young adults

Abstract

BACKGROUND:

Forward head posture (FHP) causes changes in the strengths and rigidities of cervical muscles.

OBJECTIVE:

The aim of this study was to investigate correlations between FHP and respiratory functions and the muscle activities of respiratory accessory muscles in young adults in their 20s.

METHODS:

A volunteer sample of 33 healthy young adults participated in this study. Craniovertebral angle (CVA), cranial rotational angle (CRA), vital capacity (VC), forced vital capacity (FVC), forced expiratory volume at 1 second (FEV1), peak expiratory flow (PEF), maximal voluntary ventilation (MVV), and sternocleidomastoid (SCM) and upper trapezius activity ratios were measured.

RESULTS:

Significant positive correlations were found between CVA and VC, FVC, FEV1, PEF, and MVV, and a significant negative correlation was found between CVA and SCM activity ratio. Significant negative correlations existed between CRA and VC and FVC, and significant positive correlations between CRA and SCM and upper trapezius activity ratios.

CONCLUSION:

FHP may act to lower respiratory functions, and thus, the maintenance of correct head posture is required to prevent such functional reductions.

Keywords

Forward head posture respiratory function respiratory accessory muscle activity

1. Introduction

Working on computers has become commonplace and those that do frequently complain of musculoskeletal dysfunctions [1, 2, 3]. A forward head posture (FHP) is commonly observed among those working on computers, and this posture requires that upper cervical vertebrae be extended and lower cervical vertebrae be flexed [4]. FHP also changes the strengths and rigidities of muscles, and it is usually associated with shortening of the posterior cervical extensor muscles and tightening of the anterior cervical muscles [5, 6, 7]. Furthermore, continuous FHP has been reported to lead to reduce diaphragm contraction and thoracoabdominal mobility and to elevate rib cage [8, 9, 10].

In a study on spine misalignment and respiratory functions, Jandt et al. [11] reported that poorer thorax control in stroke patients resulted in lower peak expiratory flow (PEF), Culham et al. [12] noted that a higher thoracic kyphosis angle in women with thoracic kyphosis resulted in lower inspiration and vital capacity. In a study of 631 idiopathic scoliosis adolescents, it was observed that adolescents with more severe spinal scoliosis had lower respiratory functions [13]. To the best of our knowledge, research conducted thus far on spinal posture changes and respiration has usually addressed thorax changes. In particular, research on changes in cervical posture, especially on the relationships between FHP and respiratory functions in young adults has been less studied. In view of the above, we hypothesize a negative correlation exits between FHP and respiratory function, and that FHP and the activations of respiratory accessory muscles are positively correlated. In order to investigate possible interactions between cervical vertebra alignment and the respiratory system, we designed this study to evaluate relations between FHP, respiratory function, and electromyograph findings of respiratory accessory muscles in young adults in their 20s.

2. Methods

2.1 Participants

Undergraduates at Daejeon University aged between 20 and 30 years were screened for this study. Exclusion criteria were; a history of any febrile illness during the previous three weeks, an acute or chronic respiratory disease, any drug intake that might affect pulmonary function testing, bone deformity of the chest or spine, pain in the neck or shoulder, and current smoker or a history of smoking. Thirty-three participants met the study criteria. Participants had a mean age of 21.5 $\pm$ 1.6 years, a mean height of 165.6 $\pm$ 6.7 cm, and a mean weight of 59.6 $\pm$ 8.7 kg. No distinction was made of age, sex, height, and weight.

Table 1
Means and standard deviations of forward head posture variables and pulmonary function variables

Value	Mean	Standard deviation
CVA ( ${}^{\circ}$ )	48.94	5.44
CRA ( ${}^{\circ}$ )	150.18	7.09
VC (L)	2.83	0.87
FVC (L)	2.64	0.92
FEV1 (L)	2.45	0.85
PEF (L)	5.38	2.56
MVV (L)	95.49	34.37

CVA, crainovetebral angle; CRA, cranial rotational angle; VC, vital capacity; FVC, forced vital capacity; FEV1, forced expiratory volume at one second; PEF, peak expiratory flow; MVV, maximal voluntary ventilation.

Table 1 shows the means and standard deviations of the FHP variables (expressed as angles) and spirometry variables (expressed as L). The ethics committee of our institution approved this study, which was conducted in accordance with the Helsinki Declaration of 1975 as revised in 1983. All participants ( $n=$ 33) received written and verbal information about the study and provided written informed consent beforehand.

2.2 FHP measurement

FHP was evaluated using the Image J program (National Institute of Health, Bethesda, USA) after photographing lateral sides of subjects with a digital camera. All subjects looked frontwards naturally while sitting in a chair with their hip and knee joints at 90 ${}^{\circ}$ with feet in contact with the ground and both arms placed comfortably beside the trunk. The seventh cervical vertebra (C7) and tragus were marked; photographs were taken at subject shoulder height. Craniovertebral angle (CVA) was defined as the angle between the horizontal plane at C7 and the line connecting C7 and the tragus [14]. When this angle decreases, FHP becomes more severe. The cranial rotational angle (CRA) was calculated as the angle between the line connecting C7 and the tragus and the line connecting the tragus and the canthus [15]. When this angle increases, FHP also becomes more severe.

2.3 Respiratory function measurement

Spirometry was performed in the pulmonary function laboratory using a Chestgraph HI-101 (CHEST MI, Tokyo, Japan). Each subject was tested with a spirometer while sitting, according to the standardization of spirometry of the European Respiratory Society and American Thoracic Society [16].

All evaluations involved three measurements, and average values were used in the analysis. If a subject felt dizzy or had difficulty with respiration during the evaluation, he/she was allowed to rest until the symptoms subsided.

Vital capacity (VC), forced vital capacity (FVC), forced expiratory volume at 1 second (FEV1), peak expiratory flow (PEF), and maximal voluntary ventilation (MVV) were calculated automatically.

2.4 Electromyography signal acquisition and processing

Myosystem 1400 A unit (Noraxon USA Inc, Scottsdale, Arizona, USA) was used to measure sternocleidomastoid (SCM) and upper trapezius muscle activities during respiration. Samples were secured at 1024 Hz using a personal computer (2.27 GHz processor, 2.00 GB RAM). Raw surface electromyography (EMG) signals were band-pass filtered between 10 and 100 Hz at a notch filter frequency of 60 Hz. MyoResearch software (MyoResearch XP; Noraxon, USA) was used for data processing and analysis. Before attaching the surface bipolar electrode, body hair and dead skin cells were removed in order to reduce skin resistance and after washing areas with medical alcohol swabs, electrodes were attached. After allowing the skin time to dry, pairs of circular Ag/AgCl surface bipolar electrodes (Tyco Healthcare Korea, Seoul, Korea) were placed on the skin over the two muscles unilaterally, such that, they were oriented on the medium third of the SCM and the superior portion of upper trapezius muscles on the dominant side such that the line connecting the two ran parallel to muscle fibers and the inter-electrode distance was 20 mm [17]. Dominant sides were determined by asking subjects whether they used the right or left leg to kick a ball. To avoid electromagnetic interference during the examination and for subject protection, a metallic electrode connected to a grounding electrode was fastened to the subjects’ forearm.

To measure the surface EMGs of respiratory accessory muscles during respiration, each subject was examined while seated comfortably in a chair, with the head naturally positioned, and knees flexed at 90 ${}^{\circ}$ with feet fully supported. After breathing comfortably for 10 seconds, subjects were instructed to repeat forced breathing for 10 seconds, and then breathe comfortably. Recordings of raw data of root-mean-square (RMS) signals of the two muscles were obtained during comfortable breathing and forced breathing. Mean RMS values under both breathing conditions were calculated from 2 to 8 sec during the 10 seconds.

In order to normalize RMS data, the ratio of maximal voluntary isometric contraction (% MVIC) of the SCM and the upper trapezius were calculated [18, 19]. The surface EMGs (% of MVIC) of SCM and upper trapezius during both comfortable and forced breathing were calculated, each respiratory accessory muscle ratio (%) was finally calculated as comfortable breathing/forced breathing $\times$ 100. The smaller the respiratory accessory muscle ratio, the less respiratory accessory muscles are used during comfortable respiration.

2.5 Statistical analysis

The distribution of data was checked using the Shapiro-Wilk test for normality. The relationships between FHP and other variables were evaluated using Pearson’s correlation coefficients when data were normally distributed, and Spearman’s correlation coefficients when non-normally distributed. Data were processed using SPSS ver. 21.0 (SPSS Inc, Chicago, IL, USA), and statistical significance was accepted for p values $<$ 0.05.

3. Results

Correlations between CVA and spirometry and surface EMG variables were calculated. A consistent and statistically significant correlations were found between CVA and VC, FVC, FEV1, PEF, MVV, SCM ratio ( $r=$ 0.580, $p=$ 0.000; $r=$ 0.525, $p=$ 0.002; $r=$ 0.540, $p=$ 0.001; $r=$ 0.455, $p=$ 0.008; $r=$ 0.473, $p=$ 0.005; $r=-$ 0.361, $p=$ 0.039, respectively) (Table 2). VC showed the strongest positive correlation with CVA. Figure 1 shows the positive linear correlation observed between CVA and VC.

Table 2
Pearson correlation between CVA and spirometry and surface EMG values

Value	$R$	$p$
VC (L)*	0.580	0.000
FVC (L)*	0.525	0.002
FEV1 (L)*	0.540	0.001
PEF (L)*	0.455	0.008
MVV (L)*	0.473	0.005
SCM (%)*	$-$ 0.361	0.039
Upper trapezius (%)	$-$ 0.150	0.406

*Statistically significant correlation ( $p<$ 0.05). CVA, crainovertebral angle; sEMG, surface electromyography, VC, vital capacity; FVC, forced vital capacity; FEV1, forced expiratory volume at one second; PEF, peak expiratory flow; MVV, maximal voluntary ventilation; SCM, sternocleidomastoid.

Analysis of correlations between CRA and spirometry and surface EMG variables showed a significant correlation between CRA and VC, FVC, SCM and upper trapezius ratio ( $r=-$ 0.355, $p=$ 0.043; $r=-$ 0.360, $p=$ 0.040; $r=$ 0.410, $p=$ 0.018; $r=$ 0.402, $p=$ 0.021, respectively). FVC showed a strong negative correlation with CRA. However, no correlation was found between CRA and the other spirometry values (FEV1, PEF, and MVV) (Table 3).

Table 3

Pearson correlation between CRA and spirometry and surface EMG values

Value	$R$	$p$
VC (L)*	$-$ 0.355	0.043
FVC (L)*	$-$ 0.360	0.040
FEV1 (L)	$-$ 0.337	0.055
PEF (L)	$-$ 0.256	0.150
MVV (L)	$-$ 0.140	0.437
SCM (%)*	0.410	0.018
Upper trapezius (%)*	0.402	0.021

*Statistically significant correlation ( $p<$ 0.05). CRA, cranial rotational angle; sEMG, surface electromyography, VC, vital capacity; FVC, forced vital capacity; FEV1, forced expiratory volume at one second; PEF, peak expiratory flow; MVV, maximal voluntary ventilation; SCM, sternocleidomastoid.

Figure 1.

The correlation between CVA and VC, with $R=$ 0.580, $p=$ 0.000. CVA $=$ craniovertebral angle; VC $=$ vital capacity.

4. Discussion

The main purpose of this study was to examine correlations between FHP and respiratory functions and respiratory accessory muscle activities. According to our results, FHP is significantly correlated with respiratory functions and respiratory accessory muscle activities. This result supports the primary hypothesis of this study that FHP is negatively correlated with respiratory function and positively correlated with respiratory accessory muscle activation.

In particular, positive correlations were found between CVA and VC, FVC, FEV1, PEF, and MVV, and a negative correlation between VC and FVC, showing that when CVA decreases and CRA increases, FHP becomes more severe and respiratory functions decrease. These results are somewhat supported by those of prior studies [11, 20]. Jandt et al. [11] examined the correlation between thorax control in stroke patients and pulmonary function, and found a correlation coefficient between thorax control and PEF of 0.49, that is, stroke patients with poorer thorax control ability had poorer respiratory functions. Furthermore, Pawlicka et al. [20] reported that students with an overall poor body posture had lower FVC and FEV1 values than those with a good body posture, which supports the results of the present study.

FHP is closely related to high activation levels of cervical superficial muscles, such as, the SCM and upper trapezius [21]. Patients with neck pain caused by FHP show SCM breathing patterns and not diaphragmatic breathing patterns, which increases fatigue due to excessive muscle use [22, 23].

In this study we examined respiratory accessory muscle activation levels with respect to increases in FHP during breathing. The results showed the SCM ratio was significantly and negatively correlated with CVA and significantly and positively correlated with CRA, and that the SCM and upper trapezius ratios were significantly and positively correlated with CRA. Such results show that when FHP is more severe, the activities of respiratory accessory muscles are excessive. We consider that stress of cervical muscles caused by forward orientation of the head is the cause.

Our results of more severe FHP and higher activation levels of SCMs and upper trapezius muscles are supported by the results of a previous study. Kapreli et al. [24] found as FHP severity increased, respiratory muscle strength decreased and that this decreased maximal inspiratory pressure and maximal expiratory pressure. Habitual mouth-breathing children, most of whom have a FHP, exhibit excessive SCM and trapezius activations during breathing due to their postures [8, 17, 25]. These findings are consistent with the results of the present study. In addition, Correa and Berzin [21] reported that when degree of FHP decreased, suboccipital muscle and upper trapezius activity also decreased. Such results mean respiratory accessory muscle activity is normalized by the correction of postural alignment, which supports our result that when more severe FHP was correlated with excessive activity of respiratory accessory muscles.

The limitations of this study are as follows. First, the sample size was small. Second, respiratory functions were measured in a sitting position only. Third, the relationship between FHP and primary respiratory muscles was not verified. Should these limitations be addressed in future investigations of FHP variables, we believe that it will be found that FHP acts to the detriment of respiratory and musculoskeletal functions.

Conflict of interest

The authors have no potential conflict of interest to declare.

Footnotes

Acknowledgments

The study was performed at Daejeon University, Daejeon, South Korea. No funding was received for this study.

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Correlation between forward head posture,respiratory functions,and respiratory accessory muscles in young adults

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Methods

2.1 Participants

Table 1 Means and standard deviations of forward head posture variables and pulmonary function variables

2.3 Respiratory function measurement

2.4 Electromyography signal acquisition and processing

2.5 Statistical analysis

3. Results

Table 2 Pearson correlation between CVA and spirometry and surface EMG values

Conflict of interest

Footnotes

Acknowledgments

References

Table 1
Means and standard deviations of forward head posture variables and pulmonary function variables

Table 2
Pearson correlation between CVA and spirometry and surface EMG values