Effect of cervicothoracic posture on respiratory muscle strength and upper extremity function in healthy young adults

Abstract

Background

The effects of changes in cervicothoracic posture on respiratory and exercise capacity in healthy young adults are still debated.

Objective

This study aimed to investigate the effect of cervicothoracic posture on respiratory muscle strength and upper extremity function and to compare according to the activity levels in healthy young adults.

Methods

Ninety-three healthy young adults were included in this study. Cervicothoracic posture, including the craniovertebral angle, cervical lordosis angle, forward shoulder angle (FSA), and thoracic kyphosis angle, was assessed using the photographic method. Chest wall mobility, respiratory muscle strength, upper extremity function, physical activity level, and severity of fatigue were assessed. Pearson's correlation analysis revealed significant associations between respiratory muscle strength and cervicothoracic posture, as well as anthropometric measures. Multiple linear regression identified independent predictors of MIP and MEP, adjusting for potential confounders such as smoking.

Results

The FSA demonstrated a weak but statistically significant correlation with both maximum inspiratory pressure (MIP) (r = −0.248, p = 0.021) and maximum expiratory pressure (MEP) (r = −0.219, p = 0.041). Axillary circumference measurements demonstrated a near-significant association with MEP (B = 4.93, p = 0.059). Upper extremity function did not correlate with cervicothoracic posture (p > 0.005). The MEP was significantly associated with fatigue severity (B = − 0.02, β = − 0.323, p = 0.022). Activity level was associated with MEP, chest mobility and fatigue (p < 0.05).

Conclusion

Cervicothoracic posture does not affect respiratory muscle strength or upper-extremity function in healthy young adults. The MEP is influenced by axillary chest mobility and affects fatigue. Activity is important for the respiratory health of healthy young adults.

Keywords

posture respiratory muscles exercise test shoulder chest wall

Introduction

The increasing use of technological devices and decreasing age at the onset of their use have contributed to an increasing trend of physical inactivity among young individuals.¹ The spread of sedentary lifestyles negatively affects the physical health and posture of university students worldwide. Prolonged periods of sitting, coupled with inefficient biomechanics resulting from poor posture, are known contributors to a range of musculoskeletal and respiratory issues. These include, but are not limited to, rounded shoulders, thoracic kyphosis, forward head posture, and associated pain syndromes.^2,3 Physical inactivity and sedentary behavior are associated with poor well-being in young people, with adverse effects extending into adulthood.⁴ Specifically, students with low physical activity levels and more time spent sitting have imbalanced trunk muscles, worse respiratory function, and poorer quality of life and sleep.⁴ These observations strongly suggest that sedentary behavior can precipitate significant musculoskeletal and respiratory challenges, even in young adult populations. Among these postural issues, forward head posture is particularly detrimental, as it has been shown to increase the activity of accessory respiratory muscles like the sternocleidomastoid and anterior scalene, thereby decreasing vital lung capacities such as forced vital capacity.⁵

The chest wall, a critical structure supported by a complex network of respiratory and accessory muscles spanning the thoracic and shoulder regions, necessitates adequate mobility for optimal respiratory mechanics. In healthy individuals, typical chest wall alignment ranges from 4 to 7 cm; however, this mobility tends to diminish with age and in the presence of poor postural alignment.^6,7 Existing research consistently demonstrates that altered posture significantly reduces chest wall mobility and impairs both respiratory muscle strength and overall lung function.⁶ Beyond respiratory implications, individuals who maintain poor postural habits over extended periods, such as office workers and students, are highly susceptible to developing upper limb muscle imbalances and shoulder dysfunction.^8,9 Poor posture has been associated with reduced trunk mobility, impaired shoulder kinematics, decreased upper-extremity muscle activation, and limitations in performing functional upper-extremity exercises.^8,10 Rounded shoulder, kyphosis, and forward head posture reduce trunk mobility, negatively affect respiratory muscle strength and lung volume,¹¹ and impair shoulder kinematics, leading to decreased upper limb muscle activation.⁹ This is particularly important because upper limb exercise capacity is closely related to cardiovascular endurance, fatigue levels, and perceived dyspnea, even in healthy populations.¹² Therefore, understanding the connection between exercise habits and physical activity levels, posture, respiratory muscle strength, and chest mobility in young, healthy individuals is crucial for proactively preventing potential respiratory difficulties, especially given the accelerating trend of inactivity driven by technological advancements.

A comprehensive examination of the relationship between cervicothoracic posture, chest wall mobility, and respiratory muscle strength is essential, particularly when evaluating the systemic effects of postural disorders on the respiratory system. The flexibility and mobility of the chest wall are paramount in maintaining respiratory capacity. Indeed, postural disorders in the cervicothoracic region are known to restrict chest wall mobility and subsequently reduce rib-cage movement. Research indicates a strong positive correlation between respiratory muscle strength and factors such as chest wall enlargement, diaphragm movement, and overall functional capacity in healthy participants.¹³ This connection is particularly relevant in contemporary lifestyles: prolonged sitting positions, often adopted during office tasks or device use, increase neck flexion, thereby reducing lower cervical lordosis and causing an increase in thoracic kyphosis. This combination of increased tension in neck extensors and flexion of the cervical spine creates regions of stress in the neck.¹⁴ Critically, this habitual sitting posture also leads to the contraction of chest muscles, limiting their mobility and consequently disturbing the humeroscapular rhythm.¹⁴ This restriction of chest wall and shoulder girdle mechanics can directly interfere with the optimal functioning of the diaphragm and lead to a detrimental weakening of the primary respiratory muscles.¹⁵ Furthermore, such cervicothoracic postural disorders often result in the overuse and eventual fatigue of accessory respiratory muscles. Despite the escalating concerns regarding physical inactivity and the spectrum of posture-related dysfunctions, the existing literature exhibits significant limitations. While some studies have explored the individual relationships between cervicothoracic posture, chest wall mobility, and respiratory function,¹⁶ there remains a notable lack of comprehensive analyses that simultaneously investigate these factors alongside respiratory muscle streght, upper-extremity functional exercise capacity and fatigue in healthy young individuals. Previous research primarily focuses on isolated aspects, failing to provide a holistic understanding of how these interconnected elements collectively impact overall physical function. Specifically, there is a critical absence of multivariate comparative analyses that categorize and examine these relationships across different physical activity levels. This represents a substantial gap, as it hinders a complete understanding of how varying levels of physical activity may mitigate or exacerbate these issues. Given that adolescence is a critical developmental period for establishing and managing respiratory health, acquiring robust baseline data is imperative to inform the design of effective early interventions and preventative strategies.

The primary objective of this study was to investigate the effects of cervicothoracic posture and chest mobility on respiratory muscle strength. Additionally, this study aimed to further assess the effects of respiratory muscle strength on upper extremity exercise capacity and fatigue. A crucial secondary objective was to conduct a comprehensive multivariate comparative analysis of cervicothoracic posture, chest wall mobility, respiratory muscle strength, upper extremity exercise function, and fatigue across distinct activity levels in a cohort of healthy young adults.

It is hypothesized that in healthy young adults, poorer cervicothoracic posture will be associated with reduced chest wall mobility and decreased respiratory muscle strength. Furthermore, it is hypothesized that lower respiratory muscle strength will correlate with reduced upper extremity exercise capacity and increased reported fatigue. Finally, it is anticipated that individuals with higher physical activity levels will demonstrate superior cervicothoracic posture, greater chest wall mobility, stronger respiratory muscles, better upper extremityfunctional exercises capacity, and lower fatigue levels compared to those with lower physical activity levels.

Methods

Study design and participants

This cross-sectional study was conducted at X University Department of Physical Therapy and Rehabilitation between March 2024 and March 2025. Healthy individuals aged 18–40 years with a body mass index (BMI) value between 18.5 and 30 kg/m² were included in the study. Participants diagnosed with neurological, orthopedic (such as kyphoscoliosis), cardiac, and pulmonary diseases that would affect participation in physical activity and those who underwent thorax, upper extremity, and spine surgery were excluded from the study. This study was approved by the X University Non-Interventional Research Ethics Committee (Approval Number: 2024/34). The Informed Consent Form was explained to the patients one-on-one, and was filled in and recorded in accordance with the patient's request. This study was conducted in accordance with the principles of the Declaration of Helsinki. The study was conducted on healthy adults who agreed to participate in the study. Demographic information of the included individuals was recorded and posture, chest wall mobility, respiratory muscle strength, upper extremity mobility, physical activity level, and fatigue were evaluated.

Demographic data: Demographic information (age and sex), height (cm), and body weight (kg) of the individuals were recorded, and BMI was calculated using the body weight/height2 (kg/m²) formula. The participants’ physical activity habits, smoking (pack-years), and alcohol use (L/week) were recorded. Exercise habits (yes/absence) and regular exercise frequency (1–2 days/week, 3–4 days/week, 5–7 days/week).

Upper posture analysis

The craniovertebral angle (CVA), cervical lordosis angle (CLA), thoracic kyphosis angle (TKA), and forward shoulder angle (FSA) of the participants were measured using photogrammetry, which is a highly reliable intraclass correlation coefficient (ICC: 0.78–0.83) method that allows quantitative assessment of postural changes.¹⁷ Although this method does not directly measure vertebral alignment, it offers a noninvasive and practical way to screen for postural deviations.¹⁸ Photogrammetry consists of two stages, which are based on obtaining 2D images by a standard method and analyzing the images using a video analysis software.

The protocol developed by Belli et al. is preferred for photogrammetry. First, passive markers were attached to the right mastoid process; third (C3) and seventh cervical vertebrae (C7); sixth (T6) and twelfth thoracic vertebrae (T12); medial angle of the scapula; and acromion using double-sided adhesive tape by an experienced physiotherapist.¹⁹ Participants were asked to look straight at the point at eye level and on the opposite wall to achieve natural head-body and shoulder alignment. Participants were asked to stand in their natural, relaxed posture with their arms resting at their sides and feet shoulder width apart. Thereafter, a 2D image (sagittal plane, lateral view) was captured using a camera (Galaxy S22 Ultra, 200 MP; Samsung, South Korea) positioned 2.5 meters from the participant.

In the second stage, digital images were analyzed using Kinovea software (version 0.8.15, Kinovea Open Source Project). All angle measurements were performed by the same and blinded rater to minimize inter-rater variability. A mark was placed on the ground to ensure that each participant was in the same position. The shooting was done with a height-adjustable tripod. The photographs were taken by an expert physiotherapist. The person taking the photographs and the one performing the measurements were different physiotherapists. The angles formed by the lines traced from the pre-labeled anatomical markers in the cervicothoracic posture were measured to identify possible asymmetries in cervicothoracic posture using 2D images. For CVA an angle was formed between a horizontal line passing through the C7 vertebra and a line drawn from C7 to the tragus of the ear.^19,20 The CLA was formed by the lines between the occipital protuberance and C7, and the horizontal line between C4 and the lines intersecting the true vertical line. The FSA was measured as the angle between a vertical line passing through the spinous process of C7 and a line connecting C7 to the acromion process of the scapula. Three 2D images obtained from the participants were analyzed, and the average values were recorded. A CVA <50 ° indicates poor posture and an FSA <52° indicates rounded shoulder posture (RSP).^21–24 For TKA, lines were drawn between C7, the inferior angle of the scapula (around T7), and the estimated T12. The angle between these lines reflected the curvature of the thoracic spine. A TKA angle greater than 40 °is considered hyperkyphosis.^20,25

Chest wall mobility: Chest mobility was evaluated by chest circumference measurements from the axillary (4th coastal alignment) and epigastric (xiphoid protrusion alignment) regions using a tape measure. The standardized measurement procedure was to keep the 0 point of the tape fixed on the midline of the body, horizontally aligned with the landmarks, while the other end of the tape was allowed to move. The tape was snug but not tight, so that the soft tissue contours remained unchanged. Measurements were taken in an upright sitting position during neutral inspiration, deep inspiration, and deep expiration. All measurements were performed by the same trained observer. The difference between deep inspiration and deep expiration was recorded in centimeters.²⁶

Anthropometric measurements: Measurements were taken with the arms at the sides and feet at the adjacent position with a garment, where the tape measure could be easily applied. Waist circumference was measured using a tape measure at the thinnest area of the waist, hip circumference, and trochanter major-level. The waist-hip ratio, which is the ratio of waist circumference measurement to hip circumference measurement, was calculated. Abdominal circumference, arms at the sides, feet adjacent, umbilicus level, and abdomen in a loose position were measured. The measurement was performed by ensuring that the tape measure was parallel to the ground on both sides and that its tissues were not compressed.

Respiratory muscle strength: Respiratory muscle strength was measured using a portable electronic mouth pressure-measuring device (RP Check, MD Diagnostics LTD, Kent, UK). One of the most commonly used non-invasive methods for the evaluation of respiratory muscles is the measurement of maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP). Intraoral pressure is measured during maximal inspiration, expiration, and maximal breathing against a valve that closes the airway. The estimated MIP and MEP values were calculated based on age and sex.²⁷ MIP and MEP values < 80% were defined as respiratory muscle dysfunction.²⁷

Upper extremity functional exercise capacity: Unsupported arm functional exercise capacity was evaluated using the 6-Minute Pegboard and Ring Test (6PBRT). During the test, the patient was asked to sit in front of a perforated panel with two rods placed at shoulder height and shoulder width, two upper rods placed 20 cm above these rods, and ten rings attached to these rods, and to move as many rings as possible from the lower holes to the upper holes using both hands simultaneously for 6 min, and then from the upper holes to the lower holes. The participants were asked to practice wearing a few rings before the test. For the 6PBRT score, the number of rings carried over 6 min was recorded.^28,29

Physical activity level: The International Physical Activity Questionnaire-Short Form was used to assess physical activity levels. It provides information on the time and sitting time that individuals spend on light, moderate, and vigorous activities. For each activity level, the metabolic equivalent was multiplied by days and minutes to obtain the MET-min/week score. Three levels of physical activity were identified when categorically classifying populations: ‘inactive, ‘ ‘minimum active,’ and ‘always active (a physical activity that promotes good health).’ Sitting time is an additional determinant. It is not part of physical activity scoring. This provides information on sedentary behavior. Physical Activity level is determined in three categories.³⁰ The total value was classified as inactive: < 600 MET-min/week, minimum active: > 600–3000 MET-min/week, always active: > 3000 MET-min/week.

Fatigue severity: Fatigue was assessed using a Fatigue Severity Questionnaire. This scale contains 9 items. Patients were asked to give each question a score of 1 (strongly disagree) to 7 (strongly agree). The score was obtained by dividing the total score on the scale by the number of questions. A score ≥4 or more indicates severe fatigue.³¹

Statistical analysis

All statistical analyses were performed using IBM SPSS Statistics (version 27.0; IBM Corp., Armonk, NY, USA) and GraphPad Prism version 10.4.1 (GraphPad Software, LLC, San Diego, CA, USA). The distribution of the data was assessed using both visual (histograms and probability plots) and analytical methods (Kolmogorov–Smirnov test). Descriptive statistics were presented as the number of patients and percentages for categorical variables and as mean and standard deviation (SD) for continuous variables. Pearson's correlation analyses were performed to examine the relationship between participants’ cervicothoracic posture and anthropometric measurements with MIP and MEP. Power below 80 percent was considered weak. Power was calculated only for significant interaction. Variables that showed significant associations in the univariate analysis were entered into multiple linear regression analyses conducted in the two models. The purpose of using the two models was to determine the independent predictors of MIP and MEP, while adjusting for smoking as a potential confounding factor. A single-model multiple linear regression analysis was also conducted to determine the impact of respiratory muscle strength on the upper extremity functional exercise capacity and fatigue severity. Regression assumptions, including linearity, normality of residuals, homoscedasticity, and the absence of multicollinearity, were checked to ensure model validity.

One-way analysis of variance (ANOVA) followed by Tukey's post-hoc correction was used to perform multiple group comparisons. Statistical significance was set at P < 0.05.

The sample size calculation in the present study was originally based on the effect size (r² = 0.68) reported by Morais et al.,³² who examined the relationship between chest wall mobility and pulmonary function (FVC). However, since spirometry was not included in the present study, we acknowledge that this reference may not fully reflect the variables directly assessed herein (e.g., MIP, MEP, and upper extremity functional capacity). Although the initial estimated effect size was 1.0, yielding a minimum sample size of 46 (23 per group) with α = 0.005 and 80% power using PS-Power and SISA software, this estimation may not be sufficient for subgroup comparisons (e.g., by physical activity level). Therefore, we recognize this as a limitation of the study and acknowledge the potential risk of Type II error in subgroup analyses.

Results

Ninety-three healthy young individuals (mean age 21.84 ± 5.40, 40 (%43) male and 53 (%57) female) were included in the study. Among the healthy young people who participated in the study, 60.9% had an FSA <52, 41.4% had a CVA < 50, and 94.2% had TKA > 42. Of the participants, 52.7% were minimally active. While 49.50% of participants exercise habits, 35.50% were smokers (Table 1).

Table 1.

Demographic characteristics of the participants.

	Total (N = 93)
Age, years	20.84 ± 5.40
Female, n/%	53 / 57.00
Body Mass Index, kg/m²	25.47 ± 26.84
Smoker / nonsmoker, %	35.50/ 64.50
Smoke packet*years	1.07 ± 2.05
Exercises habit, n/ %	46/49.50
1–2 days/week, n/ %	19/20.40
3–4 days/week, n/ %	19/20.40
5–7 days/week, n/ %	8/8.60
IPAQ
İnactive, %	20/21.50
Minimum active, %	48/51.70
Always active, %	25/26.90
Total, MET min/week	2489.74 ± 2481.15
Sedentary time	721.84 ± 161.20
Cervicothoracic posture analysis
CVA, °	51.18 ± 5.40
FSA,°	50.62 ± 12.64
CLA,°	43.88 ± 5.85
TKA,°	54.45 ± 7.74
Chest wall mobility
Axillar, cm	6.95 ± 2.20
Epigastric, cm	6.47 ± 2.22
Body circumference
Abdomen	82.90 ± 11.53
Hip, cm	97.65 ± 13.29
Waist, cm	76.17 ± 10.47
Waist / Hip	0.77 ± 0.80
Respiratory muscle strength
MIP, cmH₂O	83.67 ± 26.51
MEP, cmH₂O	101.03 ± 30.03
Upper extremity function exercises capacity
6PBRT score, n	239.00 ± 34.00
Fatigue severity Q, (0–9)	3.65 ± 1.52

CVA: craniovertebral angle; CLA: cervical lordosis angle; FSA: forward shoulder angle; TKA: thoracic kyphosis angle; MIP: maximal inspiratory pressure; MEP: maximal expiratory pressure; 6PBRT: 6 minute pegboard and ring test.

FSA was significantly negatively correlated with CLA (p = 0.028) and TKA (p = 0.038). The CVA, FSA, CLA, and TKA values of participants with regular exercise habits (mean values: 51.10, 52.60, 44.29, and 54.18, respectively) were similar to those of participants without regular exercise habits (mean values: 51.27, 47.98, 43.44, and 54.74, respectively) (p > 0.05). The axillary circumference difference (p = 0.001), epigastric circumference difference (p = 0.001), MIP (p = 0.010), and MEP (p = 0.007) values were higher in patients who exercised regularly than those who did not.

There was no significant correlation between CVA, CLA, TKA, MIP, or MEP (p > 0.05). However, FSA demonstrated a weak but statistically significant negative correlation with both MIP (r = −0.248, p = 0.021) and MEP (r = −0.219, p = 0.041). Axillary and epigastric circumference measurements were moderately positive correlated with MIP (r = 0.455 and r = 0.438, respectively; p < 0.001) and MEP (r = 0.413 and r = 0.389, respectively; p < 0.001) (Table 2). Multiple linear regression analyses showed that in Model 1, which included FSA and axillary and epigastric circumference measurements, none of the predictors reached statistical significance for MIP or MEP. Axillary circumference measurements demonstrated a near-significant association with MEP (B = 4.93, p = 0.059). In the adjusted model (Model 2), which included smoking along with postural and anthropometric variables, the regression coefficients for FSA and circumference measurements remained relatively stable compared with those in Model 1. The FSA continued to show a negative association with both MIP (B = − 0.37, p = 0.079) and MEP (B = − 0.36, p = 0.135), with the association for MIP approaching statistical significance. Axillary circumference measurement retained its a near-significant positive association with MEP (B = 4.87, p = 0.064), approaching significance, whereas its relationship with MIP remained nonsignificant (B = 3.35, p = 0.989) (Table 3, Figure 1).

Figure 1.

The association between participants’ cervicothoracic posture, chest mobility, respiratory muscle strength and fatigue severity RS: Rounded shoulder, ACM: Axillary circumference measurement, ECM: Epigastric circumference measurement, MIP: Maximal inspiratory pressure, MEP: Maximal expiratory pressure, UEFEC: Upper extremity functional exercise capacity.

Table 2.

Correlation of participants’ cervicothoracic posture, chest mobility, upper extremity function exercise capacity, respiratory muscle strength and fatigue severity.

	MIP			MEP			6PBRT
	Pearson's r	p-value	Power (%)	Pearson's r	p-value	Power (%)	Pearson's r	p-value	Power (%)
CVA	−0.032	0.767	NA	−0.042	0.702	NA	−0.026	0.812	NA
CLA	−0.151	0.161	NA	−0.062	0.565	NA	0.044	0.686	NA
FSA	−0.248	0 . 021	68.5	−0.219	0.041	57.2	0.191	0.760	NA
TKA	−0.163	0.131	NA	−0.081	0.455	NA	0.103	0.344	NA
Axillary	0.455	<0.001	99.8	0.413	<0.001	99.1	0.089	0.401	NA
Epigastric	0.438	<0.001	99.6	0.389	<0.001	98.1	0.049	0.644	NA
6PBRT	0.259	0.013	72.5	0.272	0.009	76.9	-	-	NA
Fatigue severity	−0.348	0.001	94.3	−0.406	0.000	98.9	−0.074	0.484	NA

CVA: craniovertebral angle; CLA: cervical lordosis angle; FSA: forward shoulder angle; TKA: thoracic kyphosis angle; MIP: maximal inspiratory pressure; MEP: Maximal expiratory pressure; 6PBRT: 6 min pegboard and ring test. Bold values indicate p < 0.05.

Table 3.

Multiple regression analysis for the association between participants’ cervicothoracic posture and anthropometric measurements and respiratory muscle strength.

	MIP			MEP
	B (SE)	Beta	p-value	B (SE)	Beta	p-value
Model 1
FSA	−0.36 (0.21)	−0171	0.086	−0,36 (0.24)	−0.151	0.139
Axillary	3.46 (2.28)	0.278	0.133	4.93 (2.58)	0.359	0.059
Epigastric	1.80 (2.22)	0.148	0.421	0.34 (2.51)	0.025	0.893
Model 2
Smoking	−5.36 (5,84)	−0.094	0.361	−3.00 (6.64)	−0.048	0.653
FSA	−0.37 (0.21)	−0.175	0.079	−0.36 (0.24)	−0.153	0.135
Axillary	3.35 (2.28)	0.270	0.989	4.87 (2.59)	0.355	0.064
Epigastric	2.26 (2.28)	0.186	0.326	0.59 (2.59)	0.044	0.819
Note	Model 1Constant (SE): 61.88 (13.21)Adjusted R²: 0.20Model 2Constant (SE): 61.86 (13.22)ΔR²: 0.01			Model 1Constant (SE): 78.06 (14.95)Adjusted R²: 0.16Model 2Constant (SE): 78.05 (15.02)ΔR²: 0.00

FSA: forward shoulder angle, MIP: maximal inspiratory pressure, MEP: maximal expiratory pressure, B: unstandardized coefficients, SE: standard error, β: standardized coefficients.

Regression analysis revealed no significant association between MIP and either fatigue severity or upper-extremity functional exercise capacity (p = 0.403 and p = 0.365, respectively). Although MEP was not significantly related to upper extremity function (p = 0.228), it showed a significant negative association with fatigue severity (B = − 0.02, β = − 0.323, p = 0.022), suggesting that greater expiratory muscle strength may be linked to reduced perceived fatigue (Table 4, Figure 1). There was no significant correlation between CVA, CLA, FSA, or TKA and 6PBRT (p > 0.05), and there was a statistically significant positive correlation between 6PBRT and both MIP (p = 0.013) and MEP (p = 0.009).

Table 4.

Multiple regression analysis for the association between participants’ respiratory muscle strength and upper extremity functional exercise capacity and fatigue severity.

	Upper extremity functional exercise capacity (6PBRT)			Fatigue severity
	B (SE)	Beta	p-value	B (SE)	Beta	p-value
MIP	0.17 (0.19)	0.133	0.365	−0.01 (0.01)	−0.116	0.403
MEP	0.20 (0.17)	0.177	0.228	−0.02 (0.01)	−0.323	0 . 022
	Constant (SE) = 204.69 (12.62)Adjusted R² = 0.06			Constant (SE) = 5.88 (0.54)Adjusted R² = 0.15

MIP: Maximal inspiratory pressure; MEP: Maximal expiratory pressure; 6PBRT: 6 Minute Pegboard and Ring Test; B: Unstandardized coefficients; SE: Standard error; β, standardized coefficients. Bold values indicate p < 0.05.

Comparison analyses showed that MEP values differed significantly across the groups (p = 0.047), with the active group showing significantly greater MEP than the inactive group. No significant differences were observed in cervicothoracic postural parameters, including CVA, CLA, FSA, and TKA, across physical activity levels (p > 0.05). However, both axillary and epigastric circumference measurements were significantly greater in the active group than in the inactive and minimally active groups (p = 0.003 and p = 0.004, respectively). Although upper extremity function was similar across the groups (p > 0.05), fatigue severity was higher in the inactive group than in the active group (p = 0.004). (Table 5, Figure 2).

Figure 2.

Variables that significantly differed across physical activity level groups MEP: Maximal expiratory pressure.

Table 5.

Comparison of respiratory muscle strength, cervicothoracic posture, upper extremity functional exercise capacity, chest wall mobility, and fatigue severity among individuals with different physical activity levels.

	Inactive (N = 20)	Minimum active (N = 48)	Active (N = 25)	Effect size (η² or Cramer's V)	p-value
Age, years	21.45 ± 5.67	22.25 ± 6.29	21.40 ± 1.84	0.006	0.756^a
Female, n/%	17/85.00	33/68.75	3/12.00	0.566	<0.001^b (Ω, †)
Body Mass Index, kg/m²	21.59 ± 3.35	28.28 ± 37.13	23.17 ± 4.40	0.012	0.575^c
Smoker, n/%	7/35.00	17/35.41	9/36.00	0.007	0.997^b
Smoke, packet*years	1.28 ± 2.64	0.91 ± 1.69	1.22 ± 2.23	0.007	0.737^a
Exercises habit, n/%	4/20.00	17/35.41	25/100	0.625	<0.001^b (Ω, †)
1–2 days/week, n/%	2/10.00	12/25.00	5/20.00	0.762	<0.001^b (Ω, †)
3–4 days/week, n/%	2/10.00	5/10.40	12/48.00
5–7 days/week, n/%	0/0	0/0	8/32.00
MIP, (cmH₂O)	77.8 ± 31.5	81.8 ± 23.5	92.0 ± 28.2	0.010	0.630^c
MEP, (cmH₂O)	87.5 ± 30.0	101.9 ± 28.0	110.0 ± 31.1	0.028	0.286^c
CVA, (^o)	52.2 ± 5.8	50.7 ± 5.6	51.3 ± 5.2	0.011	0.626^c
CLA, (^o)	44.1 ± 6.6	43.4 ± 5.0	44.9 ± 7.0	0.009	0.682^c
FSA, (^o)	38.2 ± 9.9	40.7 ± 12.4	37.9 ± 15.3	0.020	0.431^c
TKA, (^o)	56.6 ± 6.9	54.3 ± 7.7	53.1 ± 8.6	0.009	0.698^c
Axillary, (cm)	5.9 ± 1.9	6.9 ± 2.0	8.1 ± 2.2	0.023	0.350^c
Epigastric, (cm)	5.6 ± 1.7	6.2 ± 2.2	7.7 ± 2.2	0.003	0.865^c
6PBRT score, (n)	232.68 ± 39.06	235.32 ± 30.01	236.33 ± 37.62	0.008	0.693^c
Fatigue score	4.14 ± 1.11	3.88 ± 1.40	2.79 ± 1.76	0.016	0.493^c

CVA: craniovertebral angle, CLA: cervical lordosis angle, FSA: forward shoulder angle, TKA: thoracic kyphosis angle, MIP: maximal inspiratory pressure, MEP: maximal expiratory pressure, 6PBRT: 6 minute pegboard and ring test. (Ω): p < 0.05 for active vs inactive, (†): p < 0.05 for active vs minimum active. a: One way ANOVA test, b: Pearson's chi square, c: ANCOVA test gender was included as a covariate. Bold values indicate p < 0.05 p.

Discussion

The aim of our study was to investigate the relationship and effects of cervicothoracic posture angles on chest mobility, respiratory muscle strength, upper extremity function, and fatigue and to compare these parameters according to the activity levels of healthy young adults. The findings showed that in healthy young adults, MEP was affected by axillary circumference measurement, but not cervicothoracic posture, and MEP affected fatigue severity.

In healthy young adults, changes in the biomechanics of the cervicothoracic spine and thorax may contribute to the short-term impairment of respiratory power.^33,34 Forward head posture causes expansion of the upper thorax and contraction of the lower thorax; these morphological changes lead to decreased respiratory function.¹⁶ In addition, rounded shoulders may restrict chest wall mobility by narrowing the anteroposterior diameter of the thorax, which may effectively prevent respiratory muscle contractions. Round shoulder posture causes abnormal breathing due to weakening of the respiratory muscles, and normal expansion of the lungs becomes difficult; therefore, vital capacity and gas partial pressure may decrease.¹⁵ Similarly, the negative correlation of rounded shoulder posture with both MIP and MEP values in this study supports the notion that postural disorders may negatively affect thoracic expansion and, thus, the contractile power of respiratory muscles. However, the weak relationship suggests that postural change alone may not be a determining factor. These findings suggest that the relationship between chest wall mobility and respiratory muscle strength may be related to physical activity level and lifestyle habits rather than postural parameters. The FSA angles (37.9°, 40.7°, and 38.2°) decreased further when we categorized the participants as active, moderately active, and inactive according to their physical activity level. Those without regular exercise habits had an RSA <52° and kyphosis angles of 54°. Those with exercise habits had higher chest mobility, respiratory muscle strength, and fatigue perception than those without.

However, both chest wall mobility and respiratory muscle strength were higher in individuals who exercised regularly, indicating that physical activity may have a positive effect on both thoracic flexibility and respiratory muscle endurance. Changing the position of the head causes distortions in the three-dimensional shape of the chest and respiratory movements.¹⁵ Indeed, an increase in the functional capacity of inspiratory and expiratory muscles with increasing levels of physical activity has been widely reported in literature.¹³

FSA and axillary and epigastric chest mobility were associated with MIP and MEP; however, only axillary chest mobility tended to have an effect on expiratory muscle strength. Smoking did not affect the outcomes. The moderate positive correlation between chest wall mobility (axillary and epigastric circumferences) and respiratory muscle strength suggests that thoracic expansion capacity may be directly related to respiratory muscle strength. As the expansion capacity of the thorax increases, inspiratory muscles may work more efficiently, which may have a positive effect on respiratory muscle strength.¹³ In this study, axillary and epigastric circumference differences were more pronounced, especially in active individuals, suggesting that physical activity may increase the flexibility of the thorax and thus the functionality of the respiratory muscles. Rodrigues et al. reported a correlation between upper extremity function and strength of the periscapular and trunk muscles.¹⁰ In contrast, in our study, none of the cervicothoracic postures, including the round shoulder posture, were found to be associated with upper extremity function in healthy young subjects. The 6PBRT can be considered an assessment of functional arm exercise capacity in chronic diseases and healthy adults in clinical practice and research. Age was negatively associated with the 6PBRT score in healthy individuals who were mostly physically active.³⁵ Öncü et al. reported that younger age and higher PA levels were associated with better functional arm exercise performance in healthy young adults.³⁵ In our study, upper extremity function was similar between activity levels.

Padkao et al. reported a positive correlation between MIP and MEP and walking distance in their study. However, the significance values suggest that expiratory muscle strength may be more related to functional capacity than inspiratory muscle strength.¹³ In our study, in parallel with this finding, MEP values of active individuals were higher than inactive individuals. Moreover, chest wall mobility was significantly higher in individuals who exercised regularly. This finding suggests that physical activity may positively affect chest wall flexibility and mobility.

Prolonged maintenance of poor posture may cause excessive pressure on the lumbar vertebrae, potentially leading to physical discomfort and the onset of myofascial pain syndrome.³⁶ Poor posture has a negative impact on the musculoskeletal system, causing localized muscle fatigue, and can affect physical function and skill levels.³⁷ Lu et al. showed that although poor posture is characterized by a forward head position, rounded shoulders, and increased thoracic kyphosis, maintaining this posture can affect other muscle groups. In the short term, poor posture can cause muscle fatigue in specific areas of the back and impair physical activity performance both immediately and over time.³⁸ In contrast, our findings show that fatigue severity in healthy young adults is not related to cervicothoracic posture but that fatigue is influenced by MEP. In addition, fatigue severity in inactive subjects was higher than that in active subjects. These findings suggest that factors beyond posture, such as MEP and physical activity level, may play a more significant role in fatigue severity in young adults. The discrepancy between our results and those of previous studies highlights the complexity of fatigue mechanisms and the need for a multifaceted approach to understand and address fatigue in this population.

The close to traditional significance of rounded shoulder posture on MIP and MEP suggests that changes in cervicothoracic posture may affect respiratory function in young individuals. Although these early postural changes have not yet significantly affected respiratory muscle strength, chest mobility, upper extremity function, or fatigue, they can potentially lead to more pronounced effects over time. This implies that early intervention and preventive measures such as promoting regular exercise and physical activity may be crucial for maintaining proper posture and preserving respiratory function as individuals age. Further research may be necessary to establish long-term relationships between cervicothoracic posture and respiratory health as well as to develop targeted interventions for young populations.

The strengths of our study are that it is the first to examine the effect of cervicothoracic posture angles on respiratory muscle strength, chest mobility, upper extremity function, and fatigue in healthy young subjects and the effect of smoking-adjusted data on these parameters. Our findings revealed that the negative effects of the round shoulder posture on MIP and MEP were of borderline significance. This finding suggests that larger sample sizes are needed to clarify the effects of rounded shoulder posture on respiratory muscle function. The limitations of this study are that pectoral muscle shortness was not measured in postural assessments, physical activity rate was not measured with objective measurements, and pulmonary function tests were not performed. Despite these limitations, this study provides valuable information on the relationship between cervicothoracic posture, respiratory muscle strength, upper-extremity function, and fatigue in young adults. The unequal group sizes and possible presence of confounding variables (e.g., age, BMI) represent limitations of the study. The unequal distribution of participants across subgroups and the limited sample size may have reduced the statistical power of the analyses, increasing the risk of a Type II error. This should be taken into account when interpreting the non-significant findings. Difficult to explain causality due to cross-sectional studies, correlation coefficients were not high. Further studies that comprehensively investigate the effects of unfavorable posture on long-term respiratory and exercise capacity in young adults are needed. Further research is needed to investigate the relationship between posture, MEP, physical activity, and fatigue severity in populations of various age groups under different health conditions.

Conclusion

In healthy young adults, cervicothoracic posture does not affect respiratory muscle strength or upper extremity function. The MEP is influenced by axillary chest mobility and affects fatigue. Activity level was related to MEP, chest mobility, and fatigue.

Footnotes

Acknowledgments

We thank the university students who voluntarily participated in this study.

Ethical approval

This study received prior ethical approval from the Tarsus University Ethics Committee (protocol number: 2024/34).

Informed consent

An informed consent form was included at the beginning of the survey, which presented the necessary information and recorded participants’ willingness to participate in the study. All the study participants provided written informed consent.

Author contributions

NE and FKÇ contributed to the design and implementation of the research, NE and VD analyzed the results, and wrote the manuscript. NE conceived the original and supervised the project.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

ORCID iDs

Nurel Erturk

Fatma Kubra Cekok

Volkan Deniz

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