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Posture is usually defined as the relative arrangement of the parts of the body. Normal or standard posture is the state of muscular and skeletal balance that protects the supporting structures of the body against injury or progressive deformity. Forward shoulder posture (FSP) or “rounded shoulders” is one of the numerous deviations from the normal posture. Kendall et al1 describes FSP as abduction and elevation of the scapula and a forward position of the shoulders. In addition to abducted scapula, FSP also include winging of the scapula and medial rotation of the humerus.2 The aetiology of FSP has been attributed to several factors. Kendall et al1 state that posture and relative alignment of body segments are affected by muscle shortening and weakness. They describe FSP as the result of the shoulders being pulled by shortened or tight anterior shoulder girdle muscles, such as the serratus anterior, pectoralis major and minor, upper trapezius and intercostalis muscles. Additionally, FSP may be caused by weakness and lengthening of the muscles that function to pull the scapula toward the spine, such as rhomboids and the middle and lower trapezius muscles.3 4 According to Knudsen,5 FSP can be attributed to the presence of excessive and habitual flexion of the back, which will eventually cause the pectoral muscles to shorten and fix the shoulders in this forward position. Muscle length changes in FSP may result in abnormal scapulohumeral rhythm, impingement of rotator cuff tendons,6 acromioclavicular joint degeneration, bicipital tendonitis3 and painful trigger areas.7
Normal quiet breathing is accomplished by contracting of diaphragm and intercostalis externi. During expiration, the diaphragm simply relaxes and the elastic recoil of the lungs, chest wall and abdominal structures compress the lungs and expels the air.8 During forced or deep breathing, some accessory muscles can help respiration. The sternocleidomastoideus (draws sternum superiorly), serratus anterior and pectoralis minor (raise the ribs) and scalene (raise the two first ribs) muscles are accessory inspiratory muscles. Abdominal muscles (compress the abdominal contents upward against the diaphragm) and intercostalis interni are accessory expiratory muscles.4 8
Considering the effect of FSP on respiratory muscles, it is legitimate to question if FSP could alter pulmonary function. We are not aware of any previous research that has investigated this effect. Therefore, we conducted a study to evaluate if FSP alters pulmonary capacity.
In total, 40 female university students with FSP (mean (SD) age 22.4 (3.6) years, height 162 (5.4) cm, weight 55.2 (7.3) kg) were recruited. Subjects were excluded if they had a history of smoking, respiratory, cardiovascular, neuromuscular or orthopaedic disease. Details of the study were explained to the subjects and their informed consent was obtained. The study was approved by the Medical University of Shiraz for Health Sciences Research Committee Involving Human Subjects.
Measurement of forward shoulder posture degree
We developed a method for measuring sagittal plane postural alignment of the shoulder using computer-digitised photography, a technique that has been reported to provide accurate postural information.9 To perform the measurement, reflective markers were placed on the right side of each subject, on the tip of the spinous process of C7 and on the anterior tip of the acromion process. Subjects were asked to stand comfortably with arms by their sides in normal standing posture and to place their weight evenly on both feet. The lateral malleoli were placed between parallel lines, which are perpendicular to the frontal plane, 2 cm apart. These two lines were drawn to ensure that the subjects' position was kept at the same place while photographs were taken. The subject looked directly ahead. The camera was placed 2 m from the subject right side, perpendicular to the ground. The camera was used to send photosignals of the reflective markers to a computer equipped with the ability to convert this information into a file of three-dimensional coordinates. The software package utilised was Scion Image (Scion Corp, Maryland, USA). The angle formed by a line connecting C7 to the acromion process with a horizontal line was measured by the computer and provided a measurement of FSP in degrees. The measurement was chosen to coincides with those taken in the studies by Harrison et al and Chansirinukor et al.10 11 After a single series of five photographs, the subject was asked to sit for 60 seconds. To account for the variability presented by postural sway, each series of five measurements was repeated three times and a representative mean was calculated for each measurement.
Lung capacity was measured with the subject in a standing position, using a spirometer (Jaegar Co, Warzburg, Germany). A standard volume syringe (3 litres) provided by the manufacturer was used to calibrate the machine before each test. A nose clip was used during spirometry. After the method had been explained, the study participant was instructed to take a few normal breaths, inspire completely and then to exhale as hard and fast and for as long as possible until the lungs were completely empty. The experimenter provided verbal encouragement. Three acceptable trials were obtained for each subject. Vital capacity (VC), forced vital capacity (FVC) and expiratory residual volume (ERV) were recorded.
SPSS for Windows V.11.0 software (SPSS Inc, Chicago, Illinois, USA) was used for statistical analysis. To determine the variance of individual posture and pulmonary values between days, the experimenter used the method to take postural and pulmonary measurements of the 10 subjects at the same time of day on four different days over a 2-week period, and interclass correlation coefficients (ICC) were calculated. Two-tailed Pearson correlation coefficients between FSP values and spirometric parameters were calculated. Post hoc comparisons were made using Bonferroni criteria to maintain the effect of FSP degrees on spirometric values. The level of significance was set at p<0.05.
ICC was R = 0.84 for postural and R = 0.89 for pulmonary measures. Table 1 shows FSP and respiratory values of subjects. Table 2 shows that correlation was found between FSP values and VC (p = 0.009), FVC (p = 0.004) and ERV (p = 0.005). A distinct decrease in VC, FVC and ERV was seen with increasing FSP degree (p<0.05).
This study shows that FSP may affect pulmonary function and with increasing FSP degree; a distinct decrease was seen in respiratory values. FSP may affect pulmonary function by various mechanisms. Chang et al12 showed that an increase in energy expenditure due to hypertonic respiratory muscles may reduce ventilatory capacities. Shortening of respiratory muscles such as the serratus anterior, pectoralis minor and intercostalis in FSP3 4 may increase energy expenditure and reduce respiratory values. Our study supports this suggestion. Haas et al13 and Appel et al14 reported that altering the orientation of accessory muscles of respiration (as seen in FSP) has marked effects on the operating length and function of the diaphragm. Although we could not evaluate the effect of FSP on the operating length of the diaphragm, it is reasonable to assume that some alteration may occur.
McKeough et al15 reported that arm movements could alter lung volumes. They suggested that arm position may change rib cage expansion and affect respiration. FSP may decrease the expansion of the lungs during inspiration and reduce the compliance of the respiratory system.
Lai and Jones16 and Chow et al17 showed that carrying backpacks decreased FVC and ERV in normal schoolgirls. They hypothesised that such carriage increased the forward inclination of the trunk and/or increased shift of the upper trunk in the frontal plus the sagittal planes. This condition is similar to FSP, and that group’s spirometric results were consistent with ours.
There was significant correlation between FSP and respiratory values. The respiratory values are decreased with increasing FSP degree. Further studies are necessary to evaluate the exact mechanism of the effect of FSP on pulmonary function.