Influence of Hamstring Tightness on the Functions of Lumbar and Pelvic Regions among Sewing Machine Operators in a Garment Factory of Colombo District

Introduction: Clinical evidence suggests that hamstring tightness influences lumbar pelvic rhythm and shortened hamstring increase the risk of injury to the spine. Objectives: To determine the association of hamstring tightness with pelvic tilt in standing position, trunk, and lumbar range of motion during forward bending among sewing machine operators Methods: A descriptive cross-sectional study was conducted among 169 sewing machine operators aged 18-55 years using passive knee extension test, tri-goniometric method, finger to floor test and modified Schober test to measure hamstring tightness, pelvic tilt, trunk flexion and lumbar flexion, respectively. Results: A weak negative correlation between hamstring tightness and lumbar range of motion during forward bending (r=-0.28; p=0.001). A significant association between trunk flexion and hamstring tightness (r=0.47; p=0.001). Conclusions & Recommendations: Hamstring tightness affects the lumbar and trunk range of motion during forward bending.


Introduction
Muscle tightness occurs due to reduced ability of the muscle to deform and reduce the range of motion of the joints it acts on (1). Inability to achieve greater than 160° of knee extension when the hip flexes to 90° is considered as 'hamstring tightness' (2). Causes of hamstring tightness are genetic influence, muscle injury, some chronic conditions and sedentary lifestyle (3). Clinical observations suggest that hamstring tightness influences lumbar pelvic rhythm. Shortened hamstring muscle increases the risk of injury to the spine from mechanical stresses (4)(5). Furthermore, it is a possible risk factor for mechanical low back pain (4)(5)(6)(7)(8).
Sewing machine operators play a key role in the economy as the apparel industry brings the largest export income to the country (9), and forward bending is commonly seen among them during work. Sri Lanka reported high incidence in back pain (57.3%) in the study done by Lombardo (2017) among female garment factory workers 10). Therefore, hamstring tightness ( can be a significant but unrecognized cause of their back pain. This study aims to find the influence of hamstring tightness on pelvic tilt in standing position and lumbar and trunk flexion during forward bending among sewing machine operators in Sri Lanka.

Methods
A descriptive cross-sectional study was conducted among 169 sewing machine operators from a largescale garment factory in the district of Colombo. Sewing machine operators aged 18-55 years with a minimum six hours of continuous sitting at work per day for a minimum of five days per week and employed at the current position continuously for a minimum period of six months were selected using a simple random sampling method. Employees with previous musculoskeletal or neurological conditions associated with hip, knee or spine, leg length discrepancy, pregnancy and employees who were not physically and psychologically fit at the time of data collection were excluded.
Socio-demographic and work experience-related data were collected using an intervieweradministered questionnaire. Questions were explained to the participants by their preferred language and filled according to their best response. In addition, physical assessments were done to test hamstring muscle tightness, pelvic tilt, trunk flexion and lumbar flexion.

Hamstring tightness
Hamstring tightness was measured using the passive knee extension (PKE) test as described by Davis et al. (2008) (2). Validity and reliability of PKE have been described by previous studies (2,12). When hip was 0 passively extended to 90 and the leg until the participant felt maximum tolerable stretch, the knee extension angle (KEA) was measured. KEA of more than 200 indicated hamstring muscle tightness (2). The dominant leg was determined as mentioned by OʼHora, (2011) (11).

Pelvic tilt
Pelvic tilt was measured using Tri-goniometric Method. The validity and reliability of this method are established in previous studies (16). The procedure was done according to Sanders et al., 1981 (17).
When participant stood with feet approximating a designated line on the floor, the dominant side anterior superior iliac spine (ASIS) and posterior superior iliac spine (PSIS) were palpated and marked with the non-allergic marker pen. Then, depth calliper was placed over the marked ASIS and PSIS, which were compressed to 'firm resistance' and recorded the distance between them. Then, with a sliding pointer on a meter stick mounted on a wooden base, distances from the floor to the marked ASIS and PSIS were measured. All measurements were taken to the nearest millimetre. Pelvic tilt values were categorized into three categories as < 00 anterior pelvic tilt, 00-230 neutral and >230 posterior pelvic tilt (18).

Trunk flexion
Fingertip to Floor Method was used to determine trunk flexion. The validity and reliability of this method have been established in previous studies (19)(20). The procedure was done according to Perret (2001) (20). The participant stood erect on a platform 20cm high, feet together and then bent forward as far as possible while maintaining knees, arms and fingers fully extended. The distance between the middle finger of the right hand and platform was measured in centimetres using the tape.

Lumbar flexion
Modified Schöber Test, according to the Bath Ankylosing Spondylitis Functional Index (BASFI), prepared by the National Ankylosing Spondylitis Society (13) was used to determine lumbar flexion. The participant stood with the outer edge of bare feet 30cm apart and feet in a line. The midpoint of L4/L5 junction was marked; and points 10cm above and 5cm below it were also marked. Then the participant bends forward as far as possible while maintaining knees and arms fully extended. The distance between the upper and lower two points was measured. Lumbar motion was categorized into 3 groups: > 4cm -mild; 2-4cm -moderate; and <2cm -severe (13).

Data analysis
The Statistical Package for Social Sciences (SPSS) version 22.0 was used for data analysis. Descriptive statistics to analyse the characteristics and demographic features and Spearmen correlation test to determine the correlation between the variables were used. A P-value less than 0.05 was considered as statistically significant to determine association with hamstring tightness.

Discussion
No previous studies have been conducted to find out the relationship between hamstring tightness and pelvic tilt in standing position, and trunk and lumbar range of motion during forward bending among sewing machine operators in Sri Lanka. However, literature revealed a high prevalence of hamstring tightness among sewing machine operators (15).
A statistically significant, moderate correlation (r=0.47; p=0.001) between dominant side hamstring tightness and trunk flexion during forward bending was found, which was consistent with the findings of Carregaro et al. (21) and Shin et al. (22). This study also indicated a statistically significant weak negative correlation (r=-0.28; p=0.001) between dominant side hamstring tightness and lumbar motion during forward bending, suggesting that hamstring tightness is not strongly related to the excursion of lumbar spine during forward bending. These findings are consistent with other studies (23). Jhonson et al. (24) concluded that hamstring flexibility is weakly related to the amount of lumbar flexion, while Li et al. (26) revealed that stretching of hamstring was not affected by the amount of lumbar motion during partial and full-forward bending. The study of Esola et al. (25) concluded that participants with low back pain history used more lumbar flexion during the beginning phase of forward bending when the hamstrings are not in a lengthened position.
These study data revealed that the amplitude of trunk flexion is relatively higher than lumbar flexion, and this phenomenon is known as "relative flexibility", discussed in a previous study (27). The results of mean pelvic tilt in the dominant side (11.08; SD 6.69) and statistically insignificant Pearson correlation (p<0.05) between dominant side hamstring tightness and pelvic position in standing were consistent with the findings from previous studies (16,28).
These results may conflict with the popular clinical opinion that tight hamstring causes posterior pelvic tilting as the mean PKE angle was 25.69. Yet, the decreased muscle length did not significantly influence the pelvic position. This change has been discussed in previous studies (29)(30).

Public Health Implications
The findings of our study will be important to make suitable adaptations to prevent and minimize the hamstring tightness among sewing machine operators in future and consider the hamstring tightness during their treatment for musculoskeletal pain. This will be important to reduce the health care cost in the garment and will improve the quality of work of sewing machine operators, which will indirectly affect the economy of Sri Lanka.

Author Declarations
Competing interests: The authors declare that they have no competing interests.
Ethics approval and consent to participate: Ethical approval was obtained from the Ethics Review Committee, Faculty of Medicine, General Sir John Kotelawala Defence University, Sri Lanka.
Funding: This research received no specific grant or funding from any funding agency in the public, commercial or non-profit sector.

Conclusions & Recommendations
Our data indicated weak yet a statistically significant negative correlation between dominant side hamstring tightness and lumbar motion and a statistically significant moderate correlation between dominant side hamstring tightness and trunk flexion during forward bending. Previous studies mentioned that physical activity programs including stretching, weight training and warm-up exercises improve the joint range of motion, flexibility and personal values of employees while reducing work-related musculoskeletal disorders which affect the production quality of companies (14). Further studies with a larger sample size will help to generalize these findings.