A Randomized Controlled Trial of Chair Interventions on Back and Hip Pain Among Sewing Machine Operators: The Los Angeles Garment Study Pin-Chieh Wang, MS, PhD Beate R. Ritz, MD, PhD Ira Janowitz, PT, CPE Robert J. Harrison, MD, MPH Fei Yu, PhD Jacqueline Chan, MPH David M. Rempel, MD, MPH Objective: Determine whether an adjustable chair with a curved or a flat seat pan improved monthly back and hip pain scores in sewing machine operators. Methods: This 4-month intervention study random- ized 293 sewing machine operators with back and hip pain. The participants in the control group received a placebo intervention, and participants in the intervention groups received the placebo intervention and one of the two intervention chairs. Results: Compared with the control group, mean pain improvement for the flat chair intervention was 0.43 points (95% CI = 0.34, 0.51) per month, and mean pain improvement for the curved chair intervention was 0.25 points (95% CI = 0.16, 0.34) per month. Conclusions: A height-adjustable task chair with a swivel function can reduce back and hip pain in sewing machine operators. The findings may be relevant to workers who perform visual- and hand-intensive manufacturing jobs. (J Occup Environ Med. 2008;50:255–262) I n 2000, the garment industry em- ployed 11 million workers world- wide, with approximately 350,000 workers in the United States. 1 Most of the work is done by minimum wage, nonunion, immigrant women in shops that employ fewer than 20 persons. 2 The epidemiologic data linking garment work to an increased prevalence of neck and shoulder pain is relatively strong 3,4 ; while the data linking garment work to back and hip pain is mixed. A study using the data from National Health and Nutri- tion Examination Survey (NHANES) found that approximately 15% of all sewing machine operators reported lower back pain, but there was no statistically discernable difference when compared with other NHANES respondents. 5 Conversely, a cohort study of Danish workers hospitalized during a 10-year period for prolapsed lumbar intervertebral discs found that sewing machine operators were at ele- vated risk. 6 A different Danish pro- spective study of 327 sewing machine operators found that at baseline 38% experienced low back pain for more than 30 days in the past 12 months and 23% reported lower back pain during the past 7 days. 4 Comparable figures after 6 years of follow-up were 47% and 25%, respectively. Sewing machine operators per- form precision tasks while seated at a relatively fast pace with work cycles of 30 to 60 seconds. This repetitive, stereotyped work is typically per- formed on nonadjustable worksta- From the Department of Epidemiology (Drs Wang and Ritz), School of Public Health, University of California, Los Angeles, Calif; Department of Family Medicine (Dr Wang), David Geffen School of Medicine, University of California, Los Angeles, Calif; Division of Occupational and Environmental Medicine (Mr Janowitz and Dr Rempel), Department of Medicine, University of California, San Francisco, Calif; Occupational Health Branch (Dr Harrison and Ms Chan), California Department of Public Health, Richmond, Calif; Department of Biostatistics (Dr Yu), School of Public Health, University of California, Los Angeles, Calif. Address correspondence to: David Rempel, MD, University of California, San Francisco, Depart- ment of Medicine, 1301 S 46th Street, Building 163, Richmond, CA 94804; E-mail: david. rempel@ucsf.edu. Copyright © 2008 by American College of Occupational and Environmental Medicine DOI: 10.1097/JOM.0b013e318163869a JOEM • Volume 50, Number 3, March 2008 255