Effects of the Ball-backrest Chair Combined with an Accelerometer on the Pain and Trunk Muscle Endurance of a Computer Worker with LBP

Abstract

[Purpose] This study examined the effects of a ball-backrest chair combined with an accelerometer on the pain and trunk muscle endurance of a computer worker with low-back pain (LBP). [Subject and Methods] A 36-year-old male with a flat back who complained of LBP at the L3–5 level was the subject. He used the ball-backrest chair when working at a computer for 1 week. [Results] After using the ball backrest, the trunk extensor and flexor muscle endurance times had increased compared with the baseline and the VAS score had decreased from 7 to 4. [Conclusion] Combining exercises with information on motion is a useful common treatment approach for improving trunk muscle endurance in LBP.

INTRODUCTION

Poor posture while working at computers might increase the risk of work-related musculoskeletal problems by decreasing the strength of the spine-stabilizing muscles and increasing the compressive forces on the articulations of the spine¹⁾. Various chairs have been designed to promote a correct seating posture while maintaining comfort and functionality²⁾. Numerous studies have investigated the impact of chair design parameters and the position of computer monitors on the neck, shoulder, and back pain, including the backrest type³⁾. Yoo et al.⁴⁾ first designed the ball backrest to exert a continuous external load via the tension of the ball against the trunk. They reported that the activities of the serratus anterior and middle trapezius muscles, known to be weakened in subjects with upper-cross syndrome, were significantly higher when a ball-backrest chair was used⁴⁾. However, they suggested further clinical studies of the long-term effects of the ball-backrest chair on subjects with pain. Therefore, this study examined the effects of the ball-backrest chair combined with an accelerometer on pain and trunk muscle endurance of a computer worker with low-back pain (LBP).

SUBJECT AND METHODS

A 36-year-old male, with a height of 176 cm, weight of 55 kg, and a flat back, who complained of LBP pain at the L3–5 level was the subject of this study. Ethics approval was obtained from the Inje University Faculty of Health Science Human Ethics Committee, and the subject provided with written informed consent to participation before commencing the study. He complained of continuous LBP for 8 months, but had not received any specific treatment for this condition. When he flexed forward in the standing position with his knees fully extended, he experienced pain, assessed on a visual analogue scale (VAS), of score 7. He had mechanical LBP without radiating pain. The ball-backrest chair had a 25-cm-diameter ball instead of a general-purpose backrest. The center of the ball backrest was placed at the horizontal height of T5–T7⁴⁾ (Fig. 1). We attached an accelerometer to the ball backrest. The capacitive components of an accelerometer are commonly used to convert mechanical motion into an electrical signal. The analog signal was converted to a digital signal with an A/D converter (NI USB-6009, National Instruments; Austin, TX, USA). The accelerometer detected linear motion and provided visual feedback with the aid of graphic software featuring a user-friendly interface in LabVIEW (National Instruments). Motion during computer work and associated ball-backrest motions were plotted using a visual display to provide biofeedback (Fig. 1). We evaluated LBP using the VAS, and measured trunk muscle endurance. The trunk extensor endurance test measures the time a subject can hold the extended spine horizontal on a table edge with his thighs, knees, and ankles supported on the table (Biering–Sørensen test). The starting position for the trunk flexor endurance test involved positioning the subject on a plinth with his back resting against a wedge maintaining 60° flexion from the horizontal. The knees were flexed at 90°, and the feet were secured with a seat belt. The time this posture could be held was measured. These isometric trunk endurance tests have good reliability regardless of history of LBP⁵⁾. The subject generally worked 5 hours a day. He used the ball-backrest chair when working at a computer for 1 week.

Fig. 1.

Ball-backrest combined with an accelerometer

RESULTS

The initial VAS score was 7; the initial trunk extensor muscle endurance time was 40 sec; the initial trunk flexor muscle endurance was 32 sec. After using the ball backrest combined with an accelerometer, the trunk extensor muscle endurance time had increased compared with the baseline (83 vs. 40 s), as had the trunk flexor muscle endurance time (64 vs. 32 s), and the VAS score had decreased from 7 to 4.

DISCUSSION

This study examined the effects of a ball-backrest chair combined with an accelerometer on the back pain and trunk muscle strength of a computer worker with LBP. It has been shown that specific exercises are more effective than other treatments for LBP. After using the ball-backrest combined with an accelerometer, the trunk extensor and flexor muscle endurance times had increased markedly, and the VAS score had decreased. Clinically, a subject is considered to have failed the trunk extensor and flexor muscle endurance tests when times are less than 60 s and 50 s, respectively. The literature suggests that sufficient trunk muscle endurance contributes to spinal stability during prolonged, strenuous physical tasks⁶⁾. Adequate trunk muscle endurance may play an important role in injury-free performance^{6, 7)}. O’Sullivan et al.⁷⁾ showed that decreased trunk muscle endurance is associated with habitual adoption of a passive sitting posture and reduced activity levels. Biofeedback using an accelerometer can provide information on the quantity of motion. Van Dieen et al.⁸⁾ found that stature was improved after 3 hours of sitting in two dynamic chairs compared with sitting in a fixed chair. Our ball-backrest platform acts as a dynamic chair and featured biofeedback. A combination of exercise with information on motion is widely considered useful for improving trunk muscle endurance in LBP.