Erector spinae muscle activity, back comfort level and sitting pattern: Comparison between sitting without back rest and with back rest mounted by back cushions made from compressed sponge or memory foam

Abstract

Introduction: Prolong sitting in improper posture is a cause of low back pain. Sitting with back cushion supporting lordosis of lumbar spine and sitting in suitable pattern help muscle to relax, reduce intervertebral disc pressure and decrease back injury. The objectives were to investigate 1. electromyographic (EMG) activity of Erector spinae (ES) 2. back comfort level and 3. sitting pattern during typing computer and to compare the results between sitting without back rest and with back rest mounted by back cushions that made from compressed sponge or memory foam.

Method: Study design was repeated measurement. Twenty healthy female volunteers, aged between 18 to 25 years, were willing to sign an informed consent for the study. Sitting order was randomly assigned with three sitting conditions that were 1) sitting without back rest 2) sitting with back rest mounted by compressed sponge back cushion and 3) sitting with back rest mounted by memory foam back cushion. EMG signals of ES muscle were recorded and normalized EMG were calculated. Back comfort level and sitting pattern were also evaluated.

Result: Normalized EMG of ES muscle after thirty minutes sitting had no statistically significant difference (p = 1.000) when compared among sitting without back rest and with two types of back cushions on back rest. Using back cushions had a statistically significant higher comfortable level (p < 0.001) more than without back rest. Two upright sitting patterns were found 1) both thoracic and lumbar curve were in slightly flexion pattern and 2) thoracic was slightly flexion while lumbar was in extension pattern.

Discussion and Conclusion: This study found that postures during thirty minutes typing computer on seat were well controlled by ES muscle. Sitting with back cushion had more comfortable than without back rest. Both compressed sponge and memory foam cushion could be used for applying on back rest. Erect sitting posture patterns have been shown either sit with lumbar flexion or extension.