The integrated electromyographic (IEMG) activity of the erector spinae (ES) muscles and the subjective comfort levels were monitored during static sitting in two types of chairs - a conventional office chair (COC) and a semi kneeling chair or back chair (BC). IMEG readings were taken at 4, 8, and 12 minute intervals at the thrid through fifth lumbar vertebrae (L3-L5) levels of the left ES of 20 healthy adults. A questionnaire to determine subjective comfort levels in regards to the neck, back and legs was given to each subject following completion of the IEMG readings. A paired t-test and Newman-Keuls post hoc analysis were used to compare IEMG levels for both chairs. Results showed a significant difference in IEMG levels for both chairs between the 4 , 8 and 12 minute intervals, and a significant difference between the two chairs at the twelve minute interval, with the BC showing lower IEMG levels than the COC . The COC was judged to be more comfortable and desirable to sit on than the BC based on subjective data obtained from the questionnaire.
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