Analysis of Muscle Fatigue During Supported and Unsupported Sitting using Surface Electromyography

The objective of this study is to understand fatigue of leg muscles (tibialis anterior and gastrocnemius) using surface electromyography (sEMG) when the feet are supported on the floor and when they are unsupported. Twelve healthy male volunteers participated in the study. Chair height was changed to two positions, i.e., (A) suit subject height perfectly - with feet supported on the floor, and (B) height higher than A and feet were suspended in air. Each seated position was tested for 20 minutes. Surface EMG signals were recorded bilaterally from the two groups of leg muscles for 60 seconds at 5 minutes intervals from 0th to 20th minute. These signals were filtered using a 4th order Butterworth filter with a pass band of 20-250 Hz and a 4th order notch filter with a stop band of 47-49 Hz. RMS values and mean power frequency (MPF) of the signals were calculated. Linear regression analysis was performed on MPF values and the RMS Values. Mann-Whitney `U' test was performed on the slope of the regression lines and the RMS values to determine if there was any significant difference in fatigue. Results indicated a higher muscle fatigue for height B. This suggests that while adjusting height of chair, identifying optimal height should be taken into consideration. In places where adjustable chairs are not available, provision for foot rest would be advisable, to avoid muscle fatigue.