IRCT2015051122207N1 IRCT 2015-10-11 Vice Chancellor for Research of Iran University of Medical Sciences Comparison Lumbar posture, trunk muscle activation and comfort during working with a microscope when sitting on a saddle chair and traditional chair. Comparison Lumbar posture, trunk muscle activation and comfort during working with a microscope when sitting on a saddle chair and traditional chair. 2015-09-23 anticipated 12 Complete https://irct.ir/trial/19209 interventional Randomization: N/A, Blinding: Not blinded, Placebo: Not used, Assignment: Single, Purpose: Other. N/A Intervention group using each kind of seat and finally evaluation of comfort and posture with electrogoniometer is done. In fact, this is not the sham and control groups. And each participant to work with two chairs..