Sven Carlsöö

THE STATIC MUSCLE LOAD IN DIFFERENT WORK POSITIONS: AN ELECTROMYOGRAPHIC STUDY∗

Abstract In order to ascertain which muscles and muscle groups are engaged in various standing work positions an electromyographic study was performed.About twenty muscles or muscle groups were examined. Both coaxial needle electrodes and surface electrodes were employed. The analysis of the muscle activity for different postures was based on action potentials recorded in a normal symmetric standing rest position. Among the different postures the rest position appears to require the least muscular effort for counterbalancing the effect of gravity on the various parts of the body. This state of equilibrium seems to be maintained by certain muscle groups, referred to hero a.s the “ prime postural muscles ”. Only a part of the potential power of the postural muscles is utilized in maintaining the standing symmetric rest position. Some persons engage other muscles besides the prime postural muscles, possibly because they stand in such a way that the load distribution is not optimal, or thoy havo weak prime po...