Influence of arm position on the EMG-force relationship in arm muscles

Abstract

The relationship between myoelectric signal amplitude and muscle strength (EMG-force) has been used as an indirect measure of muscle strength. The aim of this study, in 18 healthy, female, right-handed volunteers, was to assess the influence of arm position on the relationship EMG-force of arm muscles in three different tasks: arm flexion, arm abduction, and neutral arm position. Both myoelectric signals and strength measures were acquired simultaneously, by coupling a load-cell to the electromyograph transducer. Signals from the biceps brachii, braquioradialis, and triceps brachii muscles were analysed, and arm extension and flexion force was estimated. Relationships between these values were statistically analysed, searching for a correlation between myoelectric signal amplitude and muscle strength. Results showed no such correlation could be found during any of the tasks. Arm position did not influence EMG-force of the assessed muscles, to the exception of the triceps brachii muscle, which showed greater activity in the neutral arm task as compared to the other tasks. In isometric contractions, the tasks may be used to activate biceps brachii and braquioradialis; neutral arm position is indicated to activate the triceps brachii muscle.