Electromyographic analysis of deltoid muscle fatigue during abduction on scapular and frontal planes

The aim of the study was to compare the fatigue rates of the deltoid muscle portions in the scapular and frontal planes. Ten healthy men without shoulder muscle impairment took part in the study. They performed isometric arm abduction for 30 seconds against a resistance of load cell while the electromyographic data were collected. The electromyographic data were transformed by the Fast Fourier Transform, to obtain the median power frequency (MDPF). The changes in MDPF of the three deltoid portions in the scapular and frontal planes were compared. The acromialis and spinalis portions fatigued during the exercises. The clavicularis portion presented no fatigue. A statistically significant difference occurred between the clavicularis and the other two portions (P < 0.05). No differences were found when the planes were compared. It represents to practice no preferential order during rehabilitation. Moreover, the acromialis and spinalis portions fatigue, although the clavicularis portion did not fatigue. The actions of other muscles of the shoulder girdle can explain this fact. Moreover, these two portions need more attention to avoid fatigue during exercises. In general, therapeutic strategies for injured patients should not only be directed towards increased force, but also towards fatigue control during shoulder exercises.