Electromyographic activity of human parasternal intercostal muscles during thoracic rotation

Abe Tadashi, Kobayashi Chisato, Namai Seiyu, Yokoba Masanori, Yamada Takumi, Katagiri Masato

The parasternal intercostal muscles (PARA) have been recognized as primary inspiratory muscles of the rib cage, but there is no information on the postural activity or phasic electromyographic (EMG) activity during thoracic rotation in humans. We examined the EMG of right PARA using fine-wire electrodes, in 5 healthy male subjects. With subjects breathing through a mouthpiece, airflow, and raw and moving-averaged EMG signals were sampled to computer, during thoracic rotation with breath holding and resting breathing with or without voluntary thoracic rotation. Maximum EMG (EMGmax) was defined as the greatest moving-averaged EMG activity recorded from each subject during slow inspiratory maneuver from functional residual capacity (FRC) to total lung capacity (TLC). With rightward thoracic rotation without breathing, obvious tonic EMG activity of right PARA was observed in all subjects. During resting breathing without thoracic rotation, there was respiratory-related phasic EMG activity of PARA during inspiration in all subjects. With rightward thoracic rotation, respiratory-related phasic EMG activity of PARA significantly (p<0.025) increased from 8.1±7.9 (mean±SD) %EMGmax to 17.5±12.9 %EMGmax. On the other hand, with leftward thoracic rotation, it significantly (p<0.025) decreased to 6.0±7.7 %EMGmax. We conclude that 1) PARA has a postural function like internal or external intercostal muscles, and 2) respiratory function of PARA is affected by thoracic rotation.

Electromyographic activity of human parasternal intercostal muscles during thoracic rotation

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