Contractions of specific abdominal muscles in postural tasks are affected by respiratory maneuvers

Hodges, Paul W., Simon C. Gandevia, and Carolyn A. Richardson. Contractions of specific abdominalmuscles in postural tasks are affected by respiratory maneuvers.J. Appl. Physiol. 83(3): 753-760, 1997.The influence of respiratory activity of the abdominal muscleson their reaction time in a postural task was evaluated. Theelectromyographic (EMG) onsets of the abdominal muscles and deltoidwere evaluated in response to shoulder flexion initiated by a visualstimulus occurring at random throughout the respiratory cycle.Increased activity of the abdominal muscles was produced by inspiratoryloading, forced expiration below functional residual capacity, and astatic glottis-closed expulsive maneuver. During quiet breathing, thelatency between activation of the abdominal muscles and deltoid was notinfluenced by the respiratory cycle. When respiratory activity of theabdominal muscles increased, the EMG onset of transversus abdominis andinternal oblique, relative to deltoid, was significantly earlier formovements beginning in expiration, compared with inspiration [by97-107 ms (P < 0.01) and64-90 ms (P < 0.01),respectively]. However, the onset of transversus abdominis EMGwas delayed by 31-54 ms (P < 0.01) when movement was performed during a static expulsive effort,compared with quiet respiration. Thus changes occur in earlyanticipatory contraction of transversus abdominis during respiratorytasks but they cannot be explained simply by existing activation of themotoneuron pool.