Postural and respiratory functions of the pelvic floor muscles

Aims: Due to their contribution to modulation of intra-abdominal pressure (IAP) and stiffness of the sacroiliac joints, the pelvic floor muscles (PFM) have been argued to provide a contribution to control of the lumbar spine and pelvis. Furthermore, as IAP is modulated during respiration this is likely to be accompanied by changes in PFM activity. Methods: In order to evaluate the postural and respiratory function of the PFM, recordings of anal and vaginal electromyographic activity (EMG) were made with surface electrodes during single and repetitive arm movements that challenge the stability of the spine. EMG recordings were also made during respiratory tasks: quiet breathing and breathing with increased dead-space to induce hypercapnoea. Results: EMG activity of the PFM was increased in advance of deltoid muscle activity as a component of the pre-programmed anticipatory postural activity. This activity was independent of the direction of arm movement. During repetitive movements, PFM EMG was tonic with phasic bursts at the frequency of arm movement. This activity was related to the peak acceleration of the arm, and therefore the amplitude of the reactive forces imposed on the spine. Respiratory activity was observed for the anal and vaginal EMG and was primarily expiratory. When subjects moved the arm repetitively while breathing, PFM EMG was primarily modulated in association with arm movement with little respiratory modulation. Conclusions: This study provides evidence that the PFM contribute to both postural and respiratory functions.