Pelvic floor muscles (PFM) contraction is often assessed during the quantification of PFM function, and it is the principal mechanism of the pelvic floor muscles training, as well as the first line of treatment of several PFM dysfunctions. However, comparisons about the effects of these muscle contractions on the cardiac autonomic modulation (CAM) in pre- and postmenopausal women are still not known.

To compare the effects of a PFM contractions protocol on heart rate variability (HRV) in rest and recovery, in apparently healthy pre- and postmenopausal women.

This is a cross-sectional study it was conducted at the Women's Health Research Laboratory, Federal University of São Carlos, Brazil. We recruited 37 apparently healthy women, aged between 20-70 years old, with a body mass index lower than 30 kg/m² and without history of pelvic surgery. Participants were divided into pre-menopausal group (PG=23, 24±3 years) and postmenopausal group (PMG=14, 57±7 years). The PFM protocol consisted of 8 min at rest in supine position, 10 sustained PFM contractions of 5 seconds each and 8 min recovery. The heart period (HP) was recorded during the protocol through a cardiac monitor (Polar® RS800CX Kempele, Finland). Resting and recovery HP variabilities (256 consecutive points of the tacogram) were assessed by representative time-domain indices (RMSSD and SDNN) and frequency domain indexes (LF and HF abs and normalized units).

PMG showed reduced time domain indices compared with PG (P<0.05). Frequency-domain indexes showed that PFM contractions can affect the cardiac autonomic control, in recovery condition, by increasing sympathetic cardiac modulation (LFabs) and reducing cardiac vagal modulation (HFabs), p<0.05, in PG only.

Postmenopause is associated with a marked reduction in heart rate variability indices. The PFM contraction can affect cardiac autonomic control physiologically, to meet the metabolic demands during exercise; however, reflecting on the increasing sympathetic cardiac autonomic and reducing vagal modulation in the recovery, mainly in PG.

Long-term safety, as well as interventions based on PFM to improve CAM in postmenopausal women, should be investigated in the future.