Hypopressive exercises (HEs) emerged in the 1990s, theorized by Caufriez [1] as a means of training automatic activation of the pelvic floor muscles (PFMs) through a reduction in intra-abdominal pressure generated by the performance of a maneuver involving volitional apnea at end expiration coupled with active expansion of the rib cage. Caufriez described HEs performed in specific hypopressive postures (HPs), although the rationale for these is unclear. Some clinicians around the globe have embraced HEs as an alternative to PFM training for the management of pelvic floor disorders despite a lack of empirical evidence of their effectiveness. 
In a separate abstract, we showed that, among 36 individuals with female genital anatomy who were naïve to HEs, the HE did not cause a reduction in IAP as suggested by Caufriez, but that it did result in contraction of the levator ani muscles (LAMs) and the external anal sphincter (EAS). We found no effect of the HP on IAP, LAM or EAS activation observed during the HE maneuver. The primary objective of this study was to determine if, among women who were evaluated when naïve to HEs, PFM strength or stiffness increased after practicing HEs for eight weeks. The secondary objective was to determine whether there is a learning effect (i.e., larger changes in IAP, electromyographic (EMG) activation of LAMs and EAS, and/or motion of urogenital structures) evident after eight weeks of HE practice.

This interventional cohort study received ethics approval from the local institutional research ethics board and all participants provided written informed consent prior to participating. 
Thirty-six healthy females who had attended two training sessions where they learned from a certified Hypopressive trainer how to perform HEs in supine (using the Demeter HP) and standing (using the Athenas HP), and a data collection session as described below, were invited to participate. Nine declined due to the time commitment (n=4), having Covid-19 (n=4) and being pregnant (n=1), thus this study included twenty-seven participants. 
The primary outcomes were PFM strength and stiffness. Secondary outcomes included transient changes observed in IAP, EMG amplitude of the LAMs and EAS, and pelvic morphology [levator plate length (LPL), bladder neck height (BNH) and levator plate angle (LPA)] observed on 2D transperineal ultrasound imaging (USI), acquired while participants performed HEs. 
At each data collection session, LAM strength and stiffness were first recorded using a custom intravaginal dynamometer. Participants were positioned in supine and the lubricated arms of the dynamometer were inserted vaginally. The arms were opened to a diameter of 35mm, and, after baseline force had stabilized, standardized instructions were provided to perform a maximal voluntary contraction (MVC), by squeezing their PFMs as hard as possible into the resistance provided by the dynamometer. Next, the dynamometer arms opened from an initial diameter of 15mm to a diameter of 40mm at a rate of 15mm/s and were held there for 7s while the participant kept their PFMs relaxed. The arms were then closed. Each task was repeated three times. 
Next, EMG electrodes were placed intravaginally over the LAMs and on the skin surface overlying the EAS, interfaced with Delsys (Boston, USA) differential preamplifiers and amplifiers. An IAP sensor [2] was inserted into the posterior fornix of the vagina. Participants performed three MVCs of their PFMs (maximal effort squeeze and lift). In random order, participants then performed three repetitions of the HE maneuver with and without the HP in supine and in standing while EMG, IAP and transperineal USI videos (GE Voluson S6; RAB6-D 4D convex curvilinear probe, GE, Toronto, Canada)] were acquired. This completed the data collection session.  
After the first assessment, participants were instructed to complete the HE program at least three times per week, completing three repetitions of each of the four tasks, until returning to repeat the data collection session eight weeks later. Adherence was monitored via regular email correspondence.
EMG data were bias corrected, full-wave rectified, and smoothed using a 4th order, dual-pass low-pass Butterworth filter (cut-off 6 Hz). The peak of the EMG signal during each HE task was normalized to the highest peak achieved during the three PFM MVCs. The greatest change in IAP, levator plate length (LPL), levator plate angle (LPA) and bladder neck height (BNH) observed during each HE was retained for analysis.
All outcomes were tested for normality (Shapiro-Wilk test). Paired t-tests were used to determine whether strength and stiffness changed after training and univariate t-tests were used to determine whether there were changes in IAP, EMG activation and/or pelvic morphology during the performance of the HE in the HP after the training period. Separate two-way, repeated-measures ANOVAs were used to determine whether there was an effect of testing session, the HP, or the interaction between testing session and HP on transient changes in IAP, EMG amplitude (LAMs or EAS), BNH, LPL, or LPA observed during the HEs in each position (i.e., supine, standing). An adjusted alpha (α=0.05/8) was used. 
A sample size of n=30 was determined apriori based on Brazalez-Navarro et al. [3] who reported moderate effect sizes for PFM tone (d=0.55) and strength (d=0.35) after an 8-week period of HE training.

Twenty-four of the 27 participants completed the second data collection session. Mean adherence was 2.86(0.66) sessions per week, with 71% reporting having performed at least three training sessions per week.
LAM strength tended to be higher at the first assessment [3.6(2.3)N] than at the second assessment (2.8(1.4)N, d=0.48, p= 0.04), while LAM stiffness remained unchanged between the first [6.6(1.8)N/mm] and second [6.1(1.6)N/mm, d=0.27, p=0.28] assessment. IAP, EMG and USI outcomes are presented by assessment visit in Tables 1 (supine) and 2 (standing). After training, there was a tendency towards a reduction in IAP (d=-0.584, p=0.012), and there was activation of the PFMs (LAMs: d=0.938, p<0.001 EAS: d=1.029, p<0.001) observed during the HE. There was no training effect on the magnitude of transient changes in any outcomes observed during the HE, nor on the influence of the HP on outcomes, with very small effect sizes.

Performing HE training for eight weeks had no effect on PFM strength or stiffness. While the training period was relatively short, it was longer than the time normally required to see improvements in force generating capacity attributable to improved contractile efficiency. The training period also failed to result in any enhanced effect of the HE on IAP, PFM activation or changes in pelvic morphology, and did not impact of the nil effect of the HP observed at the initial assessment. 
Despite the relatively small sample, the repeated-measures design was a strength. The effect sizes for the impact of the HP and visit on all outcomes were very small, supporting the lack of significant effects found on statistical testing.

Eight weeks of HE training did not induce any changes in PFM strength or stiffness and did not result in any learning effect on biomechanics observed during HEs.

Caufriez, M. Gymnastique abdominale hypopressive. Brussels: Ed. Bruxelles, 1997.
Niederauer, de Gennaro, J., Nygaard, I., Petelenz, T., & Hitchcock, R. (2017). Development of a novel intra-abdominal pressure transducer for large scale clinical studies. Biomedical Microdevices, 19(4), 80–10. https://doi.org/10.1007/s10544-017-0211-2
Navarro-Brazález, B., Prieto-Gómez, V., Prieto-Merino, D., Sánchez-Sánchez, B., McLean, L., & Torres-Lacomba, M. (2020). Effectiveness of Hypopressive Exercises in Women with Pelvic Floor Dysfunction: A Randomised Controlled Trial. Journal of Clinical Medicine, 9(4), 1149-. https://doi.org/10.3390/jcm9041149

Continence 12S (2024) 101363
DOI: 10.1016/j.cont.2024.101363