What high-quality longitudinal studies exist measuring anal sphincter pressures over time in people who practice receptive anal intercourse?

1. What exists: a notable longitudinal cohort with only baseline analyses

The clearest ongoing longitudinal effort is the Prevent Anal Cancer study network, which enrolled sexual and gender minority participants and performed standardized digital anal rectal examinations (DARE) scored for resting and squeeze tone as part of a longitudinal protocol, but the published work reported here is a cross‑sectional analysis of baseline data rather than follow‑up sphincter pressure trajectories over time ^{[7] [1] [3]}.

2. Small clinical series and cross‑sectional studies that get closest — but fall short

Several small studies cited in the literature measured anal pressures or compared groups who had engaged in anal intercourse versus those who had not — sample sizes in earlier male cohorts were tiny (for example, studies with n=58 and n=24 are explicitly referenced) — and results are inconsistent for squeeze pressures and related symptoms like fecal incontinence ^{[7] [8] [9]}. Narrative and review articles summarize these small series and report associations such as reduced resting pressure in some receptive male cohorts, but they are not longitudinal in the sense of repeated manometry over years in RAI practitioners ^{[10] [11]}.

3. Older physiologic/technical longitudinal work was not focused on sexual behavior

There is longstanding physiologic research describing radial and longitudinal pressure variation within the anal canal and repeatability of pressure measures (e.g., studies of anal canal pressure mapping and probe diameters), but these studies were aimed at normative physiology or obstetric injury and do not prospectively track RAI exposure and sphincter pressure change over time ^{[5] [6] [12]}.

4. Why rigorous longitudinal evidence is scarce: measurement and design hurdles

Producing high‑quality longitudinal data requires repeated high‑resolution manometry or validated DARE scoring, accurate, confidential behavioral exposure measurement (frequency/technique/trauma), and long follow‑up to capture gradual sphincter change or incontinence outcomes; the literature explicitly notes small sample sizes, heterogeneous methods, and the absence of studies assessing the diagnostic accuracy of sphincter tone for RAI ^{[8] [3] [12]}. The Prevent Anal Cancer baseline analysis itself underscores these methodological constraints while rejecting the forensic utility of forced anal exams based on baseline findings ^{[7] [2]}.

5. Alternative interpretations and limitations in reporting

Some reviews and narrative pieces interpret small pressure differences as biologically plausible evidence that repeated dilation could reduce resting pressure, and cite single‑study findings (Miles et al. 1993 and Speakman et al. 1991) as suggestive of reduced resting pressure after anal dilatation, but these are not definitive longitudinal cohorts specifically designed around sexual exposure and often lack contemporary measurement standards ^{[10] [13]}. The available sources caution that cross‑sectional associations cannot establish causation and that sample sizes and confounders limit inference ^{[9] [12]}.

6. Bottom line — current evidence gap and next steps

There are no high‑quality longitudinal studies currently published that repeatedly measure anal sphincter pressures over time in cohorts defined by receptive anal intercourse exposure; the best existing resource is an active longitudinal cohort whose published output so far consists of baseline analyses that argue against the forensic use of DARE to detect RAI ^{[1] [3]}. What is needed are prospective studies with repeated manometry, standardized exposure measurement, adequate sample sizes, and multiyear follow‑up — a research agenda explicitly supported by reviews calling for prospective long‑term sphincter function studies ^{[12] [10]}.