16 Apr 2026

Pelvic Floor — Core Piston Analysis

Overview

Unlike the other exercise packages (shoulders lateral raise, triceps overhead extension), the pelvic floor is not a lever system. It operates as a pressure-management system where the diaphragm and pelvic floor form a coordinated piston within the core canister.

The animation maps a breath cycle onto the same v4/v5 engine pipeline:

• Concentric → exhale with PF lift (engagement 0° → 90°)
• Isometric top → hold at full engagement
• Eccentric → inhale with controlled PF descent (engagement 90° → 0°)
• Isometric bottom → hold in lengthened position

The "joint angle" axis is replaced by PF engagement level (0°–90°), where 0° represents end-of-inhale (PF descended, IAP high) and 90° represents end-of-exhale (PF lifted, dome restored, IAP managed).

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Three Rendering Modes

Mode	What it shows
movement	Clean sagittal animation: diaphragm and PF moving with breath, piston arrows, phase labels
forces	Full pressure analysis: IAP arrows, PF reaction force, gravity on organs, dome integrity readout, hip inset
coaching	Training cues: breath phase mechanics, engagement sensation, zone coaching, tempo, hip integration callout

Visualisation: Sagittal Core Canister

The FBD panel draws a sagittal cross-section of the core "canister":

• Spine (posterior, left) — vertebral column with vertebrae dots
• Abdominal wall (anterior, right) — slight breath-dependent bulge
• Ribcage (top) — arched lines forming the rigid frame
• Pelvis (bottom) — iliac wings, sacrum, pubic symphysis
• Diaphragm (teal dome, top) — ascends on exhale, descends on inhale
• Pelvic floor (purple dome, bottom) — lifts on exhale, descends on inhale
• Visceral contents (filled area between domes) — the mass pressing down

ROM Mapping

The v4 engine's ROM panel is repurposed:

• X-axis: Engagement level (0°–90°) instead of joint angle
• Demand curve (red): IAP load on the PF — follows cos(θ), highest at 0° (inhale)
• Capacity curve (blue): PF force–length capacity — schematic bell peaked at ~42°
• Zones: STRETCHED (0–30°) = lengthened PF | MID-ROM (30–60°) | SHORTENED (60–90°) = engaged

Key Differences from Lever-Based Exercises

Aspect	Lateral Raise / Overhead Extension	Pelvic Floor
System	Joint pivot, bone lever, torque ∝ sin(θ)	Pressure canister, dome geometry
Primary variable	Joint angle (degrees)	Engagement level (0–100%)
Demand driver	Gravity + moment arm	Intra-abdominal pressure (IAP)
Training emphasis	Eccentric for hypertrophy	Eccentric for functional resilience
Visualization	Arm/forearm rotating about pivot	Diaphragm-PF piston in sagittal section
Hip connection	Not applicable	Obturator internus shares fascia with PF

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Biomechanical Model

Three Strategies (from Gemini analysis)

Demand vs Capacity

• Demand (IAP on PF) is modelled as 0.15 + 0.85 × cos(engagement°) — highest at end-of-inhale (engagement = 0°), lowest at end-of-exhale (90°).
• Capacity uses a Gaussian peaked at ~42° (mid-range engagement), reflecting the PF's force–length relationship.
• The mismatch between demand and capacity is most pronounced at low engagement (lengthened PF under high IAP) — this is the eccentric control zone.

The Trampoline Model

The PF is not a squeeze-and-hold muscle. It functions like a trampoline:

• Springs (muscles) need the right tension — not too tight, not too loose
• Frame (pelvis) must be aligned — neutral, sit-bones wide
• Function is to absorb and rebound, not to clamp

This paradigm shift from "Kegel squeezing" to "pressure geometry management" is the core teaching point of the animation.

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Statistics Tools

1. Excel Calculator (generate_xlsx_v4.py)

Generates a 4-sheet Excel workbook:

Sheet	Contents
Calculator	Input body/position/breath data → PF load analysis, breath metrics, resilience indicators, wow-factor comparisons
IAP Curve	Engagement-level table + chart: IAP demand vs PF force-length capacity, zone analysis
Training Log	20-row log with auto-calculated cycle time, ecc:con ratio, eccentric control time, quality score
Resilience Analysis	Educational: dome geometry, piston coordination, hip integration, progression ladder, trampoline model, optimal tempo

Key inputs: bodyweight (kg), position code (1–5), activity code (1–4), breath tempo (inhale/exhale/hold durations), reps per set.

Key outputs: PF load index, peak demand (N), ecc:con ratio, eccentric control fraction, training quality score, functional resilience indicators.

2. CLI Stats Calculator (load_calc.py)

Reads input_sheet.csv and produces per-cycle stats including:

• Organ mass and force on PF (derived from bodyweight)
• Baseline and peak PF load (N) for given position + activity
• PF load index (normalised to standing rest)
• Cycle time, ecc:con ratio, eccentric control time/fraction
• Breath rate (cycles/min)
• Quality score

CSV columns: set_number, cycle_number, bodyweight_kg, position, additional_load_kg, activity, inhale_sec, exhale_sec, hold_top_sec, hold_bot_sec, rpe, notes

3. Postural Alignment Guide (measurement_guide.html)

Interactive HTML page with SVG sagittal body diagram and 6 assessment cards:

1. Pelvic tilt (neutral check)
2. Ribcage-over-pelvis alignment
3. Sit-bone awareness
4. Breath pattern (diaphragmatic vs chest)
5. Hip rotator engagement
6. Bodyweight

Key Difference from Lever Exercise Stats

Aspect	Triceps / Shoulders	Pelvic Floor
Primary metric	Torque (N·m)	PF load index (×)
Inputs	Bone lengths, load mass, ROM angles	Position, activity, breath tempo
Demand model	T = m × L × g × sin(θ)	PF_load = organ_mass × g × pos × act
Progressive overload	Increase weight or ROM	Increase position difficulty or activity demand
Training quality	Volume × intensity	Eccentric control time × position × ecc:con ratio
Measurement guide	Bone landmarks (tape measure)	Postural alignment (visual check)

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Dependencies

• Python 3.10+
• numpy, matplotlib
• Shared engine: v4_engine.py, diagram_lib.py
• Optional: ImageMagick (magick CLI) for optimised GIF assembly; falls back to PIL

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