The Pelvis Isn’t Frozen: Why Millimeters Matter

In this episode of From the Ground Up, Dr. Becky Allen addresses disagreement in online pelvic health discussions by clarifying key biomechanics terms and why they matter clinically. She explains that the pelvis is neither rigid nor wildly unstable, but moves in small, meaningful ways affecting pelvic floor function, pressure management, and force transfer. Dr. Becky distinguishes pelvis-on-femur motion (pelvis rotating over a relatively fixed femur in gait, squats, lunges, etc.) from innominate/ilium rotation and from sacral nutation/counternutation, describing how these related motions influence hip external rotators and pelvic floor length-tension. Ilium internal rotation is linked with pelvic outlet widening and posterior rotation/extension, while external rotation narrows the outlet with anterior rotation/flexion. She also clarifies that mobile pelvis models exaggerate motion for teaching, but millimeters of SI joint motion still affect symptoms such as leaking, heaviness/prolapse, pain, hip pinching, bowel mechanics, and birth mechanics.(00:00) - Biomechanics Drama Setup(03:06) - Key Terms and Definitions(04:02) - Pelvis on Femur Motion(06:38) - Pelvic Floor Effects in Gait(09:40) - Innominate and Ilium Basics(12:22) - Ilium IR and Outlet Opening(15:01) - Ilium ER and Outlet Closing(17:45) - Why Models Exaggerate Motion(19:48) - Sacrum Nutation Explained(24:30) - Why Millimeters Matter Clinically(26:26) - Wrap Up and ShareJoin my email list so you don't miss what I am building next! https://www.thepelvicpowerhouse.com/sign-me-upGrab your free guides:* From the Ground Up: The Foot + Pelvic Floor Connection: https://www.thepelvicpowerhouse.com/fromthegroundup* From the Top Down: From the Ribcage to the Pelvic Floor: https://www.thepelvicpowerhouse.com/fromthetopdown Clinicians, be sure to learn about Dr. Becky and Dr. Corrie’s Pelvic Powerhouse Clinical Mastermind: https://www.thepelvicpowerhouse.com/group-clinical-mastermind-2026-live Follow Becky on Instagram: https://www.instagram.com/drbeckypelvicpt/ Follow Genesis PT and Wellness on Instagram: https://www.instagram.com/genesisptwellness Subscribe to "From the Ground Up with Dr. Becky Allen”: * Apple Podcasts: https://apple.co/47eQP84 * Spotify: https://open.spotify.com/show/4QMmH0LDL0CrCEvVpJaOzd * YouTube: https://www.youtube.com/@FromTheGroundUp-u4n/ Pelvic health professionals, if you want to grow your practice, provide great patient care, and create the life and business you love, then visit The Pelvic Powerhouse: https://www.thepelvicpowerhouse.com/ "From the Ground Up with Dr. Becky Allen” is the podcast for pelvic health pros who are done playing small in the clinic or in business. Your host is Dr. Becky Allen, a physical therapist and the founder and visionary of Genesis PT & Wellness. As your coach, Becky will share with you what it really takes to lead a mission-driven, team-powered, game-changing pelvic health practice.