Science Sunday | The Joint That Holds You Together
Put two fingers on the dimples at the base of your low back. Just below them sit your sacroiliac joints, one on each side, connecting your spine to your pelvis. Every step, stride, squat and stair sends your upper-body weight through these two joints on its way to your legs.
When they hurt, people describe it in nearly the same words. It's a deep ache on one side at the belt line or in the buttock. It gets sharper when you stand on one leg, climb stairs, roll over in bed or step out of the car.
It's also more common than most people realize. The SI joint is estimated to be the pain source for 15 to 30% of people with chronic low back pain that doesn't radiate from a nerve, and it is frequently misdiagnosed.
A joint built for load, held by muscle
The SI joint's surfaces are fairly flat and sit close to vertical. Flat surfaces are excellent at transferring load, but that near-vertical angle also exposes the joint to shear from gravity.
Your body keeps it stable in two ways. The first, form closure, comes from the joint's anatomy. The second, force closure, comes from muscles contracting and compressing the joint. The gluteus maximus is central here: it attaches right at the SI joint and stabilizes it by compressing across it.
Picture a book held between your palms. The firmer the squeeze, the steadier the book. Force closure is that squeeze, and your glutes supply much of it.
When the squeeze shows up late
In a study published in Spine, researchers compared men with SI joint pain to matched healthy controls while they stood on one leg and lifted the other. On the painful side, the internal obliques, multifidus and glute max all switched on later than normal, while the biceps femoris (a hamstring) switched on earlier. The authors concluded that this shift in timing can disrupt how load transfers through the pelvis.
The lesson is that timing matters as much as strength. When the stabilizing squeeze arrives after the load does, the joint absorbs that moment on its own, and the hamstring picks up work the glute was designed to do.
The encouraging part is that timing can be trained. Up to 95% of patients with SI joint pain report good to excellent functional improvement with physical therapy at two-year follow-up.
Outside support powers the inside system
Research on pelvic belts shows what happens when the pelvis gets external support. In one study, a belt worn high on the pelvis was most effective at reducing SI joint laxity, and a moderate tension worked as well as a firm one. In women with pregnancy-related pelvic pain, SI joint laxity dropped significantly with a belt. And in a 2019 study of 15 people with SI joint pain, hip extensor strength rose significantly when they wore a compression belt.
So the stability the joint gets from outside helps the muscles around it produce more force. External support and internal muscle work as partners.
Where The Stabilizer comes in
The Stabilizer builds these principles into something you wear through your whole workout. It works through three mechanisms:
• Direction. The integrated strapping system guides your hips and pelvis toward neutral, so every movement starts from a supported position.
• Signal. It cues the right muscles, especially the glutes, to fire at the right moment. That is the timing problem the Spine study identified.
• Adaptation. Repeated wear reinforces the pattern, so your body carries it forward after the session ends.
Our completed biomechanics study out of SDSU found improved hip moment and glute activation, faster reaction times, better control in the frontal and transverse planes, and a reduced loading rate. Ninety percent of participants reported feeling more stable. Each result lines up with what your SI joints need: glute activation for the squeeze, faster reactions for timing, and a lower loading rate for gentler impact.
Who feels this most
Anyone who spends a lot of time on one leg, which includes runners, hikers and pickleball and tennis players. It's also common during and after pregnancy. Pregnancy, falls and leg length differences are among the recognized triggers. Female and male pelvises differ, which is why Tighties designs separately for each from day one.
Is it SI or sciatica?
SI joint pain usually stays in the low back, buttock and back of the thigh, often on one side. Its symptoms can closely mimic sciatica, which makes it hard to diagnose. Numbness, tingling, or pain that shoots past the knee into the foot points toward a nerve root, and that's worth a visit to a clinician. (More on sciatica in an upcoming Science Sunday!)
The bottom line
Your SI joints stay stable when your muscles squeeze them at the right moment. The Stabilizer is built to support that squeeze while you move, and to train your body to produce it on its own.
Note: Persistent or worsening pain deserves an evaluation from a physician or physical therapist. Tighties works best alongside a strong clinical plan.
Sources
• Cohen SP, Chen Y, Neufeld NJ. Sacroiliac joint pain: a comprehensive review of epidemiology, diagnosis and treatment. Link
• Hungerford B, Gilleard W, Hodges P. Evidence of altered lumbopelvic muscle recruitment in the presence of sacroiliac joint pain. Spine. 2003;28(14):1593–1600. Link
• Damen L, Spoor CW, Snijders CJ, Stam HJ. Does a pelvic belt influence sacroiliac joint laxity? Clinical Biomechanics. 2002;17(7):495–498. Link
• Mens JMA, Damen L, Snijders CJ, Stam HJ. The mechanical effect of a pelvic belt in patients with pregnancy-related pelvic pain. Clinical Biomechanics. 2006;21(2):122–127. Link
• Choi J, Oh J, Kim M. The effect of pelvic compression belt on the strength of hip muscle and EMG activity in individuals with sacroiliac joint pain during prone hip extension. J Musculoskelet Sci Technol. 2019;3(1):14–21. Link
• Sacroiliac joint pain in the athlete. Link
