What is SI pain?

Sacroiliac joint pain is often a load-transfer and control problem expressed at the pelvis joint between trunk and legs.

What it commonly is

• A control failure during single-leg stance (walking, stairs, standing on one leg)
• A timing problem: the pelvis yields or shifts when it should be stiff
• A capacity problem: the system fatigues before the task is done
• An asymmetry that accumulates over time (one side does more work than the other)
• A pelvic floor coordination issue affecting force closure
• A hip extension failure that overloads the SI joint compensatively

What it commonly is not

• Not usually a structural misalignment that needs realignment
• Not typically caused by leg length differences alone
• Not primarily a flexibility problem (though mobility matters)
• Not a diagnosis you can make from symptom location alone
• Not always responsive to stretching (may worsen it)

The model

The SI joint’s job is to transmit force between the upper and lower body. It must be stiff at the right times and yield at the right times. This requires coordination between:

Force closure: muscles creating compression and stability across the joint (glutes, pelvic floor, deep spinal muscles, lats, thoracolumbar fascia tensioning)

Form closure: the joint’s inherent bony and ligamentous stability

Neural timing: the nervous system orchestrating when to stiffen and when to yield

Failure modes

When this system fails, common patterns include:

• Single-leg stance failure: pelvis drops, shifts, or rotates during walking or standing on one leg
• Hip extension failure: inability to extend the hip smoothly during gait; SI joint compensates by rotating or shearing
• Pelvic floor coordination issues: inadequate or mistimed force closure
• Asymmetry accumulation: one side fatigues faster or works harder, load transfer becomes uneven
• Fatigue collapse: the system holds up initially but fails after prolonged sitting, standing, or walking

Multipliers (not sole causes)

These amplify pain but are rarely the only problem:

• Poor sleep (increases sensitization and lowers pain thresholds)
• High stress (increases muscle tone and sympathetic drive)
• Inadequate fueling or hydration (reduces capacity and recovery)
• Central sensitization (nervous system amplifies normal signals)

Common patterns people report

Pain after sitting then standing

When you sit for a long time, glutes and hip extensors relax. Pelvic floor tone may drop. Standing up suddenly demands force closure and load transfer before the system is ready. The SI joint gets loaded unevenly or before stabilizers activate.

Pain late in a walk or run

Early in the activity, the system compensates. Fatigue accumulates. Control degrades. Hip extension timing fails or single-leg stance control breaks down. The SI joint starts absorbing load it can’t manage.

Pain on one side only

Load transfer is asymmetric. One side works harder, fatigues sooner, or has weaker stabilizers. Pain shows up where capacity fails first, which may not be the side with weaker muscles (sometimes the stronger side overworks).

Pain around the low back, butt, or hip

SI pain radiates. It can feel like low back pain, deep butt pain, or lateral hip pain. Symptom location does not tell you which structure is the problem. Pain often follows referral patterns that don’t match dermatomes.

Pain that improves with walking but returns later

Walking initially activates stabilizers and improves control. Over time, fatigue wins. Control degrades and pain returns. This is a classic fatigue-driven pattern.

Stretching feels good then pain rebounds

Stretching temporarily reduces tone and feels relieving. But if the problem is control or capacity, not tightness, the pain returns when you reload the system. Aggressive hamstring or hip flexor stretching can worsen instability.

Running triggers it even if biking does not

Running demands single-leg stance control and hip extension timing. Biking is bilateral and does not require pelvic stability in the same way. If single-leg control is your failure mode, running will expose it while biking may not.

Low-risk self-checks (not diagnostic)

These checks help you explore your own patterns. They are not diagnostic. Stop if pain spikes, feels sharp, or symptoms escalate for hours.

Single-leg stand

Stand on one leg for 20–30 seconds. Watch in a mirror or feel for:

• Does your pelvis drop or shift to one side?
• Do you feel unstable or have to work hard to stay upright?
• Does the standing side feel different from the other side?
• Do symptoms increase or change during or after?

Step-down control

Stand on a low step (4–6 inches). Lower the opposite foot slowly toward the ground and return. Do 5–10 reps per side. Note:

• Does your pelvis shift or rotate?
• Does one side feel harder or less controlled than the other?
• Do symptoms change?

Short walk test before and after sitting

Sit for 20 minutes, then stand and walk for 5 minutes. Do symptoms spike when you first stand or walk? Do they settle after a few steps or worsen as you walk? This pattern suggests a control or activation issue.

Suitcase carry symptom response

Carry a light weight (5–15 lbs) in one hand for 30–60 seconds while walking. Note:

• Does one side feel more stable than the other?
• Do symptoms change during or after?
• Does the loaded side feel better or worse?

This checks lateral stability and core control under asymmetric load.

Gentle hip extension check

Lie face down. Gently lift one leg a few inches off the ground, keeping the knee straight. Hold for 5 seconds. Do 3–5 per side. Note:

• Do you feel glutes activate or do you arch your back instead?
• Does one side feel weaker or less coordinated?
• Do symptoms change?

Stop rule

Stop if pain spikes, feels sharp, or symptoms escalate for hours. Self-checks should be exploratory, not provocative.

High-yield interventions (graded)

Start with low doses. Progress slowly. Stop if symptoms rebound for hours.

Single-leg stance practice

Stand on one leg for 10–20 seconds. Focus on:

• Keeping pelvis level
• Engaging glutes and core gently
• Staying tall through the spine

Start with 2–3 sets per side, once daily. Progress by adding time (up to 30–40 seconds) or adding small reaches or arm movements.

If symptoms spike, reduce time or frequency. If no improvement after 2 weeks, reassess.

Suitcase carries

Carry a light weight (5–20 lbs) in one hand while walking 20–40 meters. Keep torso upright and pelvis level. Do 2–3 carries per side, 2–3 times per week.

Progress by adding weight or distance. Stop if symptoms worsen during or rebound after.

Step-downs

Stand on a low step (4–6 inches). Lower the opposite foot slowly, then return. Focus on control, not speed. Do 5–10 reps per side, 2–3 times per week.

Progress by adding reps or height. If symptoms spike, reduce dose.

Lateral step-downs

Same as step-downs, but step to the side instead of forward. This challenges lateral pelvic control. Start with 5–8 reps per side, 2–3 times per week.

Controlled hip hinge patterning (light)

Stand with feet hip-width. Push hips back slightly while keeping shins vertical and torso upright. Return to standing. Do 8–10 reps, focusing on glute engagement and pelvic control.

Do not load heavily at first. This is about patterning, not strength. If symptoms spike, stop or reduce range.

Walking mechanics cues

While walking, try these cues:

• Push the ground back with your foot rather than reaching forward
• Feel glutes activate as your leg extends behind you
• Keep pelvis level as you step

Walk for 5–10 minutes with cues, 1–2 times daily. If symptoms worsen, revert to normal gait and reassess.

Pacing and flare logic

If an activity triggers symptoms, reduce dose by 30–50%. Gradually increase by 10–20% per week as long as symptoms stay stable. If you flare, rest 1–2 days and resume at a lower dose.

Flares are information: you exceeded current capacity. Adjust the dose, not the direction.

Conservative return-to-run progression

If running triggers symptoms:

1. Start with walk-run intervals: 1 minute run, 2 minutes walk. Repeat 5–8 times.
2. Progress only if symptoms stay stable for 3–5 sessions.
3. Gradually reduce walk time and increase run time.
4. Add distance before speed.
5. If symptoms spike, return to the last stable dose.

Do not rush. Building capacity takes weeks to months.

Rebound rule

If symptoms rebound for hours after an intervention, reduce dose by 30–50%. If symptoms still rebound, stop that intervention and reassess with a professional.

Things that often backfire (with model-linked reasons)

Aggressive hamstring or QL stretching

If the problem is control or capacity, aggressive stretching may reduce tone temporarily but worsen instability when you reload. Hamstrings and QL may be working overtime to compensate for weak stabilizers. Stretching them without addressing the control problem can make things worse.

Chasing alignment fixes daily

Daily realignment (via adjustments, self-manipulation, or stretching) may feel temporarily relieving but does not build capacity or control. If you need realignment every day, the problem is not alignment—it’s stability under load.

Long sitting without breaks

Prolonged sitting deactivates glutes and pelvic floor. Standing or walking afterward requires sudden activation and load transfer. If your system can’t handle that transition, you’ll get symptoms. Break up sitting with short walks or standing every 30–45 minutes.

Heavy bilateral lifting as first intervention

Heavy deadlifts or squats require coordinated pelvic stability. If single-leg control is failing, bilateral lifts may overload the system before it’s ready. Start with single-leg work and controlled patterning before loading heavily.

Bracing hard all day

Bracing constantly (holding abs tight, clenching glutes) fatigues the system and reduces variability. The pelvis needs to yield and stiffen at the right times, not be rigid constantly. Chronic bracing can worsen pain and reduce capacity.

Red flags and when to get evaluated

See the Safety page for full details. Seek urgent evaluation for:

• Loss of bowel or bladder control
• Saddle anesthesia or progressive weakness
• Fever with back pain
• Unexplained weight loss or history of cancer
• Major trauma or severe unrelenting night pain
• New severe neurologic symptoms

Seek prompt evaluation if:

• Symptoms worsen despite conservative management over 6–8 weeks
• Pain limits daily function significantly
• You’re unsure if this model matches your situation
• Symptoms are confusing or not responding as expected

References and further reading

This guide draws on concepts from:

• Motor control and movement science literature
• Load management principles from sports medicine and rehabilitation
• Clinical experience with pelvic and SI pain patterns
• Systems thinking applied to persistent musculoskeletal problems

No specific citations are provided to avoid fabricated references. Consult a qualified healthcare provider for evidence-based assessment and treatment recommendations.

For deeper context on principles, see:

• Principles page
• Topics: Load Tolerance
• Topics: Motor Control
• Topics: Single-Leg Stance and Gait