Sacroiliac Joint Pain in Runners: One-Sided Back and Buttock Pain Explained

What is the sacroiliac joint?

The sacroiliac (SI) joint connects the sacrum (the triangular bone at the base of the spine) to the ilium (the large pelvic bone) on each side. It transfers load between the upper body and the legs during running - every stride passes force through this joint.

Despite being a relatively stiff joint with minimal movement, it can become painful when the load distribution is disrupted. The pain is typically felt as a deep ache at one side of the lower back, into the upper buttock, and occasionally into the back of the thigh.

What causes it in runners?

• Asymmetrical loading - leg length discrepancy, running on a camber, or one-sided habits that load one SI joint more than the other
• Gluteal weakness - poor hip extension forces the pelvis to compensate, increasing SI joint stress
• Core weakness - insufficient lumbopelvic stability increases movement and load at the SI joint
• Sudden mileage increases
• Hip mobility restrictions - limited hip extension or internal rotation changes how force is transmitted through the pelvis

How to recognise it

The pain sits precisely at the posterior superior iliac spine (PSIS) - the bony dimple you can feel on either side of your lower back - and often spreads into the upper buttock.

It's typically:

• One-sided (bilateral SI pain is less common)
• Worse with prolonged standing on one leg, climbing stairs, or transitioning from sitting to standing
• Aggravated by running, especially at higher intensities

What helps

1. Glute strengthening

Hip thrusts, single-leg deadlifts, step-ups. The glutes are the primary dynamic stabilisers of the SI joint. 3 sets of 12 each.

2. Pelvic stability exercises

Side plank - lie on your side and lift the hips. 3 × 30 seconds per side. Trains the lateral stabilisers without loading the spine.

3. Bird dog

3 sets of 10 each side. Trains deep core stability in a position that doesn't provoke the SI joint.

4. Hip mobility - careful selection

Hip 90/90 stretch and figure-4 stretch are generally well-tolerated. Avoid aggressive lumbar rotation or asymmetric stretches during acute phases.

5. Running gait modifications

Increase cadence, reduce stride length asymmetry. Running on flat, symmetrical terrain is better than camber or constant turns.

When to see a professional

SI joint pain responds well to manual therapy in combination with exercise. If the pain is severe, unresponsive, or associated with neurological symptoms (numbness, tingling into the leg), a physiotherapist or sports medicine doctor should assess it.

Timeline

4–8 weeks for most runners with appropriate exercise. Addressing the asymmetry - whether structural or functional - is essential to prevent recurrence.