Single-Leg Stance and Gait

Walking and running are repeated single-leg stance events. Each step requires the pelvis to stay stable while the rest of the body moves. When single-leg control fails, the SI joint often pays the price.

What single-leg stance demands

When you stand on one leg:

The pelvis must stay level (or close to level)
The standing hip must support your body weight
Core and glutes must create stability
The opposite leg swings forward without pulling the pelvis into rotation

If any of these fail, the pelvis drops, shifts, or rotates. The SI joint absorbs load it was not designed to handle alone.

Why walking exposes control failures

Walking is dynamic single-leg stance. You have milliseconds to stabilize the pelvis before the next step. Fatigue, poor timing, or inadequate strength causes the system to break down.

Common failures during walking:

Pelvic drop: hip abductors (glute med/min) do not stabilize; pelvis drops on the swing side
Pelvic shift: trunk shifts over the standing leg to compensate for weak stabilizers
Pelvic rotation: the pelvis rotates excessively because core or glutes do not control it
Late glute activation: glutes activate after hip extension instead of during; SI joint compensates by rotating or shearing

These failures accumulate. Early in a walk, you compensate. Over time, fatigue wins and symptoms appear.

Hip extension and gait

Hip extension (leg moving behind you) is a critical phase of gait. It requires:

Glutes extending the hip
Pelvis staying stable (not rotating or tilting)
Coordinated timing so the SI joint stays compressed

If glutes are weak or late, the pelvis compensates by rotating. The SI joint moves more than it should. Over many steps, this overloads the joint.

Running amplifies this. Each step has higher force and shorter ground contact time. Less time to stabilize means more demand on timing and control.

Why biking often does not trigger symptoms

Biking is bilateral and does not require single-leg pelvic stability. Both legs work together. The pelvis stays supported by the saddle. If your problem is single-leg control, biking may feel fine while walking or running triggers symptoms.

This is diagnostic information: it points to a control problem during single-leg stance, not a general hip or pelvic strength issue.

Assessing your single-leg control

Try these self-checks (see SI Pain page for full details):

Static single-leg stance

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

Does your pelvis stay level or drop on one side?
Do you shift your trunk over the standing leg?
Does one side feel harder than the other?

Step-down test

Stand on a low step. Lower the opposite foot slowly. Does your pelvis stay level or does it drop or rotate?

Walking observation

Walk slowly in front of a mirror or record yourself. Does your pelvis drop or shift with each step? Do you lean your trunk excessively?

If any of these show pelvic drop, shift, or rotation, single-leg control is likely part of your problem.

Improving single-leg stance control

Start with static practice:

Single-leg stance: 10–20 seconds per side, 2–3 sets, once daily. Focus on keeping pelvis level and staying tall. Progress by adding time or small reaches.

Progress to dynamic tasks:

Step-downs: 5–10 reps per side, 2–3 times per week. Focus on control, not speed.
Suitcase carries: Light weight in one hand, walk 20–40 meters. This challenges lateral stability.
Walking with cues: Push the ground back with your foot; feel glutes activate as your leg extends.

Progress slowly. If symptoms spike or rebound for hours, reduce dose.

Why this takes time

Motor control and tissue tolerance both need time to adapt. Expect weeks to months of consistent practice. Single-leg stance control improves faster than tissue tolerance, but both are necessary.

Do not rush. Boring consistency beats aggressive spikes.

When single-leg work is not enough

If single-leg interventions do not improve symptoms after 6–8 weeks of consistent practice, consider:

Is load management appropriate? (See Load Tolerance)
Are multipliers (sleep, stress, fueling) amplifying symptoms? (See Sleep, Stress, and Pain)
Is there a different failure mode (pelvic floor, hip mobility, thoracic spine)?
Do you need professional evaluation?

Single-leg control is a common failure mode, but not the only one.

Summary

Walking and running are repeated single-leg stance events
Single-leg control requires pelvic stability, hip strength, and coordinated timing
Failures show up as pelvic drop, shift, or rotation
Hip extension timing matters; late glute activation overloads the SI joint
Biking does not demand single-leg control, so it may not trigger symptoms
Improve control through static stance, step-downs, carries, and walking cues
Expect weeks to months of consistent practice

Last updated: 2026-01-15