Why Does One Leg Turn Outward When You Lie Down?

The Real Biomechanical Causes & How to Correct It

Many people notice that when they lie on their back, one leg naturally flops outward.The common assumption is: “My outer hip muscles are tight—stretching should fix it.”

But research shows this explanation is incomplete.

Clinical biomechanics studies consistently indicate two major contributors:

1️⃣ Weak Internal Rotators (Not Just Tight External Rotators)

According to Neumann (2010), Lewis & Sahrmann (2006), and related hip biomechanics literature,the resting position of the hip is determined by the balance between internal and external rotator muscles.

If the internal rotators are weak, the stronger external rotators dominate, causing the leg to fall outward at rest.

Muscles commonly underactive:

• Tensor Fasciae Latae (TFL)

• Anterior fibers of Gluteus Medius

• Portions of the Adductor group

Result:

• The hip defaults to external rotation — not because of tightness alone, but because nothing is counterbalancing the rotation.

This is why stretching the outside of the hip rarely corrects the issue.

2️⃣ Pelvic Torsion or Pelvic Asymmetry

Research by Kapron et al. (2014) shows that pelvic alignment strongly influences hip resting posture.When the pelvis rotates or tilts asymmetrically, the hip joint orientation changes, leading one leg to rotate outward.

Common contributing factors:

• One-sided pelvic rotation (torsion)

• Uneven sitting habits

• Lateral weight shift while standing

• Long-term leg crossing patterns

In these cases, stretching the hip does not resolve the underlying alignment problem.

3️⃣ Evidence-Informed Correction Strategy

① Strengthen the Internal Rotators (Primary Intervention)

Biomechanics literature suggests strengthening is essential for restoring balance.

Useful exercises include:

• Supine knee-in rolling (gently guiding knees inward)

• In-toeing resistance using a mini-band between the knees

• Pelvic-neutral internal rotation activation for TFL & glute med anterior fibers

Research consistently supports hip stability training in reducing asymmetry patterns.

② Restore Pelvic Stability & Symmetry

If pelvic torsion is present, interventions may include:

• Glute med and deep core activation

• Lateral shift correction

• Bilateral loading exercises

• Habit retraining during sitting and standing

③ Correct Daily Habits

Behavioral contributors often maintain or worsen the asymmetry:

• Sitting cross-legged

• Leaning to one side

• Sleeping on one dominant side

• Carrying weight consistently on one hip

Correcting these habits is crucial for long-term improvement.

Summary

A turned-out leg is not simply the result of “tight outer hip muscles.”The most common and evidence-supported causes are:

1. Weak internal rotators

2. Pelvic asymmetry

3. Daily habit imbalance

Effective correction requires a combination of strengthening, pelvic stabilization, and movement habit modification.

At Co Recare Physio Clinic (Dubai Healthcare City), our assessments are evidence-informed and designed to identify whether the issue comes from muscular imbalance, pelvic torsion, or movement habits — and create a personalized correction plan.

🔎 References (Evidence Sources)

• Neumann DA. Kinesiology of the Musculoskeletal System, 2010.

• Lewis CL, Sahrmann SA. Hip biomechanics and movement impairment syndromes. JOSPT.

• Kapron AL et al. Hip morphology & rotational alignment. Clinical Orthopaedics & Related Research, 2014.

• Sahrmann SA. Movement System Impairment Syndromes, 2002.(High-quality, widely cited scientific literature only.)