Quick Answer
Favouring one leg while running is usually caused by a strength imbalance, an old injury that rewired your loading patterns, limited hip mobility on one side, or a functional leg length difference. The body shifts load toward the side that feels safer or more efficient — often without pain, until the compensating structures reach their limit. The fix is to find the specific cause, isolate the weaker side with unilateral exercises, and rebuild symmetrical loading over 6–12 weeks.
Why the Body Favours One Leg: The Underlying Mechanism
Your nervous system is always optimising movement efficiency. When one leg is weaker, less stable, or restricted in range of motion, the brain quietly redistributes load toward the more capable side without any conscious instruction. Research on motor adaptation shows this happens immediately — within a few steps of encountering a surface change, altered footwear, or a new pain signal. Over time, this shifted loading pattern becomes the default, regardless of whether the original trigger is still present.
This is why old injuries are such a common underlying cause of gait asymmetry. An ankle sprain from years ago that “fully healed” may have left behind subtle changes in how the nervous system controls that limb — reduced proprioception, altered timing of muscle firing, a tendency to shorten stride length on that side to reduce perceived instability. The research on this is consistent: the body continues to favour one limb long after pain disappears as a protective adaptation. By the time a runner develops knee pain, IT band syndrome, or a stress reaction on the opposite side, the compensation pattern has usually been in place for years.
A 5–15% gait asymmetry is considered normal in healthy adults, reflecting natural differences between the dominant and non-dominant leg. The dominant leg typically contributes more to forward propulsion; the non-dominant leg to support and stability. Problems arise when asymmetry grows beyond this range, particularly when it reflects a structural weakness or restriction rather than natural dominance.
The Most Common Causes
1. Strength Imbalance Between Legs
Research consistently finds that most people have a natural strength asymmetry of 10% or more between legs. For recreational runners who don’t do unilateral strength work, this gap can be significantly larger. The weaker leg generates less force per stride, which over time causes the body to unconsciously shorten ground contact time on that side and increase loading on the stronger leg. The stronger leg then absorbs more cumulative stress — which is why the injury often shows up on the side the runner doesn’t think is the problem.
Quad and glute strength asymmetry are the most common culprits. Hamstring imbalance is also significant, particularly for runners who’ve had a previous hamstring injury on one side. Even a 15–20% strength difference between knee extensors can measurably increase gait asymmetry and loading variability.
2. Old Injuries That Rewired Loading Patterns
An ankle sprain, knee injury, or stress reaction that occurred months or years ago may have permanently altered how your nervous system controls the affected limb. During injury, the brain reduces loading on the injured side to protect it. After healing, this protective pattern sometimes persists. The runner feels fine — no pain — but their motor system is still running the “protection protocol” from the old injury, routing load toward the uninjured leg.
The RunLab case study illustrates this well: a high-school ankle sprain led to subtle gait changes that were never addressed. A year later, a knee injury layered new compensation patterns on top of the old ones. By the time the runner sought help, disentangling three years of layered compensations took months of deliberate rehabilitation. The earlier the pattern is caught and addressed, the simpler the fix.
3. Limited Hip Mobility on One Side
Hip extension range of motion directly determines stride length. If one hip can’t extend as fully as the other at the back of the stride — due to hip flexor tightness, joint stiffness, or poor core control — that leg takes a shorter step, spends more time on the ground (increased ground contact time), and generates less propulsive force. The other leg compensates by working harder. This is one of the cleaner causes to identify and fix: restore hip extension mobility on the restricted side, and symmetry often improves without any other intervention.
4. Glute Medius Weakness
The gluteus medius stabilises the pelvis during single-leg stance — the phase of running where all your weight is on one foot. When it’s weak on one side, the pelvis drops toward the opposite side (Trendelenburg sign), the body leans toward the weak side to compensate, and the runner effectively shortens their stride on that side and increases lateral loading. Glute medius weakness is one of the most common causes of unilateral loading patterns in runners and is almost never trained adequately by running alone. It requires direct, targeted work.
5. Functional Leg Length Discrepancy
A true leg length difference (where one leg is anatomically longer) is relatively rare. Far more common is a functional leg length discrepancy — where pelvic tilt, hip muscle tightness, or spinal curvature creates the appearance of different leg lengths without any structural difference. Either way, the result is that one leg effectively hits the ground from a lower position than the other, changing the loading pattern with every stride. This is best assessed by a physio rather than self-diagnosed.
6. Foot Strike and Footwear Issues
Differences in how each foot strikes the ground — one heel-striking and one mid-foot, for example — create asymmetrical loading up the chain. Similarly, worn-down shoes that collapse on one side, or orthotics that only support one foot, can create or perpetuate a leg-favouring pattern. If you notice asymmetrical wear on your running shoes (one heel or midsole degraded more than the other), it’s confirming that you’ve been loading unevenly. For foot-related symptoms, our guide to why feet slap the ground when running covers related gait pattern issues.
How to Tell if You're Favouring a Leg
The Video Test
The most reliable self-check. Have someone film you running from behind and from the side for 30–60 seconds at an easy pace. Look for: one hip dropping lower than the other at mid-stance (pelvic drop — indicates glute medius weakness), one arm crossing further across the body (often compensating for trunk rotation caused by asymmetrical leg loading), one foot landing louder or with a different strike pattern, one stride appearing shorter than the other.
Single-Leg Self-Tests
These don’t require equipment and reveal differences between sides clearly:
Single-leg balance: Stand on one foot with eyes open for 30 seconds, then repeat on the other. Note differences in wobble, ankle correction, or how much trunk sway you need. Even small differences indicate proprioceptive asymmetry.
Single-leg calf raise: 10 slow calf raises on each foot. Note which side fatigues faster, which ankle is less stable, or which side produces less range of motion. Calf weakness or ankle instability on one side is a common contributor to favouring the other leg.
Single-leg squat: Squat on one leg to approximately 45–60° knee bend, 5 reps each side. Watch in a mirror. Look for the knee collapsing inward (valgus), trunk tilting to one side, or significantly different depth between legs. This test reveals quad, glute, and hip stability differences simultaneously.
Hip extension check: Lie on your back and hug one knee to your chest. The other leg should lie flat on the floor. If one leg lifts off the floor when the other knee is pulled in, that side has a hip flexor tightness that’s likely restricting stride length and contributing to asymmetry.
👉 Swipe to view full table
| Self-Test | What It Reveals | Key Sign of Asymmetry |
|---|---|---|
| Single-leg balance (30 sec) | Proprioception, ankle stability | Significant wobble or shorter hold on one side |
| Single-leg calf raise (10 reps) | Calf/soleus strength, ankle stability | Faster fatigue, less range, or instability on one side |
| Single-leg squat (5 reps) | Quad, glute, hip stability | Knee valgus, trunk tilt, or depth difference between sides |
| Hip extension test (lying) | Hip flexor tightness | One leg lifts off floor when opposite knee is hugged in |
| Video from behind (30–60 sec run) | Pelvic drop, arm swing, foot strike | Hip dropping, uneven arm crossing, stride length difference |
| Shoe wear inspection | Cumulative loading pattern | One heel or midsole significantly more worn than the other |
How to Fix It: Exercises and Strategies
Principle: Always Start with the Weaker Side
When doing unilateral exercises, always begin with the weaker or more restricted side and match the rep count on the stronger side. The goal is not to work the strong side harder — it’s to bring the weak side up. Don’t let the strong side compensate for the weak one during bilateral movements by switching to unilateral work.
Glute Medius Work (Most Important for Most Runners)
Banded lateral walks, clamshells, and single-leg glute bridges directly target the glute medius in the way running doesn’t. Start with 3 sets of 15 lateral band walk steps each direction and 3 × 15 clamshells on each side. Within 4–6 weeks of consistent work, most runners notice their pelvic drop reduces and their stride feels more even. This is the single highest-return fix for the majority of runners who favour one leg. Our guide to leg exercises for runners includes these and other key movements for addressing the common running-specific weaknesses.
Single-Leg Strength Exercises
Bulgarian split squats, single-leg Romanian deadlifts, and step-ups should form the core of your unilateral strength work. These expose the weaker leg to the same loading it would face in running — single-leg stance under load — without the speed and complexity of actual running that allows compensations to creep in. Start the weaker leg first, 3 × 8–10 reps, matching the rep count on the stronger side regardless of how the stronger side feels. Strength training for runners provides a full programme structure for integrating this work alongside run training.
Hip Flexor Mobility
If the hip extension test reveals tightness on one side, prioritise hip flexor stretching on that side daily — not just before and after runs. A kneeling lunge stretch (3 × 30–60 seconds, held passively with a neutral pelvis) after each run addresses accumulated hip flexor shortening. The hips hurt after running guide covers hip mobility strategies for runners in more detail.
Cadence and Foot Strike Adjustments
For runners with asymmetrical foot strike patterns, a slight cadence increase (targeting 170–180 steps per minute) naturally encourages a more symmetrical, lower-impact stride pattern by reducing overstriding. This doesn’t fix the underlying strength or mobility cause, but it reduces the loading asymmetry while you address the root issue. Our guide on ideal running cadence based on height covers the specific targets by runner profile.
Ankle Stability Work
If an old ankle injury is the suspected cause, ankle proprioception and stability work directly address the nervous system’s protective compensation pattern. Single-leg standing with eyes closed, single-leg mini-squats on an unstable surface (balance board, folded mat), and progressive loading on the previously injured ankle rebuild the motor confidence that tells the nervous system it’s safe to load that leg normally again.
What Not to Do
Don’t try to consciously correct your gait while running. Thinking about symmetry mid-run usually produces awkward, artificial movements that create new compensation patterns. The fix happens in the gym — rebuild the strength and mobility off the bike; the gait adapts naturally as those foundations improve.
Don’t ignore pain on the stronger leg. The leg you’re favouring is being overloaded. If you develop IT band syndrome, knee pain, or a stress reaction, it’s often on the side doing more work — the stronger leg — not the side causing the problem. Addressing the weaker side’s underlying issues is the fix. Our guides to tensor fasciae pain from running and inside knee pain after running cover common overuse injuries on the compensating side.
Don’t expect overnight results. Strength imbalances that took years to develop take 6–12 weeks of consistent unilateral work to meaningfully reduce. Old injury patterns embedded in the nervous system take longer. Progress is real but gradual.
When to See a Physio
Self-directed work handles most cases of leg favouring in runners. However, see a physiotherapist or sports medicine doctor if: the asymmetry developed suddenly after a specific event; you have pain on either side that correlates with your running; you’ve been doing unilateral work consistently for 6 weeks with no improvement in your self-tests; or you suspect a structural cause like leg length discrepancy, scoliosis, or nerve involvement. A gait analysis with a physio or specialist running clinic can also confirm whether your self-assessment is accurate and provide more targeted interventions — including orthotics if a structural discrepancy is confirmed. The step length vs stride length guide explains the biomechanical measurements physios use to quantify gait asymmetry.
Putting It Together: A 6-Week Plan
Weeks 1–2: Assessment and activation. Complete all six self-tests. Identify your specific weak points (glute medius, ankle stability, hip mobility, or strength imbalance). Start banded glute medius work 3× per week, hip flexor stretching daily on the restricted side.
Weeks 3–4: Unilateral strength loading. Add Bulgarian split squats and single-leg RDLs 2× per week, starting the weaker side first. Continue banded activation work as a warm-up. Re-test single-leg calf raise and single-leg squat weekly to track progress.
Weeks 5–6: Integration. Continue unilateral strength work, add ankle stability drills if needed. Check cadence during runs and aim for the symmetrical range. Re-run the video test and compare to week 1. Most runners notice measurable improvement in balance and confidence on the weaker side by this point.
If asymmetry persists beyond 6 weeks of consistent work, consult a physio. Structural causes or deeply embedded compensation patterns may need hands-on assessment to disentangle.
Running Unevenly? Coaching Helps Identify the Cause
Gait asymmetry is one of the most common — and most fixable — causes of recurring running injuries. Our running coaching identifies what's driving your imbalance and builds the strength and mobility work into your training plan so you address the root cause, not just the symptoms.
FAQ: Favoring a Leg While Running
Why do I favour one leg when running?
Usually strength imbalance, an old injury that altered loading patterns, limited hip mobility on one side, or a functional leg length difference. The body shifts load toward the more efficient or safer side — often without pain, until the compensating structures become overloaded.
How do I know if I’m favouring one leg while running?
Signs include: one foot landing louder, one leg feeling heavier during long runs, one hip feeling tighter, or asymmetrical shoe wear. Video from behind while running reveals pelvic drop and stride differences. Single-leg exercises expose strength and stability asymmetries between sides.
Is it bad to favour one leg when running?
Some asymmetry is normal (5–15%). It becomes a problem when it’s large (>15–20%), increasing, or causing the overloaded side to develop injuries. Consistently loading one leg more raises stress fracture, tendon, IT band, and hip/knee injury risk on that side.
What exercises fix a leg imbalance for runners?
Banded lateral walks and clamshells for glute medius, Bulgarian split squats and single-leg RDLs for quad and hamstring strength, single-leg calf raises for ankle and calf strength, and single-leg balance work for proprioception. Always start with the weaker leg and match rep counts.
When should I see a physio?
If asymmetry developed suddenly, if you have pain correlating with your running, if 6 weeks of targeted work hasn’t improved your self-tests, or if you suspect structural causes like leg length discrepancy or nerve involvement.
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