Effects of artificially induced leg length discrepancy on treadmill-based walking and running symmetry in healthy college students

Key points

1. 01Gait asymmetry in spatiotemporal parameters and ground reaction forces was detectable from 1 cm LLD during walking and from 2 cm during running
2. 02The long-limb side showed longer stance time and greater midfoot loading, while the short-limb side showed increased rearfoot loading and longer swing time
3. 03Stride length and cadence changed by no more than 1% even at 3 cm LLD, suggesting the body compensates effectively at an overall stride level
4. 04EMG activity of the thoracic and lumbar erector spinae and gluteus medius was not significantly changed by any level of LLD during walking or running
5. 05Instrumented treadmill gait analysis may be a practical tool for detecting LLD and monitoring the effects of shoe-lift interventions

How it was conducted

Design

Lab-based experimental study with within-subject (LLD magnitude: 0, 1, 2, 3 cm) and between-subjects (long-limb vs. short-limb side) mixed design

Participants

26 healthy physically active college students (15 male, 11 female), mean age 21.2 years, no musculoskeletal injuries or LLD >5 mm at baseline

LLD induction

Rubber shoe lift (EVEN Up, OPED) worn over running shoes to artificially raise one limb by 1, 2, or 3 cm; order of conditions randomized

Speeds tested

Walking at 5.6 km/h and running at 8.1 km/h on an instrumented treadmill (Pluto Med with Zebris 7168-sensor pressure platform)

Outcomes

Spatiotemporal gait parameters, plantar ground reaction forces (rearfoot, midfoot, forefoot), and EMG activity of thoracic and lumbar erector spinae and gluteus medius

Analysis

One-way repeated measures ANOVA and mixed-design ANOVA with Bonferroni-adjusted pairwise comparisons; significance set at p<=0.05

What they found

• Step length increased on the long-limb side and decreased on the short-limb side during walking, with significant side differences at >=1 cm LLD (interaction F=36.485, p<=0.001, partial eta2=0.422)
• During running, step length increased only on the short-limb side (significant at 3 cm LLD, p<=0.01), while the long-limb side remained unchanged (interaction F=3.144, p<=0.05, partial eta2=0.059)
• Step time decreased on the long-limb side and increased on the short-limb side as LLD increased during walking (F=120.340, p<=0.001, partial eta2=0.706) and running (F=53.382, p<=0.001, partial eta2=0.516)
• Stance phase time increased on the long-limb side and decreased on the short-limb side during both walking (F=66.688, p<=0.001, partial eta2=0.572) and running (F=47.903, p<=0.001, partial eta2=0.489)
• Step width increased significantly with greater LLD during walking (F=10.254, p<=0.001, partial eta2=0.291) and running (F=5.814, p<=0.001, partial eta2=0.189), most pronounced at 3 cm (walking) and >=2 cm (running)
• Stride length and stride time increased significantly with LLD during both walking and running but by no more than 1% at 3 cm LLD compared to 0 cm
• Rearfoot GRFs during walking were unchanged on the long-limb side but increased on the short-limb side; midfoot GRFs increased on both sides but more on the long-limb side; forefoot GRFs decreased on the long-limb side and were unchanged on the short-limb side (all interactions p<0.001)
• Similar GRF patterns were seen during running for midfoot (F=10.933, p<0.001, partial eta2=0.179) and forefoot (F=15.549, p<0.001, partial eta2=0.237); rearfoot GRFs were not significantly affected during running
• EMG activity of the thoracic erector spinae, lumbar erector spinae, and gluteus medius showed no significant main effects of LLD, side, or LLD-by-side interaction during walking or running
• Heart rate and perceived exertion did not differ significantly between LLD conditions during walking or running

Limitations

• The LLD was artificially and acutely induced, simulating sudden-onset discrepancy rather than chronic structural LLD, which may produce different compensatory adaptations over time
• The rubber shoe lifts added over running shoes may have attenuated impact forces, potentially masking the true biomechanical effect of LLD
• Familiarization time with each LLD condition was limited and may have affected results; longer adaptation periods could yield different outcomes
• The mixed-sex sample limits direct comparison with single-sex studies, given known sex differences in pelvic structure, gait kinematics, and plantar pressure distribution

Why it matters

For patients

Patients with a leg length difference as small as 1 cm may experience subtle but measurable changes in how they walk, including uneven foot loading that could contribute to injury risk over time.

For clinicians

Instrumented treadmill gait analysis can detect asymmetries in step timing and ground reaction forces from 1 cm LLD during walking and 2 cm during running, making it a useful tool for guiding and monitoring shoe-lift interventions.

For readers

This controlled experiment quantifies how LLD progressively disrupts spatiotemporal gait symmetry and plantar force distribution without detectably altering core trunk and hip muscle activity, which has implications for understanding LLD-related injury mechanisms.