Ankle kinematics, center of pressure progression, and lower extremity muscle activity during a side-cutting task in participants with and without chronic ankle instability

Key points

1. 01CAI group had significantly greater ankle internal rotation from 35-54% of stance phase (mean difference 6.62 degrees, large effect size d = 1.03-1.05)
2. 02Center of pressure stayed more medial in the CAI group during late stance (81-100% of stance phase), suggesting a protective movement strategy
3. 03Tibialis anterior muscle activity was significantly higher in CAI from 86-94% of stance phase (mean difference 21.91 %MVIC, d = 0.89-1.48)
4. 04No significant differences were found in fibularis longus, fibularis brevis, medial gastrocnemius, vastus medialis, or semitendinosus activity
5. 05Greater variability in COP position throughout stance in the CAI group may indicate less consistent motor control

How it was conducted

Design

Cross-sectional biomechanical study with CAI and matched healthy control groups

Participants

30 physically active adults: 15 with self-reported CAI and 15 matched controls (by age, mass, height, sex)

Task

45-degree anticipated side-cutting task performed on an embedded force platform

Measurements

3D ankle kinematics (Vicon, 200 Hz), surface EMG from 6 lower-limb muscles (1500 Hz), and medial-lateral COP position (1000 Hz)

CAI criteria

2+ prior lateral ankle sprains, recurrent instability or giving way, CAIT score below 24

Analysis

Statistical parametric mapping (SPM1D) for continuous kinematic and EMG data; independent t-tests for discrete COP increments

What they found

• Greater ankle internal rotation in CAI from 35-54% of stance phase: mean difference 6.62 +/- 0.10 degrees, p = 0.032, effect size d = 1.03-1.05
• More medial COP position in CAI from 81-90% of stance phase: p = 0.035, effect size d = 0.75-1.01
• More medial COP position in CAI from 91-100% of stance phase: p = 0.008
• Greater tibialis anterior activity in CAI from 86-94% of stance phase: mean difference 21.91 +/- 3.95 %MVIC, p = 0.022, effect size d = 0.89-1.48
• CAIT scores: CAI group 18.0 +/- 3.0, controls 29.8 +/- 0.5 (p < 0.001)
• No significant differences in ankle inversion, plantar flexion, or EMG from fibularis longus, fibularis brevis, medial gastrocnemius, vastus medialis, or semitendinosus

Limitations

• Small sample size (n = 15 per group) powered for COP outcomes only, likely underpowered for EMG and kinematic variables
• EMG recorded only on the injured limb, so within-person limb comparisons were not possible
• Knee and hip kinematics were not collected, limiting interpretation of full lower-limb movement strategy
• Variability in EMG normalization and processing methods across the literature makes direct comparison with other studies difficult

Why it matters

For patients

If your ankle frequently gives way, you may unknowingly adjust how you cut and push off during sports in ways that partially protect the ankle but may not eliminate the risk of re-injury.

For clinicians

Greater ankle internal rotation during mid-stance and a more medial late-stance COP suggest both a potential giving-way mechanism and a compensatory neuromuscular strategy in CAI; rehabilitation programs targeting transverse-plane ankle stability and motor control during directional changes may be warranted.

For readers

This small biomechanical study adds to evidence that CAI alters multi-planar ankle motion and muscle activation during sport-specific cutting, but larger studies including hip and knee kinematics are needed before firm clinical guidelines can be drawn.