Individuals with chronic ankle instability exhibited significantly lower compressive and higher shear ankle joint contact forces during walking compared with both copers and uninjured controls, with differences driven by altered muscle force contributions, suggesting altered joint loading is specific to CAI rather than ankle sprain history alone.
Key Findings
Results
Individuals with CAI exhibited significantly lower compressive ankle joint contact forces compared with both uninjured controls and copers.
Comparison was made among three groups: 21 uninjured controls, 21 copers, and 21 individuals with CAI.
The difference in compressive JCF was statistically significant (p = 0.007).
Lower compressive JCF in CAI was primarily attributable to reduced triceps surae force.
Copers and uninjured controls did not differ significantly from each other in compressive JCF, indicating the difference was specific to CAI.
Results
Individuals with CAI demonstrated higher posteriorly directed shear ankle joint contact forces relative to both controls and copers.
The difference in posteriorly directed shear JCF was statistically significant (p ≤ 0.008).
Increased posteriorly directed shear JCF in CAI was driven mainly by increased tibialis anterior force during early stance.
This finding distinguishes CAI from both successful post-sprain adaptation (copers) and uninjured individuals.
Results
Individuals with CAI showed higher laterally directed shear ankle joint contact forces compared with uninjured controls.
The difference in laterally directed shear JCF was statistically significant (p ≤ 0.041).
Altered contributions from shank muscles and ground reaction forces were identified as the primary drivers of elevated lateral shear JCF.
This comparison was significant between CAI and uninjured controls; the relationship with copers was not reported as significant.
Results
Altered ankle joint loading during walking appears specific to CAI rather than a history of ankle sprain alone.
Copers, who had a prior ankle sprain but no persistent symptoms, did not show the same aberrant loading patterns as individuals with CAI.
Differences in muscle force contributions distinguished CAI from successful post-sprain adaptation (copers).
Participants completed treadmill gait analysis at a self-selected speed with musculoskeletal modeling used to estimate muscle contributions to tri-axial ankle JCF.
The coper group served as a key comparison to isolate the chronic effects of instability from the acute effects of a single sprain event.
Methods
Musculoskeletal modeling was used to estimate muscle contributions to tri-axial ankle joint contact forces across all three participant groups.
The study included 21 uninjured controls, 21 copers, and 21 individuals with CAI.
Treadmill gait analysis was performed at each participant's self-selected walking speed.
The modeling approach decomposed ankle JCF into compressive, posteriorly directed shear, and laterally directed shear components.
Specific muscles identified as key contributors included the triceps surae (compressive JCF), tibialis anterior (posterior shear JCF), and shank muscles broadly (lateral shear JCF).
Discussion
The authors suggest rehabilitation strategies targeting muscle coordination may help restore more coper-like joint loading patterns in individuals with CAI.
Differences in muscle force contributions between CAI and copers suggest a neuromuscular basis for altered joint loading.
Copers represent a model of successful post-sprain adaptation, and their loading patterns may serve as a rehabilitation target.
CAI is associated with abnormal joint loading and an increased risk of early joint degeneration, providing clinical motivation for addressing these biomechanical differences.
What This Means
This research suggests that people with chronic ankle instability (CAI) — a condition where the ankle remains unstable and symptomatic after repeated sprains — walk differently in ways that could contribute to long-term joint damage. Specifically, individuals with CAI experienced lower downward (compressive) forces and higher sliding (shear) forces at the ankle joint compared to both people who had never sprained their ankle and people who had sprained their ankle but recovered fully without ongoing problems. These differences were traced to specific muscles: the calf muscles (triceps surae) were less active in CAI, reducing compressive force, while the shin muscle (tibialis anterior) was more active early in the walking cycle, increasing backward shear force.
An important aspect of this study is the inclusion of 'copers' — people who experienced an ankle sprain but did not develop chronic instability. Because copers had normal-looking joint loading patterns similar to uninjured individuals, the study suggests that the abnormal forces seen in CAI are not simply a result of having sprained an ankle at some point, but are specifically linked to the ongoing instability and symptoms. This means the joint loading differences reflect something particular about how the body adapts (or fails to adapt) after repeated ankle injuries.
This research matters because abnormal joint loading over time may contribute to early cartilage breakdown and osteoarthritis. The findings suggest that rehabilitation programs for CAI might benefit from focusing on restoring normal muscle coordination — particularly retraining the calf and shin muscles — rather than only addressing pain or mechanical stability. The 'coper' pattern may offer a useful target for what successful recovery looks like biomechanically.
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Jang J, Franz J, Pietrosimone B, Blackburn J, Tennant J, Wikstrom E. (2026). Ankle joint contact forces and muscle contributions during walking differentiate chronic ankle instability from copers and uninjured controls.. Gait & posture. https://doi.org/10.1016/j.gaitpost.2026.110227