Peroneal Muscle Size and Quality Changes after Impairment-Based Rehabilitation in Patients with Chronic Ankle Instability.

Twenty-six young adults (mean age 22, 18 female) with bilateral chronic ankle instability completed 8 supervised sessions over 4 weeks of individualized impairment-based rehabilitation. The program included joint mobilizations, stretching, four-way ankle resistance, PNF patterns, balance drills, hip strengthening, and functional exercises (lunges, step-ups, jumps), plus a home exercise program. Exercise selection, dosage, and progression were tailored to each person's deficits. A physical therapist (5 years' experience) and an athletic trainer (2 years') delivered the sessions. Ultrasound (8-MHz linear probe, standardized settings) measured peroneal muscle cross-sectional area and echogenicity before and after. The design was pre-post with no control group; data were pooled from two arms of a larger trial that found no between-group difference in peroneal outcomes. A single blinded examiner analyzed all images.

In the trained leg, peroneal CSA increased significantly in both lying (p < 0.01) and standing (p < 0.01) positions. Baseline CSA was 3.44 ± 0.99 cm² in lying, rising to 3.72 ± 0.98 cm² (a 9.67% increase); the standing-position increase was 29%. Echogenicity decreased significantly in the trained leg (p = 0.01), indicating improved muscle quality. In the untrained leg, CSA also increased significantly (lying p = 0.01, standing p < 0.01), with gains of 9% (lying) and 11.7% (standing), but echogenicity did not change significantly (p = 0.15). Effect sizes were moderate to large in standing (Cohen's d 0.37–0.84) and smaller in lying (d 0.28–0.30). Home-program compliance was 80.2%.

This is the first ultrasound-based evidence that a 4-week, 8-session impairment-based program can increase peroneal muscle size and improve tissue quality in chronic ankle instability. Two practical takeaways: first, measuring peroneal muscles in a standing (weight-bearing) position captures larger and more meaningful changes than lying, so if you are tracking peroneal adaptation with ultrasound, test in stance. Second, the untrained leg also grew, which is consistent with cross-education, but its quality did not improve — so if a patient's non-symptomatic side is your concern, size gains alone may not translate to better tissue quality. The program was individualized, so the finding supports the approach of targeting each patient's specific deficits rather than a one-size-fits-all protocol. However, with no control group, no long-term follow-up, and a small young sample, this should inform your confidence in the rehabilitation approach rather than change your clinical decision-making on its own.

No control group; all changes are pre-post comparisons, so maturation, testing effects, or other factors cannot be ruled out. Small convenience sample of 26 young adults (mean age 22, 69% female) from a single university setting; generalizability to older or more heterogeneous populations is limited. All participants had bilateral chronic ankle instability, so the findings do not apply to unilateral cases. Rehabilitation was individualized in exercise selection, dosage, and progression, making it impossible to attribute changes to any specific component. No dynamic assessment (e.g., during walking); all ultrasound measurements were taken in static positions. No follow-up beyond the 4-week intervention; durability of the gains is unknown. No minimal detectable change has been established for peroneal CSA, so the functional significance of the observed changes is uncertain.

No conflicts of interest declared.

Do not read the 29% standing-position CSA increase or the echogenicity drop as proof that this specific 8-session protocol caused the change. There was no control group, the rehabilitation was individualized to each participant's deficits, and the sample was 26 young adults with bilateral CAI. The pre-post design cannot separate the effect of the exercises from maturation, repeated testing, or the natural course of the condition. Treat these results as a signal that impairment-based rehab is associated with peroneal adaptation, not as a validated dose-response finding you can prescribe with confidence.