Normative values of ankle strength and its importance for rehabilitation and return to activity: A cross-sectional study.

Abstract

Background: Ankle normative values are limited compared to isokinetic knee assessments. Chronic ankle instability correlates with agonist-antagonist imbalances, decreased evertor/invertor ratio, and plantar flexion deficits. Strengthening programs targeting evertor/invertor and dorsiflexor/plantar flexor balance help reduce injury recurrence. Bilateral neuromuscular deficits compromise the contralateral side, rendering healthy limbs unsuitable as recovery references. Defining normative healthy ankle parameters is crucial for establishing precise limits in non-surgical treatments and sports return criteria. While the limb symmetry index (LSI) is used for knees with a cutoff of > 90%, no such standardization exists for the ankle.

Aim: To comprehensively evaluate isokinetic ankle strength profiles in non-athletic individuals.

Methods: This is a cross-sectional study. Two hundred ankles were evaluated using the Biodex 3 System to assess eversion, inversion, dorsiflexion, and plantar flexion. Healthy individuals with an active lifestyle and no previous injuries were evaluated. The Maximum Torque, Agonist/Antagonist Ratio, LSI, and Muscular Deficiency Index (MDI) and the correlation with demographic variables were evaluated.

Results: The mean age (mean ± SD) was 38.5 ± 13.5 years, and the body mass index (BMI) was 25.8 ± 4.2 in 69 men and 31 women. The mean maximum torque values by gender were (mean ± SD): 22.3 ± 6.6 female (F) and 33.4 ± 9.9 male (M) N/m for eversion; 30.10 ± 10.0 (F) and 37.0 ± 11.6 N/m (M) for inversion, 37.4 ± 10.0 (F) and 53.6 ± 13.0 N/m (M) for dorsiflexion, and 100.4 ± 37.2 (F) and 158.1 ± 33.4 (M) N/m for flexion. There was no correlation between age or BMI and maximum torque. The evertors/invertors ratio was 88.8%, and the dorsiflexors/plantar flexors ratio was 36.1%. The MDI and LSI were balanced between sides for every movement, having an average global difference of less than 10%.

Conclusion: These findings provide gender-specific normative isokinetic values for the ankle in healthy, physically active adults. These reference parameters-especially LSI and MDI above 90%-can support clinical decision-making in rehabilitation planning and return-to-sport assessment, offering objective benchmarks for functional recovery.