New Values of Normal Ankle Strength and Its Importance for Rehabilitation and Return to Play

Abstract

Background: the isokinetic test has been broadly used to assess the functional results after the rehabilitation of musculoskeletal injuries. Particular in the ankle, most studies are related to injuries of the lateral ligaments and the Achilles tendon, without the knowledge of normative values. This study aimed to comprehensively evaluate the ankle isokinetic strength profile. Methods: 200 ankles were evaluated using the Biodex 3 System for the movements of eversion, inversion, extension, and plantar flexion. Healthy individuals with an active life and without previous injuries were widely assessed. The Maximum Torque, Agonist / Antagonist Ratio, Limb Simmetry Index, among others and their relationships with demographic variables were also evaluated. Different statistical analyzes were performed for each parameters and ratios. Results: the mean age was 38.5 years and the BMI was 25.8 in 69 men and 31 women. In 78 participants, the dominant ankle was the right one. The non-dominant side was consistently stronger in every moviment. The mean values ​​obtained for the torque in each movement were 29.9 N/m for eversion, 34.8 N/m for inversion, 48.6 N/m for extension, and 140.2 N/m for flexion. Such parameters for men and women were also obtained and there was no correlation between age or BMI with maximum torque. The evertors/inverters ratio was 88.8% and the extensor/flexor ratio was 36.1%. The Muscular Deficiency Index and Limb Simmetry Index showed a balance between the sides for each movement, with an average global difference of less than 10% between them (eversion 8.66; inversion 4.2; extension 3.41 and flexion 5.18). Conclusion: the sample was considered homogeneous, which allows to propose a new profile of normative values ​​for the isokinetic strength of the ankle. Values ​​of torque forces and agonist/antagonist balances have been accomplished. The results have implications for rehabilitation protocols and return-to-sport criteria.