Ankle strength assessed by one repetition maximum: A new approach to detect weaknesses in chronic ankle lateral instability

Background: Ankle muscle strength should be assessed after a lateral ankle sprain (LAS) because a strength deficit can lead to chronic ankle instability (CAI). No field method is available to obtain quantitative ankle dynamic strength values. This study aimed to assess the reliability of the one-repetition maximal (1-RM) method and to compare ankle muscle strength between healthy volunteers and those with CAI using 1-RM strength assessment approach. Methods: We recruited 31 healthy volunteers and 32 with CAI. Dorsiflexor, evertor, and invertor 1-RM were performed twice at a one-week interval. The intraclass correlation coefficient (ICC) and minimal detectable change (MDC) were calculated. Strength values were compared between healthy volunteers and CAI. Results: The 1-RM method is reliable for assessing ankle dorsiflexor, evertor, and invertor strength, with an ICC ranging from 0.76 to 0.88, and MDC ranging from 19 to 31%. Volunteers with CAI obtained evertor (3.0 vs. 3.5 N/kg), invertor (2.9 vs. 3.7 N/kg), and dorsiflexor (5.9 vs. 6.5 N/kg) strength values that were lower than healthy volunteers (p < 0.05). Conclusion: The 1-RM test can be used in practice to assess evertor, invertor, and dorsiflexor strength during the rehabilitation of LAS. This field method could help practitioners to detect a strength deficit and individualize a strengthening programme if necessary. (c) 2024 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.