The gastrocnemius and soleus muscles deficits in functional ankle instability: an observational study

Functional ankle instability (FAI) is a common condition affecting active populations, often caused by deficits in postural and neuromuscular control. This study aimed to compare the differences in gastrocnemius and soleus muscles strength (eccentric and concentric) between the affected and non-affected limbs at velocities of 60°/120° seconds and find out the relationship between muscle strength, balance, and functional performance of the affected limb in participants with FAI.

Thirty-eight participants with unilateral FAI, their ages ranging from 15 to 32 years, with a body mass index between 18.5 and 24.9 kg/m²were recruited. They had a history of at least one unilateral lateral ankle sprain that required immobilization for three days or longer, in addition to at least one recurring sprain within the three-to-six-month period before study participation. The FAI was identified if the total score was 11 or above on the identification of functional ankle instability (IdFAI) questionnaire. Participants were assessed using Cybex isokinetic dynamometry, a single-leg stance (SLS) (Eyes open and closed), a Y-balance test (YBT) and a side hop test (SHT), for concentric and eccentric plantarflexion strength at 60°/s and 120°/s, static and dynamic balance, and functional performance, respectively. Data analysis included t-tests, Pearson correlation coefficients, and multi-regression analysis.

Significant differences were found in eccentric torque at 60°/s between affected and non-affected limbs (p = 0.048). Moderate indirect correlations were observed between SHT and all strength measures in the affected limb (r = -0.51 to -0.61, p < 0.001). The YBT showed moderate to strong direct correlations with strength measures. Multiple regression analysis revealed that strength deficits significantly predicted static balance with eyes closed (R² = 0.417, p < 0.05).

The deficit of gastrocnemius and soleus muscles eccentric strength significantly impairs function in participants with FAI, especially in SHT and YBT. Strength deficits significantly predicted a lack of functional performance by 41% in the SLS with eyes closed. Velocity-specific strength assessments are crucial for effective interventions, and rehabilitation should focus on eccentric strengthening exercises to enhance dynamic stability and reduce recurrent instability.

The study was registered to ClinicalTrials.gov with the number NCT06715033(Retrospectively registered on 27/11/2024).