Is Achilles tendon structure associated with functional ability and chronic ankle instability in military recruits?

Objective: To determine the relationship between Achilles tendon (AT) structure, functional ability and chronic ankle instability (CAI) in military recruits. Methods: Three hundred and sixty newly recruited infantry male soldiers recruited in April 2022 were assessed for AT structure by Ultrasound Tissue Characterization (UTC), for functional abilities (included proprioception ability, heel-raise test, dynamic postural balance, and hopping agility ability) and for CAI (recurrent sprains and a positive perceived instability). Results: Soldiers that were identified with disorganized tendon had significantly lower heel-raise and agility scores compared to those with organized tendon structures (33.6 ± 18.1(n) vs. 49.9 ± 28.9(n), p < 0.001; and 5.39 ± 2.12(n) vs. 6.16 ± 1.90(n), p = 0.002, respectively). The best discriminator between soldiers with organized vs. disorganized structure, was heel-raise test (AUC = 0.741). Moreover, soldiers with disorganized AT structure had a higher prevalence of CAI compared with those with organized tendon structures (p < 0.05). Conclusion: Recruits with disorganized tendon structures displayed reduced heel-raise score, agility ability and dynamic postural-balance and greater ankle instability. Inferior tendon quality at the onset of military service is an important physical indicator to consider when seeking to manage future injuries and potential for physical performance. Pre-recruitment screening of the AT structure, CAI, and functional abilities, especially in high-intensity infantry programs, needs to be considered.