Differential changes in plantar fascia and achilles tendon tissue properties between pregnancy trimesters: Implications for arch stability and foot pain

Background Pregnancy induces physiological and biomechanical changes that may affect connective tissue properties. Given the functional relationship between the plantar fascia (PF) and Achilles tendon (AT), these tissues may exhibit trimester-specific changes. Objective This study aimed to investigate the biomechanical and viscoelastic properties of PF and AT in pregnant women at different trimesters. Methods This cross-sectional study included primigravida women aged 18–40 years with a pre-pregnancy BMI <30 kg/m 2 . Participants were grouped by trimester (G 1 : n = 64; G 2 : n = 52; G 3 : n = 55). Biomechanical and viscoelastic properties of PF and AT were assessed using myotonometry, and navicular drop was measured bilaterally. Results PF elasticity and navicular drop increased significantly in both feet in parallel with the progression of pregnancy (p ≤ 0.05). In contrast, Achilles tendon tissue properties showed no significant differences between the three trimesters (p > 0.05). Conclusions Increased PF elasticity accompanied by reduced medial longitudinal arch stability may increase plantar fascia strain under load, potentially predisposing pregnant women to microtrauma and foot-related pathologies such as plantar fasciitis and persistent foot pain. Monitoring navicular drop and PF tissue properties throughout pregnancy may facilitate early identification of individuals at risk.