Associations of Lower Limb Muscle–Tendon Properties with Dual-Task Gait Variability: A Cross-Age Study

Objectives: This study is the first to investigate the association between lower limb muscle–tendon mechanical properties and dual-task gait variability using a handheld, non-invasive myotonometer (MyotonPRO). Methods: A cross-sectional design was employed, involving 48 participants (older adults: 72.05 ± 3.52 years; younger adults: 24.8 ± 2.36 years). The stiffness and elasticity of dominant lower limb muscles and tendons were assessed using the MyotonPRO. Gait variability—including step length, stride length, and gait cycle time—was measured using the OptoGait system. Results: Compared to the younger group, older adults showed increased stiffness of the patellar tendon (p < 0.001) and decreased stiffness of the Achilles tendon (p < 0.047). Additionally, both the rectus femoris and biceps femoris exhibited significantly higher stiffness (p < 0.05) and reduced elasticity (p < 0.001). Patellar tendon stiffness was positively correlated with gait variability (r = 0.55 to 0.68, p < 0.01), whereas Achilles tendon stiffness showed a negative correlation (r = −0.32 to −0.40, p < 0.05). Conclusions: This study provides preliminary evidence linking muscle–tendon mechanical properties with dual-task gait stability in older adults. Increased stiffness in the patellar tendon and decreased stiffness in the Achilles tendon suggest these structural characteristics may play a crucial role in gait control and hold potential as predictive markers of fall risk. Linking non-invasive MyotonPRO-derived mechanical properties with key spatiotemporal gait parameters may support its potential use in the early detection of gait instability in older adults.