"Age is associated with Achilles tendon thickness in older adults: an ultrasound case-control study with intra-observer reliability".

Introduction: Obesity is associated with metabolic, inflammatory, and mechanical alterations that may affect the structure of the Achilles tendon, especially in older adults, who present increased tendon vulnerability due to age-related degenerative changes. To compare the ultrasound thickness of the Achilles tendon between sedentary older adults with obesity and those with normal weight, and to evaluate the intra-observer reliability of ultrasound measurements. Methods: A case-control study was conducted with 120 sedentary older adults (60 obese; 60 normal weight). The thickness of the right Achilles tendon was measured by ultrasound in the longitudinal plane at 4cm from the calcaneal insertion. Each participant was assessed using three consecutive measurements. Groups were compared using the independent samples t-test. Intra-observer reliability was analyzed using ICC (2,1). Results: The obese group showed a significantly greater tendon thickness compared with the control group (p = 0.003). However, the obese group was significantly younger than the control group. After adjusting for age in a linear regression model, age was the only significant factor associated with tendon thickness (p = 0.002), whereas obesity lost its significance (p = 0.143). Intra-observer reliability was excellent in both groups (ICC = 0.998 in controls; ICC = 0.986 in obese participants), with low SEM and MDC values. Discussion: Ultrasound measurement of Achilles tendon thickness demonstrated excellent intra-observer reliability in sedentary older adults. Although obese participants showed greater tendon thickness in the unadjusted analysis, age was significantly associated with tendon thickness after adjustment, suggesting that aging may play an important role in tendon structural characteristics in this population.