Structural and Functional Properties of Lower Extremity Tendons in Men.

Comstock, BA, Flanagan, SD, Denegar, CR, Newton, RU, Häkkinen, K, Volek, JS, Maresh, CM, Kraemer, WJ. Structural and functional properties of lower extremity tendons in men. J Strength Cond Res 39(2): 184-191, 2025-The purpose of this study was to understand further patellar and Achilles tendon structure and function, body composition, and serum collagen turnover biomarkers in young men who performed heavy resistance training (RT, n = 13, age: 22.2 ± 1.4 years) compared with recreationally active men who were not resistance-trained (NR, n = 13, age: 22.8 ± 2.2 years). Tendon properties were measured at rest and during maximal voluntary isometric efforts using ultrasonography and dynamometry. Lean body mass (LBM) and bone mineral density (BMD) were assessed with dual X-ray absorptiometry. Serum collagen turnover markers were analyzed and related to tendon measures. Resistance-trained men had significantly ( p ≤ 0.05) greater LBM and BMD compared with recreationally active men. Resistance-trained men also showed significantly greater patellar tendon (PT) stiffness (45%) and Young's modulus (36%), though the PT cross-sectional area (CSA) did not differ significantly between groups. Achilles tendon CSA was significantly larger in resistance-trained men. Still, other properties such as stiffness and modulus did not differ significantly between the groups. Serum collagen turnover markers showed no significant differences between groups and were not correlated to any tendon or bone biomarkers. The findings support that resistance-trained men have greater LBM and BMD. However now, it reveals that tendon adaptations differ, as not all measures were similarly affected in both tendons. The blood biomarkers did not show any obvious roles in explaining the differential changes in tendons. Heavy RT induces differential tendon changes potentially due to complex interactions of training variables.