Effects of Maximal Concentric Contractions on Myotendinous Mechanical Properties in Prepubertal Boys

This study aimed to compare the effects of a fatiguing concentric exercise on the myotendinous mechanical properties of the knee extensors between men and prepubertal boys. Ten prepubertal boys and 10 men performed a fatiguing exercise consisting of five sets of 20 maximal isokinetic concentric knee extensor contractions. Before the exercise, the mechanical properties of the vastus lateralis (VL), the rectus femoris (RF), and the patellar tendon (PT) were assessed using shear wave elastography to measure the shear wave velocity (SWV) at 70° of knee joint flexion for PT and 70° and 110° for VL and RF. The tests also included maximal voluntary isometric (MVIC) and concentric (MVCC) contractions. These measurements were repeated after the exercise (Post), 30 min after (Post30), and 48 h after (Post48 h). Significant main time effects were observed for SWV VL 70° (p = 0.007) and RF 70° (p < 0.001), with lower values at Post compared to Pre. No age effect or interaction were observed for VL and RF SWV 70°. For SWV PT, a main age effect was observed, highlighting lower values for boys (p < 0.001), without a time effect or interaction. A significant decreased MVIC was observed for men at post, returning to baseline at Post30, whereas no changes in MVIC were observed in boys. These findings suggest that, under acute conditions, maximal concentric contractions induce comparable changes in myotendinous mechanical properties between prepubertal boys and men, while men exhibit a greater force production decline.