Shear-wave velocity of the patellar tendon and quadriceps muscle is increased immediately after maximal eccentric exercise

To determine whether stiffness of the patellar tendon and quadriceps muscles is altered immediately after and 48 h after a single bout of maximal eccentric exercise of the knee extensor muscles. Thirteen healthy individuals [group mean (SD) age 22.4 (3.5) years; 7 female] performed a single bout of maximal eccentric exercise of the non-dominant knee extensors, using an isokinetic dynamometer. Shear-wave velocity (an index of tissue stiffness) was recorded from the patellar tendon, vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL), before, following (post(0)), and 48 h after (post(48)) exercise. To investigate features of exercise induced muscle damage, maximal voluntary isometric contraction (MVIC) and self-reported pain and stiffness (numerical rating scales 0 = no pain/stiffness to 100 = worst imaginable pain/stiffness) were measured before, post(0), and post(48) exercise. Serum creatine kinase (CK) was measured before and post(48) exercise. Compared to preexercise, MVIC decreased and self-reported pain and stiffness increased at post(0) and post(48) and CK levels increased at post(48) (all p < 0.01). Compared to preexercise, shear-wave velocity was greater at post(0) for the patellar tendon [15.9 (24.6)%, p = 0.01] and RF [23.6 (16.7)%, p < 0.001], each returning to baseline by post(48). No significant differences were observed for VL or VM post(0) or post(48) exercise. Maximal eccentric exercise produced an immediate increase in the stiffness of the patellar tendon and RF, resolving by 48 h. As this change was not observed in VL and VM, future studies may explore heterogeneity within synergist muscles following eccentric exercise.