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

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 (post₀), and 48 h after (post₄₈) 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, post₀, and post₄₈ exercise. Serum creatine kinase (CK) was measured before and post₄₈ exercise.

Compared to preexercise, MVIC decreased and self-reported pain and stiffness increased at post₀ and post₄₈ and CK levels increased at post₄₈ (all p < 0.01). Compared to preexercise, shear-wave velocity was greater at post₀ 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 post₄₈. No significant differences were observed for VL or VM post₀ or post₄₈ 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.