Effects of isometric quadriceps strength training at different muscle lengths on dynamic torque production

This study aims to (1) determine whether isometric training at a short vs. long quadriceps muscle length affects concentric torque production; (2) examine the relationship between muscle hypertrophy and concentric torque; and (3) determine whether changes in fascicle length are associated with changes in concentric torque.Sixteen men performed isometric training at a short (SL, n=8) or a long muscle length (LL, n=8). Changes in maximal concentric torque were measured at 30, 60, 90, 120, 180, 240 and 300rads(-1). The relationships between the changes in concentric torque, cross-sectional area, volume and fascicle length were tested.Concentric torque increased significantly after training only in LL and at angular velocities of 30 and 120rads(-1) by 12-13% (P<0.05). Muscle size increased in LL only, the changes were correlated (r=0.73-0.93, P<0.05) with the changes in concentric torque. Vastus lateralis (VL) fascicle length increased in both groups (5.44.9%, P=0.001) but the change was not correlated with changes in concentric torque in either group.Isometric training-induced increases in muscle size and concentric torque were best elicited by training at long muscle lengths. These results highlight a clear muscle length dependence of isometric training on dynamic torque production.