The effect of range of motion and isometric pre-activation on isokinetic torques

Summary

The effect of an increased angle of excursion and isometric pre-activation on isokinetic torques of knee extensors was investigated in five male subjects, mean age 35.0 years, SD 9.6. Peak torque and isoangular torque at 0.52 rad from full knee extension (FKE) were measured when contractions were carried out at 3.14, 4.19 and 5.24 rad·s⁻¹ starting: 1) from a standard knee angle (SA) of 1.57 rad from FKE, 2) from the same starting angle as SA, plus an isometric preload (P) equivalent to 25% of isometric maximal voluntary contraction and 3) from an increased angle of knee flexion (1A), 2.09 rad from FKE plus P. Surface integrated electromyograms (iEMG) of the vastus lateralis muscle in SA and IA+P were also recorded. The IA+P had the effect of increasing peak torque, as compared to SA, on average by 12.0%, SD 7.5% (P<0.001) at 3.14 rad·s⁻¹, 19.5%, SD 5.5% (P<0.001) at 4.19 rad·s⁻¹, 21.6%, SD 10.7% (P<0.001) at 5.24 rad·s⁻¹ and of increasing mean iEMG by 15.7%, SD 7.0% (P<0.001) at 5.24 rad·s⁻¹. The IA+P also had the effect of increasing the angle from FKE at which peak torque occurred: from means of 0.80 rad, SD 0.11 to 1.00 rad, SD 0.07 at 3.14 rad·s⁻¹, from 0.65 rad, SD 0.11 to 0.92 rad, SD 0.09 at 4.19 rad·s⁻¹ and from 0.60 rad, SD 0.11 to 0.88 rad, SD 0.11 at 5.24 rad·s⁻¹ (P<0.0001). Mean isoangular torque rose by 12.6%, SD 5.1% at 5.24 rad·s⁻¹ (P<0.01); mean iEMG values by 8.5%, SD 5.2% (P<0.02) and 11.6%, SD 6.4%(P<0.02) at 4.19 and 5.24 rad·s⁻¹, respectively. The mean time for both peak and isoangular torque development was significantly increased (P<0.0001). The effect of SA+P on peak torque was smaller than that of IA+P, a mean increment of 3.4%, SD 6% (P<0.02) only being observed at 5.24 rad·s⁻¹. The increase in isoangular torque was of the same magnitude as that of IA+P. It was concluded that when isokinetic contractions were carried out from a standard position of the knee at a right angle, neuromuscular activation at high angular velocities (>4.19 rad·s⁻¹) was submaximal. The underestimation of torque seemed to be counteracted by starting the contraction from a flexed position and by utilizing a submaximal P.