Testing knee extension and flexion strength at different ranges of motion: an isokinetic and electromyographic study.

The main objective of this study was to explore the mechanical and electrical output of thigh muscles derived from a range of motion (RoM) of 90 degrees (0-90 degrees flexion, LR) and the three successive RoMs: 0-30 degrees (SR1), 30-60 degrees (SR2) and 60-90 degrees (SR3). Thirteen men took part in the study. In view of the torque-velocity relationship and in order to render the test conditions as equivalent as possible, LR was tested at 90 degrees /s while the corresponding velocity for all SRs was 30 degrees /s. The findings indicated very good agreement between LR and SR2 in terms of absolute strength (particularly the concentric), within muscle eccentric to concentric strength ratios, between muscles (agonist to antagonist) strength ratios and the normalized IEMG (expressed in muV/Nm). An agreement was also noted between the mean eccentric peak torque of the knee flexors at LR and SR1 and between the mean eccentric peak torque of the knee extensors at LR and SR3. However, in general there was a lesser agreement between LR and SR1 or SR3. It is suggested that testing thigh muscles in the middle sector of knee motion (SR2) yields strength and EMG data that are close and well correlated with those derived from testing the knee along the commonly used (0-90 degrees ) RoM.