Comparison of N-k table offset angles with the human knee flexor torque curve.

The purpose of this study was to dynamically examine various offset angles on the N-K table to determine which offset produces a torque pattern corresponding most closely to the isokinetic torque curve of the knee flexor musculature when tested at 60%. Subjects for the study were five college-age male volunteers (age=21.8+/-1.8 yrs, ht=181.9+/-4.3 cm, wt=88.4+/-12.6 kg). Mean peak isokinetic torque values for the five subjects were measured at 5 degrees increments to represent the human knee flexor torque curve. These were converted to relative mean values by dividing each value by the maximum mean peak torque. Torque curves from four offset angles (90 degrees ,110 degrees ,135 degrees , and 160 degrees ) for the N-K table were obtained by using the Kin Com in the passive mode at 20 degrees /s to push the exercise arm of the N-K table through a range of motion of 0 degrees to 90 degrees while recording torque and angular position. The four torque curves were converted to relative values in a similar manner as for the subjects. Qualitative analysis reveals that the 160 degrees offset angle most closely corresponded to the representative knee flexor isokinetic torque curve, while the 90 degrees offset angle corresponded least. Although these findings would seem to support reconsideration of common clinical practice relative to the use of the N-K table for knee flexor strength development, the 160 degrees offset angle is awkward because it has a tendency to force the user into hyperextension at the beginning phase of motion. As such, practical compromises might include the use of the 110 degrees or 135 degrees offset angle in lieu of the traditionally employed 90 degrees offset angle, or the development of an extension stop that would prevent hyperextension of the knee.