Relationship between Isokinetic Average Force, Average Torque, Peak Force, and Peak Torque of the Knee Extensor and Flexor Musculature

The purpose of this study was to determine the relationship between average force, average torque, peak force, and peak torque produced by the knee musculature. Twenty women were assessed for isokinetic concentric and eccentric knee extensor and flexor muscular strength at a velocity of 90 deg/sec. Correlational analyses showed relationships ranging from r = 0.89 to r = 0.94 for concentric extension, r = 0.92 to r = 0.99 for eccentric extension, r = 0.81 to r = 0.95 for concentric flexion, and r 0.90 to r = 0.96 for eccentric flexion. The strong relationship between the tested variables suggests that any of these variables are appropriate when reporting isokinetic strength data. However, because average values are dependent on the preload and range of motion through which a joint is assessed, it is imperative that these variables remain consistent between and among subjects. If this is not possible, the use of peak measures is recommended. Article: INTRODUCTION Hislop and Perrine 2 introduced the concept of isokinetics in 1967 and with it the ability to rapidly quantify human muscular performance of a moving limb. Traditionally, isokinetic strength has been reported as peak torque. 2,5,13 However, technological advances and new isokinetic systems have made possible the quantification of isokinetic strength as average force, average torque, peak force, or peak torque. The Kinetic Communicator (KinCom; Chattecx Corp., Chattanooga, TN) is one such device. The load cell of the KinCom is located at the distal pad attachment and thus measures force (N) from the point of application as produced by a specific muscle group. The software enables the entry of the distance of the load cell from the axis of rotation, allowing for the conversion of force to torque values (Nm). After data collection, the software has the capacity to report the data in terms of average force (N), average torque (Nm), peak force (N), and/or peak torque (Nm). Although isokinetic strength has typically been reported as peak torque, 2,5 there are several examples where data have been reported in terms of average force 6 , 7 , 10 and average torque 9,12; data also can be reported in terms of peak force. However, the use of these measures interchangeably has only been established for the shoulder rotator musculature. 8 Therefore, the purpose of this study was * Assistant Professor and Coordinator of Graduate Sports Medicine, Department of Kinesiology and Health, Georgia State University, Atlanta, GA. † Associate Professor and Director, Sports Medicine Research Laboratory and Graduate Athletic Training Education, University of Virginia, Charlottesville, Virginia to determine the relationship between isokinetic average force, average torque, peak force, and peak torque of the knee extensor and flexor musculature. METHODS Twenty women (age 20.2 ± 1.01 years, height 169.0 6.8 cm, weight 60.8 5.5 kg) participated in the study upon giving their informed consent in accordance with institutional human investigation committee guidelines. Subjects were excluded from the study if they reported any history of injury sustained to the dominant knee. Subjects were assessed for isokinetic concentric and eccentric average and peak force (N) and torque (Nm) of the dominant knee extensor and flexor musculature on a KinCom isokinetic dynamometer at a velocity 90 deg/ sec. Subjects were assessed through a range of motion of 5 to 90 degrees. A preload of 75 N was used, and all data were gravity corrected. Strength of the knee extensor muscle group was assessed in an upright, seated position using the KinCom back rest attachment. The hip was positioned in approximately 80 degrees of flexion, and subjects were stabilized at the distal thigh and across the waist. The axis of the dynamometer was aligned with the axis of rotation of the knee, and the distal pad was placed slightly proximal to the malleoli. Strength of the knee flexor muscle group was assessed in a prone position. Subjects were secured at the pelvis and distal thigh with Velcro straps. The distal pad was placed slightly proximal to the malleoli, and the axis of the dynamometer was aligned with the axis of rotation of the knee. Before testing, subjects participated in familiarization procedures that included stretching exercises for the quadriceps and hamstring muscle groups and three to five submaximal and one maximal concentric and eccentric contractions for both the knee extensor and flexor muscle groups. After a 1-minute rest period, subjects performed several maximal concentric and eccentric contractions of the knee extensor muscle group. Three reproducible torque curves were selected using the overlay technique. After assessment of knee extensor strength, subjects were positioned for assessment of knee flexor strength. Data collection procedures were identical for the knee flexor muscle group. Average force and torque values were obtained from the entire isokinetic strength curve. Peak force and torque values were obtained from the highest point of the strength curve. Correlational matrices were then produced to determine the relationship between average force, average torque, peak force, and peak torque. RESULTS The correlation coefficients for concentric and eccentric average force, average torque, peak force, and peak torque of the knee flexor and extensor musculature are presented in Tables 1-4. The relationship between the concentric knee extensor variables ranged from r = 0.82 to r = 0.94. The relationship between the eccentric knee extenTable 1 Correlations between concentric knee extensor average force (AF), average torque (AT), peak force (PF), and peak torque (PT).