REPRODUCIBILITY OF ISOMETRIC AND ISOKINETIC TESTING OF ANKLE PLANTAR FLEXION STRENGTH AND ENDURANCE

Abstract

142 Use of isometric and isokinetic strength measurements has helped many athletic trainers, exercise physiologists, physical therapists, and others to reliably measure voluntary production of force, power, torque and work. Although there have been ample studies concentrated on the knee, quadriceps, shoulder, and back, the reliability of the ankle has not been well studied. The purpose of this research was to conduct reproducible strength measurements of ankle plantar flexion over a 10 week period. Seven healthy subjects, ranging in physical activity from moderate to active, were studied. The subjects were tested on three different occasions: week 1 (W1), week 5 (W5), and week 10 (W10). The neutral position (0 °) was set at a 90 ° angle between the foot and the tibia. Maximal isometric strength was tested with the ankle at the defined 0 ° neutral position and at 10 ° plantar flexion. Maximal voluntary contractions (MVCs) were performed for 5 seconds. Isokinetic contractions were performed between the neutral position and the maximal plantar flexion position that the subjects experienced as being comfortable. Isokinetic strength was measured at angular velocities of 30, 60, 120 and 180 degrees/sec. Maximal isokinetic endurance was tested by monitoring fatigue and total work done over 50 repeated isokinetic plantar flexions at 60 °/sec. ANOVA statistics showed little variation between isometric and isokinetic measurements taken at each time point. The average p-value of isometric and isokinetic plantar flexion was 0.0039±0.0012 and 0.0791±0.0415, respectively. The isokinetic endurance test, however, showed a significant amount of variance between time points; ANOVA p-values in peak torque and work were 0.7779±0.1300 and 0.5549±0.1182, respectively. This study suggests that measurement of isometric and, to a lesser extent, isokinetic MVCs can potentially be used as a reliable, diagnostic tool to monitor patients' rehabilitation and recovery of strength following ankle joint trauma, disuse and consequent skeletal muscle atrophy in surrounding plantar flexors.