Validation of the Johnson Anti-Shear Accessory as an Accurate and Effective Clinical lsokinetic Instrument

This article reports two separate investigations into the validity of the Johnson Anti- Shear Accessory (JASA) as an isokinetic evaluation and exercise instrument. Experiment I attempted to verify the shear prevention aspect of the device on 10 anterior cruciate ligament injury patients and experiment I1 sought to establish the testing accuracy of the tool in comparison to the standard Cybex(R) knee input shaft (CKIS) on a qualified sample of eight subjects. A Cybex II-CDRC system protocol of five test knee extension/flexion repetitions at velocity spectrum speeds of 60, 120, 180,240, and 300 degrees /sec, preceded by a warm-up of three gradient submaximal and one maximal repetitions, was used for both studies. The null hypothesis was rejected in experiment 1 as an ANOVA test revealed significant factoral differences and Pearson correlation tests showed noncomparison between the JASA (r = 0.79 quadriceps, r = 0.89 hamstrings) and the CKIS (r = 0.23 quadriceps, r = 0.91 hamstrings) relative to the design control. The null hypothesis was accepted in experiment I1 as ANOVA testing failed to show a significant factoral difference while the JASA and CKIS demonstrated strong correlations (r = 0.97 quadriceps, r = 0.99 hamstrings). It was concluded that the JASA effectively controls anterior tibial shear during isokinetic activity and that the JASA is an accurate and valid isokinetic evaluation and exercise device. J Orthop Sports Phys Ther 1986;7(6):298-303.