Isokinetic measurements of muscle strength in hysterical paresis

The torque during isokinetic knee extensions and flexions was determined in repeated tests at 3 speeds of angular rotation in 25 patients with pareses considered to be hysterical after relevant examinations and follow-up. The torque records were combined with surface EMG from the quadriceps and the hamstring muscles in some patients. Besides the weakness, 3 signs were observed that are not usually seen in patients with pareses due to verified peripheral or central lesions. These signs were: Enlarged variability of torque in repeated tests of the same movement (larger than 20% of maximum torque in 22 patients). Higher torque in fast movements than in slow movements (8 patients). Force production in knee flexion less than that expected from the weight of leg and lever arm due to restraining activation of the quadriceps muscle (12 patients). The restraint was present although there was no spasticity. The signs reflect inconsistent and contradictory motor performance that is not compatible with a genuine paresis. Thus, they aid the identification of weakness of functional origin.