The effect of Jendrassik manoeuvre on the latency, amplitude and left-right asymmetry of tendon reflexes.

In order to determine the effect of the Jendrassik manoeuvre (JM) on the latency and amplitude of the electrically recorded compound action potentials of the tendon reflexes (TR) as well as on their left-right asymmetry, the above parameters of the knee (KR) and Achilles (AR) TR were measured in 52 normal subjects (32 men and 18 women) aged 18-74 years (33 +/- 12.2) both at rest and during the JM, using a commercially available tendon hammer connected with the electromyograph. The left-right difference of the latencies was not statistically significant under both conditions. The knee reflex latency--on both sides--was shortened during the JM, while that of the Achilles tendon reflex was not significantly altered. The difference of the TR amplitude between the two sides in percentage of the lower value was not significant at rest and showed a marked diminution during JM. The manoeuvre caused also a net increase of the absolute values of the compound action potentials amplitude of both reflexes.