Activation history and constant errors in human force production.

Spinal proprioceptive reflexes and muscle tension are transiently potentiated in the aftermath of isometric muscle contractions. To determine if such alterations may bias ongoing motor commands, subjects were tested for accuracy of matching a criterion force following relaxation or a maximum contraction. Large postcontraction overestimations of the criterion force were consistently found. Errors progressively decayed to postrelaxation control values within 50 s. It is proposed that transient postcontractile potentiation of spinal reflex pathways may summate with previously set motor commands to produce inadvertent errors in perceived effort.