Catch property in single mammalian motor units.

The tension output of single motor units in the cat triceps surae muscle was studied during patterned stimulation of the innervating motoneurons. With repetitive stimulation within a rather narrow frequency range, the tension output of slow-twitch (type S) motor units may be quite sensitive to the pattern of stimulus intervals in the train. The presence of only one stimulus interval that is much shorter than the others in the train can cause marked, long-lasting tension enhancement, provided that the stimulus repetition rate in the basic train is within certain limits.