THE AREA UNDER THE RECORD OF CONTRACTILE TENSION - ESTIMATION OF WORKPERFORMED BY A CONTRACTING MOTOR UNIT

The area under twitch tension records was measured for motor units in rat medial gastrocnemius. These measures were compared to measures of tension. The tension varied in significantly larger range than the are a. The area of slow motor units was similar to the area of fast resist ant units, whereas their tensions differed significantly. The area dep ended mainly on the amplitude of contraction and to a smaller degree o n its time course. The measure of area under the tension record gives a more exact evaluation of the work performed by contracting motor uni ts than the measure of tension alone. The obtained results show that m otor units in mammalian muscle are less variable in their ability to p erform contractile work and moreover, that slow motor units play a mor e significant role during contractions than was supposed based on tens ion measures.