Mechanomyographical signals during prolonged intermittent muscular contractions at low levels under various duty cycles

Abstract

To obtain one of the possible factors on the abrupt increment of mechanomyographic (MMG) signal during prolonged isometric constant contraction (PICC; <20%MVC), the present study focused on the iMMG changes from m. vastus medialis (VM) and/or lateralis (VL) during the intermittent isometric constant contractions (IICC) at various condition of the duty cycle (or relaxation/contraction ratio: R-C ratio) and the target tension. Target tension set at 5, 10 and 15 %MVC and the duty cycle set at 16s-ON/4s-OFF, 56s-ON/4s-OFF and 116s-ON/4s-OFF. Simultaneous recording of myoelectrical signal (MES) was made on VM and/or VL. 1) IMMG increased weakly and monotonously with the cumulative load which is accumulated the acreage of tension and time through the IICC. Also, iMES sustained or increased weakly but the increment ratio was lower than iMES under PICC condition. 2) The increment ratio of iMMG (or gradient of linear regression formula with the cumulative load: G-iMMG) from both muscles increased depend on the increment ratio of the cumulative load (or gradient of linear regression formula with the time) in the stored data under the IICC conditions. But there could not be seen the distinct relation in that of iMES. 3) The G-iMMG decreased with R-C ratio. But G-iMES did not show distinct relationship with R-C ratio among subjects and between muscles. Linear incremental tendency of iMMG would originate from the inserted muscle relaxation during IICC. Therefore, the abrupt increase of iMMG during PICC suggests to be caused from the continuous muscle contraction itself.