Measurement Reliability and Kinetic Chain of the Thickness of the Transverse Abdominal Muscle and Action Potential of the Levator Ani Muscle

This study examined the measurement reliability and the kinetic chain of the thickness of the transverse abdominal muscle (TA) and the action potential of the levator ani muscle (LA). In other words, the change in the muscle output was examined during simultaneous contraction of both TA and LA. [Subjects] The subjects were seven healthy adult women (40.1 ± 12.8 years). [Method] Thicknesses of TA and integration electromyograms (iEMG) of LA were measured in five tasks in the supine position. The tasks were: 1) Resting state, 2) Maximal contraction of TA, 3) Maximal contraction of LA, 4) Maximal simultaneous contraction of both TA and LA, and 5) Maximal simultaneous contraction of both TA and LA with resistance added to both knees. To examine the measurement reliability, the tasks were tested twice. [Results] The interclass correlation coefficient (ICC) of the thickness of TA and the iEMG of LA showed high reproducibility during maximal simultaneous contraction. The thicknesses of TA during maximal simultaneous contraction and maximal simultaneous contraction with resistance were greater than during the resting state and maximal contraction of TA. The iEMG of LA during maximal simultaneous contraction was greater than during the resting state, maximal contraction of TA and maximal contraction of LA. In regression analysis, a significant relationship was found between the thickness of TA and iEMG of LA. [Conclusion] The muscle output during simultaneous contraction was larger than that of each individual muscle, suggesting that it is easier to contract LA when TA is contracted from the aspect of the kinetic chain.