Electromyographic response of the abdominal musculature to varying abdominal exercises

This study examined the electromyographic (EMG) response of the upper rectus abdominis (URA), lower rectus abdominis (LRA), internal obliques (IOs), external obliques (EOs), and the rectus femoris (RF) during various abdominal exercises (crunch, supine V-up, prone V-up on ball, prone V-up on slide board, prone V-up on TRX, and prone V-up on Power Wheel). The subjects (n = 21) performed an isometric contraction of the abdominal musculature while performing these exercises. Testing revealed no statistically significant differences between any of the exercises with respect to the EOs, the URA, or the LRA. However, when examining the IO muscle, the supine V-up exercise displayed significantly greater muscle activity than did the slide exercise. In addition, EMG activity of the RF during the crunch was significantly less than in any of the other 5 exercises. These results indicate that when performing isometric abdominal exercises, non-equipment-based exercises stressed the abdominal muscles similarly to equipment-based exercises. Based on the findings of the current study, the benefit of training the abdominal musculature in an isometric fashion using commercial equipment could be called into question.     

Evolution of body wall musculature

A body wall musculature comprising an outer layer of circularfibers and an inner layer of longitudinal fibers is generallyseen as the basic plan in Annelida. Additional muscles may bepresent such as oblique, parapodial, chaetal, and dorsoventralmuscles. The longitudinal muscle fibers do not form a continuouslayer but are arranged in distinct bands in polychaetes. Mostlythere are four to six bands, usually including prominent ventraland dorsal bands. However, other patterns of muscle band arrangementalso exist. The ventral nerve cord lies between the two ventralbands in certain polychaetes, and is covered by an additionallongitudinal muscle band of comparatively small size. In manypolychaetes with reduced parapodia and in Clitellata a moreor less continuous layer of longitudinal fibers is formed. Clitellatais the only group with a complete layer of longitudinal musculature.Circular fibers are usually less developed than the longitudinalmuscles. However, recent investigations employing phalloidinstaining in combination with confocal laser scanning microscopyrevealed that absence of circular muscles is much more widelydistributed within the polychaetes than was previously known.This necessitates thorough reinvestigations of polychaete musclesystems, and this feature has to be taken into account in furtherdiscussions of the phylogeny and evolution of Annelida.