Effects of exercise intensity on shear modulus in regional lateral abdominal muscles during the abdominal draw-in...

The abdominal draw-in maneuver (ADIM) is designed to enhance neuromuscular function of the transversus abdominis (TrA) by distinguishing its activation from the internal oblique (IO) and external oblique (EO). However, a standardized implementation method has not yet been established, and previous studies have not quantitatively defined ADIM exercise intensity or examined regional muscle activation patterns. The lateral abdominal muscles have multiple anatomical attachment sites, suggesting region-specific functional differences. Therefore, identifying the optimal exercise intensity for ADIM requires a regional approach. This study investigated the effects of exercise intensity-defined as a length change in abdominal circumference-on the shear modulus in different regions of the lateral abdominal muscles. Twenty healthy young male participants were included in this study. Five exercise intensity levels (0 %, 25 %, 50 %, 75 %, and 100 %) were established based on the change in length between the abdominal circumference at resting expiration (0 %) and during ADIM retraction of the abdomen with maximum effort (100 %). The shear modulus of the TrA, IO, and EO were measured using shear wave elastography (TrA: upper, middle, lower; IO: middle, lower; EO: upper, middle). The shear modulus of the upper, middle, and lower TrA and lower IO increased progressively from 25 % to 100 % (p < 0.05). The middle IO and upper and middle EO increased from 75 % to 100 % (p < 0.05), but not from 0 % to 50 %. This finding suggested that the optimal ADIM exercise intensity is between 25 % and 50 % when the TrA and lower IO are selectively activated.