Surface Electromyographic Activity of the Abdominal Muscles During Pelvic-Tilt and Abdominal-Hollowing Exercises

Abstract

OBJECTIVE: To investigate surface electromyographic (EMG) activity of the rectus abdominus and external oblique abdominus muscles during pelvic-tilt and abdominal-hollowing exercises performed in different positions. DESIGN AND SETTING: 2 x 3 (exercise by position) within-subjects design with repeated measures on both factors. All testing was performed in a university laboratory. SUBJECTS: Twenty-six healthy, active young adult females. MEASUREMENTS: Surface EMG activity was recorded from the left and right rectus abdominus and external oblique muscles while the 2 exercises (pelvic tilt and abdominal hollowing) were performed in different positions (standard, legs supported, and legs unsupported). The standard position was supine in the crook-lying position, the supported position was with hips and knees flexed to 90 degrees and legs supported on a platform, and the unsupported position was with hips and knees flexed to 90 degrees without external support. Peak EMG activity was normalized to a maximum voluntary isometric contraction for each muscle. RESULTS: For the rectus abdominus, there was an interaction between position and activity. Abdominal hollowing produced significantly less activity than the pelvic tilt in all positions. The difference between the 2 exercises with the legs unsupported was of a greater magnitude than the other 2 positions. For the external obliques, there was significantly lower activity during the abdominal hollowing compared with the pelvic tilting. The greatest muscle activity occurred with the legs-unsupported position during both exercises. CONCLUSIONS: Abdominal-hollowing exercises produced less rectus abdominus and external oblique activity than pelvic-tilting exercises. Abdominal hollowing may be performed with minimal activation of the large global abdominal muscles.

Figure 1

The exercises were performed with subjects lying with the biofeedback cuff under their lumbar spine in 3 positions: normal (crook lying), legs supported, and legs unsupported.

Figure 2

The exercise-by-position interaction for rectus abdominus surface electromyographic activity was significant (F_2,80 = 7.59; P = .001). *Rectus abdominus activity was greater during the pelvic tilt versus the abdominal hollowing in all 3 positions (P < .05). Although the activity during the hollowing was unchanged in the standard and supported positions, the activity during the pelvic tilt decreased in the unsupported position. #Rectus abdominus activity was greater in the unsupported position than in the other positions during the abdominal hollowing (P < .05). MUIC indicates maximum voluntary isometric contraction.

Figure 3

For the external oblique muscle, main effects were significant for exercise (F_1,49 = 116.6; P = .0005) and position (F_2,98 = 72.81; P = .0005). *Surface electromyographic activity was significantly greater for the pelvic tilt than for the abdominal hollowing (P < .05). #Electromyographic activity was also significantly greater when performing the exercises with the feet unsupported, compared with the other 2 positions (P < .05).