An investigation into the inter-rater reliability of ultrasound imaging of abdominal muscles in adults

  • Fiona Alston
  • Carmen Britz
  • Tarryn Du Preez
  • Sandile Mthembu
  • Chrissie Pavon
  • Natasha Pells
  • Martin Sarembock
  • Janeen Hughes
  • Jennifer Jelsma


Ultrasound imaging is a non-invasive tool that could be useful in observation of bodily structures, diagnostic purposes, bio-feedback and as an outcome measure. As core stability has become a focal point in rehabilitation, the ability to observe the muscles involved could prove to be clinically useful.

This study was therefore conducted to determine the inter-rater reliability of the ultrasound imaging machine.

Rectus Abdominus (RA), External Obliquus (EO), Internal Obliquus (IO) and Transversus Abdominus (TrA) were imaged in both a relaxed and a contracted condition. Fifty one participants of thirty years and older were recruited from visitors to a tertiary hospital. Two investigators independently measured the thickness of the abdominal muscles.

Generally there was a strong relationship when measuring RA, IO and EO, although strong contractions did not meet the criteria set for reliability. RA relaxed had the strongest correlation between raters (r=0.89, p<0.01) while IO oblique crunch (OC) showed the weakest correlation (r=0.58, p<0.01. A significant difference was found in thickness from the relaxed state
to measuring EO hollowing-in-manoeuvre (HI) (p=0.02), Oblique Crunch (p<0.01) and RA chin-to-chest (p<0.01). Generally, males showed a significantly larger muscle thickness compared to females and a
high Body Mass Index (BMI) was associated with unclear images (p<0.01).

The use of the ultrasound imaging machine results in reliable measurement regarding the more superficial muscles in a state of relaxed or moderate activity, even when used by relatively inexperienced therapists. It is recommended that US can be used as a reliable outcome measure of most abdominal muscle activity.


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