Submitted on July 20, 2007
Accepted on January 3, 2008
A new method for the non-invasive determination of abdominal muscle feedforward activity based on tissue velocity information from tissue Doppler imaging
Anne Frances Mannion1*, Natascha Pulkovski2, Peter Schenk2, Paul W. Hodges3, Hans Gerber4, Thanasis Loupas5, Mark Gorelick1, and Haiko Sprott2
1 Spine Center Division, Dept Research and Development, Schulthess Clinic, Zurich, Switzerland
2 Rheumatology and Institute of Physical Medicine, University Hospital Zurich, Zurich, Switzerland
3 Physiotherapy, The University of Queensland, Brisbane, Queensland, Australia
4 Institute for Biomechanics, Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology, Zurich, Switzerland
5 Philips Medical Systems, Athens, Greece
* To whom correspondence should be addressed. E-mail: annefmannion{at}yahoo.com.
Rapid arm movements elicit anticipatory activation of the deep-lying abdominal muscles; this appears modified in back pain, but the invasive technique used for its assessment (fine-wire-electromyography (EMG)) has precluded its widespread investigation. We examined whether tissue-velocity changes recorded with ultrasound (M-mode) tissue Doppler imaging (TDI) provided a viable non-invasive alternative. Fourteen healthy subjects rapidly flexed, extended and abducted the shoulder; recordings were made of medial deltoid (MD) surface EMG, and of fine-wire EMG and TDI tissue-velocity changes of the contralateral transversus abdominis, obliquus internus and obliquus externus. Muscle onsets were determined by blinded visual analysis of EMG and TDI data. TDI could not distinguish between the relative activation of the three muscles, so in subsequent analyses only the onset of the earliest abdominal muscle activity was used. The latter occurred <50ms after the onset of medial deltoid EMG (i.e. was feedforward) and correlated with the corresponding EMG-onsets (r=0.47, p<0.0001). The mean difference between methods was 20ms, and was likely explained by electromechanical delay; limits of agreement were wide (-40 to +80ms) but no greater than those typical of repeated measurements using either technique. The between-day standard error of measurement of the TDI onsets (examined in 16 further subjects) was 16ms. TDI yielded reliable and valid measures of the earliest onset of feedforward activity within the lateral abdominal muscle group. The method can be used to assess muscle dysfunction in large groups of back-pain patients and may also be suitable for the non-invasive analysis of other deep-lying or small/thin muscles.
