Submitted on August 2, 2006
Accepted on February 8, 2007
Tonic to phasic shift of lumbo-pelvic muscle activity during 8-weeks of bed-rest and 6-months follow-up
Daniel Ludovic Belav
1*, Carolyn Anne Richardson2, Stephen James Wilson3, Dieter Felsenberg4, and Joern Rittweger5
1 School of IT and Electrical Engineering, The University of Queensland, The University of Queensland, Queensland, Australia; School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia; Zentrum für Muskel- und Knochenforschung, Charité Campus Benjamin Franklin, Belin, Berlin, Germany
2 School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia
3 School of IT and Electrical Engineering, The University of Queensland, The University of Queensland, Queensland, Australia
4 Zentrum für Muskel- und Knochenforschung, Charité Campus Benjamin Franklin, Berlin-Steglitz, Germany
5 Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Alsager, United Kingdom
* To whom correspondence should be addressed. E-mail: belavy{at}gmail.com.
Prior motor control studies in unloading have shown a tonic to phasic shift in muscle activation, particularly in the short extensors. Tonic muscle activity is considered critical for normal musculoskeletal function. The shift from tonic-to-phasic muscle activity has not been systematically studied in humans in unloading, nor at the lumbo-pelvic (LP) region. Ten healthy young male subjects underwent 8-weeks of bed-rest with 6-months follow-up as part of the "Berlin Bed-Rest Study". A repetitive knee movement model performed in the prone position is used to stimulate tonic holding LP muscle activity, as measured by superficial electromyography. Tonic and phasic activation patterns were quantified by relative height of burst versus baseline electromyographic linear-envelope signal components. Statistical analysis shows a shift towards greater phasic activity during bed-rest and follow-up (p<0.001) with a significant interaction across muscles (p<0.001) specifically affecting the short lumbar extensors. These changes appear unrelated to skill acquisition over time (p all 
0.196). This change of a shift from tonic LP muscle activation to phasic is in line with prior research on the effects of reduced weightbearing on motor control.
