title: Tonic-to-phasic shift of lumbo-pelvic muscle activity during 8 weeks of bed rest and 6-months follow up.
abstract: 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 wk of bed rest with 6-mo 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 EMG. Tonic and phasic activation patterns were quantified by relative height of burst vs. baseline electromyographic linear-envelope signal components. Statistical analysis shows a shift toward 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 > or = 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 weight bearing on motor control.
authors.affiliation: School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia. belavy@gmail.com
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Belavy
authors.forename: Carolyn A
authors.initials: CA
authors.lastname: Richardson
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Wilson
authors.forename: Dieter
authors.initials: D
authors.lastname: Felsenberg
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
mesh_terms: D001510:Bed Rest / Q000009:adverse effects*; D004576:Electromyography; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D008161:Lumbosacral Region; D008297:Male; D009048:Motor Skills; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009135:Muscular Diseases / Q000209:etiology* / Q000503:physiopathology; D010388:Pelvis; D015203:Reproducibility of Results; D013026:Space Flight; D013997:Time Factors; D016474:Weight-Bearing