title: Impact of muscle length during stretch-shortening contractions on real-time and temporal muscle performance measures in rats in vivo.
abstract: The objective of the present study was to investigate the impact of muscle length during stretch-shortening cycles on static and dynamic muscle performance. Animals were randomly assigned to an isometric (control, Con, n = 12), a short-muscle-length (S-Inj, 1.22-2.09 rad, n = 12), or a long-muscle-length (L-Inj, 1.57-2.44 rad, n = 12) group. The dorsiflexor muscles were exposed in vivo to 7 sets of 10 stretch-shortening contractions (conducted at 8.72 rad/s) or 7 sets of isometric contractions of the same stimulation duration by using a custom-designed dynamometer. Performance was characterized by multipositional isometric exertions and positive, negative, and net work before exposure, 6 h after exposure, and 48 h after exposure to contractions. Real-time muscle performance during the stretch-shortening cycles was characterized by stretch-shortening parameters and negative, positive, and net work. The S-Inj group recovery (force difference) was similar to the Con group force difference at 48 h, whereas the L-Inj group force difference was statistically greater at 1.39, 1.57, and 1.74 rad than the Con group force difference (P < 0.05). Negative work (P < 0.05) and net work (P < 0.05) were statistically lower in the S-Inj and L-Inj groups than in the Con group 48 h after exposure to contractions. Of the real-time parameters, there was a difference in cyclic force with treatment during the stretch-shortening cycles (P < 0.0001), with the L-Inj group being the most affected. Thus longer ranges of motion result in a more profound isometric force decrement 48 h after exposure to contractions and in real-time changes in eccentric forces.
authors.affiliation: Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia 26505, USA. rgc8@cdc.gov
authors.forename: R G
authors.initials: RG
authors.lastname: Cutlip
authors.forename: K B
authors.initials: KB
authors.lastname: Geronilla
authors.forename: B A
authors.initials: BA
authors.lastname: Baker
authors.forename: M L
authors.initials: ML
authors.lastname: Kashon
authors.forename: G R
authors.initials: GR
authors.lastname: Miller
authors.forename: A W
authors.initials: AW
authors.lastname: Schopper
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000293:injuries* / Q000502:physiology*; D016059:Range of Motion, Articular; D051381:Rats; D017207:Rats, Sprague-Dawley; D013180:Sprains and Strains / Q000503:physiopathology*