title: Characterization of isometric contractions of rat skeletal muscle in vivo: duty cycle effects.
abstract: Many work related injuries stem from the exertion of skeletal muscle forces over an extended period of time. Musculoskeletal injury can be caused by muscle's inability to maintain force during occupational exposure. The goal of the present study is to test how various rest times (duty cycles) between long isometric contractions will affect decrements in force, and develop a model that characterizes force decrements due to skeletal muscle fatigue. All tests were performed in vivo on the tibialis anterior muscle of anesthetized Sprague-Dawley rats. Animals were randomly assigned to either a 10 second (N=8), 1 minute (N=8), or 5 minute (N=8) duty cycle group. All animals were then subjected to 7 isometric contractions (duration of 2.8 seconds). A model was constructed to characterize forces changes over the duration of a contraction and over multiple contractions. The model consisted of a power law and an exponential component; these two components were combined by using an exponential weighting function. Overall, the combination of a power law and exponential model with a weighting function satisfactorily characterized the changes in isometric force for the 10 second duty cycle, but a simpler exponential model could be used where longer duty cycles are performed.
authors.affiliation: National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Geronilla
authors.forename: John Z
authors.initials: JZ
authors.lastname: Wu
authors.forename: B A
authors.initials: BA
authors.lastname: Baker
authors.forename: Robert G
authors.initials: RG
authors.lastname: Cutlip
mesh_terms: D000818:Animals; D007537:Isometric Contraction; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors