Jeffery, Jay Melvin (2007-12). Quantifying the strain response in the rat tibia during simulated resistance training used as a disuse countermeasure. Master's Thesis. Thesis uri icon

abstract

  • Disuse of weight bearing bones has been shown to cause bone loss. This poses a health concern for people exposed to microgravity, such as astronauts. Animal studies are used to study factors related to bone loss and countermeasures to prevent bone loss. This study used a hindlimb unloaded (HU) rat model to simulate microgravity and a muscle stimulation countermeasure to simulate resistive exercise. Uniaxial strain gages were implanted on the antero-medial aspect of the proximal tibia to measure the mechanical strain during a typical exercise session. In a separate but parallel study, the exercise was shown to be an effective countermeasure to disuse related bone loss. The current study sought to understand the loading of the bone during the exercise. To determine if the strain response changes during a protocol using this countermeasure, strains were measured on a group of weight bearing animals and a group that were hind limb unloaded and received the countermeasure for 21 days. Strain magnitudes and rates were considered and related to torques at the ankle joint. No significant differences in strain magnitudes were noted between the baseline control group and the hindlimb unloaded group that received the countermeasure. The two kinds of contractions used in an exercise session are isometric and eccentric. The isometric contractions are used to adjust the stimulation equipment for the eccentric contractions, which constitute the exercise. Peak strain levels during the isometric contractions ranged from 900 to 2200 microstrain while the eccentric were 38% lower and ranged from 600 to 1400. Eccentric strain rates were 62% lower than the isometric contractions strain rates. These results indicate that the strain environment during the isometric contractions may be causing more of the osteogenic response than the eccentric contractions, which have previously been thought to be the primary part of the countermeasure.
  • Disuse of weight bearing bones has been shown to cause bone loss. This poses a
    health concern for people exposed to microgravity, such as astronauts. Animal studies
    are used to study factors related to bone loss and countermeasures to prevent bone loss.
    This study used a hindlimb unloaded (HU) rat model to simulate microgravity and a
    muscle stimulation countermeasure to simulate resistive exercise. Uniaxial strain gages
    were implanted on the antero-medial aspect of the proximal tibia to measure the
    mechanical strain during a typical exercise session.
    In a separate but parallel study, the exercise was shown to be an effective
    countermeasure to disuse related bone loss. The current study sought to understand the
    loading of the bone during the exercise. To determine if the strain response changes
    during a protocol using this countermeasure, strains were measured on a group of weight
    bearing animals and a group that were hind limb unloaded and received the
    countermeasure for 21 days. Strain magnitudes and rates were considered and related to
    torques at the ankle joint. No significant differences in strain magnitudes were noted
    between the baseline control group and the hindlimb unloaded group that received the
    countermeasure.
    The two kinds of contractions used in an exercise session are isometric and
    eccentric. The isometric contractions are used to adjust the stimulation equipment for
    the eccentric contractions, which constitute the exercise. Peak strain levels during the
    isometric contractions ranged from 900 to 2200 microstrain while the eccentric were
    38% lower and ranged from 600 to 1400. Eccentric strain rates were 62% lower than the
    isometric contractions strain rates. These results indicate that the strain environment during the isometric contractions may be causing more of the osteogenic response than
    the eccentric contractions, which have previously been thought to be the primary part of
    the countermeasure.

publication date

  • December 2007