Alcorn, Justin Dow (2003-05). Osteogenic effect of electric muscle stimulation as a countermeasure during hindlimb unloading. Master's Thesis. Thesis uri icon

abstract

  • Rats that undergo hindlimb unloading (HU) as a simulation for space flight experience bone changes similar to astronauts in microgravity. The purpose of this research was to assess whether an exercise countermeasure would be effective in preventing or mitigating bone degradation during HU. Controlled electrical muscle stimulation was applied to the lower left hindlimb to simulate resistive exercise. Adult 6-mo. old male rats were assigned to 3 groups of 12 each: hindlimb unloaded (HU), aging cage control (CC), and baseline (BL). The CC group was pair-fed to match the nutritional intake of HU animals during the 28 days of the study. The left leg was exercised 3 days a week for the duration of the study, with the unexercised right leg serving as a contra-lateral control. Mechanical tests were conducted to assess the strength of cancellous bone in the proximal tibia metaphysis. Although isolated specimens of cancellous bone are not feasible, reduced platen compression (RPC) was employed to directly load only the cancellous core region of each specimen. There was no significant difference in ultimate stress or elastic modulus between BL, CC, and HU-Ex (exercised). However, HU-Ex results were dramatically and significantly higher than HU-No Ex (contra-lateral unexercised control) for both ultimate stress (68%) and elastic modulus (81%). It is also notable that ultimate stress was 32% higher (but not statistically significant) for HU-Ex compared to CC. The total bone mineral density in the tibial metaphysis was significantly larger, 11%, in the HUEx compared to the HU-No Ex group's values. The results clearly demonstrate the efficacy of the exercise protocol in preventing the substantial mechanical deterioration induced by HU.
  • Rats that undergo hindlimb unloading (HU) as a simulation for space flight
    experience bone changes similar to astronauts in microgravity. The purpose of this
    research was to assess whether an exercise countermeasure would be effective in
    preventing or mitigating bone degradation during HU. Controlled electrical muscle
    stimulation was applied to the lower left hindlimb to simulate resistive exercise.
    Adult 6-mo. old male rats were assigned to 3 groups of 12 each: hindlimb
    unloaded (HU), aging cage control (CC), and baseline (BL). The CC group was pair-fed
    to match the nutritional intake of HU animals during the 28 days of the study. The left
    leg was exercised 3 days a week for the duration of the study, with the unexercised right
    leg serving as a contra-lateral control. Mechanical tests were conducted to assess the
    strength of cancellous bone in the proximal tibia metaphysis. Although isolated
    specimens of cancellous bone are not feasible, reduced platen compression (RPC) was
    employed to directly load only the cancellous core region of each specimen.
    There was no significant difference in ultimate stress or elastic modulus between
    BL, CC, and HU-Ex (exercised). However, HU-Ex results were dramatically and
    significantly higher than HU-No Ex (contra-lateral unexercised control) for both
    ultimate stress (68%) and elastic modulus (81%). It is also notable that ultimate stress
    was 32% higher (but not statistically significant) for HU-Ex compared to CC. The total
    bone mineral density in the tibial metaphysis was significantly larger, 11%, in the HUEx
    compared to the HU-No Ex group's values. The results clearly demonstrate the
    efficacy of the exercise protocol in preventing the substantial mechanical deterioration
    induced by HU.

publication date

  • May 2003