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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Voluntary run training but not estradiol deficiency alters the tibial bone-soleus muscle functional relationship in mice

¹Division of Physical Therapy, Georgia State University, Atlanta, Georgia; ²Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis, Minnesota; ³Department of Mechanical Engineering, Texas A&M University, College Station, Texas; and ⁴Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia

Submitted 7 August 2007 ; accepted in final form 18 September 2007

The study's objective was to investigate how estrogen deficiency and run training affect the tibial bone-soleus muscle functional relationship in mice. Female mice were assigned into one of two surgical conditions, ovariectomy (OVX) or sham ovariectomy (sham), and one of two activity conditions, voluntary wheel running (Run) or sedentary (Sed). To determine whether differences observed between OVX and sham conditions could be attributed to estradiol (E₂), additional OVX mice were supplemented with E₂. Tibial bones were analyzed for their functional capacities, ultimate load, and stiffness. Soleus muscles were analyzed for their functional capacities, maximal isometric tetanic force (P_o), and peak eccentric force. The ratios of bone functional capacities to those of muscle were calculated. The bone functional capacities were affected by both surgical condition and activity but more strongly by surgical condition. Ultimate load and stiffness for the sham group were 7–12% greater than those for OVX animals (P = 0.002), whereas only stiffness was greater for Run than for Sed animals (9%; P = 0.015). The muscle functional capacities were affected by both surgical condition and activity; however, in contrast to the bone, the muscle was more affected by activity. P_o and peak eccentric force were 10–21% greater for Run than for Sed animals (P 0.016), whereas only P_o was greater in sham than in OVX animals (9%; P = 0.011). The bone-to-muscle ratios of functional capacities were affected by activity but not by surgical condition or E₂ supplementation. Thus a mismatch of bone-muscle function occurred in mice that voluntarily ran on wheels, irrespective of estrogen status.

biomechanics; functional capacity; exercise; estrogen