Submitted on August 7, 2007
Accepted on September 18, 2007
Voluntary Run Training But Not Estradiol Deficiency Alters the Tibial Bone:Soleus Muscle Functional Relationship in Mice
Gordon L Warren1*, Amy L. Moran2, Harry A. Hogan3, Angela S. Lin4, Robert E. Guldberg4, and Dawn A. Lowe2
1 Physical Therapy, Georgia State University, Atlanta, Georgia, United States
2 Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis, Minnesota, United States
3 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
4 Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States
* To whom correspondence should be addressed. E-mail: gwarren{at}gsu.edu.
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 if 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 (Po) 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 condition were 7-12% greater than those for OVX (p=0.002) while only stiffness was greater for Run compared to Sed (9%; p=0.015). The muscle functional capacities were affected by both surgical condition and activity but in contrast to the bone, the muscle was more affected by activity. Po and peak eccentric force were 10-21% greater for Run compared to Sed (p
0.016) while only Po was greater in Sham compared to OVX (7%; p=0.011). The bone: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.
