Exercise research traditionally has focused on the effects of training, rather than underlying genetic mechanisms. But physiologists wondered what would happen if they took a single strain of rats meaning they all had the same basic genetic background and bred two separate lines purely on the basis of "continued selecting of untrained rats with either high- and low-running endurance." In this way, they could study the genetic role in endurance performance and oxygen delivery systems.
Results of this large longitudinal study have been coming out generation by generation, and now a group of researchers at the University of California, San Diego have found some surprising results at generation #15 (G15), compared with G7. The G7 untrained rats from the "athletic" line had a greater running endurance and increased oxygen consumption (12%) than the "couch potatoes." These differences were mainly due to peripheral improvements (skeletal muscle) rather than central physiological changes in the cardiovascular or respiratory systems.
Wider endurance, oxygen usage differences reflect system-wide changes
As would be expected, the UCSD physiologists found that the continued selection led to significantly greater differences in endurance and oxygen consumption (44%) between the two groups of G15 rats than were seen at G7.
"This enhanced divergence at G15 was due in part to an increased skeletal muscle oxygen conductance that allowed for better transport of the oxygen to the muscle mitochondria of the athletic rats." according to Richard A. Howlett, lead author of one of three papers on the experiment. Howlett and the other two lead authors, Scott