Artificial selection for intrinsic aerobic endurance running capacity in rats

Artificial selection for intrinsic aerobic endurance running capacity was s tarted using genetically heterogeneous N:NIH stock of rats as a founder pop ulation (n = 168). Selection for low and high capacity was based upon dista nce run to exhaustion on a motorized treadmill using a velocity-ramped runn ing protocol. The starting velocity was 10 m/min and was increased by 1 m/m in every 2 min (slope was constant at 15 degrees). At each generation, with in-family selection was practiced using 13 families for both the low and hi gh lines. A rotational breeding paradigm maintained the coefficient of inbr eeding at less than 1% per generation. On average the founder population ra n to exhaustion in 355 +/- 11 m. Six generations of selection produced line s that differed in running capacity by 171%, with most of the change occurr ing in the high line. At generation 6 the low line ran 310 +/- 8 m and the high line 839 +/- 21 m at exhaustion. Selection for running capacity produc ed changes in body weight as a correlated trait. By generation 6, the low-l ine females were 20% heavier than the high-line females, and the low-line m ales were 16% heavier than the high-line males.