During the suckling period, mammals progress through critical periods for the central nervous, musculoskeletal, and cardiovascular systems. As a result, various aspects of maternal behavior and physiology can affect offspring in ways that have lasting effects. We tested for possible maternal effects on adult physical activity and exercise physiology using one of 4 replicate lines of mice that have been selectively bred for ~90 generations for high voluntary wheel-running behavior (High Runner; HR) and one of 4 non-selected Control (C) lines. Adult HR mice run ~3-fold the daily distances of C mice and have evolved various other differences associated with exercise capacity, including elevated maximal aerobic capacity (VO2max). At birth, we cross-fostered offspring to create 4 experimental groups: C pups to other C dams, HR pups to other HR dams, C pups to HR dams, HR pups to C dams (all individuals were fostered). Mice were weaned 3 weeks later and adult testing began at ~6 weeks of age. As expected, adult HR mice weighed less than their C counterparts and females weighed less than males; in addition, mice raised by HR females had reduced body masses. Also as expected, adult HR mice ran approximately 3-fold more than their C counterparts and females ran more than males, but fostering did not statistically affect running. Similarly, with body mass as a covariate, HR mice had higher VO2max than C, and males had higher VO2max than females, but fostering did not affect running. With body mass as a covariate, both triceps surae muscle mass and liver mass had a 3-way interaction. Analyses of home-cage activity, food consumption, body fat, and other organ masses are in progress. NSF DEB-1655362 to TG.