 [ Symptoms ] im pregnant but i had sex yesterday and he came in me is that bad [ Disease ] many aerobic exercises are also weight bearing    the kind where you stand on your feet and exercise weight bearing aerobic exercises include walking aerobics dancing tennis climbing stairs and running weight bearing exercise stimulates the cells that make new bone and boost bone strength this is especially important for teenagers because your bone mass peaks between the ages of 25 and 30 adolescence is the time to build the strongest bones possible