When I first started running with C25k I heard to use your core to run and to concentrate on breathing. In order for me to tighten my core, concentrate on breathing and to run at the same time I used a back support belt. It helped me to run without leaning forward and able to breath when running. Now in 2014 I did 5k's events now in 2015 in already doing 10k's event. My first run was the NewYearRace 10k in Los Angeles 1hr15min due to some hills on the course. I didnt train myself running on hills lol
