You can just vary the intensity. The general approach is go as hard as you can for brief bursts then back to a comfortable pace to recover, then burst again. Yo

You can just vary the intensity. The general approach is go as hard as you can for brief bursts then back to a comfortable pace to recover, then burst again. Your peak burst may be pretty slow at first, but if it gets your heart pumping, then you're doing it. That peak should just go up as you train and build your strength.