Performing an 800-meter run or a 2-to-6 minute hard work interval with equivalent rest provides significant cardiovascular benefit.

“Well in your particular case, just do the 800 meter. So do 800 meters. Do something that takes two to six minutes of work. It is a lower intensity than the max stuff, but is a much higher workload. That is probably going to give you, you might even argue the most cardiovascular benefit, because it is sustained work output.”