Nice job.

I don't want to presume anything. Did you purposefully shorten the workout from that described in the ACSM article? It indicated 30 seconds on and 10 seconds off. (Your total duration variable should be 480--don't ask me how they added that up to "7 minutes"!) This has lead to some confusion in the comments here. And, although their intervals are somewhat arbitrary, and asserting this routine is "scientific" is debatable to begin with, it would be more accurate.

Again, great job.