It is not for building serious body mass though, or for very serious cardio workouts. (homefitnessguru.net)
This is the most important question to ask yourself - what is it you're trying to achieve by incorporating running or some sort of serious cardio into your routine? (completehumanperformance.com)
Let's assume that approximately six months from now, I'm about to undertake a pretty serious cardio challenge. (evilcyber.com)