"There has been a debate for years in exercise physiology about whether the limiting factor in aerobic performance comes from the cardiovascular supply side or oxygen utilization within the muscles themselves. There are arguments for both sides within the literature and I don't think there is really a clear answer yet but regardless, performance depends on both supply and utilization as well as contractile properties of the muscles, technique and skill, etc. It's probably a bit simplistic to say there is any one piece of the physiological puzzle that is single most important. When it comes to performance, it's all important."
Can I ask which forum? as that's a great reply