One way to gauge the intensity of your cardio day is the talk test. Basically, if you’re easily able to carry on a conversation while running, you’re probably in the 4 to 5 range of perceived exertion. On this scale, 1 is very low intensity while 10 is maximal. If you become breathless, like you would during high intensity interval training, your effort rates 8 or 9 on that 1 through 10 scale. At that point, it becomes almost impossible to talk.
This simple test is fine for recreational athletes and weekend warriors, but what about professionals? A study published in the Journal of Strength and Conditioning Research took the talk test to the pro ranks of cycling. Eighteen elite cyclists tried to read a standard paragraph after racing a time trial. The stage when they couldn’t talk comfortably was very close to their ventilatory threshold, and when they had trouble speaking at all, they had reached their respiratory compensation threshold.
True Strength Moment: Ventilatory threshold is the point during exercise where breathing increases significantly. When you reach your respiratory compensation threshold, oxygen consumption begins to increase at a much greater rate than carbon dioxide output from exhaling. It turns out that the talk test is a pretty good indicator of effort for all levels of skill and experience.