One comes across a series of terms such as UT2, UT1, AT, TR, AN for example. Yet at the same time people talk of aerobic threshold, anaerobic threshold, lactate threshold and OBLA (onset of blood lactate accumulation). You can then add to that various discussions as to apparently significant blood lactate levels (e.g. 2mmols/l and 4mmols/l). Then to cap it off, you have to consider VT (ventilatory threshold), VT1 and VT2. Oh, and don’t forget you are meant to know what percentage of VO2max you are working at and the percentage of your maximum heart rate (or is that the percentage of your heart rate reserve?). And how many METs is that?

Confused? Well, maybe there is some justification for that if you are. Let’s face it, physiologists over the last 30 years do not appear to have gone to any particular effort as a group to make it nice and simple, particularly given that precisely the same terms have been used to mean different things over the years. Of course in their defence, physiology has been an evolving science and those studying and writing in the 1960s or even the 1980s did not have the benefit of the cumulative knowledge we have today. If only someone would write something linking together all these concepts together that was simple and straightforward. One day perhaps, but for the time being this will have to suffice.

To help get our heads around the problem, let’s consider an example. You are driving in your car – how fast are you going? Well, there are a number of ways that one might measure this. A traditional way would be miles per hour. You could also answer the question in kilometres per hour (a simple shift in unit, but precisely the same concept).

However there are a whole host of other ways of doing it: by reference to the length of time it takes to drive from London to Oxford; by reference to the number of engine revs per minute in 3rd gear; by reference to the number of times the wheels turn in one second, by reference to the amount of fuel burnt in an hour, the amount of oxygen taken in by the engine, or the amount and content of exhaust gas produced. 

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