Miller JZIf you have any physiology, performance, or nutrition related questions, email Ben at


 There is a lot of lingo thrown around during group rides and racing.  It becomes apparent that although these words are familiar to many, there are far fewer who understand what they actually mean.  In an effort to clear up some of these meanings, I am offering a glossary below and in some cases add some common misconceptions.  


VO2max:  Refers to the maximum volume of oxygen that can be used for aerobic energy production.  The volume of oxygen refers to the amount of oxygen that is used by mitochondria in order to make ATP by aerobic respiration.  There is an oxygen “cascade” in order to get the oxygen to the mitochondria in which: 1) air is breathed into the lungs, 2) oxygen is loaded onto red blood cells, 3) red blood cells are delivered to tissues by the heart, 4) oxygen is unloaded from the red blood cells and into the tissues, 5) the oxygen goes to the mitochondria in the tissues, and 6) the oxygen is used in the electron transport chain of the mitochondria to make ATP.  Under normal conditions, the lungs have very little to do with the limits of VO2max, but rather the limits are either the heart’s ability to deliver the oxygen or the tissues ability to use it (debated heavily where that limit occurs).  When I say aerobic respiration I am referring to a chemical process that is not the same as breathing.  A common error I hear is that someone is limited by this/her breathing when in reality there are limits in either delivering the oxygen to the muscles or using it at the muscles.  VO2max can go up somewhat with training, but it tends to have a genetic limit (you need to have good parents).  A high VO2max by itself does not guarantee success, but having a relatively high VO2max is extremely beneficial to cycling success.  You will see VO2max values as L/min (liters of O2 consumed per minute) or ml/kg/min (milliliters of oxygen consumed per kg body weight per minute).  Most are more familiar with the ml/kg/min value, which varies from 30-45 in healthy sedentary individuals, to 50-65 in trained cyclists, to 70+ in elite cyclists.  For freakishly high values, see the values of elite cross-country skiers that can approach 85-90 ml/kg/min.  For a off the charts VO2max, racing sled dogs approach 240 ml/kg/min.  One thing to remember is that VO2max is often a bragging point and in reality it is not the size of the VO2max that matters, but rather how it is used.  


Lactate threshold:  A concept that there is a breaking point at which lactate starts to accumulate in the blood at an increasing faster rate and that this breaking point represents a point at which exercise becomes increasingly difficult and unsustainable.  Often this threshold point has been associated with an “anaerobic threshold”.  In a previous column I have argued why this is a false concept.  Although lactate threshold testing can provide some useful information for monitoring training or establishing “training zones” I have several issues with it.  For one, there is at least 10 different ways to identify a lactate “threshold” and depending on which technique you use, you may get a different answer.  Second, the technique uses a blood measure to define a point at which sustaining work becomes hard. The sampling of blood for lactate gives the illusion that the measurement is very scientific.  I actually think it is far from it.  The sampling of blood for lactate to define when something is hard is a false premise because it assumes that lactate is what is causing the work to become hard – something that is simply not true.  It is at best a correlation and many other things can be correlated as well (heart rate, breathing rate, sweat rate, etc), but none of these cause the difficulty.  To me, if you want to determine if something is hard and sustainable, get on your bike and find what you can sustain for 5, 10, 30 or 60 min.  If you want numbers to define workloads, look at your powermeter for average watts or heart rate and assign those numbers to your zones.  I hope to see the death of lactate threshold testing in my lifetime.  


Watts:  For those of you with powermeters, watts have become an important term.  A watt is a unit of power.  Power in turn refers to energy used over time.  The units for power are joules per second (or kilojoules).  To help understand the role of the rate constant in this definition, an example is helpful.  When you consume food, there is potential energy contained within the food.  We use the unit calorie for that energy although the rest of the world uses kilojoule.  Whatever the unit there is a discrete amount of energy contained in that food.  Power on the other hand is expressed in joules/sec as an indication of how much energy is used over time.  At the end of a ride, you will have performed a given amount of work (calories or kilojoules) but at any given time in the ride, you are using a certain amount of joules/sec.    


Efficiency:  When there is a transfer of energy there is usually some unintended loss. Efficiency refers to how well energy is transferred. For example, engines in cars have different efficiencies in regard to transferring the energy contained in petroleum to movement of the car.  The human body is no different.  There are several places in the human system where efficiency can vary.  For example, at the mitochondria, some potential energy that could be made into ATP is lost as heat.  Although heat is beneficial to keep us at 98.6°, under high-energy flux (e.g. exercise) the amount of heat generated must be dissipated and dealt with (e.g. evaporative cooling from sweat).  I often hear people discussing improving the efficiency of their pedal stroke.  There are several ways to measure efficiency, but we can call this mechanical efficiency.  One way to think of this efficiency can be expressed is by measuring much work is generated on the bike per amount of oxygen consumed.  When you consider that we all have a maximum amount of oxygen we can use (VO2max) to generate energy it would be of great to get as much work out each unit of oxygen as possible.  There is actually a great deal of debate about whether cyclists become more efficient with training.  For runners there is a great amount of variability in efficiency and it can be trained.  However, in cycling, there is a constrained range of motion (the pedal stroke) that limits changes in efficiency (as long as you are not wildly waving your arms while pedaling or something).  There has been the emergence of oddly shaped chain rings and cranks to help change this limitation, but I have not looked to see if they are effective.  


If you want to know the physiological basis for any other performance related terms, please feel free to e-mail me (unless your name is Tom Bondurant).