Interpreting Results from your VO2 max Running Test
General comments on our VO2 max test
Many other labs use procedures for determining VO2 max that differ from ours (such as 1 minute steps), but our protocol was designed to provide a wealth of information beyond just VO2max. We used 3 minute intervals because they are often long enough so that your body will reach steady state conditions in about the last 1.5 minutes within a step. Thus, we have very good estimates of your metabolic rates at intermediate efforts in addition to your maximal aerobically sustainable power. In essence you now have a good calibration curve for how your heart rate is related to power under steady state conditions (see heart rate vs. power graph). Having the metabolic rates at several intermediate sub-maximal levels along with your mechanical power output also allows us to calculate your efficiency, which has many important consequences for your performance.
The effects of training vary depending on both the duration and intensity of an effort. As you go faster different muscle fibers are used, and if you never go fast certain physiological systems will never be challenged and then improve after a recovery period. In The Cyclist' Training Bible, Joel Friel proposes one of many schemes of establishing different training zones based on percentages of values such as VO2 max, and his articles and books do a great job of explain how training at different intensities challenges and changes different aspects of your physiology. In a nutshell if you want to race fast you need to train fast. When I was a distance runner LSD (long slow distance) workouts became popular for awhile, but the current consensus is that such training is helps build a base, but it is insufficient without some accompanying high intensity work. Although distance runners do need some high intensity training, their effort during a running race is very steady compared to that in most road cycling events. Thus, cycling places even more of a premium on training with variable intensity and duration because layered on top of a requirement of endurance are the additional requirements of generating some very high transient powers (often more than twice the average power) and recovering from them after covering breaks, climbing up hills etc. The training zone worksheet in your Excel workbook provides you with a tabular summary of your training zones based on some of Friel's proposed schemes. Incorporating the right variety of these training zones is essential for you to be a well rounded cyclist.
When you train with high intensity short duration (< 2 minute or so) intervals monitoring heart rate is nearly useless for determining your level of exertion because of the lag time it takes for your heart rate to increase and the fact that many aspects of your physiology simply are not operating under steady state conditions. There is simply no way around the fact that a power meter is far and away the best method for establishing and monitoring high intensity efforts. However, over a range of longer efforts that are sustainable long enough for steady state conditions to be met, you can tell a lot using a heart rate monitor.
Because of the relatively long duration of our test, it is NOT a good test for experimentally determining your maximal heart rate. If you train with a heart rate monitor, after a good warm up perform some all out sprint up shallow hills for about 45 sec â€“ 1 min and that should give you a good handle on your real maximal heart rate. On average maximal hear rate declines with age, but endurance athletes commonly have much higher maximal heart rates (beats per minute) than those predicated by formulas such as subtracting your age from 220. There is also a tendency for smaller individuals to have higher heart rates than larger individuals.
Because a stepped effort test in a lab is so carefully controlled compared to conditions on the open road, repeated testing can give you some idea if you fitness is improving. Within increased fitness your heart rte at a given level of exertion will usually decrease and your ability to sustain a particular power level will increase. As your fitness increases, you should also be able to sustain a power output that is a higher % of your power at VO2 max.
Interpreting the data from the VO2 max workbook
Within the Microsoft Excel workbook with your stepped effort VO2 max test, the summaries likely to be of most interest to you are the means, graphs, and training_zones worksheets.
All three of these worksheets are preformatted so that if you simply go to these sheets and print them they should print out legibly. In the graphs work sheet, take care to not accidentally click on a chart before printing or then only a single graph will be printed out at a time rather than all of the graphs.
For real data junkies the raw data can be viewed in the other worksheets
The following is an explanation of the variables in the means worksheet.
Column A: The average heart rate for approximately the second half of each 3-minute step (near steady state conditions) is given in bets per minute.
Column B: Mechanical power in Watts is the power (= work divided by time) that your muscles generated that was useful fro propelling the bike. Note a 0 is entered for the resting data since no mechanical work was being performed.
Column C: These times in seconds were just used by me to cross reference what portion of the data were used to calculate values for each step. Don't worry about the fact that the time for the resting measurement does not come before that of the first value while riding the bike.
Column D: VE is the minute ventilatory volume. This corresponds to how many liters of gases you exhaled each minute. It is the product of the tidal volume (Vt in liters) times your breathing frequency (breaths/minute). This value was the average over the last 100 seconds of each step, whereas the tidal volumes and breathing frequencies were only measured for the last five successive steps. Consequently, there may be some minor differences between the product of the individual values shown and those in this column which are over a much longer interval. Some physiologists have suggested that a sharp rise in VE is an indication that the lactate threshold has been reached, but objective methods for determining exactly what a "sharp increase" is are elusive at best. Some literature will refer to such a "sharp rise" in VE as a ventilatory threshold.
Column E: This is your rate of oxygen consumption in liters per minute. The proper designation for this is a V with a dot over it O2, hence know as V dot O2. However, my fonts do not have the character need to put a dot over all of the "V"s that indicate units of volume per unit time. Note that this value is not corrected for the size of an individual. Larger individuals have more metabolically active tissue that requires oxygen, and hence they will generally have higher values than smaller individuals.
Column F: This is the rate of CO2 production in liters per minute. Note that this value also is not corrected for the size of an individual.
Column G: This value is the Respiratory Exchange Ratio (RER) which is also sometimes known as the Respiratory Quotient (RQ). This is the ratio of CO2 production to oxygen consumption. Values of this are lowest and often around 0.8 when only fat is being metabolized aerobically. As increasingly more carbohydrate are burned to provide energy for the muscles this value increases to 1 or a bit more is the individual is going anaerobic. Getting accurate CO2 measurements is a bit tricky on our instrumentation because the sensor tends to drift over long periods of time, and inaccurate CO2 measurements affect RER. So, we have to take these values with a grain of salt. Commonly, a terminal value of RER (at VO2 max) should be around 1 to be considered a "good" test. RER is also sensitive to what an individual has eaten and how recently they have done so. That is why we prefer to do the VO2 max test more than three hours after the last (light) meal. Values of RER are used to convert rates of oxygen consumption into amounts of metabolic energy since the energy gained from breaking down a given fuel source depends on what it is metabolized (fat vs. carbohydrate, etc.) and the chemical pathways that are used to extract energy.
Columns H, I and L are more stuff to help me make sure I have the right data in the right place and that the data make sense.
Columns J and K are the average volumes (liters) and breathing frequencies (breaths/minute), respectively, based on the last five successive breaths within each 3-minute step of the test. Most individuals will not have these values unless they volunteered to be a subject for the exercise physiology class or were some of earliest tests we performed.
Columns M-Q are different ways of expressing your metabolic rate or effort.
Column M: is the rate of oxygen consumption per kilogram of your body mass per minute. The largest value in this column is your value of VO2 max, and this is the value that is usually used to compare the fitness of different size individuals. Note that fat is relatively inert metabolically. Consequently, if your body weight includes a fairly large % of fat, then you may have an unexpectedly low value of mass specific VO2 max. For example, if a 200 lb individual lost 20 lb of fat and maintained a constant level of fitness, then the mass specific VO2 max would increase by about 10%. Such a difference between 50 and 55 ml O2/kg min is a huge difference when you look up values relative to the norms for age and sex. Also note that VO2 and VO2 max depend mainly on the demand for oxygen that the muscles are creating. Thus, aerobically sustainable activities requiring work from a greater muscle mass will demand more O2. Running and cross country skiing usually use more muscles (because of the arms and abdomen) than cycling. Thus, VO2 max tests are activity specific, although experienced cyclists often can attain values of VO2 max that are a very high fraction of those attained during a running treadmill test. Beware that many web sites that give percentile ranking of VO2 max without specifying the activity used during the test. Our VO2 max for cycling might be a conservative estimate of your VO2 max for a running test. Yet, all this gets even more complicated as the effects of training are also activity dependent, and running uses slightly different leg muscles and in slightly different ways than in cycling. Thus, a really good cyclist may not be able to sustain very high running speeds aerobically because of the lack of specific training in running. The ExRX.net web site has a calculator that you can use to get a better idea of how good your mass-specific VO2 max values are compared to the general population (but realize these values are for a running test). In the left hand column of the calculator (which is for a variety treadmill stepped effort protocols):
- In the top field select the Bruce protocol (no relation to me)
- Select your sex
- Enter your age in years
- Enter some value of time such as 10 minutes for the total duration of the treadmill test.
- Click on the calculate button. The corresponding mass-specific value values of VO2max (in ml O2/kg min) for this treadmill time will then be displayed in the second box from the top in the right hand column, and this is the same value as obtained in your test. The percentile ranking (% of population that is lower than you) in the score box will give you a good idea of how extraordinary (or ordinary) your values are.
- If the value of VO2max displayed for the time you entered is too small, then enter a longer time and click the calculate button again to get the new corresponding values of VO2max and percentile rating. If the value of VO2max displayed for the time you entered is too large, then enter a shorter time and click the calculate button again to get the new corresponding values of VO2max and percentile rating. Keep repeating these procedures until a value of VO2max is displayed that approximates the value you got for the test we performed.
Column N is in term of units of heat energy (kcal) per minute. For those of you interested in weight control these values may be of particular interest.
Column O is in terms of metric units of mechanical units of work (kiloJoules, kJ) per minute. Note that a Joule is a metric unit of work and units of work divided by time equals power. Metric units of mechanical power are Watts (=1 Joule per second).
Column P is in terms of kJ per second.
Column Q is in terms of Watts (J/sec).
Column R: MET or metabolic equivalents are the metabolic rate at a given level of exertion divided by the resting metabolic rate. This is a convenient way for exercise physiologists to compare levels of exertion among different size individuals and for different activities. For example many physiology books have tables indicating how many METS are used during running at different speeds, swimming, cycling etc. The more muscles that are used during an activity the higher the level of exertion and this will be reflected in higher values of MET. Diverse species of animals can often perform locomotion from 10-20 MET.
Column S: This is the difference between your metabolic rate during exercise and at rest. Thus, this metabolic power (in Watts) is the rate your body is using energy to perform the mechanical and physiological work required to cycle at different intensities.
Column T: This net efficiency (or sometimes called delta efficiency) is probably the most meaningful measurement of efficiency. No engine, and that includes our bodies, is 100% efficient as a variety of chemical reactions combine ultimately to produce muscle force and perform mechanical work against the external environment. This efficiency is calculated as (mechanical power during step N+1 minus that at step N) divided by (metabolic rate of using energy during step N+1 minus that at step N). Thus, this measure only uses the metabolic cost associated with exercising rather than including the resting metabolic rate. Physiologists often use the rule of thumb that this efficiency is 25% in order to estimate mechanical work for a given metabolic rate when mechanical work has not been measured directly. A nice feature of our methods is the direct measurement of both the metabolic energy used and the mechanical work produced. Hence, we need not make any assumptions about efficiency. A small change in efficiency can have a profound effect on you sustainable power levels. For example for net efficiencies of 20and 22% when metabolic rate is 1000 Watts will produce 200 and 220 Watts of mechanicl work, respectively. This extra 20 W corresponds roughly to riding one gear higher and going about 20 vs. 22 m.p.h. on the flats with no wind or drafting. That is a big difference! A recent study of Lance Armstrong over the course of several years fond that one of the most conspicuous changes in his physiology was in his efficiency. Similarly, a recent study of Kenyan distance runner found that they were much more exceptional for their efficiency rather than just having high VO2 max. For the measurements in our lab, many experienced cyclists have values of 20-23% net efficiency, and this efficiency is affected both by the mechanics of an individual's pedaling and well as that individual's efficiency at extracting energy from the fuels that the muscles are using. If you have a net efficiency much below 20%, then you may want to consider whether your pedaling mechanics could use some improvement.
Column U: This value of "gross efficiency" (for lack of a better word) indicates the fraction of your total metabolic rate that is being used to generate the mechanical power to pedal your bike. At slower speeds your resting metabolic rate is a larger fraction of your total metabolic rate (= resting rate + rate due only to pedaling), which causes this value to increase with increased mechanical work. Keep in mind if an adult male goes on a 6 hour ride, his body will require about 500 kcal just existing without any additional exertion. These calories would be used regardless of whether or not somebody exercises. Thus, the energetic benefits of exercise are usually more obvious if one considers the energetic expenditure above and beyond the resting metabolic rate. If you ride with a power meter, the work performed and recorded over the course of a ride is just such a figure rather than one that includes resting metabolic rate.
Columns V and W are the %concentrations of CO2 and O2 in your exhaled breaths (in air the %O2 is 20.93 and % CO2 is 0.03%), respectively (you will not usually have these values unless you were a volunteer for the exercise physiology class). When you are active you use up O2 and produce CO2, which results in concentrations in your exhaled breaths that are less than and greater than those in air, respectively. However, one point of confusion often is that during strenuous exercise the concentration of O2 in your breath goes up and that of CO2 goes down when you work harder. At first this does seem to make sense since as you work harder you need more oxygen and will produce more CO2. However, the total amount of oxygen extracted is the product of the O2 extracted in each breath and the total volume of all breaths per unit time. Consequently, even if the %O2 in your breath decreases, the amount of O2 consumed can increase as a result of a very large increase in the total volume of air passing over the lungs. Similarly, even if the % CO2 in your breath goes down, if the total air exchanged increases by a large amount, then the total CO2 expelled (% concentration times volume) can still increase.
Column X is the blood lactate concentration determined from the finger stick. If some rows in this column have no values after we started making measurements, then we did not have a valid value for this time interval. The lactate threshold, LT is commonly designated as the point at which this concentration exceeds 4 mMoles/liter. One should keep in mind however that different individuals do have some variation in the amount of lactate they can tolerate for a prolonged period. One of the desirable features of using LT to establish training zones is that it occurs below a maximal effort, and thus it is likely to be more repeatable than some measures of a maximal capacity. Determining maximal physiological capacities such as VO2 max can be fiendishly difficult because of the motivation of the individual as well as their nutritional state, daily biorhythms, etc. VO2 max is also rather minimally sensitive to training compared to the %of VO2 max at which LT occurs and the % of VO2 max that can be sustained for long periods. Thus, some of these submaximal indicators may be more useful for tracking your fitness.
Column Z: This is the equivalent speed expressed in minutes per mile.
Column AA: This is the equivalent speed expressed in minutes and seconds per mile.
The training zone worksheet
I have entered formulas to indicate heart rate for your different training zones based on the data I have for you. If you want to determine training zones based on maximum heart rate (probably less reliable than using HR at VO2 max or LT), then do some trials to determine yours and enter the result in cell B5. The formulas in the table below will update automatically.