article by Makenzie Madison: Zoom Performance Level 1 Coach; B.S., Exercise Physiology - ISU; USAT Level 1 Certified Coach

Today, the metabolic testing that professional athletes receive is now available to the age groupers. However, there are many misconceptions that come along with metabolic testing that undermine all of its full potential benefits. The most widespread misconception is that the only information you’ll get from metabolic testing is your VO2max number. Well, I have even more news for you- there is way more to metabolic testing than that VO2max number. In fact, that number isn’t too important at all; it’s the abundance of other valuable information that you’ll get from being tested that is worth it’s weight in gold to your coach and to you as an athlete. Metabolic testing gives specific physiologic responses for monitoring and the right guidance to train your body to help you become your best. Go ahead and glance down to see what types of buried treasure you can discover from a small health investment. Here’s more about the what, where, when and why right now- the peak-post season is one of the best times to get metabolic testing. So what kinds of physiologic tests can you get?

RMR. Resting Metabolic Rate

Know how many calories your body burns each day to maintain your vital functioning

It’s the end of the season and you still haven’t lost those last couple pounds… Or perhaps you weigh the same but your caloric needs have skyrocketed. Perhaps you are losing weight and NOT regenerating the muscle mass you damaged during training or losing weight in a negative way. How can you tell or know how much your body needs in fuel each day? Your daily exercising can combat hunger- a good and a bad thing. After training, circulating catecholamines, endorphins and other substances suppress your hunger, exactly the point when you need to refuel your body to recover and rebuild your muscle mass into a stronger than before state which is the sole the purpose of your training. 

A resting metabolic rate test will give you the baseline value of what your body burns each day- ranging from 1300 -3500+ calories per day (small, petite, very sedentary older woman to taller, middle aged, very active male, Lee et al).  It will give you better guidance of exactly HOW many calories you need each day. On the other end of the spectrum, you could want to lose those extra pounds. Metabolic testing will cue you in if you’re actually not eating enough and forcing your body to not let go of those extra pounds or if it’s that you are eating too much. Again, knowing your resting metabolic rate gives you the specifics on how much calories you burn just “existing” or for all your organs and vitals to operate. Obviously, activity levels vary from each individual and so do metabolic rates. Pinpointing how much your resting metabolic rate is and then further adding the calories you burn during exercise can give you a pretty good estimate of how to balance your bodies energy and improve your training, recovery and how you feel. 

Know your ratio of how much fat and carbohydrate you are burning

The body has a combination of three different fuel sources to burn: fat, carbohydrate and muscle. Each individual has different combinations of how much fat to carb ratio they burn at rest. Testing your resting metabolic rate will give you how much of your baseline metabolic rate is contributed from each of the three different fuel sources- carbs, fat and protein. Specifically, your fat and carbohydrate contribution can be shown through your expired gas ratio of oxygen and carbon dioxide. This ratio changes depending on whether you’re burning more fat or carbohydrate- identifying which substrates your body is using for fuel and allowing you to adjust your diet accordingly. The higher the ratio the more carbohydrate base you are burning. The lower the ratio, the more fat sources you are burning. Interestingly, it’s been found that an increase in RMR is noted by a decrease in RER- meaning that you are burning of more fat and your body is capable of greater levels of increased fat oxidation. (Leemer et al., 2001) 

Know if your metabolism is lower, normal or higher 

As an endurance athlete, resting metabolic rates have been scientifically found to be about 54% higher than sedentary counterparts- meaning that if you do not take your higher RMR along with the total amount of energy burned during training into the fuel equation, you will be looking at a negative body energy balance. This can cause your body to store more fat and actually decrease your metabolism, preventing those numerous guilt-free chocolate indulgences to happen. It can also cause your body to not be an efficiently trained fuel burner, disrupt your metabolism and hinder proper recovery and improvement. 

Know your muscle mass and fat body composition 

A decline in RMR highly associated with an increased fat mass and a decreased muscle mass. Metabolic rate is very closely associated with body composition. Detraining or calorie deprivation/excess are often culprits of a decline in resting metabolic rates… as well as an increase in age. Getting your RMR tested sheds light on how to find the balance by knowing how many calories you need as well as giving you guidance if you are taking the necessary steps to increase and prevent declines in your RMR. Just by instigating a strength-training program, you can increase your RMR up to 9% or about 600 kcals per day due to an increase in muscle mass and a decrease in fat mass.  As an endurance athlete, your strength training not only is shown to increase your VO2max but also prevents a decrease in your RMR. Other RMR influential sources in your body include increased levels of thyroid hormone concentrations (T3, T4), norepinephrine and epinephrine levels (catecholamines, “go”endorphins) which induce lipolysis or the break down of fats, the rate of protein synthesis and glycogen resythesis in your muscles. Genetics also play a role and give variation to RMR just as some people might as well be garbage disposals and some rabbits. Interestingly, in a study done by Lee et al., human RMR was found to be highest in the winter and lowest in the summer. However, this does not entitle you to eat more during the holidays just because a study found RMR to be higher.

Again, fine tuning your caloric needs and making sure you meet them helps your body to rebuild, recover and make you a stronger athlete. If you are to expect anything from getting your RMR tested it in fact might slightly underestimate your RMR by about 3%, especially if you are an endurance athlete due to your bodies capacity to conserve when needed and burn when needed. But indirect calorimetry measurements have been scientifically proven to have extremely high test-retest reliability. (Yates et al, 2004) When testing your Resting Metabolic Rate under controlled conditions, the results are a very stable and reliable representation of exactly what your RMR truly is. (Thompson, 2002) It might also be beneficial for you to go over such results with a nutritionist or dietitian to get even more information and direction for your daily and long term diet goals.

What to do before your RMR test:

• Get your RMR tested early, first thing in the morning after you wake ~7-9 AM
• Do not consume caffeine or any food. You should fast and only drink water 12 hours before the test (Lemmer et al., 2001) 
• Wake up as slowly as possible- avoid showering before the test
• Wear comfortable clothing

VO2max. Exercise Metabolic Rate  

Know if you are becoming more efficient 

You will be able to see how efficient you are which can be thought of as your economy in terms of total energy costs at given workloads. Throughout your exercise metabolic testing, our New Leaf machine will be analyzing the gas you are expiring and measuring how much oxygen you take in. Your endurance capacity is considered your aerobic zone, or where your oxygen uptake meets your oxygen demand from your working muscles.  The data gives us values of your RER or respiratory exchange ratio (RER) or quotient, which consists of the two types of gases you are expiring- oxygen and carbon dioxide. Depending on the given workload during the test, either on the treadmill or the bike, the less CO2 you produce and expire off, the lower the RER. As mentioned previously from the RMR test, the lower the RER 0.7-0.9, the more fat you are burning and less fuel is required for a given workload meaning that you are a more efficient athlete. 

Know if you have improved your endurance capacity

Again, adding more onto your efficiency factor, you can further discover your endurance capacity or how strong of an aerobic, endurance base and range you possess. The exercise metabolic rate test will give you an idea as of how big of range your aerobic zone is by defining it with multiple pieces of information such as your wattage, effort, heart rate, and running speeds. It is very beneficial to be retested in a couple months time, perhaps after a base training season or pre and post season to see how your aerobic and endurance capacity has changed. Seeing a widening in your endurance range signals that you’re training is on track and that your body has responded to the types of training you completed in the past couple months. On the other hand, it can let you and your coach know which areas you need to work on for next season, or for future training. 

Besides knowing your endurance capacity ranges, it provides you with excellent information as to what paces, efforts and zones you should stay in for longer distance events such as 70.3’s to Ironman races, or perhaps those long rides and runs on the weekends for the upcoming base season. 

Know your heart rate responses at given running paces and wattages for your intensity zones

Throughout the test your heart rate will be constantly recorded at all of the workloads you are capable of up until your absolute max, giving a complete range of your heart rate responses at all of your training zones. Your training intensities can therefore be divided into recovery, endurance, tempo, threshold and high intensity or interval training heart rate zones. The heart rates recorded will be applied to the metabolic data to pinpoint and fine-tune your intensity zones with the physiological turn point information. However, heart rate is variable and the heart rate zones are not marked as a definitive endpoint for a given intensity zone. If you want to stop and hinder improvement, you can strictly stay and focus your whole workouts around staying in particular heart rate zones. The benefit of this would only work well for recovery- when you are forced to complete a recovery training session it keeps you from pushing harder than your should. Heart rate zones should be used as guidelines and not as an ultimatum. Heat, hydration status, your overall bodies’ condition- sick, healthy, lack of sleep, etc. can manipulate your heart rate responses meaning that you should use it as a guild line for underlying physiological issues. As the saying goes “nothing will happen if you don’t push the envelope”- same thing with heart rate zones. Don’t be afraid to go for it and push into a higher zone if you’re feeling good and ready for it, it’s how you improve. For instance it’s been stated that when you see the deflection from linear rise in heart rate it’s not per se your anaerobic threshold or lactate threshold point. In fact, it is caused by factors unrelated to the metabolic events contributing to the LT or VO2max- meaning that you can’t just gauge your threshold when your heart rate starts to spike- you need to be metabolically tested. There is a day-to-day fluctuation in what your heart rate actually is at your LT. (Parker et al., 1997) Inevitably, your heart rate zones can be used as guidelines. Guidelines that can be looked at as “Wow, I’m pushing harder and riding faster than I normally am at a lower heart rate” or “my heart rate is 10 beats lower than usual zone 3 or tempo… maybe I should scale back the training a bit.” Metabolic Exercise testing gives you your typical cardiac responses and how to gauge if a workout feels really good or off. It’s one of the valuable physiologic markers at different intensities you’ll get from the test results. 

Know what your race paces are for the bike and run legs for sprint to Ironman distances 

Metabolic testing takes out the guesswork of pacing- for the bike leg and run leg and gives you tools to monitor your progress so you can nail that race. Metabolic exercise testing can give you the paces, wattages and heart rates that you can sustain from sprint distance triathlons to Ironman distance triathlons. Again, it gives you’re your aerobic range, or endurance capacity that you are physically capable of performing for an Ironman to the short lactate or anaerobic threshold speed you can hold off for an hour of that sprint triathlon. It let’s you know what your pace, wattages and heart rates should be for the swim, bike, and run you can sustain with proper training giving you a physically, feasible goal. It makes it easy to predict your perfect race as well as prepare for the proper paces for your perfect race for you as the athlete and your coach. 

Know your Anaerobic Threshold (AT, Lactate Threshold LT)  

Anaerobic threshold has been suggested to be used as a predictor of endurance performance and fitness level of athletes. Increasing lactate threshold is key for endurance athletes performing in races lasting from 1+ hours in other words it is KEY for endurance events. Elevating your lactate threshold allows you to race better below, at and above your lactate threshold more efficiently.

During a VO2max test your blood lactate levels cannot be directly measured by the gas analyzer machine.  However, VO2max testing provides an indirect way of indicating at what intensity of running or cycling your lactate threshold does occur. Instead of taking two tests, one VO2max test and one lactate threshold test; you get two tests in one. If you’re the elite athlete who wants to measure precisely when your LT occurs then taking the two tests might be beneficial if you monitor your training every couple of weeks. Otherwise, the information provided from the VO2max test should provide you with enough detail… unless you’re at the Olympic Training Center. This can give you your marathon pace, the wattage for that 56 mile or even 114 mile bike leg in an Ironman. It tells you what your body is physically capable of sustaining the highest aerobic workload possible for about 1 hour at your LT and how much lower you should stay below that workload for longer race durations… so you KNOW that you won’t blow up and those extra matches aren’t burned.

The metabolic cart looks at a couple key factors to determine your anaerobic threshold or lactate threshold which is defined as the highest exercise intensity corresponding to the steady state between the diffusion of lactate into the blood and the elimination from the blood (Stegmann et al., 1982). It’s essentially the point in which your body starts to have troubles delivering enough oxygen to your exercising muscles and needs more fuel in which your lactate system kicks in. Lactate is an energy source that you probably know as the burning point- this is due to its acidic compound in nature while giving energy signals to your body I need more oxygen. The point in which your body can no longer take up and utilize the lactate as fast as it is being created means you have reached your lactate threshold or anaerobic threshold. Once you have hit your AT or LT, the accumulation of lactate rises at a steeper rate until your VO2max. 

So what does the metabolic cart look at to determine your anaerobic threshold? It looks at your Ventilatory Threshold, or the point at which you start breathing heavily and is known to correspond to your AT.  Stemming from your increase in respiration, typically the gas analyzers recognize the greater exponential-like increase in CO2 concentration which is generally the cause of your disproportional, sudden rise in ventilation. (Leemer et al., 2001) It’s the point at which your body starts calling for help and really wanting more oxygen. Additionally, the significant rise in VCO2 causes a break of your RER ratio above 1.0. Anaerobic threshold can also be identified with a significant elevation in HR. The fact that we can measure all of these variables at once gives us a non-invasive technique to measure your Lactate Threshold. (Anderson et al., 1989) 

Know your VO2max 

Heck, why not include it in the list of things you can get from your exercise metabolic rate test. As some of you may know, if you’re already a seasoned athlete your VO2max won’t change too much unless your weight does or with increasing age. All in all you won’t be able to drastically change your VO2 +/- 10 ml/kg/min after you’ve been endurance trained for a couple years- you’re pretty much stuck with that number for the rest of your life due to your genetics.  What the VO2max number does give you is your exercise limitations or your current limit to what you can accomplish. It’s the limit or max amount of oxygen your body can consume or take up while you are working at your hardest. After all, this does make sense in which the greater oxygen consumption capacity, the greater capacity you have to swim, bike and run harder and faster. The amount of oxygen that can be delivered to your muscles does limit what you as an athlete is capable of performing since oxygen is the rate limiter for the ATP cycle and only aerobic fuel source. Your other energy systems, anaerobic or lactate metabolism, creatine phosphate systems are anaerobic and are even more limited as well as rate limiting. However, it’s important to take steps to stop the decrease in your VO2max that occurs beginning around the age of 40 resulting in a typical, expected 5% decrease per decade thereafter.  This is just one of the many other reasons to get tested and figure out what your exercise capacity playing field range is at your current age.

What to do before your Metabolic Test: 

Dehydration and lack of food will mess up your metabolic readings. Do not try to magically lose weight and starve yourself from water and food a day or two before the test in hopes of getting an increase in your VO2 number by a couple ml/kg/min, or increasing your VO2 number by trying to lose weight. Unless you magically gained 10 lbs overnight- you fluctuate in weight while you train anyways. Plus, there’s an absolute VO2 that you can take away which allows you to compare against other individuals or yourself regardless of body size or weight. After all, a metabolic test on how you REALLY burn fuel and your VO2’s at a given workload won’t REALLY be what your body really does during exercise. Lesson and advice- train, sleep, eat as normal before the test. 

Currently, with it being the end of the typical season, it’s safe to say that you are currently near or at your peak condition. This is the perfect time to get your exercise metabolic rate tested. The major benefit of getting tested now  gives you your peak ending point to look to compare your fitness to next season, for base training and to help you know if you have improved your overall physiologic responses to the training, workouts and conditioning. Then come again in the spring, getting tested again can prove if all that endurance training you completed over the winter REALLY did benefit you. When you start to race again, you will know the ACTUAL numbers and workloads you can put out or in the past. 

Testing our limit- the VO2max test brings across the issue of is it truly your limit? The best you can do- eliminating any possible hopes for improvement? The answer is yes… and no. As a coach and athlete, I don’t necessarily believe in limiting factors or in thinking that an accomplishment at a capacity beyond what your test results say isn’t impossible. On that note, don’t be afraid to push the envelope; just because your training zone 4 was set from 154-167 doesn’t mean you can’t go 1 heart beat above or that your easy mile pace just dropped down to 6:50 from 7:15. If you believe that your test results are an ultimatum and you stick strictly to those zones, improvement can’t be guaranteed. Taking baby steps by cruising up the pace a little more when you’re feeling good- now that’s stretching your limit. What are your current limits? For more information and to get an even better understanding of the numbers you’ll get from metabolic testing visit:

http://www.getzoomperformance.com/page.php?pageID=2&moduleInstanceID=32

Feel free to contact Zoom Performance with any questions you have or on how to get your numbers (not just one) from our own metabolic testing equipment with Zoom’s knowledgeable and experienced endurance coaches.  

References

• Anderson, G.S. & Rhodes, E.C. (1989) A review of blood lactate and ventilatory methods of detecting transition thresholds. Sports Medicine. 8:43-55. 
• Befroy, D. E., Petersen, K. F., Dufour, S., Mason, G.F., Rothman, D.L., Shulman, G.I. (2008) Increased substrate oxidation and mitochondrial uncoupling in skeletal muscle of endurance-trained individuals. Proceedings of the National Academy of Sciences of the United States of America. 105:43. 16701-16706. 
• Lee, M., Sedlock, D.A., Flynn, M.G. & Kamimori, G.H. (2009) Resting metabolic rate after endurance exercise training. Medicine and Science in Sports and Exercise. 41:7. 1444-1451. 
• Lemmer, J.T, Ivey, F.M., Ryan. A.S., Martel, G.F., Hurlbut, D.E., Metter, J.E., Fozard, J.L., Fleg, J.L. & Hurley, B.F. (2001) Effect of strength training on resting metabolic rate and physical activity: age and gender comparisons. Medicine and Science in Sports and Exercise. 33:4. 532-541. 
• Parker, D, Robergs, R.A., Quintana, R., Frankel, C.C. & Dallam, G. (1997) Heart rate threshold is not a valid estimation of the lactate threshold. (1997) Medicine and Science in Sports and Exercise. 29:5. 235. 
• Plato, P.A., McNulty, M., Crunk, S.M. & Ergun, T.A. (2008) Predicting lactate threshold using ventilatory threshold. International Journal of Sports Medicine, 29:732-737. 
• Stegmann, H. & Kindermann, W. (1982) Comparison of prolonged exercise tests at the individual anaerobic threshold and the fixed anaerobic threshold of 4 mmol l lactate. International Journal of Sports Medicine. 3:105-10. 
• Thompson, A.E. & Golding, L.A. (2002) The day-by-day reliability of resting metabolic rate. Free Communication/Slide Resting and Recovery Metabolic Rate. 34:5. S217. 
• Wasserman, K., Whipp, B.J., Koyal, S.N. & Beaver, W.L. (1973) Anaerobic threshold and respiratory gas exchange during exercise. Journal of Applied Physiology. 35:236-43. 
• Yates, J.W., Cullum, M. & Pittsley, J. (2004) Validation of a portable, indirect calorimeter for the measurement of resting metabolic rate. Medicine and Science in Sports and Exercise. 36:5. S247.