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This is a post from Dr. Carrie Smith PT, DPT
Your palms are a little sweaty, and there may even be a small bead of perspiration pushing its way through your scalp and trickling down your forehead. You notice your breathing tick up and your hands shaking. Garmin tells you that your heart rate is a little high. Sound like a race start line? Could be. But in this moment, you’re sitting at your computer and have just clicked the “submit payment” button for your biggest race of the season. In the spirit of Ricky Bobby, many of us then say “I wanna go fast!”
Great! So what are the next steps? What are you capable of? How do you even know? Performing a VO2/threshold test can provide valuable physiologic information to help you establish appropriate training zones, identify areas of strength and weakness relative to your goals, identify how many calories you’re burning at different intensities and help you dial in race day planning and preparation.
What are VO2 max, VT1 and VT2?
Activities requiring energy expenditure for 90 seconds and longer rely heavily on your body’s ability to supply oxygen to working muscles. VO2 max is your body’s maximal aerobic capacity—how hard you can go and still have your cardiorespiratory system and muscles supply and use oxygen to fuel performance. The VO2 max is often expressed relative to bodyweight as mL (of O2)/kg (of body weight)/min, and the higher the number is, the more likely you are to perform well in endurance events. Many professional endurance athletes fall in the 70-85 mL/kg/min range [1,2]. Several of the triathletes we’ve tested who are frequent fliers on the World Triathlon Corporation podiums have been testing in the 55-65 mL/kg/min range. While it is fun to know your VO2 number and obtain an idea of your current potential, this is one of the least important values from testing. Beneath this VO2 ceiling are submaximal thresholds that are better predictors of endurance performance and keys to establishing appropriate training ranges for each individual athlete.
The first and second ventilatory thresholds (VT1 and VT2) are two key submaximal values that can be obtained from testing. Factors like pace, power and how economically you burn calories at these thresholds are more important for training and race performance. VT1 is often referred to as the aerobic threshold. This is identified by the first measurable increase in ventilation, and as intensity increases beyond this point, we begin expending more calories and using more carbohydrates instead of fat for fuel. This threshold is reflective of the heart rate and pace you can maintain for several hours with adequate training. This value is important for long-distance events, such as marathons, ultramarathons and long-distance triathlon, as glycogen (carbohydrate) depletion is thought to be one of the limiting factors in performance [3]. The faster you are at this threshold and the more economically you burn calories (fewer is better!), the more likely you are to perform well. VT2 occurs at a higher exercise intensity than VT1 and is often called the respiratory compensation point (RCP). This represents the power or pace that can be held for approximately 60 minutes. This value is closely correlated with lactate threshold, and cyclists might identify this with their functional threshold power (FTP). The power and pace at this value are closely related to race times in 10-15k runs and 20-40k cycling events. As exercise intensity increases beyond this threshold, our bodies begin producing metabolic waste faster than it can be cleared, and the time for which we can maintain this effort decreases dramatically.
How does the test work?
Prior to testing, we’ll ask you some questions about your goals, current training loads and recent race times to help us dial in a test protocol to capture your VT1, VT2 and VO2 max values. To do this, the test will start at a relatively easy pace for your current fitness level and will increase in intensity every three minutes until a maximal workload is obtained. Throughout the test, you’ll be wearing a heart rate monitor and a mask that covers your mouth and nose. We will capture the exhaled air that will then be analyzed to find your threshold and max numbers, along with the heart rate, power and/or pace that occurs there.
Since the test requires maximal effort, we ask you to treat the test as you would a 5k running race or sprint triathlon. The day before the test should be a rest day or relatively short effort. The morning of the test you’ll want to eat and drink as you are accustomed to on race day. If you’re performing a run test, wear clothing and shoes you would race in. If you are cycling, you will bring your own bicycle and shoes to hook up to the computrainer so we can control the power output. Once you’re in there, your job is to run or pedal as long as possible! Most tests last approximately 20-30 minutes.
Test results and application
You made it! After the last few minutes of hard work are over, then it is time to sit down and discuss the results. This is the fun part, and each conversation is different based on your specific goals and current fitness level. Here’s what you’ll receive:
Your heart rate, pace or power and calorie burn (and percent coming from fat and carbohydrates) at VO2 max, VT1 and VT2
We’ll also use your heart rate and paces from VT1 and VT2 to establish training zones.
A detailed description of what these training ranges mean, as well as tips on how to structure these into your training season
For example, a typical zone 4 (VT2 or threshold) workout may include 30-40 minutes’ worth of interval time broken up into six to 20 minute intervals. We include a customized two-week sample schedule to help you see how you might balance interval work with recovery.
Identification of strengths and weaknesses relative to your goals
For example, if your 10k goal time is 50 minutes (~8:03 min/mile) but your VT2 pace is currently 8:20 min/mile, then working on some zone 4 threshold intervals can be beneficial to increase your speed at VT2. Or, if you feel like you’re always running out of steam at the end of your long cycling rides, we can check your VT1 heart rate, power, calorie burn and carbohydrate burn to see if pacing and/or nutrition are limiting your performance. For most long course training and events, the primary mistake we see athletes making is going too hard too often to make adequate changes to the aerobic energy system. Using VT1 values as a guide, we can help you start to understand how to better maximize your training time.
Race pacing, hydration and nutrition strategies for your best performance
Even pacing from start to finish is the best way to reach peak performance on race day. We’ll discuss what this looks like using common training software like Training Peaks (you can create a free account), as well as easy ways to take a quick look at your training to see if you hit your desired targets in your workout. For example, if your workout goal that day is to train your aerobic energy system, you can check the heart rate histogram to make sure the majority of your workout was spent in zone 2.
Identification of “training errors” for injury risk and poor performance using your VT1 and VT2 values
Once these are entered into your training software, you can check both individual workouts and accumulated data over months and years to see if you are at risk. Consistency in training over time and understanding which physiological systems you need to work on to reach your goals are keys to success in endurance sports. We can’t wait to help you identify these things and set you up for your best training season and race day! References:
Noakes, T. (2003). Lore of Running, 4th ed. Champaign, IL: Human Kinetics.
Faria EW, Parker DL, Faria IE. The Science of Cycling—Physiology and Training Part 1. Sports Med, 2005; 35(4): 285-312.
Brooks GA, Fahey TD, Baldwin KM. (2005). Exercise Physiology: Human Bioenergetics and Its Applications, 4th ed. New York: McGraw Hill.