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Measure What Matters: Fitness Tracking in Every Training Phase

BY Matt Fitzgerald

This periodized approach to fitness tracking helps you prioritize which metrics you should be monitoring based on your racing goals.

This article is about how to track your fitness during the build phase of endurance training. But before I can supply you with specific guidelines to follow in your next build phase, I must first give you some context.

Understanding Periodization and the Three Phases of Training

For starters, what is a build phase? Good question. There are three phases of an endurance training cycle, each with its own purpose. The build phase is the second of these, falling between the base and peak phases. It’s important to know the purpose of each phase if you’re going to track your fitness within it in a meaningful way. 

Base Phase

The purpose of the base phase (i.e., the first of the three phases) is to develop overall training capacity, a process that is sometimes referred to as “training to train.” Your goal here is to prepare your body to handle the more intensive training that will follow in the build and peak phases. This is accomplished through increasing amounts of low-intensity training with a dusting of high-intensity work on top.

Build Phase

The purpose of the build phase is to maximize your all-around endurance fitness and begin the process of honing race-specific fitness. In the early part of the build phase, training should be highly varied, featuring workouts that challenge and develop all components of endurance fitness, from anaerobic power to endurance. As the phase progresses, your key workouts should become increasingly specific to the demands of your upcoming “A” race.

Peak Phase

In the peak phase, this process continues. The most challenging workouts are highly race-specific in nature, and less emphasis is placed on fitness components that are less relevant to performance in the type of race you’re aiming at. To oversimplify somewhat, between the beginning of the build phase and the end of the peak phase you’re looking to transform from a jack of all trades to a one-trick pony, fitness-wise.

Measuring Relevant Fitness Markers Based on Training Phase

The most common mistake that athletes make in monitoring progress is expecting to improve at all times in anything they measure. As a coach, I find that no matter what I put in front of an athlete — whether it’s a functional threshold power (FTP) test, a critical velocity test, a VO2max test, a maximum-strength test, a sit-and-reach test, or what have you — they want to get a better result each time they repeat it and are disappointed if they don’t. The problem with this mindset is that, as an endurance athlete, you’re not supposed to get better at everything all the time. 

Athletes get themselves into trouble when they interpret a lack of improvement in a certain fitness component as problematic at a time when that component is a lower priority. This loss of perspective lowers confidence unnecessarily and prompts some athletes to deviate from their training for the sake of improving a fitness component that’s less important than one or more others that are then neglected as a result of the deviation. 

To keep things simple, let’s start by looking at how you can monitor the four major components of endurance fitness — including endurance (low intensity), lactate threshold (moderate intensity), VO2max (high intensity), and anaerobic power (very high intensity) — during your training. Then, we’ll look at some race-specific examples that illustrate how to prioritize these metrics as your race draws nearer.

1. Endurance

How do you know if your endurance is increasing? One way is to monitor cardiac drift. During prolonged exercise at a steady pace or power output, your heart rate will hold steady for a while and then begin to slowly increase due to fatigue. This phenomenon is known as cardiac drift, and it provides a reliable indication of endurance. As your endurance increases, you will be able to go longer at a given pace or power before your heart rate and pace/power become decoupled, and the degree of cardiac drift will decrease.

There are a couple of ways to measure cardiac drift. One is the eyeball test. After you complete a long endurance workout, go to the workout graph on TrainingPeaks and scan it in search of the time point at which your heart rate visibly begins to rise. You will know your endurance is increasing if, in future endurance workouts, your heart rate decouples from your pace or power at later time points.

The eyeball test only works when you maintain a steady pace or power throughout an endurance workout. When your pace or power varies during a workout, you can measure cardiac drift by comparing your time-in-zones charts for heart rate and pace or power. Specifically, you’ll want to compare the percentage of time spent in Zone 2 by heart rate against your percentage of time spent in Zone 2 by pace or power. You will always find that you spent a higher percentage of your workout time in the Zone 2 pace or power range than you did in the Zone 2 heart rate range due to cardiac drift, but as your endurance increases, this discrepancy will shrink.

2. Lactate Threshold

If endurance is a measure of fitness at low intensity, lactate threshold (LT) is a measure of fitness at moderate intensity. In functional terms, LT is the fastest pace or highest power output an athlete can sustain for about an hour. 

Many athletes conduct periodic lactate threshold tests in their training for the purpose of updating their training zones, and if you’re one of them, you have all the information you need to track improvements in your lactate threshold. The most commonly used test of this type is a 20-minute time trial. If your average pace or power in this test changes from one time trial to the next, your lactate threshold has improved.

An even easier way to track changes in your lactate threshold is to enable auto-calculation of your lactate threshold in TrainingPeaks. Note that changes in lactate threshold heart rate are less indicative of changes in fitness than are changes in lactate threshold pace or power, so it’s these metrics you’ll want to watch.

3. VO2max

VO2max is a measure of aerobic capacity, or the ability to use oxygen to power muscle work. In functional terms, VO2max equates to the fastest pace or highest power output an athlete can sustain for about six minutes. The simplest way to monitor your VO2max, therefore, is to track your peak pace or power over a six-minute duration as you train.

To do this, go to your dashboard and pull up your peak pace or peak power graph and move your cursor along it until the info bubble shows your best recent six-minute pace or power number. Improvement in this number over time indicates increasing VO2max.

4. Anaerobic Power

Anaerobic power measures an athlete’s fitness at high intensity. The most straightforward way to estimate your anaerobic power is by looking at your average pace or power over a 30-second span. You can track this metric in the same way you track VO2max: Go to your dashboard on TrainingPeaks and pull up your peak pace or peak power graph and move your cursor along it until the info bubble shows your best recent 30-second pace or power number. Improvement in this number over time indicates increasing anaerobic capacity.

Prioritizing Fitness Markers Based on Your Goal Event

Common sense tells us that an athlete can’t expect improvement in a fitness component they aren’t actively working to develop. Whether it’s endurance, lactate threshold, VO2max, or anaerobic power, your fitness in this area won’t increase unless you’re regularly targeting it in workouts that are becoming increasingly challenging. It makes no sense to look for improvement in a fitness component in which you’re training at a maintenance level.

In the early part of build-phase training, when you’re working to develop well-rounded fitness through challenging workouts of various intensities that target all components of fitness, you should see improvements in cardiac drift, FTP tests or similar time trials, six-minute pace or power, and 30-second pace or power. This is true whether you’re training for an Ironman, a 5K, or anything else, although the relative improvements will differ based on your emphasis.

As you move through the build phase toward the peak phase, your focus will switch from developing well-rounded fitness to developing race-specific fitness, which means that you will gradually deemphasize less race-specific fitness components in order to prioritize race-specific components. Following are the four fitness components we’ve focused on in this article, listed in order of increasing specificity for a 5K and an Ironman:

infographic that illustrates Matt Fitzgerald's article for TrainingPeaks about tracking fitness during the build phase using race-specific metrics

This means that, in the build phase of 5K training, endurance is the first major fitness component you will deemphasize, hence the first component in which it’s okay to stop seeing improvement. By the end of the build phase, you should still be seeing some improvement in VO2max, and that’s about it. 

If you’re training for an Ironman, anaerobic power is the first fitness component you will deemphasize and stop improving during the build phase. By the end of this phase, you might be improving in endurance only.

Remember, There’s More Than One Periodization Method

Note that the so-called nonlinear periodization model I’ve described here is not the only valid model of periodization. If you use a different model in your training, one in which your training emphases are sequenced differently than in the linear model, then some of the specifics I’ve presented won’t apply to you. 

But regardless of how you approach build-phase training, you should only expect to see improvement in metrics related to the fitness components you are actively developing. If you take away nothing else from this article, let it be that!

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Trainingpeaks Author Matt Fitzgerald
About Matt Fitzgerald

Matt Fitzgerald is a journalist, author, coach and runner specializing in the topics of health, fitness, nutrition, and endurance sports training (read more about Matt on his blog). Matt uses TrainingPeaks to train, coach and deliver pre-built training plans for runners including training plans built specifically to be used with a Garmin Forerunner. View Matt’s 80/20 running plans here and his 80/20 triathlon plans here.

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