How to Understand All That Data for Triathlon Training

And no, you don’t need to log everything.

Here’s How to Understand All That Data for Triathlon Training

You’ve got your gear and perhaps settled on a goal race and a training plan. Now it’s time to start collecting data to maximize your triathlon training. Whether you’re a seasoned athlete in one discipline—swim, bike, run—or trying your hand at all three, you might be overwhelmed when you first dip into the world of training data, but that’s why it’s important to start slow, says Jennifer Vollmann, a Phoenix-based triathlon coach and owner of Finding Endurance.

“Data is important no matter where you are [in your triathlon journey], and over time it actually starts to matter,” Vollmann says. 

But early on, for that first-timer and early novice, Vollmann collects and uses very little, if any data because it can be so overwhelming. But, she says, once her athletes have a couple of months of base training under their belts, she emphasizes the importance of tracking certain data points. 

Read on for information about key data points, when to track them, and how to implement them in your triathlon training. 

Heart Rate 

Your heart rate is how many times your heart beats per minute (bpm), and it’s a key data point when you’re looking to build endurance, Vollmann says. Ultimately, you want to be able to move for as long as possible with as few bpms as possible—that means your heart is working efficiently. 

When it comes to training, your heart rate plays an important role in determining heart rate training zones. In order to do this, you need to calculate your maximum heart rate (MHR). 

Zone 1: A very light effort, you can maintain a conversation, 50 to 60 percent of MHR

Zone 2: Light effort, you can still hold a conversation, 60 to 70 percent of MHR

Zone 3: Moderate effort, it’s hard to talk but not impossible, 70 to 80 percent of MHR

Zone 4: Hard effort, you can barely get a word out, 80 to 90 percent of MHR

Zone 5: Very hard effort, you can only hold for a minute or so, 90 to 100 percent of MHR

Endurance-building, Vollmann says, happens largely in zones 1 and 2, while tempo or threshold work happens in that gray zone 3—a gray zone because you’re not quite getting the benefit of slow, easy workouts, but you’re not adapting like you would during harder efforts. 

“Heart zones are the most important method when you first get started [in triathlon training],” she says. 


Your aerobic zone—where you’ll really build that endurance—falls into your heart rate zones 1 and 2. 

“Endurance takes a lot of time to develop,” Vollmann says. “It’s a pace you can sustain for a very long time and not feel tired.” 

The hardest thing for most athletes about staying in an aerobic zone is being okay with moving that slowly, Vollmann says. But over time, as your aerobic ability improves, your pace or power (more on that in a minute) will improve, too. 

VO2 max

VO2 max measures the maximum rate at which your body can take oxygen from the air and deliver it through your lungs and into your bloodstream for your muscles. In practice, it’s the maximum effort you can sustain for 30 to 60 seconds—so it’s an all-out effort. Working at your VO2 max increases your anaerobic ability, Vollmann says, and for triathletes, it can be particularly helpful during cycling. 

“In cycling you have long spurts of riding slowly and then when somebody attacks, you ramp up into zone 5 plus, plus, plus before easing back down,” she says. 

Benefits from training at VO2 max will carry over to other training zones, but it’s important to time this training with a coach or seasoned athlete because of the toll it can take on the body, especially during running. 

Most GPS watches have a VO2 max calculator: You’ll run for at least 10 minutes and the watch will measure your pace and heart rate. Vollmann points out that chest heart rate straps are much more accurate than wrist sensors found on most watches these days. She recommends running on a track or riding on a trainer to take out all variables like hills, wind, traffic, and weather. 

Variability Index

Variability index is a very niche measurement, Vollmann says. (She never uses it for her athletes.)  Essentially it looks at how well you can pace a ride. An evenly paced ride would have a variability index of 1.05 or less, which is calculated on your power meter. 

Intensity Factor

Intensity factor is just what it sounds like: How hard or difficult a workout was in relation to your overall fitness. GPS watches and bike trainers have the ability to measure this, but Vollmann says for newer athletes, she recommends writing lots and lots of notes in their training logs. 

While Vollmann might look at her athletes’ numbers, she says without knowing their context it’s not a useful tool in dictating training. These notes might include the weather conditions, how well an athlete slept, what he or she ate, how the workout felt compared to what was prescribed. For example, if the intensity factor felt challenging, but the prescribed workout was a zone 2, there might be other factors at play like an illness, poor conditions, or fatigue. 


The power measurement is incredibly useful, Vollmann says, because “power doesn’t lie.” It’s used specifically for assessing bike fitness—how much energy, measured in watts, is needed to move the bike forward. 

A power meter is commonly found on smart trainers and you can purchase meters for your bike. 

Unlike heart rate, which can be thrown off by race-day excitement, for example, your power is your power. For example, let’s say your heart rate going into a workout or a race is 160 bpm, not because you’re working hard but because you’re excited or nervous. You’re going to expend a lot of energy trying to ramp up that heart rate to 180, that reading will actually be delayed by about a minute. 

“Then you’re gassed,” Vollman says. 

Similarly, if you’re looking at your speed as a measure of fitness or to stay on pace, you might be trying to hit 20 miles per hour in a headwind, uphill. It’s going to take a lot more effort to hold that speed. 

Instead, Vollmann often prescribes workouts in power measurements, say 170 to 190 watts. If it feels too hard, you and your coach can assess why—the same goes for if it feels too easy. 

But Vollmann waits to use power for her newer athletes because they can get fixated on holding a specific power no matter what. 

“If you’re only looking at your power meter you might miss an opportunity on the course to ride faster,” she says. A downhill, for example. “You’re not figuring out how to actually ride a bike faster.” 

Muscular Endurance 

Your muscular endurance is how much stress your muscles can tolerate. When logging endurance training, notably time on the bike or running, your muscles are going to break down well before your aerobic ability struggles, Vollmann explains. 

For example, at the end of an Ironman or half Ironman, your muscles are completely spent, while your heart could keep going, she says. 

There are different ways to test your muscular endurance, including P20 and P60 tests. These look at the best average power or pace you’ve held during a workout or race for 20 and 60 minutes. 

Vollmann doesn’t prescribe her athletes these tests specifically—”Athletes get scared of tests”—and instead looks at recent race results to get a better understanding of muscular endurance and ability. 

Using the Data 

These numbers can inform training and recovery, and help avoid injury especially for newer athletes. 

“It’s so easy to overtrain,” Vollmann says. “People think the more the better and that’s not true, especially when you’re increasing your run volume.” 

Data points can show you how your training is adapting, where to push harder and where to pull back. Vollmann doesn’t want her athletes to focus on numbers during the off-season, a time to just enjoy activity before starting another training cycle. 

“After a race, back off and go enjoy the sport,” she says. “Otherwise, you’ll lose the fun.”

Heather Mayer Irvine is a freelance journalist based in Pennsylvania. She is the former nutrition and training editor for Runner’s World and the author of the Runner’s World Vegetarian Cookbook (2018). Her work has appeared in Runner’s World, Bicycling, Popular Mechanics, The Boston Globe, Cooking Light, CNN, Glamour, and The Associated Press. She’s a seven-time marathoner with a personal best of 3:31 but is most proud of her 1:32 half marathon, 19:44 5K, and 5:33 mile. She’s done one sprint triathlon and is terrified of open water.