How to use data to improve your training

By Dave Colley | 11 Minute Read

Mikael Eriksson from Scientific Triathlon and the excellent That Triathlon Show podcast has written an in-depth piece on how to use data to optimise your training and performance. As you'd expect, it was written with triathletes in mind, but all endurance athletes should find most of this useful too. Over to you Mikael... 

Thanks guys. As I'm sure all of your athletes are aware, using technology to track your performance data is incredibly easy these days. Most endurance athletes use GPS-watches, heart rate monitors, mobile apps, and other gadgets to track and monitor all sorts of data on their training, racing, and general health.

But tracking and monitoring data is one thing. Actually using the data to drive better decisions on how to train and race is a different story. Knowing how to filter and decipher all the information that you're logging can be difficult and confusing. Focus on the wrong metrics and numbers, and your training is likely to stagnate, or worse, you might get yourself injured or become overtrained and fatigued.

Those athletes and coaches that do learn how to effectively use their data stand to gain significant advantages. You can learn exactly when you need to push or back off on in your training sessions, how to plan your training to peak perfectly in time for a race, decide when to move on from one training phase to the next, and so on.

In short, endurance sports are at a crossroads where those not embracing and mastering data-driven training will inevitably get left behind by their data-savvy competitors.

In this article you’ll learn some high return on investment ways to use data to improve your training and racing performance. I’ll show you specific examples of how I use data to drive my own training (and the athletes I coach). So, let's dive in...


1. Regular fitness assessments - a must for data-driven training

To improve your fitness you have to find the right dose of training load - or training stress - on your body, and this dosage should be progressive.

You can measure training stress and use this knowledge to manage your training load progression. However, measuring training stress accurately requires you to know what your fitness level is in each discipline.

Although there are some variations in terminology, essentially you’ll always assess your fitness level in terms of functional threshold pace for swimming, functional threshold power (FTP) or functional threshold heart rate for cycling, and functional threshold pace or functional threshold heart rate for running.

Knowing your functional thresholds allows you to set training zones (pace, power and heart rate), and that in turn will help make your training that much more effective.


How should I use my stats to improve my training?


There are a few different test protocols you can use to test your fitness. As long as you stay consistent and test the same way each time, it doesn’t matter that much whether you pick one over another, but the tests I like to use are...

  • A 400m and 200m swim time trial to calculate your Critical Swim Speed (functional threshold pace) when swimming. See the exact protocol and plug your times into the calculator here.
  • A 20 minute bike time trial (ideally on the indoor trainer), where 95% of the average power you can hold is your functional threshold power.
  • A 30 minute time trial run, where your average pace is your functional threshold pace and your average heart rate over the last 20 minutes is your functional threshold heart rate.

It’s critical that you reassess your fitness regularly. I recommend doing it every 8 weeks at the very least, but during times of the season when you're progressing a lot (such as during the base and build phases), every 4-6 weeks is preferable.

If you don’t reassess regularly, not only will you be potentially doing a lot of your training at incorrect intensities, but all of the rest of your data-driven training efforts and analysis will be wasted, since everything we measure in data-driven training is based on your functional thresholds.


2. Assess your aerobic endurance

Your aerobic endurance is essentially your “base fitness”. Your ability to keep going for a long period of time at a relatively low intensity (around 80% of your functional threshold heart rate).

Since all triathlon distances, even the fast and furious sprint distance, are primarily aerobic in nature it’s critical for triathletes to have a well developed aerobic system, or a “good aerobic base”.

Once your aerobic base is good enough, you can maintain it with a relatively small amount of low to moderate intensity training, and turn your attention to developing other aspects of fitness, like muscular endurance.

But, how do you know whether your base is good enough or if you need to keep working on it? By measuring your decoupling and efficiency factors.

Decoupling refers to a drift in heart rate compared to pace (in running) or power (in cycling). It’s measured as a percentage, where a high percentage indicates that your heart rate increases a lot even if your pace or power stays constant, and a low percentage indicates that if your pace or power stays constant, then so does your heart rate.

Look at the chart below... 

Using heart race and pace data to be more efficient


Here you can see that heart rate (red line) follows pace (green line) very closely. There’s only a very small increase in heart rate towards the end of this workout even though the pace stays the same.

The decoupling ratio here is 3.01% (decoupling is “Pa:Hr” in the right sidebar). In the Triathlete’s Training Bible, author Joe Friel states that aerobically fit athletes have a decoupling ratio of 5% or less. When you see a decoupling ratio this low in your longer workouts, you can be confident that your aerobic endurance is where it should be.

Contrast the above decoupling ratio with a ratio of 7.18% in the screen below...

Using heart rate data to improve your training


Whilst the heart rate stays fairly constant here, the pace seems to drop towards the end of the workout. This results in the greater decoupling ratio and is a sign that building up aerobic endurance should still be a focus for this athlete.

A second way to measure your aerobic endurance is by using the efficiency factor (EF). EF is simply the distance you can cover per heartbeat, so a higher value is better (though, it's not comparable between athletes, since different athletes can have very different heart rates for the exact same effort).

You can use EF to assess your aerobic endurance by comparing similar workouts you’ve done over time and checking your EF trend. The workouts should be done at a steady pace and at a low to moderate intensity. Ideally, select a route that you can repeat in the exact same way every couple of weeks at a similar effort, and monitor your EF for these workouts.

As long as your EF is increasing, your efficiency at aerobic intensity levels is also increasing and you still have gains to be made. Once your EF starts plateauing and no significant improvements have happened over the course of several test workouts, it’s a clear sign that you’re close to maxing out on the gains you can make from this kind of training and it’s time to move on to the next training phase.


3. Monitor your muscular endurance

Muscular endurance is, in simple terms, your ability to push from moderately high (tempo or zone 3 efforts) to high intensities (up to threshold efforts) for extended time periods. Your muscular endurance plays a huge part in determining how fast an athlete you are.

This is such an important ability for endurance athletes, so you should be monitoring it closely.

During the periods of the season when your goal is to increase muscular endurance, you should be seeing a steady increase in certain key metrics that indicate increased muscular endurance. If you don’t, take some time to analyse whether you need to change something up in your training.

The key metrics I recommend you track are P20 and P60. These metrics show the best average power you have held in training (or racing) for 20 and 60 minutes on the bike, and the best average pace you’ve held for 20 and 60 minutes of running.

Take a look at the images below. I’ve marked the P20 and P60 columns for an athlete’s power progression (first image) and pace progression.

For power, you can see a clear trend of increasing P20 and P60, which is indicative of increased muscular endurance. For example, the last 3 complete weeks show a progression of 192, 202, and 220 watts for P60.

Can I use my FTP scores to track my training progress?


For running, the P20 data is not increasing. This is a sign that we need to keep an eye on run training and start seeing a progression soon, otherwise we may need to change things up a bit.

How to use analyse FTP scores to improve your training

A word of caution here. Things like fitness assessments (FTP tests and the likes) and races can skew this data. If that happens, you may want to filter out dates when you raced or did your assessments to get a more realistic overview of your muscular endurance.


4. Reverse engineer your key workouts

This is another trick I learned from Jim Vance’s Triathlon 2.0. It applies specifically to 70.3 and Ironman racing, as for those distances your “big days” of training (long ride, potentially followed by a brick run) start to play a big role.

To reverse engineer your key workouts you need to know your...

  • FTP
  • Target race intensity (as a power number or percentage of FTP)
  • Goal time for the bike leg of your race

You need to have a fairly realistic estimate of what power output is required to achieve your goal time. For example, let’s say your FTP is 250W and you want to ride the Ironman bike leg at 70% of FTP. That’s 175W (0.7 x 250W). Then you can have a look at roughly what average speeds you’ve been holding for training rides at that power, and extrapolate that to the Ironman distance.

Of course, this assumes that the terrain you've been training on is fairly similar to the race course, that there aren’t extreme wind conditions to account for, and that you ride with about the same overall weight (rider + bike + nutrition/hydration) and aerodynamics.

For example, let’s say you’ve been training with the right setup on a similar terrain as the race course and you tend to average 31km/h at 175W. Then just divide 180.25 km by 31km/h and get a time estimate of 5.81 hours, or 5 hours 49 minutes.

You can use this handy calculator to get a second opinion on whether your time estimate is realistic. Here are some reference values to give you an idea of what percentage of FTP might be realistic to hold for the Ironman bike leg...

  • If your goal is to finish: 60-65%
  • If you’re a mid-packer: 65-75%
  • If you’re very competitive in your age group: 75-80%

For the 70.3 distance, you can add about 5% to these values.

If it makes more sense for you to work off target watts rather than target intensity as a percentage of FTP, you can do that just as well. Let’s say you think that 170W is what you can hold for the bike leg. Then your target intensity is simply 170W divided by 250W (the example FTP), in this case 68%.


How do you use this in training?

Build your long ride up towards the bike goal and include longer and longer segments of riding at race intensity to see if you can handle it. If not, perhaps you need to re-evaluate your goals.

You should try to run off the bike at target run intensity to make sure that you’re not burning all your matches on the bike.

Reference values for run intensity (again from “Triathlon 2.0”) for a full Ironman are 70% to 80% for mid-packers and 75%-85% for competitive age-groupers. Add 5% if you’re targeting a 70.3.

Even if you don’t do extremely long brick runs in training (for most athletes long brick runs are more risky for it to be worth any potential reward), you’ll probably be able to tell whether it’s a realistic target or not based on a 30 minute run off the bike at target intensity.

If it isn’t, was your bike too hard, is your run intensity target too high, or do you just need to keep training to be able to sustain that pace?

These are the questions that reverse engineered race-specific workouts help you answer before the race, so you can make any necessary corrections to your race or  training plan in time.

The power (Watt) values used in these calculations are all normalised power (except for FTP). Normalised power takes variations in power output into account. If you ride perfectly evenly, your normalised power equals your average power for a ride, but given that there’s always some degree of variation present, you can expect normalised power to be around 2% to 5% higher than average power. The difference may be even bigger for challenging courses with a lot of climbs, descents and turns.


5. Objectively assess your progression by comparing key performance indicators in-season and season-to-season

Comparing your key performance indicators over time allows you to assess how your current season is progressing and how you’re doing this season compared to previous seasons.

We already talked about this to some extent for aerobic and muscular endurance specifically. In those cases, we monitored how decoupling, efficiency factor, P20 and P60 developed over time.

Was your decoupling ratio significantly better this year than last year? Did you notice that in your race performances?

Was your fitness level clearly higher for your goal races this season than last and how did that translate to results? Did you get sick or injured at some point during the season? 

These are just a few examples of the questions you can ask yourself and answer using your data. A thorough analysis at the end of the season, where you chart out these comparisons and write down your conclusions, can help a lot in planning in even more effective training for next year.

Here are a few examples of what kind of analyses you can do...


Analysing training periodisation
Analysing training volume and performance across a season

If you’re completely new to data-driven training, I realise that this can be a bit too much information to digest all in one go! But I hope that I've helped you realise how massive the potential benefits from data-driven training can be.

If you do, and you need some more help and clarifications on these topics, don’t hesitate to send me an email and I’ll be glad to help you get started. This is a cut down version of a post on my own blog where I cover some metrics specific to the Training Peaks platform. If you're a TP user, you might find the extra content over on my site useful in addition to this blog here on Precision Hydration.

Thanks and train smart,

Mikael Eriksson is a triathlon coach and the host of the popular That Triathlon Show podcast. His articles have been featured in magazines like Triradar and Beginner Triathlete. He offers data-driven, customised online training plans via his business Scientific Triathlon. He'll be regularly contributing to the PH blog going forwards.

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