Start training smarter with Xert

With new advanced training systems, athletes have greater flexibility in deciding how they wish to train.  Gone are the days of sitting on your trainer during the off-season doing workout after workout.  Athletes are now able to incorporate different types of training – from indoor rides and races to outdoor coffee rides to more sophisticated indoor workouts to using the latest in training tools like Xert Magic Buckets.  All these types of training activities can now be included as part of your day-to-day training.

Xert Breakthrough Training was the first system to allow athletes to train using a variety of methods, quantifying their training strain scores in multiple dimensions giving athletes the confidence to pick and choose how they prefer to train on any given day.

Athletes are often using more than one system, using one system for a while and switching to another for variety or to save costs. From using Zwift, Rouvy and MyWhoosh, to using the Garmin, Hammerhead or Wahoo device, to TrainerRoad, icTrainer, TrainingPeaks Virtual or just watching a movie or race footage as they work out.  They record on all these systems, sometimes recording on multiple devices to take advantage of features available on one system that are not available on another.  Magic Buckets is a great example where athletes may be riding on Rouvy, say, but also using their Garmin with Magic Buckets to guide their training.  Sometimes users record on multiple devices in order to separate their power data from one source vs. another. For example, they may use a trainer power for Zwift but prefer to use their power meter for their training data.

Many systems today also record multiple rides one after the other to ensure race files are not combined with warmups and cooldowns.  For Xert users, this separation of activities can pose issues as fatigue isn’t carried over from one activity to the next.  Single, contiguous activities are better for Xert’s analysis as well as better for long term record keeping purposes. These will be provide a better view of your responsiveness to training and provide greater information on how you fatigue.

Our Solution – Xert’s New Training Manager – The Xert Today Page

Watch 2 minute intro video on YouTube

Xert’s Today page is our response to requests by our users to help them better manage all their training activity using an intuitive and easy-to-understand page with all their essential information and features they need to manage their training.  Our goals in the development of your Today page were:

1. The UI/UX needs to be simple to understand and use.
2. Users can see what their training is for today and decide how they will do their training.
3. Users can easily adjust their daily training to suit their availability, motivation or readiness to train.
4. Users can dual/multi-record their activities and decide which ones to use for their training data and which to just keep for their own records.
5. Users can merge one or more consecutive activities to better track fatigue and overall training strain scores.
6. Users can decide which activities to share on Strava.
7. The page needs to be fully-featured on mobile devices.
8. The page performance has to use the latest website technology to make it reactive and highly-responsive to user actions.

With all these in mind, we developed a new page that sets a new bar for how athletes will manage their day-to-day training in terms of planning and managing their information after recording activities.

A New User Experience

Xert’s new Today page has a number of key elements on the page, all laid out in an easy-to-understand and use format.  At the top is your training for today and if you planned anything specific for today, that will show at the top of the screen.  This is your daily training front and center.

Below this is any activities you have recorded.  These are shown in chronological order with duplicates indicated if you recorded the activity on multiple devices.

If your recordings come in separate, consecutive activity recordings, you can merge them quickly and easily. Note: Activities that came from Strava cannot be merged with other activities at this time.

You can decide to send your activity to Strava manually and take advantage of the new features to decide which activities to send to Strava, which to use for training and which to keep hidden and not counted.  Be sure to disable the Sync New Xert Activities to Strava on the Strava Sync page for greater control and management.

You can see which targets are going to be sent to Magic Buckets when it fetches your current targets.  No more wondering where the XSS values came from when Magic Buckets runs on Xert EBC or your Garmin.

You can decide which system is going to receive a given workout.  Perhaps you prefer to do one workout outdoors but would opt to do another indoors.  You can manage each individually now.

Filtering workouts could not be easier with the sidebar that allows you to filter instantly.

Not behind your desktop or laptop?  No problem, just use your mobile browser and get the same functions and features.

Summary

With Xert’s new Today page functionality, you can consult it before your daily training rides to manage your day’s training, decide on what training you will do and send workouts to platforms you utilize.  In addition, you can review your daily activities, manage them as part of your training,  retain them for future reference and apply them towards your training.

For Xert users, we are now your go-to system for all your training data.

Always remember: If it ain’t on Xert, it doesn’t count.

1. Why am I doing this particular workout?
2. Why do I need to do these intensities and these durations?
3. Am I hitting the workout interval targets sufficiently well and if not do I stop or keep going?
4. What is about these specific interval targets anyway and how precise do I need to be?
5. Could I do something a bit different that I would prefer and get the same benefit?
6. Can I get the same benefit by just riding or racing?  Workouts can be a drag.

You’re not the only one.  Pretty much every athlete will ask themselves these questions at various points in their training.  Wouldn’t it be great to have all these questions answered?

Answer These Questions with Xert Strain Scores, Forecast AI and XSS Buckets

After many new innovations in training, including capabilities like Smart Workouts with dynamic intervals (first and only platform ever to do this), and diving deep into understanding the process of training and improvement, we developed Xert Strain Score and more recently Forecast AI and XSS Buckets.  XSS Buckets allows you to train for improvement, without the need of doing structured workouts. With Forecast AI, athletes not only could understand what the workouts did but also why the were doing the workouts as part of their training plan.

But one question lingered:

How do I fill these buckets without following a workout?

Answering this question is key since without an answer, athletes are left to use trial-and-error to do their training and may often consume valuable training time unnecessarily.  Some structure and guidance would be very useful.

Introducing Magic Buckets

Magic Buckets brings a new dimension to training and workouts that has never existed previously – interval targets and durations are calculated on-the-fly for each athlete at each moment.

Re-read that last statement a few times and let it sink in.  Magic Buckets essentially recommends and builds a workout as you ride, adjusting the workout to you.  Now with Magic Buckets, all you have to do is follow the guidance it provides.

Magic Buckets operates in two separate modes depending on whether your daily training goal is a high-intensity training session or a low-intensity / endurance training session.  We’ll describe these two different modes as:

• Magic Intervals
• Magic Endurance

Watch this video where Scott will walk you through how to use Xert Magic Buckets for your training. This demo will show you how to seamlessly integrate Magic Buckets into your routine without rigid workout plans. It’s a great way to adapt your training and optimize your results with the flexible guidance that Magic Buckets provides.

Magic Intervals

Magic interval workouts are a unique experience like you’ve never experienced before.  Your target interval power is calculated for you based on what you’ve done so far and what you need to do to complete the training.  Your recovery / rest-in-between power targets are also calculated as well as their durations.  Calculating the power and the duration for your recovery is important since this helps ensure you achieve your training goal for the workout and ensures you’re recovered enough to do the intervals.  That’s part of the magic the method uses.

What do I need to do?

Simple.  You warm up and start filling your low bucket.  When you’re ready, hold the high-intensity interval power for as long as you wish to fill your high and peak buckets.  Once you back off from that, the recovery/rest interval is computed – both target power and duration and you continue to fill your low bucket.  Follow that and repeat.  Once your high and peak buckets are full, you can ride easy and fill the remaining low bucket while you cooldown.  Done.

Challenge Levels

To make Magic Buckets more engaging and to motivate athletes to go a bit deeper and get more out of their available training time, we’ve introduced the concept of Challenge Levels.  Challenge Level is a value between 0 and 10 that represents how much fatigue *at the interval power* you’ve reached.  The deeper you go, the higher the Challenge Level you reach.

Reaching higher Challenge Levels is great motivation but the other added benefit is that you get to complete the workout sooner.  This means that athletes with time crunched schedules can do more training in less time by focusing on doing their training at higher Challenge Levels.  Here’s an example of how long a given workout would take at different Challenge Levels. We use a typical 5×5 VO2 interval workout as a benchmark:

Now Available on Garmin Watches!

Magic Buckets is now supported on over 100 Garmin watches! Enjoy real-time, colour-coded training guidance on your wrist whether you’re riding indoors or out!

Read more here →

Magic Intervals User Interface for Garmin ConnectIQ

Key things to know when doing Magic Intervals:

1. It takes 5 seconds for the gauge to switch from one interval type to another.  When you start your high intensity interval, hold it for 5 seconds for the  INTERVAL state to show.  Similarly, after completing your interval, hold the recovery power for 5 seconds to see the gauge switch to the RECOVERY interval.
2. Once your recovery is complete, you can continue to recover and collect more low intensity XSS or can start a new interval to stay at the same Challenge Level.
3. Recovery intervals are calculated to give you the precise recovery and low intensity strain and maintain your current Challenge Level (Challenge Level on the left of the bar).  If you sustain the RECOVERY power for the RECOVERY duration, you’ll start the next INTERVAL at the start of the Challenge Level.
4. Let Challenge Level be a workout objective.  The higher the level, the more efficient each second of the workout becomes.
5. Reaching higher challenge levels requires you to sustain the target interval power longer.
6. Stop or start high intensity or recovery intervals at any time.  You don’t need to be precise to complete your training since this will continuously adjust for you.  However, the less training that remains, the more precise you’ll need to become to finish the targets without spending unnecessary training time.
7. Start your intervals at any time. Because things continuously adjust, you can do the intervals at anytime during a ride.   For example, you could start your magic intervals after a competitive group ride to finish off your training.  You’ll likely notice that the target interval power will change over the course of the riding you do beforehand.  This is because Magic Buckets is continuously recalculating what you’ll need to do to complete the remainder of your training based on what you’ve done so far.
8. It’s ok to be a bit off target or stop/start at random times if you need to / would like to.  It will recalculate what you need to do to complete the remainder of the training.
9. Use the integrated cadence optimizer.  Your cadence is shown as a triangle on the gauge.  Aim the triangle along the thin bar to have your cadence within a range that is suitable to your usual cadence pattern.

Magic Endurance

For those days when you need to ride easy and avoid high intensity so that you can recover sufficiently, Magic Buckets will run in Endurance mode, where your buckets fill if you can maintain discipline in avoiding high intensity.

Magic Endurance has different buckets as compared to Magic Intervals:

1. Low Intensity XSS – This is the main bucket that needs to be filled to complete the required training.  You can fill this bucket simply by riding.
2. Zone XSS – This bucket shows you how much XSS you’ve accumulated in the ideal zone.  You should aim to keep this number the same as the Low Intensity XSS number.
3. Fat XSS – This bucket shows you how much of the XSS you’ve accumulated as *fat* XSS.  This is an additional piece of information for those that are looking to focus on improving their fat contribution to their training.  This number is always less than your Low Intensity XSS since there are always fat and carbs being utilized during exercise.

Magic Endurance User Interface for Garmin ConnectIQ

Installing & Registering Magic Buckets for Garmin – 4 Easy Steps

Step	Description	Instructions/Screenshot
1	Download and install the data field from the Garmin App Store on your Garmin device	Link to Garmin Data Field: https://apps.garmin.com/apps/e8c1828f-0b0d-461d-82ba-033d7ea7c7d3
2	Add it to a full-screen (single data field) page of your preferred Activity Profile on your Garmin device	Instructions: https://support.garmin.com/en-US/?faq=gTIEqA7g6h9md50pQsDpl6
3	Start your recording and move to your Magic Buckets page.  Then immediately Save the recording.  If you you have Garmin Health/Connect sync set up on Xert, you’ll see the registration notification.  If you don’t have Garmin Heathl/Connect set up, upload the FIT file to Xert to complete the registration process.	You’ll get an empty recording in Xert that can be removed.  You’ll also receive a notification that your Garmin has been registered.
4	Send or upload the FIT file recorded to Xert. (Be sure the activity is processed before proceeding to the next step.)	There are two ways to get your FIT file from Garmin into Xert: First have Garmin Health/Connect set up on your Xert account, or Upload the FIT file that is saved to Xert Online.
5	Start a new recording.  Xert will automatically send your workout targets to the data field.

Now Available on Android and Hammerhead Karoo!

Garmin was the first platform to support Magic Buckets, but the experience on Android and Karoo takes it a step further! Xert EBC gives you more screen space, responsive swipes, and touch-based navigation — making the training experience feel modern, clean, and intuitive. Your Low, High, and Peak XSS targets are automatically fetched based on your training goals for the day—no need to pick a workout or configure anything manually!

Installation

• Android: To get started, install the Xert EBC app from the Google Play Store and register for the Beta to access the Magic Buckets feature.
• Karoo: On Hammerhead Karoo devices, install Xert EBC from the Extensions menu, which will allow you to install and launch the Xert EBC app directly.
  • Alternatively, once installed, you can add the MPA data field to any Karoo profile. During a ride, tap the MPA field to launch the Xert EBC app and access the Magic Buckets interface. To return to your Karoo’s recording screen, swipe up or press the bottom-left button.
  • This integration allows you to use all Karoo features – like navigation – while also accessing Xert Magic Buckets. Enjoy the full experience with swipe-based app navigation and dynamic, target-driven feedback—just like on Android!

Magic Buckets User Interface for Android & Karoo

• Access the Magic Buckets Power Gauge and Challenge Level gauge by swiping the top half of the app screen.
• See your current interval state, upcoming targets, and interval power guidance at a glance below the Power Gauge. 
• Swipe the bottom half of the screen to view your real-time XSS buckets and estimated workout (and endurance) time remaining.
  • Tap data cells for deeper insights
• Your Power Targets constantly update throughout your ride based on your progress—perfect for outdoor or unstructured rides.

Magic Buckets on Android and Karoo give you intelligent, adaptive guidance that helps you hit your training targets in a fun, unstructured way!

Frequently Asked Questions

Q: What happens if I need to stop early or if I do too much?

A: No worries! Magic Buckets is just one part of your overall training being managed by Xert, whether you are following a Forecast AI plan or taking advice from the Adaptive Training Advisor.  Anything you miss or overdo will be incorporated into your future training requirements.

Q: Can I use Magic Buckets with non-cycling activities?

A: Currently, Magic Buickets is optimized for cycling only but will adapt in any activity that aligns with Xert’s system of tracking fitness across Low, High, and Peak energy systems.

Q: What devices support Magic Buckets?

A: The Magic Buckets feature is supported on:

• Android smartphones & tablets via the Xert EBC app
• Hammerhead Karoo devices via the Extensions menu
• Compatible Garmin Edge devices & watches via the ConnectIQ store.  See the Garmin App Store page for a list of devices.

Q: When will Magic Buckets come out on my device?

A: Over time, we will plan to bring Magic Buckets to Xert EBC for iOS as well as other devices that have support for open programming interfaces.

Last updated: 10 October 2025

In recent years, adaptive training has grown in prominence within training circles.  Static training plans have become a thing of the past.  Xert’s Adaptive Training Advisor was an early adaptive training platform, providing athletes day-to-day training advice that changed and adapted to each athlete over the course of their training.  Almost a year ago, Xert announced the Forecast AI Beta Program.  Forecast AI was a bold new initiative that raised the bar on how training could be prescribed.  Before Forecast AI, athletes trained with the hopes of achieving the goals and outcomes they were looking for.  With Xert’s Forecast AI, hopes have been upgraded to predictions.  Outcome-driven training plans are now available for the first time.

In the past year, we’ve taken a lot of feedback from coaches and athletes and have made many improvements over this time. We’ve also added substantial new capabilities.  At its core, Forecast AI (XFAI) generates training plans that are outcome-driven – goals, events, races, achievements – and have the following important features:

1. Optimized and Outcome-Driven – XFAI generates a training plan using a sophisticated outcome-driven algorithm that takes you from where you are today towards the outcome you are looking for, and generates a plan to reach it.
2. Personalized and Tailored to You – It uses a deep analysis of your training history and your preferences to create a training plan that’s unique to you.
3. Highly Flexible – It fits the training program into your day-to-day availability but also enables you to do the prescribed training following structured workout or unstructured rides, both indoor and outdoor, solo or with others.
4. Adaptable – Accommodates changes based on your availability or preference adjustments as well as adjustments needed to reach your desired outcome.

Next Level Personalized, Outcome-Driven Training Plans

We set out originally to simply take the Xert Adaptive Training Advisor and have it *forecast* the training you need to perform in the upcoming week.  What would seem like a simple endeavour mushroomed into something far more complex but also far more capable and valuable to athletes.  The team discovered many aspects of training that underlie successful training plans.  It’s been an incredible learning experience and hopefully we’ve been successful in transferring what we’ve learned over to you and enabled you to reap the rewards of all of our efforts.

Making it Personal

To say there is a “best” training plan that is suitable for everyone and we can use AI methods to find this training plan is a misunderstanding of how human physiology works.  There is simply no “one size fits all” training plan.  A good coach will go to great lengths to learn about their athlete.  They need the specifics and the details in order to prescribe the training that is best suited to them.  They recognize that everyone is different and the training that’s best for you may not be the training that’s best for another athlete.  We believe to properly prescribe training requires a deep understanding of the athlete. It’s the most important step.  Here’s how Xert characterizes each individual athlete:

1. Every athlete has a unique fitness signature – Your TP, HIE and PP reflect your specific strengths and weaknesses as an athlete.
2. Every athlete is at a unique point in their training – Low, High and Peak Training Loads and Recovery Loads are based on the training you’ve been doing and the unique mix of intensities that you have performed.
3. Every athlete responds to training differently – Low, High and Peak Training Responsiveness reflect how you have responded to training in the past.
4. Every athlete has a different pattern of training – The volume, durations, days-of-the-week you normally train form a baseline weekly training pattern.
5. Every athlete has other differences and preferences:
   1. Recovery Demands – Do you prefer more or less recovery time between training sessions?  Preference may be related to previous injuries or other personal factors.
   2. Polarization Level – Do you dislike doing long endurance workouts or prefer stricter 80/20 polarized training?
   3. Degree of difficulty – Can you handle a lot of suffering or prefer easier workouts?
6. And most importantly, every athlete has a desired outcome for the investment they expect to make in following a training plan.

All these are elements that will make the training plan generated by XFAI unique to you and unlike any other program.  A great coach will spend a lot of time working with you to establish all of these elements in order to craft a training plan that is right for you.  XFAI does the same.

Making it Flexible

Flexibility in a training program is key because people like to do things in different ways.  A training plan has to be something you not only can follow but you want to follow.  A training plan that might meet an outcome objective is nice but if you don’t want to do the training, then it’s not a great plan.  We sought to use your historical data as the starting point for the training since this is the pattern of training you already do.  It’s also very important to use your historical data since the principle of progressive overload depends on this historical knowledge.

Here, you can adjust your availability for any day of the week or even adjust individual days.  Mark the day as Flex to instruct XFAI to add time in order to achieve Progressive Overload.  Mark the day as Fixed if that’s all the time you have that day throughout the plan.

An important change we made over the course of developing XFAI was the change from prescribing workouts, to prescribing workouts and outdoor rides, to eventually landing on forecasting the training you’ll need to do.  You’ll notice that every training day is either “Low Intensity” or “High Intensity”.

Low intensity training days are days where you will ride easy and avoid high intensity.  XFAI will put these in your plan either because your status is projected to be yellow (“Tired” status) that day or it plans to hold back on intensity because you don’t have enough time that day to do what’s needed and a subsequent day is better for doing the high intensity training.

High intensity training days are days where your training status is expected to be blue (“Fresh” status) and you will be expected to be rested enough to handle a high intensity workout or ride.  XFAI will show you how much intensity is needed on that day and defines this so that you can continue to progress your high and peak training loads towards the target fitness levels needed.

Recovery days are days where your training status is red (“Very tired” status) and you should be taking downtime for recovery.  Rest days are simply days that you don’t need to be training and can focus on other activities but will not affect your ability to achieve the target fitness by the target date.

How the Training Plan Gets Generated

XFAI generates a training plan and displays progress on screen.  You can watch it as it works.  For many of you that were part of the original beta, XFAI rolled forwards and backwards generating and laying out a plan, rethinking decisions along the way.  It took a long time to run.  Since then, we found ways to improve the performance and improve how it lays out the training plan.  What makes this really unique and valuable is that you can see the end result and understand how and why it made the decisions in the process of laying out the plan.  Once this process is complete, you’ll see a plan that will make sense to you and you can even confirm for yourself that it’s indeed a plan that will achieve the outcome you requested.

Unlike other AI systems that may generate a training plan but won’t show their work, XFAI lays everything out for you, letting you see and appreciate how the outcome will be reached.  This helps you have confidence in the program which in turn will provide greater motivation for you to follow and stick with it.  You don’t have to place trust in the system.  It’s all laid out and understandable.

Executing the Training Plan and Updating it Along the Way

We took flexibility and personalization one step further and made these a part of the process of following and updating the training plan as you execute the training.  Next, next, next level stuff.  Here’s what you can do on a day-to-day basis:

Choose your own workouts or activities	You can choose from a variety of workouts and activities for each foreacasted training activity. You can even auto-generate a workout that will more precisely match the needs of the training for that day. Recently, we published a new “XSS Buckets” Garmin datafield on the Connect IQ App Store.  When you install and place this datafield on your Garmin activity profile, it logs into your Xert account and fetches the forecasted training XSS values (low, high and peak) that you need to fulfill for the current day.  This provides yet another advancement in training where you can ride unstructured to achieve the same training benefit as compared to a completely structured workout – both low and high intensity workouts of any kind.
Perform the training needed and compare results	Once you upload your ride, you can compare the training XSS targets against what you achieved on your ride.  Xert will conveniently post a chart to your Strava activity that’ll make it easy to check on progress right from Strava.
Plan your week of training if you prefer	Whether you have a rigid schedule and have to plan things out in advance or you have some flexibility and can easily handle training plan changes, XFAI will work with this.  You choose when to re-analyze and re-run the Forecast AI process to update your training plan when you want, whether that’s immediately after every ride or once-a-week.
Pin your chosen workouts and activities	Workout pinning is a new concept in training and provides a way to have pre-scheduled rides as part of your training plan.  Perhaps you prefer to do the high-intensity workout on a Thursday rather than the Friday or you always do a hard club ride on Saturdays.  Simply assign the workout you wish to do on a given day or pick a similar activity to the one you plan on doing on the weekend and click the pin icon.  This tells XFAI that you are planning to do these and to work the plan around them, using their XSS as part of the plan to achieve the target outcome.
Add in other rides and activities	Sometimes you have other rides planned but would still like to do an appropriate workout on the same day.  A great example is when you commute with your bike to work. Click the + icon and add the ride to your calendar.  Use this feature to add days you go to the gym or do other activities. Note: Since the XSS you specify or choose on this planned activity gets included in reaching your goal, be sure to assign meaningful training values that represent the benefit this activity will have towards reaching your target outcome.

Once all this is done, click the Adapt button to take all this new information and XFAI will update and re-optimize the training plan for you:

How much flexibility can be accommodated?

One thing we learned in the process of developing Forecast AI is that the flexibility you have in a training plan is dependent on how tight you will be to reach the target fitness by the target date.  A plan loses its flexibility when you miss too many days, for example, and a suitable training plan can no longer be forecasted.  Simple example: if you have a week left in your plan and had targeted to reach a TP of 250 but it’s still at 230 because of all the training you’ve missed, no training plan exists that you can follow to reach your target.  A plan can be flexible .. but at some point the flexibility goes away and if you miss the required training, the target outcome can’t be reached.

Forecast AI helps you see this happening when it highlights “magenta” days on your planner and chart.  When a plan is created, future training days depend on you achieving a certain fitness level by that date.  For example, as you build your fitness, your High Training Load may start very low, perhaps quite low after a period of Base training but as you progress in the training plan, High Training Load increases towards your target fitness.  This in turn requires more High XSS to maintain the controlled, achievable progressive overload towards the target.  If at some point XFAI expects your High Training Load (or Low or Peak) to be a certain value in order for you to complete the required training and your projected training load will be less such that you can’t complete the training on that day, it’ll be marked as magenta.  Similarly, if XFAI had mapped out a high intensity day but due to the increases that are projected in high/peak training loads and recovery loads on that day, your status may be projected to go from blue to yellow or red.  Again, these days will be marked as magenta on the plan, highlighting that the plan has an issue that may need to be addressed.  Often, it may just be a matter of clicking the Adapt button.  But if the plan has become super tight, the Adapt button might not succeed in finding a plan and you’ll need to consider either changing availability or perhaps modifying your targets.

Mouse over the magenta bar to see how the training has been affected.

Checking Progress

We’ve added a new page that provides feedback on the progress you have achieved as well as the progress you will make in the training plan.  This provides a complete picture of changes to your fitness signature both past and future as well as the corresponding training loads.  Use the slider to navigate through the past and future dates.

Conclusion

Xert’s Forecast AI has set a new high-bar when it comes to planning your training.  Ultimately, the plan you will follow:

1. Has you reaching the fitness and performance you are looking for.
2. Is highly-personalized to you, your specific situation and your unique interests in training.
3. Allows you the greatest flexibility to train in ways you prefer.  This is motivating and encourages you to stick to the training.
4. Continuously adapts to your changing schedule and the progress you have made, ensuring you can stay on track as life gets in the way.

What is a Fitness Breakthrough (BT)?

Many software training platforms use some method to track your fitness progression throughout the course of a training program or season. Typically, these require some form of test – whether a FTP test, ramp test, or other type of testing. With Xert, we can track improvements in your fitness without the direct use of testing (although you can still do the tests if you like). We use the term breakthrough to indicate a significant change in your fitness signature, which consists of your Threshold Power, High Intensity Energy, and Peak Power. When one fitness signature parameter increases, you’ll be awarded a bronze medal, for two parameters – silver, and when all three parameters increase – you’ll earn a gold breakthrough.

How is a BT detected?

Older training methods looked for signs of increased fitness by simply tracking your best 20 minute power, and taking a set percentage (usually 95%) of that value as your FTP. They presume if your 20 minute power increases, your threshold must also be increasing – likely a pretty safe assumption. But what if you’re not an athlete that focuses on 20 minutes efforts (such as Puncheurs, Roleurs, Sprinters, etc.)? How could tracking 20 min power provide any indication about your ability to generate power over 10 sec, 4 min, or anything other than 20 min? Answer: it can’t! Furthermore, tracking your average power over 20 minutes cannot tell us the whole story about your fitness. Did you go out too soon and blow up early? Did you go too easy at the start and finish with a powerful sprint in the last 30 seconds? These sorts of details can only be discovered by looking at your data second by second.

Instead of tracking your 20 minute average power, Xert looks second by second at your power output and compares it to what you could have done – your Maximal Power Available (MPA). When you perform a maximal effort and reach muscular failure, your power will approach (and hopefully exceed) your MPA. Xert’s signature extraction algorithm uses those moments where Power and MPA interact and identifies a fitness signature that matches your power data. In this way, Xert is able to use your moments of failure to identify your unique fitness signature. Because of the way in which MPA limits your ability to produce power, the longer/closer you’re able to continue riding near MPA, the better insight Xert has into your unique fitness signature. This is important since two athletes with very similar thresholds but different PP/HIE’s might experience fatigue very differently above threshold. If we were only to track their 20 minute power, it might be impossible to differentiate them. However, Xert is sensitive to the way in which they fatigue above threshold and will derive a unique power duration curve for each of those athletes.

When you’re able to exceed what the system thinks you’re able to achieve (i.e. riding above MPA), the system must now re-calculate the ride based on the new fitness signature. The ride is analyzed in such a way that MPA only reaches your power output once. For example, look at the micro-intervals below. Notice that during the ride, this user exceeded MPA several times. However, by definition, power cannot be above MPA. Therefore, when the ride is uploaded to the system, the fitness signature was increased and the activity correctly shows only one point of failure, where power is equal to MPA:

Prior to analyzing the breakthrough, this athlete was able to repeatedly ride above MPA during each 30’ effort. Since you cannot, by definition, ride above MPA, the system needs to increase your TP, HIE, and/or PP in such a way that power never exceeds MPA.

When the ride is uploaded and analyzed, Xert is able to detect changes in your fitness signature parameter(s). Since the new fitness siganture is higher than the old, many data points that were previously displayed as being “over” MPA are now displayed correctly beneath MPA. Note that the change in your fitness signature will also results in changes to the activity’s Focus, XSS, difficulty, etc.

Maximal Effort Time

As stated above, the more time that you spend near MPA during a breakthrough activity, the longer the maximal effort time will be. Activities that only contain a few short seconds at/near MPA will result in short maximal effort times, while activities that contain several minutes of power close to MPA. In general, the longer the maximal effort time is, the better the resulting fitness signature from the activity will be. This concept can help explain why a 20 min test or a ramp tests are not always ideal for extracting your fitness signature, since they generally have relatively low maximal effort times. For example, during a 20 minute test, MPA will only approach your power output in the final few minutes. With respect to ramp tests, there are almost infinite combinations of TP and HIE/PP that can result in failure at one particular part of a ramp test. Thus, it can be difficult for the system to determine exactly which fitness signature is the “correct” one.

Finally, Xert works best when you’re able to fatigue naturally instead of various tests which feature “unnatural” fatigue. We call it unnatural since there are hardly any instances in normal riding where you increase your power output minute by minute until you can’t. The other type of unnatural fatigue is during an 8 min or 20 minute test, where you push yourself until the testing period is over, where most athletes will typically immediately stop pedaling. The abrupt stop does not permit Xert’s extraction algorithm look at the way you fatigue. Instead, Xert is looking to see natural fatigue in your power data, which typically manifests in your power slowly diminishing as MPA decreases and continues to limit your ability to produce power. Thus, with Xert, the last minute or two of the fitness tests – when you’re under the most fatigue – tells more about your fitness than the rest of the test.

Look at the difference in maximal effort time between a ramp test, 20 min test, and an all-out maximal effort during a Ronnestad workout below. Also pay attention to the interaction of power and MPA during each of those efforts:

Ramp Test

Maximal Effort Time: 00:26

FTP Test

Maximal Effort time: 00:31

Ronnestad (30/15’s)

Maximal Effort Time: 06:00

Pro Tip: The XPMC clearly indicates your Breakthrough activities with circles that correlate with the breakthrough – bronze for 1 parameter, silver for 2 parameters, gold for all 3 parameters. Fakethroughs (see below) are displayed as an empty circle. Note that the size of the Breakthrough/Fakethrough circles on your XPMC chart correlate with the maximal effort time of the activity, not the size of the increase in your fitness signature parameters

Types of Breakthroughs

There are several different ways in which a breakthrough can be achieved, since Xert is sensitive to changes in Peak Power, High Intensity Energy, and/or Threshold Power.

• “Pull” down MPA

  • This type of BT is helpful for teasing apart the relationship between HIE and TP, since you are able to accumulate a large amount of time near MPA (high maximal effort time). The effort can either be steady state (at a relatively constant power output) or performed as shorter on/off intervals (20/10’s, 30/15’s, 30/30’s, etc)

• “Push” over MPA

  • These breakthroughs are usually seen as a result of very short, bursty sprints. This type of breakthrough will result mostly in an updated PP/HIE, but can sometimes affect TP as well, depending on how far above & how long you exceed MPA

• Multiple Breakthroughs

  • Sometimes you may exceed MPA several times during the course of an activity (see image below). When this occurs and the ride is uploaded to Xert, the extraction algorithm looks for the point that results in the largest increase in fitness signature. So, although you may have seen yourself riding above MPA several times (and/or for several minutes), the ride will be adjusted after the upload such that MPA will only meet your power output once (see images below for an example:

Notice that the original signature resulted in many intervals of both sets being completed above MPA. However, once the breakthrough is analyzed, MPA only touches this athlete’s power at one point during the ride.

• Near Breakthroughs/Fakethroughs

  • Near breakthroughs are the scourge of all Xerters. Near breakthroughs – more commonly called fakethroughs – are cases where you were able to get your power very close to MPA, but you weren’t quite able to exceed it. In these scenarios, Xert will slightly decrease your fitness signature to make MPA meet your power output. The small changes to your fitness signature aren’t usually too substantial to your daily training, but they will allow you to more easily reset your fitness signature with a breakthrough at a later date.

In the top panel (starting signature), the athlete’s power (358 W) didn’t quite reach MPA (379 W). In this scenario, the system reduces the fitness signature to make MPA meet the athlete’s power at the point of the ‘best effort’. In the second panel (once the fakethrough slightly reduced the fitness signature), the athlete’s power now meets MPA at the point of failure.

• • These near-breakthroughs can sometimes indicate true losses in fitness, but at other times they are indicators that you truly had more to give and you simply stopped early
  • Fakethroughs can be prevalent in racing, where you were may have been very close to reaching MPA, but were trying to avoid cracking and being dropped. Other times, its possible that you ran out of  sufficient resistance to achieve a breakthrough, such as cresting a climb before you reached your MPA. In other scenarios, you may not have been actively watching MPA, and may not have known you were so close to a breakthrough. In these scenarios, you can use the flag feature for the activity.

Pro tip: Flagging a fakethrough or breakthrough tells the extraction algorithm not to update your signature based on that particular activity. This means that your fitness signature will remain unchanged, despite a near maximal (or non-repeatable) effort.

How to perform a Breakthrough?

Now that we’ve covered what a Breakthrough is, you might be wondering “How should I get a breakthrough?” The signature extraction algorithm that is used to determine your unique fitness signature will obviously require some form of maximal effort that brings you to muscular failure. What type of maximal effort you want to do will likely be dependent upon which part of your signature you’re hoping to update. If your peak power is a little low, you may want to attempt a few 10-15 sec maximal effort sprints, aiming to push over MPA & update your peak power. If your threshold is lower than what you might expect, you may want to consider a relatively longer effort, attempting to pull MPA down for a breakthrough.

Since your fitness signature is determined from those moments where MPA and power are close together, its always a good idea to try and maximize your maximal effort time. You can use an FTP test, Ramp test, or some other type of fitness test if you would like. In fact, you will find some Fitness Tests for Breakthroughs in the library that are designed to bring you to the point of failure (and exceed MPA, if possible). For those tests, we recommend performing the workout in SLOPE mode (SLOPE set to ~2%), so that you can push yourself all the way to the limit and guarantee a breakthrough, even if that means extending an interval by a few seconds. However, keep in mind that Xert does not require any form of rigid test – you can add in maximal efforts to your normal high intensity workouts, using our Xert Segment Hunter outdoors, or from all-out efforts during Zwift races or club rides. If you’re riding along with MPA displayed on your Android, iOS, or Garmin, another thing to remember is that you should not treat reaching MPA as the “finish line”. Rather, continue to push as hard as you can once you have reached MPA – this is the time where Xert really gets to learn your fitness.

Frequently Asked Questions

“I got a BT on my Garmin. Why doesn’t it show on Xert?”

• Unfortunately the Garmin and other apps are not performing the same sophisticated calculations that are being performed by the server when you upload your activity.  In addition, the server may remove data errors like spikes and other erroneous data from the data stream.  This may impact the determination of the Fitness Signature obtained through the extraction process and may indeed not show that you had a BT in the end.  Fortunately, the level is precision usually indicates that things are dialed-in for your fitness signature and that the system is precisely tracking your fitness changes.

“Xert gives a different Threshold Power than my 20 minute test. What’s up with that?”

• Remember that the results of all tests are going to be dependent upon the testing protocols themselves. Since Xert doesn’t require any sort of test, it doesn’t need to adapt or adhere to the protocols of the test. Instead of taking a simple 95% of your 20 minute power, Xert is looking at how the effort was performed and using that information – especially when you’re under fatigue – to determine not only your Threshold Power, but also HIE and PP. Further, other systems can’t really account for your total power duration curve from a 20 minute test, whereas Xert can account for your Threshold Power, and your ability to generate power above threshold through the signature parameters of HIE and PP.

“How does Xert know which fitness signature parameter(s) to change?”

• The manner in which MPA was exceeded sheds light into the improvements in your fitness signature. Each fitness signature parameter has a certain influence on certain parts of your power duration curve. For example, exceeding MPA on a sprint will likely cause changes to your HIE/PP, while a sustained 20 min effort that pulls down & exceeds MPA will likely leave Peak Power unchanged, but will result in a significant bump in your Threshold Power. To get an idea for where each fitness signature parameter has the largest influence, look at our blog post on Work Allocation Ratios

“I got a Breakthrough that lowered part of my Signature! What happened?”

• When looking at maximal data, Xert is determining which of your three signature parameters were the source of the breakthrough. It’s possible on occasion that an increase in one or two parameters comes at the expense of another. This is good, since the model is self-correcting and arriving at your “true” fitness signature.

In a previous post, we looked at how the body responds to the demands of cycling by tight regulation of metabolic pathways: aerobic respiration, anaerobic glycolysis, and phosphocreatine. In this article, we’re going to expand on that thought and show how we can manipulate our training to enhance our metabolic machinery. We’ll begin with a discussion of how work performed relates to Xert’s quantification of strain, then discuss how our bodies respond to this strain, and finish with a discussion on adaptations to training.

Energy Systems and Focus/Strain

Strain is a direct result of exercise. Xert quantifies this strain as work performed relative to Maximum Power Available (MPA) measured in kJ’s, and then normalizes it to every athlete’s fitness signature to obtain the Xert Strain Score (XSS). This strain is subdivided into low, high, and peak strain, depending on the relative intensity of the work.

Sports scientists have long been interested in studying the effects of manipulating both the intensity and duration of exercise in order to optimize adaptations and performance. Typically, time and a measure of average power are used to describe time and intensity, respectively. However, by looking at power and MPA, we can look to quantify strain since work can be evaluated in the context of MPA. By then subdividing that strain into low, high and peak strain, we can determine the Focus of the strain generated, aggregating each second into activities, training blocks and even seasons, by evaluating their ratios of contribution. Focus Duration and Specificity Rating provide an easy way to interpret which systems are being stimulated by using the ratios of strain contribution and comparing these to the ratios that are associated with different durations on the Power Duration curve (see Figure 1 in The Science: Metabolic Pathways and How They Affect Your Riding and Racing).

In the following figure, you can see how manipulating the distribution of low, high, and peak strain results in differing Focus Durations. Low intensity endurance activities are comprised of almost exclusively low strain, while high intensity activities include significant amounts of high & peak strain. The proportions of low, high, and peak strain are directly related to the Focus Duration of the activity, as shown in Figure 1 below.

Fig 1. Differences in the ratio of accumulated strain directly relate to the Focus Duration of the activities. Greater contribution from high/peak strain results in a lower Focus Duration. For example, the Focus Duration of the highlighted activity on the left was 03:45, while the focus of the highlighted activity on the right was –:–.

Notice that the height of the bars from Figure 1 are based only on strain, and are independent of time. Thus, it is possible to provide similar total amounts of strain in a shorter workout. This notion is supported in the literature by the rising popularity of low volume, high intensity interval training (HIIT) and sprint interval training (SIT) over traditional high-volume endurance training (McInnis & Gibala, 2017). Xert’s calculations of strain reinforces this evidence, and even pushes the idea a little farther, since the strain rate for a given power output can be increased by first decreasing Maximum Power Available (MPA). This means that performing intervals under fatigue leads to accelerated accumulation of strain, and arguably, physiological adaptations. 

How The Body Responds To Strain

The physiological strain from exercise results in adaptations, both physical and biochemical, including increases in capillary density, recruitment of new mitochondria, and increases in metabolic enzymes.

Several researchers have attempted to determine the relationship between exercise intensity/duration and the physiological  adaptations they induce. In a study published in 2013, Stephen Seiler and colleagues wanted to investigate the impact of interval length on increases in performance. A control group performed all moderate intensity endurance training, while the other cyclists were divided into 3 groups that performed either 4×4 minute, 4x8min, or 4×16 min intervals with 3 minute recoveries between intervals. Intervals were performed at maximal sustained effort, or isoeffort. All groups performed these HIIT sessions twice weekly in addition to 2-3 low intensity workouts for 7 weeks. The investigators measured the changes in key physiological variables, including VO2max and power at 4mmol/L lactate (a physiological estimate of Threshold Power). What did they find?

All groups of cyclists observed increases in both VO2max and power at 4mmol/L lactate. However, they found that the greatest increases were observed in the group that performed 4x8min intervals. It should be noted that, in this study, the exercises were matched for effort, not for total work performed. Therefore, the results suggest that 4×8’s provided the largest gains for a given level of effort.

Fig 2. Increase in VO2peak and Power at 4mmol/L (TP) following 7 weeks of training. Notice that although all groups improved, the 4×8 group observed the largest increases. Seiler, et al., 2013.

When replicating the 4x8min style workout in Xert, we see that each interval results in drawing down MPA, exponentially increasing the strain rate as each interval progresses. However, the intervals were just long enough to prevent a large amount of time being spent at or near MPA.  In 4×16’s the strain rate is lower, since each interval is performed around Threshold Power, which does not pull down MPA. On the other hand, 4×4’s were found to be very difficult to complete – Seiler’s group reported that rate of perceived exertion was significantly higher for participants completing the 4×4 protocol. Thus, the 4×4’s also did not allow a large amount of time to be spent near MPA, and the adaptations following the training intervention were similar to the group that performed 4×16’s.

Fig 3: Personal experience with the 4×8 protocol. It is best to perform these in slope mode or on the road, so that you can control the power output through shifting and cadence. Notice that even as power decreased slightly during each set, the strain rate still increased. The focus of this entire activity was 11:50 (or a ‘Climber’ Athlete Type).  The last two intervals saw an increase in central fatigue making them difficult to complete.

Another researcher, Dr. Rønnestad, wanted to investigate the varying effects of short vs. long duration intervals. In their 2015 paper, the investigators divided participants into 2 training groups: a short interval group and long interval group. The short group performed 3 sets of 9.5 minute intervals consisting of 30s work intervals and short 15s recoveries, with 3 min recoveries between sets. The long interval group completed 4x5min intervals with 2.5min recoveries – similar to Seiler’s 4×4 protocol. Intervals were to be completed at each participant’s maximal sustainable work intensity, aiming to achieve the highest average power output possible (isoeffort). These high intensity sessions were completed twice weekly for 10 weeks.

What did they find? The primary finding was that superior adaptations were observed in the group that performed high intensity training using short intervals, despite similar effort and work duration between groups. Furthermore, the short interval group observed increases along several points of the power-duration curve, including a 30s Wingate, 5 min all-out, and 40 min all-out time trials.

Once again, it should be noted that the groups were not matched on total work performed, but were matched by effort instead. Part of the explanation for why the short group may have seen larger fitness gains was that short intervals have been shown to elicit a higher amount of time spent above 90% VO2max (Rønnestad & Hansen 2016). Additionally, the 2:1 work to rest ratio has also been shown to increase the time spent above 90% VO2max when compared to a 1:1 work to rest ratio (Rozenek, et al, 2007).

Fig 4. Increases in VO2peak and power at 4mmol/L lactate (analogous to TP) for both the short interval and long interval groups following the 10 week intervention period. Ronnestad, et al., 2015.

When replicating the 30/15 protocol with Xert, the analysis shows that short intervals are a highly effective potent stimulus because one can complete large amounts of work near MPA. The micro-rests allow just enough recovery in between reps to continue putting out suprathreshold power. However, it is essential to attempt these workouts when fresh in order to perform them well and to get the most out of these workouts. Other examples of highly effective short intervals include Tabatas (20/10’s), 30/30’s, and 15/15’s.

Fig 5: Personal experience with Rønnestad’s 30/15 protocol. Notice that the difficulty of this activity is much higher than 4×8’s, since a large amount of work is being performed near MPA. The focus of this activity was 3:52.

Notice that although both activities were approximately 1 hour long, the short intervals resulted in a slightly higher strain score (144 vs 135 XSS), even though less total work was performed (782 vs 884 kJ). Here we can see that the math behind Xert supports previously published results in the scientific literature. It also shows the importance of understanding strain and focus, and how they are affected by manipulating the intensity and duration of work and rest intervals.

Relationship to Fitness Signature 

Skeletal muscles are divided into three categories: fast-twitch type IIa, fast-twitch type IIb, and slow-twitch type I, which are consistent with the three parameters of your fitness signature (PP, HIE, and TP, respectively). Athletes have varying capabilities to perform aerobic, anaerobic and neuromuscular exercise, based partially on their muscle fibre distribution, capillary supply to the muscle, mitochondrial density, and partially upon maximal oxygen consumption.

Athletes that have a higher distribution of fast-twitch fibres generally tend to have relatively large Peak Power/High Intensity Energy values (cyclists like Chris Hoy or Elisa Longo Borghini). In contrast, slow-twitch athletes will generally have a fewer fast twitch fibres, and relatively lower PP/HIE values (Chris Froome or Marianne Vos). These differences manifest themselves in Xert’s measure of Lower Threshold Power, where LTP is inversely related to HIE.

Because some riders have recruited enzymes to more efficiently burn carbohydrates and produce large amounts of work anaerobically, they are less suited to utilize fats – even at sub-threshold power outputs. Conversely, aerobic athletes have superior adaptations in mitochondrial density and aerobic enzymes, meaning that they are capable of riding relatively closer to threshold while still staying predominantly aerobic/fat burning. The thought is that aerobic athletes – especially cyclists – will do their best to conserve glucose for those key moments in races, like establishing breakaways, final sprints, etc. Thus, the driving force behind training for many athletes is to increase their body’s ability to sustain work aerobically.

How To Train Your Fitness Signature 

The studies quote above are insightful, but how do we apply these results to your training? The Xert Adaptive Training Adviser guides you through a 120 day training cycle, broken into 4 phases: base, build, peak, and taper. As you work through your base phase, the advisor will guide you to increasing your low training load by predominantly recommending workouts with and Endurance Focus. This is a crucial step in the training cycle, since your low intensity training load takes the longest to increase and requires the most training investment in terms of time. There are no shortcuts to increasing your low intensity fitness without increasing the volume of your training but it is an important step because high and peak strain can only be accumulated with a good foundation of low strain. If your body is not in good aerobic condition, it will be hard for you to accumulate high & peak strain.

After building a deep base and you will enter build & peak phases, and the recommended high intensity workouts will change from endurance workouts, to workouts with progressively shorter Focus, eventually recommending workouts of your chosen Athlete Type/Focus as your target event date approaches.

In Xert, the ‘low’ energy system is trained through low and moderate intensity exercise (below Threshold Power and even below Lower Threshold Power). The high energy system is best trained by repeatedly drawing down MPA with, for example, micro-intervals or intervals at a rider’s 3-5 minute power (these workouts often have a Rouleur, Breakaway Specialist, or Puncheur Focus when the warm-up and warm-down are accounted for). The intervals in these workouts are often called ‘VO2max intervals’. Finally, the peak energy system is best improved by accumulating peak strain (< 6 second, max power sprints) with only light riding between sprints.

If you’d like to learn more about the information provided in this article, you can consult these published scientific articles:

Seiler S, Jøranson K, Olesen BV, Hetlelid KJ.. Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration. Scand J Med Sci Sports. 2013;23(1):74-83.

Rønnestad BR, Hansen J, Vegge G, Tønnessen E, Slettaløkken G. Short intervals induce superior training adaptations compared with long intervals in cyclists – an effort-matched approach. Scand J Med Sci Sports. 2015 Apr;25(2):143-51.

Rønnestad BR, Hansen J. Optimizing Interval Training at Power Output Associated With Peak Oxygen Uptake in Well-Trained Cyclists. J Strength Cond Res. 2016 Apr;30(4):999-1006.

Rozenek R, Funato K, Kubo J, Hoshikawa M, Matsuo A. Physiological responses to interval training sessions at velocities associated with VO2max. J Strength Cond Res. 2007 Feb;21(1):188-92.

MacInnis MJ, Gibala MJ. Physiological adaptations to interval training and the role of exercise intensity. J Physiol. 2017 May 1;595(9):2915-2930. doi: 10.1113/JP273196. Epub 2016 Dec 7.