Training with EvoLab for Trail Running

As growth in trail running and ultrarunning explodes, more and more athletes are turning to coaches and exercise physiology principles to guide their training. And not just elites! Middle-of-the-pack and back-of-the-pack athletes are also using these tools and resources to optimize their performances.

As both a coach and an athlete, I love good data that tells a story. I’m excited about this embrace of science, and I’m excited as technology continues to advance and offer us enhanced opportunities to learn and grow throughout the training process!

As we try to make sense of the training process, we need two things:

  1. Analysis Tools (e.g. GPS watches, power meters, heart rate monitors, and assessment algorithms)
  2. Training Benchmarks

I’ll discuss the latter in more detail below, but think VO2 Max, race performances, and algorithm-based metrics that tell us if our fitness is improving or declining.

When it comes to tools that capture good data, EvoLab, recently launched by COROS Global, offers an improved way to analyze training metrics. COROS Global is, in my opinion, the most innovative and hungry GPS sports watch company in the world.


I run trails a lot, so one of the first things I noticed was that some of the EvoLab algorithms rely heavily on flat paved roads, available only in Run and Track Run activity modes. But what about us runners who mostly log miles on trails? Can we still utilize these metrics? Absolutely. In fact, the most important training metrics do not require you to run on flat roads indefinitely. Let me explain some of the basic benchmarks and how you can use them to benefit your training.


There are really only a few ways to measure some of the important physiological benchmarks. If you go into a lab to find out your VO2 Max or your Lactate Threshold, you’ll be asked to run on a treadmill. Alternately, I frequently ask my athletes to run on flat roads or tracks for field tests to determine baseline fitness and training zones. COROS doesn’t ask you to run on a treadmill, but you may need to run on some flat road surfaces to closely estimate some of these benchmarks. Hey, it’s better than a treadmill! But with EvoLab, you’re getting far more than just VO2 Max and Lactate Threshold estimates.

Training benchmarks include different ways to measure and gauge progression and better understand current fitness, as well as limitations. These include a variety of subjective feedback mechanisms such as rate of perceived exertion (RPE) and toughness. I primarily use RPE for pacing during ultra marathons and trail races. But due to the high variability of those such events, I lean heavily on other metrics during training to calibrate perceived exertion with physiological markers, such as pace zones and (very occasionally) heart rate zones. The goal is to align our feelings with what is actually happening in our bodies. If we know approximately at what pace our lactate threshold is, we can learn what that effort feels like. We can then apply this calibrated intuition to the trails. This is why establishing some base fitness metrics and training zones can be really beneficial for trail runners. If that requires some road running, so bet it!

I want to specifically address more of the technical benchmarks that you have available to you, right on your wrist, through COROS EvoLab.

EvoLab Specific Metrics: Here is where things start getting exciting! Many 3rd party software providers (e.g. TrainingPeaks, Final Surge, and Strava) offer some robust metrics to determine fitness, fatigue, and race readiness. …for a fee. COROS EvoLab offers the same robust metrics to their entire user base. As a coach, I benefit from the detailed analysis that a 3rd party can offer, but as an athlete, you don’t need an exercise science degree to understand how COROS EvoLab interprets your data. These metrics can be applied to all activities, including trail run mode! This is where you, as a trail and ultra runner, can really benefit from the new COROS EvoLab.


Training Load (TL). A metric tied to an individual workout that measures how stressful the activity was. This algorithm is determined by several factors, including duration and HR metrics.

Base Fitness. The chronic accumulation of 6 weeks worth of average TL. If you average 130 TL per workout for 6 weeks, your base fitness score is 130.

Load Impact. The seven-day acute accumulated average TL. If your base fitness is 130, and your load impact is 145, you applied more stress over the last 7 days and should get a positive adaptation to the increased workload.


7-Day Load. The sum of the last 7 days of TL. COROS EvoLab provides a suggested range to optimize progression and avoid detraining. To stick with our simple example, 130 TL per day for a week equals a 7-day load of 910.


Fatigue. A score between 0-100. The lower your score, the more ready you are to take on TL. A lower score might also indicate that you are prepared and peaking for a race. A higher score indicates the need for a recovery phase or a complete rest day.


4-Week Training Distribution. A good training approach is polarized, meaning it has a variety of intensities. Your program should include hard days, moderate days, and easy days. This graph categorizes your intensities and helps you see how well, or poor, you are doing at adding variety to your training. More on this below.


Observing the trends of these metrics over time can tell a cool story, but what is really powerful is when you can use them to plan out future training.

Here are three ways you can use the Training Load metric to improve your fitness.

  1. Application of the Overload and Recovery Training Principle.

This universal physiological principle states that, in order to establish a new baseline fitness, we must overload the body with stress and then have adequate time to recover from the stress. Consider bicep curls. We perform the movement, break down muscle tissue, and then give the biceps time to rebuild and come back stronger. Using the TL metric, in order to establish overload, the TL value must be higher than the current base fitness score (whether through higher volume or higher intensity). For example, a workout with a TL of 300 will improve base fitness at 130. A load impact score that is higher than base fitness lets you know you added more stress over the last 7 days and that you are on track for improved fitness.

However, recovery is the other aspect of this principle. We should not aim to be above 130 TL for every single workout; we need to polarize training (more on this in our next point) and have some days well above 130 and some days below. Essentially, keep your hard days hard and your easy days easy. Every athlete needs rest and/or active recovery runs built into their program, so look at improving your base fitness score from a 30,000 ft view.

On a larger scale, we can apply the same principle to the 7-day training load. We need to accumulate enough TL in the week to improve upon previous weeks. The 7-day training load must trend upward to move the base fitness score up. But increasing 7-day training load every week is unsustainable, so we must implement a recovery phase every few weeks. This varies between athletes, ranging from once every 3-6 weeks. Your fatigue metric and suggested recovery on your COROS watch are great tools to help guide your recovery phases. My recovery phase lasts 5 days and includes only very easy running: no high intensity and no long runs during this recovery focus. This recovery time allows your body to “absorb” all the hard work and come back fitter. 

  1. Polarized Training.

The 80/20 rule is a common practice that states 80% of your total training should consist of lower intensity aerobic running and the other 20% can consist of higher intensities, such as VO2 max and lactate threshold work. Your 4-week training distribution graph will keep you in check! While planning out your training, always consider how much time you plan to spend running hard and running easy.

  1. Executing the taper.

Tapering is as much an art as it is science, but there are metrics we can use to better execute a taper. We want to hold onto as much base fitness as possible and simultaneously reduce fatigue. We accomplish this by maintaining consistency (how many days we run per week), reducing volume (time spent running), and maintaining intensity (how hard we run). So if you run five days per week, don’t change that in your taper. You also don’t need to limit yourself to easy jogging. Short, hard efforts can help you maintain your peak fitness without adding additional fatigue. Staying with our above example, your 7-day training load needs to average around 130 per day during your taper to maintain base fitness. You absolutely do NOT want to overload with training load during your taper.


Additionally, there are some basic and general metrics you can track through COROS EvoLab, that also serve as benchmarks. Both VO2 Max and Lactate Threshold approximates require that you run on flat road surfaces, within your “Run” and/or “Track” activity modes.

VO2 Max is the maximum amount of oxygen you can process. It represents your “fitness ceiling”, or more accurately, your aerobic capacity. In a lab, this is measured by mL/kg/min. It’s very hard for an assessment tool such as a watch, based largely on HR and pace, to get this value correct. However, it’s still a valuable metric to track over time and see progression. VO2 Max, as a performance indicator, has so many limitations within trail running and ultrarunning, because of all the variability involved: multiple surfaces, mental toughness, environment, and ability to consume and absorb nutrients on the go. It’s not uncommon for successful ultra runners with lower VO2 Max values to beat athletes with higher aerobic capacity. Nevertheless, it’s still a great fitness benchmark, and the higher your value, the bigger advantage you have. VO2 Max is trainable, and it gets an entire training block early in most of my trail and ultra runner programs. Don’t put too much value in the actual reading, just pay attention to the trend. My reading is 17 mL/kg/min below my lab results, but when it trends upward in my app, I know my training is effective.


Lactate Threshold is a far more valuable benchmark for long distance runners than VO2 Max. While VO2 max measures an athlete’s max ceiling, lactate threshold defines an upper sustainable limit, just under that ceiling. Lactate threshold describes a hard effort during which the body starts to produce lactate faster than the body can clear and process it for fuel. When lactate spills out into the blood, we experience that all too familiar bonk. In a lab, this is measured through blood. In the field, we can administer tests, such as 30-minute time trial and estimate both lactate threshold pace and lactate threshold HR. Both indicate this turning point from aerobic to “anaerobic”. COROS estimates this via algorithms and gets fairly close. To get a more accurate measurement, run a 30-minute max effort time trial. Your average pace is likely your lactate threshold pace. By training at or near lactate threshold, we improve our upper sustainable limit, making our easier paces feel more sustainable and faster. It’s important to know your lactate threshold because you never approach this during any race that you expect to last much longer than an hour. Also, seeing this threshold pace increase over time is a great benchmark for fitness progression!


Whether you’re on the roads or blazing the trails, I hope you have a better understanding of how these metrics can help you dial in your training. A good training process not only improves your fitness, but it also helps you have a much better race-day experience and increase your longevity in this sport!

Written by Cliff Pittman @Fit2Endure Coaching
Certified Run & Mindset Coach

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