Talus

It’s human nature to learn.

We learn and use that knowledge to our advantage; mistakes, new information, and discoveries shape how we move through the world. High-information watches mean we have more information at our fingertips than ever. 

But is technology helping us become better ultrarunners, or is it making us too dependent on numbers to understand our own bodies? 

Modern GPS watches, heart-rate monitors and training apps provide a constant stream of information about performance, fatigue and recovery. For ultramarathon runners, who may spend anywhere from several hours to multiple days on the trails, these measurements can be incredibly useful. They can help runners manage their effort, monitor training progression and recognise when they need to recover.

However, data has limitations. A runner can have a poor recovery score yet feel fantastic, or receive an excellent score while carrying an injury or struggling with accumulated fatigue. Terrain, elevation, weather, nutrition, sleep and psychological stress can all influence performance in ways that a single metric cannot fully capture.

So instead of relying on the number on our watches, we need to see it as a tool to support judgment rather than replace it. 

Why is running data becoming so important?

Ultramarathons place unusual demands on the body. Unlike shorter races, performance depends not only on speed and aerobic fitness, but also on pacing discipline, muscular endurance, fuelling, hydration, sleep management and the ability to respond to changing conditions over many hours.

Wearable technology like watches, WHOOP bands, heart rate monitors and Aura Rings give runners measurable indicators of these demands. Rather than relying solely on how they feel, athletes can monitor trends and compare their training sessions over time.

Data can help answer questions such as:

– Am I running too hard during easy training sessions?

– Is my heart rate unusually high at a familiar pace?

– Am I accumulating more training stress than I can recover from?

– Is my body adapting to training, or showing signs of excessive fatigue?

– Should I follow my planned session or adjust it based on how I feel today?

These are all valuable questions to ask when training for endurance. The problem arises when runners treat a watch or app’s answers as objective truth rather than estimates that require interpretation. 

There is also a psychological dimension. Constant access to performance data can create pressure to improve every session, hit predetermined targets and quantify every aspect of fitness. An easy run may feel unsuccessful if the pace is slower than expected, even when your body needed a slow run.

The five key metrics: what do they actually tell us?

PACE

Our most used metric: pace describes how quickly you cover a distance, usually in minutes per kilometre or mile. Pace helps with structured interval training, tracking progress, and controlling effort on runnable terrain. However, pace becomes an unreliable universal measure of effort when elevation, mud, technical trails, heat, and altitude change. Running at 6:00 min/km on flat ground can require far less effort than maintaining the same pace going uphill. So, pace is good for knowing how fast you are going; but are you chasing a target pace when you should be responding to, and accounting for, the terrain? 

HEART RATE

Your heart rate measures how many times your heart beats per minute, helping you estimate exercise intensity and understand your cardiovascular response to training. However, many people focus heavily on this metric when training within their ‘heart rate zone.’ 

Training within these zones has benefits: building endurance and an aerobic base, preventing you from pushing yourself on ‘easy runs’, and providing objective progress tracking. However, focusing too much on this metric has downsides, including response lags, environmental and external skewing of data, inaccurate zone formulas, and hardware issues. 

Your heart rate is affected not only by exercise but also by heat, dehydration, stress, caffeine, illness, and fatigue. It can also drift upwards during prolonged exercise even when pace remains constant.

HEART RATE VARIABILITY (HRV)

Your HRV score measures the variation in the time between consecutive heartbeats. This metric is common alongside your sleep score and can be used as an indirect indicator of how the autonomic nervous system is responding to training and other stressors. While the metric can offer some context about fatigue and stress, sleep, illness, alcohol, psychological stress, and other factors influence your HRV score. A low HRV score does not automatically mean a runner is unfit to train, and a high reading does not guarantee readiness.

A 2021 systematic review and meta-analysis examined eight studies involving 198 participants across nine training interventions. It found that HRV-guided endurance training improved some submaximal physiological measures, but its overall advantage for endurance performance and maximal oxygen uptake was small and not statistically significant.

This is an important finding because it challenges the assumption that more personalised data automatically leads to better race results. HRV may help some athletes adjust their training and avoid poorly timed hard sessions. However, the evidence does not show that following HRV readings consistently makes runners faster.

TRAINING LOAD

Your training load score combines information such as duration, intensity, heart rate or perceived exertion to estimate accumulated training stress. Your training load may help you monitor overall training progression over a longer period instead of judging your fitness based on each isolated training session. However, a numerical score cannot fully represent the impact of technical descents, muscle damage, prolonged hiking, carrying a pack, or the demands of back-to-back long runs. So while the number is good for seeing whether you’re getting a steady amount of training, it can quickly become a target-hitting game that can lead to injury and fatigue. 

RECOVERY SCORE

Many wearables combine factors like sleep, HRV, resting heart rate and recent activity into a score intended to estimate recovery or readiness to train. While it can be a useful metric for recognising consistent patterns of poor sleep or elevated resting heart rate, which can alert you to need more recovery time, a single metric built from other imperfect metrics cannot fully capture whether you are fully recovered. Many can feel motivated to run before viewing their score and make decisions based on it. 

A study of 28 runners who completed a 100-mile ultramarathon found substantial changes in heart rate and HRV following the race, with HRV not fully returning to baseline within a week. The researchers also noted that HRV alone could not fully quantify recovery, particularly because muscular and tendon-related damage contributes to post-race fatigue. 

This highlights a key distinction:

– Cardiovascular recovery: how the heart and autonomic nervous system respond after exercise.

– Muscular recovery: how the muscles recover from prolonged effort and downhill running.

– Musculoskeletal recovery: how tendons, joints and other tissues tolerate accumulated stress.

– Psychological recovery: how motivation, mood, sleep and mental fatigue respond to training and competition.

These processes do not necessarily recover at the same rate. A watch may detect improvements in one area while the athlete is still recovering in another.

Are subjective feelings as valuable as objective measurements?

A 2025 study following 20 elite endurance athletes for a year combined wearable data with mood assessments and subjective readiness ratings. It found that the relationship between feeling ready and the data said they were ready varied by athlete, and over time athletes preferred using the recovery score as guidance rather than a single metric. 

This suggests that runners should not dismiss their own experience simply because their watch reports favourable numbers. Perceived exertion, mood, soreness, sleep quality and motivation provide information that sensors cannot directly capture. They are not perfect measurements either, but they can complement physiological data.

The strongest approach is to combine objective measurements with subjective feedback and training context.

How data can change decisions during an ultramarathon

Running data becomes especially influential during a race, when small decisions can add up to a major difference in performance. 

Scenario A: Chasing pace on a climb

A runner sees their pace fall well below their target. They push harder to compensate, despite the steep gradient and rising fatigue. The runner expends unnecessary energy early in a long race, increasing the risk of later fatigue and risking a DNF.

Scenario B: Following heart rate too rigidly

A runner tries to stay within a fixed heart-rate zone, even as heat, dehydration, and terrain change their cardiovascular response. This can lead to poor pacing decisions if the runner treats a target zone as an absolute rule instead of considering symptoms and conditions.

Scenario C: Trusting a recovery score too much

A runner receives a high readiness score before a long training session but feels unusually tired and has persistent leg soreness. They can then ignore relevant warning signs because the technology suggests that the body is ready.

Scenario D: Using data as guidance

A runner notices that heart rate is higher than usual at an easy effort. They check how they slept, assess their fatigue, consider the weather and reduce the session’s intensity. Making an informed adjustment that respects both the training plan and the body’s current response is a great benefit.

These scenarios illustrate that data does not inherently improve or undermine performance. Its value depends on how the runner interprets it, the quality of the measurement and the decision being made.

During an ultramarathon, runners also need to manage fuelling, fluid intake, changing weather, terrain and mental fatigue. A watch cannot make all these decisions for them, and a numerical target should never override serious symptoms or safety concerns.

The psychological side: when tracking becomes an obsession

With this cycle in place, several psychological things can happen. While they may not happen in the extreme, data obsession can cause issues with motivation, running for enjoyment and anxiety around recovery. When you chase statistics instead of listening to your body, you may feel guilty about missing a target or start comparing your data to others without accounting for differences in experience, fitness, or recovery needs. 

Nevertheless, don’t assume every data-focused runner is obsessed. Many athletes find tracking motivating and reassuring. The concern is whether the technology begins to dictate your behaviour in ways that conflict with your health, goals or enjoyment.

The Balance

This does not mean abandoning all technology. A healthy balance can be found in how you use running data, as it offers many benefits that, when used effectively, can help your running improve. Reviewing pace, heart rate, recent training load and HRV trends and comparing them with your own usual patterns alongside your sleep quality, mood, soreness and perceived exertion. 

Also consider elevation, weather, terrain, and fuelling, as these can explain an unusual score. Interpret your patterns with discernment instead of taking them at face value. 

Ultimately, the best ultrarunners are not necessarily those who collect the most data. They are those who can interpret it critically, recognise its limitations and combine it with an informed understanding of their own bodies.