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Eight years after her last CCC, Yao Miao returned to the race carrying an injured knee. She still finished third—her fifth Chamonix podium in six starts across eight years, giving her the second-highest number of top-three finishes in UTMB Finals history. The challenge was formidable even before the race began. An emergency reroute increased the course from the planned 101 km to 107.8 km, with 6,198 m of climbing. Torrential rain turned the trails slick and muddy, while three former CCC champions—representing three generations of winners across six years—lined up in one of the deepest women’s fields the race had seen. Yao stopped the clock in Chamonix at 12:15:41. When asked how she had remained at the top of the sport for so long, she gave a two-word answer: HARD WORK. The numbers show how much work went into her return. But this is not simply a story about how far she ran or how high she climbed. It is a story about what happened when her preparation stopped going to plan—and how, each time the race presented a new problem, she found a way to respond. Build: Six Weeks of Relentless Preparation 878 km and 31,234 m of Climbing In the six weeks before CCC, the SUUNTO APP recorded 98 hours and 34 minutes of training for Yao, covering 878 km with 31,234 m of elevation gain. That is more than 16 hours of training and 5,000 vertical meters per week. To put the climbing in perspective, 31,234 m is roughly equivalent to ascending Mount Everest three and a half times. Athletes at a similar level typically accumulated around 20,000 to 25,000 m over the same period; Yao logged 5,000 to 10,000 m more. The volume gave her the aerobic strength and climbing durability she would need in the Alps. Living and training in Lijiang at more than 2,400 m above sea level provided a strong altitude base, while arriving in Chamonix a month early gave her time to adapt before race day. The foundation was there. Then, three weeks before the start, the plan changed. Break: An Old Knee Injury Returns On August 8, Yao aggravated an old knee injury at the Swiss round of the Golden Trail World Series. Her response was not to train harder. It was to back off. Over the following week, her elevation gain fell from approximately 5,000 m to 1,300 m—a reduction of more than 70%. Rehabilitation and active recovery replaced much of the workload. The change was visible in her SUUNTO data. After consecutive mountain sessions and the strain of adapting to a new environment, her fitness balance had fallen to approximately -79. In the final week before the race, her fitness level stood at 117, fatigue at 68, and fitness balance at +40. Her long-term fitness had dipped slightly, but fatigue had fallen much faster. She had not trained her way back to a perfect peak. Instead, she had reduced fatigue faster than she lost fitness and arrived at the start line ready enough to compete. That distinction would shape everything that followed. Rebuild: Training for the Race She Could Still Run Yao’s preparation shifted along with her condition. Across the six-week block, Yao logged approximately 91 hours across five heart-rate zones. Zone 2 aerobic work accounted for 31 hours and 3 minutes, while Zone 3 aerobic endurance and threshold work added another 25 hours and 30 minutes. During the taper, she reduced her highest-intensity Zone 5 work by approximately 40 minutes while adding around five and a half hours in Zone 4. The emphasis moved away from all-out effort and toward sustained work closer to race intensity. It was a measured compromise: preserve the engine, protect the knee, and reach the start line without making the injury worse. Between July 29 and August 27, her average recovery reading was approximately 75%. It fell to around 20% at the worst point in early August, then returned to 80%–100% on most days from mid-August onward. She had done what she could. The rest would depend on how well she adapted once the race began. Race: Making Her Intentions Clear The First 10 km: 1,400 m Up at 169 bpm CCC offered no gentle introduction. The opening 9.4 km climbed approximately 1,400 m to Tête de la Tronche, with gradients reaching 35%. Yao did not choose a conservative start. She averaged 8:47 min/km and approximately 169 bpm over the first 10 km, reaching the checkpoint as the leading woman in 1:22:34. She also raced without poles. On gradients of up to 35%, that demanded exceptional leg strength and core stability while allowing her to conserve upper-body energy for the later stages. It was a clear statement: the knee injury had changed her preparation, but not her ambition. The next challenge was very different. Over roughly 20 km, the course dropped about 1,500 m—the kind of terrain most likely to expose an injured knee. Yao ran the 30–40 km split at 4:50 min/km, descending 989 m. From kilometers 40 to 50, she accelerated to 4:32 min/km while descending another 584 m. Downhill running can expose the knees to impact forces equivalent to three to five times body weight. At Yao’s approximate weight of 50 kg, each foot strike represented an estimated load of 150 to 250 kg. Over a 20 km descent—roughly 20,000 foot strikes—the cumulative stress was immense. The speed was there, but the cost was becoming visible. Race footage showed her downhill movement tightening, a common protective response when the knee is painful. Toni McCann passed her from behind. Yao adjusted again. Her original strategy had been to conserve energy uphill, run normally on the descents, and attack the flatter sections. With the long downhill aggravating her knee, that plan was no longer realistic. She began pressing on climbs, where the discomfort was less severe, and easing back on descents and flatter terrain. She could not control the injury. She could control how she raced around it. Interrupted by a Train, Back Into the Lead At around kilometer 68, CCC delivered another problem no training plan could anticipate. Toni McCann reached a railway crossing just as a train was passing and officials stopped her for approximately two minutes. Yao arrived shortly afterward and was also held briefly. Her watch captured the interruption. At around 7:07 into the race, her heart rate dropped sharply from approximately 145 bpm to 132 bpm. When the route reopened, it returned to around 150 bpm within minutes. Yao refueled quickly, settled back into her rhythm, and retook the lead. Then came one of the race’s decisive climbs. Between kilometers 70 and 80, the course gained 1,155 m. Yao averaged 9:24 min/km, 156 bpm, and approximately 145 W through the section. The steady power and heart-rate data showed that she had regained the lead without a reckless surge. She reached Trient more than three minutes ahead of McCann. The gap narrowed to approximately 1:58 at kilometer 82.9, then to around one minute as Yao entered Vallorcine at kilometer 90.1. The race remained finely balanced. The train had stopped her momentum. It had not stopped her race. Endure: Passed Late, but Never Falling Apart The final 17 km still contained approximately 787 m of climbing. By then, the accumulated fatigue, rain-soaked terrain, and persistent knee pain were converging. Yngvild Kaspersen and Toni McCann both passed Yao in the closing stages. On the final climbs, the drive in her stride became visibly more restrained. But she did not unravel. Her heart rate remained mostly between 145 and 150 bpm, even as the terrain forced her pace to slow. Once she completed the final climb, she found another gear. Over the last 6.1 km, she averaged 6:11 min/km. The podium order had been decided, but Yao was still racing. She reorganized her effort, kept moving, and ran across the finish line. Afterward, she smiled and described the ordea: “MY KNEE A LITTLE PAIN.” The Result Was Third Place. The Story Was Adaptation. Yao did not control the injury, the course change, the rain, the train crossing, or the two rivals who passed her late in the race. What she controlled was her response. She built an enormous training base. When her knee failed, she reduced the workload and prioritized recovery. When descending became painful, she changed her race strategy. When a train interrupted the competition, she reset and retook the lead. When she was passed in the final stages, she kept her effort together and finished running. Third place was the result. But the real story was everything it took to get there. It was also Yao’s fourth consecutive podium in Chamonix—another chapter in a record built through consistency as much as speed. HARD WORK. For Yao, those words were not a slogan. They were the thread connecting every adjustment, every setback, and every step back to the podium. The SUUNTO APP will keep recording the work behind whatever challenge comes next. And for Yao, as she turns the page to her next challenge, her journey promises to remain as extraordinary as ever—or simply put, Miao-velous.

A tempo run looks simple from the outside: run a little faster than your easy pace. What it actually tests is your control of intensity. The effort has to be hard enough to create a real training stimulus and restrained enough to stay clear of an all-out effort that costs you days of recovery. Placed well in a training plan, tempo work becomes the bridge between everyday running and race day, teaching you to hold your breathing, your form, and your pace together as the effort builds. At a Glance A tempo run is a sustained effort at a moderately hard intensity. Judge tempo intensity using pace, RPE, and heart rate together. Runners at different fitness levels need different approaches to tempo training. Plan your tempo runs around your overall training load and recovery. Suunto helps you plan, track, and analyze your tempo training over time. Table of Contents What Is a Tempo Run? Why Should You Do Tempo Runs? How to Find Your Tempo Run Intensity? Example Tempo Run Workouts for Different Levels How Suunto Helps You Track and Improve Your Tempo Runs FAQ What Is a Tempo Run? A tempo run is a sustained effort at a moderately hard intensity. Next to an easy run it is faster and carries a higher heart rate. Next to interval training it sits below maximal intensity and runs continuously rather than in short repeats. You can run it as one continuous block or break it into several long tempo segments with short periods of easy running between them. What defines it is a steady, challenging effort, not a specific pace or a specific duration. Typically: Intensity: Close to lactate threshold Duration: Around 20–60 minutes, depending on fitness level Perceived effort (RPE): 7–8/10 Simply put, a tempo run should feel comfortably hard. The effort is clearly challenging, but you can still maintain a steady pace and good running form without pushing yourself close to exhaustion. Why Should You Do Tempo Runs? The main benefit of tempo running is that it trains your body to hold a steady effort at higher intensities. 1. Improve Lactate Threshold Tempo runs are a mainstay of lactate threshold training and one of the most effective ways to raise your threshold and your ability to sustain higher intensities. Lactate threshold is the intensity at which blood lactate starts rising more rapidly as exercise intensity increases. Consistent tempo training improves your body’s ability to process lactate, which lets you hold a steady effort at a faster pace. 2. Improve Running Economy Tempo runs can also improve running economy, which describes how efficiently your body uses energy at a given pace. Regular higher-intensity running helps your body adapt to faster speeds and hold efficient form and steady pacing once fatigue arrives. 3. Improve Race-Specific Endurance Tempo runs get you familiar with the intensity and pace that racing demands. For longer events such as the half marathon and marathon, they prepare your body for sustained work at higher intensity and build your ability to hold pace and effort when tired. Depending on your training plan, tempo work can sit alongside race-pace training, though the two are not identical. 4. Build Mental Resilience Tempo runs train more than your legs. They also build your tolerance for fatigue and discomfort. Holding a higher intensity for an extended period means keeping your pace and effort under control while fatigue steadily builds. How to Find Your Tempo Run Intensity? Getting the intensity right is what makes a tempo run work. Too easy and the session lacks enough stimulus to drive adaptation. Too hard and it becomes interval training, with the fatigue and recovery cost that comes with it. The three common ways to judge it are pace, rate of perceived exertion (RPE), and heart rate zones. Use them together rather than trusting any one on its own. 1. Pace Pace helps you control your speed during a tempo run, but no single tempo pace works for everyone. Your tempo pace shifts with fitness level, race performance, terrain, weather, and how you feel on the day. Two runners will have different tempo paces, and the same runner will need different paces under different conditions. Treat pace as an external measure of output, read alongside RPE and heart rate, to confirm you are training at the intensity you intended. 2. Rate of Perceived Exertion (RPE) RPE uses how the effort feels to judge exercise intensity. In the commonly used 0–10 scale: 0: No effort at all 1–2: Very easy, with almost no strain 3–4: Easy, with comfortable conversation 5–6: Moderate effort, with a noticeable training load 7–8: Hard effort, requiring focus to maintain your pace 9: Very hard, close to maximal effort 10: Maximal effort, impossible to sustain for long Tempo runs typically land at RPE 7 to 8 out of 10. Breathing is noticeably faster at that intensity. You can still exchange a few words, though holding a normal conversation is difficult. 3. Heart Rate Zone Heart rate gives you a more direct read on the load your body is carrying than pace alone, which makes it a useful reference through a tempo run. Some training systems place tempo intensity at around 85% to 90% of maximum heart rate, though the exact range varies by system and by individual. Because zone models draw their boundaries differently, defining a tempo run simply as zone 3 or zone 4 is unreliable. Percentages of maximum heart rate are a general reference, and different zone models produce different training zones. Suunto lets you set heart rate zones from your own data, so you can use real-time heart rate to gauge your intensity through a tempo run. Example Tempo Run Workouts for Different Levels The workouts below are examples. Set your actual tempo intensity from your own pace, RPE, or target heart rate zone. 1. Beginner: Short Tempo Intervals For runners new to tempo training, breaking the work into shorter efforts with easy running between them is a good place to start. Example: 5 minutes of easy running to warm up 3 minutes of tempo running, followed by 1 minute of easy running; repeat twice 5 to 10 minutes of easy running to cool down This structure gets beginners familiar with tempo intensity. As they adapt, they can gradually add repetitions. 2. Intermediate: Longer Tempo Efforts Once shorter tempo efforts feel comfortable, extend the length of each tempo segment. Example: 15 to 20 minutes of easy running to warm up 15 to 30 minutes of tempo running 10 to 15 minutes of easy running to cool down Compared with shorter intervals, this asks you to hold a steady intensity for longer, which puts the emphasis on sustained effort. 3. Advanced: Continuous Tempo Run Runners with a solid endurance base and experience of tempo training can focus on holding a steady effort through one longer continuous block. Example: 15 minutes of easy running to warm up 30 to 40 minutes of continuous tempo running 10 to 15 minutes of easy running to cool down For half marathon and marathon training, longer tempo runs work as race-specific sessions that prepare you for sustained higher intensity. McMillan also lists 15 to 40 minutes of continuous tempo running as a form of lactate threshold training in its half marathon training guide. Tip: Progress your tempo runs gradually. As the effort becomes more manageable, extend the tempo duration, shorten the recovery between intervals, or build toward a longer continuous block. If you struggle to maintain the target intensity or your pace drops noticeably in the second half, reduce the tempo duration or allow more recovery before progressing further. How Suunto Helps You Track and Improve Your Tempo Runs Suunto sports watches support tempo training from end to end: planning the workout, following it through the run, and reviewing it afterward. 1. Before Running Create a  Workout & Set Target Zones On Suunto watches that support structured workouts, you can build a session in the Suunto app and sync it to your watch. Some models also let you create simple structured workouts on the watch itself. For example: 15 minutes of warm-up 30 minutes of tempo running with a target heart rate zone Repetitions and workout steps set as needed 10 minutes of cool-down During the session, your watch guides you through each step and helps you hold your target intensity. 2. During Running Through a tempo run, Suunto tracks your training in real time: Heart Rate Check that you are holding your target training zone. It keeps the intensity high enough to create a real stimulus and controlled enough to stay clear of interval territory. Pace and Distance Watch that your pace stays steady while the session meets its intended goal. A tempo run is built on consistent effort, so steady pacing matters. The aim is to finish the workout as planned rather than let fatigue cut it short. 3. After Running Afterward, Suunto helps you review: Training Load See what the tempo run contributed to your overall training load, so you can keep the stimulus meaningful and spot a sudden jump before it disrupts the sessions ahead. Progress Over Time Tracking CTL, ATL, TSB, and VO₂ max shows how your training load, training status, and aerobic fitness are moving over time. The Suunto app and compatible watches let you review long-term training data, including training history and training trends. Recovery Needs Recovery after a tempo run depends on sleep, HRV, training fatigue, and your daily condition. The Suunto app and your watch help you read your recovery status and decide whether to run the next session as planned or ease the intensity and give yourself more time. Learn more about Recovery here. Finding the right intensity, and adjusting your volume as your fitness changes, is what makes every tempo run serve your long-term goals. Read training intensity, body feedback, and long-term data together and a tempo run becomes more than a faster session. It becomes a deliberate, adaptable part of your training plan. FAQ What Is a Tempo Run for 5K? For 5K runners, tempo pace usually sits slower than 5K race pace but hard enough to create a training stimulus, typically held for 20 to 40 minutes. Set the exact pace from your fitness level, using RPE 7 to 8 out of 10 as a reference alongside heart rate and perceived effort. Is a 20-Minute Tempo Run Good? Yes. A 20-minute tempo run is a classic workout format. For beginners, 20 minutes already delivers an effective training stimulus. More advanced runners can extend it to 30 to 40 minutes or move to longer tempo intervals. What Is a 3:2:1 Tempo Run? A 3:2:1 tempo run is a progressive tempo workout built from segments of different lengths, typically 3 minutes, 2 minutes, and 1 minute, with intensity rising through each one. It is good practice for pace control and for holding a higher effort as fatigue builds. Do Tempo Runs Increase VO₂ Max? Tempo runs can contribute to VO₂ max, though they are not the primary type of training used to develop maximum oxygen uptake. Those gains come mainly from high-intensity interval training and repeated efforts close to VO₂ max intensity. Tempo runs primarily improve lactate threshold, aerobic endurance, and your ability to sustain higher intensities.

In endurance sports, one workout only tells part of the story. Long-term fitness is built from the training you accumulate across weeks and months, and from how well your body adapts to it. Chronic Training Load (CTL) is the metric that tracks that longer arc. Here is how it is calculated, how to read it, and how to use it to plan your training and recovery. At a Glance CTL reflects long-term training load and the fitness you have accumulated. TSS measures the stress of a single workout, while CTL, ATL, and TSB track long-term load, short-term fatigue, and the balance between them. There is no single best CTL. The right one is the level you can sustain. Build your training load gradually and give recovery enough room. Read CTL alongside performance and recovery rather than chasing a higher number. Suunto tracks CTL, training load, and recovery so you can follow your long-term progress. Table of Contents What Is CTL? How Is CTL Calculated? From TSS to CTL, ATL, and TSB What Is a Reasonable CTL? How to Build Your CTL Safely How Does Suunto Help You Track CTL and Training Progress? What Is CTL? As training accumulates, your body adapts to the stress of exercise and your fitness moves with it. A run that felt hard a few months ago can feel comfortable after a consistent block of training. That change is the product of accumulated load rather than any single session. CTL (Chronic Training Load) is the metric that tracks the accumulation. It is a useful reference for your training base and your fitness trend, though it measures load rather than fitness itself. In the Suunto training load system, CTL is a weighted average of your training load across the past 42 days by default, so it reflects how the last several weeks of training have fed your long-term base. How Is CTL Calculated? From TSS to CTL, ATL, and TSB In training load analysis, CTL, ATL, TSS, and TSB are not independent metrics. They are all part of the same training load framework: Metric Meaning What It Reflects TSS Training stress The impact of a single workout CTL Chronic Training Load Long-term training accumulation and training base ATL Acute Training Load Fatigue from recent training TSB Training Stress Balance The relationship between long-term load and recent fatigue From TSS to CTL and ATL CTL is not built from training time, distance, or the intensity of any one session. It is built from the TSS (Training Stress Score) each workout generates. Think of CTL as a weighted average of daily TSS across the past 42 days, with recent training carrying more weight than older training. TSS scores the stress of a single workout, usually from duration and intensity together. A long easy session and a short hard one can land on a similar TSS despite being very different workouts. As training accumulates, past TSS values feed both the long-term and the short-term view of your load. CTL holds the long view. ATL is a weighted average of TSS over the past 7 days, so it reflects recent load and the fatigue that comes with it. TSB is the gap between the two, which is what tells you how long-term load and recent fatigue are sitting relative to each other. Because CTL covers a long window, one heavy session barely moves it. It shifts slowly as load accumulates. ATL is far more reactive and climbs quickly when volume jumps, which is exactly what makes it a good read on recent fatigue. TSB: Connecting Training Load and Recovery In the training load system used by Suunto: TSB = CTL − ATL A simple way to understand TSB is: TSB < 0: Recent fatigue is relatively high, which is common when training load is increasing. TSB ≈ 0: Long-term training load and recent fatigue are relatively balanced. TSB > 0: Recent training load is lower than long-term training load, generally indicating lower levels of fatigue. How Do These Metrics Work Together in Training? During a training load build-up, increasing TSS usually causes ATL to rise more quickly, while CTL gradually increases as training accumulates. TSB may fall, reflecting the buildup of fatigue alongside the increased training stimulus. During a pre-race taper, reducing training volume causes ATL to drop more quickly, while CTL declines more slowly. As a result, TSB rises. This allows athletes to reduce recent fatigue while maintaining the training base built through long-term training. What Is a Reasonable CTL? There is no single best CTL that works for everyone. A reasonable CTL depends on factors such as the sport, training experience, race goals, weekly training volume, and ability to recover. For cyclists, CTS Coaches notes that CTL can vary widely. Century and non-competitive Gran Fondo riders are often around 40–100, while Masters racers and other competitive cyclists commonly fall around 70–120. These numbers are best used as reference ranges, not fixed targets. Instead of asking how high your CTL should be, start by asking: Does this CTL match your current training level, and can you maintain it consistently over time? Your CTL Trend Matters More The trend in your CTL can help you understand how your training is progressing: CTL steadily increasing: Usually indicates that your long-term training load is building and can be a sign of growing training fitness. CTL staying stable: May mean you’re maintaining your current training base or going through a period of race preparation or training adjustment. CTL gradually decreasing: Doesn’t necessarily mean your fitness is declining. Recovery periods, reduced training, or a pre-race taper can all cause a temporary drop in CTL. However, if training volume stays low or stops for a long period, a continued decline may reflect reduced training stimulus. CTL quickly increasing: Means training load is building rapidly. If the increase outpaces your ability to recover and adapt, you may experience accumulated fatigue, lower training quality, longer recovery times, or declining performance. How to Build Your CTL Safely TrainingPeaks coaching resources have suggested adding around 5–8 CTL points per week as a general reference, but this is a rule of thumb for training planning, not a target that applies to every athlete. Training experience, current CTL, injury recovery, sleep quality, life stress, and recovery capacity all affect how quickly you can safely build your CTL. For beginners, those returning to training, or anyone who hasn’t been recovering well, a much slower rate of increase may be more appropriate. When building CTL, the key is to find the right balance between training and recovery: Progress gradually: Avoid large increases in training volume or intensity over a short period. Stay consistent: Consistent training over time is more effective for building CTL than occasional sessions with an extremely high training load. Plan recovery periods: CTL may temporarily drop when training load is reduced, but that doesn’t mean you’ve lost the benefits of your previous training. Listen to your body: If you’re experiencing persistent fatigue, declining workout quality, or poor recovery, adjust your training rather than continuing to chase a higher CTL. How Does Suunto Help You Track CTL and Training Progress? For endurance athletes, the value of training load data lies in understanding whether your training is driving positive adaptations and how to adjust your training next. By tracking data such as heart rate, workout duration, exercise intensity, and training history, Suunto helps you monitor long-term changes and plan your training more effectively. Where Can You See CTL in Suunto? Supported Suunto watches and the Suunto App let you view training load, training trends, and progress over time. In the Suunto App Go to DASHBOARD > PROGRESS or TRAINING ZONE > PROGRESS to view your training trends. On your watch You can add the PROGRESS or TRAINING widget from the app menu. The metrics available may vary by model. On Suunto Run, you can use the Training Volume widget to view your training information for the current week. Ramp Rate shows how quickly your CTL is increasing or decreasing over time. How Can CTL Guide Your Training? CTL is steadily increasing, with good recovery and performance: Your current training load is generally manageable. You can maintain your current training rhythm and gradually increase the load according to your plan. CTL is rising too quickly, ATL is climbing rapidly, and TSB remains low: Your recent training load may be increasing too fast. Look at your performance and recovery to decide whether to reduce training volume or schedule more recovery. CTL temporarily drops, while recovery and performance improve: This may be a normal part of a recovery week or pre-race taper. There’s no need to increase training load just to keep CTL from dropping. You can also consider sleep, HRV, perceived fatigue, muscle soreness, and training performance to get a more complete picture of whether your current training load is right for you. Learn more about recovery here. Takeaways CTL is not a score to push higher. It is a way of understanding your long-term training. Rather than chasing a specific number, find a training rhythm you can sustain, built around your goals, your recovery, and what your performances are actually telling you.

Heart rate zones turn a number on your wrist into something you can train by. In endurance sports like running and cycling, most systems split effort into five zones, Zone 1 through Zone 5, so you can see how hard you are actually working and choose the right intensity for the session in front of you. Zones are personal. They can be built from your maximum heart rate, your resting heart rate, or your lactate threshold heart rate, depending on the method behind them. That is also why the zones on one device can differ from the zones on another. At a Glance Heart rate zones turn effort into a scale you can train by, most commonly Zone 1 through Zone 5. Each zone serves a different purpose, from recovery and aerobic base work through to near-maximal efforts. Zones can be set from maximum heart rate, heart rate reserve, or lactate threshold heart rate, and each method draws different boundaries. Devices show different zones because they use different methods, different settings, and different ways of measuring heart rate. Check your zones against your breathing, your perceived effort, and how long you can hold each intensity. What Are Heart Rate Zones? A heart rate zone is a range of intensity defined by your heart rate in beats per minute (BPM). The five-zone model is the most widely used, running from Zone 1 up to Zone 5 as effort climbs from easy movement toward near-maximal work. Three-zone and four-zone models also exist, built on different thresholds for different training purposes. Heart rate, breathing, and overall physiological stress all climb together as intensity rises. That is what makes zones useful for more than a snapshot of effort. They tell you whether the intensity you are holding actually matches the purpose of the session. What Do the Different Heart Rate Zones Mean? The five-zone model splits heart rate into Zone 1 through Zone 5. Each zone sits at a different level of intensity and does a different job in your training. Here is what each one feels like and where it is normally used. Zone 1: Recovery and Low-Intensity Training Zone 1 is typically used for warm-ups, cool-downs, and recovery sessions. Breathing should feel very easy, and the overall training load is low, making it possible to keep moving for a long time without much strain. For example, after a high-intensity interval workout, easy movement in Zone 1 can help you gradually recover without adding much additional training stress. Zone 2: Aerobic Endurance Training Zone 2 is a common low-intensity zone for endurance training. The effort feels relatively easy, with steady breathing that you can maintain for an extended period. It’s often used for easy runs, long runs, and other aerobic base training. Over time, this type of training helps your body adapt to sustained exercise and improve its ability to maintain aerobic effort for longer periods. Zone 3: Tempo and Steady-State Training Zone 3 is more demanding than easy aerobic training. Your breathing becomes noticeably faster, but you can generally maintain a steady effort for a reasonable amount of time. Zone 3 can be used for steady-state runs, sustained moderate-intensity workouts, and some easier tempo runs. For runners, this type of training can help build the ability to maintain a faster pace for longer. Zone 4: High-Intensity Training Around Lactate Threshold Zone 4 generally represents a high level of training intensity and, in some heart rate zone models, includes intensities around the lactate threshold. Breathing becomes noticeably harder, and the effort is no longer as easy to sustain as Zone 2. However, you can still train in this zone through sustained runs or longer intervals. Zone 4 is commonly used for threshold workouts, higher-intensity tempo runs, and longer intervals to help runners improve their ability to maintain performance at high intensities. Zone 5: High-Intensity and Near-Maximal Effort Zone 5 generally corresponds to exercise intensity close to your maximum heart rate. Breathing is very heavy, and the effort can only be maintained for a relatively short period. It’s commonly used for VO₂ max intervals, short high-intensity repeats, and some sprint workouts. These sessions provide a strong cardiovascular and high-intensity stimulus, but they also place a greater amount of stress on the body, so adequate recovery is especially important. How Are Heart Rate Zones Calculated? There are several ways to calculate heart rate zones. The most common methods use Maximum Heart Rate (Max HR), Heart Rate Reserve (HRR), or Lactate Threshold Heart Rate (LTHR) as the basis for setting your zones. % Maximum Heart Rate The maximum heart rate method is one of the simplest ways to calculate heart rate zones. It uses a percentage of your maximum heart rate to define each training zone. Your maximum heart rate can be estimated using an age-based formula, such as the familiar “220 − age,” or determined through maximal-effort exercise testing, field testing, or laboratory testing. Age-based formulas are convenient, but individual differences can be significant, so the result may not accurately reflect your actual maximum heart rate. In a common five-zone model, the following percentages of maximum heart rate can be used as a general guide: Heart Rate Zone % Maximum Heart Rate Zone 1 Approx. 50–60% Zone 2 Approx. 60–70% Zone 3 Approx. 70–80% Zone 4 Approx. 80–90% Zone 5 Approx. 90–100% For a deeper look at maximum and resting heart rate, see Know Your Max and Resting Heart Rate. % Heart Rate Reserve The Heart Rate Reserve (HRR) method takes both maximum heart rate and resting heart rate into account, making it more personalized than simply using a percentage of maximum heart rate. However, the accuracy of the resulting zones still depends on having reliable maximum and resting heart rate values. First, calculate your heart rate reserve: HRR = Maximum Heart Rate − Resting Heart Rate Source: American Society for Preventive Cardiology Clinical Practice Statement You can then use the Karvonen method to calculate your target heart rate: Target Heart Rate (THR) = Resting Heart Rate + (% Intensity × HRR) Source: University of Minnesota For example, if your maximum heart rate is 190 BPM and your resting heart rate is 50 BPM, your heart rate reserve is 140 BPM. At 70% intensity, your target heart rate would be: 50 + (0.7 × 140) = 148 BPM % Lactate Threshold Heart Rate The Lactate Threshold Heart Rate (LTHR) method uses the heart rate associated with your lactate threshold as the reference for setting training zones. Lactate threshold can be thought of as a key point where, as exercise intensity increases, blood lactate begins to accumulate at a faster rate. It provides an indication of how well your body can sustain higher exercise intensities. The most direct approach is a graded exercise test in a laboratory, where blood lactate is measured at different exercise intensities and the lactate threshold is identified from the resulting curve. You can also estimate LTHR through structured field tests, such as a 30-minute Time Trial. One advantage of using LTHR to set heart rate zones is that it ties training intensity more closely to your individual threshold performance. However, the exact testing protocol and zone boundaries can vary depending on the training system being used. Why Are My Heart Rate Zones Different on Different Devices? If your heart rate zones look different across watches, apps, or training platforms, it does not necessarily mean one of them is wrong. The differences usually come down to three things: how the zones are calculated, the personal data used in the calculation, and how heart rate is measured. Different calculation methods and zone boundaries: One device may work from maximum heart rate, another from heart rate reserve or lactate threshold heart rate. Even on the same method, boundaries and algorithms differ. Some systems use three-zone or four-zone models built on physiological thresholds such as lactate threshold or ventilatory threshold, so both the number of zones and their edges can change from device to device. Inaccurate maximum or resting heart rate settings: If either value is set incorrectly on your device, every zone it calculates inherits that error. Different heart rate measurement methods: Wrist-based optical sensors estimate heart rate from changes in blood flow under the skin, while chest straps read the electrical signals produced by your heart. When intensity changes quickly, the two respond at different speeds, so the reading at any given moment can differ slightly, and so can the zone your device shows. In short, the first two factors move the boundaries of your zones. The third moves the heart rate that gets recorded against them. How to Know If Your Heart Rate Zones Are Right You can’t tell whether your heart rate zones are accurate by looking at the numbers on your watch alone. It’s also important to consider how you actually feel and perform during your workouts. Pay Attention to Breathing and Perceived Effort If your device shows that you’re in Zone 2 but you’re already struggling to catch your breath, your zone settings may need a second look. Likewise, if a workout classified as high-intensity Zone 4 feels easy from start to finish, your heart rate zones may not be aligned with your actual effort. If you want a better understanding of how your intensity changes during a workout, Suunto ZoneSense uses heart rate data to identify changes in exercise intensity, helping you see whether your actual effort matches the heart rate zone you’re targeting. Combine Heart Rate with Pace or Power If you can maintain the same pace at a lower heart rate over time, or run faster at the same heart rate, it generally indicates that your aerobic fitness is improving. Using a Suunto sports watch to track heart rate, pace, and training history can help you monitor these changes over time. During workouts, pairing it with a heart rate belt can also provide more responsive and consistent heart rate data. Otherwise, heart rate does not respond instantly to changes in exercise intensity. During short intervals lasting only a few dozen seconds, your effort may already be very high even though your heart rate has not yet reached Zone 5. For short intervals, heart rate alone may not tell the whole story, so it’s best to consider pace, power, and perceived effort together. Use Workout Duration as a Guide Lower-intensity zones like Zone 1 and Zone 2 should generally be sustainable for longer periods, while Zone 4 and Zone 5 are typically much harder to maintain for extended periods. If how a zone feels and how long you can sustain it consistently differ significantly from what the zone is supposed to represent, it may be worth taking another look at your maximum heart rate, resting heart rate, lactate threshold heart rate, and the zone model your device uses. Takeaways Heart rate zones are a moving target. As your fitness, maximum heart rate, resting heart rate, and lactate threshold shift, the zones built on them need revisiting too. Read them alongside training load, pace, power, and perceived effort, and heart rate stops being a number you glance at and becomes a tool you train with.

Yao Miao has always known how to run. But becoming a better athlete isn't simply about running more. Over the past year, she has changed the way she trains — moving from relying on instinct and experience to building a more structured, professional approach. “Only through competition can you find a stronger version of yourself.” A More Complete System Today, Yao's training goes beyond running. With support from her coach and specialists in strength, nutrition and recovery, every part of her preparation has a purpose — from building strength and climbing ability to improving her speed and technical descents. The goal isn't simply to train harder. It's to train better. From Pace to Heart Rate When Yao first started training, she mainly focused on pace and distance. Today, heart rate has become a much more important part of her training strategy. Her training plans and race strategies are built around heart rate, helping her understand how hard she is actually working and how to manage her effort. For Yao, relying only on how her body feels isn't always accurate. The data gives her another layer of feedback — helping her control her pace, manage her effort and make better decisions throughout training and racing. Her Suunto watch puts that information on her wrist, turning every session into a clearer picture of how her body is responding. The data informs the strategy. Yao makes the decisions. Stronger Through Competition For Yao, racing is more than a test. It's a way to discover what she can improve. Every competitor, every difficult section and every race reveals another opportunity to become stronger. Her love for running hasn't changed. What changed? The way she trains to become better.

Toni McCann knows Chamonix well. She won the UTMB OCC in 2023, then stepped up to the UTMB CCC in 2024 and took the win. After not finishing the race in 2025, Toni is returning to the UTMB CCC in 2026 — but with a different mindset. “Just run for me, instead of running for other expectations.” For Toni, the past year has been about stepping away from the pressure of results and reconnecting with why she runs in the first place. A different approach Success can bring expectations. After winning in Chamonix, the pressure to perform can become part of the race itself. This time, Toni is focusing on her own process — enjoying the training, trusting her preparation and taking on the challenge on her own terms. Her preparation combines running, strength work, cycling, recovery and time in the mountains. Rather than focusing only on performance, she is also learning to listen to her body, knowing when to push and when to recover. Training and racing with Suunto Her Suunto Race 2 is part of that process, helping her understand both her body and the course. With HRV-based recovery insights, Toni can monitor how well her body is recovering and make more informed decisions about her training. Combined with heart rate and Climb Guidance, Suunto helps her prepare for the physical and mental demands of the UTMB CCC. The technology provides the information. Toni makes the decisions. Back to Chamonix The CCC course hasn’t changed. But Toni’s relationship with it has. This time, there is less pressure to prove and more freedom to run — on her own terms, for herself. What changed? The reason she runs.