Heart-Rate Zones
Understanding how your body produces and uses energy is essential for improving performance in running and HYROX. Training in the right heart-rate zones targets different energy systems, allowing you to build endurance, speed, strength, and race-specific efficiency.
Zone 1 – Recovery (50–60% max HR):
Very easy intensity used for warm-ups, cool-downs, and recovery runs. Helps blood flow and promotes adaptation without fatigue.
Zone 2 – Aerobic Base (60–70% max HR):
Comfortable and sustainable. Builds aerobic capacity, improves fat-oxidation, and increases mitochondrial density. You should be able to talk in full sentences.
Zone 3 – Tempo (70–80% max HR):
Moderately hard, often called the “grey zone.” Improves aerobic power but creates more fatigue than Zone 2. Breathing is deeper but still controlled. Not much of training should be done in zone 3 when you become more experienced. Many do a lot of their training in this zone though, as you feel like you’re working hard but you’re still comfortable.
Stroke volume, the amount of blood you pump with one heartbeat, is maxed out at 60% heart rate. So most cardiovascular aerobic gains are already being achieved in zone 2 and then plateaus a bit. However, the recovery period doesn’t plateau but increases still. You’re better off spending increased time at zone 2 and small amounts of zone 4, with minimal in zone 3. This will be expanded on soon. When you start running though or begin to run more consistently, it’s hard to run in zone 2 no matter sometimes no matter how slow you go. So, unless you want to walk in parts, getting into zone 3 is no harm.
Zone 4 – Threshold (80–90% max HR):
Hard but repeatable. This is where lactate production and lactate clearance balance each other. Great for improving speed endurance.
Zone 5 – VO₂max (90–100% max HR):
Very hard, used for 1–5-minute intervals. Trains your maximal aerobic capacity and ability to use oxygen under high stress.
The Three Energy Systems
ATP-PC / Phosphagen System (0–10 seconds):
Provides instant power from stored ATP and phosphocreatine. No oxygen required. Fuels explosive movements like sprinting, starts, and heavy sled drives.
Anaerobic Glycolysis (10 seconds – 2 minutes):
Breaks down carbohydrates quickly to produce energy. Produces lactate. Drives high-power efforts like burpee broad jumps, sleds and wall balls. ATP-PC and anaerobic glycolysis can kick in and out during a race as needed.
Aerobic System (2 minutes – hours):
Uses oxygen to create energy in the most efficient way. Dominates longer, steady efforts like running, sustained rowing, and the main pacing of a HYROX race.
How Heart-Rate Zones and Energy Systems relate
Lower heart-rate zones rely mostly on the aerobic system, where the body efficiently uses oxygen and burns a mix of fats and carbohydrates. As intensity increases, the body shifts toward anaerobic glycolysis, producing lactate and creating fatigue. The highest intensities rely on both anaerobic energy and your maximal aerobic capacity (VO₂max).
- Zones 1–2: Aerobic, low fatigue, builds endurance
- Zone 3: Mixed aerobic + anaerobic
- Zone 4: High lactate production and clearance (threshold)
- Zone 5: VO₂max + anaerobic power
HYROX Key Training Types
Aerobic Base Training (Zone 2)
Aerobic base training is the foundation of all HYROX performance. It develops the low-intensity engine that allows you to run efficiently, recover faster between stations, and handle long race duration’s without your heart rate drifting too high. Zone 2 training strengthens the cardiovascular system, increases mitochondrial density, improves fat utilisation, and stabilises your pacing ability. It should feel easy and conversational. Steady breathing, low stress, and sustainable for long periods. The goal is consistency, building time on feet with relaxed runs, longer bikes/row/ski, and steady-state conditioning. A stronger aerobic base makes threshold work smoother, VO₂ intervals more effective, and high-intensity sessions easier to recover from. It’s the ‘quiet’ training that sets up all the performance gains later. 70-80% of your cardiovascular training, so excluding mobility or strength specific workouts that aren’t circuits, should be in zone 2. The other 20-30% should be in zone 3-5, with more and longer zone 4 training being best bang for buck.
Lactate Threshold Training
Lactate training, often called threshold training, is the most effective way to build sustainable race speed and fatigue resistance for hybrid endurance events. It’s the most important training type for HYROX. Terms like anaerobic threshold, lactate threshold, and ventilatory threshold 2 all describe the same point. That is they are the fastest pace you can hold for the longest amount of time before lactate production spikes faster than your body can clear it. Once you cross that line, acidosis builds rapidly, your breathing rate surges, and fatigue hits hard. Threshold training focuses on finding this limit and spending more time just under it. This is where the biggest improvements in endurance performance come from.
Training at threshold sits around low Zone 4, roughly an RPE 8/10, and most people can maintain it for 45–90 minutes depending on fitness. It feels hard, controlled, but rhythmical. You’ll have heavy breathing, heavy and warm legs, but nowhere near the burn of VO₂ max work. The aim isn’t to sprint, it’s to sustain a strong effort while teaching your body to process lactate more efficiently. This delays fatigue and enables you to hold higher speeds with less stress.
Intervals are often performed with a 5:1 work-to-rest ratio, such as five minutes on and one minute off. If you finish the five-minute segment and feel you need more than a minute to recover, you’ve pushed too fast. If you could have continued well past the five minutes, you were too conservative. On machines, a 3:1 ratio works well. But unlike VO₂ max training, where shorter intervals are ideal, HYROX benefits far more from longer threshold bouts because the event itself is one long grind without significant recovery. Long intervals of 10 minutes or more allow your heart rate to stay elevated, preventing the heart rate dip that comes from short rest periods and forces your body to stay in that sustained discomfort zone that mirrors race conditions.
You don’t need to use intervals every time. Continuous threshold efforts are often even more valuable because they train you not just to hit a certain intensity, but to endure it. Runners and hybrid athletes can also blend in station work, such as sled pushes, skier, or wall balls. This is while keeping their heart rate anchored in Zone 4. This trains the ability to maintain threshold output even when switching modalities, which is exactly what HYROX demands.
Because threshold work is so taxing, one to two sessions per week is enough. Athletes with a lower aerobic base can start with around 30 minutes per week of threshold time, while highly trained athletes can push up to about 100 minutes, but going beyond that offers diminishing returns and risks overreaching. If there’s a few days between these sessions that is much preferred, don’t do them back-to-back days.
HYROX is fundamentally a threshold event. The better your body becomes at staying just below the red line, processing lactate, controlling breathing, resisting the urge to slow down. The stronger and more consistent your race performance will be. Threshold training is where that ability is built.
What VO₂ Training Actually Is (and Why It Matters for HYROX)
VO₂ training targets your uppermost aerobic ceiling. This is the point where your body is using the maximum amount of oxygen it can. This sits in Zone 5, an intensity most people can only hold for one to five minutes. These sessions are performed as intervals with a 1:1 or 2:1 work-to-rest ratio, allowing you to repeatedly hit high power without completely blowing out. Running intervals are typically done at your 1.5–5 km pace, rower intervals at around your 1–2 km pace, and the assault bike is often measured in aggressive bursts like 40–50 calories at maximal sustainable output.
The purpose of VO₂ max training is to help you produce more power while fatigued. By working at this intensity, you teach your body to function where oxygen supply becomes limiting, and it must shift into anaerobic metabolism. When this shift happens, lactate is produced as a usable energy source, but it also comes with acidosis (the burning, fatiguing sensation that forces you to slow down). VO₂ training improves your tolerance to this acidosis and increases your ability to keep pushing even as lactate rises. Over time, your perceived effort at high intensities drops because your body becomes more efficient at handling these byproducts.
Intervals in VO₂ training are kept short so you can move faster or push heavier wattage’s. This is where you develop genuine power. For effective programming, aim for 10–30 minutes of total interval time per session, with 3–5-minute work periods separated by enough rest to maintain quality. These sessions are potent, stressful on the cardiac and metabolic systems, and harder to recover from. They also come with a higher injury risk if overused or performed without sufficient foundation.
For HYROX athletes, VO₂ max training isn’t the top priority. I’ve included though as VO2max as a whole and training is mentioned quite a lot. Anaerobic threshold and aerobic capacity work matter more for race performance. But VO₂ intervals still have a place. They’re most valuable at the start of a training block, to build power and speed, and at the end of a block, to sharpen race intensity, get used to surging under high lactate, and feel fast leading into competition. Group fitness classes often unintentionally lift you into VO₂ territory, which can be useful occasionally for form, fun, and social energy, but they shouldn’t replace structured conditioning.
When used intelligently, VO₂ max training elevates your top-end engine, improves your power output, and teaches you how to stay composed when everything is burning, which is a skill that absolutely shows up in the later stages of a HYROX race. It will also show up if you go out too hard too early which hopefully you learn how to avoid with your prior research and discipline.
Strength, HYROX-Specific Strength & Muscular Endurance Training
Strength work in HYROX has two roles: building general muscular force production and developing specific capacity for the stations. Base strength involves compound movements like squats, deadlifts, lunges, upper body presses, and rows to reinforce joint stability, protect connective tissue, and improve the overall force you can produce. This makes the stations feel lighter, improves running economy, and reduces injury risk. This is built on weekly any time that’s more than 1 month out from race day.
During this time and especially closer to race day before your 7-10 day taper: Strength needs to become sport-specific. Training begins to mimic the event, doing the stations plus slight variations with high cross-over: heavy sled pushes and pulls to build maximal strength and technique, loaded carries to strengthen the trunk and grip, lunge variations to condition the hips and knees, and squat-to-press patterns to support wall balls. These movements blend strength with conditioning so they transfer directly to race execution. I have gone into detail about this more particularly in a separate blog.
Muscular endurance ties everything together. It’s not enough to be strong, you must repeat submaximal efforts for long periods without breaking down. This means longer sets of wall balls, sustained lunge efforts, pull down and row pieces that challenge leg and shoulder endurance, and circuits that keep you moving under accumulating fatigue. The goal is to build durability. This is the ability to maintain form, speed, and power deep into the race. Strength, specific conditioning, and muscular endurance combine to create the resilience needed for each station and the capacity to transition smoothly back into running without losing pace.
Running
Running training for HYROX can be broken into five key types, each serving a different purpose in building speed, efficiency, and race-specific conditioning. Easy runs sit in Zone 2 and can last anywhere from around 25 to 60 minutes. They build your aerobic base, increase time on feet, and require minimal recovery. Adding short “mechanical intervals” within easy runs helps sharpen technique. These are running for a couple of minutes with perfect form before letting the mind relax again.
Aerobic intervals sit at the low end of Zone 3, around 70–75% of your maximum heart rate. This is close to your HYROX running pace during the first few runs, and lets you accumulate more quality running time. A session like three sets of 1.5 km with a 400-metre jog between efforts is a strong example.
Anaerobic threshold intervals live at the high end of Zone 3, low end zone 4, right before the body crosses into anaerobic work. Here you run around or slightly faster than HYROX pace but keep the intensity the same. It should feel “comfortably hard,” around an eight out of ten. With rest set at roughly a quarter of your work interval, this style of training is one of the most effective ways to get faster. You can also use these sessions to push further into zone 4 and do 20-40 minutes harder, however you will be in anaerobic work here.
Long runs stay in Zone 2 at about 65–75% of max heart rate and last 70–90 minutes. These sessions build muscular endurance, improve your ability to tolerate sustained effort, and help you recover better from tougher workouts.
Finally, there’s compromised running. This is running after station work when your legs are heavy, heart rate is elevated, and biomechanics start to shift. A session like 30 wall balls, 30 metres of walking lunges, and a 1 km run repeated three times is a classic example. This is the closest simulation of what HYROX running truly feels like. These are arguable just as important as lactate training and running.
In another blog I’ve discussed techniques and pacing about the stations during the HYROX race. In terms of running and what pace to run during the race, the best guesstimate is your half-marathon time trial. If you have never run that far before or recently, you can multiply your 10km time trial by ~2.22. For e.g. a 46-minute 10km time (4:36min/km) would be around 1 hour 42 minutes for a half marathon. This is 4:50min/km to 5:05 min/km pace.
You could go slightly faster on race day, but risk decrease station performance significantly. You can recover but will have to go quite slow for a period to do so. My advice, go out comfortably hard at around the estimated pace previously discussed. Make sure the ski-erg and rower feel almost too easy with the damper on 3-5, to make it easier to keep a good running pace. After the rower, if you stick at a similar pace for the rest of the runs of the race, your RPE will be closer to 8/10. It’s vital to make sure that you have just enough in the tank to do the wall balls without needing to have a rest every 5 reps. Running in-between stations should act as a small recovery, despite increasing your heart rate continuously, so there’s no need to go faster than your half marathon pace. The stations are demanding.
