Checked 2 Sep 2026
HIIT, high intensity interval training, is short hard work bouts with recovery in between. It is one of the most researched training methods and one of the most misunderstood: many people do a 45-minute circuit and call it HIIT, even though the intensity never gets anywhere near the level at which intervals actually work. This guide has five ready-made sessions, work/rest ratios for different goals and a clear answer to how often HIIT should be done and when it should not.
What HIIT is and what it is not
The definition of HIIT is simple: work bouts are done close to maximal effort, typically 85 to 95 % of maximum heart rate or so hard that talking is not possible, and rest periods are long enough that the next work bout can again be done hard. Work bouts range from 20 seconds to 4 minutes. The whole session is short, usually 15 to 30 minutes including the warm-up.
In research, HIIT improves maximal oxygen uptake (VO2max) at least as well as steady-state endurance training and often with less time. The meta-analysis by Milanović and colleagues (2015) found HIIT produced slightly larger VO2max improvements than continuous training. The group of Little and Gibala (2010) showed that a short interval session done 3 times a week increases the number of mitochondria in muscle. Mitochondria are the cell's power plants, and their number determines endurance.
HIIT is not:
- A 45-minute circuit where the heart rate sits at 150 the whole time. That is a good workout, but it is endurance training, not HIIT.
- Tabata every day. Tabata is one HIIT format (20 s work, 10 s rest, 8 rounds), not a weekly programme.
- A fat-loss magic trick. HIIT burns energy and improves fitness, but fat loss is decided by energy balance, not by the training format.
- A replacement for strength training. Bodyweight HIIT maintains muscle, but it does not build it the way progressive gym training does.
Work/rest ratios for different goals
The ratio of work to rest determines which quality the session develops. Short hard work with long rest builds speed and power; longer work with shorter rest builds oxygen uptake and fatigue tolerance. Below are the most common ratios and what they suit.
Work/rest ratios and their purpose
| Ratio | Example | Develops | For whom |
|---|---|---|---|
| 1:3 or 1:4 | 15 s hard, 45-60 s rest | Speed, power, explosiveness | Team sport athletes, sprinters, beginners in the first weeks |
| 1:2 | 30 s hard, 60 s rest | Anaerobic capacity | Hyrox, CrossFit, exercisers with a base |
| 1:1 | 1 min hard, 1 min rest | VO2max, fatigue tolerance | Endurance athletes, experienced exercisers |
| 2:1 | 4 min hard, 2 min rest | VO2max (the Norwegian 4 × 4) | Runners, skiers, solid base |
| Tabata 2:1 | 20 s hard, 10 s rest, 8 rounds | Anaerobic and aerobic at once | Short intense session for the experienced, not for beginners |
A beginner should start with a 1:3 ratio and shorten the rest only when the work bouts stay hard to the end. If the last work bout is clearly slower than the first, the rest is too short or the work bout too long.
5 ready-made HIIT workouts as tables
Every session starts with a warm-up and ends with a cool-down. Effort in the work bouts is 8 to 9 on a scale of 1 to 10, hard but such that the same effort is repeated in the last round. If the effort collapses, shorten the work or lengthen the rest. The first time, do half the rounds.
Workout 1: bodyweight, 20 minutes
No equipment, works at home, in a hotel and on the road. Four exercises, four rounds, 30 seconds work and 30 seconds rest. If the burpee is too heavy, replace it with an air squat.
Workout 1: bodyweight 20 min, no equipment
| Part | Exercise | Work | Rest | Rounds |
|---|---|---|---|---|
| Warm-up | Jog in place, jumping jacks, air squats | 5 min easy | ||
| Round | Jump squat | 30 s | 30 s | 4 |
| Push-up | 30 s | 30 s | ||
| Mountain climber | 30 s | 30 s | ||
| Burpee | 30 s | 30 s | ||
| Between rounds | Walk | 60 s | ||
| Cool-down | Walk and stretch | 3 min |
Workout 2: gym
Uses the gym's cardio machine and dumbbells. Part A is a pure heart-rate interval, part B combines strength and power. Choose weights so that the 40-second work bout is completed under control.
Workout 2: gym, machines and dumbbells, 25 min
| Part | Exercise | Work | Rest | Rounds |
|---|---|---|---|---|
| Warm-up | Bike or elliptical | 5 min, rising effort | ||
| Part A | Assault bike or stationary bike | 20 s all out | 40 s easy | 6 |
| Break | Walk | 2 min | ||
| Part B | Dumbbell goblet squat | 40 s | 20 s | 3 |
| Dumbbell row (alternating) | 40 s | 20 s | ||
| Sled push or treadmill at 8 % incline | 40 s | 20 s | ||
| Cool-down | Walk | 3 min |
Workout 3: running intervals
Three options by fitness level. Option C is the Norwegian 4 × 4 VO2max session, which is well researched and suits experienced runners. Beginners choose A.
Workout 3: running intervals on the track, road or treadmill
| Part | Content | Work | Rest | Reps |
|---|---|---|---|---|
| Warm-up | Jog + 4 × 50 m strides | 10 min | ||
| Option A (beginner) | 400 m faster than 5 km race pace | about 90 s | 90 s walk | 6 |
| Option B (experienced) | 1,000 m at 10 km race pace | 4-5 min | 2 min jog | 5 |
| Option C (VO2max) | 4 min hard, heart rate 90-95 % of max | 4 min | 3 min jog | 4 |
| Cool-down | Jog and walk | 10 min |
Workout 4: kettlebell
One bell, four exercises, 16 minutes. The kettlebell swing is the core of the session: the hips do the work, the arms are just hooks. If your swing technique is not solid, replace it with the goblet squat and learn the swing separately.
Workout 4: kettlebell 16 min (one bell, 12-16 kg women, 16-24 kg men)
| Part | Exercise | Work | Rest | Rounds |
|---|---|---|---|---|
| Warm-up | Kettlebell halo, light goblet squats | 4 min | ||
| Round | Kettlebell swing | 30 s | 15 s | 4 |
| Kettlebell goblet squat | 30 s | 15 s | ||
| Kettlebell row (alternating) | 30 s | 15 s | ||
| Kettlebell press (alternating) | 30 s | 15 s | ||
| Between rounds | Walk | 60 s | ||
| Cool-down | Walk, hip flexor stretch | 3 min |
Workout 5: Hyrox-style circuit
Simulates the structure of a Hyrox race in miniature: a run and straight into a station. The purpose is to teach the body to do stations tired. If you are preparing for a race, this is the most important HIIT session of the week.
Workout 5: Hyrox-style circuit, 30 min
| Part | Content | Work | Rest | Rounds |
|---|---|---|---|---|
| Warm-up | Jog and mobility | 8 min | ||
| Round | Run 400 m at race pace | about 2 min | no rest, straight to the station | 4 |
| SkiErg or row 250 m | about 1 min | no rest | ||
| Burpees 10 reps | about 45 s | no rest | ||
| Wall balls or medicine ball squats 15 reps | about 45 s | 90 s walk | ||
| Cool-down | Walk | 5 min |
Exercises in the exercise library with animations: Burpee, Jump squat, Mountain climber, Push-up, Air squat, Jumping jack, Kettlebell goblet squat, SkiErg, Assault bike. You can find all exercises in the exercise library.
How often should you do HIIT?
For most people 1 to 2 HIIT sessions a week is enough. Three is the upper limit for the experienced, and even then the rest of the training has to be lighter. The reason is simple: HIIT taxes the nervous system and metabolism in the same way as heavy gym training, and recovery takes 48 to 72 hours. If you do HIIT every day, the intensity drops and the session is no longer HIIT.
A good weekly structure for an exerciser: 2 to 3 strength sessions, 1 to 2 HIIT sessions and 1 to 2 easy runs or walks. HIIT should not be placed next to a heavy leg day, because both take the legs.
Results come quickly: oxygen uptake improves measurably in 4 to 6 weeks when HIIT is done twice a week. After that progress slows down and intensity or duration has to be raised. The same progression rule as in the gym.
When HIIT is not worth it
HIIT is a good tool, but it is not the right tool for every day. Skip the session or swap it for an easy run if:
- You are a beginner who cannot yet manage 30 minutes of brisk walking or jogging. Build a 4 to 6 week aerobic base first, then intervals.
- Sleep has been under 6 hours for a couple of nights in a row or resting heart rate is higher than usual. A hard interval while tired does not build anything, it only adds load.
- It has been less than 48 hours since the last heavy leg session or HIIT and the legs feel heavy.
- You are ill or recovering from a cold. During a fever or respiratory symptoms, hard training is off the table.
- You have joint or tendon pain that gets worse with jumping. Switch to a low-impact option (bike, row, SkiErg) or rest.
- You are on a deload week. The purpose of a deload week is to recover, and HIIT is anything but light.
Rule of thumb: if you cannot keep the effort in the last work bout close to the first, the body was not ready for this session. That is not a failure but information that next week's planning needs.
How SisuLift calculates HIIT load into recovery
In SisuLift, cardio and HIIT are not separate notes; they are calculated into the same recovery model as gym sets. When you log an interval session, the app converts it into so-called effective sets using three pieces of information:
- Intensity: primarily the heart-rate distribution from your watch (the weight is calculated from every minute's heart rate, so the hard moments of intervals do not disappear into the average), secondarily the average heart rate, and without heart rate the sport's MET value, 9 for HIIT.
- Duration: 45 minutes is the anchor; a shorter session gets a correspondingly smaller load, a longer one a larger load.
- The sport's muscle distribution: HIIT splits the load across quads and abs (20 % each) and glutes, back, chest and shoulders (15 % each).
A hard 45-minute session with an average heart rate of about 65 % of heart rate reserve equals 1.5 effective sets in the model, roughly a third of a leg workout. An easy walk stays close to zero. A pure cardio session also recovers faster in the model than a strength session, because metabolic fatigue clears faster than mechanical muscle damage.
The result shows on the recovery map by muscle group and in the week's total load, which is compared to your four-week average. When you open the app the morning after HIIT and ask the Grind coach whether to train legs today, the answer is based on this calculation, not on a guess.
Sources
- Little JP, Safdar A, Wilkin GP, Tarnopolsky MA, Gibala MJ. A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle. Journal of Physiology 2010.
- Milanović Z, Sporiš G, Weston M. Effectiveness of high-intensity interval training (HIT) and continuous endurance training for VO2max improvements: a systematic review and meta-analysis. Sports Medicine 2015.
- Wewege M, van den Berg R, Ward RE, Keech A. The effects of high-intensity interval training vs. moderate-intensity continuous training on body composition in overweight and obese adults: a systematic review and meta-analysis. Obesity Reviews 2017.
- Helgerud J et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine and Science in Sports and Exercise 2007 (the 4 × 4 model).
→ Read also: Hyrox for beginners | Hyrox training programme, 12 weeks | Beginner workout programme