That workout you’ve been doing that calls itself high-intensity interval training? It might not actually be HIIT. I know that’s a spicy opener, but hear me out.
I’m Dr. Alyssa Olenick, I have a PhD in exercise physiology, and I did an entire PhD dissertation using high-intensity interval training. If I’ve learned anything along the way, it’s that HIIT has become the most misapplied and misunderstood concept in the entire fitness industry. We love to slap the HIIT label on just about anything that seems slightly fast or intense. But those group fitness classes with kettlebell swings and box jumps and burpees? They aren’t inherently bad. But they also aren’t inherently HIIT.
This matters because if you’re doing “HIIT” for specific reasons, like maximizing your cardiovascular fitness in minimal time, improving your metabolic health, or because someone told you it’s the best type of cardio for perimenopausal or menopausal women, you deserve to know whether what you’re doing is actually delivering those benefits.
“I do HIIT three times a week. It’s a circuit with burpees, box jumps, kettlebell swings, and battle ropes.”
NOT SO FAST: That circuit might be hard and sweaty, but it’s not true HIIT. Real high-intensity interval training requires sustained cardiovascular effort on a cardio modality, not a series of resistance or plyometric exercises strung together.
True HIIT or SIT (sprint interval training) needs to be purely cardiovascular in nature. That means running, cycling, rowing, the air bike, elliptical, or any modality where you can reach a high enough intensity and sustain it for the prescribed interval duration. The reason is that HIIT isn’t just about getting your heart rate up. It’s about stressing your cardiovascular system (heart and lungs) AND your metabolic system (energy systems within your muscles, oxygen delivery, and the metabolic strain that drives adaptation).
KEY POINT:
Even if your heart rate gets high during kettlebell swings or burpees, it’s not truly because it’s associated with the oxygen consumption demand of that exercise. Your heart rate and your actual aerobic effort become disconnected. Your heart rate reads “high intensity” but you’re not actually working at the percentage of VO2 max that drives the adaptations HIIT is known for. That’s the critical difference.
For those of you who aren’t trained runners or don’t have a strong cardio base yet, the bike is one of the best pieces of equipment for this. The air bike or echo bike specifically is absolutely brutal in the best way. It’s full body, it lets you get your heart rate high enough, and it doesn’t require a lot of technical skill. Almost anybody can hop on a bike and go hard if it’s programmed appropriately for their fitness level.
High-intensity interval training consists of intervals of 1 to 4 minutes of hard cardiovascular effort with adequate rest and recovery in between, usually about equal to the interval duration.
HIT Protocol Examples:
10 x 1 minute on, 1 minute off → More rounds, shorter intervals. A great and brutal workout.
4 x 4 minutes on, 3-4 minutes off → The Norwegian HIT protocol. Fewer rounds, longer intervals. It’s not more magical than other protocols, but it really works. Trust me, it’s pretty terrible.
3 minutes on, 2 minutes off → Another solid option. The principle is the same: hard, intentional bouts of aerobic exercise with enough recovery to repeat at a similar effort.
HIT Targets and Execution:
HIT is still very aerobic in nature even though you’re working in zone 4 or 5. You’re sustaining effort for 1 to 4 minutes, which means your aerobic energy system is doing a lot of the heavy lifting. You’re using oxygen, delivering it to your muscles, executing the round, and recovering. It should feel sustainably hard.
Sprint interval training is HIIT’s sibling, and they often get lumped together. But SIT is a different animal. These are short, maximal, above-VO2-max efforts for 10 to 30 seconds with full recovery of 1 to 2 minutes in between. The key word is FULL recovery. You’re not doing go-hard-recover-go-hard in quick succession. You’re going maximally hard, like you would with a heavy strength training set, and then actually recovering before doing it again.
SIT Protocol Guidelines:
Duration: 10-30 seconds per interval, maximal effort
Recovery: 1-2 minutes of FULL recovery between intervals
Volume: 5-10 reps. Beginners start with fewer. More isn’t always better.
Intensity: Above VO2 max. This is an effort you physically cannot sustain into the 1-4 minute range. If you could keep going, you didn’t go hard enough.
KEY POINT:
Because SIT intervals are so short, you may not see your heart rate peak at max during them. There’s a delay in heart rate response, and you’re recovering before it catches up. That’s why heart rate isn’t the best metric for SIT. Instead, focus on maximal power output and effort. If you’re not gasping and needing every second of that recovery, you probably weren’t truly at a sprint interval intensity.
One of the easiest ways to tell whether you just did a HIT interval or a SIT interval is your breathing pattern when you finish.
HIT vs. SIT Breathing Response:
After a HIT interval → Your breathing rate is elevated but still somewhat rhythmic and regular. It was hard, but you can feel yourself recovering in a controlled way.
After a SIT interval → You have a massive oxygen debt. Your breathing is heavy, gasping, and your body is pulling in as much air as possible to recover from that anaerobic effort. You need every second of that 1-2 minute rest before you can go again.
SIT is intentionally anaerobic. You’re working with energy systems that don’t use oxygen (phosphocreatine, rapid glycogen breakdown) and producing energy so fast that you can’t sustain it for long. When you stop, your body has to repay that oxygen debt, which is why you’re breathing so hard after a 20 second effort.
The reason HIIT and SIT show up in the research as being so effective for cardiovascular health, metabolic adaptation, type 2 muscle fiber recruitment, and mitochondrial integrity as we age isn’t just because they’re “hard.” It’s because they are massive stressors on your muscle tissue and metabolism in a way that drives specific adaptations. Kettlebell circuits and plyometric classes generate power and get your heart rate up, but they don’t create the same isolated, sustained cardiovascular and metabolic stress that true HIIT and SIT protocols do.
Not here to shame any type of exercise. Move the way that gets you moving. But if you want the true benefits of HIIT and SIT, you deserve honest and accurate information on what they actually are and what they actually look like.
Because these are genuinely hard stimuli, you don’t need them every single day. One to two sessions per week of HIT or SIT is enough for most people. If you’re not doing a ton of other cardio, you might get away with three. Complement these with easier zone 2 work and moderate intensity sessions so that your hard days stay actually hard and everything doesn’t blend into moderate mush.
THE BOTTOM LINE
True HIIT is 1-4 minute intervals of hard cardiovascular effort at 80-95% max heart rate with equal rest. True SIT is 10-30 second maximal, above-VO2-max sprints with full recovery. Both need to be done on a cardio modality like a bike, rower, or running. Circuit classes with burpees and kettlebell swings can be great workouts, but they aren’t delivering the same cardiovascular and metabolic stimulus. If you want the specific benefits that the research attributes to HIIT and SIT, you need to do the actual thing.
Your Action Plan:
✓ Pick a cardio modality – bike, rower, running, elliptical, air bike. Something where you can sustain a high effort for the prescribed interval duration.
✓ Start with HIT – try 6-8 x 1 minute on, 1 minute off on the bike. Aim for consistent effort across all rounds at ~85-90% max heart rate. Beginners start with 3-5 rounds.
✓ Try SIT when you’re ready – 5-8 x 20 seconds all out with 1.5-2 minutes full recovery. This should feel maximal. If you’re not gasping, go harder next time.
✓ Use your breathing as a check – HIT should leave you breathing hard but rhythmically. SIT should leave you gasping with a massive oxygen debt. If everything feels the same, adjust your effort.
✓ Program 1-2 sessions per week – complement with zone 2 and moderate intensity work. Not everything needs to be hard.
✓ Meet yourself where you’re at – if you’re new to cardio, aiming slightly below the prescribed intensity is still beneficial. Build up over time. More rounds isn’t always better.
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I’m Exercise Physiologist, sports nutritionist, weight lifter, and ultra runner. I am here to bring science to your training in a no-nonsense way. I have helped thousands of women crush big lifting goals, cross race finish lines, and even do both. I’m here to help you do the same!
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