How Hard Should HIIT Actually Feel?
You don't need a heart rate monitor to do HIIT right. You need to understand one number: your effort on a scale of 1 to 10. Here's what each level feels like — and where you should be aiming.
The most common beginner mistake in HIIT isn't going too easy. It's going too hard, too early, and quitting. A 2017 study found that when HIIT intervals were longer than 60 seconds, people rated the exercise as significantly less enjoyable and more unpleasant 📄 Thum et al. 2017 — PLOS ONE. The intervals that felt best — and produced the strongest motivation to come back — were 30–60 seconds at a hard but manageable pace.
The secret to effective HIIT isn't maximum suffering. It's finding the right effort level — hard enough to trigger adaptation, comfortable enough that you'll do it again on Wednesday.
Here's a visual guide you can reference every time you train.
The Effort Scale — What Each Level Feels Like
This is based on the RPE scale — a tool used by exercise scientists to measure how hard something feels. No equipment needed. Just honesty with yourself 📄 Garber et al. 2011 — Med Sci Sports Exerc.
A 2019 meta-analysis found that HIIT performed at 80–95% of max heart rate — roughly RPE 7–9 — produced the largest improvements in cardiovascular fitness 📄 Wen et al. 2019 — J Sports Med Phys Fitness. But here's the nuance: even intervals at RPE 6–7 produce significant gains when sustained over 4+ weeks. You don't have to suffer to improve.
The talk test is free and surprisingly accurate. If you can sing during your work interval, you're at a 4–5 — too easy. If you can speak short phrases, you're at 6–7 — perfect for beginners. If you can only grunt single words, you're at 8–9 — ideal for intermediate and advanced. No tech required 📄 Woltmann et al. 2015 — J Sports Sci.
The Two Biggest Mistakes
Mistake #1: Going to a 10 every round. That's not HIIT — that's sprinting until you collapse. Research shows all-out sprint protocols reduce enjoyment significantly and aren't necessary for health benefits in most people 📄 Thum et al. 2017 — PLOS ONE. Save the 10s for Tabata days, if ever.
Mistake #2: Never getting past a 5. If your "high-intensity" intervals feel like a brisk walk, you're doing moderate-intensity continuous training — which is fine, but it's not HIIT and you'll miss out on the specific cardiovascular adaptations that make intervals powerful .
A Workout to Calibrate Your Effort
Use this session to find your RPE 7–8. Start each round slightly harder than the last until you find the pace where talking becomes difficult. That's your baseline for all future HIIT sessions.
How to use it: Round 1 at RPE 5. Round 2 at RPE 6. Keep adding. By round 4–5 you should be at 7–8. Hold that effort for the remaining rounds. Now you know your pace. Use it in every HIIT workout from here on.
SUPER INTERVAL TIMER — THE APP
A simple app to organize your workouts.
Free for 14 days · one-time unlock · no subscription
SOURCES (5 peer-reviewed studies)
- Thum JS, Parsons G, Whittle T, Astorino TA. "High-Intensity Interval Training Elicits Higher Enjoyment than Moderate Intensity Continuous Exercise." PLOS ONE. 2017;12(1):e0166299.
- Garber CE, Blissmer B, Deschenes MR, et al. "Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise." Medicine & Science in Sports & Exercise. 2011;43(7):1334-1359.
- Wen D, Utesch T, Wu J, et al. "Effects of different protocols of high intensity interval training for VO2max improvements in adults: A meta-analysis of randomised controlled trials." Journal of Science and Medicine in Sport. 2019;22(8):941-947.
- Woltmann ML, Foster C, Porcari JP, et al. "Evidence that the talk test can be used to regulate exercise intensity." Journal of Sports Sciences. 2015;33(1):18-23.
- Li F, et al. "Effects of high intensity interval training and moderate intensity continuous training on enjoyment and affective responses in overweight or obese people: a meta-analysis." Frontiers in Public Health. 2024;12:1487789.
