“Should I do HIIT or steady-state cardio?”
This is the question I get asked most often at the gym.
The short answer: it depends on what you want.
But the more accurate answer: you probably need both, and the ratio matters.
First, Let’s Clarify the Basics
Aerobic Exercise (Steady-state cardio)
- Intensity: Moderate
- Heart rate: 60-75% of max
- Examples: Jogging, cycling, swimming
- Energy source: Primarily fat
HIIT (High-Intensity Interval Training)
- Intensity: High
- Heart rate: 80-95% of max
- Examples: Sprints, jump rope, burpees
- Energy source: Primarily glycogen
Fat Loss: The Comparison
Many people believe cardio is the “king of fat burning” because it burns more fat during exercise.
But research tells a more complex story.
A meta-analysis by the American College of Sports Medicine (ACSM) found:
- HIIT burns 15-25% more calories in the 24 hours after exercise (EPOC effect)
- HIIT significantly improves insulin sensitivity, with effects lasting 24-72 hours
- While cardio has higher fat oxidation during exercise, HIIT’s total lipid consumption is greater
Research from the University of Queensland found the HIIT group lost 17% more abdominal fat than the cardio group over 12 weeks.
But here’s the catch: HIIT isn’t for everyone.
When HIIT Works
HIIT is effective when:
- Movement technique is correct
- Joints can handle impact
- Recovery time is adequate
- A fitness foundation exists
If you’re a beginner or have knee/hip issues, HIIT can cause injury.
For beginners: Lower the intensity (keep it at 70-80% max heart rate) and extend recovery time. This is called “Moderate-Intensity Interval Training” (MIIT)—similar benefits, lower barrier to entry.
When Steady-State Cardio Works
Cardio’s advantages:
- Low barrier to entry—almost anyone can do it
- Low joint stress
- Short recovery—can be done daily
- Low psychological burden—less likely to cause exercise aversion
For people just starting their fitness journey, I usually recommend establishing a cardio base first (6-8 weeks) before introducing HIIT.
Cardiovascular Adaptation
If you’re focused on cardiovascular fitness (VO2max), research gives a clearer answer:
A study in the British Journal of Sports Medicine found that HIIT improves VO2max 2x better than steady-state cardio.
This is because HIIT forces more muscle fibers to participate in exercise, demanding the heart pump more blood.
But this doesn’t mean cardio is unimportant. Cardio strengthens the heart’s pumping efficiency, while HIIT improves muscles’ oxygen utilization.
Only by combining both can the oxygen system work at maximum efficiency.
My Recommendation: Time Ratios
Based on different goals, here’s my suggested ratio:
Goal: Fat loss
- 60% cardio
- 40% HIIT
- Reason: Cardio provides fat oxidation environment, HIIT provides metabolic stimulus
Goal: Athletic performance
- 50% cardio
- 50% HIIT
- Reason: Both provide complementary cardiovascular stimulation
Goal: General health
- 80% cardio
- 20% HIIT
- Reason: Lower injury risk, more sustainable
On “Fasted Cardio”
Many believe “exercising on an empty stomach burns more fat.”
Physiologically: After overnight fasting, blood sugar is low and the body does rely more on fat for energy.
But research shows the additional fat burned from fasted cardio is minimal (just 2-4 more grams per day), while the risk of muscle loss is higher.
Conclusion: Instead of obsessing over fasted vs. fed exercise, focus on total volume and intensity.
The Bottom Line
HIIT and cardio aren’t opposing choices—they’re complementary tools.
Key questions:
- What’s your fitness foundation? (Determines if you can do HIIT)
- What’s your goal? (Determines the ratio)
- Can you recover? (Determines HIIT frequency)
For most people, I recommend starting with cardio to build a foundation, then introducing moderate interval training—making both part of your exercise routine.
This is Article 7 in our “Science of Exercise” series. To learn more about the importance of proper form, read Why Proper Form Matters More Than Reps. If you’re concerned about sedentary behavior, The Dangers of Sitting has the details. To learn how AI is transforming fitness, Article 8: Why You Don’t Need Just a Fitness App—You Need an AI Coach has an in-depth analysis.