Which Interval Training Is Best for Improving Endurance?
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If you want to run faster, last longer, and improve your overall fitness, interval training is one of the best methods. But not all interval workouts are the same. A new study looked at two popular types of training and found some clear winners when it comes to boosting endurance and fitness.
Let’s break it down in simple terms.
What Is VO₂max and Why Does It Matter?
VO₂max is a measure of how much oxygen your body can use during intense exercise. The higher your VO₂max, the better your endurance. It's especially important for long-distance running and other aerobic sports. Training that improves your VO₂max helps your heart, lungs, and muscles work more efficiently.
The Two Types of Interval Training Compared
The study looked at 48 well-trained young men and split them into three groups for 8 weeks of training:
1. HIIT (High-Intensity Interval Training)
- Workout: 4 rounds of 4 minutes running at about 95% of max speed
- Rest: 3 minutes of active rest between intervals
- Goal: Stay at high heart rate and oxygen use for several minutes
2. Sprint Interval Training – Short Recovery (SIT 8x20)
- Workout: 8 rounds of 20-second sprints at 150% of max speed
- Rest: Just 10 seconds of rest between sprints
- Goal: Push to exhaustion in a short time
3. Sprint Interval Training – Long Recovery (SIT 10x30)
- Workout: 10 rounds of 30-second all-out sprints
- Rest: 3.5 minutes between intervals
- Goal: Full power sprints with long recovery
All groups trained three times a week for eight weeks.
What Did the Study Find?
The researchers looked at changes in VO₂max, endurance, sprint performance, and anaerobic capacity (how well the body works without oxygen).
HIIT was the clear winner for VO₂max.
- VO₂max increased by 6.5% in the HIIT group
- The short-recovery SIT group saw a smaller increase of 3.3%
- The long-recovery SIT group had no significant change
Why? HIIT kept participants at high oxygen use for longer periods. That means more work for the heart and lungs, which leads to bigger improvements.
Which Training Helped Endurance the Most?
All three groups improved in a 3000-meter run test, but again:
- HIIT had the biggest improvement at almost 6% faster
- The SIT 8x20 group improved by about 4%
- The SIT 10x30 group improved by just 2%
If your goal is to run longer and faster, HIIT is the best choice.
What About Sprint Performance?
Sprint training did have its benefits.
- The SIT groups both improved their 300-meter sprint times by 3-4%
- The HIIT group did not improve in sprinting
So if your goal is short, fast bursts like in sports or sprints, sprint intervals help more than HIIT.
Boosting Anaerobic Capacity
Anaerobic capacity is important for short, intense efforts. Only the SIT 8x20 group improved this ability. The other two groups did not show big changes.
This suggests that short, repeated sprints with little rest are better for improving your body’s ability to perform without oxygen.
What’s the Best Training for You?
If your goal is to improve overall endurance, VO₂max, and long-distance performance:
Go for HIIT – the 4x4-minute intervals at high effort are best.
If you want to get better at short sprints or explosive sports:
Use Sprint Intervals – especially 8x20 seconds with short rest.
If you want to improve both endurance and anaerobic power:
Combining both types over time may be ideal.
Final Thoughts
This study shows that not all high-intensity workouts are equal. Training smart means picking the right type of intervals for your fitness goals. If you’re aiming for endurance, longer intervals at high effort work best. For speed and short bursts, sprint intervals with short rest can be powerful.
Whatever your goal, consistency and effort matter most. Choose the right workout and stick with it. Your body will thank you.