Effects of High-Intensity Interval Training at 100% vs. 120% of VIFT on Physical Performance in U-17 Male Soccer Players
In a study of U-17 male soccer players, a 6-week high-intensity interval training program prescribed at 120% of the 30–15 Intermittent Fitness Test velocity (VIFT) yielded superior improvements in aerobic capacity, maximal velocity, standing long jump, and agility compared to training at 100% VIFT, while both protocols enhanced overall physical performance.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine you are coaching a team of teenage soccer players. You want them to get faster, jump higher, and run longer, but you only have a short window of time before the season starts. The big question is: How hard should you push them during their interval training?
Should you tell them to run at their absolute maximum sustainable speed, or should you push them slightly beyond that limit?
This study by researchers from Shiraz University and Universidad Andres Bello set out to answer that question using a "speed-based" approach rather than just watching heart rates. Here is the story of what they found, explained simply.
The Setup: Two Groups, One Goal
The researchers gathered 26 male soccer players (around 16–17 years old) and split them into two teams. Both groups did the exact same amount of running, but the speed they were told to run at was different.
To figure out their speed, everyone first took a "fitness test" called the 30–15 Intermittent Fitness Test (30-15IFT). Think of this as a ruler that measures exactly how fast a player can run while stopping and starting repeatedly (just like in a real soccer game).
- Group A (The "Standard" Team): They did their high-intensity training at 100% of the speed they achieved on that test. If the test said they could run at 18 km/h, they ran at 18 km/h.
- Group B (The "Supramaximal" Team): They did their training at 120% of that same speed. If the test said 18 km/h, they were pushed to run at 21.6 km/h.
Both groups trained for 6 weeks, doing two sessions a week, alongside their normal soccer practice.
The Analogy: The Gas Pedal
Imagine the players' fitness is a car engine.
- Group A was told to drive at the car's top speed limit on the highway.
- Group B was told to floor the gas pedal and drive 20% faster than that limit, even if it felt like the engine was screaming a bit.
The researchers wanted to see if "flooding the engine" (Group B) would make the car perform better than just driving at the limit (Group A).
The Results: Who Won?
After six weeks, both groups got better. Everyone ran faster, jumped higher, and had better endurance. This proves that doing high-intensity intervals works, no matter which speed you pick.
However, the "Supramaximal" group (the 120% group) pulled ahead in specific areas:
- Aerobic Engine (VO₂max & VIFT): The 120% group improved their overall endurance and their ability to run at high speeds for longer periods significantly more than the 100% group. It's as if their engines became more efficient at burning fuel.
- Explosive Power (Standing Long Jump): The 120% group jumped significantly farther. This suggests that pushing the speed limit helped their legs generate more explosive power.
- Agility (T-Test): The 120% group showed a strong trend toward getting better at changing direction quickly, though the difference wasn't statistically "perfect" compared to the other group.
Where they were the same:
- Straight-line Sprinting: Both groups got faster at running 30 meters in a straight line, but neither group was clearly better than the other.
- Ball Handling Agility: When players had to dribble a ball while changing direction, neither group improved significantly. The researchers noted that dribbling is a complex skill involving brain power and technique, not just running speed. Since the training was just running without a ball, it makes sense that this specific skill didn't change much.
The Takeaway
The study concludes that while training at your maximum sustainable speed (100%) is good, pushing slightly beyond that limit (120%) for short bursts might give young soccer players a bigger boost in their endurance and jumping power.
It's like telling a runner: "Don't just run as fast as you can hold; sprint a little faster than you think you can, even if it's just for a few seconds." For these teenage athletes, that extra push seemed to pay off in their overall fitness and explosive strength.
Important Note: The study only looked at running drills. It did not find that this method automatically makes players better at dribbling or tactical skills, because those require different kinds of practice. Also, because the study was short (6 weeks), the results show what happens in the "short term" (like pre-season training), not necessarily what happens over a whole career.
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