Can a few minutes of sprinting really change your fitness?

If this sounds familiar, you’re not alone. But there’s good news: if finding time for cardio is the thing holding you back, the answer might not be running more, but running differently.

Research suggests that high-intensity interval training (HIIT), done in short sessions throughout the week, can match or even outperform longer endurance runs when it comes to improving fitness.

One study in particular has examined how short HIIT sessions after work compared favourably with doing long, steady endurance runs at the weekend in terms of fitness, body composition, and the ability to complete a half marathon.

Here’s what the study found, what’s happening in your body when you train this way, and how to build intervals into your runs with a method that takes less than 30 minutes.

Short HIIT sessions can match long endurance runs for fitness

In the 2012 study, published in the Journal of Sports Science & Medicine, researchers followed the progress of 34 recreational endurance runners for 12 weeks. The researchers divided the runners into two groups, with both groups training for 2 and a half hours per week. 

One group would go for steady endurance runs on Saturdays and Sundays, running for 30–60 minutes on one day and 60–120 minutes on the other. 

The other group would do their training after work. On four days, the runners would complete 30 minutes of high-intensity training, with one less intense 30-minute run on the other day.

At the end of the 12-week study period, the participants all took part in a half marathon.

The researchers found that both training programmes helped to improve the runners’ aerobic capacity and body composition. It also helped them successfully complete the race. 

However, the high-intensity group had significantly larger improvements in their VO2 max (the amount of oxygen used by the body during exercise and a key measure of fitness) compared with those who did weekend endurance training.

Why interval training improves fitness more efficiently

Interval training is useful because it helps you squeeze in more high-intensity exercise than you would by always moving at the same pace. 

The use of intervals and shorter periods of exercise makes it easier for the overall intensity of a week’s worth of workouts to be higher than it otherwise would be.

In the 2012 study, the high-intensity group was able to fit in spurts of running at top speed. This meant they were trained to access this higher pace when they needed it. 

Counterintuitively, your high-intensity training can actually benefit your endurance. Researchers believe that fitting in more high-intensity exercise helps your body to adapt to working at a higher capacity and for longer.

How HIIT changes your body beyond cardiovascular fitness

Interval training can have several effects on your body, but VO2 improvement is regarded as one of the most important. It’s a marker of both physical fitness and longevity, and one of the key metrics we’ve chosen to include in the Thriva Healthspan Dashboard.

Explore the Healthspan Dashboard to see all your health data in one place. 

The increase in VO2 we see in the 2012 study could be attributed to factors such as the heart pumping a greater volume of blood from the left ventricle with each beat (known as stroke volume) and an increase in the number of working blood vessels called capillaries in body tissue (referred to as capillary density).

There’s also plenty of evidence to suggest that HIIT can provide other benefits on top of improving performance.

In the 2012 study, the high-intensity group saw improvements in their body composition. While there wasn’t a significant reduction in total body fat, visceral fat amounts fell significantly by 16.5%. Visceral fat is the harmful form of body fat that surrounds your organs, making it particularly important to pay attention to.

Other research has suggested that HIIT is linked to increasing your metabolic rate, better insulin sensitivity, and a lower risk of chronic conditions like breast cancer, cardiovascular disease, and type 2 diabetes.

What this study doesn’t tell us

There are a few drawbacks to the 2012 study that mean we need to be cautious when thinking about how its findings might apply in a general sense.

The researchers compared HIIT with steady-state endurance running, as is the case with many other studies investigating the effects of interval training. They didn’t examine how adding intervals to runs might change their impact, so we can’t be certain of this from what the study shows us.

This study was both a small one, featuring a total of 34 participants, and a short one, running for just 12 weeks. We don’t get any sense of how the effects of interval running might change over time, or how sustainable the training plan might be in the long run.

It’s also important to note that the runners who took part in the study were already doing 1–2 hours of moderate endurance exercise a week for several months before the study began.

So, while these findings might apply to people who are already quite active, it may not be the case for those who are looking to start a brand new routine. This also makes the finding that all participants completed a half marathon a little less impressive.

How to add interval training to your running routine

Despite this, there’s a substantial amount of research supporting the fitness and general health benefits of high-intensity exercise.

If you’re physically able to add some to your routine and don’t have injuries or medical conditions that prevent you from doing so, you may want to give it a try. Always consult your doctor first if you're unsure.

• Start with the 10-20-30 method. It’s a simple, well-studied approach to adding intervals into your runs. Run at a low intensity for 30 seconds, speed up to a moderate pace for 20 seconds, then switch to a high intensity for the next 10 seconds. An example session could consist of two to four 5-minute blocks following this pattern.
• Find what works for you: The best exercise plan is the one you can stick to. If 10-20-30 intervals don’t suit you, there are plenty of other options, both structured and casual. If you don’t like running with a watch, try adding a short spurt of speed at the end of each song on your workout playlist.
• Weekend runs still work: If you can’t face squeezing in a run after a hard day’s work, you’ll be fine focusing your efforts on Saturday and Sunday without a deadline in sight. Consistency is important when it comes to building fitness, so be realistic about what you can commit to week on week.
• Track the impact: If you’re looking to improve your health and fitness, it can be helpful to measure your progress. You can track physical metrics like VO2 max and HRV by syncing your wearable with the Thriva app, and you can also try home blood tests to see changes in health markers like blood lipids and HbA1c (long-term blood glucose).

Learn more about tracking your health over time with Thriva’s home blood tests.

Takeaway

If time is the thing standing between you and better fitness, short bursts of high-intensity running could be a more efficient route than longer, steadier sessions. The evidence suggests HIIT can improve your VO2 max and body composition, and the wider research supports these findings. 

You don’t need to overhaul your routine; even small shifts in intensity can make a measurable difference.

Disclaimer: This information is for general educational purposes only and isn’t a substitute for professional medical advice, diagnosis, or treatment. Always speak with a qualified healthcare professional first if you have concerns about your health.