HIIT Workouts Are Proven To Boost The Efficiency Of Your Mitochondria
You probably know of high-intensity interval training (HIIT) as a workout that's great for your heart and endurance. But new research suggests HIIT is doing something even more impressive at the cellular level.
Not only does eight weeks of HIIT increase the number of mitochondria in participants' muscles, but it also made those mitochondria more efficient1 at producing energy, according to a new study from the University of Southern Denmark. These benefits also held true for people with type 2 diabetes.
What the study found
Researchers divided 44 men aged 40 to 65 into three groups for this study. 15 had type 2 diabetes, 15 were overweight but did not diabetes, and 18 were of normal weight. All participants completed high-intensity interval training three times a week for eight weeks. The workouts consisted of short, intense bursts of rowing or cycling, followed by rest periods.
Before and after the training program, the team took muscle biopsies from participants' thighs and analyzed them using electron microscopy—a method that allows scientists to see mitochondria in extremely fine detail.
Not only did researchers see the number of mitochondria increase in these men, but they also found that the cristae, the mitochondria's active inner membrane where energy production happens, expanded by about 7%.
Why this matters for your energy
Mitochondria are super important in our bodies, acting as tiny power plants inside your muscle cells. They convert the food you eat into a the form of energy your muscles can actually use called ATP.
Inside each mitochondrion, the cristae form a folded inner membrane, kind of like a crumpled paper bag. The more tightly packed and folded the cristae are, the greater the surface area is for converting energy.
So what this study shows is that HIIT doesn't just build more power plants, it also upgrades the ones you already have. More efficient mitochondria mean your muscles can produce more energy without the cellular network needing to expand. This has a big deal for effect on endurance, muscle function, and how you generally feel day to day.
The muscle adaptations were observed across all three groups, including those with type 2 diabetes.This challenges a common assumption that diabetes may impair the muscle's ability to respond to training.
What makes this research unique
Previous studies like this hadn't been able to detect changes in the internal structure of mitochondria, but this team spent a year manually analyzing around 11,000 individual mitochondria. This enabled an exceptionally high level of precision, allowing them to see the 7% change in cristae density.
That said, there are still limitations to this research. While the number of mitochondria assessed was high, the study itself only included a small number of men, so these findings need to be confirmed in larger, more diverse groups. The study also doesn't tell us whether these changes are maintained long-term, though continued training would likely preserve or even improve them.
The takeaway
This study shows us that HIIT isn't just about burning calories or building cardiovascular fitness (though it certainly does!). It's also upgrading your muscle's energy system at the cellular level, making your mitochondria not just more numerous, but more efficient.
The protocol in this study was straightforward: short, intense intervals with rest, three times a week, using rowing and cycling. You don't need hours at the gym or fancy equipment.
And perhaps the most empowering message from this research? Your muscles are more adaptable than scientists previously thought. Whether you're healthy, managing your weight, or living with type 2 diabetes, your cells can respond to training. It's never too late to start.