In recent years, interval training has taken off, with many gyms and online workout apps offering high-intensity interval training (or HIIT) sessions or videos.
These short, high-energy sessions involve pushing yourself hard until you reach as close to your peak heart rate as you can for anywhere between a few seconds to a few minutes, then allowing yourself to cool down with a less intense exercise before starting the cycle again by picking up the speed and intensity.
Loyal HIIT-ers claim that this is the best and most effective way to exercise and that you can reap the heart and muscles benefits that longer endurance-based workouts offer but in a much shorter time. Though this seems too good to be true, scientists support this claim and may have an explanation for how and why.
Why is HIIT the best?
Professor of physiology and pharmacology at the Karolinska Institute, Hakan Westerblad, rounded up some colleagues to help him conduct an experiment. The team examined the muscle samples taken from a group of volunteers once they had alternated between pedaling a stationary bike for 30 seconds and peak intensity and then resting for three minutes for six cycles.
They found that certain chemical channels in the muscle cells that regulate calcium changes in the cells broke down when the muscle was stressed by high-intensity exercise. Calcium is necessary for cell signaling, and the extreme demands trigged by the exercise cause the cell to adjust its energy production and become more efficient.
“What we found was a breakdown of these channels that was totally unexpected,” explains Westerblad. “We have never seen anything similar. We saw a large production of free radicals, and these free radicals were specifically hitting the calcium channels. Normal training also increases the number of free radicals, but not by as much as interval training.”
Producing more free radicals is the muscle cells’ way of responding to and coping with the extreme duress the body goes through during high-intensity exercise. “During any physical training, the cell senses, ‘I have a problem here,” says Westerblad. “So it’s better safe than sorry, they adapt so the next time they experience the intense exercise, the problem is lessened.”
Does HIIT work for everyone?
It’s worth noting that HIIT only works to a certain extent. Elite athletes who’ve trained their bodies and are accustomed to strenuous and demanding physical work begin to tolerate HIIT regimes, so their muscle cells don’t react in quite the same way.
For recreational athletes, on the other hand, the effect can remain rather remarkable. Westerblad discovered that one session of HIIT for recreational athletes triggered molecular changes in muscle cells that remained detectable 24 hours later in a muscle biopsy.
So, if you’ve been wanting to get in shape but don’t have a lot of time in your schedule, consider squeezing in some high-intensity interval training to maximize benefits while minimizing the time commitment.