Scientists Discover Why High Intensity Interval Training Can Match Endurance Training


Scientists have always struggled to understand exactly how a few short minutes, intense interval exercises can produce similar effects to much more time consuming endurance training.

High intensity interval training, also known by its acronym HIIT, has become very popular in recent years with beginners, professional athletes and patients with reduced muscle functions as it has clear health benefits. Now, researchers from Stockholm’s Karolinska Institutet have discovered cellular mechanisms behind the positive benefits of HIIT and the reason endurance training is undermined by antioxidants.

Short bursts of just a few minutes of exhausting physical activity can prepare muscles to work harder, boosting the production of new mitochondria (powerhouses of the cells, generating the energy that our cells need to do their tasks), which culminates endurance enhancement much like more time consuming endurance training. High-intensity exercise triggers the breakdown of calcium channels as a result of an increased production of free radicals (highly receptive radicals which can act as oxidants for cellular metabolism). The muscle cells thus have anti-oxidative systems for trapping and nullifying the radicals.

The scientists also discovered that antioxidants like Vitamins C and E, very common ingredients of dietary supplements, remove the effect on the calcium channels, resulting in the weakening of the muscle response to endurance training.

Hakan Westerblad, a professor of physiology and pharmacology, said :

“Our study shows that three minutes of high-intensity exercise breaks down calcium channels in the muscle cells.
This causes a lasting change in how the cells handle calcium, and is an excellent signal for adaptation, such as the formation of new mitochondria.
Our study shows that antioxidants remove the effect on the calcium channels, which might explain why they can weaken muscular response to endurance training and they also show that the calcium channels aren’t affected by the three minutes of high-intensity interval exercise in elite endurance athletes, who have built up more effective antioxidative systems. “

The research included male subjects who cycled for 30 seconds for maximum-exertion, followed by 4 minutes of rest and repeat this routine 6 times altogether. Twenty-four hours after the test, tissue samples of their thigh muscles were taken and revealed an increased rate of free radicals, showing that just a few minutes of intense exercise is all it takes for benefits to kick in.

The research has been published in the journal PNAS in an article: “Ryanodine receptor fragmentation and sarcoplasmic reticulum Ca2+ leak after one session of high-intensity interval exercise”.