Scientists Figure Out Why High Intensity Training Can Be As Effective As Longer Exercise

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Researchers from Stockholm’s Karolinska Institute have discovered how high-intensity interval training (HIIT) can deliver similar health benefits to prolonged endurance exercises. HIIT is an exercise strategy that alternates short, intense anaerobic activity with a less intense recovery period. 

“Our study shows that three minutes of high-intensity exercise breaks down calcium channels in the muscle cells,” principal investigator Håkan Westerblad, professor at Karolinska Institutet’s Department of Physiology and Pharmacology, said in a statement. “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.”

Mitochondria are the components of the cell whose primary job is to burn sugar and to release energy for the cell to use. They are usually described as the powerhouses of the cell. An increase in the number of mitochondria signals an increase in muscle endurance. 

Strenuous exercise increases the number of free radicals (oxidants) in the body, which in the case of HIIT causes the breakdown of the calcium channel. The same breakdown happens when muscles are put under strenuous endurance. Calcium ions allow muscles to contract and relax and they are activated by nerve impulses. 

Cells have a natural mechanism to nullify the free radicals, and depending on the level of fitness, it could take between two and seven days for the muscle to recover. 

The team asked active men to perform one session of three to six sets of high-intensity cycling for 30 seconds, with a four-minute rest between each set. They took a thigh muscle biopsy 24 hours after the exercise and discovered an extensive release of free radicals. 

When the same experiment was repeated with elite endurance athletes, they found the release wasn’t as impressive since they are used to intensive exercise. The researchers also looked at how antioxidants like vitamins E and C affect muscle recovery by looking at mice treated with antioxidants before and after simulated high-intensity interval exercise. 

“Our study shows that antioxidants remove the effect on the calcium channels, which might explain why they can weaken muscular response to endurance training,” added Professor Westerblad. “Our results 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 paper was published in Proceedings of the National Academy of Sciences.  

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