New research suggests that incorporating sprint interval exercise into a fitness regimen can significantly enhance cellular health, particularly by promoting a unique “clean-up and rebuild” process for mitochondria, the powerhouses of cells. This effect, detailed in a study published in the journal Nature Communications, was found to be more pronounced with sprint intervals compared to traditional steady-state moderate-intensity cardio.

The small but impactful study involved 28 participants divided into two groups over an eight-week period. One group performed sprint intervals on a bike, consisting of four to eight 30-second all-out sprints interspersed with four minutes of rest, three to four times a week. The other group engaged in moderate-intensity continuous exercise, such as running at a steady pace, for the same duration. Researchers meticulously collected health data, including muscle biopsies and advanced imaging, to analyze participants' mitochondria and various other cellular markers.

While both exercise types supported various health markers and mitochondrial function, the sprint interval exercises uniquely triggered a “clean-up and rebuild” response that moderate-intensity cardio did not replicate. Dr. Javier Botella, the lead study author and postdoctoral fellow at the Institute for Health and Sport (IHES) at Victoria University, highlighted that previous research had established sprint interval exercise as highly efficient for improving cardiorespiratory fitness, but the underlying mechanisms remained partially unknown. This new study sheds light on that mystery, explaining the cellular benefits.

According to Dr. Botella, the “clean-up” process involves the body removing old or suboptimal components from cells. He likened it to removing broken furniture from a house, or cell, explaining that sprint exercise stresses mitochondria, causing 10-15% of them to become damaged. This damage, however, is beneficial as it activates cellular mechanisms to eliminate these less fit mitochondria, simultaneously stimulating the creation and maintenance of new, healthy ones. The ultimate outcome is a more robust population of mitochondria capable of efficiently meeting the energy demands of cells.

The findings advocate for integrating speedwork into exercise routines to support cellular health, rather than replacing all workouts with sprints. Dr. Botella emphasized that while most exercise positively impacts mitochondrial and cardiorespiratory adaptations, adding vigorous sprint and high-intensity sessions periodically can boost mitochondrial quality. This ensures that less fit mitochondria are efficiently removed, making way for newer, better-functioning ones.

Albert Matheny, RD, CSCS, co-founder of SoHo Strength Lab, concurs with this recommendation. He suggests aiming for a heart rate of at least 80% of your maximum (or an eight out of 10 on a perceived exertion scale) for a minimum of four minutes, two to three times per week. This could translate to four one-minute treadmill or bike sprints, each followed by two minutes of walking recovery. However, he advises individuals new to this type of exercise to progress slowly and consult their doctor, especially if they have pre-existing health conditions, to ensure safety and effectiveness.