Covid-19 brought quarantine, toilet paper shortages, and also…the rise of High-Intensity Interval Training (HIIT) workouts with influencers like Chloe Ting or Pamela Reif? In reality, HIIT isn’t something created by a fitness influencer, but rather olympic coach and physiologist Dr. Izumi Tabata for speed skating in the 1990s (Tabata, 2022). HIIT training contains an “on” period of high intensity where 90%+ of max heart rate is reached, paired with an “off” period, which in tandem has effects like excess post-exercise oxygen consumption (EPOC) and appetite suppression (Li, 2025).
Then there’s mitochondria, or the ‘powerhouse of the cell’ that creates adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS) for the cell function. In skeletal muscle, mitochondria go through fission (splitting) and fusion (merging) to fulfill bioenergetic demands to maintain homeostasis (Li, 2025). Mitochondrial biogenesis is the process where cells increase their mitochondrial mass and number, which in turn increases energy production (Bishop, 2018). This involves synthesis of new parts in the mitochondrial reticulum that is regulated by mitochondrial DNA (mtDNA) and nuclear-encoded proteins (Li, 2025).
HIIT has been shown to stimulate mitochondrial biogenesis (Mahatme, 2022). While studies have shown that both HIIT and moderate-intensity continuous training (MICT) increase mitochondrial activity, HIIT consistently shows greater ability to promote mitochondrial biogenesis (Li, 2025). This is due to several factors: greater activation of kinases (AMPK, CaMKII), stronger metabolic signals (ATP turnover, accumulation of intracellular lactate) (Li, 2025). Research has also shown that HIIT increases the expression of genes like PGC1-∝ which are related to mitochondrial biogenesis while decreasing the expression of genes like Drp1 associated with mitochondrial fission (Jahanjiri, 2025). PGC1-∝ (peroxisome proliferator-activated receptor gamma coactivator 1-alpha) is a regulator of mitochondrial biogenesis; upregulation of this gene increases the capacity for mitochondrial biogenesis.
Not only does HIIT play a role in mitochondrial biogenesis, but it also has been shown to counteract mitochondrial dysfunction. Mitochondrial dysfunction is linked to a plethora of conditions, such as obesity, diabetes, and neurodegenerative disorders (i.e., Parkinson’s) ( Bishop, 2018; Jahanjiri, 2025). HIIT has been shown to mediate mitochondrial dysfunction through mitochondrial biogenesis and metabolism, for example (Jahanjiri, 2025). Specifically, HIIT is shown to mediate HFD’s effects on mitochondrial function by changing gene expression (Jahanjiri, 2025).
High-Intensity Interval Training, or HIIT, has been shown to positively impact mitochondrial biogenesis and act as a preventative measure for mitochondrial dysfunction. Mitochondria may already be powerhouses, but HIIT can make them grow stronger and more efficient.
References:
Bishop, D. J., Botella, J., Genders, A. J., Lee, M. J., Saner, N. J., Kuang, J., Yan, X., & Granata, C. (2018). High-Intensity Exercise and Mitochondrial Biogenesis: current controversies and future research directions. Physiology, 34(1), 56–70. https://doi.org/10.1152/physiol.00038.2018.
Li, Y., Zhao, W., & Yang, Q. (2025). Effects of high-intensity interval training and moderate-intensity continuous training on mitochondrial dynamics in human skeletal muscle. Frontiers in physiology, 16, 1554222. https://doi.org/10.3389/fphys.2025.1554222.
Jahangiri, M., Shahrbanian, S. & Gharakhanlou, R. High intensity interval training alters gene expression linked to mitochondrial biogenesis and dynamics in high fat diet fed rats. Sci Rep 15, 5442 (2025). https://doi.org/10.1038/s41598-025-86767-5.
Mahatme, S., K, V., Kumar, N., Rao, V., Kovela, R. K., & Sinha, M. K. (2022). Impact of high-intensity interval training on cardio-metabolic health outcomes and mitochondrial function in older adults: a review. Medicine and pharmacy reports, 95(2), 115–130. https://doi.org/10.15386/mpr-2201.
Tabata, I. (2022). Tabata Training the Science and History of HIIT. Google Books. https://books.google.com/books?hl=en&lr=&id=UNpVEAAAQBAJ&oi=fnd&pg=PP1&dq=who+created+hiit&ots=yMqSLsicle&sig=1QkSPQUcYbaizpJc54pKILA6rv0#v=onepage&q=who%20created%20hiit&f=false.