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\title{Science AMA Series: I'm Niklas Ivarsson, co-author of the recent ``why
High Intensity Interval Training works'' paper, AMA!}



\author[1]{Niklas-Ivarsson }%
\author[1]{r/Science AMAs}%
\affil[1]{Affiliation not available}%


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  \date{April 23, 2026}


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\begin{abstract}
Hello redditors of /r/science. I am Niklas Ivarsson, PhD student at
Karolinska Institutet, Stockholm, Sweden. Yesterday you showed a great
interest in our work regarding why high intensity interval training
works. In the article we found that free radicals produced during high
intensity interval training (HIIT) react in particularly with the
ryanodine receptor, a critical calcium channel in excitation-contraction
coupling. The reaction causes the channel to leak calcium from the
specialized subcellular compartment (sarcoplasmic reticulum), into the
cytoplasm. This causes a prolonged period of increased basal levels of
calcium in the muscle cell. Increased baseline calcium acts as a signal
for transcription factors important for mitochondrial improvements (e.g.
Peroxisome proliferator-activated receptor gamma, coactivator 1 alpha
(PGC-1\selectlanguage{greek}α\selectlanguage{english}). HIIT, which is extremely intensive, causes a greater
production of free radical than `regular exercise'. This results in the
`damage' to the ryanodine receptor, and subsequent `leak' is more
severe, and last longer than after a marathon. The ryanodine receptor
modification and leak can be prevented if the exercise is done with
strong antioxidants. Explaining why antioxidants prevents the positive
effects of exercise (Ristow M. et al 2009) A little bit about me: I have
a background in biomedicine. For my master thesis I decided to leave the
world of cell culture and try my best in, what to me was a great
unknown, physiology. For the master project I focused on insulin
signaling in skeletal muscle. From there I kind of just stuck around in
the research group of Professor H\selectlanguage{ngerman}åkan Westerblad. During my master I got
kind of bored. As per usual with large lab groups, there are often
several ``unfinished'' projects laying around waiting for someone to
come along. One of those side project eventually led us to applying for
research money, namely `How does a muscle cell know it need to improve
after endurance exercise'. We already knew calcium had to be involved
somehow. Now 4.5 years later I am about to present my PhD thesis, which
includes 6 (4 published, 2 waiting) different manuscripts around the
subject of calcium's role in training adaptation. Tl;dr I am a
biomedical lab rat who stumbled onto the discovery that free radicals
produced during exercise stress the muscle cell, which teaches the it to
improve for the next shower of free radicals, resulting in improved
endurance. I will be back later today to answer your questions, Ask me
anything! edit: I will start answering your questions around 4pm USA
East Coast Time edit: ok, you guys seem really interested so I'll try
and squeeze in some answers early edit: Thank you everyone for your
questions. It is very late over here and time for me to go. Hope my
answers satisfied your curiosity. //Niklas%
\end{abstract}\selectlanguage{ngerman}%



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