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🏃🏽♀️ Want Strong, Healthy Mitochondria? Sprint!
When it comes to your health, mitochondria matter. As an active woman, you know them as the powerhouses of the cell, helping us to turn fuel into ATP—the fuel that powers muscle contraction, brain activity, and every metabolically active tissue. But they also act as control centers for cell signaling, calcium handling, and programmed cell death.
When mitochondrial function declines, energy production falters and these regulatory systems go off-track, contributing to fatigue, accelerated aging, and a wide range of chronic diseases, including cardiovascular disease, diabetes, and cancer. In short, mitochondrial health underpins both day-to-day performance and long-term vitality and longevity.
We know exercise is good for stimulating the production of mitochondria and for strengthening them, but research is ongoing—and online debate is never ending—as to what works best and why.
Now a new study in Nature Communications shines some light on the topic, showing that while moderate intensity exercise, like endurance rides and runs, are great for increasing the mitochondrial quantity, sprint interval exercise improves the performance of existing mitochondria. Specifically, sprint interval exercise temporarily disrupts mitochondrial structure, which appears to activate key cleanup and stress-response pathways that ultimately improve mitochondrial function.
For the study, researchers had 28 healthy young men (more on that in a bit) perform either:
Sprint Interval Exercise (SIE)
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6 × 30-second all-out cycling sprints
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~4 minutes of rest between sprints
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Very high intensity, very low total volume
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Moderate-Intensity Continuous Exercise (MICE)
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Continuous cycling at ~90–100% of first lactate threshold (zone 3 - 4 in a 5 zone model)
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Duration: ~90 minutes
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Much higher total volume, much lower intensity
Note: The protocols were designed to emphasize intensity vs volume, not to match total work.
They performed three to four sessions per week for 8 weeks, while researchers measured mitochondrial structure, damage, function, and more. In this study, they found that sprint interval training didn’t make people grow more mitochondria. Instead, it made the mitochondria they already had work better. After sprint training, mitochondria were able to produce energy more efficiently and at higher capacity.
How Hard Efforts Make Mighty Mitochondria
The secret was in the stress: sprinting disturbed the structure of some mitochondria in muscle cells. About 16% of them swelled and showed changes in their internal folds right after the workout–something that did not happen with steady, moderate exercise.
Importantly, this wasn’t lasting damage. Within 24 hours, the mitochondria returned to normal, and that short-term stress switched on the cell’s built-in clean-up and repair systems. These include pathways that refold damaged proteins, flag worn-out mitochondria for removal, and help maintain a healthier, more efficient mitochondrial pool.
Steady, moderate exercise primarily increased mitochondrial content, or the number of mitochondria and related enzymes, but those mitochondria didn’t improve their energy-producing performance as much.
The million dollar question, of course, is would our demographic show the same response? I reached out to the researchers, but got no response, and of course, the only way to say with certainty is to run the same experiment on midlife women (or hell, any women, but I digress…). After digging in on some of the mechanistic pathways involved, I think it’s biologically plausible we would, and it might be even more beneficial for us as we lose the mitochondrial protection of our pre-menopause hormonal environment.
Until we get more research, I think it’s safe to say that sprint intervals remain a powerful tool for active midlife women to build speed, power, and muscle, enhance metabolic health, and hey, maybe maybe improve mitochondrial function, too. |
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Come lift with us!
No egos. No competition. No body judgment. Just solid strength training, real confidence, and a community of Feisty women who lift heavy sh*t — and lift each other up. This is the strength retreat that was made for YOU!
Led by strength coach Cassi Niemann, you’ll spend the weekend building real skills: dialing in technique, understanding the “why” behind your lifts, asking all your questions, and gaining the confidence to move heavier weights on your own. Expect hands-on coaching, supportive energy, and a room full of women who are there to get stronger together.
Join us in Atlanta, April 17-19, 2026! Learn more here. |
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👀 What Caught My Eye
Want to eek out that last rep for a PR? Try dropping an F-bomb! (Provided you’re not in polite company). Research shows that swearing can boost physical performance by helping us overcome our inhibitions and push ourselves harder on tests of strength and endurance, according to research published by the American Psychological Association.
To test how and why, researchers ran two carefully planned experiments where the same people completed a short, upper-body strength task twice: once while repeating a self-chosen swear word and once while repeating a neutral word.
The task involved pushing down on a chair with straight arms to hold their body weight off the seat for as long as possible (up to 60 seconds). After each trial, they answered brief questions about how focused, confident, distracted, or amused they felt. Researchers then compared how long people held the position and how their mental state differed between the swearing and non-swearing conditions to see whether swearing changed performance and why.
They found that participants who swore during the chair pushup task were able to support their body weight significantly longer than those who repeated a neutral word. They also found that this difference could be explained by increases in participants’ reports of psychological flow, distraction, and self-confidence.
“In many situations, people hold themselves back—consciously or unconsciously —from using their full strength,” said study author Richard Stephens, PhD, of Keele University in the U.K. said in a press release. “Swearing is an easily available way to help yourself feel focused, confident, less distracted, and ‘go for it’ a little more.”
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🔥Badass Athlete of the Week Goes To…
Hands up for Veteran U.S. bobsled pilot Kaillie Humphries, who at age 40, captured a World Cup victory in the two-woman bobsled with teammate Emily Renna–her first win since returning from pregnancy leave. Humphries is a multi-Olympic champion and remains a medal contender toward the 2026 Winter Games.
"Being back on top after three years feels great," Humphries told The Straits Times. "This is my first win as a mom, and a first win ever for Emily, this is a special one for us both.”
We’re stoked for you both! Good luck at the Games!
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👉Want a chance to be featured? Click here to share your badass story |
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The Women's Performance Podcast is BACK! 💪
We’ve relaunched the Feisty Women’s Performance podcast, hosted
by Dr. Erin Ayala, to provide women with science-backed answers to their health and performance questions based on research actually designed for women.
Too often sports science is based on men and answers to even our most basic health and training questions come through a male lens.
This podcast aims to cut through that noise and get active women the insights they need, whether it’s how much protein you actually should be eating or how to manage sleep disruptions.
The Feisty Women’s Performance podcast is out now with new episode every Monday! Listen to this week's episode here or watch on YouTube. |
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👩🏻💻 Hit Play Research Round Up
We spend a lot of time scouring the latest research for news you can use to stay strong and feisty forever. Here’s what’s making waves this week:
🌞People who experience brighter, more stable daytime light—and who keep earlier sleep schedules—tend to feel more alert and perform better on attention and memory tasks. And it doesn’t have to be a time-consuming outing. Even short-term light exposure positively influences reaction speed and sleepiness, according to a study that followed 58 adults in the UK over seven days. Just another study showing that living in alignment with circadian rhythms is good for us.
⚖️Women with obesity had about 75% higher odds of reporting more severe menopausal symptoms (hot flashes, sleep problems, mood symptoms, joint pain, urogenital symptoms), even after accounting for age, education, hormone therapy, and other factors, according to a study published in Menopause. Being active helped mitigate some of the symptom severity. As we know, movement matters no matter what your body comp.
📝Making sense of your menopause story through structured storytelling, education, and supportive counseling can significantly reduce hot flashes and improve sleep, even without medication, according to a study in Menopause. It’s a strong argument that how we support women through menopause matters just as much as what treatments we offer.
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🚴♀️ TWO New Bike Mechanic Camps On Sale Now!
After the success of our two bike mechanic camps in Patagonia this fall, we're bringing in two more brand-new camps for 2026.
These 4-day camps are built to help you feel truly confident and capable with your own bike – from understanding how it works to getting hands-on with the tools. Each day combines practical “classroom” learning with focused wrenching sessions on your bike, giving you the confidence to troubleshoot problems, make needed repairs, and understand your bike at a deeper level. You’ll also have time to unwind on with group rides and connect with other feisty women in a supportive, judgment-free space.
Vermont | Madbush Falls
June 10-14, 2026
Tucson
November 12-16, 2026 |
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What's On My Mind...
Fun. I worry that all the advice on how to be healthier in midlife is squeezing some of the fun out of midlife. I personally don’t feel like there’s much use of living longer if it all becomes a chore that I must monitor rather than a joyful pursuit. This year, I’ll be sure to infuse our content with healthy amounts of plain old fun.
Listen to this week's episode of Hit Play Not Pause - Why Rest Feels Hard: Midlife Training, Anxiety & Identity with Dr. Erin Ayala
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Feisty 40+ is written by Selene Yeager. Edited by Maya Smith. Ads by Ella Hnatyshyn
Live Feisty Media Corporation, 2031 Store St #30, Victoria, British Columbia V8T 5L9, Canada
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