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This week's issue of Feisty 40+ is brought to you by the Feisty Strong Barbell Club, a 12-week strength program designed for women who want real coaching, expert barbell programming, and a supportive community to help them build true, lasting strength. Sign up before Friday, Dec 12 at Noon PT for $50 off. Learn more here. |
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🥵 Sweat, Power, and Performance: A New Study on Heat Adaptation in Women
When I was doing a lot of mountain bike stage racing, I often had early spring races in hot places, which left me needing to acclimate while training over the winter in Pennsylvania. One of my go-to strategies was hopping on my indoor trainer overdressed without a fan. It was miserable, especially since I’ve always run warm, and by my mid-40s even warmer. But it worked. I could drop into Central Florida or even South Africa and be good to go.
Now, a new study—the first modern, protocol-driven, female-only heat acclimation and heat maintenance study in trained endurance athletes (YAY!)—verifies my ragtag approach. I’d like to give props to the researchers for doing this one, because as the lead researcher noted in an email, >90% of heat/exercise research is done in males. Also, a cool footnote: our own Megan Eastwood was part of this study.
Home-Based Heat Acclimation Boosts Power & Speed
The researchers recruited 15 trained women (ages 18–55; naturally cycling, IUD users, postmenopausal, etc.). Eleven completed a home-based heat-acclimation protocol, and four did the same workouts in cool, comfortable conditions. The control group was intentionally small—its job was simply to show that any performance improvements weren’t from the training itself.
Before, during, and after the intervention, the team measured hematological markers (blood and plasma volume, RBC volume, hemoglobin mass), sweat rate, VO₂max, peak power output (PPO) in a temperate 18°C (64°F) environment, and performance in a 20 km time trial at 35°C (95°F).
The heat-training group completed:
The attire was intense: long underwear, wool socks, multiple fleece layers, a rain jacket, gloves, wool hat, and an industrial-size perforated polyethylene bag. Sessions were 60 minutes: 5-minute warm-up, 50-minute steady riding at 70–75% max HR (35–45% PPO), 5-min cool-down. They were instructed to feel “dripping wet” and “very hot” by the final 15 minutes, maintaining an RPE ≤ 7/10. The control group did the same workouts, just kept cool.
By the end of the study, the heat-trained women improved their sweat rate and their performance:
Peak Power Output (temperate test, 18°C)
20 km Time Trial in the Heat
Times improved both from PRE to MID and MID to POST, showing that heat maintenance not only preserved gains, it added to them.
Time-Trial Power
Power was higher overall and especially in the last 10 km. They held more power deeper into the effort, with less fade and more durability.
Temperate Thresholds and Warm-Up Responses
Peak and threshold power also improved in cool conditions. Heart rate during the same warm-up power was lower, signaling less cardiovascular strain for a given workload.
What Didn’t Change
Contrary to expectations (and previous mixed-sex studies):
In other words, heat training didn’t build a bigger engine—but it helped the existing engine run better under heat stress and at submaximal intensities. The control group’s metrics and performances were essentially unchanged.
What This Means for You
I never did anything this structured or intense and honestly, climbing into a plastic bag is probably a bridge too far for me. Megan also told me she found the protocol “a bit brutal” after the first week or so. “It was type 2 fun....bordering on type 3,” she said.
But there’s real value in getting comfortable being uncomfortable and building heat tolerance, especially if you’re prepping for early-season, warm-weather races. Based on my own experience, I think even a dialed down version of this can be beneficial.
Just be smart: stay well hydrated, keep your heart rate and RPE moderate, and watch for red flags like dizziness, lightheadedness, nausea, headache, or chills. The goal is adaptation, not a self-inflicted meltdown.
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Join me in Mallorca!
After an awesome trip to Girona last summer, we're excited to be heading to Mallorca!
We're partnering with our friends at The Cyclist's Menu to offer a cycling trip on the Baleric Islands in Spain from May 17-22. This women's-only adventure includes six days of riding and five nights of dining in Mallorca.
Want to come ride beautiful roads and eat good food with Kathryn and I?
Learn more here. |
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👀 What Caught My Eye
Going into the New Year, I’ll be using this bit of newsletter as a place to chat about all things 40+ women related that catches my eye…This week let’s look at sleep and the brain.
A new study published in Nature Neuroscience shows that the lapses of attention or ‘zoning out’ you experience after being sleep deprived for a night is actually your brain calling a time out to take out the trash—a task it usually reserves for deep sleep, when it drives large, slow waves of cerebrospinal fluid (CSF) through brain tissue to help clear metabolic waste.
When researchers kept a group of healthy adults up all night, they saw, unsurprisingly that the sleep-deprived folks had more lapses in attention and delayed reactions. But those lapses also lined up with a biological sequence of events that included a drop in neural activity, pupil constriction, blood vessel dilation, and a big CSF pulse, like a brief sleep-like wash, all while they were otherwise awake. Of course, those mini cleaning cycles aren’t nearly as effective or efficient as nighttime cleaning—and they come at the cost of our attention and performance (and can be outright dangerous during tasks like driving).
It also made me wonder if what some menopausal women experience as brain fog could be linked back to this process given how poorly some women sleep during this time. Either way, it’s a good reminder to prioritize sleep.
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🔥Badass Athlete of the Week Goes To…
This week our jaws drop as we put our hands together for Jill Walker, 57, who completed her 100th Ironman triathlon in Florida last month. A true Ironman junkie, Walker has completed the “six in six” challenge where you complete six Ironmans on six continents in six weeks along with her husband Dougin.
And she’s not done yet. As she told Triathlete magazine, “After Cozumel this year, I’ll have done 77 in the past seven years,” she says. “Dougin told me I should go for 100 in 10 years, so I only need 23 more in the next three years. We already have 17 scheduled for next year.”
We’ll be cheering you on, Jill!
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🏋🏻♀️Join the Feisty Strong Barbell Club!
You've been asking for more guidance on lifting heavy and we listened. The Feisty Strong Barbell Club is a 12-week strength program designed for women who want real coaching, expert barbell programming, and a supportive community to help them build true, lasting strength.
You’ll get 3 strength workouts per week, optional HIIT finishers, monthly coaching calls, weekly form reviews, guest experts, and thoughtful guidance from coach and Feisty 40+ favorite Cassi Niemann.
Throughout the program, you’ll learn foundational barbell lifts, build confidence under the bar, and follow a training plan that meets you where you are—no cookie-cutter workouts, no AI, just sustainable, expert-led programming. Perfect for beginners to intermediates with access to a barbell, rack, and bench.
Learn more and sign up here! |
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👉Want a chance to be featured? Click here to share your badass story |
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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:
🧠 More muscle, less belly fat slows brain aging. Higher muscle mass combined with a lower visceral fat to muscle ratio tracks with a younger brain age, according to a study presented at the annual meeting of the Radiological Society of North America (RSNA).The fat just under the skin wasn’t related to brain aging. Keep lifting those weights. Sprint interval training and HIIT are also effective, time-efficient strategies for reducing visceral fat in menopausal women, with added benefits for muscle mass and metabolic health.
🆒 Self-hypnosis can help cool hot flashes, according to a study published in JAMA Network Open. This trial found that doing daily, 20-minute self-hypnosis audio sessions with cooling imagery for 6 weeks cut hot flash scores (frequency and severity) by 53%, compared with about a 41% reduction from listening to “sham hypnosis” (white noise labeled as hypnosis). Women in the hypnosis group also reported less disruption to daily life (work, sleep, mood, sex, enjoyment of life) and were more likely to say their hot flashes were “very much better.” Benefits were particularly strong in women with a history of breast cancer.
🫀 Women need less weekly exercise than men to get the same coronary heart disease (CHD) risk reduction, according to a UK Biobank accelerometer study of data from 85,000+ people. To cut coronary heart disease (CHD) risk by 30%: women need about 250 min/week of moderate–vigorous physical activity (MVPA) while men need ~530 min/week (more than double). Just nice to know we get a great ROI on our exercise time.
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What's On My Mind...
Hibernation. When it comes to exercise, I’m a very self-motivated soul. And I’ll tell you, this time of year is still rough. The pull to stay inside rather than layer up and go run or ride is strong. (And to be clear, if it's cold rain or other crap, the treadmill is a godsend) But I know the natural light and fresh air will keep me from slipping into a winter funk. It’s these times when you need the present you to remind the future you that the extra effort is worth it.
Listen to this week's episode of Hit Play Not Pause - Is It Burnout or Perimenopause? How to Tell (And What To Do About It)
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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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