I follow Dr Stacy Sims as she is evidence based in everything she writes about.
I have taken some main points from her, about the differences between long & steady & HIIT on a woman’s body. I’ve done this as I want more women to read it and understand it for their own education and their body.
Stacy Sims loves loves busting myths—especially in women’s training. One of the most persistent? “More long, steady cardio is always better.” So today I am focusing on this, especially for those of you who are over 40 yrs.
Zone 2 / longer cardio session
Zone 2 training has its place. It builds your aerobic base, supports mitochondrial health (essential for energy production) and improves fat oxidation (how the body breaks down fat for energy)
However, for women there is a problem here. As we age, we’re already naturally well-adapted for endurance. We are born with more endurance muscle fibres and have a higher mitochondria density than men. Also, we have oestrogen, which helps increase our body’s ability to use fat as a fuel.
Basically women are naturally super endurance queens who are built for the “steady grind,” which means Zone 2 alone won’t give us enough stimulus to keep progressing—or to protect muscle, bone, metabolism, and even brain function long-term.
Also, as we age we no longer have the all important oestrogen to help the body burn fat!!
Why Intensity Matters for Your Body
This is where High-Intensity Interval Training (HIIT) and Sprint Interval Training (SIT) come in:
- HIIT: Short bursts (45 seconds up to a few minutes) of near-max effort (85-90%), typically with 1:1 work to rest interval durations.
- SIT: Even shorter (20–30 seconds) all-out, max-effort sprints with longer recovery (up to 3-4 minutes).
Both push you well above your lactate threshold, forcing your body to adapt in powerful ways:
- Improved VO₂ max: The strongest predictor of cardiovascular fitness and longevity
- Increased stroke volume: A stronger, more efficient heart
- Better insulin sensitivity: Improved blood sugar control and metabolic health (important in the menopause)
- Fast-twitch fibre recruitment: Key for strength, power, and maintaining muscle mass as you age
- Hormonal benefits: Stimulates anabolic pathways that protect lean mass and bone density
Why Intensity Matters for Your Brain
Stacy Sims has recently looked into new research that shows the benefits of HIIT and SIT aren’t just physical—they’re cognitive too.
This research shows that HIIT can:
- Sharpen executive function: It can help boost planning, decision-making, precision, and thoroughness
- Improve mood: This study showed HIIT lessened feelings of tension, anger, and depression in female subjects, irrespective of menstrual cycle phase
- Improve brain health and mental health—but this study showed the effects were not as pronounced in postmenopausal women as they were in perimenopausal women
- Enhance working memory and attention: It can make it easier to focus, demonstrate self-control, and process information quickly
- Preserve brain structure: Long-term HIIT training can protect hippocampal volume (the brain’s memory centre) and improve connectivity in brain networks
- Improve symptoms of anxiety and depression
Even a single session of HIIT or SIT can deliver short-term boosts in attention, memory, and mental clarity.
This same study also found that people who had bigger increases in blood lactate tended to show more improvement in attention. Over weeks and months, these benefits build, supporting long-term brain health and resilience.
A big reason? HIIT increases BDNF (brain-derived neurotrophic factor)—a key chemical that supports neuroplasticity, learning, brain health, and mood. Higher BDNF levels are linked to better mental health and may help protect against conditions like depression, schizophrenia, and bipolar disorder.
For those interested in diving into the research around exercise, cognition, and brain health, I highly recommend reading this article. It highlights how some early research suggests that exercise might help reduce brain changes linked to Alzheimer’s and improve conditions like small vessel disease, a common cause of dementia.
So far, studies have mostly looked at how exercise affects grey matter in the brain (like the hippocampus, which is tied to memory). But new research shows exercise may also improve white matter (which helps with brain communication), brain blood flow, and overall brain connectivity.
We still don’t fully understand how these changes relate to actual improvements in thinking and memory, but it’s exciting to know that there are more high-quality studies on the way that’ll help answer some of these questions.
How to Add HIIT/SIT to Your Week
If your training calendar is a wall of Zone 2 (and for all you endurance athletes out there, I get it!), here’s a simple shift & actually SO much less time consuming.
- Replace one or two Zone 2 sessions per week with HIIT or SIT
- If new to exercise, start with 2x easy HIIT sessions a week, then add in a longer, steady zone 2 session.
- Warm up thoroughly, especially before all-out sprints
- Pair intensity with proper recovery (sleep, rest, meditation)—this is where the real adaptation happens – this is an absolute must! Take day’s off after HIIT sessions, to really reap the benefits.
Here are a couple of examples of main sets (remember to always warm-up and cool down too):
HIIT Workout: 5 x 4 minutes as (2 minutes @ 85-90% effort, 2 minutes easy) – this can be body weight exercises
SIT Workout: 5 x (30 seconds all-out, 2-3 minutes recovery) – this can be walking – varying speeds / hills in your walks.
If you want to keep doing what you love for life—whether that’s running, riding, lifting, playing with your kids or grandkids, or staying sharp at work—the research clearly shows that you need more than steady-state training.
HIIT and SIT give you the best of both worlds—a stronger, fitter body, and a sharper, more resilient brain. That’s a combination that will pay off for decades.
Ive heard about higher Cortisol doing HIIT – isn’t that worse when menopausal?
Cortisol, the body’s natural stress hormone, can often be misunderstood. There are always lots of questions about it in relation to the impact HIIT and SIT can have on our cortisol levels. It is important to know that it is chronically elevated cortisol levels over time which has a negative impact on the body. HIIT has peaks and dips, it is not a constant, and is for a short time.
Have a look at this Instagram reel with Stacy Sims. You can learn more about the natural exercise-induced rise and drop of cortisol in this
Get in touch if you want a 1:1 with me to see how YOU can change what YOUR body needs now you are getting older. Listen to the research. Remember, I’m not saying stop doing what you love BUT I am saying if it isn’t bringing you the results you are after now, then maybe you have to change something!!
