Can exercise really kick cancer's ugly ass?
Read time: 5 minutes
I usually open my newsletter with a recent experience I've had and a sprinkling of humour, but today I'm going to let these two pictures do the talking instead.
This chap started with me on March 1st, and he's already lost over 6kg! Even more impressive when you factor in starting a new job and going away with this family for a big ski trip during that time.
I got this message yesterday as I was hiking through the Albanian mountains, and it literally stopped me in my tracks.
Hopefully, this lights a fire under your arse and provides some much-needed motivation to go and change your life with the power of health and fitness.
This guy signed up for a year's coaching with me, can you imagine what his story is going to be in 10 months!! 🤯
If you fancy the details, all you have to do is ask.
Right, let's get cracking with this week's newsletter, it's a good 'un...
As far as health research goes, I would put the following piece of research in the 'sexy as hell' category!
It'll take you 0.3 seconds to understand why.
It's from 2025 and was authored by Bettariga, F., et al., and is titled "A single bout of resistance or high-intensity interval training increases anti-cancer myokines and suppresses cancer cell growth in vitro in survivors of breast cancer." (1).
Quite the mouthful to say at a dinner party ha.
They set out to examine the effects of a single bout of resistance training (RT) versus high-intensity interval training (HIIT) on anti-cancer myokines and in vitro cancer cell suppression.
Anti-cancer myokines are proteins released by skeletal muscles during contraction, especially through exercise, that inhibit tumour growth and boost immune function.
In vitro cancer cell suppression is when researchers put your blood on cancer cells in a dish, and the cancer grows less.
The Study Design
Participants: 32 breast cancer survivors with an average age of 58.6 years, randomised 1:1 to RT or HIIT
The protocol was as follows:
- Blood drawn at three time points: baseline (fasted), immediately post-exercise (0P), and 30 min post-exercise (30P).
- Each workout was 55 minutes, including a 10-min warm-up.
- RT group:
- 5 sets of 8 reps across 8 compound exercises (chest press, row, shoulder press, lat pulldown, leg press, leg extension, leg curl, lunges).
- Used a load >80% of their 1 rep max (aka the most they can lift once).
- Kept sets within a range of 7-9 of the rate of perceived exertion (RPE).
- 60–120s rest between sets.
- HIIT group:
- 7 × 30s high-intensity / 30s active recovery - 4 sets.
- Equipment used included a stationary bike/treadmill/rower/cross-trainer.
- Intensity was 70–90% of their Max Heart Rate.
- RPE 7–9
- 180s rest between sets
Here's the cool part: Researchers took each woman's blood before and after her workout, then poured it onto live breast cancer cells in a petri dish. They watched the cancer cells for 3 days straight, measuring whether they grew or died.
The question: Would post-workout blood kill cancer better than pre-workout blood?
Now, before I give you the results of the research, let me first share why research like this is so damn important!
Breast cancer is the most diagnosed cancer in women globally.
In 2022, there were 2.3 million new cases and ~660,000 deaths.
Recurrence rates run 10–30% even years after treatment.
Existing data already show that:
- Exercise reduces recurrence and mortality risk by ~20%.
- Higher fitness levels are linked to a 31–46% reduction in all-cause mortality in cancer patients.
I'm extremely fortunate that I've not experienced much death in my life, but the one person I have lost who I was very close to was my granny, and she sadly passed away in her early 60s due to breast cancer.
It's one of those things that seems to literally affect every person on this planet.
Right, so what were the findings?
Key Results
Right after exercise, three of the four anti-cancer chemicals jumped up in both groups.
HIIT gave a bigger spike across the board, most dramatically with IL-6, which shot up 47% versus just 9% for the resistance training group.
Cancer-fighting chemicals:
Decorin: After lifting +23% | After HIIT +30%
IL-6: After lifting +9% | After HIIT +47%
SPARC: After lifting +15% | After HIIT +26%
Thirty minutes later, IL-6 was still elevated in both groups.
Now, what did the blood do to the cancer cells in the dish?
This is where things get interesting and very exciting!
- After lifting: cancer cell growth dropped 21% immediately, 19% at 30 minutes
- After HIIT: cancer cell growth dropped 20% immediately, 29% at 30 minutes
To keep it as simple as possible, this means that a single workout made these women's blood roughly 20–29% better at suppressing aggressive breast cancer growth!
Howdy f*cking do!
These results boast well for exercise and are another feather in the cap of strength training, but it's clear to see who the winner here is.
Both workouts were the same length (45 min) and felt equally hard. The difference was metabolic intensity:
- HIIT: 8–10 METs (much harder on your system)
- Lifting: 5–6 METs
Metabolic equivalents of task (METs) measure the energy cost of physical activity, with 1 MET representing the resting metabolic rate. METs indicate how many times more energy is exerted compared to sitting still.
The harder you push your cardiovascular system, the bigger the adrenaline surge.
A bigger adrenaline surge means more IL-6 pumped out by your muscles. More IL-6 means a stronger anti-cancer signal in the blood.
The takeaway: Intensity is the lever. Push harder, get more of the good stuff.
Ok, so this is all brilliant news, but there are a few things to take notice of:
This research involved breast cancer survivors. There haven't really been any similar studies done on people currently battling cancer.
Indeed, cancer and the related treatments may alter several physical (e.g., low muscle mass/strength and cardiorespiratory fitness) and physiological components (e.g., reduced immune and metabolic function), limiting patients’ adaptation to changes induced by exercise (1).
There is one piece of research by Dethlefsen et al from 2016 that examined the acute effects of a 2-h bout of combined exercise training (i.e., RT and HIIT) at moderate to high intensity on IL-6 and IL-8 levels in patients with breast cancer undergoing chemotherapy (2).
They observed an increase of 20 - 110% for these myokines, and when applying the exercise, boosted blood to the cells in vitro, significant reductions in cancer cell viability by 9% were observed.
So that further strengthens the research we've been discussing.
But again, this all needs further investigation by people WAYYYYY smarter than me, as sustained elevations in IL-6 have been associated with chronic inflammation and may promote tumour progression in other contexts (3).
Ugh, just when you think it's all good news 🫠
The HIIT-menopause friction
For women in perimenopause and menopause, high-intensity work isn't a free lunch.
A few reasons:
Cortisol load. Estrogen is a buffer against stress. As it drops, the same HIIT session that energised a woman at 35 can leave her wired, depleted, and gaining belly fat at 50. The cortisol response is bigger, and the recovery is slower.
Sleep disruption. Menopausal sleep is already fragile. Pushing intensity, especially late in the day, can wreck it further. And poor sleep tanks recovery, hormones, and the very anti-cancer benefits you're chasing.
Joint and tendon vulnerability. Falling estrogen reduces collagen and connective tissue resilience. Repeated high-impact intervals on a body that's losing tissue elasticity is a recipe for injury.
Muscle preservation is the bigger priority. From 40 onward, women lose muscle fast, and muscle is the engine releasing these myokines in the first place. If HIIT eats into recovery so much that strength sessions suffer, the math flips against you.
The nuance the study doesn't capture...
This was a single-session snapshot. It tells you nothing about what happens when you do HIIT 4x a week for a year in a 55-year-old woman.
The acute spike might be bigger, but if it comes with chronic cortisol elevation, sleep loss, and overtraining, the long-term picture could be worse, not better.
The authors even flag this themselves: chronically elevated IL-6 is associated with inflammation and can promote tumours. Acute spikes good. Constantly elevated, bad.
The actual balance
For midlife women, the smart read of this study isn't "do more HIIT." It's:
- Strength training is the foundation. It still produced 20% cancer cell suppression. It builds the muscle that makes all this possible. It's the non-negotiable.
- HIIT is a tool used sparingly. One, maybe two short sessions a week. Not the daily driver.
- Intensity matters, but so does recovery. A hard session you can't recover from is a net loss.
- Walking, Zone 2, sleep, and protein do more for long-term outcomes than chasing maximum acute spikes.
The biggest mistake midlife women make with research like this is reading "more intensity = more benefit" and pushing themselves into a hole.
The real lesson is that working muscle hard enough to matter, through whichever modality your body can recover from, is what unlocks the anti-cancer signalling.
For most women in menopause, that's mostly lifting, with HIIT as a careful supplement.
Balance beats maximisation....
Every time!
Here's what I want you to take from this, man and woman:
When you train, your blood can literally become cancer-suppressive.
Not metaphorically. Literally. Your muscles flood your bloodstream with chemicals that hunt down and slow cancer cells.
That's not some BS wellness slogan!
That's a measurable, repeatable result in a god damn petri dish.
So the next time you're slammed and tempted to skip your workout, remember what you're actually skipping.
It's not a workout. It's a dose of medicine your body can't get any other way.
So smash that damn workout, my friend!
Catch you soon,
I'm rooting for you,
Mark ✌️
