You go for your run. You feel strong. Then you sit back down at your desk for six hours and undo half the good work.
That’s not me being dramatic, it’s what a major new study has just confirmed, and it’s exactly what my physio Charlotte and I talked about a while ago on YouTube. “Sitting is the new smoking” is a phrase that’s been doing the rounds again, and Charlotte’s research backs it up more than either of us expected. If you’re a runner in your 40s, 50s or 60s with a desk job either side of your training, this one’s for you.
Is sitting really the new smoking?
A study of over 91,000 people, tracked for more than 12 years using activity monitors, has just been published in the journal PLOS Medicine, led by researchers at the University of Glasgow. The headline finding: every extra hour of uninterrupted sitting was linked to a 9% higher risk of dying from cancer.
The important word there is “uninterrupted.” It’s not sitting itself that’s the problem, it’s sitting for long, unbroken stretches. The researchers found that replacing just one hour of prolonged sitting a day with light movement cut that risk by 12%. Getting up, walking to make a drink, standing while you’re on the phone, all of it counted.
It’s a big observational study, so it can’t prove sitting causes cancer on its own. But when I mentioned to Charlotte that I’d read the phrase “sitting is the new smoking” some time ago, she agreed it’s more accurate than it sounds. We know smoking kills people and while sitting isn’t in that league, the comparison is there to make a point: something this ordinary, this normalised, is doing us far more harm than most of us realise.
What sitting all day actually does to a runner’s body
I asked Charlotte, my physio, to break down what’s really happening physiologically when we sit for long periods. Here’s what stood out:
- Your glutes switch off. Charlotte was clear on this, sitting for years at a time leads to muscle atrophy, particularly through the glutes and thighs, because you’re simply not using them. For a runner, that’s a problem. Your glutes are meant to be doing a huge amount of the work driving you forward and stabilising your pelvis with every stride.
- Your support structure weakens. Once the glutes and hips stop pulling their weight, your back starts picking up the slack. Charlotte sees this constantly in clinic, weak glutes compounding into lower back pain.
- Your posture habits change how you move. Years of sitting train us to bend from the waist with straight legs, rather than hinging through the hips and knees the way children do naturally when they squat. That poor movement pattern doesn’t stay at your desk it shows up in your running form too.
- Your gut and metabolism slow down. Charlotte explained that your digestive and cardiovascular systems are designed to work best when you’re upright and moving. Sitting compresses your abdomen and makes your body less efficient at processing glucose and fat a factor in weight gain and insulin resistance over time.
- It affects your head as much as your hips. Both Charlotte and I noticed the same thing in ourselves, concentration and mood dip during long sitting stretches, and a short walk or standing break clears it almost instantly.
“But I already work out” is that enough?
This is the bit that surprised me most. Charlotte pointed out that even if you train hard in the morning or evening, six hours of unbroken sitting during the day still has its own separate impact. A hard Pilates session or a good run doesn’t cancel out an entire day spent still the two things affect your body differently.
The research Charlotte’s been reading suggests you don’t need much to counter it: two to three minutes of movement, roughly every 30 minutes, breaks the cycle. If you’re older, less conditioned, or carrying extra weight, even a gentle walking pace round the kitchen is enough to make a difference. If you’re already fit and active, that break needs to be a bit more purposeful get the heart rate up, not just wander to the kettle.
Practical ways to break up your sitting time
None of this needs to be complicated:
- Stand up every time you take a phone call
- Turn a sit-down meeting into a walking one where you can
- Set a timer for every 30 minutes as a stand-up prompt
- Do your reading or admin standing at a worktop or mantelpiece for a stretch
- Use your Pilates practice specifically to reactivate the glutes and hips that sitting switches off
That last one is really the point of Pilates for runners over 40, it’s not just about getting stronger for your next race. It’s about undoing the damage your desk does before it turns into the back pain, hip tightness, or injury that stops you running altogether.
Try this as a weeks challenge: every time you’re on the phone, stand up. Every meeting that can be a walk, make it a walk.