Let me take you back to Monday this week.

I went for a 30-minute run, clocking up about 7000 steps in the process.

Yet by 4pm, my Garmin said I’d barely done another 1000 steps across the whole day.

You see, I’m more active than most people - but I can also be quite inactive when I’m not pounding the pavement.

Which always gets me thinking…

Does all this sedentary time undo some of the benefits of my exercise?

You can see why my eyes widened when I came across a new debate in Medicine & Science in Sports and Exercise.

Because it asked some of the world’s leading sedentary behaviour researchers to look at the same body of evidence, and essentially answer the same question, but from the opposite angle:

Can enough exercise offset the health risks of too much inactivity?

And funnily enough, they came to opposite conclusions.

One group argues if you do enough exercise, you effectively cancel out the health risks of prolonged sitting.

Yet the other group says it doesn’t…

So let’s dig into the main arguments for each side, and see what we can actually conclude about whether too much sitting really “undoes” your exercise.

Why scientists don’t quite agree

The “debate” here was two perspective papers published at the same time.

The idea is they deliberately present opposing viewpoints, and draw on the same evidence base to support their arguments.

This included studies that (among others):

• Followed large populations over many years to compare health outcomes in people with different levels of physical activity and sedentary time
• Compared people with different combinations of sitting time and physical activity (e.g., high sitting/high activity vs. high sitting/low activity)
• Experimentally tested how breaking up prolonged sitting or adding exercise affects markers such as blood glucose, blood pressure and vascular function

Despite what the titles of the articles suggest, the disagreement was actually fairly narrow.

It really came down to one word:

Whether the harms of prolonged inactivity can be”fully” offset by exercise.

So here’s what each side of the argument had to say - and what it means for you.

The case for “exercise cancels out sitting”

The first group essentially argued that if you do enough exercise, it doesn’t really matter how much time you spend inactive.

Their argument was based largely on large prospective cohort studies involving hundreds of thousands to more than one million adults, which show people with the highest physical activity levels had little or no excess mortality risk despite prolonged sitting.

They also pointed to joint analyses comparing different combinations of physical activity and sedentary time (e.g., high sitting/high activity vs. high sitting/low activity), which suggested high levels of exercise could offset the increased mortality risk associated with sitting.

And finally, they highlighted accelerometer-based studies that found people achieving around the upper end of the physical activity guidelines (or more) had substantially lower - or in some analyses no statistically significant increase in - mortality risk despite high sedentary time.

Their overall message was exercise is extremely powerful, and can overcome the harms of sedentary behaviour (primarily for increased mortality risk) - if you do enough of it.

The case against “exercise cancels out sitting”

The second group argued that while exercise substantially reduces the health risks of prolonged sitting, it probably doesn’t eliminate them completely.

Their interpretation also drew on many of the same large epidemiological studies, but they interpreted them more cautiously, arguing that reduced risk is not the same as no risk and that observational studies cannot prove complete elimination of harm.

They also pointed to so-called compositional and isotemporal analyses, which suggest replacing sitting with movement improves health, but that the overall balance of movement, sitting and sleep across the day may matter more than exercise alone.

Lastly, they highlighted experimental laboratory studies, showing prolonged sitting can impair glucose regulation, vascular function and other physiological processes, and that regularly breaking up sitting often improves these outcomes - even when overall exercise levels remain unchanged.

This group also agreed exercise matters a lot, but argued it probably can’t fully cancel out the negative effects of inactivity - especially when physical activity levels are on the lower end.

What both sides actually agree on

Despite this being a “debate”, both groups actually agreed on more than the title of their articles suggest.

They both agreed that:

• Exercise is one of the best things you can do for your health
• Too much sitting or inactivity is obviously not a good idea
• And moving more across the day is better than less

Again, it really came down to whether the benefits of exercise are “fully” blunted by lots of inactivity.

The reality is, most people would benefit from moving a little more, and sitting a little less, rather than worrying about how much their risk might be reduced, or which is more important.

But for what it’s worth, this debate shifted my perspective a little.

My interpretation of the evidence is that regular exercise substantially reduces the downsides of prolonged inactivity - particularly in people who are very active.

But of course, most people don’t fall into the “very active” category.

This doesn’t mean inactivity is harmless - but it does mean the biggest gains for most people probably still come from exercising regularly.

So, what should you do?

For most people, the “default” is lots of sedentary time with not enough exercise.

If this applies to you, the biggest “bang for your buck” is getting some regular exercise. It might not completely offset the negative effects of inactivity, but it will certainly benefit your health.

On top of that, look for opportunities to get up and move regularly across the day. Try and see it as exactly that - an opportunity - rather than an inconvenience.

And finally, be wary of common mindset traps, like: “I sit too much anyway, so what’s the point of exercising”, or “I went to the gym today, so it doesn’t matter if I barely move for the rest of the day.”

Clearly, the answer is somewhere in the middle - and finding a way to build both regular exercise and regular movement into your routine.

Final thoughts

I get it - debates like this can be a little confusing.

When even scientists can’t agree on something, it can be hard to know what to think (or do).

But they can also be reassuring - because in this case, the “what to do” part doesn’t really change.

We could spend years debating exactly how much inactivity reduces the benefitsof exercise, while in the meantime, millions of people still aren’t exercising at all.

So we just need to do what we already know is good for us:

Exercise regularly, move more across the day, and sit less where you can.

But most importantly - do it in a way that’s safe, enjoyable, and sustainable for you.

Don’t let scientific uncertainty become another reason for not taking action.

Hope you enjoyed this!

Until next week,

Jackson

​​​

If you've got a moment, I'd love to hear your thoughts on this edition of The Weekly Exerciser.

Send me a quick message or email - I'll reply to every one!

PS: Did someone forward you this email? You can sign up to The Weekly Exerciser here.

IMPORTANT:

The information contained herein is of general nature only and does not constitute personal advice. You should not act on any information without considering your personal needs, circumstances, and objectives. Any exercise program may result in injury. We recommend you obtain advice specific to your circumstances from an appropriate health professional before starting any exercise program.