The headline that's about to land in your feed

A new paper just published in the British Journal of Sports Medicine looks set to upend the longstanding 150-minute-per-week physical activity guideline. Liang and colleagues, using UK Biobank accelerometer data, report that meeting the current World Health Organization recommendation of 150 minutes per week of moderate-to-vigorous physical activity (MVPA) is associated with only an 8-9% reduction in cardiovascular disease risk. To get a "substantial" 30 percent reduction, they say, you would need to clock 560 to 610 minutes per week. That is roughly 80 to 90 minutes per day, every day.

The paper also includes a Mendelian randomisation (MR) analysis, which they offer as causal triangulation, with a single nominally significant finding: genetically proxied higher cardiorespiratory fitness is associated with lower heart failure risk, odds ratio 0.79 (95% confidence interval 0.63 to 0.99).

You are about to see this carved into Instagram squares with captions like "The 150-minute guideline is a lie" and "You need to triple your training to actually benefit."

Before that happens, let's slow down. The cohort analysis is meticulous. The MR is honestly reported. But the headline finding is, in my view, a textbook example of how a careful statistical exercise can produce a deeply misleading clinical message when interpreted without the methodological context. Let me walk you through why.

The trick at the centre of the paper: they adjusted away the main mechanism. This is the single most important thing to understand about this paper, and almost no one in the share-and-comment cycle is going to notice it.

The traditional dose-response meta-analyses, which give the figure of roughly 20 to 30 percent lower cardiovascular mortality at 150 minutes per week (work by Wahid, Kyu and Kodama is representative here), estimate the total effect of MVPA. Total effect means: if you take a sedentary person and they start meeting the guideline, what happens to their cardiovascular risk, end to end?

Liang and colleagues did not estimate the total effect. They estimated the conditional effect of MVPA at a fixed level of cardiorespiratory fitness (CRF). In epidemiology, when you condition on a downstream variable that sits between your exposure and your outcome, you are adjusting away the very pathway through which the exposure does most of its work. This is called overadjustment, or mediator adjustment, and it is a well-known way to make a real effect look small.

Here is the basic chain everyone in the field accepts:

> MVPA → improved CRF → lower CVD risk

Most of the protective effect of physical activity on the cardiovascular system is delivered through improvements in fitness. Higher stroke volume, better endothelial function, lower resting heart rate, better insulin sensitivity, improved lipid profile, lower blood pressure. These are CRF-mediated.

When Liang and colleagues conditioned on CRF, they kept only the direct effect of moving around, the residual after fitness adaptation is mathematically subtracted out. Of course that number is smaller. It has to be. And to their credit, the authors say this almost explicitly in their discussion:

This is buried in the discussion. The abstract simply says the 150-minute guideline yields a "modest" 8 to 9 percent reduction. The "we removed the main pathway" caveat does not appear there.

So when you read that 150 minutes a week only delivers an 8 to 9 percent reduction in this study, what you are really reading is: after we subtract out the fitness adaptations that 150 minutes a week produces, the leftover signal is 8 to 9 percent. That is not the same as saying the guideline is weak. It says that most of what the guideline delivers comes from making you fitter. Which, of course, was the whole point.

The 560-minute figure has the same problem, doubled

Now apply the same logic to the headline-grabbing number. The paper says you would need approximately 560 to 610 minutes per week to achieve a 30 percent reduction in CVD risk.

But this is the volume of MVPA required to deliver a 30 percent reduction through the direct, non-CRF-mediated pathway alone. They are asking: in a counterfactual world where doing 600 minutes per week of MVPA somehow did not change your fitness, how much risk reduction would you get? That counterfactual does not exist in nature. You cannot do 600 minutes per week of MVPA without dramatically raising your VO2 max. The two are not independently dialable.

One week of accelerometry is one week. Movement varies substantially week to week with weather, work, illness, holidays, caregiving load. Classifying someone as "below guideline" based on a single seven-day snapshot misclassifies a lot of people. Misclassification of exposure attenuates effect estimates and biases dose-response curves.

The Cox-GAM significance pattern is mixed. The continuous smooth interaction was significant. The dichotomised analysis showed a non-significant additive interaction (RERI −0.09, 95% CI −0.45 to 0.22), a non-significant multiplicative interaction (ratio of HRs 0.90, 95% CI 0.70 to 1.15, p = 0.39) and a synergy index of 0.84 with very wide CIs. When the categorical interaction is null and the smooth one is significant, the signal is being driven by curvature in regions of the joint surface where data are sparse. That deserves more humility than the paper offers.

So what should you actually do with this paper?

Three things.

First, the existing 150-minute-per-week guideline is not undermined by this paper. The 8 to 9 percent figure is what is left over after the authors mathematically removed the fitness-adaptation pathway, which is the main pathway. The total-effect estimate from previous dose-response meta-analyses, which is in the range of 20 to 30 percent lower mortality at 150 minutes per week, is the number that should still anchor public health messaging and personal target-setting.

Second, the MR analyses are interesting but should not be treated as causal proof. The one nominally positive finding (CRF and heart failure) is borderline, single-outcome, and fragile to multiple testing. The null PA results almost certainly reflect weak instruments, not biological absence of effect. The paper triangulates less than it claims.

Third, more is more, up to a point. There is good biology and good observational data suggesting that going beyond 150 minutes a week confers additional benefits, especially in metabolic health, body composition, mental health and functional capacity, and almost certainly cardiorespiratory fitness itself. But the way to get those additional benefits is to do more activity, not to chase a fictitious 600-minute prescription that the data do not actually support as a hard target.

You do not need more than 150 minutes a week to be healthier and live longer. You need at least that. More helps, especially if it raises your fitness. Less is the real problem. About half the adult population is not meeting even the 150-minute floor. That is the number we should be writing about.

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Dr. Stuart Phillips is a Canada Research Chair and Distinguished University Professor in the Department of Kinesiology at McMaster University and host of the Exercise Science podcast

Reference: Liang Z, Du S, Zhao S, et al. Joint non-linear dose-response associations of device-measured physical activity and cardiorespiratory fitness with cardiovascular disease: a cohort and Mendelian randomisation study. Br J Sports Med. 2026. doi.org/10.1136/bjsport…