How much exercise is enough, and when does it work best?

The science, in full

The current international benchmark comes from the World Health Organization, which in 2020 advised adults to accumulate at least 150 to 300 minutes of moderate-intensity aerobic activity each week, or 75 to 150 minutes of vigorous activity, or an equivalent mix, and to add muscle-strengthening work on two or more days. A striking feature of these guidelines is the explicit message that some activity is better than none, and that any movement counts toward the total. The lower bound of 150 minutes is roughly 30 minutes on five days, but the same benefit can be reached in shorter blocks spread through the week.

The shape of the benefit is not a straight line. A pooled analysis by Arem and colleagues, combining six cohorts with more than 660,000 adults, found that people who met the minimum recommendation had about a 20 per cent lower risk of dying during follow-up than inactive people. The curve then rose more gently, reaching a reduction of roughly 39 per cent at three to five times the minimum, after which it flattened. Even a small amount of activity, below the recommended minimum, already lowered mortality risk by around 20 per cent compared with doing nothing, and very high volumes showed no harm. This is why the biggest relative gain sits at the very start, in the step from almost nothing to a little.

Step counts tell the same story in a more tangible unit. A meta-analysis by Paluch and colleagues of fifteen cohorts found that mortality fell as daily steps rose, with the steepest benefit in the first few thousand steps and a levelling off at higher counts. The plateau arrived at roughly 6,000 to 8,000 steps a day for adults aged 60 and over, and around 8,000 to 10,000 for younger adults, with little extra gain beyond those points. Walking faster added a modest benefit on top of the total number of steps.

For metabolic outcomes specifically, both aerobic and resistance exercise help, and the combination tends to help most. A meta-analysis by Umpierre and colleagues found that structured exercise training lowered HbA1c by about 0.67 percentage points in people with type 2 diabetes, an effect comparable to some glucose-lowering medicines, whereas advice alone worked only when paired with dietary support. Yang and colleagues, comparing resistance with aerobic training head to head, found that both improved glycaemic control, with combined programmes generally producing the largest improvements.

The reason exercise reaches blood sugar so directly lies in the muscle. During contraction, muscle cells pull glucose out of the blood through a route that does not depend on insulin, by moving GLUT4 transporters to the cell surface, as reviewed in detail by Richter and Hargreaves. Working muscle acts as a sink that drains glucose from the circulation while you move. Because skeletal muscle is the largest site of insulin-stimulated glucose disposal, having more muscle and using it regularly gives your body more room to store and burn sugar.

This helps explain a finding that surprises many people: exercise improves insulin sensitivity even when body weight does not change. A single session of activity raises insulin sensitivity for roughly the next day to few days, and regular training keeps that effect topped up, independent of any weight loss, a point emphasised in the American Diabetes Association position statement by Colberg and colleagues. The practical implication is that movement is worthwhile for metabolic health even in weeks when the scale does not move.

Building and keeping muscle also lowers longer-term risk. In a prospective study of men, Grøntved and colleagues found that regular weight training was associated with a substantially lower risk of developing type 2 diabetes, with the largest reduction when resistance and aerobic activity were combined. For those short on time, a meta-analysis by Jelleyman and colleagues found that high-intensity interval training improved insulin resistance and glucose control, often in less total time than moderate exercise, though moderate continuous activity remains effective and easier to sustain for many.

How you distribute movement across the day matters too. Dempsey and colleagues showed that interrupting prolonged sitting with brief bouts of light walking or simple resistance activities every half hour markedly lowered post-meal glucose and insulin in people with type 2 diabetes. Reynolds and colleagues found that a ten to fifteen minute walk taken shortly after meals lowered post-meal glucose more than the same walking done at other times. At the population level, Ekelund and colleagues reported that about 60 to 75 minutes of moderate activity a day appeared to offset much of the increased mortality risk linked to long sitting.

As for when exercise works best, the honest answer is that consistency matters more than the clock. There is no strong evidence that a particular hour is decisive for most people, and the timing that works best is the one you can keep up. What is well established is that sustained activity changes hard outcomes, because in the Diabetes Prevention Program by Knowler and colleagues a lifestyle programme including 150 minutes of activity a week, alongside modest weight loss, cut the incidence of type 2 diabetes by 58 per cent over about three years, outperforming metformin. And it need not be formal exercise, as Stamatakis and colleagues found that short, vigorous bursts of everyday activity, such as climbing stairs or walking quickly with shopping, were linked to lower mortality.

Taken together, the evidence points to a reassuring conclusion. Aim for the guideline range if you can, combine aerobic movement with two strength sessions, break up long periods of sitting, and use short walks after meals. But the single most valuable move, in terms of health return per unit of effort, is simply to go from doing almost nothing to doing something regular. Anyone with an existing heart condition, diabetes on medication, or other health concerns should discuss a sensible starting point with their own doctor.

Putting this into practice. Aim for a brisk half hour on most days, and anchor it to something you already do, like a walk straight after lunch or before dinner. If you are starting from almost nothing, that first twenty minutes a day gives you the biggest return, so do not wait for the perfect plan. Add two short strength sessions a week using your body weight or weights, since muscle is where your body parks extra sugar. When you can, take a ten to fifteen minute walk after your largest meal to blunt the blood sugar peak. The best schedule is simply the one you keep repeating.