Aerobic activity and daily steps: the guideline numbers, the step-count evidence, and what the trials asked

Aerobic activity is the part of the programme the trials actually asked for. It is also the part that does least for body composition on its own. Both facts matter.

The guideline

The US Physical Activity Guidelines (2018) and the WHO guidelines (2020) agree: adults should do 150 to 300 minutes a week of moderate-intensity aerobic activity, or 75 to 150 minutes of vigorous, or an equivalent mix, plus muscle-strengthening activity on two or more days, and should reduce sitting time (PubMed 30418471; PubMed 33239350). Moderate means you can talk but not sing: brisk walking, easy cycling, swimming at a conversational pace. Vigorous means a few words at a time.

Both guidelines state that some activity is better than none and that benefits accrue below 150 minutes; the number is a target, not a threshold below which nothing counts.

Steps

The 2022 Lancet Public Health meta-analysis pooled 15 cohorts with device-measured step counts and nearly 50,000 adults followed for a median of seven years. Mortality risk fell progressively with more steps and levelled off at around 6,000 to 8,000 steps a day in adults 60 and over, and around 8,000 to 10,000 in adults under 60 (PubMed 35247352). Ten thousand was a marketing number; the evidence puts the point of diminishing returns somewhat lower, and it puts the steepest part of the benefit curve at the bottom, between 3,000 and 6,000. If you currently do 3,000, the next 2,000 matter more than any 2,000 after 8,000.

Steps are the easiest activity measure to track on a GLP-1 because they need no session, no kit and no appetite. Every phone counts them.

What the trials counselled

STEP 1 and SURMOUNT-1 encouraged 150 minutes a week of physical activity alongside the 500 kcal deficit, in both arms, reviewed at counselling visits (PubMed 33567185). Activity was self-reported, not measured, so nobody knows what participants actually did. The placebo arms, doing the programme without drug, lost 2.4 and 3.1 percent. See what the trials asked participants to do.

Why aerobic alone is not enough for body composition

In Villareal's trial of older adults with obesity on a diet, the aerobic-only group lost as much weight as the other exercise groups but lost more lean mass and more bone density than the groups that included resistance training (PubMed 28514618). Aerobic exercise improves fitness, cardiovascular risk, glucose handling, mood and sleep, and burns energy; it does not by itself signal muscle to stay. That is why the guidelines pair it with strength work and why the 2025 GLP-1 advisory asks for three strength sessions on top of the 150 minutes. See resistance training basics and lean mass evidence.

Fitting it around therapy

• Walking is the default. It is tolerable when nauseated, it aids gastric emptying, and it adds up: three 15-minute walks a day is 315 minutes a week.
• Plan the harder sessions for your better days. Most people have a within-week pattern after each injection. Put intervals or long sessions on the days furthest from it.
• Fuel and fluids. Under-fuelled cardio on a suppressed appetite is where fatigue and dizziness come from. A small protein-and-carbohydrate snack beforehand and fluids throughout; see exercise when nauseated.
• Heat. Fluid loss plus reduced intake plus the labels' kidney warning: train cool and drink.
• Do not chase calories with cardio. The drug is already producing the deficit. Cardio's job here is fitness and health, and the hour is better split with lifting than spent entirely on a treadmill.

A week that meets the guidelines

Illustrative, not prescribed:

That is roughly 180 to 220 minutes of moderate activity and three strength sessions, which meets both the general guidelines and the GLP-1 advisory. Scale it down on bad weeks rather than skipping it; the total over a month is what counts. If you want to see how exercise interacted with a GLP-1 in a randomised trial, the exercise plus GLP-1 trials page covers S-LiTE.