What You'll Learn
Table of Contents
The Short Answer
Resistance training, if you have to choose.
The reasoning is narrow and specific. During weight loss the body draws on lean tissue unless something signals that the tissue is in use. Mechanical loading is that signal. Cardiovascular exercise has real benefits — covered below — but it does not provide that particular signal.
Joint guidance names structured resistance training alongside adequate protein as the two priorities during pharmacotherapy. Cardio is not on that list, and its absence is informative:
A joint advisory from four major U.S. nutrition and obesity societies sets a protein target of 1.2–1.6 g/kg body weight per day (or about 1.5 g/kg of lean body mass) during active weight loss, distributed at roughly 25–30 g per meal, and recommends structured resistance training alongside pharmacotherapy.
Read the advisory ↗Legion Creatine Monohydrate
Creatine is the most studied supplement in strength training, and the case for it is strongest exactly where this page lands: preserving lean mass during a deficit.
Check price at Legion →Disclosure: we earn a commission if you buy through this link, at no extra cost to you. It does not change what this page says. Supplements do not treat or replace a GLP-1 medication, and nothing here is medical advice.
What The Randomised Trial Showed
The most relevant trial ran for a full year and tested exercise against the drug and against both together:
195 adults completed a low-calorie diet then spent a year randomised to supervised exercise, liraglutide, both, or placebo. Weight change versus placebo was −9.5 kg for the combination, −6.8 kg for liraglutide alone and −4.1 kg for exercise alone. Body-fat percentage fell 3.9 points with the combination — roughly double exercise (1.7) or liraglutide (1.9) on their own.
PubMed PMID: 33951361 ↗Bottom line: Note what this trial does and does not settle. It shows exercise plus medication beats either alone by a wide margin. Its exercise programme was not purely resistance training, so it does not by itself rank the two modalities against each other.
The Real Case For Cardio
None of the above makes cardio pointless. It does things resistance training does not:
- Cardiovascular fitness. The strongest independent predictor of long-term health outcomes, and not something lifting develops well.
- Everyday capacity. Stairs, walking, carrying — the things people notice improving.
- Accessibility. Walking requires no equipment, no technique and no gym, which matters on low-energy days when a session would otherwise be skipped entirely.
The point is not cardio versus strength. It is that during a period of rapid weight loss, one of them is protecting something you are actively at risk of losing.
Fat mass fell 14% at month 7 and 18% at month 12. Lean mass dropped initially (−3 kg at month 7) then stabilised rather than continuing to fall. Handgrip strength improved by 4.5 kg at month 12, and sarcopenic obesity prevalence fell from 49% at baseline to 33%.
Full study on PMC ↗Where Cardio Can Work Against You
Two specific problems on a GLP-1, neither obvious.
Large volumes of cardio increase appetite. On an ordinary diet that is an inconvenience. Here it partly opposes the mechanism you are paying for, and it does so without protecting lean mass in exchange.
Energy is already limited. Spending an hour on the treadmill when total intake is 1,300 calories means the resistance session later that week happens at lower quality, or does not happen. On a restricted energy budget these compete.
A Practical Week
Assuming limited time and limited energy, which is the realistic case:
- 2–3 resistance sessions. Full body, compound movements first. Non-negotiable part.
- Daily walking. Low cost, does not interfere with recovery, and covers most of the cardiovascular benefit that matters.
- 1 optional harder cardio session, if energy allows, placed away from your heaviest lifting day.
Full structure in our routine guide and resistance training guide.
What To Cut When Energy Is Low
Some weeks you will not do everything. The order to sacrifice in:
- Cut the extra cardio session first.
- Then cut resistance volume, not frequency. Two short sessions beat one long one for keeping the signal present.
- Keep the walking. It costs almost nothing in recovery.
- Never cut protein to compensate. That is the one that makes everything else worse.
Important: If you have a cardiovascular condition, or have been inactive for a long period, get clearance before starting either. Rapid weight loss changes cardiovascular and electrolyte status, which is a reason to be more careful here, not less.
