Steady cardio for the scales, HIIT for the waist

Adults carrying excess weight are routinely told to exercise, but the advice rarely specifies which kind. Aerobic exercise, resistance training, the two combined, and high-intensity interval training all have their advocates, and each targets metabolic health through a different route. Direct head-to-head trials of every possible pairing are scarce, which leaves an obvious gap in the evidence: if the goal is a lighter body, a smaller waist, better blood sugar or a fitter heart and lungs, does the choice of training mode actually matter? This analysis set out to compare and rank all four modes on the key metabolic indicators at once.

The researchers searched PubMed, Cochrane, Embase and Web of Science for randomised controlled trials published from 1990 to February 2023 that tested exercise training in adults with overweight or obesity. They used a network approach, which combines direct and indirect comparisons across trials to rank interventions against one another. Twenty-eight studies with 1,620 participants were included in the analysis. Outcomes spanned anthropometry, lipid profiles, glucose metabolism, blood pressure and cardiorespiratory fitness, with results expressed as weighted mean differences between the four modes: aerobic exercise, resistance training, combined aerobic and resistance training, and high-intensity interval training.

Aerobic exercise came out best for reducing body weight, at 2.35 kg, and body mass index, at 0.9 units. High-intensity interval training led everywhere else: waist circumference fell by 5.93 cm, body fat percentage by 3.93 points, serum triglycerides by 20.55, and fasting blood glucose by 14.31, while VO2 max improved by 7.41. The nulls matter as much as the wins: no training mode produced a significant benefit for total cholesterol or blood pressure. Neither resistance training alone nor combined training topped the rankings for any of the outcomes the review reported.

The ranking suggests a division of labour between training styles: steady aerobic work appears most efficient for shifting total body mass, while interval training looks better at improving body composition, blood markers and cardiorespiratory fitness. That complicates the assumption that one exercise prescription serves every goal equally. Network rankings, though, rest partly on indirect comparisons between trials that never competed directly, so the ordering carries more uncertainty than a straightforward head-to-head result would. Open questions include whether these differences persist over the long term, and how much total exercise volume rather than mode is really driving the gaps.

For anyone with excess weight deciding how to train, this is a reason to think the mode can be matched to the goal. If the number on the scales is the priority, steady aerobic exercise ranked best; if waist size, body fat, blood sugar, triglycerides or fitness matter more, interval training led the field. It is also a reason to keep expectations grounded: no mode significantly moved total cholesterol or blood pressure in these trials. And as with any pooled ranking, the differences between modes are smaller and less certain than a league table makes them appear.