Weights plus cardio won on lean mass, not on fat

Aerobic exercise has long been the default prescription for people carrying excess weight, on the reasoning that it burns the most energy per session. Adding resistance training is widely recommended too, but the comparative question is rarely posed cleanly: for the same population, does a combined programme actually beat aerobic training alone, and on which outcomes? That distinction matters because weight, body composition and metabolic health do not always move together, and preserving muscle while losing fat is a different goal from simply reducing the number on the scale. This review set out to test whether combined training is genuinely superior, or superior only on selected measures.

The authors conducted a systematic review and meta-analysis of randomised trials that directly compared combined exercise with aerobic exercise alone in adolescents and young adults aged 6 to 45 years with overweight or obesity. Twenty-nine studies involving 1,383 participants were included. Outcomes spanned body composition — lean body mass, body weight, BMI, body fat percentage and waist circumference — alongside cardiometabolic markers including insulin, HOMA-IR, systolic blood pressure, HDL cholesterol and other lipids. The certainty of the pooled evidence was formally graded, and the authors distinguished primary comparisons from secondary and exploratory analyses supported by fewer studies.

Compared with aerobic exercise alone, combined exercise was associated with greater improvements in lean body mass and in insulin-resistance indicators, specifically insulin and HOMA-IR. The nulls were extensive and equally informative: no consistent between-group differences emerged for body weight, BMI, body fat percentage, waist circumference, systolic blood pressure or lipid outcomes. One result ran the other way, with HDL cholesterol showing a small difference favouring aerobic exercise. The authors caution that secondary and exploratory analyses should be read carefully, because several outcomes were supported by a limited number of studies and rested on low-to-very-low certainty evidence. Their overall verdict is that combined exercise is not universally superior.

This tempers the common assumption that adding resistance work improves everything at once. It confirms the most mechanistically expected benefits — muscle mass and insulin sensitivity markers — while contradicting the idea that combined training reliably produces greater fat or waist reduction than cardio alone in this population. The HDL signal favouring aerobic exercise is a reminder that different modes may serve different endpoints. Open questions remain over the exact prescriptions used, whether the effects hold across such a wide age span from 6 to 45 years, and how much weight the low-certainty outcomes can bear given the small number of contributing studies.

The practical reading is that the argument for adding resistance training to cardio rests on body composition and glucose handling rather than on faster weight loss. If lean mass and insulin-resistance markers matter to you, this is a reason to think combined training has an edge; if you are judging success purely by scale weight, waist measurement or body fat percentage, the pooled evidence did not separate the two approaches. The certainty grading is a real constraint, so this is a directional finding rather than a settled one. Individual responses and the specific programme design will vary.