Several meta-analyses have detailed the effect of physical activity on muscle mass
It is not clear whether exercise has any effect on muscle mass when aerobic and resistance training studies are pooled together. Hsu et al looked at 15 studies with participants aged 41-90 and sarcopenic obesity. No significant difference in muscle mass was found. Lee at al did not demonstrate a significant difference when looking at 16 studies with a variety of types of exercise .
However, Clark et al looked at 66 studies investigating patients between ages 18-65 with a BMI above 25 and found that resistance training utilising progressive volume of 2-to-3 sets for 6-to-10 reps at an intensity of ≥75% 1RM, utilizing whole body and free-weight exercises were effective at increasing fat free mass with a pooled effect size of 2.23 compared to control . When added to dietary control, resistance training allowed fat free mass to be retained, as opposed to dietary control alone. Aerobic training alone induced a loss of fat free mass.
Resistance training may be particularly useful in reducing loss of muscle induced by caloric restriction. Sardeli et al looked at 6 studies on older adult (mean > 57 years old) and found that combining resistance training with caloric restriction reduced 93% of the lean body mass loss induced by caloric restriction alone 
Chu et al performed a network meta-analysis on 34 studies with 3563 participants with a mean age of 64.7 with sarcopenic obesity with osteoarthritis . Exercise therapy alone and combined treatment with diet exerted favourable effects on muscle mass gain. Combined treatment with resistance training and diet was the most effective. In this study, diet alone did not induce any negative effects on muscle mass.
Quality of evidence
A: Consistent evidence from meta-analysis and systematic review
Strength of recommendation
1 – Small, but significant benefit, low risk of physical activity
Resistance training utilising progressive volume at high intensity of 2-to-3 sets for 6-to-10 reps at an intensity of ≥75% 1RM, utilizing whole body and free-weight exercises is very effective at increasing fat free mass in patients who were overweight or living with obesity. This effect may be present in older individuals as well. Aerobic training alone may induce loss of lean body mass. High-load resistance training may reduce loss of lean body mass whilst being in a caloric deficit and should therefore be incorporated in every exercise plan with dietary control.
1. Hsu K-J, Liao C-D, Tsai M-W, Chen C-N. Effects of Exercise and Nutritional Intervention on Body Composition, Metabolic Health, and Physical Performance in Adults with Sarcopenic Obesity: A Meta-Analysis. Nutrients. 2019 Sep;11(9).
2. Lee HS, Lee J. Effects of Exercise Interventions on Weight, Body Mass Index, Lean Body Mass and Accumulated Visceral Fat in Overweight and Obese Individuals: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Int J Environ Res Public Health. 2021 Mar;18(5).
3. Clark JE. Diet, exercise or diet with exercise: comparing the effectiveness of treatment options for weight-loss and changes in fitness for adults (18-65 years old) who are overfat, or obese; systematic review and meta-analysis. J Diabetes Metab Disord. 2015;14:31.
4. Sardeli A V, Komatsu TR, Mori MA, Gáspari AF, Chacon-Mikahil MPT. Resistance Training Prevents Muscle Loss Induced by Caloric Restriction in Obese Elderly Individuals: A Systematic Review and Meta-Analysis. Nutrients. 2018 Mar;10(4).
5. Chu S-F, Liou T-H, Chen H-C, Huang S-W, Liao C-D. Relative Efficacy of Weight Management, Exercise, and Combined Treatment for Muscle Mass and Physical Sarcopenia Indices in Adults with Overweight or Obesity and Osteoarthritis: A Network Meta-Analysis of Randomized Controlled Trials. Nutrients [Internet]. 2021;13(6). Available from: https://www.mdpi.com/2072-6643/13/6/1992