Comparison of concurrent, resistance, or aerobic training on body fat loss: a systematic review and meta-analysis

Background: This systematic review and meta-analysis compared the differential effects of resistance training (RT), aerobic training (AT), and concurrent training (CT) on body mass and body fat loss in metabolically healthy individuals. Methods: A systematic search of PubMed, SportDiscus, and Web of Science databases for randomized controlled trials published between January 1980 and January 2023, comparing RT, AT, and CT in healthy adults was conducted. Primary outcomes of interest included changes in fat mass and body fat percentage; secondary outcomes were body mass and fat-free mass (FFM). Sub-analyses on intervention duration (< or >= 10 weeks), CT timing (aerobic and resistance exercises done on the same day versus different days within a week), and workload matching (equating workloads between AT, RT, and CT), were conducted. Study protocols followed PRISMA 2020 guidelines and were pre-registered on PROSPERO (CRD42023396530). Results: In total, 36 studies with 1564 participants were included in the systematic review, with only 31 studies included in the meta-analysis due to missing data. For studies lasting at least 10 weeks, AT outperformed RT in reducing body mass (mean difference (MD) = -1.82 kg [95% CI = -2.72 to -0.93]; p < 0.001) and fat mass (MD = -1.06 kg [95% CI = -1.88 to -0.24]; p = 0.01) but led to less FFM retention (MD = - 0.88 kg [95% CI = -1.73 to -0.03], p = 0.04). CT reduced significantly more fat mass compared to RT (MD: -1.09 kg [95% CI = -0.27 to -1.91]; p = 0.009). No significant differences were found between CT, AT, and RT in altering body fat percentage (p > 0.05). For studies shorter than 10 weeks, no significant differences were noted across exercise modalities (p > 0.05). Under conditions where AT, RT, and CT workloads were matched, similar fat mass, body mass, body fat percentage, and FFM changes were observed between exercise modalities (p > 0.05). Similar body mass and body fat percentage loss was observed between same-day and different-day CT (p > 0.05); body fat mass loss only differed in a single study (n = 1) when comparing RT to different-day CT (aerobic and resistance exercises done on different days within a week). Conclusions: While there are no differences in percent body fat loss between exercise modes, AT and CT are more effective than RT alone in reducing absolute fat mass; however, RT neither improved nor impeded fat mass loss when incorporated into CT. Combining aerobic and resistance exercises on the same-day or different-day does not appear to influence the effectiveness of CT. When exercise interventions are short in duration (<10 weeks), there does not appear to be a difference in fat loss between exercise modalities. These results support the concurrent use of aerobic and resistance exercises for fat mass reduction, as well as an emphasis on workload and duration when programming exercise for fat loss.