Effects of Functional Training on Body Composition in Adults with Overweight or Obesity: A Systematic Review and...

Background: Obesity is a chronic condition that compromises health and quality of life, with physical exercise representing a relevant therapeutic strategy in its management. Functional training (FT) has been adopted as a modality that integrates neuromuscular and cardiorespiratory stimuli, promoting both physical and psychosocial benefits. However, gaps remain in the literature regarding the effects of FT on body composition in individuals with excess weight. In this context, a systematic review was conducted to analyze the current state of scientific knowledge on this approach. Methods: Randomized controlled clinical trials investigating FT were selected, including interventions classified as high-intensity functional training (HIIT-F), multicomponent programs, and CrossFit-like interventions when they fulfilled the predefined FT eligibility criteria. Participants were required to be between 18 and 65 years of age, physically independent, and in generally good health. The systematic search was conducted in the PubMed/MEDLINE, Embase, Web of Science, Cochrane Library, PEDro, and LILACS databases. The risk of bias (RoB 2.0) and the certainty of the evidence (GRADE) were assessed. Results: A total of 2,972 records were identified. Seven studies met the eligibility criteria, comprising 296 participants. Two randomized controlled trials (61 participants) were eligible for meta-analysis. The pooled analysis demonstrated a significant reduction in body fat percentage (%BF) in favor of FT/HIIT-F compared with non-exercising controls (mean difference = -4.44 percentage points; 95% confidence interval -7.08 to -1.80; p = 0.001). Risk of bias assessment showed moderate methodological limitations across studies. None were classified as low risk. Three had high risk due to missing outcome data and deviations from intended interventions, whereas four showed some concerns related to allocation concealment and analysis reporting. Bias in outcome measurement was consistently low. Conclusions: Current evidence suggests that FT/HIIT-F may be associated with reductions in %BF among adults with overweight or obesity. However, these findings should be interpreted with caution because the certainty of the evidence was rated as very low according to the GRADE approach, the quantitative synthesis included only two studies, and important methodological limitations were identified. As the available data are predominantly derived from female participants, the applicability of these findings to men remains uncertain.