Impact of the Magnitude and Duration of Weight Loss Procedures in Combat Sports Athletes: A Systematic Review

Background: Weight manipulation is standard practice in combat sports to compete in lighter divisions, but the thresholds of duration and magnitude impairing performance remain unclear. Objectives: To evaluate the effects of progressive (PWL) versus rapid weight loss (RWL) across three magnitudes of body mass (BM) reduction, moderate (<5%), aggressive (≥5% to <10%), and extreme (≥10% BM), on performance in combat sport athletes. Methods: PubMed, Medline, Scopus, Scielo, and SportDiscus were searched for interventions published from January 2000 to 30 September, 2025. Two independent researchers performed screening, data extraction, and quality assessment (PEDro scale). Results: Twenty reports corresponding to 18 independent studies met the inclusion criteria (mean PEDro score 5.30; fair quality), comprising 363 unique athletes (322 men, 41 women). Extreme weight loss (≥10% BM) via PWL was associated with impaired technical skill, decision-making, and mood profile, although this evidence was derived from only three independent samples. Aggressive RWL (≥5% to <10% BM) through acute dehydration reduced maximal strength, power, and sport-specific fitness in several but not all studies, with deficits still present 24 h after the weigh-in. Moderate reductions yielded heterogeneous findings, with impairments of mood, balance, and resting maximal voluntary contraction in some reports and no significant effects in others. Conclusions: Effects appeared graded by the magnitude of BM reduction, but the evidence is unevenly distributed, and no study examined extreme RWL. Findings should be interpreted with caution.