From acute responses to long-term monitoring: a scoping review of the reliability and validity of biomechanical and physiological assessment tools in elite and highly trained swimmers

BACKGROUND: Scientific monitoring is fundamental to optimizing swimming performance, but its effectiveness relies on the validity and reliability of assessment tools. OBJECTIVE: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR), this scoping review aimed to synthesize physiological and biomechanical indicators applied in swimmers, with a particular focus on acute and long-term responses, as well as the reliability and validity of these indicators. METHODS: Web of Science, PubMed, and SPORTDiscus were searched using predefined keyword combinations, and study screening was conducted using ASReview. All extracted indicators were classified according to established conceptual definitions and predefined quantitative criteria (e.g., reliability: intraclass correlation coefficients and coefficients of variation; validity: Pearson correlation coefficients and coefficients of determination). RESULTS: A total of 41 studies were included, and 297 evaluation indicators were extracted for analysis. Existing research has predominantly concentrated on highly trained adult male swimmers, with limited discussion given to elite or world-class athletes, adolescents, and female swimmers. Acute testing dominates the literature (83.5%), far outweighing long-term monitoring approaches. In terms of indicator composition, biomechanical measures account for the majority (59%), with kinematic variables being the most frequently applied (61%). However, the overall methodological quality remains suboptimal: only approximately 8% of acute indicators and 3% of long-term indicators simultaneously achieved at least moderate standards of both reliability and validity. This indicates that the reliability and validity of acute swimming performance assessments have been discussed; there is a lack of research achieving high levels of reliability and validity, which is even more pronounced in long-term monitoring indicators. CONCLUSION: Results reveal a fragmented landscape dominated by acute analysis of stroke mechanics in adult males, with a severe lack of multi-season monitoring evidence for female and adolescent swimmers. Crucially, key determinants of aquatic performance-specifically propulsive kinetics and metabolic cost-lack confirmed reliability for tracking adaptations across training macrocycles. Consequently, the field requires a shift from the proliferation of novel swim indices to the rigorous methodological consolidation of existing aquatic assessment protocols.