Monitoring External Load and Internal Responses Across Selected Endurance Sports: A Scoping Review

Background: Endurance-sport monitoring combines external-load measures with physiological and subjective responses, but studies vary in their measurement techniques, interpretation, and links to action. This scoping review mapped how these indicators have been studied and the types of evidence linking them to training and athlete outcomes. Methods: PubMed, SPORTDiscus, Scopus, and Web of Science were searched on 24 October 2026. Eligible original research evaluated at least one non-invasive indicator on at least two days during a documented training period or endurance exposure of seven days or longer in six selected endurance sports. Age eligibility was a sample mean/median of at least 18 years or explicit adult recruitment. Findings were summarized descriptively without meta-analysis or formal critical appraisal. Results: Of 8398 screened records, 83 database-derived reports and six reports from other methods were assessed in full, and 56 reports were included. Of these, 15 reports concerned training-load quantification, 32 examined autonomic or physiological responses, and 9 studied subjective responses. By evidence type, 13 examined measurement properties or response behavior, 20 considered concurrent or longitudinal associations, 12 assessed prospective relationships, and 11 examined monitoring-informed action rules. Relationships varied with calibration, measurement protocol, time window, sport, and outcome. Conclusions: The mapped comparisons do not establish broad transferable action thresholds or comparative effectiveness. Future research should evaluate explicit monitoring-and-action rules against adaptations, performance, and health outcomes.