Is Zone 2 training optimal? Protocol, data and code for a systematic review and multilevel network meta-analysis by physiological intensity domain

Protocol, extracted data, analysis code and verification files for a systematic review and multilevel network meta-analysis comparing aerobic adaptations to training in the moderate, heavy, severe and extreme physiological intensity domains (49 controlled trials, 1,793 participants). The protocol (version 1.1) was finalised on 17 October 2026, before study selection, and was not registered in a public registry. The file protocolo_registro.md is deposited unchanged; its SHA-256 checksum is 110630d3eabb99676ddf73262a514ee9e9afc2ba5c8769e142a5ca3e86775345. Zone2_NMA_data_and_code.zip contains: search and eligibility records; the inputs and code of the preliminary analysis of the open-access subset (44 trials), run before the extracted data were verified; the data and results of the final analysis (multilevel model with CR2 inference, network meta-analysis, meta-regression, dose-response, sensitivity analyses and decision-rule quantities); and the R and Python code. README.txt describes each folder and the order of execution. Publisher PDFs of the included trials are not included.