Data and code for: Within-Session Relative Reliability and Absolute Measurement Error of Multimuscle Surface Electromyography Amplitude Normalized to Maximal Voluntary Contraction During Repeated Sit-to-Stand and Timed Up-and-Go Trials

De-identified trial-level derived data and analysis code supporting the measurement-property results reported in the associated article. The package contains trial-level surface electromyographic (sEMG) amplitude summaries for 200 community-dwelling adults performing three repeated trials each of single-repetition sit-to-stand (1STS), five-repetition sit-to-stand (5STS) and the Timed Up-and-Go (TUG), with amplitude recorded from eight lower-limb muscles and expressed as a percentage of a fixed participant- and muscle-specific maximal voluntary isometric contraction (MVIC) reference (%MVC). It also contains the published cell-level results, the analysis code that produces them, and a self-contained reproduction script. Running reproduce_release.py recomputes, from the released trial-level data alone, the 48 task x muscle x amplitude-summary cells of relative reliability and absolute measurement error, the 48 chronological trial-position contrasts, the 96 sensitivity cells, and the trial accounting, and checks each against the published values shipped in the package. The two figures and Supplementary Tables A-D can likewise be regenerated from the released files. The post hoc robustness diagnostics reported in the associated article, and the supplementary tables derived from them, are not regenerated by this package. Raw participant-level sEMG recordings are not included in the public dataset because they were not designated for public release under the present data-sharing plan. Steps that operate on the raw signals - filtering, artefact masking, and extraction of the MVIC normalization reference - therefore cannot be reproduced from this package. Participant identifiers are pseudonyms generated by a one-time system-random permutation; the crosswalk to the original identifiers is not released, and original acquisition filenames have been removed. Data are licensed CC BY 4.0; code is licensed MIT. See LICENSE_DATA.txt and LICENSE_CODE.txt in the package, and README.md and CODEBOOK.md for full documentation.