A de-identified GPS dataset of match running performance, playing position, and altitude exposure in elite youth (U21) soccer players

De-identified dataset and reproduction code for a study of match running performance in elite youth (U21) soccer players, examining the relative contributions of playing position, altitude exposure, match context, and pre-match training load. The dataset comprises 212 valid player-match observations from 16 male U21 players of a Chinese professional club reserve squad, monitored across 32 official matches during the 2024 competitive season, with venues spanning sea-level, moderate-altitude (500–1500 m) and high-altitude (>1500 m) categories. Variables include per-minute match-day high-intensity running distance (>19.8 km·h⁻¹), sprint distance (>25.1 km·h⁻¹) and total distance, seven-day and three-session pre-match training load, and match-context covariates (opponent strength, match importance, formation, temperature, humidity, between-match interval). Player names, opposing-team names, exact calendar dates, and venue city names have been replaced with anonymous codes to protect player and club privacy. The accompanying R script reproduces the descriptive statistics, the linear mixed-effects models (player and match entered as crossed random intercepts), the variance-component and intraclass-correlation analyses, and all figures. Tested under R with the lme4 and lmerTest packages. Files included: U21海拔研究_原始数据.xlsx (analytic dataset, 212 player-match observations) and U21_LMM_Analysis.R (R reproduction script).