The current observational study aimed to monitor the physiological performance over 4 weeks of living and training at a moderate altitude in elite Chinese cross-country skiers (8 males, mean age 20.83 ± 1.08 years). Lactate threshold, maximal oxygen uptake, blood, and body composition tests were performed at different time points to investigate the changes in physiological performance. The data were analysed by a one-way repeated measures ANOVA and a paired sample T-test between the test results. During the training camp, systematic load monitoring was carried out. Lactate threshold velocity, lactate threshold heart rate, and upper body muscle mass increased significantly (p < 0.01) after moderate altitude training. Maximum oxygen uptake was reduced compared to pre-tests (p < 0.05). Aerobic capacity parameters (maximal oxygen uptake, haemoglobin, red blood cell count) did not significantly increase after athletes returned to sea level (p > 0.05). These findings suggest that 4 weeks of moderate altitude training can significantly improve athletes’ lactate threshold and upper body muscle mass; no significant improvement in other aerobic capacity was seen. Exposure time, training load, and nutritional strategies should be thoroughly planned for optimal training of skiers at moderate altitudes.

Talent identification in youth football is a critical process for recognizing players with the requisite aptitude and long-term potential. This study investigated the influence of maturity status and relative age on physical performance metrics in Chinese male youth footballers aged U13–U15, aiming to provide empirical data for the development of a more equitable and scientific talent selection framework. A cross-sectional design was employed to assess the anthropometric characteristics and physical performance of 199 Chinese male youth footballers using standardized testing protocols. Hierarchical regression analyses were conducted to examine the independent and combined effects of chronological age, maturity status, and relative age on physical performance. Regarding relative age effect, a significant effect was observed in the U13 group and the total sample ( P < 0.01), but it diminished and became non-significant in the U14 and U15 groups ( P > 0.05). Maturity status was a significant predictor of most performance measures ( P < 0.01). Relative age demonstrated a weak yet significant independent effect solely on the 30-meter sprint ( β = 0.13, P < 0.05) and pull-ups ( β = −0.15, P < 0.05). No significant interaction effects were observed between maturity status and relative age for any performance variable (∣ β ∣ ≤ 0.14, P > 0.05). In conclusion, maturity status is a robust predictor of physical performance, while relative age exerts a task-specific influence that weakens with chronological age. These findings confirm they are distinct concepts and should be treated separately in talent identification.