Author(s): WANG, T., LU, Y., Institution: BEIJING SPORT UNIVERSITY, Country: CHINA, Abstract-ID: 1888

INTRODUCTION:
To explore the load structure characteristics of a 4-week altitude training program for adolescent swimmers and the physiological changes induced by training in a special environment, analyze the relationship between load quantification indicators and heart rate variability (HRV) changes, and provide data and theoretical support for load management and scientific training of adolescent swimmers during altitude training.
METHODS:
A longitudinal study was conducted in 16 adolescent swimmers during a 4-week altitude training. Incremental tests were performed pre- and post-training, and HRV was assessed weekly. Changes in HRV were analyzed using one-way repeated-measures ANOVA, while paired t-tests evaluated pre-post differences in lactate threshold variables and maximal performance. Training load was systematically monitored, including external (session frequency, time, distance) and internal (heart rate, eTRIMP, sRPE) indicator. Pearson correlations and stepwise regression analyses were performed to examine associations between load indicators and HRV responses.
RESULTS:
The total training time over the 4-week altitude training period was 70.1 hours, averaging 18.4 hours during basic training week and 14.9 hours during recovery week. The proportion of training time in zones 1-5 was 13.46%, 37.00%, 38.33%, 7.55%, and 0.82%, respectively. After altitude training, the athletes' lactate threshold and lactate threshold speed significantly increased (P < 0.01). The time main effects of HRV time-domain indicators over the 4 weeks were statistically significant (P < 0.05), as were the time main effects of Total Power, LF Power, and HF Power (P < 0.05). Among load quantification methods, sRPE and eTRIMP were highly positively correlated (r = 0.90, P < 0.01), and 90%-100% of maximum heart rate (Z5) significantly positively influenced sRPE changes. Between load quantification methods and HRV, sRPE and eTRIMP showed significant negative correlations with time-domain indicators (P < 0.01), as well as with Total Power, HF Power, and HF Peak (P < 0.01). 70%-79% of maximum heart rate (Z3) significantly negatively influenced RMSSD changes, while Z2 and Z3 significantly positively and negatively influenced SDNN changes, respectively.
CONCLUSION:
(1) A 4-week "threshold" training intensity distribution improves the lactate metabolism capacity of young swimmers and the maximal speed of the 200-meter incremental load test; (2) HRV proved to be an effective indicator of changes in training load during altitude training, with time-domain indices demonstrating greater sensitivity than frequency-domain indices; (3) Both sRPE and eTRIMP can reflect the relationship between exercise load and ANS regulation, providing a data foundation for effective management of load-related HRV changes. (4) Moderate-to-high intensity training may exert short-term negative effects on HRV, whereas low-to-moderate intensity training may enhance autonomic activity, thereby improving HRV and alleviating post-training fatigue.