Author(s): WANG, W., ZI, W., Institution: CHINA INSTITUTION OF SPORT SCIENCE, Country: CHINA, Abstract-ID: 1188

INTRODUCTION:
Integrative analyses of race-process dynamics in adolescent half-marathon athletes remain limited. This study aimed to systematically characterize pacing patterns, relative intensity distribution, and the dynamic progression of heart rate–speed decoupling during a simulated half-marathon. Furthermore, we examined the association between decoupling metrics and late-race pacing decline, in order to provide empirical evidence for the quantitative representation of durability-related performance characteristics and endurance training monitoring.
METHODS:
Thirteen adolescent endurance-trained athletes (8 males, 5 females; 16± 1 years) completed an incremental treadmill test to determine VO₂peak, HRpeak, and velocity at VO₂peak (vVO₂peak). Participants subsequently performed a simulated 21.1-km half-marathon under standardized conditions. Running speed and heart rate were recorded at 1-km intervals. Relative running speed (%vVO₂peak) and relative heart rate (%HRpeak) were calculated. Heart rate–speed decoupling was quantified using 2-km segments. Decoupling onset, maximal magnitude, and stage-specific values were extracted. Spearman correlations assessed associations between decoupling indices and pacing decline.
RESULTS:
Relative speed demonstrated a stage-dependent pattern. Males exhibited higher relative intensity during 1–7 km (83.27 ± 0.94 vs. 79.11 ± 1.05 %vVO₂peak), with convergence mid-race and greater late-stage decline compared with females, who maintained more stable pacing. Relative heart rate increased progressively, reaching 92–95% HRpeak in the final segment. Notably, relative speed declined during later stages while heart rate remained elevated.The decoupling index increased from ~1.00 (3–4 km) to ~1.06 (17–18 km). Stage-specific decoupling rose from 2.07% (5–10 km) to 5.51% (15–20 km), with maximal decoupling of 9.3% ± 2.7%. Decoupling onset occurred primarily between 7–10 km. Late-stage decoupling was strongly associated with pacing decline (ρ = 0.77, p < 0.01).
CONCLUSION:
Half-marathon performance in adolescent athletes demonstrated progressive cardiovascular strain and a gradual dissociation between internal and external load throughout the race. As the event progressed, relative running speed declined while heart rate remained elevated, indicating an increasing internal physiological cost required to sustain a given external workload. The magnitude of heart rate–speed decoupling was significantly associated with late-race pacing decline, suggesting that the degree of internal–external load dissociation may reflect the deterioration of durability capacity during prolonged exercise. Therefore, heart rate–speed decoupling may serve as a process-based quantitative marker for assessing endurance durability and fatigue regulation capacity in adolescent athletes.