Time-Domain Heart Rate Variability as a Practical Tool to Assess Readiness and Recovery in Youth Soccer Athletes

Heart rate variability (HRV) is a non-invasive biomarker widely used to assess autonomic regulation, training adaptation, and recovery status in athletes. However, studies involving soccer players under 17 years of age remain scarce, particularly those integrating physiological and psychophysiological markers in real competitive contexts. This study aimed to analyze autonomic modulation using time-domain HRV (natural logarithm of the root mean square of successive difference LnRMSSD) and its relationship with subjective indicators of recovery and load in under-17 elite soccer athletes. An observational longitudinal study was conducted with fourteen elite male soccer players from Santos Futebol Clube (age: 16.2 ± 0.42 years) monitored over four competitive weeks. Morning HRV was recorded using a validated ultra-short two-minute protocol, while psychophysiological measures included perceived recovery status (PRS), session rating of perceived exertion (sRPE), perceived stress, and mood. The athletes demonstrated no statistically significant temporal changes in RMSSD or LnRMSSD throughout the monitoring period, with mean values of LnRMSSD = 4.06 ± 0.68 and RMSSD = 68.78 ± 33.62 ms. Significant associations were observed between LnRMSSD and PRS (r = 0.61; p < 0.04), sRPE (r = −0.67; p < 0.03), and perceived stress (r = −0.77; p < 0.01), indicating, under the conditions of this study, coherence between physiological and perceptual indicators of internal load and recovery status. In conclusion, the results suggest that elite under-17 soccer players maintained stable autonomic modulation during the competitive period analyzed. Furthermore, the observed associations between HRV and subjective measures support the potential value of integrating physiological and perceptual indicators when monitoring recovery and readiness in youth soccer athletes.