Introduction. Monitor and regulate training loads is imperative among highly-trained athletes to ensure that they receive the correct overload progression and to guarantee a proper recovery between training sessions (1). Both pre-session vertical jump performance and Heart Rate Variability (HRV) assessment have been proposed as tools to regulate training loads (2, 3). Our target was to evaluate whether flight time in Drop Jump (DJ) and resting HRV measured prior to a high-intensity endurance training were related to each other or not.Methods. 19 male 800m-runners (21.4±5.3 y, personal best=116.55 ± 5.53 s) were involved. Training consisted of a high-intensity interval training (2x4x200-m) performed at a velocity above athletes’ competitive pace. RR intervals were registered using a heart rate monitor (Polar RS800CX) in a sitting position during 10 min immediately before the warm-up. Afterwards, subjects performed 3 consecutive DJ with a brief break between them (<15s). HRV data was treated by means of KUBIOS HRV 2.0 software and low-frequency spectral power (LF), high-frequency spectral power (HF) and LF/HF ratio were retained for further analysis. Flight time in DJ was registered using photoelectric cells connected to a high-precision timer (ChronoMaster, Sportmetrics) and the best attempt was retained for statistical analysis. After testing for normality (Shapiro-Wilks), HRV variables were log transformed (ln). A partial correlation, controlling for age and total spectral power, was conducted to explore possible relationships between resting HRV and DJ performance.Results. An inverse association was found between lnLF and DJ (r=-0.486; p<0.05), whereas lnHF and LF/HF were unrelated to DJ.Conclusions. Our outcomes showed that resting HRV and pre-session vertical jump performance before a high-intensity endurance training keep relationship. Specifically, a lower level of baroreflex-mediated modulation of HR (i.e., lnLF) (4) seems to be related to a larger flight time in DJ. Therefore, both pre-session vertical jump performance and resting HRV might be suggested as interchangeably in-field tools aimed at adjusting training loads. Notwithstanding, recording a baseline line for each athlete and track day-to-day variations would probably improve the sensitiveness of HRV pre-training assessment (5).