Heart rate cost as a tool for monitoring recovery between acute training sessions

Purpose Effective recovery monitoring is crucial to optimise performance and prevent overreaching, injuries, and overtraining. This study evaluated the heart rate cost (HRC) during submaximal running as a simple, non-invasive, and costeffective tool to assess recovery after a high-intensity training session. Methods Fifteen male recreational runners (aged 18–31 years) participated in this investigation. Assessments included anamnesis, blood tests (CPK, cortisol, testosterone), body composition analysis, blood pressure, heart rate (HR), heart rate variability (HRV), pain scale, vertical jump (VJ), and a 6-minute submaximal running test to determine HRC (HR/running velocity). Afterwards, participants completed a high-intensity training session, consisting of six 1-minute treadmill runs and 10 strength exercises in a circuit format. Results HRC increased 24 h post-training, indicating higher physiological cost, but significantly decreased after five days of recovery (p = 0.044). VJ performance returned to normal after five days compared to 24 h post-training (p = 0.013), with a significant correlation between the delta reduction in HRC and performance recovery on VJ (r = –0.689). No significant changes were found in the testosterone/cortisol ratio or HRV (HRV) (p > 0.05), likely due to the fact that these variables reflect chronic stress more than acute stress. CPK levels mirrored HRC and VJ trends, worsening 24 h post-training and improving after five days (p = 0.01). Conclusions HRC proved effective in distinguishing recovery status after high-intensity training, showing sensitivity comparable to VJ and CPK measurements. These findings are relevant for researchers, coaches, and athletes in daily recovery assessments.