Acute Glucose Response to Maximal Exercise is Associated with Cardiorespiratory Fitness and Heart Rate Variability in Healthy Subjects

Andrea Nemcova1, Lucie Saclova2, Tobiáš Goldschmidt3, Martin Kralik2, Daniela Chlibkova4, Lukas Smital1, Radovan Smisek1, Jaromír Hubálek2
1Brno University of Technology, Faculty of Electrical Engineering and Communication, Department of Biomedical Engineering, 2Brno University of Technology, 3Department of Biomedical Engineering, Faculty of Electrical Engineering and Communication, Brno University of Technology, 4Centre of Sport Activities, Brno University of Technology

Abstract

Aims: High-intensity exercise acutely affects blood glucose levels. However, the relationship between exercise-induced glucose response, cardiorespiratory fitness, and cardiac autonomic function remains unclear. It is investigated whether an acute increase in glycamia after high-intensity exercise, specifically after cardiopulmonary exercise testing (CPET), is associated with VO₂max, heart rate variability (HRV), and glucose variability (CV) in the days following CPET. Methods: Using the BUT CGM dataset (n=47 healthy active adults), participants were categorized by their acute glucose response (ΔCGM) post-CPET into glycaemia increase group (ΔCGM > 2 mmol/L, n=20) and a no-increase group (ΔCGM ≤ 2 mmol/L, n=27). We analyzed VO₂max, short-term HRV (pre- and post-exercise), and nocturnal HRV across four nights (one before, three after CPET) alongside glycaemia variability (CV). Results: The increase group demonstrated significantly higher VO₂max (median 52.5 vs 45.0 ml/min/kg, p=0.009). This group exhibited higher resting SDNN: (84.7 vs 64.3 ms, p=0.022) and total power (908 vs 377 ms², p=0.010), greater post-exercise LF/HF ratio (7.9 vs 3.8, p=0.011), and higher nocturnal vagal tone (pNN50: 33.1 vs 23.2%, p=0.031). Notably, nocturnal HRV differences peaked two days post-exercise (total power: 1,602 vs 1,041 ms², p=0.007). CV was also significantly elevated in the increase group 1–2 days post-test (day 1: p=0.029; day 2 CV: p=0.012). Conclusion: An acute glycaemia increase >2 mmol/L after high intensity exercise is associated with higher cardiorespiratory fitness and robust autonomic modulation. However, it also identifies individuals experiencing prolonged metabolic and autonomic perturbations lasting up to 2 days post-exercise. Integrating CGM with HRV monitoring provides a multidimensional view of athletic performance and recovery status.