Aims: We study the behavior and variability of QT and RR intervals (QTI and RRI) from 30-second electrocardiogram (ECG) recordings to assess physiological recovery after different types of athletic training. The goal is to determine whether interval variability can serve as a reliable marker of post-exercise autonomic recovery in different types of exercise.
Methods: We analyzed ECG data from eight athletes (1 male, 7 females, age: 18 +/- 2 years) from the Sport D.B. 2.0 database. Each athlete completed three training sessions: velocity, competition, and strength. ECGs were recorded (i) before (baseline), and (ii) after warm-up, (iii-iv) after training-specific exercises, and at (v) 5, (vi) 10, and (vii) 15 minutes post-exercise. We assessed mean RRIs, QTIs, and Fridericia-corrected QTc's. To quantify variability, we used RMSSD, Poincaré's SD1/SD2, and second-order detrended fluctuation analysis (DFA) short-scale scaling exponent a1 for RRIs, and standard deviation for QTIs (SDQT).
Results: RRIs and QTIs decreased during exercise and increased post-exercise in all session types. Velocity training caused the largest reductions for all mean measures, with incomplete recovery within 15 minutes. RMSSD and SDQT remained suppressed, while SD1/SD2 and DFA a1 rose above baseline after 5–10 minutes. Competition training also led to marked reductions, but most values recovered by 15 minutes. Strength training showed the smallest changes and quickest return to baseline, indicating faster autonomic recovery. QTc remained relatively stable across all sessions. These short ECG-derived metrics may offer a practical tool for monitoring autonomic recovery in athletes.