AIM To investigate the dynamic changes of electrocardiogram (ECG) before/during/after 3km high-load exercise in military trainers and analyze the occurrence of abnormal ECG and its possible influencing factors.

METHODS 130 grassroots trainees who have received long-term training in a certain part of the Central Theater Command were selected to wear a long-term wearable dynamic electrocardiogram monitoring recorder before training to record 24-hour electrocardiogram data. During daily training, they completed a 3000 m long run according to the prescribed time, and collected electrocardiogram data to compare heart rate, arrhythmia incidence rate, and heart rate variability indicators before/during/after the long run

RESULTS Compared with the heart rate before and after exercise, the heart rate of military trainees significantly increased during exercise, and the difference was statistically significant (all P<0.01); 56.7% of the subjects experienced premature atrial contractions during exercise, with an increased incidence compared to before and after exercise (both P<0.05). 9.2% of participants experienced sinus arrest (2-2.4) seconds after exercise, 4.2% experienced sinus arrest before exercise, and no sinus arrest occurred during exercise, with significant differences compared to before and after exercise (both P<0.05). There was no statistically significant difference in the incidence of premature ventricular contractions, atrioventricular block, and ST-T changes in the three stages before, during, or after exercise; In the time-domain results of heart rate variability, compared with before exercise, the SDANN of the subjects increased, the SDNN index decreased, and the PNN50 decreased during exercise (all P<0.01); Compared with before exercise, SDNN decreased and SDNN index decreased after exercise (all P<0.01); Compared with the exercise process, after exercise, the SDNN, SDANN, and PNN50 of the subjects decreased (all P<0.01). In the frequency domain results of heart rate variability, after correction using the Bonferroni method, compared with before exercise, the LF values during and after exercise increased (both P<0.01). Compared with before and after exercise, the value of HF during exercise decreased (all P<0.01). Compared with before exercise, LF/HF increased during exercise (P<0.01) and after exercise (P<0.05). Compared with exercise, LF/HF decreased after exercise (P<0.01).

CONCLUSION Malignant arrhythmia does not occur during exercise in military trainers, but common exercise-induced arrhythmia such as atrial premature beats, ventricular premature beats and ST-T changes may emerge. The occurrence of arrhythmia increases during exercise, which may be related to a decrease in heart rate variability.