Background: Previous studies reported that exercise training can attenuate the cardiovascular complication of waterpipe tobacco smoking (WPS). The present study aimed to determine the effect of moderate endurance exercise training on heart rate variability (HRV) in Wistar rats exposed to long-term hookah smoke.

Method: The 28 adult male Wistar rats, weighing 180-220 g, were allocated into four groups, including the control group (CTL), the group that did exercise training for 8 weeks (Ex), the group that was exposed to waterpipe tobacco smoke for 8 weeks (S), and the group that did exercise training and received waterpipe tobacco smoke (Ex+S). Finally, the animals' electrocardiograms were recorded, and HRV parameters, including time domains, frequency domains, and non-linear analysis, were calculated.

Results: The results revealed that hookah smoking significantly reduced heart rate (HR) and SD2 (an index of long-term HRV variability) and increased RR interval (P<0.05) compared to the control group. Exercise training reduced Low Frequency (LF) band and increased  high Frequency (HF) band (P<0.05) and non-significantly decreased the LF/HF compared to the CTL group. When animals were exposed to hookah smoke, and they also did exercise training, Corrected QT (QTc) interval, and HF were reduced, and SD2 was increased (P<0.5) in the Ex+S group compared to the S group.

Conclusion: Overall, our findings showed that 8 weeks of moderate-intensity endurance training has a mild effect on improving the frequency domains of HRV in rats, and hookah smoking suppresses this positive effect and reduces heart rate.