Purpose:
Heart rate variability (HRV) is a key indicator of autonomic nervous system function and cardiac adaptability, both of which are markedly reduced in smokers with metabolic syndrome. This study aimed to compare the effects of endurance, resistance, and concurrent training on HRV components in male smokers with metabolic syndrome.
Methods:
In this quasi-experimental study, forty male smokers diagnosed with metabolic syndrome were randomly assigned to four groups: endurance, resistance, concurrent, and control. Training programs were performed for 12 weeks, three sessions per week. HRV indices including HF, LF, RMSSD, SDNN, HR, and LF/HF were measured before and after the intervention. Data were analyzed using multivariate analysis of covariance (MANCOVA) and paired t‑tests (p < 0.05).
Results:
The results of the Wilks’ Lambda test indicated that the group effect on the combination of HRV components was significant (p < 0.001). Significant differences were observed between the training groups in HF (p = 0.002), HR (p < 0.001), LF (p < 0.001), LF/HF ratio (p = 0.004), RMSSD (p < 0.001), and SDNN (p < 0.001) (p < 0.05). Aerobic training produced the greatest effects on HF and RMSSD indices, while concurrent training elicited the largest changes in SDNN, HR, LF, and the LF/HF ratio. Resistance training led to more limited improvements in RMSSD and SDNN.
Conclusion:
All three training modalities improved autonomic cardiac regulation, but concurrent training—combining aerobic and resistance elements—showed the most comprehensive effect in enhancing sympatho‑vagal balance. Consequently, concurrent training can be recommended as an effective and non-pharmacological strategy for cardiovascular rehabilitation in smokers with metabolic syndrome.