The aims of this project are to compare the effects between 8-week moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on improving HRV.

Background: Both heart rate variability (HRV) and visceral adipose tissue (VAT) are crucial factors predicting cardiovascular diseases, and both can be improved by exercise training. HRV can provide information regarding sympathetic and parasympathetic activity. Studies have demonstrated that HRV and VAT are correlated. VAT accumulation may dysregulate the balance of the sympathetic and parasympathetic nervous system. However, the correlation between sympathetic activation and VAT is controversial and limited by a paucity of studies, and the optimal exercise modality for improving HRV remains debatable. Therefore, the aims of this 1-year project are to compare the effects between 8-week moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on improving HRV.

Methods: Purposive sampling will be used to enroll at least 72 community residents aged 40-64 years with VAT over 100 cm2. A two-phase crossover design will be used to understand the change patterns of HRV and VAT in the 8-week different exercise phase and with 8-week washout period insertion. Participants will initially be randomized into either the MICT or HIIT group for 8 weeks, and the groups will then be exchanged for the later 8 weeks. HRV parameters and VAT will be measured at four time points at baseline (T0), the end of the first phase (8-week later, T1), the initial of second phase (16-week later, T2), and the end of the second phase (24-week later, T2). Linear mixed models (LMMs) with random effects will be used to compare the effects of 8-week different exercise modalities on HRV and explore the effect of VAT changes on HRV over the 24-week intervention.

Relevance to clinical practice: The results of this study can reveal the optimal exercise modality for improving HRV among community residents with higher VAT and clarify HRV and VAT change patterns in exercise and rest phase and the correlation between HRV and VAT. These findings would provide evidence that clinical health professionals can use to promote health benefits through exercise intervention.

Inclusion Criteria:

• Community residents (a) who are 40-64 years old, (b) with a VAT of ≧ 100 cm2 measured using a body composition analyzer, and (c) who can communicate in Mandarin or Taiwanese will be included.

Exclusion Criteria:

• This study will exclude (a) residents with recent unstable conditions (stroke, cardiovascular and respiratory diseases, handicap, pregnancy, mental disorders, systolic blood pressure > 200 mmHg, or diastolic blood pressure > 110 mmHg), (b) residents with contraindications to body composition analyzer measurement (e.g., people with pacemakers, artificial metal joints, and amputated hands or feet) and residents who cannot stand during testing, and (c) residents with habits or lifestyles that may affect HRV (e.g., smoking or alcohol abuse and shift work).