Introduction

Tai Chi, a form of martial art originating in China over four centuries ago, has gained worldwide popularity for its numerous health benefits1,2. This moderate-intensity aerobic exercise combines deliberate deep breathing with slow, meditative movements, promoting meditation and concentration3,4. Tai Chi emphasizes upper-body movements while maintaining a squatting posture in the lower body5. These movements, referred to as "form" are performed sequentially to create a "routine"6. A complete Tai Chi set comprises 24 distinct postures, allowing practitioners to adapt their practice to their individual fitness needs and abilities7. This versatility makes Tai Chi suitable for individuals of all ages and health conditions8. Notably, Tai Chi has proven to be safe not only for those in good health but also for individuals with chronic illnesses9.

The global appeal of Tai Chi can be attributed to its demonstrated health advantages. Studies have shown that Tai Chi effectively alleviates symptoms associated with conditions like Parkinson's disease10 and cognitive impairment11. It also reduces anxiety and stress levels while enhancing overall strength, balance, and flexibility12,13. Tai Chi contributes to improved aerobic capacity, positively impacts cardiovascular risk factors, and lowers blood pressure14. Moreover, its versatility allows it to be practiced individually or in group settings, making it accessible to individuals with busy lifestyles and fostering social engagement15. Furthermore, Tai Chi requires no special equipment and can be enjoyed by virtually anyone, anywhere16.

The cardiac autonomic nervous system comprises sympathetic and parasympathetic nerves, which innervate the atria and ventricles through post-ganglionic fibers, often passing through the stellate ganglion17. Parasympathetic nerves primarily originate from the nucleus of the vagus nerve, mainly innervating the atria, and are commonly referred to as the vagus nerve due to their presence within it18. The rhythmic heartbeat results from the balanced regulation of both sympathetic and parasympathetic nerves19. This coordination and antagonism between parasympathetic and sympathetic nerves are central to cardiac autonomic regulation20. Research has highlighted the close association between dysregulated autonomic function and various diseases, particularly cardiovascular ailments and the risk of sudden death21. Heart Rate Variability (HRV) analysis, a non-invasive method, serves as a robust means of assessing cardiac autonomic regulation and its dynamic activity changes22. HRV parameters offer insights into the sympathovagal balance in the body and the extent of parasympathetic influence on sympathetic nerves, making it valuable for prognosis in various clinical scenarios, including acute myocardial infarction, coronary heart disease (CHD), and heart failure23.

Deep breathing and aerobic exercise are effective strategies for enhancing parasympathetic nerve activity, consequently improving Heart Rate Variability (HRV)24,25. Tai Chi uniquely combines these characteristics, positioning it as an effective exercise modality for HRV enhancement26. Existing studies have predominantly focused on 24-form Tai Chi single-practice protocol for health interventions. The SR protocol allows practitioners to roughly understand the fundamentals of Tai Chi skills and master its basic forms. Nonetheless, the SR protocol poses challenges for practitioners in comprehending the functions of individual Tai Chi movements and the overall movement pattern, potentially hindering a deep mastery of Tai Chi skills. Traditional Tai Chi entails systematic training, encompassing standing poles (gong fa), routines, and self-defense applications. Emphasis in Traditional Tai Chi training lies in introducing standing poles, exploring methods through routines, and uncovering truths through self-defense applications. The Standing Pole component primarily focuses on cultivating various static and dynamic fundamental Tai Chi movements, establishing a foundation for subsequent routine practice. The routine part comprises individual Tai Chi movement exercises and multiple movement combinations, constituting the essence of Tai Chi practice. The self-defense application part primarily emphasizes the practical implementation of both individual movements and combinations within routines, serving as a test of practitioners' mastery of routine skills. The GRA protocol assists practitioners in mastering the distinctive movement pattern characterized by synchronous movement of the upper and lower limbs, propelled by the core area. It enhances appreciation for the application of each Tai Chi movement and stimulates practitioners' interest in Tai Chi. The GRA protocol effectively addresses certain limitations inherent in the single routine by seamlessly integrating standing poles, routines, and self-defense applications. This approach serves to enhance the practitioner's accuracy in routine skills and fosters a deeper mastery of Tai Chi skills. However, the evolving GRA protocol, designed to aid practitioners in mastering Tai Chi skills, raises questions regarding its ability to induce exercise load stimulation similar to that of traditional SR protocol. In this study, we aimed to compare the 24-form Tai Chi GRA protocol with the SR protocol, particularly with regard to heart rate variability. Our purpose was to elucidate the autonomic load stimulation characteristics of these different protocols, offering biological evidence to support the development of Tai Chi health-promotion intervention programs.

Methods

Calculation of sample size

The required sample size for the study was pre-estimated using G-power 3.1.9.7 software.The study set Partial ŋ2 to 0.06, resulting in an effect size of 0.2526456. ɑ err pob, Power (1-βerr prob),Corr among rep measures, and Nonsphericity correction were set to 0.05, 0.96,0.5, and 1, respectively. The results showed that 45 subjects were needed for the trial.

Participants

All participants provided written informed consent and understood the experimental process and purpose. All methods in this study were carried out following the Declaration of Helsinki's relevant guidelines and regulations, and this study was reviewed and approved by the ethical review of the Bei**g Sport University (NO.2023161H), and informed consent was obtained from all subjects.

For the purpose of this experiment, a total of 45 college students specializing in martial arts set direction were recruited. Inclusion criteria consisted of the following: (1) Negative responses to all seven questions on the American College of Sports Medicine Physical Activity Readiness Questionnaire (PAR-Q). (2) No abnormalities detected on the electrocardiogram (ECG).

Exclusion criteria were defined as follows: (1) Chronic illnesses or a history of major illnesses. (2) Experiences of sports-related injuries or fractures within the past three years. (3) Engagement in high-intensity physical activities (e.g., basketball, running, skiing, etc.) within 72 h preceding the test.

All recruited students held a minimum status of Martial Art National Level 2 Athlete or higher. They demonstrated proficiency in executing the 24-form Tai Chi SR protocol and had completed a minimum of one semester, equivalent to 32 h, of classroom training in the GRA protocol. Furthermore, they exhibited the capability to execute all elements of the 24-form Tai Chi GRA protocol to a satisfactory standard. The participant group comprised 26 males and 19 females, as outlined in Table 1.

Table 1 List of basic conditions of Tai Chi practitioners.
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Experimental procedure

The experiments were conducted daily between 9 a.m. and 12 p.m. The experiment took place in a serene and uninterrupted martial arts gym. Participants entered the martial arts gym, where their height and weight were measured before donning a Polar belt. All participants consistently wore a Polar during the entire data collection process. Heart rate variability data were concurrently gathered for 15 min during a quiet state, 15 min during the GRA protocol, and 15 min during the SR protocol. Subsequent to the GRA and SR protocols, participants promptly completed the BFS Mood Scale. To mitigate any potential sequential effects resulting from the different protocols, the 45 Tai Chi subjects were randomly assigned to two groups for data collection. The ABBA design employed in this study aims to minimize autonomic differences between the two protocols arising from sequential issues.

Group A (n = 23): This group underwent testing first in the GRA protocol and then in the SR protocol.

Group B (n = 22): Conversely, Group B participants were tested initially in the SR protocol and subsequently in the GRA protocol. For a visual representation of the experimental design, please refer to Fig. 1.

Figure 1
figure 1

Schematic diagram of the experimental data collection process.

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Tai Chi exercise protocol

The two distinct Tai Chi protocols employed in this study are as follows: SR protocol: In this protocol, participants executed a sequence consisting of three repetitions of the 24-form Tai Chi routine. GRA protocol: This protocol was further divided into three practice sections, each lasting for 5 min. Basic Movements Section (Gong Fa/Zhan Zhuang): Focused on the development of foundational skills, particularly emphasizing standing pole exercise training. Routines Section: Comprised movements like the "Peng" movement and the 24-form Tai Chi routine. Self-defense Application Training Section: Participants engaged in paired practice, applying Tai Chi self-defense techniques in a cooperative manner. For a visual representation, please refer to Fig. 2.

Figure 2
figure 2

Schematic diagram of the 24-form Tai Chi's gong routine application protocol.

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Evaluation of autonomic activity

Participants ensured optimal conditions by adhering to the following criteria the day before the test:

A minimum of 6 h of uninterrupted sleep. Abstention from smoking, alcohol consumption, staying up late, as well as the use of coffee or stimulant drugs. Participants refrained from eating and maintained emotional stability for at least one hour prior to the test. Autonomic activity was assessed using the HRV method. RR intervals (iRR) were obtained using the Polar Team 2 Heart Rate Monitor. Kubios software was employed to calculate R-R intervals and associated variability from the recorded data. The following time-domain indicators were selected for analysis: The Square Root of The Mean Squared Differences of Successive NN Intervals (RMSSD): Low Frequency Power (LF), High Frequency Power (HF), Low Frequency Power to High Frequency Power ratio (LF/HF). The study standardized LF and HF values as LF (nu) and HF (nu) to facilitate between-group comparisons.

Mindfulness states of Tai Chi practitioners were evaluated using the BFS Mood Scale after GRA and SR protocol. The BFS Mood Scale was developed by Zerssen in 197027. The BFS Mood Scale is a mindfulness measurement tool based on the theory of the two-dimensional components of mindfulness (positivity and negativity)28. The scale assesses changes in the subject's state of mind, prompting them to report their true feelings at the time. The scale comprises eight subscales, including Vitality, Pleasure, Thoughtfulness, Calmness, Anger, Excitability, Depression, and Inactivity. Each subscale comprises five questions, resulting in a total of 40 questions. All questions were randomly mixed and presented, and respondents provided ratings on a 5-point Likert scale, ranging from "not at all" to "completely". The BFS Mood Scale is user-friendly, requiring subjects approximately 5 min to complete. The Chinese version of the BFS Mood Scale was utilized for language consistency, aiming to facilitate subjects' completion. In 1997, the BFS Mood Scale was translated into Chinese, and validity tests were conducted

Conclusion

The findings suggest that the intensity of cardiovascular stimulation during 24-form Tai Chi practice plays a more critical role in influencing autonomic activity compared to psychological factors. Specifically, heart rate levels are higher in the SR protocol than in the GRA protocol. This is accompanied by increased sympathetic activity in the SR protocol and decreased parasympathetic activity. The findings are limited to college students, and more research may be needed to provide support for frail older adults and adults with limited mobility issues. In light of these observations, it is advisable to make thoughtful choices when designing Tai Chi health promotion intervention programs. During the teaching phase, employing the GRA protocol can provide a low autonomic intensity for beginner practitioners to grasp the technical intricacies of Tai Chi. Combining the GRA protocol with the SR protocol allows Tai Chi practitioners to enhance their understanding of both the internal and external dimensions of Tai Chi skills. This approach acknowledges the varying impacts of different Tai Chi methods on autonomic activity and tailors the practice regimen accordingly. In addition, it is recommended that suggest more robust (experimental), larger trials to corroborate the findings.