Ancient China knowledge is deeply present in its Medicine. Some of its pillars are adequate nutrition, phytotherapy, acupuncture, massage and regular physical exercise. One of these pillars is Qì Gōng.
Qì Gōng is a physical exercise that involves meditation and is widely used for health. With a background from the martial arts, it is known also as an auto healing exercise with three main elements according to Traditional Chinese Me- dicine (TCM): body focus (posture and movement), breathing and mind focus (meditative elements).
Qì Gōng means “vital energy work”, where Qì is everything that controls our body, our vital energy and Gōng is work, the work that might improve and cultivate this energy. It’s understood as a traditional biofeedback therapy and the Qi activation can be reached by breathing control and the achievement of a special mental state  . Wang et al., (2014) divided Qì Gōng in some categories: static, dynamic, internal (nei qi) and external (wei qi) and states that it can be practiced in several ways, for example, standing or seated  .
The autonomic nervous system is divided in 2 parts that act in a balanced way, the sympathetic nervous system and the parasympathetic nervous system. The balance of these systems results in homeostasis  .
As Qì Gōng is an active meditative strategy, it helps to balance the autonomic nervous system and all the structures controlled by it. For example, theautonomic nervous system influences the cardiovascular system in two ways, tonic and reflexively and there are some elements that might interfere positively in this control such as Qì Gōng or negatively as daily stress, posture changes and involuntary breathing control  .
Heart Rate Variability (HRV) assessment helps to understand how the cardiovascular system adapts to the changes caused by the environment, and to mea- sure the autonomic system velocity to detect and respond to unexpected stimuli  .
Autonomic control assessment by HRVin Qì Gōng practice has been made in some studies. But because of different variables considered, different age groups and different measuring techniques, there are several aspects of this phenomenon that need to be further investigated.
The objective of this study is to further understand the effects of Qì Gōng on autonomic control, especially on its sympathetic and parasympathetic system branches, through a systematic literature review.
We searched PUBMED, EBSCO and Science Direct.
In all databases we used the following key terms (MeSH): 1) “Heart Rate Variability”; 2) “Ch'i Kung” OR “Qi Gong” and 3) “Heart Rate Variability” plus “Ch’i Kung” OR “Qi Gong”, all searches were did with a 10 years filter (2006-2016).
After a more detailed investigation, 2 more articles were excluded. The first one mentioned HRV, but didn’t have any results about it and the second one used only HR and not HRV as an assessment tool. Figure 1 below shows the articles search and selection fluxogram.
Of the 5 remaining studies, we found a total number of 334 participants. From the 5 studies, one had only one experimental group of Qì Gōng while the others had two groups, one is experimental and other control group. The 5 studies can be seen in Table 1.
All studies used Internal Qì Gōng. Amongits many types we found the following: Qì Gōng: BāDuànJĭn (8 Pieces of Brocade), Dharma Drum (Dharma drum),
Figure 1. Article search and selection in all database.
Table 1. Articles selected to compose the systematic review. (é= increase; ê = decrease)
Laughing Qì Gōng Program (Smile Qì Gōng), Chinese Qì Gōng (there was no style specification, but it was reported that it was a practice of Qì Gōng in the sitting position) and the Ho-gong (a type created for wheelchair users and elderly people). This type is acombination of some methods such as yi-ging-xi- sueygong (column adjustment method), yang shu sheng (method to nourish vital energy), dao yin shu (method of guidance and leadership) and Tu-na (breathing control method), and this combination of methods was intended to frail peo- ple to be practiced in any place and time with the objective of strengthening the Vital Energy, as well as all the other methods, types and/or styles of Qì Gōng  .
The practice time ranged from 4 to 16 weeks, although we found 3 studies with 12 weeks of practice    used 16 weeks of practice between 30 and 60 minutes. In  there was an acute data collection after 1 hour of meditation, but the required practice time (participant experience) of Qì Gōng to engage in the experiment was around 4 to 12 weeks.
The Qi Gong sessions had at least 30 minutes and a maximum of 60 minutes of duration, with two studies of 30 minutes   . In  this time ranged from 30 to 60 minutes, meanwhile Chang, Tsai and Hsieh (2013) presented a variable time amount: 45 minutes to the group sessions and 60 minutes for the sessions done at home.
Weekly frequency ranged from 3× a week (2 studies)   ; 1 time  , 5 times  and an acute collection  .
The participants of the studies were heterogeneous regarding their ages. There were studies with teenagers (age not defined)  ; adults (29 to 34.2 years)   ; elderly (62.98 or more)  in one study(with elderly people), the main feature was to be in a wheelchair.
When we analyze the HRV results, one study  (using a heart rate monitor, Polar RS 800CX, Polar Finland) with adults (~34.2 years) found no significant difference. They analyzed the RR interval, the very low frequency (VLF), low frequency (LF), high frequency (HF) and Total Power.
In the study of Goshvarpour and Goshvarpour (2013)  , used bispectrum magnitude analysis, estimated through three techniques, tendencious, parametric and direct (FFT). They found variations of different components of HRV in young adults (~29 years) with a significant decrease in the magnitude of the heart rate bispectrum. This type of analysis generates extra data that gives more information than the traditional power spectrum analysis.
That study was reinforced by another research with a meditation technique called Vipassana. The author analyzed LF and HF from adults (~43.8 years) after 10 days of an intensive course of the technique. Normalized HF data was significantly different and the authors believed that happened due to a decrease in LF values instead of an increase of HF itself  .
According to these authors, normalized data represents an advantage because it presents the measurement of the vagal output, not presented by other spectral analysis. These oscilating data (LF increase, HF increase or HF increase due to LF decrease) happens because meditation techniques have a slow breathing pattern that influences HRV components, as described in another study published by Leher (1992)  . Therefore, a careful analysis is needed when pure data is compared to normalized data in situations where the respiratory frequency might change the results  .
HF, LF and the low frequency/high frequency (LF/HF) ratio were analyzed in the teenager group doing the Smile Qi Gong. Although the authors didn’t specify the tool used to analyze this variable, there was a significant difference in the control group, with different results when compared to some other studies from the literature. That probably happened because the control group was submitted to stress relief activities such as reading and writing. Besides, the experimental group suffered cross contamination, they did not comply with the rules of pre- determined rest for the proper measurement of the variable, probably because of inadequate behavior related to their age.
The above results are in opposition with those obtained by  and  , they found gains in the parasympathetic nervous system modulation reflecting in a better HRV in teenagers. In the first study Sharma et al. (2015)  , the better HRV was associated to a larger estrogen concentration. This hormone, according to this study  , increases the parasympathetic system modulation, when female teenagers are compared to their counterparts (male teenagers). In the second study  when teenageathletes from both genders were compared, the difference found was not related to the gender, but to a better parasympathetic modulation imposed by physical training. In another gender and ethnic differences study, HRV was improved in black teenagers, especially those who did moderate cardiovascular activities  .
One of the studies analyzed HRV (BFM 5000 plus) with spectral analysis in the elderly, they analyzed SDNN, total power, HF, LF and the LF/HFratio. They found an increase of SDNN, total power, HF, LF and no significant difference in the LF/HF ratio. These results are in opposition to the findings of another study with Qì Gōng and HRV (presented below).
Elderly individuals that were wheelchair users were also submitted to an adapted form of Qì Gōng, so they could perform the movements. Their HRV was measured by a portable equipment manufactured by DailyCare. No significant differences were found for HRV  .
Lopes et al., (2007)  found in their study that strength training can improve HRV, especially in young people, but that was not seen in the elderly, since variability declines with the physiological process of aging because of depletion of the vagal tonus, increase in the sympathetic activity and the presence of diseases such as hypertension or heart failure.
Jandackova et al. (2016)  corroborates the notion that aging impairs HRV. They show that individuals present a decrease in autonomic control with a considerable reduction of heart rate variability. Therefore, the absence of results with the Qi Gong intervention in HRV is expected since different studies used different strategies with varied magnitudes.
We believe that meditative activities such as Qì Gōng promote changes in the autonomic nervous system (ANS), depending on the level of concentration of the participant and that is improved when it is synchronized to a slow breathing rhythm.
However, because this practice has several types with different forms of Qì Gōng presented in the studies used in this review, HRV analysis can be performed with different equipment, and finally the age differences of the experimental groups in the studies, studies with similar methods are needed to assure the Qì Gōng positive effects in HRV pointed in this review.
We concluded that Qi Gong promotes improvement in some of the Heart rate variability parameters, but there is no evidence to further detail this improvement.
Therefore, we suggest that further studies regarding both, longer time of practice and equal time interval and instruments used to analyze HRV are necessary to confirm such benefits.