The effects of health Qigong Baduanjin on the prevention,treatment, and recovery of COVlD‑19

Yi‑Zhen HAN, Meng‑Wei FU, Zi‑Jie CHEN,Fei‑Hong REN, Dan‑Dan XIE, Jing‑Lei LI,Si‑Yu ZHAO, Qian SHEN

1Department of Nephrology, Dongzhimen Hospital Affiliated to Beijing University of Chinese Medicine, Beijing, China;2Department of Cardiovasology, Guang'anmen Hospital,China Academy of Chinese Medical Sciences, Beijing,China; 3Teaching and Research Office of Huangdi's Internal Classic, Beijing University of Chinese Medicine, Beijing,China; 4Department of Rehabilitation Medicine, School of Acupuncture‑Moxibustion and Tuina, Beijing University of Chinese Medicine, Beijing, China; 5Department of Massage, Dongfang Hospital of Beijing University of Chinese Medicine, Beijing, China

ABSTRACT

To summarize the application and modern studies on health Qigong Baduanjin by domestic and foreign scholars, combined them with clinical practice of mobile hospital in Wuhan, we explore the prevention, treatment, and recovery of Baduanjin in the war against COVID‑19. On the basis of studying ancient classics, such as Huangdi’s Internal Classic, and the concrete exercise methods of Baduanjin, we propose three ideas: prevention before disease onset, promoting healing during illness, and strengthening the body after recovery. We aimed to give full play to Baduanjin in the battle against COVID‑19 to popularize correct prevention and health knowledge for the patients and the healthy as well as to provide a reference for medical workers to use Traditional Chinese Medicine to prevention and treatment.

Keywords: Baduanjin, COVID‑19, Health Qigong, prevention, recovery, treatment

INTRODUCTION

After the first case of COVID-19 appeared in Wuhan, Hubei Province, in December 2019, it just broke out and swept across the country in just 1 month, and its susceptible population was mainly middle-aged and old men.[1]As of February 16, 2020, 68,592 cases have been confirmed,1666 cases have died, and 9,671 cases have been cured.With the deepening of the understanding of the disease and the accumulation of diagnosis and treatment experience,the cure rate is significantly higher than the initial stage of the epidemic. COVID-19 has been cured greatly after the interventional therapy of Chinese medicine. Beijing Ditan Hospital has found that the effective rate of using Chinese medicine plus symptomatic treatment is 87.5%, and the effective rate of the combination of Chinese and Western medicine is 92.3%. The COVID-19 patients in Wuhan mobile hospital were treated with medical treatment. Meanwhile,health Qigong was used as an auxiliary treatment, such as Tai Chi and Baduanjin. In this article, the author will explore the specific roles that Baduanjin can play in the prevention,treatment, and rehabilitation of COVID-19 in combination with its application, modern research, and the characteristics of the epidemic.

BACKGROUND

According to the records of The History of Epidemic Diseases in China, since the Western Han Dynasty, China has experienced 321 epidemics. Traditional medicine, represented by Traditional Chinese Medicine (TCM), has been playing an important role in the prevention and control of each epidemic. As a treasure of traditional medical health culture, health Qigong was established as the 97thsports project by the General Administration of Sport of China in February 2003. As Plain Questions--Ancient Ideas on How to Preserve Natural Healthy Energy said, “there were so-called Zhenren in ancient times grasping the law of nature.They followed the principles of Yin and Yang, inhaling fresh air,cultivating their spirit and keeping their muscles integrated. So their life expectancy was as long as that of the earth and the heavens”. This record is the “dance” created by ancient people to get rid of the pain and the disease. Later, it evolved into the Guiding Technique, which is now health Qigong. San Guo Zhi--A Biography of Hua Tuo recorded Hua Tuo’s understanding of Guiding Technique that “People’s bodies should be exercised,but they should not be tired. If you exercise, you will be able to digest nutrition well, have smooth blood circulation, and be free from diseases, just as the rotating axis of a portal will not rot due to rotation. Therefore, ancient immortals often do exercises such as Qigong, imitating bears hanging branches and harriers looking around, stretching the waist and body, and making joints move, so as to avoid aging.” Hua Tuo paid great attention to strengthening the body by Guiding Technique and invented the famous Wuqinxi (also named five-animal exercises), a kind of health Qigong to benefit future generations. Guiding Technique makes “Qi” more peaceful and makes “body” softer. Through active self-exercise, it can make the bones and tendons soft and the Qi mechanism smooth. It can well stimulate self-conditioning ability, improve immunity, eliminate disease, and prolong life as well. There are nine kinds of specific sports forms in health Qigong, the main sports form is the combination of physical activity, breathing, and psychological regulation, among which Baduanjin is the most popular and has the greatest influence on the development of guiding technique. The strength and time of Baduanjin are suitable for the weak people to exercise at home, so it is loved by the middle-aged and old people. This time, COVID-19 mostly infects middle-aged and old men who are weak and vulnerable to pathogenic Qi. After infection, they have symptoms such as weakness, coughing, headache, body pain, fever, and slimy white greasy fur caused by cold–dampness and deficiency of healthy Qi. Although it mainly invades the lung system, it injures the spleen, stomach, and other organs as well.As Baduanjin is easy to learn, moderate in intensity, recuperate the viscera, dredge the meridians, and so on, it may play an auxiliary role in the treatment of COVID-19.

HEALTH QIGONG BADUANJIN

Historical origin of Health Qigong Baduanjin

The name of Baduanjin (also named eight-section brocade)first appeared in the book Yijianzhi written by Hong Mai in the Northern Song Dynasty. The basic skills were detailed in the book Daoshu compiled by Zeng Yun in the Southern Song Dynasty. In addition, Baduanjin is recorded in the collection of Medical Prescriptions and the Guide Of Lingjianzi to Ziwu. It shows that Baduanjin has been widely spread in the Song Dynasty and has a history of thousands of years. At present,what is widely known is the rhyme (like seven-character poem) of the late Qing Dynasty, including the eight-section movements: holding up your hands to regulate the triple energizer; drawing a bow like shooting a hawk; raising one arm to regulate the spleen and stomach; turning your head back to treat consumptive diseases and injuries; swaying your head and swinging your buttocks to expel the heart-fire;holding your feet by the hands to reinforce the loins and kidneys; clenching your fist to punch with anger to increase the strength; and shaking the spine to help prevent diseases.The word “ba (eight)” of Baduanjin does not refer to a single segment or eight movements, but means that there are many elements in its function, which restrict, contact, and circulate each other. Furthermore, the word “Jin” can also be understood as a collection of single guiding techniques, such as silk brocade, which is a complete set of fitness methods. In the process of training Baduanjin, it is necessary to be “soft and slow, round and coherent; elastic and tight, dynamic and static; spirit and form, and Qi in it.”[2]The theory of Baduanjin is based on the meridian and collateral theory and follows the holistic view. Every rhyme of Baduanjin is related to disease prevention, meridian dredging, and viscera conditioning.The meridians and collaterals run through the whole body,connecting the inside and outside of the human body, the viscera, the limbs, and the organs into an organic whole. If the body’s Yin and Yang are out of balance, the meridians will be blocked, the Qi activities will not be smooth, and the Qi and blood will not be in harmony. Therefore, the meridians and collaterals should be dredged and the Yin and Yang should be reconciled.[3]It is just indicated in Spiritual Pivot--Channels and Collaterals that the channels can determine life and death,treat various diseases, and regulate Xu (deficiency) and Shi (excess). Hence, they must be thoroughly understood.It can be seen that the dredging effect of Baduanjin on meridians and collaterals is the basis and key to its prevention and treatment of diseases.

Modern research

Modern research shows that Baduanjin has a good auxiliary treatment effect on the heart, liver, kidney, diabetes, joint disease, and emotional disease. Zhang and Guo[4]investigated 30 elderly people over 60-year-old who took Baduanjin exercise for 5 months and found that their blood pressure was effectively regulated, their vital capacity, their cardiovascular system, and respiratory system functions were improved, their serum triglyceride and low-density lipoprotein cholesterol levels were significantly reduced, high-density lipoprotein cholesterol levels were increased, and atherosclerosis and cardiovascular system diseases were prevented. In addition,the balance ability and flexibility of the subjects were also significantly improved. He et al.[5]investigated 36 elderly patients with phlegm-dampness constitution who were doing Baduanjin exercise. It was found that Baduanjin could enhance the function of viscera, invigorate Yang and Yin, promote the circulation of Qi and blood, benefit physical and mental health, and foster the transformation of Qi deficiency, Yang deficiency, Yin deficiency, damp heat,blood stasis, and Qi stagnation. Bi[6]observed the effect of Baduanjin on electroencephalography and heart rate variability after 8 weeks of exercise. The results showed that Baduanjin exercise could improve the ability of vagus nerve regulation and enhance the protective effect of the vagus nerve on the heart. In addition, the practice of Baduanjin requires to calm the mind, regulate the breath, eliminate the distractions, and achieve “nothing in the heart, empty and quiet”. Many studies[7-9]show that Baduanjin can play a positive role in reducing tension, anxiety, and melancholy. It has also been improved in hostility, obsession, paranoia, and psychosis. Long-term practice of Baduanjin can promote the development of mental health to a positive aspect.

Lung‑related research

Apart from the above modern research on the heart, kidney and spirit, it is particularly worth mentioning the auxiliary treatment and rehabilitation effect for lung diseases. Chen et al.[10]found that the third section of “recuperation of spleen and stomach by single lifting your hand” method of Baduanjin can improve the quality of life and exercise endurance of the patients with chronic obstructive pulmonary disease (COPD)in the stable stage of lung-spleen Qi deficiency syndrome and reduce the related symptoms of lung-spleen Qi deficiency syndrome. Lei et al.[11]used Baduanjin for 1-year intervention in the rehabilitation process of patients with COPD in stable stage and found that Baduanjin can effectively delay the deterioration of lung function and improve the dyspnea symptoms of patients. Xia et al.[12]applied Baduanjin to pneumoconiosis patients and found that it can increase peripheral resistance and airway internal pressure, avoid premature stenosis and entrapment of small airway when exhaling, promote gas volume removal, significantly improve gas exchange, slow down respiratory frequency, significantly prolong exhalation and inspiratory time, significantly increase alveolar ventilation and gas volume, significantly improve hypoxia state, to improve blood oxygen partial pressure,and improve the lung function of patients. In addition,Tang et al.[13]carried out 8-week Baduanjin exercise on 39 asthmatic patients and found that the asthma control test,life quality score, and 6-min walking distance of the patients were significantly improved. They believed that Baduanjin as a lung rehabilitation exercise method could significantly enhance the asthmatic control level, exercise ability, and quality of life of the patients. All the above studies show that Baduanjin can improve lung function, exercise endurance, and quality of life of patients with lung diseases, especially COPD,pneumoconiosis, and asthma, compared with no exercise or regular exercise.

BADUANJIN’S PREVENTION, TREATMENT, AND REHABILITATION OF COVID‑19

Disease prevention

Through the research of front-line TCM workers, it is found that COVID-19 belongs to the category of epidemic disease,and the average age of patients is about 50 years old, and most of them are men.[14]As Plain Questions--Ancient Ideas on How to Preserve Natural Healthy Energy said, “For a woman, her kidney-qi becomes prosperous and her teeth begin to change at the age of seven. At the age of fourteen, Tiangui begins to appear, conception vessel and thoroughfare vessel are vigorous in function. Then she begins to have menstruation and is able to conceive a baby. At the age of twenty-one, as kidney-qi is in vigor, the wisdom teeth begin to grow and then her body has fully developed. At the age of twenty-eight, her musculature and bone become strong, her hair grows long enough. Her body has reached the summit of development.At the age of thirty-five, Yangming Channel starts to decline,her face begins to wither and her hair starts to lose. At the age of forty-two, as the three Yang Channels are deficient in both blood and Qi, her countenance becomes wane and her hair begins to turn white. At the age of forty-nine, as both the conception vessel and thoroughfare vessel become deficient and menstruation stops, she becomes physically feeble and is no longer able to conceive a baby. For a man, at the age of eight, his kidney-Qi becomes prosperous and his teeth begin to change. At the age of sixteen, as kidney-Qi is abundant and Tiangui occurs, he begins to experience spermatic emission.If he has copulated with a woman at this period, he can have a baby. At the age of twenty-four, his kidney-Qi is full, his musculature and bone become strong, the wisdom teeth appear and the whole body is fully developed. At the age of thirty-two, his musculature and bones have well developed and are very strong. At the age of forty, as kidney-Qi declines,his hair begins to drop and his teeth start to wither. At the age of forty-eight, Yang qi over the upper part of the body collapses, his face starts to wither and his hair begins to turn white. At the age of fifty-six, as liver-Qi declines,his musculature becomes inflexible. With the exhaustion of Tiangui and the reduction of kidney-Qi, his kidney is weakened and his body becomes very weak, his teeth and hair begin to lose.” Spiritual Pivot--Life Span said, “At the age of 40, the five Zang-organs, the six Fu-organs and the twelve channels are all perfectly developed and maintain stable, the muscular interstice begins to become flabby; at the age of 50, the liver-Qi begins to decline, the liver lobes begin to become thin, the bile begins to reduce and the eyes begins to become blurred.sudden occurrence of serious disease,emaciated face, weak channels with insufficient blood, weak muscles, frequent attack by wind and cold, Xu (deficiency)of blood and Qi, obstruction of the channels and vessels,struggle between healthy-Qi and pathogenic factors, and disorders caused by the invasion of pathogenic factors. That is why they die when they are just middle-aged.”

It can be seen that the people who are easy to get COVID-19 are women aged 42 or so and men aged 64 or so. They are suffering from kidney failure, insufficiency of kidney-Qi and kidney essence, yin-yang disharmony, and lack of healthy Qi. Plain Questions--Discussion on Acupuncture Methods said,“If one is not infected when the five kinds of pestilence have occurred, it is due to the fact that he/she has sufficient healthy-Qi inside the body.” Plain Questions--Comments on Febrile Diseases said, “The accumulation of pathogenic Qi means the deficiency of Qi.” Therefore, the Qi of four seasons is easy to attack the human body when it is weak.[15]

Plain Questions--Discussion on Regulation of Spirit According to the Changes of the Four Seasons said, “In ancient times, sages treated disease before it arises instead of the diseases that had already happened.” In the treatment strategy for COVID-19, controlling the source of infection and cutting off the route of transmission can effectively prevent the spread of the epidemic. The state has formulated a series of home-based epidemic prevention measures, the purpose of which is to reduce the possibility of “pathogenic QI infecting people.” “When the sages in ancient times taught the people,they emphasized the importance of avoiding deficiency-evil and thief-wind in good time and keep the mind free from avarice. In this way, genuine-Qi in the body will be in harmony,essence-spirit will remain inside, and diseases will have no way to occur. Therefore people in ancient times all lived in peace and contentment, without any fear. They worked, but never overstrained themselves, making it smooth for Qi to flow. They all felt satisfied with their life.” That is to say, we should resist external evils by avoiding evil spirits, having a certain degree of work and leisure, clearing the mind and having few desires, and being in the peace of mind.[16]In recent years, the concept of “treating disease before it arises” of TCM has been deeply rooted in the people’s mind.Its essence is to enhance the immunity and self-regulation ability of the body and resist the invasion of external evils.Besides diet and nutrition, exercise is also an essential part.[17]Baduanjin, as a typical representative of traditional body-building skills, has been recognized through a large number of clinical practices. It has a good regulatory effect on nerve, cardiovascular, digestive, respiratory, and sports organs, and can also relieve shoulder, waist, and leg pain and fatigue, in particular, the sixth section and the seventh section of Baduanjin. By shaking the body back and forth, two hands from the foot to the gate of life, it can exercise internal Qi,strengthen the spleen and kidney, and has the function of strengthening the body. Moreover, Baduanjin is also a kind of aerobic exercise with low and medium intensity. It has high safety, which is not limited by the venue, equipment, weather and environment, and easy to learn. It is suitable for ordinary people, especially the middle-aged and old people, to exercise at home and strengthen their physique and immunity.

Disease recovery

According to the Guidelines on the Novel Coronavirus-Infected Pneumonia Diagnosis and Treatment (Trial Version 5), the clinical treatment period of COVID-19 can be divided into initial,middle, critical, and convalescent.[18]In the early stage, the TCM syndrome type is mainly cold–dampness attacking the lung, and the recommended prescription is the addition and subtraction of Membrane-Source-Opening Beverage;in the middle stage, the TCM syndrome type is mainly epidemic toxin blocking the lung, and the recommended prescription is the addition and subtraction of Ephedra,Apricot Kernel, Gypsum, and Licorice Decoction; in the severe stage, the TCM syndrome type is mainly internal blockage and external collapse, and the recommended prescription is the addition and subtraction of Ginseng and Aconite Decoction with Liquid storax Pill or Peaceful Palace Bovine Bezoar Pill; in the recovery stage, the TCM syndrome type is mainly lung–spleen Qi deficiency, and the recommended prescription is Six Gentlemen Decoction. According to TCM,the disease is located in the lung and spleen, and the disease is characterized by dampness, toxin, stasis, and closeness.The treatment principle and method are mainly to repel foulness, resolve turbidity and remove dampness with aroma,to eliminate pathogenic factors as the first meaning, and to clear damp–heat and to disseminate Qi dynamic as the key.[19]Disseminating and facilitating Qi dynamic is the key to the treatment, and “the lung is hidden on the right” in Plain Questions--Discussion on the Contraindication of Needling Therapy,the lung is the key to the treatment, management, and regulation, which plays an important role in regulating the ascending and descending of Qi mechanism. The above views not only guide clinical medication but also play a certain role in the selection of correct self-supporting exercise methods.For the early- and middle-stage patients, the disease is in the development stage, and the treatment purpose is to alleviate the clinical symptoms as soon as possible and avoid the development to the severe stage. At this time, it is mainly to eliminate pathogenic factors, which will inevitably hurt the healthy Qi. However, if too many drugs are used in the prescription to strengthen the healthy Qi, it will promote the evil Qi. Therefore, it is a good way to improve the healthy Qi by practicing Baduanjin. In the early and middle stage of COVID-19, In addition to cough, expectoration, dry throat and other respiratory symptoms, fever, tiredness and fatigue, chest depression and shortness of breath, distention,constipation or loose stools, greasy fur and slippery pulse are often seen, which have the symptoms of damp toxin and stagn ation of Qi. At this time, practicing Baduanjin can not only relax the meridians but also activate the collaterals and relieve the pain of the whole body; the most important thing is to coordinate Qi dynamic. For example, the first form of Baduanjin can adjust the upper, middle, and lower energizer and coordinate Qi dynamic, in addition, there is a saying in Plain Questions--Discussion on the Secret Cannons Stored in Royal Library “Sanjiao (triple energizer) is the organ similar to an official in charge of dredging and is responsible for regulating the water-passage in the body,” unblock triple energizer can also help smooth the water channel, which is conducive to the discharge of dampness from urine. From the perspective of modern medicine, the first section of baduanjin strengthens the extension of limbs and trunk,which can affect the redistribution of blood flow in chest and abdomen, is conducive to lung expansion, promote deep breathing, increase lung capacity, and is also beneficial to the treatment of pneumonia. The second section of “left and right drawing the bow like shooting an eagle” will expand the chest and shoulders to do more in place and pay attention to the traction of the index finger, emphasizing the regulation of the lung meridians. As Introduction to Medicine stated, “although Baduanjin can promote Qi and blood circulation, people with weak middle energizer and fire should not exercise”.Therefore, those patients with a severe stage of depressed heat should not practice Baduanjin by themselves due to the increasing risk of heat accumulation. For the patients in the recovery period, it is the best way to “protect stomach Qi and body fluid”, because spleen and stomach, which are the source of life and nutrition and the hinge of Qi ascending and descending, play important roles in the transportation of water and grain essence. At this time, the weakness of the spleen and stomach should be mainly treated based on strengthening the spleen, supplemented by eliminating pathogenic factors, to avoid decline of healthy Qi to eliminate pathogenic Qi. As Treatise on the Three Categories of Pathogenic Factors and Prescriptions said, after being ill, eating or working hard more than before will make one’s illness aggravate and not help one’s recovery, at this time, the third and fourth sections of Baduanjin should be practiced in combination with the use of Chinese herbs dangshen, Baizhu, Fuling,and Chenpi, which can strengthen the spleen and stomach,helping the spleen to move healthily and the stomach to receive food to digest, and promote the Qi and blood transformation of middle energizer to strengthen the body.

Rehabilitation

According to news reports, recently, the prevalence rate of patients with COVID-19 has become higher and higher.The cured patients have experienced this pneumonia,and their respiratory symptoms and systemic symptoms have almost disappeared. However, there are still some damages to the lung system, so the recovery of pneumonia has attracted more and more attention. The rehabilitation of pneumonia is similar to other lung diseases. It refers to the lung rehabilitation program, which is a comprehensive rehabilitation program with sports rehabilitation as the core, including health education, nutrition intervention,psychological intervention, and respiratory physical therapy.[20]However, it is impossible to carry out such a pulmonary rehabilitation plan in the light of the current epidemic trend and medical resources, although the program is very perfect due to the high workforce and equipment costs and the designated exercise locations. Therefore,finding the appropriate alternative is an important problem to be solved in the current study of COVID-19. From the perspective of the rehabilitation effect of Baduanjin in lung diseases,[10-13]Baduanjin exercise can effectively improve lung ventilation and lung function and improve exercise ability and quality of life, and moreover, it belongs to low-intensity aerobic exercise. The action essentials include breathing and exhalation and inhalation, which do not occupy a large area and do not need auxiliary equipment. In general, Baduanjin is an ideal alternative exercise for comprehensive rehabilitation program. After the recovery of pneumonia, suffering from the deficiency of both Qi and Yin after fever, there is an image of deficiency fire disturbing the heart spirit of the patients. It is necessary to boost Qi and nourish Yin and practice the last four sections of Baduanjin. These four-section movements involve the heart and kidney, mainly regulating the essence,Qi and spirit, playing the functions of promoting heart–kidney interaction, benefiting Qi and nourishing Yin, and calming the heart and tranquilizing the mind. It is expected to alleviate the deficiency of Qi and Yin in the patients after the pneumonia is cured, promote the repair of lung injury through rehabilitation exercise, and turn to the healthy people as soon as possible. Especially in the final section,it is not just on tiptoe. Spiritual Pivot--Normal and Abnormal Flow of Channel-Qi and Heavy and Emaciated Physique said, “The three Yin Channels of the hand run from the Zang-organs to the hand; the three Yang Channels of the hand run from the hand to the head. The three Yang Channels of the foot run from the head to the foot; the three Yin Channels of the foot run from the foot to the abdomen.” It can be seen that the foot is the intersection of the three Yin and three Yang Channels of the foot. On the basis of breathing, this action can stimulate the three Yin and three Yang Channels of the foot to regulate the corresponding viscera, while the action of heel vibration can stimulate the spine and the Du-meridian to unblock the Qi and blood of the viscera and meridians of the whole body.

SUMMARY AND PROSPECT

At present, COVID-19 is in the effective control stage. The newly diagnosed cases show a continuous downward trend,but the war on prevention and control of the epidemic is not over. Learning from the Huangdi’s Internal Classic and other ancient medical books, we should take the performance of Chinese medicine in the prevention and treatment of pestilence as an opportunity to further explore the role of Baduanjin in preventing and curing COVID-19 in TCM.The research shows that Baduanjin has therapeutic and regulatory effects on cardiovascular system, respiratory system, urinary system, and endocrine system diseases, and has the function of prevention, treatment, and rehabilitation.In the prevention of COVID-19, Baduanjin can be used as a healthy way to enhance the healthy life of the healthy people,mainly in the sixth section and the seventh section. In the aspect of auxiliary treatment, Baduanjin can be used as the first choice of self-care and body building for patients in the early, middle, and recovery stages. The first and second sections can increase vital capacity and lung function. The third and fourth sections can help to strengthen the spleen and stomach and generate Qi and blood. The fourth section can promote the patient’s recovery. However, Baduanjin exercise should not be carried out in the severe stage to prevent the aggravation of heat accumulation. In the aspect of rehabilitation, Baduanjin can be a reasonable substitute for comprehensive rehabilitation program because of its effectiveness in the rehabilitation of pulmonary diseases.The latter four sections can benefit Qi and Yin, dredge three Yin and three Yang channels of the foot, clear the whole body organs, channels, and blood, which is conducive to the rehabilitation of the pulmonary system. On the basis of the above exploration, combined with the clinical practice of mobile hospital in Wuhan, it is suggested that Baduanjin can play three important roles in COVID-19, i.e., prevention before disease onset, promotion of recovery after disease,and strengthening the body immunity after recovery. It is hoped that the innovative application of fitness skills in the current era can provide more traditional medical prevention and treatment ideas for TCM workers engaged in the front line of epidemic prevention.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.