stress affects all body systems ( e.g. , cardiovascular , respiratory , neuromuscular , and endocrine ) , resulting in psychological and physiological changes . during stress the sympathetic nervous system becomes activated and sympathetic activity increases , resulting in increased hr and changes in hrv [ 15 ] , decreasing peripheral blood flow and renal blood flow , and increased blood pressure and vascular resistance [ 610 ] . moreover , preganglionic nerves of the sympathetic nervous system send signals to epithelial acinar cells in the salivary gland , leading to increases saliva secretion and saa levels [ 1113 ] . furthermore , in the stress condition many sympathetic nerve signals into the kidney increase renal sympathetic nerve activity ( rsna ) , which consequently and complexly leads to a decreased blood circulation to the kidney . increased this also stimulates the rennin - angiotensin - aldosterone system ( raas ) to release renin , because since rennin hydrolyzes angiotensinogen released from the liver and then converts it to angiotensin i ( ai ) . ai is converted to angiotensin ii ( aii ) by angiotensin converting enzyme ( ace ) , which is released from the lung . aii causes glomerular afferent arteriole contraction , resulting in increased bp and decreased blood circulation . in addition , previous studies also found that mental stress can decrease renal blood flow ( rbf ) [ 610 ] . traditional thai massage ( ttm ) is an alternative treatment using the thumbs to apply deep massage , often combined with muscle stretching at the end of the session . the benefits of massage have been found to include increased skin temperature and blood flow [ 1820 ] , decreased anxiety [ 2124 ] , decreased depression , increased rbf , decreased sympathetic activity and increased parasympathetic activity , and decreased cortisol levels . it has been suggested that the mechanism by which massage causes these physiological changes is the gentle mechanical pressure applied during massage , which may increase muscle compliance , blood flow , muscle temperature , and parasympathetic activity , and decrease neuromuscular excitability , anxiety , and stress hormone level , thus , resulting in a relaxation response . although many studies reported the effects of massage on physiological mechanisms , none have explored the effects of massage on plasma renin activity , which may be associated with changes in psychological stress . the current study aimed to determine whether ttm decreases saa levels , increases hrv , increases ans function , decreases stress , and decreases plasma renin activity . this study was a crossover randomized controlled trial , which was approved by the ethics committee of khon kaen university , thailand ( he561485 ) . thirty participants were recruited in this study ; 1 participant dropped out at the beginning of the study because of personal obligations , leaving 29 healthy participants ( male=7 , female=22 ) , average age 35.176.35 years old , and they participated in and completed all procedures . all of the participants had mild stress levels ( 21.721.41 ) as assessed by the suanprung stress test-20 . the participants were advised to refrain from eating , drinking alcohol , smoking , and consuming caffeine for at least 2 hours before participating in this study . the participants were excluded from this study if during the study they had any kind of medication or other medical treatments , moderate to severe of muscle or joint pain , impaired skin sensation or hypersensitivity to massage , history of serious disease that must be treated by a doctor , or who had moderate - to - severe stress recently as assessed by the suanprung stress test-20 , or menopause . twenty - nine healthy participants were randomly allocated into either traditional the thai massage ( ttm ) group or the control ( c ) group , after which they were switched to the other group , with a 2-week wash - out period ( figure 1 ) . they were given a 10-minute mental arithmetic test to induce mental stress before a 1-hour session of ttm or rest . immediately after mental arithmetic and ttm or rest , we measured the participants hr , sdnn , rmssd , hf , lf , lf / hf ratio , ans activity , ans balance status , stress index , stress resistance , mental stress , and pra and saa levels . the participants were asked to spit before assessment in order to get newly - produced saliva . then after chewing cotton wool for 1 minute to induce excretion of saliva , participants put the edge of the test strip ( saliva - collecting paper ) into the mouth , and left it underneath the tongue ( sublingual ) for 2 minutes . after that , the test strip was fit into the handle sleeve and slid into the cocoro meter ( niproco . , the outcome appeared as a numerical display on the screen , with the unit of measurement in ku / l . the participants sat on a comfortable chair with a backrest , with eyes opened and breathing normally throughout the 5 minutes of data collection . the hrv parameters were measured by use of a sa-3000p device ( medicore co. , ltd . hr , sdnn , rmssd , hf , lf , and lf / hf ratio were used to evaluate hrv . ans activity , ans balance status , stress resistance , and stress index were used to reflect ans function and stress , respectively . the participants lay on the bed for 5 minutes , after which 5 ml of blood was drawn from the median cubital vein . the blood sample was delivered for measurement of plasma renin activity and was tested at a standard laboratory center at king chulalongkorn memorial hospital . the participants received a 1-hour session of the ttm or rest in the control experimental room ( 2526c ) . moderate thumb and palm pressure of the ttm was applied along the meridian lines on all parts of the body , including lower limbs , back , neck , head , and upper limbs . the massage was performed in supine , lying on the left side , and lying on the right side ( figure 2 ) . at the end of the massage for each part , the participants had passive stretches for the corresponding muscle groups . in the c group , the participants lay on the bed in supine or side - lying positions , based on their preferences . crossover study design analysis was used to compare the mean within group and between groups . ancova using baseline as covariate was calculated to compare between groups in case of carry over effect ( hr and mental stress ) . this study was a crossover randomized controlled trial , which was approved by the ethics committee of khon kaen university , thailand ( he561485 ) . thirty participants were recruited in this study ; 1 participant dropped out at the beginning of the study because of personal obligations , leaving 29 healthy participants ( male=7 , female=22 ) , average age 35.176.35 years old , and they participated in and completed all procedures . all of the participants had mild stress levels ( 21.721.41 ) as assessed by the suanprung stress test-20 . the participants were advised to refrain from eating , drinking alcohol , smoking , and consuming caffeine for at least 2 hours before participating in this study . the participants were excluded from this study if during the study they had any kind of medication or other medical treatments , moderate to severe of muscle or joint pain , impaired skin sensation or hypersensitivity to massage , history of serious disease that must be treated by a doctor , or who had moderate - to - severe stress recently as assessed by the suanprung stress test-20 , or menopause . twenty - nine healthy participants were randomly allocated into either traditional the thai massage ( ttm ) group or the control ( c ) group , after which they were switched to the other group , with a 2-week wash - out period ( figure 1 ) . they were given a 10-minute mental arithmetic test to induce mental stress before a 1-hour session of ttm or rest . immediately after mental arithmetic and ttm or rest , we measured the participants hr , sdnn , rmssd , hf , lf , lf / hf ratio , ans activity , ans balance status , stress index , stress resistance , mental stress , and pra and saa levels . the participants were asked to spit before assessment in order to get newly - produced saliva . then after chewing cotton wool for 1 minute to induce excretion of saliva , participants put the edge of the test strip ( saliva - collecting paper ) into the mouth , and left it underneath the tongue ( sublingual ) for 2 minutes . after that , the test strip was fit into the handle sleeve and slid into the cocoro meter ( niproco . , ltd . the outcome appeared as a numerical display on the screen , with the unit of measurement in ku / l . the participants sat on a comfortable chair with a backrest , with eyes opened and breathing normally throughout the 5 minutes of data collection . the hrv parameters were measured by use of a sa-3000p device ( medicore co. , ltd . hr , sdnn , rmssd , hf , lf , and lf / hf ratio were used to evaluate hrv . ans activity , ans balance status , stress resistance , and stress index were used to reflect ans function and stress , respectively . the participants lay on the bed for 5 minutes , after which 5 ml of blood was drawn from the median cubital vein . the blood sample was delivered for measurement of plasma renin activity and was tested at a standard laboratory center at king chulalongkorn memorial hospital . the participants received a 1-hour session of the ttm or rest in the control experimental room ( 2526c ) . moderate thumb and palm pressure of the ttm was applied along the meridian lines on all parts of the body , including lower limbs , back , neck , head , and upper limbs . the massage was performed in supine , lying on the left side , and lying on the right side ( figure 2 ) . at the end of the massage for each part , the participants had passive stretches for the corresponding muscle groups . in the c group , the participants lay on the bed in supine or side - lying positions , based on their preferences . the data were presented as mean sd . shapiro - wilk test was used to evaluate for normal distribution . crossover study design analysis was used to compare the mean within group and between groups . ancova using baseline as covariate was calculated to compare between groups in case of carry over effect ( hr and mental stress ) . table 1 shows within - groups comparison , showing that saa was significantly decreased ( p<0.05 ) in the ttm group but not in the c group . sdnn , rmssd , hf , lf , stress resistance , and ans activity were significantly increased ( p<0.05 ) , whereas hr , stress index , psychological stress , and pra were significantly decreased ( p<0.05 ) in both groups . however , low frequency per high frequency ratio ( lf / hf ratio ) and ans balance status were not changed . when comparing the outcomes between groups , we found that only saa was significantly different ( p<0.05 ) and other variables showed no significant differences between the comparison groups ( table 2 ) . stress stimulates sympathetic activity and causes increased hr and hrv changes [ 15 ] . in addition , it can increase blood pressure , increase vascular resistance , decrease renal blood flow [ 610 ] , and saa levels [ 1113 ] . this study showed that ttm can significantly reduce psychological stress , as well as decrease saa levels , increase hrv , increase ans activity , and decrease plasma renin activity ( table 1 ) . salivary glands respond to stress by increasing saliva secretion from stimulation of the sympathetic nervous system . although the decreased saa was also found in the c group , the between - group comparison revealed that the decrease of saa was also significantly different . it is possible that ttm can decrease stress and sympathetic activity and lead to decreased saa levels . previous studies have shown that massage can increase ans activity , decrease sympathetic activity , and increase parasympathetic activity . the results found in the current study , although we used a different type of massage , were in line with those found in previous studies , which can be seen from the decreased hr , and increased sdnn , rmssd , hf , and ans activity . although lf was shown to be significantly increased after ttm , it des not measure sympathetic activity directly , but the increase in lf represents the increased baroreflex function . the lf / hf ratio and ans balance status were not significantly changed , but they were slightly increased after ttm . this could be because both variables increased to maintain the balance between sympathetic and parasympathetic activity . this study found that stress index and psychological stress were decreased and stress resistance was increased after ttm . stress resistance is the adaptability of the body against stress , whereas the stress index is the level of stress in the body . stress affects the renal sympathetic activity , stimulating rennin - angiotensin - aldosterone system ( raas ) to release rennin . renin is an important substrate to increase aii , which causes an increase in blood pressure and decreased blood circulation . the present study found that ttm can decrease stress and sympathetic activity and increase parasympathetic activity , resulting in decreased pra . although many variables were found significantly changed after ttm , only saa was found to be significantly different from the c group . when compared between groups we calculated the sample size from salivary cortisol , which was similar to salivary alpha - amylase , thus , only the saa levels showed a significant difference between the comparison groups . the current study focused on the immediate effects of massage , and we do not know whether long - term and cumulative effects of ttm would alter these parameters . therefore , studies in the future should verify the long - term effects of ttm on hrv , ans function , mental stress , and pra . if ttm has these long - term effects , it may be useful as a complementary therapy for patients who have chronic stress , anxiety , and depressive disorders . the current study has demonstrated that ttm can reduce psychological stress , as indicated by decreased saa levels . we also found that ttm can increase hrv , as indicated by the increase of sdnn , rmssd , hf , and lf . the increase in ans function was indicated by increased ans activity and stress resistance , and decreased stress index and plasma rennin activity .
backgroundstress can cause psychological and physiological changes . 
 many studies revealed that massage can decrease stress . 
 however , traditional thai massage has not been well researched in this regard . 
 the purpose of this study was to investigate the immediate effects of traditional thai massage ( ttm ) on salivary alpha - amylase levels ( saa ) , heart rate variability ( hrv ) , autonomic nervous system ( ans ) function , and plasma renin activity ( pra).material / methodstwenty - nine healthy participants were randomly allocated into either a traditional thai massage ( ttm ) group or control ( c ) group , after which they were switched to the other group with a 2-week wash - out period . each of them was given a 10-minute mental arithmetic test to induce psychological stress before a 1-hour session of ttm or rest.resultswithin-groups comparison revealed that saa was significantly decreased ( p<0.05 ) in the ttm group but not in the c group . 
 hrv and ans function were significantly increased ( p<0.05 ) and pra was significantly decreased ( p<0.05 ) in both groups . however , low frequency per high frequency ratio ( lf / hf ratio ) and ans balance status were not changed . 
 only saa was found to be significantly different between groups ( p<0.05).conclusionswe conclude that both ttm and rest can reduce psychological stress , as indicated by decreased saa levels , increased parasympathetic activity , decreased sympathetic activity , and decreased pra . 
 however , ttm may have a modest effect on stress reduction as indicated by a reduced saa .