cardiovascular diseases in the older adults are often associated with perturbed autonomic 
 balance , manifested by an increase in sympathetic modulation , a decrease in parasympathetic 
 modulation or a combination of both1 . in 
 aging , the autonomic control of the cardiovascular system
favours heightened cardiac 
 sympathetic tone with parasympathetic withdrawal , which can magnify the effects of 
 concomitant cardiovascular disease2 . 

studies have shown that parasympathetic control of the heart during exercise is important 
 for cardiac health3 , and long - term 
 physical endurance training increases parasympathetic activity and decreases sympathetic 
 activity in humans at rest3 . aging is often associated with changes in cognitive functioning .
these changes can be 
 normal as in normal aging , or as a result of pathological modification in people with mild 
 cognitive impairment or dementia4 .
much 
 attention has been placed on interventions which attempt to reverse or slow down the 
 progression of cognitive decline in older adults with and without cognitive impairment5 .
recent evidence has shown that exercise may 
 protect older adults against cognitive impairments in aging6 .
, 30 days of wheel - running exercise was found to increase blood flow in the 
 cerebellum , motor cortex , and hippocampus of rats7 . in older adults reaching their retirement age , regular
tai chi ( tc ) is regarded as a mind - body exercise , as its practice requires subjects to be 
  mindful  of the intrinsic energy from which she / he may ultimately perceive greater 
 self - control and empowerment9 .
like other 
 mind - body exercises , such as yoga , qigong and aikido , tc involves meditation , imagery , 
 concentration on the self and diaphragmatic breathing during its practice10 .
a question then naturally arises : is 
 there a difference in the autonomic control of the heart between a mind - body exercise such 
 as tc and a body - focused exercise such as cycling ?
therefore , the first objective of this 
 study was to investigate the effects of tc versus arm ergometer cycling ( ego ) on the 
 autonomic control of cardiac activity
. the effect of mind - body exercise on cerebral 
 oxyhemoglobin level , especially in the prefrontal cortex , may be different from that of 
 body - focused exercises such as ego . therefore , the second objective of this study was to 
 compare the effects of tc and ego on prefrontal cortex activity . to address these two 
 objectives , measurements of heart and brain activities
were conducted before , during , and 
 immediately after exercise for comparison between tc and ego .
a healthy tc master ( age 65  years , 168  cm tall , weighing 56  kg ) was invited to participate 
 in this study .
the tc master had been practicing and teaching tc for more than 20  years .
she 
 signed a written informed consent which was approved by the department of rehabilitation 
 sciences of the hong kong polytechnic university .
the subject attended our laboratory on two separate afternoons at similar times to ensure 
 consistent assessment conditions .
she was asked to perform a 12-form yang 
 style tc routine11 in a sitting position 
 on the first day , and exercised with the arm ergometer ( monark electric ergometer model 
 829e , monark , ab , usa ) in a similar sitting position on the other day . measurement started 
 with the subject sitting quietly for 10  min , followed by 12  min of exercise while sitting , 
 and then another 10  min of quiet sitting .
the intensity during ego cycling was kept at the 
 same level based on the calculated oxygen consumption during the tc practice . both the heart 
 rate variability and
prefrontal oxygenation were measured throughout the 10- , 12- , 
 and10-minute intervals as described as below .
heart rate variability ( hrv ) was measured using an electrocardiogram , and the r - to - r peak 
 intervals were continuously recorded using an rr recorder ( polar rs800 , polar electro ltd . , 

finland ) , attached around the chest , at a sampling frequency of 1,000  hz . pulse signals were 
 transmitted to a polar watch and stored for off - line spectral analysis . to standardize tc 
 and ego exercise intensities , breath - by - breath oxygen consumption , respiratory frequency and 
 tidal volume during the two exercises
were recorded with a metabolic cart ( k4b2 , cosmed , 
 pavona di albano , italy ) which was calibrated prior to data collection .
spectral analysis of hrv is a well - established method for assessing autonomic control of 
 the heart .
power at high frequencies ( hfs ) is considered to indicate 
 parasympathetic control , while power at low frequencies ( lf ) is considered to be an index of 
 sympathetic control .
studies using this method have found that concentration and meditation 
 have significant neuro - physiological effects on autonomic nervous control , causing an 
 increase in parasympathetic tone and a decrease in sympathetic activity13 , 14 .
the brain s prefrontal cortex controls various cognitive functions , including motor 
 planning and delayed response15 , as 
 reflected by neuropsychological tests of its activation such as the continuous performance 
 test16 , and the wisconsin card 
 test17 .
oxygenation of the prefrontal 
 area during exercise can be investigated non - invasively using near - infrared spectroscopy 
 ( nirs ) .
it measures tissue oxygenation through comparing the light absorption spectra of 
 oxygenated hemoglobin ( o2hb ) and deoxygenated hemoglobin ( hhb ) at their specific 
 wavelengths based on the lambert - beer law18 .
nirs was employed in this study to measure the prefrontal cerebral 
 o2hb and hhb levels , and to infer total hemoglobin ( chb ) ( the sum of 
 o2hb and hhb)19 . a niro 200 
 spectroscope ( hamamatsu photonics , japan ) was used with the sampling frequency set at 1  hz . 

analysis of hrv was performed using a short - time fourier transformation ( stft ) of the rr 
 intervals during exercise .
the rr interval signals were transmitted to a computer running 
 polar protrainer 5 software ( polar electro ltd . , oulu , finland ) through an infrared usb 
 adapter .
then the rr 
 intervals were processed using matlab 7.1 software ( the mathworks inc . ,
since the rr intervals were not constant during exercise , stft was 
 employed to calculate the frequency spectrum of the hrv20 , 21 , instead of using the 
 conventional fast fourier transformation ( fft ) spectrum analysis to generate the power 
 spectral density in the hf range ( between 0.15 and 0.4  hz ) and the lf range ( 0.040.15  hz ) . 

the hf and lf power in normalized units ( hfnu and lfnu ) were also 
 calculated , according to the methods recommended by the task force on measurement standards 
 of the european society of cardiology and the north american society of pacing and 
 electrophysiology ( 1996)22 , as 
 percentages of power with respect to total power minus very low frequency power .
the two 
 parameters emphasize controlled and balanced behavior of the two branches of the autonomic 
 nervous system .
the lf / hf ratio , which is commonly regarded as an indicator of 
 sympatho - vagal balance22 , was also 
 computed . for comparison ,
the parameters were averaged every 1  min during exercise and over 
 10  min in the rest and recovery periods .
levels of o2hb and hhb were recorded over the 10  min of rest and then averaged . 

the average was used as the baseline value to normalize the subsequent data recorded during 
 the 12  min of exercise ( averaged over each one minute ) , and during the 10  min recovery which 
 followed .
c statistic 
 analysis23 of oxygen consumption 
 between resting and exercise gave a z value of 4.61 for tai chi and 4.63 for ergometer 
 cycling .
the spectral analysis of heart rate variability showed that the hf power spectrum decreased 
 at the start of both exercises and increased in the recovery phase ( fig .
1.hf power ( a ) and normalized hf power ( b ) during the two exercises .
time  0  
 represents the average value of the 10  min at rest , and  13  the 10-min recovery 
 periods .
hf power ( c ) and normalized hf power ( d ) during the two 12-min exercises . ) .
the between - exercises comparison 
 showed that during tc , the decrease in hf power was less than during ego .
the overall 
 display also shows that during tc , the hf power in normalized units was generally higher 
 than during ego ( fig .
hf power ( a ) and normalized hf power ( b ) during the two exercises .
time  0  
 represents the average value of the 10  min at rest , and  13  the 10-min recovery 
 periods .
hf power ( c ) and normalized hf power ( d ) during the two 12-min exercises . comparing the two exercise periods , hrv during tc had higher hf power than that during 
 ergometer cycling , as shown in fig .
the two figures show the changes during the 
 12-min exercise periods without the baseline and recovery periods .
the lf / hf ratio was higher in ergometer cycling than in tc , especially from the 7th minute 
 onwards ( fig .
time  0  represents the average value of the 
 10  min at rest , and  13  the 10-min recovery periods . ) .
time  0  represents the average value of the 
 10  min at rest , and  13  the 10-min recovery periods .
however , both 
 levels initially decreased , then increased in the later phases of ego exercise ( fig .
left ( c ) and right ( d ) 
 hemispheric o2hb activities during the two conditions .
time  0  represents 
 the average value of the 10  min at rest , and  13  the 10-min recovery periods . ) .
the z values were 4.06 and 3.81 for tc and ego , respectively , based on the c 
 statistic .
the 
 left /right hemisphere difference in o2hb during the two exercises is shown in 
 fig .
3c , d. the figures clearly show that the 
 difference between the exercises was more obvious in the left hemisphere .
o2hb ( a ) and chb ( b ) during the two exercises . left ( c ) and right ( d ) 
 hemispheric o2hb activities during the two conditions .
time  0  represents 
 the average value of the 10  min at rest , and  13  the 10-min recovery periods .
in a cross - sectional study , lu and kuo24 
 observed that experienced tai chi practitioners had higher hf power and lower lf / hf ratios , 
 implying more dominant parasympathetic control of the heart .
their protocol included 20 
 minutes of tai chi , 10  min of warm - up and 10  min of cooling down .
however , they investigated 
 hrv only before and after , not during tai chi practice .
therefore , the behaviors of the 
 sympathetic and parasympathetic systems during tai chi exercise remained unclear . also , 
 there was no control ( body - focused ) exercise to compare the autonomic control of the heart 
 with that of tai chi which has a mind - body component . in this study ,
the tai chi master 
 displayed higher hf power and a lower lf / hf ratio in hrv during tc than during ego performed 
 at a similar exercise intensity , suggesting more parasympathetic control of the heart during 
 tc than during cycling .
dimsdale and mills25 found that 
 meditation could override a powerful adrenergic stimulus ( iosproterenol ) administered 
 through blood infusion .
we theorized that tai chi s mind component might similarly override 
 the tendency of the exercise to tip the sympathetic - vagal balance towards more vagal 
 mediation .
a tc master , who exercises in a meditative manner resulting in relaxation , might 
 raise parasympathetic control of the heart , to dominate that of sympathetic control , in 
 contrast to cycling which has no meditative component .
our results do indeed show that 
 during tai chi practice , the subject appeared to have had greater parasympathetic control of 
 the heart than during cycling performed at a similar intensity .
related to this , a previous study reported that experienced tai chi practitioners with an 
 average of 6.7  years experience had better arterial compliance than older control 
 adults26 .
a randomized clinical trial 
 also found that older adults increased their large and small arterial compliances ( 26.2% and 
 17.9% , respectively ) after performing tai chi training , three sessions per week , for 16 
 weeks27 .
it is our suggestion that the 
 improved arterial compliance after tc training could be due to increased parasympathetic 
 control of the cardiovascular system .
the findings of the present study , suggesting 
 increased parasympathetic modulation of the heart during tai chi , are consistent with the 
 hypothesis of improvement of arterial compliance proposed by previous studies .
however , a 
 prospective study with a large sample of subjects is needed before firm conclusions can be 
 drawn .
timinkul and 
 colleagues18 showed that mild intensity 
 exercise increased oxygenation of the prefrontal area in young subjects while they performed 
 incremental exercise cycling .
furthermore , the intensity of only about 2.5 mets used in this study could be used to 
 increase cerebral oxygenation in older subjects . the prefrontal activity monitored in this study showed that tc and ego elicited different 
 oxygenation despite similar exercise intensities .
the comparatively greater o2hb 
 and chb increases during tc may suggest that the subject had more prefrontal neuronal 
 activation than when cycling .
the physical intensities of both forms of exercise being 
 similar , it could be argued that the additional prefrontal activation during tc resulted 
 from the mental involvement during tc practice .
litscher and colleagues28 found that during qigong , another mind - body exercise , 
 there were increased o2hb and chb levels in the practitioners frontal area even 
 while they were sitting without any physical movement .
however , that study did not involve a 
 physical component and did not use another body - focused exercise for comparison .
the present results demonstrate that , although differences were observed on both sides of 
 the prefrontal cortex , the left prefrontal area showed a more obvious difference between tc 
 and cycling ( fig .
the left prefrontal area 
 was activated more during tc than the right side , especially after the 7th minute ( fig .
the tc in this study involved mainly upper 
 limb activity , like the arm ergometer cycling performed in a similar sitting position .
both 
 exercises were bimanual , so motor arousal could be presumed to be equally distributed on the 
 two sides of the brain .
previous research has proposed that the right brain is responsible 
 for sympathetic control of the heart , while the left side is related to parasympathetic 
 control29 .
the present results which 
 show more activation of the left prefrontal cortex during tc than during ego cycling , may 
 indicate greater parasympathetic control of the heart during tc , as also indicated by the 
 higher hf power and lower lf / hf ratio . however , any direct connection between increased 
 pre - frontal oxygenation during tc practice and dominant parasympathetic control of the heart 
 could not be established in the present investigation .
the findings of the present case study will form the basis for larger scale investigation . 
 if proven effective , mind - body practice could be conducted in different target populations , 
 such as older adults with a history of falls , patients with parkinson s disease , stroke 
 survivors and subjects suffering from cardiopulmonary diseases .
therefore , an exercise 
 regime that enhances parasympathetic activities and simultaneously increases the oxygenation 
 of the brain more than body - focused exercise would be a good choice for physical therapy 
 rehabilitation .
also , tai chi can be practiced anytime and anywhere without the use of 
 equipment .
this might increase the sustainability of the exercise habit and is especially 
 important for older adults in the community where rehabilitation services are often 
 lacking .
first , there was only one female subject participating in 
 this study and she was a master of tc .
therefore , our findings can not be generalized to male 
 subjects or to novice practitioners .
second , although the participant performed the 
 exercises in a quite environment , her mental state was not controlled . in conclusion ,
the present study compared the effects of tc and ego on heart rate 
 variability and concurrent prefrontal lobe activities during these two exercises .
our 
 results suggest that both exercises increase the parasympathetic modulation of the autonomic 
 nervous system and prefrontal lobe activities , with more activity being observed during tc 
 practice .
confirmation these findings in a larger sample , preferably through a prospective 
 study , would indicate tc , a mind - body exercise , may be a better choice than cycling for 
 improving the cardiovascular health and cognitive function of older adults .
 [ purpose ] exercise has been shown to improve cardiovascular fitness and cognitive 
 function . whether the inclusion of mind over exercise would increase parasympathetic 
 control of the heart and brain activities more than general exercise at a similar 
 intensity is not known . 
 the aim of this study was to compare the effects of tai chi 
 ( mind - body exercise ) versus arm ergometer cycling ( body - focused exercise ) on the heart 
 rate variability and prefrontal oxygenation level . 
 [ subjects and methods ] a tai chi master 
 was invited to perform tai chi and arm ergometer cycling with similar exercise intensity 
 on two separate days . 
 heart rate variability and prefrontal oxyhemoglobin levels were 
 measured continuously by a rr recorder and near - infrared spectroscopy , respectively . 
 
 [ results ] during tai chi exercise , spectral analysis of heart rate variability 
 demonstrated a higher high - frequency power as well as a lower low - frequency / high - frequency 
 ratio than during ergometer cycling , suggesting increased parasympathetic and decreased 
 sympathetic control of the heart . also , prefrontal oxyhemoglobin and total hemoglobin 
 levels were higher than those during arm ergometer exercise . 
 [ conclusion ] these findings 
 suggest that increased parasympathetic control of the heart and prefrontal activities may 
 be associated with tai chi practice . having a  mind  component in tai chi could be more 
 beneficial for older adults cardiac health and cognitive function than body - focused 
 ergometer cycling . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION