The Impact of Blood Flow Restriction (BFR) on Exercise and Hemodynamic Responses
Phase: NA
Conditions: Exercise Training, Hemodynamic Response
Sponsor: University of Texas at Austin

Study Protocol and Statistical Analyses 
 
“The impact of blood flow restriction (BFR) on exercise and hemodynamic responses” 
 
NCT03540147 
 
February 7, 2019 
 
 

 
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Study Protocol 
Participants 
A total of 20 young, apparently healthy adults between the ages of 18 and 35 participated 
in this study (Table 1). Exclusion criteria included 1) smoking within the past 6 months; 2) 
uncontrolled hypertension; 3) a history of heart disease, peripheral artery disease, kidney disease, 
or other known cardiovascular problems; 4) a history of diabetes, gout, or other metabolic 
disease; 5) obesity, defined as a body mass index (BMI) >30 kg/m2; 6) major surgeries or 
changes in health within the last 6 months; 7) have been told by physicians to refrain from 
exercise; and 8) vulnerable populations (pregnant women, children, unable to consent, etc.). All 
participants where novice yoga practitioners. The Institutional Review Board reviewed and 
approved this study, and all participants provided written informed consent.  This study meets 
ethical standards enforced by the journal [10].  
Protocols 
Participants visited the laboratory on 2 separate occasions for 2 hours per visit. During 
the first visit, anthropometric measures of height, body weight, and body fatness were taken.  
Prior to all visits, participants fasted for a minimum of 6 hours, abstained from alcohol and 
caffeine for the previous 12 hours, and from strenuous physical activity for the previous 24 hours 
[11].  After 20 minutes of supine rest, baseline measurements consisting of blood pressure, heart 
rate, blood lactate, endothelial function, and arterial stiffness were taken.  
After baseline measurements, a randomized crossover study design was implemented, 
where participants acted as their own control and performed 20 yoga poses for 30 seconds each 
with blood flow restriction (BFR) bands and without (non-BFR) inflation of BFR bands placed 
on the upper thighs (BStrongTm, Park City, Utah). The BFR bands were inflated to the pre-

 
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determined pressures recommended by the manufacturer according to BFR band size (44.5-60 
cm thigh circumference band was inflated to 250 mmHg and 60-78.5 cm thigh circumference 
band was inflated to 300 mmHg; both bands measured 6 cm in width). During the non-BFR 
condition, BFR bands were worn, but the bands were not inflated.  The sequence started with 
taking baseline hemodynamic measurements while standing at anatomical neutral. Following 
baseline, the yoga poses were performed in the following sequential order: 1) Warrior I, 2) 
Warrior II, 3) Reversed warrior, 4) Extended side angle, 5) Forward fold, 6) Halfway lift, 7) 
High plank, 8) Up dog, 9) Down dog, 10) Wide-legged forward fold, 11) Goddess, 12) Crescent 
lunge, 13) Half moon, 14) Chair pose, 15) Mountain pose, 16) Camel, 17) Easy pose, 18) Bridge 
pose, 19) Happy baby, and 20) Savasana [12] (Supplemental Figure).  
The order of these sessions, with inflated and deflated BFR bands, were randomized 
between the visits. Each testing session was separated by at least 2-3 days to control for potential 
fatigue or training effects.  All yoga sessions were led by a certified yoga instructor. Blood 
pressure and heart rate were measured continuously throughout the session using beat-by-beat, 
finger plethysmography (Portapress Finger Plethysmograph, Finapres Medical Systems BV, 
Amsterdam, Netherlands) as previously described [8].  Participants were asked to keep the hand 
with the finger plethysmography at heart level during the entire exercise session. Participants 
performed a familiarization session in order to learn and accommodate minor modifications to 
yoga poses, which restricted the movement of one arm to place the plethysmography at the heart 
level.  Physiocal was turned on during the measurement.  Double products or rate pressure 
products were calculated by systolic blood pressure multiplied by heart rate.  Additionally, 
participants gave a rating of perceived exertion (RPE: the original Borg Scale) that corresponded 

 
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to the perceived difficulty of the exercise task after every 5 yoga postures. Measurements were 
repeated immediately post yoga performance.  
Measurements 
Arterial stiffness was measured noninvasively using the cardio-ankle vascular index 
(CAVI) (Vasera, VS-1500AU, Fukuda Denshi Co., Ltd, Tokyo, Japan) as previously described 
[13, 14]. Blood pressure cuffs were placed on both arms and both ankles for the measurements of 
blood pressure and arterial stiffness. Electrocardiogram electrodes were attached to both wrists 
of the participant. Finally, a heart sound microphone was attached to the sternum of the 
participant between the second ribs to monitor electrocardiogram and phonocardiogram.  CAVI 
score was calculated from vascular length (distance) divided by the time taken from the pulse 
wave to propagate from the aorta to the ankle (calculated from the difference between the aortic 
valve closure sound (taken from the phonocardiogram) and the rise of the ankle pulse wave) 
[14].   
After 20 minutes of supine rest, endothelial function was measured via flow-mediated 
dilation (FMD) technique [15] by measuring the brachial artery’s diameter increase following a 
brief period of occlusion using an automated diagnostic ultrasound system (UNEXEF-38G, 
UNEX Corp., Nagoya, Japan)[16]. A blood pressure cuff was placed on the forearm with the 
proximal edge of the cuff above with the participant’s antecubital fossa and a second blood 
pressure cuff was placed on the contralateral arm for standard blood pressure measurements. 
Two cross-sectional images of the artery were acquired utilizing the automated ultrasound probe 
(equipped with 3 linear-array ultrasound probes with a frequency of 10 MHz) proximal to the 
antecubital fossa. Once a clear cross-sectional image was acquired, a novel stereotactic probe-
holding device with a probe self-adjusted automatically to provide a clear longitudinal image of 

 
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the artery and begin baseline measurements.  Images of the brachial artery were obtained at the 
end of diastole from each of 10 cardiac cycles. The baseline brachial artery diameter was 
calculated by taking the average diameter obtained from the 10 cardiac cycles. Pulsed doppler 
velocity signals were additionally obtained for 10 cardiac cycles at baseline. Following baseline 
metrics, the cuff was inflated to 50 mmHg above resting systolic blood pressure for 5 minutes to 
occlude blood flow. After 5 minutes of occlusion, the cuff was deflated, and both brachial artery 
diameter and blood flow velocity were measured simultaneously and continuously for two-
minutes immediately post occlusion. These obtained digitized images generated the maximum 
diameters of the brachial artery from which the absolute change from baseline and percentage 
brachial FMD was computed using online semi-automatic analysis software provided by the 
machine manufacturer (UNEXEF-38G, UNEX Corp., Nagoya, Japan) [17, 18]. FMD 
measurement was repeated at 1-hour post exercise to evaluate residual hemodynamic effects.  
FMD was calculated as a percent increase in brachial artery diameter at the post-blood flow 
occlusion compared with the pre-blood flow occlusion [15]. 
Blood samples were taken using standard aseptic techniques; sterilizing the finger with an 
alcohol swab, followed by pricking a finger with a lancet and taking a 0.3 µL sample volume of 
blood. The blood sample is collected onto a testing strip that is inserted into a blood lactate meter 
(Blood Lactate Pro, Arkray; Kyoto, Japan).  
Statistical Analyses 
Two-way ANOVA with repeated measures was used to identify significant differences in 
hemodynamic variables during the yoga exercise. The Greenhouse-Geisser correction of degrees 
of freedom was used when sphericity assumptions were violated. Normality and homogeneity 
assumptions were not violated after inspection of skewness, kurtosis and Shapiro-Wilk analyses. 

 
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Cardiovascular responses to each yoga posture must have met the following steady state criteria; 
10 consecutive beat-by-beat measurements where heart rate did not vary by more than 10 beats 
per minute and systolic blood pressure did not vary by more than 20 mmHg to be valid for 
analyses [8]. All yoga postures achieved steady state and peak blood pressure was used for 
analysis. A 2x2 repeated measures ANOVA was used to compare blood lactate concentrations 
between BFR and non-BFR groups. Significance was set at p<0.05, and the data were reported as 
mean±SD.  
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