J Exerc Nutrition Biochem. 2018;22(2):007-011, http://dx.doi.org/10.20463/jenb.2018.0010
30
Physical Activity and Nutrition. 2020;24(2):030-037, http://dx.doi.g/1.20463/pan.2020.0012
30
Muscle oxygenation, endocrine and 
metabolic regulation during low-
intensity endurance exercise with 
blood flow restriction
1. Graduate school of Sport and Health Science, Ritsumeikan University, Shiga, Japan 
2. Department of Physical Education, Hanyang University, Seoul, Korea
3. Physical Activity and Performance Institute (PAPI), Konkuk University, Seoul, Korea
4. Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan
5. Department of Sports Science, Japan Institute of Sports Sciences, Tokyo, Japan
6. Research Center for Urban Health and Sports, Osaka City University, Osaka, Japan
[Purpose] The present study investigated the effect of 
endurance exercise with blood flow restriction (BFR) 
performed at either 25% maximal oxygen uptake (V
3
O2 
max) or 40% V
3
O2 max) on muscle oxygenation, ener-
gy metabolism, and endocrine responses.
[Methods] Ten males were recruited in the present 
study. The subjects performed three trials: (1) endur-
ance exercise at 40% V
3
O2 max without BFR (NBFR40), 
(2) endurance exercise at 25% V
3
O2 max with BFR 
(BFR25), and (3) endurance exercise at 40% V
3
O2 max 
with BFR (BFR40). The exercises were performed for 
15 min during which the pedaling frequency was set 
at 70 rpm. In BFR25 and BFR40, 2 min of pressure 
phase (equivalent to 160 mmHg) followed by 1 min 
of release phase were repeated five times (5 × 3 min) 
throughout 15 minutes of exercise. During exercise, 
muscle oxygenation and concentration of respiratory 
gases were measured. The blood samples were col-
lected before exercise, immediately after 15 min of ex-
ercise, and at 15, 30, and 60 minutes after completion 
of exercise.
[Results] Deoxygenated hemoglobin (deoxy-Hb) level 
during exercise was significantly higher with BFR25 
and BFR40 than that with NBFR40. BFR40 showed 
significantly higher total-hemoglobin (total-Hb) than 
NBFR40 during 2 min of pressure phase. Moreover, 
exercise-induced lactate elevation and pH reduction 
were significantly augmented in BFR40, with concom-
itant increase in serum cortisol concentration after ex-
ercise. Carbohydrate (CHO) oxidation was significantly 
higher with BFR40 than that with NBFR40 and BFR25, 
whereas fat oxidation was lower with BFR40.
[Conclusion] Deoxy-Hb and total Hb levels were sig-
nificantly increased during 15 min of pedaling exercise 
in BFR25 and BFR40, indicating augmented local 
hypoxia and blood volume (blood perfusion) in the 
muscle. Moreover, low-and moderate-intensity exercise 
with BFR facilitated CHO oxidation.
[Key words] low-intensity exercise, blood flow restric-
tion, muscle oxygenation, endocrine response, energy 
metabolism
 
 
Received: 2020/06/13, Revised: 2020/06/24,
Accepted: 2020/06/26, Published: 2020/06/30
©2020 Hyejung Hwang et al.; Licence Physical Activity and 
Nutrition. This is an open access article distributed under 
the terms of the creative commons attribution license (http://
creativecommons.org/licenses/by/2.0), which permits unre-
stricted use, distribution, and reproduction in any medium, 
provided the orginal work is properly cited.
*Corresponding author : Kazushige Goto
Graduate school of Sport and Health Science, Ritsumeikan 
University, Shiga, Japan.
Tel: +81-77-599-4127 / Fax: +81-77-599-4127
E-mail: kagoto@fc.ritsumei.ac.jp
©2020 The Korean Society for Exercise Nutrition
OPEN ACCESS
http://dx.doi.org/10.20463/pan.2020.0012
2020;24(2):030-037
INTRODUCTION
In traditional training procedures aimed to increase muscular 
strength and muscle hypertrophy, exercise intensity above at least 
70% of one repetition maximum (1RM) is commonly recommend-
ed1 However, high-intensity exercise entails the risk of injury due to 
excessive stress on muscle joints as well as connective tissues in un-
trained or older people. In contrast, low intensity exercise (e.g., 20% 
of 1RM) with blood flow restriction (BFR) has beneficial effects even 
with short periods of training2-4. In particular, resistance exercise with 
BFR is effective in improving muscle strength and muscle hypertro-
phy5-8. 
Exercise with BFR augments local hypoxia in muscle. The low-
ered muscle oxygenation during exercise is expected to elicit erythro-
poiesis with subsequent increases in oxygen transport capacity9, cap-
illary density, mitochondrial biosynthesis, and myoglobin level in the 
tissues10-11. These cascades are stimulated by increased expression of 
hypoxia-inducible factor-1 (HIF-1) and vascular endothelial growth 
factor (VEGF), which are two major factors involved in angiogene-
sis12. 
Several studies have shown that low-intensity endurance exercise 
(30-40% V. O2 max) with BFR increases oxygen uptake, heart rate, 
and metabolite levels during and after exercise compared with nor-
mal exercise without BFR13-15. However, the influence of endurance 
exercise with BFR and the difference in effects with respect to low 
and extremely low intensity exercise on muscle oxygenation and 
metabolic regulation is currently unknown.
Therefore, the purpose of the present study was to investigate the 
effects of endurance exercise with BFR performed at 25% V. O2 max 
or 40% V. O2 max on muscle oxygenation, energy metabolism, and 
endocrine responses.
Hyejung Hwang1,2,3 / Sahiro Mizuno4 / Nobukazu Kasai5 / 
Chihiro Kojima5 / Daichi Sumi6 / Nanako Hayashi6 / Kazushige 
Goto6**
Physical Activity and Nutrition. 2020;24(2):030-037, http://dx.doi.org/10.20463/pan.2020.0012
31
Muscle oxygenation, endocrine and metabolic regulations during exercise with blood flow restriction
METHODS
Subjects
Ten males (mean± standard deviation [SD] age: 24.7 ± 
2.1 years, height: 171.2 ± 5.7 cm, and body weight: 68.0 
± 7.8 kg) were recruited for the present study. They were 
healthy and had regular physical activity (few days/week, 
e.g., resistance exercise, endurance exercise). However, 
none of the subjects were involved in any training pro-
gram at the start of the study. All subjects were explained 
the purpose of experiment, procedures, and the potential 
risks of the study. A written informed consent was sub-
sequently obtained from each participant. The present 
study was approved by the Ethics Committee for Human 
Experiments at Ritsumeikan University.
Experimental design
All subjects visited our laboratory four times during 
the experimental period. At the first visit, an incremental 
pedaling test was conducted to assess maximal oxygen 
uptake (V. O2 max) using an ergometer (Aerobike 75XLIII; 
Konami Corporation, Tokyo, Japan). From second through 
fourth visits, three experimental trials were performed in 
a random order. The three trials consisted of endurance 
exercise at 40% V. O2 max without BFR (NBFR40), endur-
ance exercise at 25% V. O2 max with BFR (BFR25), and 
endurance exercise at 40% V. O2 max with BFR (BFR40). 
At least 7 days were prepared among trials.
For BFR25 and BFR40, specially designed tourni-
quets (E20 Rapid Cuff Inflator and Rapid Version Cuff, 
Hokanson, USA) were used to apply pressure during 
exercise, and the tourniquets were inflated at 160 mmHg 
pressure. Necessary information to accustom the subjects 
with the device was shared during the preliminary ses-
sion. The tourniquet was placed at the proximal site of 
the middle thigh, both legs.
Blood flow restriction and exercise protocols
The tourniquet was designed to be 11 × 85 cm wide. 
It was used in conjunction with a rapid cuff inflator. The 
air inflator was controlled to maintain a stable level of 
required pressure (160 mmHg) during the pressure phase. 
Based on previous studies, we had set up 15 min pedal-
ing exercise with a BFR protocol using an ergometer4,32. 
During the 15 min exercise in each trial, the pedaling fre-
quency was set as 70 rpm. In BFR25 and BFR40, 2 min 
of pressure phase (equivalent to 160 mmHg) followed 
by 1 min of release phase were repeated five times (5 × 
3 min) throughout the exercise. In NBFR40, the subjects 
wore a tourniquet, but no pressure was applied through-
out the exercise (Fig. 1). 
Muscle oxygenation
During exercise, the muscle oxygenation level in the 
vastus lateralis muscle was evaluated noninvasively using 
near infrared spectroscopy (NIRS) (Hb14-2, Astem Co., 
Ltd. Kanagawa, Japan). The probe emitted two different 
wavelengths from the LED and photo diode, and detected 
the light transmitted through the body with the help of the 
light receiving element. The probe was placed on the right 
vastus lateralis (VL) muscle (at midpoint between the 
greater trochanter and lateral condyle of the femur), and 
the sampling rate was 10 Hz. The data were expressed as 
relative values to the baseline values obtained during rest. 
The oxygenated-hemoglobin (oxy-Hb), deoxygenated 
hemoglobin (deoxy-Hb) and total hemoglobin (total-Hb) 
levels were determined.
Respiratory variables
Respiratory samples were collected using breath by 
breath method and analyzed using an automatic gas ana-
lyzer (AE300S, Minato Medical Science Co., Ltd., Tokyo, 
Japan) to determine V. O2, carbon dioxide output (V. CO2), 
minute ventilation (VE), and the respiratory exchange ra-
tio (RER). The carbohydrate and fat oxidation rates were 
also calculated from V. O2 and V. CO2 using the following 
equations16. The collected data were averaged every 30 s.
Figure 1. Exercise protocol with or without BFR
Physical Activity and Nutrition. 2020;24(2):030-037, http://dx.doi.org/10.20463/pan.2020.0012
32
Muscle oxygenation, endocrine and metabolic regulations during exercise with blood flow restriction
Exercise energy metabolism equations: 
CHO oxidation(g/min) = 4.210 × V. CO2 −2.962 × V. O2
FAT oxidation(g/min) = 1.695× V. O2 −1.701× V. CO2
EE(kcal/15min) = 4.07×CHO oxidation + 9.75×FAT oxidation
 
Blood sampling and analysis
Subjects arrived at the laboratory at approximately 
8:00 AM following an overnight fast (at least 10 h after 
the previous meal). They rested about 20 min before the 
first blood collection. After rest, a 22-gauge polyethylene 
catheter was inserted into an antecubital vein and base-
line blood sample was obtained. After exercise, subjects 
rested on the chair for an hour for blood collection. Blood 
samples were collected before exercise, immediately after 
15 min of exercise, and at 15, 30, and 60 min after com-
pletion of exercise. Blood glucose and lactate concentra-
tions were measured using a glucose analyzer (FreeStyle, 
Nipro Co., Osaka, Japan) and a lactate analyzer (Lactate 
Pro, Arkray Co., Kyoto, Japan) immediately after blood 
collection. The serum samples were obtained after 10 min 
of centrifugation at 4 ºC, and these samples were stored at 
-80 ºC until analysis. Serum growth hormone (GH), corti-
sol and myoglobin (Mb) concentrations were measured at 
a clinical laboratory (SRL, Inc., Tokyo, Japan). Heparin 
syringes (2.5 mL) were used to collect blood samples for 
determination of blood gas and electrolyte levels. From 
obtained blood samples, blood pH, HCO3−, base excess 
(BE), partial pressure of oxygen (pO2), partial pressure of 
carbon dioxide (pCO2), and sodium (Na+) and potassium 
(K+) concentrations were measured using an automatic 
blood-gas analyzer (OPTI CCA TS, Sysmex Co., Hyogo, 
Japan). Blood gas and electrolyte analyses were per-
formed immediately after blood collection.
Statistical analysis
All data are expressed as means ± SD. Time-dependent 
changes in variables were analyzed using two-way re-
peated measure analysis of variance (ANOVA) to confirm 
significant interaction (trial × time) and main effects for 
trial and time. When a significant interaction (time × trial) 
or main effect was detected, a post-hoc Tukey test was 
performed to identify differences. A P-value < 0.05 was 
considered to indicate statistical significance.
RESULTS
Muscle oxygenation
Figure 2 shows the relative changes in the variables 
of muscle oxygenation during 15 min of exercise. Oxy-
Hb did not show a significant interaction (trial × time, 
p=0.83). Moreover, significant main effects of trial 
(p=0.24) and time (p=0.24) were not noted. The oxy-Hb 
level rapidly reduced during the pressure phase in BFR40, 
while NBFR40 revealed a slight increase in the over oxy-
Hb level during the 15-min exercise session. Deoxy-Hb 
showed a significant interaction (trial × time, p<0.001), 
and the main effects of time (p<0.001) were noted. Al-
though a marked increase in the deoxy-Hb levels were 
noted in during the pressure phase when exercise was 
performed with BFR (for the BFR25 and BFR40 trials), 
this decrease rapidly recovered during the subsequent re-
lease phase (1 min). In contrast, NBFR40 revealed slight 
elevation over 15 min of exercise.  Total Hb showed a 
significant interaction (trial × time, p<0.001), and the 
main effects of time (p<0.001) were noted. The total-Hb 
levels increased during the pressure phase when exercise 
was performed with BFR (for the BFR25 and BFR40 tri-
als), with a decrease in the levels during the subsequent 
release phase. In the NBFR40 trial, the total-Hb level 
gradually increased during the 15-min exercise session. 
Figure 3 presents the averaged muscle oxygenation 
variables during the pressure phase (2 min) and release 
phase (1 min) of the 15-min exercise session. The oxy-
Hb level was significantly lower during the pressure phase 
in the BFR40 trial (p<0.05, Fig. 3A), while no significant 
difference was noted during the release phase. Particularly, 
the deoxy-Hb level was significantly increased during the 
pressure phase in the BFR25 and BFR40 trials. Further-
Figure 2. The percent changes of muscle oxygenation vari-
ables during exercise in the NBFR40, BFR40 and BFR25 
every 5 s.
(A) : The changes of oxygenated hemoglobin during exercise 
in the NBFR40, BFR25 and BFR40. (B) : The changes of 
deoxygenated hemoglobin during exercise in the NBFR40, 
BFR25 and BFR40.  (C) : The changes of total hemoglobin 
during exercise in the NBFR40, BFR25 and BFR40 trials.
Physical Activity and Nutrition. 2020;24(2):030-037, http://dx.doi.org/10.20463/pan.2020.0012
33
Muscle oxygenation, endocrine and metabolic regulations during exercise with blood flow restriction
Figure 3. The percent changes of muscle oxygenation variables during 2 min pressure and 1 min release phase of 15min exercise in 
NBFR40, BFR25 and BFR 40.
* p<0.05 between trials
Physical Activity and Nutrition. 2020;24(2):030-037, http://dx.doi.org/10.20463/pan.2020.0012
34
Muscle oxygenation, endocrine and metabolic regulations during exercise with blood flow restriction
more, increased deoxy-Hb levels were noted during the 
release phase in the BFR40 trial (p<0.05, Fig. 3B). The 
total-Hb level significantly increased during the pressure 
phase in the BFR40 trial. During the release phase, the 
total-Hb level was significantly lower in the BFR25 trial 
than in the NBFR40 and BFR40 trials (p<0.05, Fig. 3C).
Blood variables
Table 1 presents the changes in the blood variables before 
exercise and during the 60-min post-exercise period. The 
blood glucose, HCO3
−, pO2, pCO2, Na
+ and K
+ concen-
trations did not differ significantly at any time point among 
the three trials. However, the blood lactate concentrations 
significantly increased after exercise only in the BFR40 trial 
(main effect for time, p<0.05), whereas a significant change 
was not observed over time in the NBFR40 and BFR25 
trials. Immediately after exercise, the blood pH was sig-
nificantly lower in the BFR40 trial than in the NFR40 and 
BFR25 trials. A significantly lower blood base excess was 
noted immediately after the 15-min exercise session in the 
BFR40 trial than in the BFR25 and NBFR40 trials.
Serum GH, cortisol and myoglobin
Figure 4 presents the changes in the serum GH, cortisol 
and myoglobin concentrations. After exercise, the serum 
GH concentrations tended to be higher in the BFR40 trial 
than in the BFR25 and NBFR40 trials. However, there was 
no significant interaction (trial × time, p=0.07) or main 
effect for trial (p=0.17, Fig. 4A). The serum cortisol con-
centration showed a significant interaction (trial × time, 
p<0.001), and the main effects of trial (p<0.001) and time 
(p<0.001) were noted. Moreover, serum cortisol concen-
trations were significantly higher in the BFR40 trial than 
in the BFR25 and NBFR40 trial immediately after exercise 
and at 15 and 30 min after exercise (p<0.05, Fig. 4B). The 
serum myoglobin concentration showed a significant inter-
action (trial × time, p<0.001), and the main effect of time 
(p<0.001) was noted. In the BFR40 trial, the serum myo-
globin concentration 60 min after the exercise session was 
significantly higher compared to that in the NBFR40 trial 
(p<0.05). However, no significant difference was observed 
between the NBFR40 and BFR25 trials (Fig. 4C).
 
Energy metabolism during exercise
The averaged CHO and fat oxidation during the 
15-min exercise session are presented in Fig. 5. CHO 
oxidation was significantly higher in the BFR40 trial 
than in the BFR25 and NBFR40 trials. Moreover, no 
significant difference was observed between the BFR25 
and NBFR40 trials, although exercise intensity was dif-
ferent (25% V. O2 max for BFR25 and 40% V. O2 max for 
NBFR40, Fig. 3A). Fat oxidation was significantly lower 
in the BFR25 and BFR40 trials than in the NBFR40 
trial. Furthermore, the lowest fat oxidation value among 
Variable
Trials
Pre
Post-exercise (min)
0
15
30
60
Glucose 
(mmol/L)
NBFR40
88.8 ± 3.9
81.8
85.0 ± 5.1
87.4 ± 4.7
83.1 ± 5.3
BFR25
88.1 ± 4.8
86.8 ± 5.1
86.3 ± 3.9
85.6 ± 5.2
87.1 ± 5.5
BFR40
89.2 ± 8.0
89.3 ± 10.0
94.3 ± 10.6
90.6 ± 9.7
88.9 ± 7.2
Lactate 
(mmol/L)
NBFR40
1.1 ± 0.3
1.5 ± 0.4
1.1 ± 0.2
1.1 ± 0.3
1.3 ± 0.2
BFR25
1.3 ± 0.31
2.0 ± 0.5
1.5 ± 0.3
1.3 ± 0.3
1.4 ± 0.3
BFR40
1.3 ± 0.3
5.2 ± 1.5 *#†
3.1 ± 1.0 *#†
2.3 ± 0.5 *#†
1.7 ± 0.4
pH
NBFR40
7.41 ± 0.01
7.41 ± 0.02
7.42 ± 0.01
7.42 ± 0.01
7.41 ± 0.02
BFR25
7.42 ± 0.02
7.40 ± 0.02
7.42 ± 0.02
7.41 ± 0.01
7.41 ± 0.03
BFR40
7.41 ± 0.02
7.36 ± 0.05*#†
7.39 ± 0.03
7.42 ± 0.04
7.41 ± 0.02
HCO3-  
(mmol/L)
NBFR40
27.3 ± 2.0
27.3 ± 1.8
27.5 ± 1.6
27.5 ± 1.3
26.4 ± 6.6
BFR25
27.2 ± 1.3
26.6 ± 1.7
26.1 ± 1.9
27.3 ± 1.3
27.5 ± 1.3
BFR40
26.8 ± 1.7
23.0 ± 2.2
23.8 ± 2.7
25.2 ± 2.5
27.1 ± 1.8
Base Excess 
(mmol/L)
NBFR40
2.3 ± 1.8
2.1 ± 1.6
2.6 ± 1.3
2.7 ± 0.9
2.9 ± 1.3
BFR25
2.3 ± 1.4
1.4 ± 1.7
1.4 ± 1.7
2.3 ± 1.1
2.4 ± 1.0
BFR40
1.9 ± 1.4
-2.5 ± 2.3*# †
-1.0 ± 2.4*#
0.8 ± 1.6
2.1 ± 1.7
PO2
(kPa)
NBFR40
8.45 ± 1.83
9.40 ± 1.66
8.87 ± 2.71
9.20 ± 1.85
6.53 ± 2.60
BFR25
8.21 ± 2.31
8.84 ± 2.24
9.37 ± 2.65
5.77 ± 3.15
6.34 ± 1.55
BFR40
9.14 ± 2.87
7.06 ± 1.84
9.06 ± 1.60
8.47 ± 2.14
7.88 ± 2.64
PO2
(kPa)
NBFR40
5.80 ± 0.32
5.93 ± 0.33
5.76 ± 0.36
5.75 ± 0.37
6.11 ± 0.43
BFR25
5.73 ± 0.20
5.85 ± 0.28
5.52 ± 0.38
5.80 ± 0.26
5.91 ± 0.48
BFR40
5.70 ± 0.45
5.63 ± 0.73
4.85 ± 1.81
5.37 ± 0.83
5.78 ± 0.37
Na+
(mmol/L)
NBFR40
138.7 ± 1.1
140.0 ± 1.4
138.8 ± 0.5
138.3 ± 1.1
138.7 ± 1.0
BFR25
138.8 ± 1.6
139.1 ± 1.3
138.2 ± 1.1
138.7 ± 2.0
138.3 ± 1.1
BFR40
137.9 ± 1.8
140.0 ± 1.5
138.9 ± 2.5
138.6 ± 2.0
138.6 ± 1.1
K+
(mmol/L)
NBFR40
3.65 ± 0.26
4.17 ± 0.19
3.83 ± 0.20
3.76 ± 0.27
3.50 ± 1.06
BFR25
3.52 ± 0.15
3.96 ± 0.16
3.71 ± 0.15
3.69 ± 0.15
3.70 ± 0.11
BFR40
3.49 ± 0.11
4.26 ± 0.38
3.72 ± 0.30
3.63 ± 0.12
3.76 ± 0.15
Table 1. Changes in blood variables before exercise and during post-exercise period.
Values are presented as means ± SD. * Significant different from Pre ; p<.000, # Significant different from NBFR40 : p<0.05,  † Significant dif-
ferent from BFR25 : p<0.05
Physical Activity and Nutrition. 2020;24(2):030-037, http://dx.doi.org/10.20463/pan.2020.0012
35
Muscle oxygenation, endocrine and metabolic regulations during exercise with blood flow restriction
all the trials was noted in the BFR40 trial, and the value 
was significantly lower than those noted in the NBFR40 
and BFR25 trials. The total energy expenditure during 
the 15-min exercise session was significantly lower in 
the BFR25 trial than in the NBFR40 and BFR40 tri-
als (NBFR40: 99.7 ± 21 kcal; BFR25: 64.9 ± 16 kcal; 
BFR40: 112.1 ± 23.4 kcal, p<0.05). However, significant 
differences were not noted between the NBFR40 and 
BFR40 trials with respect to the total energy expenditure 
during the 15-min exercise session.
DISCUSSION
The primary findings of the present study were that 
the deoxy-Hb level was significantly higher during the 
exercise session in the BFR25 and BFR40 trials than in 
the NBFR40 trial. A significantly higher total-Hb level 
was noted during the 2-min pressure phase in the BFR40 
trial than in the NBFR trial. Moreover, exercise-induced 
increase in the lactate level and decrease in the pH were 
significantly higher in the BFR40 trial, with a concomi-
tant increase in the serum cortisol concentration after ex-
ercise. Notably, the substrate oxidation pattern was altered 
with BFR during low-intensity endurance exercise. CHO 
oxidation was significantly higher in the BFR40 trial than 
in the NBFR40 and BFR25 trials, while fat oxidation was 
lower in the BFR40 trial. These findings suggest that BFR 
during low-intensity endurance exercise promotes muscle 
deoxygenation and CHO metabolism compared to that 
when the same exercise is performed without BFR.
During endurance exercise, the muscle blood flow 
is increased in response to the metabolic demands of 
the muscle17,18. NIRS is commonly used for evaluating 
the oxygenation levels and hemodynamics in a work-
ing muscle. As an individual starts the exercise, oxygen 
consumption and delivery to the skeletal muscle rapidly 
increases, up to 50-fold or more19. In the present study, 
significantly lower oxy-Hb levels were noted during the 
2-min pressure phase in the BFR40 trial compared to 
those in the NBFR40 trial. Moreover, the deoxy-Hb and 
total-Hb levels were higher during the 2-min pressure 
phase and 1-min release phase in the BFR40 trial than in 
the NBFR40 trial. Several studies have reported that the 
oxy-Hb dissociation curve promoted the rate of deoxy-Hb 
at or close to the lactate and ventilatory thresholds [33, 
34]. Moreover, the deoxy-Hb level during the pressure 
phase was significantly higher in the BFR25 trial than in 
the NBFR40 trial, despite lower exercise intensity in the 
BFR25 trial. The total-Hb level measured using NIRS 
reflects the blood volume in the muscle. As shown in 
Figure 3, the total-Hb level was significantly higher in 
Figure 4. Exercise-induced changes in serum growth hor-
mone (A), cortisol (B) and myoglobin concentrations (C) in 
NBFR40, BFR25 and BFR40.
* Significant different from BFR40 at Pre ; p<.000, # Signifi-
cant different from NBFR40 at Post 60 ; p<0.002, Values are 
presented as means ± SD.
Figure 5. Carbohydrate (A) and fat oxidation (B) rate during 
15 min of exercise.
Values are presented as means ± SD. **p<0.05 between trials.
Physical Activity and Nutrition. 2020;24(2):030-037, http://dx.doi.org/10.20463/pan.2020.0012
36
Muscle oxygenation, endocrine and metabolic regulations during exercise with blood flow restriction
the BFR40 trial than in the NBFR40 trial, suggesting that 
the cuff pressure during low-intensity endurance exercise 
augmented the muscle blood volume (blood perfusion). 
Endurance exercise with BFR augmented hyperemic 
blood flow in the local region, leading to increased shear-
ing stress on the vascular endothelial cells20. Therefore, 
the augmented blood volume in the BFR40 trial may be 
because of the increased nitric oxide production induced 
by augmented shear stress21-23.
Notably, no difference was noted in the blood lactate lev-
els or pH between the BFR25 and NBFR40 trials, despite 
the difference in the exercise intensity. In a previous study24, 
unilateral plantar flexion (30 repetitions/min) using 20% 
1RM with BFR promoted a decrease in the in intramuscular 
phosphocreatine (PCr) and intramuscular pH, as measured 
by 31P-magnetic resonance spectroscopy (MRS), than ex-
ercise using 20% 1RM without BFR. Exercise with BFR 
induces metabolite accumulation and may affect endocrine 
response. In the present study, the serum GH level increased 
till 60 minutes after exercise in the BFR40 trial; however, 
but there was no significant difference in the serum GH 
levels among the trials. This result may be attributed to the 
short exercise duration (only 15 min). However, the serum 
cortisol concentration was significantly elevated in the 
BFR40 trial till 60 min after exercise; the serum cortisol and 
myoglobin concentrations were significantly elevated in the 
BFR40 trial at 60 min after exercise. Significant differenc-
es in the serum GH levels were not observed between the 
NBFR40 and BFR25 trials. Significant differences were not 
noted in the BFR40 trial; however, the serum GH tended 
to increase significantly in the BFR40 trial. Although the 
exercise-induced increase in the GH levels is dependent on 
the exercise intensity, the present findings suggest that BFR 
training effectively increases the serum GH levels. This may 
be an important finding with respect to prescribing exercise 
for untrained individuals, including elderly people.
In the present study, HR during the exercise was signifi-
cantly increased in the BFR40 trial than in the NBFR40 
and BFR25 trials (NBFR40: 106 ± 11; BFR25: 102 ± 13; 
BFR40: 137 ± 18, p <0.05). BFR stimulated autonomic 
cardiovascular (CV) response through a chemical stim-
ulus of accumulation of metabolites and a mechanical 
stimulus, such as muscle exercise pressor reflex (EPR)25. 
The rating of perceived exertion (RPE) during the 2-min 
pressure phase was significantly higher in the BFR25 and 
BFR40 trials than in the NBFR40 trial (NBFR40: 1.6 ± 0.1; 
BFR25: 4.0 ± 0.4; BFR40: 5.8 ± 1.0, p<0.05). Stimulation 
of EPR through BFR may increase exercise-induced fa-
tigue. Therefore, BFR during low-intensity endurance ex-
ercise augmented the score of subjective fatigue, probably 
owing to augmented central command26,27. Several studies 
have reported that endurance exercise with BFR enhanced 
the recruitment of the fast twitch fibers (FT fibers) during 
muscle activity. Enhanced FT fiber recruitment activates 
anaerobic glycolysis and alters the substrate oxidation 
pattern4,28-30. A 30-min low-intensity endurance exercise 
session with BFR increased CHO metabolism13. The mus-
cle glycogen content significantly decreased after low-in-
tensity resistance exercise with BFR compared to that 
when the same exercise is performed without BFR31. Our 
results indicate that CHO oxidation did not differ between 
the BFR25 and NBFR40 trials, despite the difference in 
the exercise intensity. The exercise intensity was same 
between the BFR40 and NBFR40 trials; however CHO 
oxidation was higher in the BFR40 trial. Therefore, we 
found that low-intensity exercise with BFR altered energy 
substrate utilization during exercise.
The present study has several limitations. Firstly, 
we did not evaluate the long-term training effects (e.g., 
change in the muscle strength, endurance, and muscle 
volume). Secondly, the present study recruited only 
healthy young male subjects. Although we applied the 
same pressure of 160 mmHg , the pressure intensity may 
vary depending on the muscle mass in the legs of the sub-
jects. To clarify the benefit of low-and moderate-intensity 
exercise with BFR, further investigations in elderly peo-
ple or clinical populations are required.
During the 15-min low-intensity (either 25% or 40% 
of V. O2 max) endurance exercise session, the levels of de-
oxy-Hb and total Hb were significantly increased, when 
BFR was repeatedly applied. Moreover, lower levels of 
oxy-HB were noted during endurance exercise with BFR at 
40% V. O2 max achieved compared to those when the same 
exercise was performed without BFR. These findings sug-
gest that BFR during low-intensity endurance exercise aug-
mented local hypoxia and blood volume in the muscle. Fur-
thermore, endurance exercise with BFR at 40% V. O2 max 
promoted exercise-induced acidification in the blood (i.e., 
lower pH and higher blood lactate levels) compared to that 
when the same exercise was performed without BFR. Final-
ly, BFR during low-intensity endurance exercise augmented 
CHO oxidation and impaired fat oxidation. Although the 
present study was performed as an acute experiment, the 
findings may suggest the spotential benefits of BFR during 
low-intensity endurance exercise for health promotion.
ACKNOWLEDGMENTS
This work was supported by the Ministry of Educa-
tion of the Republic of Korea and the National Research 
Foundation of Korea(NRF-2016S1A5B5A01021612).
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Muscle oxygenation, endocrine and metabolic regulation during low-intensity endurance exercise with blood flow restriction.
Hwang, Hyejung,Mizuno, Sahiro,Kasai, Nobukazu,Kojima, Chihiro,Sumi, Daichi,Hayashi, Nanako,Goto, Kazushige