TITLE: The effects of bodyweight-based exercise with blood flow restriction on
isokinetic knee muscular function and thigh circumference in college
students

  ABSTRACT:
[Purpose] The purpose of this study was to investigate the effects of bodyweight-based
exercise with blood flow restriction on isokinetic muscular function and thigh
circumference in college students. [Subjects and Methods] The subjects were 17 college
students who were recruited and randomly assigned to bodyweight-based exercise with blood
flow restriction and bodyweight-based exercise groups. Participants performed front lunges
and squats at ratings of perceived exertion of 11–13 three times a week during a 6-week
training period. The peak torque/ body weight (%) of the knee flexor and extensor was
measured using a HUMAC NORM System (Cybex 770-NORM®, Cybex International,
Medway, MA, USA), and the circumference of the thigh was measured. PASW Statistics was
used for data analysis. [Results] There were significant differences in the peak torque/
body weight (%) of the flexors in both thighs (at 180°/sec) after bodyweight-based
exercise with blood flow restriction. In addition, the circumference changes in both
thighs were significant after bodyweight-based exercise with blood flow restriction and
between the two groups. [Conclusion] This study suggests that bodyweight-based exercise
with blood flow restriction may be an effective method to improve the muscle power and
hypertrophy of the lower extremity in a clinical setting.

BODY.INTRODUCTION:
With resistance training, more than 70% of the one-repetition maximum (1RM) has
traditionally been recommended as the optimal load for muscular strength and
hypertrophy1). However, this has recently
been challenged by a number of studies2,3,4,5,6)
demonstrating that substantial muscular strength and hypertrophy can be achieved with
low-load (20–50% of the 1RM) resistance exercise combined with blood flow restriction.  Previous researchers suggested that skeletal muscle could be subjected to high mechanical
stress as a result of increased motor unit recruitment, cellular signaling events from
mechanical changes in the muscle fibers or various endocrine responses7, 8). Therefore, blood
flow restricted exercise may be a potentially useful method for promoting muscle hypertrophy
in people with various problems, avoiding exercises with heavy loads9). However, although this has been confirmed as safe and
effective exercise by studies9,10,11) on skeletal
muscle, measurement of the 1RM is not easy in frail or elderly patients. Specifically, the
American College of Sports Medicine (ACSM)12) has recommended relative contraindications not only for resistance
training but also for testing of the 1RM for cardiovascular disease patients with low
functional capacity (< 4 METs) or musculoskeletal limitations. Therefore, in the case of
rehabilitation for patients after cast immobilization, for example, rehabilitation programs
should be designed to increase muscular strength and hypertrophy using bodyweight-based
exercise in a physical therapy setting, and this would be a safe and effective intervention
for increasing muscular strength and hypertrophy. To date, there is no information regarding
this. Therefore, it is important to determine whether there are beneficial effects of
bodyweight-based exercise using blood flow restriction in physiotherapy. It was previously
reported that blood flow in a muscle could be decreased in blood flow restriction training
by application of a wrap.  Most of these studies2,3,4,5,6) were performed using the
Kaatsu Master system (Sato Sports Plaza, Tokyo, Japan). However, the Kaatsu Master system
may not be a practical approach for most populations due to cost and accessibility13).  Therefore, the purpose of this study was to investigate the effects of bodyweight-based
exercise with blood flow restriction using a wrap on isokinetic muscular function and thigh
circumference in college students. In addition, it will provide the basic data necessary for
therapeutic interventions, such as surgery, neurophysiological treatment, and specific
treatments for elderly people.

BODY.SUBJECTS AND METHODS:
The subjects of this study were 17 college students. They were divided into two groups: a
bodyweight-based exercise with blood flow restriction (BFR) group and a bodyweight-based
exercise (WBE) group. There were 10 subjects in the BFR group (3 male, 7 female) and 7
subjects in the WBE group (2 male, 5 female). Their general characteristics were as follows:
age, height, weight, percent body fat, and lean body mass were 24.0±3.2 years and
26.8±4.6 years, 166.2±7.2 cm and 166.5±8.0 cm, 58.3±12.1 kg and 67.6±11.7 kg, 21.7±6.4% and
26.8±8.1%, and 45.4±8.6 kg and 49.1±7.9 kg for BFR and WBE groups, respectively. All
participants understood the purpose of this study and provided written informed consent
prior to participation in accordance with the ethical principles of the Declaration of
Helsinki.  An isokinetic knee muscular function test was performed using a HUMAC NORM System (Cybex
770-NORM®, Cybex International, Medway, MA, USA), and it measured muscular
strength and power. The test protocol was based on those of the previous studies14, 15). The extensor and flexor of the both knee joints were evaluated 10
times each at 60°/sec (muscular strength) and 15 times each at 180°/sec (muscular power),
and the peak torque/body weight (%) was calculated from the results. Thigh circumference was
measured directly below the gluteal fold of both thighs16). All measurements were taken 24 hours before the first round of
exercise and 24 hours after the last round of exercise. As for the wrap, studies that used
an elastic wrap13) or the Kaatsu Master
system (Sato Sports Plaza, Tokyo, Japan)2,3,4,5,6) were
referred to. The wrap's width was set at 5 cm, and its length was set at 100–130 cm, about
two times the thigh girth; when applied, it resulted in a rating of perceived exertion (RPE,
Borg's 6–20 scale) of 11–13 at the end of each motion.  Front lunges and squats were performed using the wrap around the proximal aspect of the
thigh in the BFR group, and conventional exercise without blood flow restriction was
performed in the WBE group. The exercise protocol was performed with an RPE of 11–13 for 30
minutes once a day and 3 times a week for 6 weeks. Regarding exercise intensity, the initial
intensity was set as the number of times in which the RPE was 11–13 at the end of 10–15
repetitions of each motion, and the intensity was reset every 2 weeks.  The data were statistically processed, paired sample t-tests were conducted for
within-group comparisons, and the changes before and after the training program were
calculated. Comparisons between the two groups were conducted by independent sample t-tests.
Statistical significance was set at p < 0.05, and PASW Statistics 18.0 version was used
for the analysis.

BODY.RESULTS:
Isokinetic knee muscular function was compared between the BFR and WBE groups (Table 1Table 1.Comparisons of muscular strength and power of the lower extremities60 ̊/secKnee extensor peak torque / body weight (Nm)Knee flexor peak torque / body weight (Nm)PrePostDifference (%)PrePostDifference (%)RightBFR181.7±66.3190.8±44.39.4±19.3107.2±37.6126.5±38.1**20.2±15.2WBE165.5±57.3154.0±45.8−5.1±8.091.8±30.298.7±26.511.0±18.7LeftBFR177.3±49.3169.8±39.8−2.8±11.1108.8±29.7116.3±35.56.5±12.1WBE174.5±50.3151.1±37.1−11.7±12.098.1±30.590.8±27.6−7.4±16.2180 ̊/secKnee extensor peak torque / body weight (Nm)Knee flexor peak torque / body weight (Nm)PrePostDifference (%)PrePostDifference (%)RightBFR107.5±40.4117.8±30.414.3±20.178.8±24.892.3±24.8*14.1±15.3WBE108.4±25.6111.8±25.13.8±11.668.5±15.479.4±18.6***13.3±4.1LeftBFR111.2±32.3111.0±20.4−0.0±19.679.3±20.286.0±18.05*10.2±14.09WBE114.4±30.3111.0±24.412.6±10.674.5±19.076.5±19.83.0±14.5Mean ± SD. BFR: bodyweight-based exercise with blood flow restriction, WBE:
bodyweight-based exercise. *p < 0.05, **p < 0.01, ***p < 0.001). The BFR group showed a significant improvement in 60°/sec peak torque/body
weight (%) at the flexor of the right knee (p < 0.01) and 180°/sec peak torque/body
weight (%) at the flexor of both knees after exercise (p < 0.05). In addition, the WBE
group's 180°/sec peak torque/body weight (%) at the flexor of the knee after exercise
increased significantly (p < 0.001). There was no significant difference between the two
groups in isokinetic knee muscular function (p < 0.05).  Thigh circumference was compared between the BFR and WBE groups (Table 2Table 2.Comparisons of thigh circumferenceRight (cm)Left (cm)PrePostDifference (%)PrePostDifference (%)BFR45.5±3.847.9±4.5***5.3±2.8***45.4±4.147.8±4.5***5.1±2.6**WBE49.7±5.549.4±5.0−0.4±2.150.1±6.850.4±6.30.7±2.1Mean ± SD. BFR: bodyweight-based exercise with blood flow restriction, WBE:
bodyweight-based exercise. **p < 0.01, ***p < 0.001). The BFR group saw a significant increase in the right and left legs after
the exercise compared with before (p < 0.001). In comparison between the BFR and WBE
groups, the circumferences of both thighs in the BFR group increased significantly (p <
0.001, p < 0.01) after the exercise compared with before the exercise.

BODY.DISCUSSION:
Although BFR exercise has been confirmed as safe and effective exercise by studies9,10,11) on skeletal muscle, it was reported that
reperfusion after a BFR leads to impairment of local endothelial function17), and the mechanisms of restricted blood
flow exercise were not clarified. However, it is certain that, BFR exercise can bring about
improvements in muscle strength and muscular hypertrophy. Previous researchers have thought
that muscular hypertrophy was attributed to decreased oxygen available to the muscle and
accumulation of metabolites such as lactic acid during BFR training. In addition, early
recruitment of fast twitch (type II) fiber might occur to maintain the muscular force and
protect against conduction failure during restricted blood flow exercise because of reduced
oxygen supply to slow twitch (type I) fiber2, 3, 18).  The main objective of this study was to compare with the effects of BFR using wraps on the
isokinetic muscular function of the lower extremity and thigh circumference in college
students. Our major findings showed that BFR using wraps could elicit improvements in the
muscular power of the knee flexor and hypertrophy in college students. In particular,
significant differences in the circumferences of the thighs were found between the two
groups. This was in agreement with an earlier study. In that study, soccer players (n = 16)
performed 3 sets of blood flow restriction training (bench press, squat) with a wrapping
consisting of an elastic band, 3 times a week for 4 weeks at 20% of 1RM, and the 1RM values
of the upper and lower extremities (bench press and squat) increased significantly, that is,
by 7.0% and 8.0%, respectively (p < 0.05)19).  This result was similar to that of a study20) of 21 subjects (22.1±1.8 years) who were divided into four groups,
without any pressure (n = 5), with a pressure of 50 mmHg (n = 5), with a pressure of 150
mmHg (n = 5), and with a pressure of 250 mmHg (n = 6), and performed straight leg raises,
hip adduction, and hip abduction 3 times a week for 8 weeks at 20% of 1RM. A significant
improvement in 180°/s peak torque/body weight (%) (muscle power) was observed (p < 0.05,
p < 0.01) after training in the low-pressure group (50 mmHg).  We believe these results were induced by the wraps restricting blood flow in the exercised
muscle. In the current study, bodyweight-based exercise with a wrap was performed without an
air compressor. However, it brought about improvements in muscular power. We believe the
improved muscular power was due mainly to neural adaptations of the lower extremities. The
reason for this is as follows. It has been reported that the neural factors were the
greatest contributors to increasing muscular strength during the initial 8 to 10 weeks of
resistance training. In particular, fast twitch fiber is associated with speed or power
activities21).  It was particularly noteworthy that BFR using wraps for 6 weeks resulted in a clear
increase in muscular power and hypertrophy in the lower extremities in this study. The
results of this study were similar to those of blood flow restriction exercise with knee
wraps, which showed the same degree of muscle hypertrophy in high-intensity resistance
training in a previous study13).  We consider that the increase in the circumference of the thigh after intervention is due
to the combination of training effects on the hamstring muscle not used ordinarily and the
BFR effect through the front lunge and squat exercises in the college students because front
lunge and squat exercises are primarily performed in a bodyweight-based position22) and the knee flexors, the hamstring
muscles, are mainly used when the front lunge and squat motions are performed. Moreover,
previous investigators reported that squatting helps to strengthen the quadriceps and
stimulates coactivation of the hamstrings23).  In conclusion, this study suggested bodyweight-based exercise with blood flow restriction
is a useful method to improve the flexor functions of the legs in a clinical setting.

Question: Compared to Bodyweight-based exercise groups what was the result of Bodyweight-based exercise with blood flow restriction on Changes in 60°/sec peak torque/body weight (%) at the right knee flexor?
Evidence: The peak torque/ body weight (%) of the knee flexor and extensor was
measured using a HUMAC NORM System (Cybex 770-NORM®, Cybex International,
Medway, MA, USA)
Answer: significantly increased