The effects of upper body exercise across different levels of blood flow
restriction on arterial occlusion pressure and perceptual responses
Kevin T. Mattocks, Matthew B. Jessee, Brittany R. Counts, Samuel L. Buckner, J. Grant Mouser, Scott J. Dankel,
Gilberto C. Laurentino, Jeremy P. Loenneke
⁎
Department of Health, Exercise Science, and Recreation Management. Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, MS, United States
H I G H L I G H T S
• Higher relative pressures result in the greatest cardiovascular responses. • Perceptual responses are augmented with increasing applied pressure.
• Due to the cardiovascular response, the relative restriction pressure decreases during exercise.
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 16 September 2016
Received in revised form 28 October 2016 Accepted 9 January 2017
Available online 11 January 2017
Recent studies have investigated relative pressures that are applied during bloodflow restriction exercise ranging from 40%–90% of resting arterial occlusion pressure; however, no studies have investigated relative pressures below 40% arterial occlusion pressure. The purpose of this study was to characterize the cardiovascular and per-ceptual responses to different levels of pressures. Twenty-six resistance trained participants performed four sets of unilateral elbowflexion exercise using 30% of their 1RM in combination with blood flow restriction inflated to one of six relative applied pressures (0%, 10%, 20%, 30%, 50%, 90% arterial occlusion pressure). Arterial occlusion pressure was measured before (pre) and immediately after the last set of exercise at the radial artery. RPE and discomfort were taken prior to (pre) and following each set of exercise. Data presented as mean (95% CI) except for perceptual responses represented as the median (25th, 75th percentile). Arterial occlusion pressure increased from pre to post (pb 0.001) in all conditions but was augmented further with higher pressures [e.g. 0%: 36 (30– 42) mm Hg vs. 10%: 39 (34–44) mm Hg vs. 90% 46 (41–52) mm Hg]. For RPE and discomfort, there were signif-icant differences across conditions for all sets of exercise (pb 0.01) with the ratings of RPE [e.g. 0%: 14.5 (13, 17) vs. 10%: 13.5 (12, 17) vs. 90%: 17 (14.75, 19) during last set] and discomfort [e.g. 0%: 3.5 (1.5, 6.25) vs. 10%: 3 (1, 6) vs. 90%: 7 (4.5, 9) during last set] generally being greater at the higher restriction pressures. All of these differ-ences at the higher restriction pressures occurred despite completing a lower total volume of exercise. Applying higher relative pressures results in the greatest cardiovascular response, higher perceptual ratings, and greater decrease in exercise volume compared to lower restriction pressures. Therefore, the perceptual responses from lower relative pressures may be more appealing and provide a safer and more tolerable stimulus for individuals. © 2017 Elsevier Inc. All rights reserved.
1. Introduction
Bloodflow restriction training has been shown to increase muscle size and strength similar to high-load resistance training[1,2]with loads as low as 20% of the one repetition maximum (1RM). Throughout the bloodflow restriction literature, a variety of pressures have been ap-plied ranging from relative pressures that are based on brachial systolic
pressure (130% brachial systolic blood pressure) to applying an arbi-trary pressure to all individuals[3]. This may be a concern because ap-plying an arbitrary pressure may restrict blood flow to a greater extent than what was intended, leading to an exaggerated cardiovascu-lar response[4]. Therefore, it is suggested that when applying pressure to the cuff, the pressure should account for the individual's limb circum-ference and width of the cuff[5–7]. One method to do this is to apply a percentage of the resting arterial occlusion pressure which ensures that all participants will receive a similar stimulus and may also reduce the risk of a negative cardiovascular event[4,8].
Recent studies have investigated relative pressures ranging from 40%–90% of resting arterial occlusion pressure during blood flow
⁎ Corresponding author at: Kevser Ermin Applied Physiology Laboratory, Department of Health, Exercise Science, and Recreation Management, The University of Mississippi, 231 Turner Center, MS 38677, United States.
E-mail address:[email protected](J.P. Loenneke).
http://dx.doi.org/10.1016/j.physbeh.2017.01.015
0031-9384/© 2017 Elsevier Inc. All rights reserved.
Contents lists available atScienceDirect
Physiology & Behavior
restriction exercise[9–11]. However, there seems to be little augmenta-tion in muscle adaptaaugmenta-tion beyond a relative pressure of 40% arterial oc-clusion pressure[9]. To our knowledge, no studies have investigated relative pressures below 40% arterial occlusion pressure during blood flow restriction exercise. We hypothesize that there is likely a point at which the relative pressure is too low to be efficacious. It is conceivable that a pressure of 20% arterial occlusion may be high enough at rest but during exercise drops outside of the hypothetical pressure range need-ed for muscle adaptation due to the elevatneed-ed cardiovascular response
[12,13]. Thus, the purpose of this study was to characterize the cardio-vascular response to pressures below 40% arterial occlusion pressure (0%, 10%, 20%, 30% arterial occlusion) and compare them to a moderate (50% arterial occlusion pressure) and higher (90% arterial occlusion pressure) relative pressure. We also sought to investigate the perceptu-al response across these pressures to determine whether or not they dif-fer from simply completing the exercise protocol in the absence of blood flow restriction. This is important because higher perceptual responses, despite the effectiveness of bloodflow restriction, may deter its use in practice.
2. Methods 2.1. Participants
Twenty-six resistance trained participants (20 men, 6 women) com-pleted all of the testing sessions. Individuals were classified as “resis-tance trained” if they performed resistance training two or more days per week for at least the past 6 months in the upper body. All partici-pants were instructed to refrain from: 1) eating 2 h prior in all visits; 2) consuming caffeine 8 h prior to all visits; 3) consuming alcohol 24 h prior to all visits; and 4) upper body exercise 24 h before all visits. Participants were excluded if they had more than one risk factor for thromboembolism [14] which included the following: obesity (BMI≥ 30 kg/m2); diagnosed Crohn's disease; a past fracture of the
hip, pelvis or femur; major surgery within the last 6 months; varicose veins; a family or personal history of deep vein thrombosis or pulmo-nary embolism. Also, participants who were currently using tobacco products were excluded. The study received approval from the University's institutional review board and each participant gave writ-ten informed consent before participation.
2.2. Study design
During visit 1, the participantsfilled out an informed consent form, adult health history questionnaire and physical activity readiness ques-tionnaire (PAR-Q). After confirming that they did not meet any exclu-sion criteria, height and body mass were measured using a standard stadiometer and an electronic scale. Next, the participants were seated in a quiet room for 10 min. Following the rest period, participants had their standing arterial occlusion pressure determined in both arms at the radial artery in a randomized fashion. The participants then tested their unilateral concentric elbowflexion one-repetition maximum (1RM) for each arm and were then familiarized with isometric testing. Following this, participants were familiarized with the bloodflow re-striction stimulus. After visit 1, participants were scheduled for their testing visits with a minimum offive and a maximum of 10 days be-tween visits at the same time of day. During visits 2, 3, and 4, partici-pants performed two exercise conditions of unilateral elbowflexion in combination with bloodflow restriction at 30% of their concentric 1RM in a random order (one condition per arm). The participants exercised at 0%, 10%, 20%, 30%, 50%, or 90% of their standing resting ar-terial occlusion pressure. The goal repetitions for the exercise protocol consisted of one set of 30 repetitions followed by three sets of 15 repe-titions with 30 s rest periods between sets. Upon completion of thefinal set, arterial occlusion pressure was determined again. A metronome was used to ensure that the participants held the cadence of 1 s for
the concentric muscle action and 1 s for the eccentric muscle action dur-ing the unilateral elbowflexion exercise. Ratings of perceived exertion (RPE) and discomfort were taken prior to (pre) and following each set of exercise.
2.3. Determination of arterial occlusion pressure
Following 10 min of seated rest, arterial occlusion was measured on both arms. The arm randomly assigned to exercisefirst, was measured first. The cuff was then removed and placed on the other arm to deter-mine resting arterial occlusion for that limb. The cuff used was a 5 cm wide nylon cuff applied to the most proximal portion of the arm. The lowest pressure at which bloodflow at the radial artery was no longer present was determined in the standing position using a Doppler hand-held probe (MD6 Doppler Probe, Hokanson, Bellevue, WA, USA). Pressure was regulated by the E20 Rapid Cuff Inflator (Hokanson, Belle-vue, WA) and was inflated to 50 mm Hg before being progressively in-creased by 1 mm Hg increments until a pulse was no longer detected. The participants exercised with the cuff in place and upon completion of the exercise, the applied pressure was increased until bloodflow was no longer present and the cuff was deflated immediately. Thirty minutes after thefirst condition, the participants were seated in a quiet room for 5 min. Following the rest period, participants had their standing arterial occlusion pressure determined on the arm that was not trainedfirst and then that arm completed an additional exercise protocol. Although the arterial occlusion pressure was deter-mined in this arm after thefirst 10 min rest, the arterial occlusion pressure used for exercise was based on the assessment obtained immediately prior to exercise in that arm. This was done to ensure that if there was an augmented cardiovascular response from the first exercise condition, it would be accounted for by the “new base-line”. It should be noted that there were only minor differences between thefirst and second measurements [mean difference (95% CI); 5 (4–6) mm Hg].
2.4. One-repetition maximum testing
A one-repetition maximum (1RM) for the unilateral elbowflexion exercise was obtained on both arms for each individual on visit 1. Brief-ly, participants warmed up with a relatively low load corresponding to an estimated 30% 1RM. Following the brief warm-up, the load was in-creased to approximately 90% of the individuals 1RM and participants performed one repetition. Thereafter, the load was adjusted to an esti-mated 1RM and the load was either increased or decreased in 0.5 kg in-crements until a 1RM was obtained. The dumbbell was handed to each individual at full elbow extension and participants were instructed to keep their back and heels against the wall during all 1RM attempts to ensure strict form. Only those attempts that maintained proper form were counted.
2.5. Ratings of perceived exertion (RPE)
RPE was taken before the start of exercise and immediately follow-ing each set usfollow-ing the standard Borg 6–20 scale as previously described
[15]. Participants were explained in depth how to rate their RPE and to ensure they understood the scale being used. Participants were told, “We want you to rate your perception of exertion, that is, how heavy and strenuous the exercise feels to you. The perception of exertion de-pends mainly on the strain and fatigue in your muscles. We want you to use this scale from 6-20, where 6 means‘no exertion at all’ and 20 means‘maximal exertion’; any questions?” Participants confirmed that they fully understood how to rate RPE prior to actual testing. RPE was taken immediately after sets 1, 2, 3 and 4.
2.6. Ratings of discomfort
A rating of discomfort was taken prior to the start of exercise and fol-lowing each set using the Borg Discomfort scale (CR-10+) as described previously[15]. For example, participants were asked,“What was your worst experiences of discomfort?‘Maximum discomfort (rating of 10)’ is your main point of reference; it is anchored by your previously expe-rienced worst discomfort. The worst discomfort that you have ever ex-perienced, the‘Maximum discomfort’ may not be the highest possible level of discomfort. There may be a level of discomfort that is still stron-ger than your 10; if this is the case, you will say 11 or 12. If the discom-fort is much stronger, for example, 1.5 times‘Maximum Discomfort’ you will say 15; any questions?” Participants confirmed that they fully un-derstood how to rate discomfort prior to actual testing. Ratings of dis-comfort were taken before exercise, as well as 20 s after sets 1, 2, 3, and immediately after set 4. Discomfort was taken 20 s after each set be-cause participants in previous bloodflow restriction studies anecdotally noted greater discomfort later in the rest periods.
2.7. Statistical analysis
All data were analyzed using the SPSS 22 statistical software package (SPSS Inc., Chicago, IL). For arterial occlusion pressure, a 6 (condition) × 2 (time) repeated measures of analysis of variance (ANOVA) was con-ducted. If there was a significant interaction, paired sample t-tests de-termined differences from pre-to-post exercise within each condition and one-way repeated measures ANOVAs determined differences across conditions within each time point. To compare differences in the perceptual responses (RPE and discomfort), a Friedman non-parametric test was used to determine if differences existed between conditions at different time points (Pre, 1st set, 2nd set, 3rd set, 4th set). If there were significant differences, Wilcoxon related samples nonparametric tests were used to determine where the difference oc-curred. For exercise volume, a one-way repeated measures ANOVA de-termined differences in exercise volume across conditions. All data are presented as means and 95% confidence intervals except for the percep-tual responses which are represented as 50th (25th, 75th) percentiles. Statistical significance was set at an alpha level 0.05.
3. Results 3.1. Participants
A total of 26 resistance trained males (n = 20) and females (n = 6) [mean (95% CI); Age: 22 (21−23) yrs; Height: 175.3 (171.2–179.4) cm: Body mass: 78.7 (73.4–84.1) kg; Left arm 1RM: 22.6 (19.9–25.4) kg; Right arm 1RM: 22.9 (20.1–24.6) kg] completed the study protocol. 3.2. Arterial occlusion pressure
There was a significant condition × time interaction with arterial oc-clusion pressure (F = 3.527, p = 0.014). Follow up tests found that all conditions increased arterial occlusion pressure from pre to post (pb 0.001). No significant differences were noted between conditions at pre (F = 0.461, p = 0.805), however, differences between conditions were found at post (Fig. 1, F = 4.128 p = 0.002). Supplementary Fig. 1 displays the pre-post change score (95% CI) in arterial occlusion pres-sure across relative prespres-sures. Given the increase in arterial occlusion pressure with exercise, there were noted decreases in the relative ap-plied pressure which is displayed inFig. 2.
3.3. Ratings of perceived exertion (RPE)
There were no differences in RPE at pre (Table 1,χ2
= 3.5, p = 0.623); however, there were significant differences across conditions for sets 1 (χ2= 18.893, pb 0.05), 2 (χ2= 30.364, pb 0.001), 3 (χ2=
24.616, pb 0.001), and 4 (χ2= 29.334, pb 0.001) of exercise with the
RPE generally being greater at the higher applied pressures. 3.4. Ratings of discomfort
There were no differences in ratings of discomfort at pre (Table 1, χ2= 2.722, p = 0.743); however, there were significant differences
across conditions for sets 1 (χ2
= 48.820, pb 0.001), 2 (χ2
= 58.885, pb 0.001), 3 (χ2= 58.724, pb 0.001), and 4 (χ2= 55.748, pb 0.001)
with the ratings of discomfort generally being greater at the higher ap-plied pressures.
3.5. Exercise volume
There was a significant difference between conditions (F = 22.526, pb 0.001) in exercise volume, with the higher restriction pressures completing less volume compared to lower restriction pressures (Fig. 3). When displayed as total repetitions completed across arterial occlu-sion pressures [mean (95% CI)], the majority of individuals were unable to complete the goal number of repetitions [0%: 65 (62–69); 10%: 65 (61–69); 20%: 65 (61–69); 30%: 64 (60–68); 50%: 62 (58–67); and 90%: 50 (44–55) repetitions].
Fig. 1. Mean arterial occlusion pressure before (pre) and immediately after exercise (post). An asterisk indicates a significant difference from pre-to-post (p ≤ 0.05). Conditions with different letters represent significant differences between conditions for post values (p≤ 0.05). If two conditions contain at least one of the same letter, they are not significantly different from each other. Data represented as mean (95% CI).
Fig. 2. Relative applied arterial occlusion pressure differences from pre to post. Data represented as mean (95% CI).
4. Discussion
The current study uncovered threefindings: 1) the application of a relative restriction pressure decreases following upper body exercise due to an augmented cardiovascular response, 2) perceptual responses were significantly different across conditions and for all sets with the higher relative pressure coinciding with the greatest ratings of RPE and discomfort, and 3) exercise volume was different between condi-tions with the higher relative pressure completing less volume com-pared to the lower relative pressures.
The current study sought to further investigate the change in the cardiovascular response to six different relative restriction pressures following 4 sets of bloodflow restriction exercise. It has recently been observed by Brandner et al.[16]that bloodflow restricted exercise (10.5 cm wide cuff used for exercise) with intermittent high-pressure (130% systolic blood pressure measured with an 8 cm wide cuff) caused a similar hemodynamic (i.e. heart rate, blood pressure, cardiac output, rate pressure product) response compared to traditional high load exer-cise. Further, they observed that exercise in combination with low-continuous pressure (80% systolic blood pressure measured with an
8 cm wide cuff) produced a response in between that observed with high load and low load exercise. This suggests that when performing bloodflow restriction exercise, greater levels of blood flow restriction will augment the cardiovascular response but not necessarily augment the muscle adaptation[9,11]. Additionally, low-intensity aerobic exer-cise in combination with bloodflow restriction has demonstrated a greater increase in the cardiovascular response compared to exercise without bloodflow restriction[17]. However, the restriction pressure applied to the participants in the aforementioned studies were not made relative to the participant or the cuff used during the exercise which may have had some individuals under complete arterial occlu-sion. This augmented cardiovascular response could be due to the me-chanical compression of the vascular tree which may augment the exercise-induce pressor response[18]. Although the magnitude of change in pressure may not be of concern to a healthy participant, this may be more concerning for aging individuals and/or individuals with a compromised cardiovascular system (e.g. hypertension). It can be hy-pothesized that applying a lower relative pressure may maximize mus-cle adaptation while causing less mechanical compression. Less mechanical compression may minimize the exercise-induced pressor response which may lessen the chances of an adverse event[4,8]. How-ever, it is also important to understand that the relative restriction pres-sure will decrease with exercise. Thus, a prespres-sure sufficient at the beginning of exercise may no longer restrict the same amount of bloodflow following exercise. A previous study found that the relative restriction pressure of 40% arterial occlusion pressure decreased ~ 8% immediately after a bout of bloodflow restriction exercise in the upper body indicating an increase in the cardiovascular response during exercise[12]. In agreement with the previous study, we also observed a decrease in the relative restriction pressure following a bout of upper body exercise with the addition of incorporating multiple levels of bloodflow restriction pressures. Examining the cardiovascular response to this type of exercise can help determine an appropriate restriction pressure to minimize the exaggerated cardiovascular response while maximizing muscular adaptation.
In regards to perceptual responses (RPE and discomfort), there is limited information on RPE throughout different levels of restriction pressures[10,19,20]. Yasuda et al.[19]applied two different pressures to the participants when performing unilateral bicep curls and observed that a restriction pressure of 160 mm Hg induced a higher RPE com-pared to 100 mm Hg; however, these pressures were not individualized to the cuff or participant. Therefore, some individuals may have been fully occluded with 160 mm Hg which may have augmented their RPE. Conversely, when applying a relative restriction pressure based on the participant's arterial occlusion pressure[10,20], there were no differences in RPE. While applying a relative restriction pressure to the participants in the current study, however, there were differences in
Table 1
Perceptual responses to differing levels of arterial occlusion pressure. Sets with different letters represent significant differences between pressures (p ≤ 0.05). If conditions contain at least one of the same letter, they are not significantly different from each other. Values are represented as median (25th, 75th percentile).
Ratings of perceived exertion
% Arterial occlusion Pre Set 1 Set 2 Set 3 Set 4
0% 6 (6, 6) 12 (9, 14)a 13 (12, 15)ab 14.5 (12.75, 17)abc 14.5 (13, 17)a 10% 6 (6, 6) 10 (9, 13)b 12 (9, 15)b 14 (11, 16)c 13.5 (12, 17)a 20% 6 (6, 6) 11 (9, 13.5)ab 13 (11, 15.5)abcdef 14 (11, 16)c 15 (12, 16.25)a 30% 6 (6, 6) 13 (9.75, 14)abc 14, (12, 15.5)af 15 (13, 16.25)b 15 (13, 16.25)a 50% 6 (6, 6) 12.5 (11, 14)c 14 (12.5 16)cdef 15 (13.75, 17)b 15 (13, 17)a 90% 6 (6, 6) 13 (9.75, 15)c 15 (13, 16.5)g 16 (14.5 17.5)d 17 (14.75, 19)b Ratings of discomfort
% Arterial occlusion Pre Set 1 Set 2 Set 3 Set 4
0% 0 (0, 0) 2 (0.5, 3)a 3 (0.875, 3)a 3 (1, 4.5)a 3.5 (1.5, 6.25)a 10% 0 (0, 0) 1 (0.45, 3)a 2 (0.650, 3)ab 2.5 (0.85, 4.5)a 3 (1, 6)ab 20% 0 (0, 0) 1.75 (0.5, 3)a 2 (0.925, 3)b 2.5 (1.25, 4)a 3 (1.375, 4)b 30% 0 (0, 0) 2 (0.65, 3)ab 2.75 (1.5, 4.25)a 3 (2, 5)a 3.5 (2.375, 6)ac 50% 0 (0, 0) 2.25 (0.925, 3)b 3.5 (1.875, 5)c 4 (2, 6.5)b 4.5 (3, 7)c 90% 0 (0, 0) 4.5, (2.75, 6)c 5 (3.75, 7)d 7 (5, 9)c 7 (4.5, 9)d
Fig. 3. Average total exercise volume completed across conditions. Conditions with different letters represent significant differences between conditions (p ≤ 0.05). If two conditions contain at least one of the same letter, they are not significantly different from each other. Data represented as mean (95% CI).
RPE. A possible reason for the discrepancy between Loenneke et al.[10, 20]and the current study is that the authors in that study applied mod-erate to high restriction pressures while we applied low to high restric-tion pressures. Although the pressures applied were randomized, participants had a greater probability of exercising at a lower restriction pressure (4 conditions compared to 1 condition) before exercising at a higher restriction pressure. For example, the participant may have re-ceived a relative restriction pressure ofb40% in the first condition and used the ratings from this condition as their anchor for subsequent pres-sures; thus, when receiving a relative restriction pressure of 90% their ratings were altered due to the large difference in mechanical compres-sion (or vice versa).
The results from the current study display that discomfort ratings were greatest when a higher relative pressure (90% arterial occlusion pressure) was applied which agrees with a previous study conducted by Counts et al.[9]. The authors of that study examined discomfort in the upper body at 40% and 90% arterial occlusion pressure and found that 90% arterial occlusion pressure resulted in a greater rating of dis-comfort. Interestingly, however, the results from our study and Counts et al.[9]differ from Loenneke et al.[10]where there were little differ-ences in discomfort with pressures ranging 40%–90% arterial occlusion pressure. There are a few possible reasons for the divergences between the studies. Counts et al.[9]examined untrained participants while Loenneke et al.[10]examined resistance trained individuals which sug-gests training status may be playing some role. There were also differ-ences in baseline 1RM between the two studies which may suggest that the pressure applied may have less of an impact on the ratings of discomfort in those who are training with an overall higher absolute load (Baseline 1RM: Counts et al.– 11.2 kg; Loenneke et al. ~19 kg). We examined resistance trained individuals with similar strength levels (Baseline 1RM: 22.9 kg) as Loenneke et al.[10]but observed an in-creased discomfort at the higher relative pressures. Possible reasons for the discrepancy between the current study and the aforementioned study could be that they examined relative pressures ranging from moderate to high while the current study examined relative pressures ranging from low to high. It may be that participants could not notice a big difference between moderate to high relative pressures applied (40%, 50%, 60%, 70%, 80%, and 90% arterial occlusion) due to the small in-creased increments of pressures applied which resulted in little differ-ences in ratings of discomfort between pressures. Thus, similar to RPE, part of the discrepancy may be due to the probability that lower pres-sures were experiencedfirst altering the subsequent ratings of the higher pressure condition or vice versa.
5. Limitations
In view of the results presented herein, our study has some limita-tions. We measured the pressure required for resting arterial occlusion but did not quantify the change in bloodflow. Future studies should quantify the change in bloodflow through different levels of relative re-striction pressures in-between sets and/or arterial occlusion pressure to determine where the change is occurring. Additionally, we used a 5 cm nylon cuff and it is possible that these results could differ with cuffs of different widths. It may be that a wide cuff, inflated to a relative pres-sure, may still induce a greater cardiovascular or perceptual response since it covers up both more area of the muscle as well as more of the vascular structures. Regardless, the results of the present study are spe-cific to 5 cm wide nylon cuffs.
6. Conclusion
Applying a relative restriction pressure based on arterial occlusion pressure during bloodflow restriction exercise has been shown to pro-duce favorable adaptations while also ensuring a common stimulus. It appears for muscular adaptations, 40% arterial occlusion[9]is all that is required at 30% 1RM; however, the cardiovascular response is
different depending on the relative restricted pressure applied. Current-ly it is unknown whether pressuresb40% arterial occlusion pressure with a load of 30% 1RM induces similar muscular and vascular adapta-tions compared to moderate and high pressures. The current investiga-tion sought to characterize the cardiovascular and perceptual responses to bloodflow restriction exercise through different levels of restriction pressures. Applying a lower relative restriction pressure resulted in lower perceptual responses which may be more appealing to individ-uals and result in better adherence to bloodflow restriction exercise. Fu-ture research could investigate if a lower load (20% 1RM) and different levels of pressures produce different or similar cardiovascular and per-ceptual responses. Overall, these results provide additional information to the bloodflow restriction literature by categorizing the cardiovascu-lar and perceptual response to pressuresb40% arterial occlusion. In ad-dition, thesefindings may guide future studies to provide a safer and more tolerable stimulus for the individual who still wants to increase muscle size while concomitantly minimizing the cardiovascular response.
Supplementary data to this article can be found online athttp://dx. doi.org/10.1016/j.physbeh.2017.01.015.
Acknowledgements
This study was supported in part by the Biolayne foundation (SJD and JPL).
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