EFFECT OF EXERCISE WITH CONTINUOUS AND INTERMITTENT BLOOD FLOW RESTRICTION ON HEMODYNAMICS

Introduction: Strength training with blood flow restriction (BFR) involves the use of low loads (20-30% of 1RM) with restriction of blood flow to promote gains in physical fitness. The restriction can be applied continuously or intermittently; however, it is unclear how it affects the hemodynamics of hypertensive women. Objective: To analyze the acute effect of resistance exercise (RE) on the upper and lower limbs with continuous and intermittent blood flow restriction (BFR) on the hemodynamic variables of women with hypertension. Methods: Thirteen women with controlled hypertension (40 to 65 years) underwent eight experimental protocols, with a randomized, counter balanced, crossover design; four exercise sessions for the right upper limb (elbow flexion) and four for the right lower limb (knee extension). The systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and heart rate (HR) were measured before, during, immediately after and 15, 30, 45 and 60 minutes after the exercises. Results: There were no significant interactions between the protocols vs. segments vs. time, protocols vs. segments, protocols vs. time, segments vs. time, protocol, segment and time, on the variables SAP, DAP, and HR during and after the RE (p>0.05). Although all these protocols had significantly elevated SAP, DAP and HR, the values remained within the normal range. The protocols of this study did not cause hypotensive effect. Conclusion: Low-load RE combined with continuous and intermittent BFR, on the upper and lower limbs, appears to promote similar variations in the hemodynamic variables of women with hypertension. Level of evidence II; Randomized clinical trial. clínico


INTRODUCTION
Resistance exercise (RE) has been recommended to people with hypertension two to three times per week with 8 to 10 exercises for the main muscle groups, prioritizing the unilateral execution with one to three series of 10 to 15 repetitions until moderate fatigue and intervals from 90 to 120 seconds. 1 However, people with hypertension often do not perform RE due to a fear it may lead to an unsafe cardiovascular event and, consequently, increasing the risk of mortality.
A possible alternative to high load (HL) RE for this population, is the method called RE combined with blood flow restriction (BFR), which is performed with low loads (20-30% of 1-RM) and consists on the using of inflatable cuffs or elastic bands placed on the proximal portion of the exercising muscles, which has been shown to promote significant changes aerobic capacity, muscle strength and hypertrophy. 2 Investigations on the BFR effects in hemodynamics usually use continuous [3][4][5][6][7][8] (cuff remains inflated between sets) or intermittent [4][5][6][9][10][11] (pressure released between sets) BFR and usually exercise only the upper or lower limbs. As mode of BFR application and limbs exercised may influence in the effects of exercise on hemodynamic variables, this can implicate a safety issue for the application of BFR specially in clinical populations such as people with hypertension. 12 This study aimed to compare the changes promoted during RE sessions with continuous and intermittent BFR on the upper and lower limbs on hemodynamic variables in hypertensive women.

Subjects
Thirteen physically active women (performed physical activity with moderate intensity, three times a week, for 60 minutes) 13 with hypertension aging between 40 and 65 years participated in the study. (Table 1) Sampling was performed on the software G*Power 3.1, according to the procedures proposed by Beck. 14 Using a priori analysis, with power of 0.80, α = 0,05, correlation coefficient of 0.5, non-sphericity correction of 1 and an effect size of 0.30, the sample size was sufficient to provide 80.0% of the statistic power.
Inclusion criteria were: have stage 1 controlled hypertension (SBP 140-159 mmHg and DBP 90-99 mmHg), 1 body mass index between 18.3 and 35.0 Kg/m², ankle-brachial index (ABI) between 0.90 and 1.4, 15 free of target organ damage and/or musculoskeletal and other cardiometabolic diseases that could interfere in the execution of RE protocols, non-smokers.
All subjects were taking the following anti-hypertensive drugs once a day, in the morning: angiotensin receptor antagonist (or ACE inhibitor) (50 mg) and diuretic (25 mg). After being explained about the risk and benefits of the research, informed consent was sought according to the Helsinki Declaration. The study was approved by the local Ethics Committee (protocol nº 0476/13).

Study design
Brachial-ankle index (BAI), blood pressure (BP), determination of the blood flow restriction point, anthropometric measures and 1-RM test were assessed on the first visit to the laboratory. Subjects returned 48 hours later to perform the reproducibility of the 1-RM test and the familiarization with the exercises with and without BFR. After familiarization, participants went to the laboratory in eight different days, separated by 48 hours, to execute eight different exercise protocols (P).
All the exercise protocols were performed on the same time of the day, during the afternoon, to control the daily variation of blood pressure and heart rate. The participants were instructed to not eat two hours before the experimental sessions, avoid ingestion of caffeine, chocolate, to not perform exercises 24 hours before the training sessions and to not use the Valsalva maneuver during exercises.

Determination of blood flow restriction (BFR)
Determination of restriction pressure was performed according to the protocol by Laurentino et al. 16 Subjects rested in the supine position for 10 minutes while a cuff (Riester ® , Jungingen, Alemanha) was placed on the proximal portion of the arm (6x47 cm) and leg (10x54 cm). The cuff was inflated until the moment when the auscultatory pulse of the brachial artery (right upper limb) or posterior tibial artery (right lower limb) ceased, with the value in mmHg being considered as 100% of BFR. The auscultatory pulse was verified using a portable doppler (DV2001, Medpej, Ribeirão Preto, São Paulo) in which the probe was placed on the skin on the path of the artery with a 60º inclination from the longitudinal axis of the vessel. The pressure used on the experimental sessions was 50% of the blood flow restriction pressure in mmHg. Average pressure for BFR protocols were 89,23±10,37 mmHg and 93,07±12,33 mmHg for the upper and lower limb, respectively.
One repetition maximum (1-RM) For the warm-up, each subject performed a series of five to ten repetitions at 40 to 60% of the maximum strength perceived with a one-minute interval between series. After the one-minute interval, the strength assessment began and the subjects should reach their maximum strength in no more than five attempts, the load was adjusted at each new attempt. The recovery time between each attempt was from 3 to 5 minutes and a 15 minutes interval was stablished between exercises. The test was interrupted when the individual could not execute correctly the movement, being considered as the 1-RM, the load lifted on the last well-succeed attempt.

Experimental sessions
The following protocols were performed: (P1/P5) high load RE with 65% of 1-RM (HLRE); (P2/P6) low load RE with 20% of 1-RM (LLRE); (P3/ P7) low load resistance exercise with continuous blood flow restriction with 20% of 1-RM and addition of 50% of BFR (LL+CBFR); (P4/P8) low load resistance exercise with intermittent blood flow restriction with 20% of 1-RM and addition of 50% of BFR (LL+IBFR); BFR (LL+CBFR); Being P1-P4 for the upper and P5-P8 for the lower limbs, totaling eight experimental protocols. For all protocols, the sessions consisted of four sets of unilateral right elbow flexion using halters and four sets of unilateral right knee extension on the extensor chair, with speed execution of two seconds for each phase of the movement.

Statistical analysis
The data was analyzed on the statistical software Statistical Package for the Social Science (SPSS) version 20.0. Analysis to verify normality (Shapiro-Wilk test), homogeneity (Levene test) and sphericity (Mauchly test) of data was performed. To verify possible significant differences on the dependent variables the repeated measures ANOVA between (protocols × segments × time), (protocols × segments), (protocols × time), (segments × time), (protocols) and (segment) followed by Bonferroni post-hoc were conducted. Effect size (ES) was used the verify the magnitude [trivial < 0.35, small = 0.35-0.80, moderate = 0.80-1.50 e large > 1.5] of the changes between the evaluations of the study protocols (RHEA, 2004), and was used the percent variation (Δ%), to express the possible differences between significant changes. Significance was stablished as p<0.05.
In the LL+IBFR protocol, there was a significant increase for the right upper limb when comparing the 2 nd series with rest (p=0.006, Δ%=12.9, ES=1.0) and for the right lower from rest to the 4 th series (p=0.002, Δ%=13.6, ES=1.1). In the LL protocol there was significant increase from the 2 nd series vs. rest (p = 0.032, Δ% = 11.0, ES = 0.6) on the right lower limb. However, there was no significant increase throughout the session nor significant reductions after exercise on the right upper limb (p> 0.05) nor for the HL protocol, on both upper and lower right limb, throughout the session when comparing series vs. rest (p> 0.05), as shown in Table 2.
Regarding the LL protocol, on the right upper limb there was a significant increase on the 3 rd series vs. rest (p = 0.005, Δ% = 8.5, ES = 0.6). As for the right lower limb, only after the 3 rd series a significant increase was observed (p = 0.010, Δ% = 12.9, ES = 0.7). For the HL protocol, on both right upper and lower limb there was no significant increase throughout the session when comparing series vs. rest (p> 0.05), as shown in Table 3.

Heart rate (HR)
There were no significant interactions between protocols × segments × time, protocols × segments, protocols × time, segments × time, protocol and segment (p> 0.05), however, there were significant interactions in time (p <0.001). After post hoc HR analysis it was found that in the LL+CBFR protocol in both the right upper and lower limbs there was no significant increase throughout the session of the series vs. (p> 0.05). In the LL+IBFR protocol, in the right upper limb there was a significant increase comparing the 2 nd and 4 th series with rest (p = 0.001, Δ% = 12.3, ES = 0.6; and p=0.048, Δ% = 8.7, ES = 0.4). On the other hand, in the right lower limb there was no significant increase throughout the session of the series vs. (p> 0.05), not even in the LL and HL protocols, on both upper and lower right limb, during the session of the series compared to rest (p> 0.05), as shown in Table 4.

DISCUSSION
The present study analyzed the acute effect of RE performed on the upper or lower right limb, combined with continuous or intermittent BFR on the hemodynamic variables. To our knowledge, this was the first study to analyze those interactions in people with hypertension. The main findings were: a) there were no significant changes on the SAP, DAP, and HR when comparing continuous and intermittent BFR or upper and lower right limb, although all these protocols elevated significantly the SAP, DAP, and HR within the expected; b) the protocols of the study did not promote hypotensive effect.
The results of the present study provide evidenced that there were no significant changes on the hemodynamic variables between the treatment protocols during and after the sessions. However, it is possible to verify that a greater increase happened during the session of the protocols with both intermittent and continuous BFR on the upper and lower limb than in the LL and HL protocols without BFR. This phenomenon may have occurred due to an increased metabolic stress caused by hypoxia on the BFR protocols, as observed in the study by Pinto et al. 8 where one session of BFR without exercise elevated the hemodynamic variables compared to rest.
Higher percentages of BFR apparently result in greater elevations of the hemodynamic variables. 4 In the study by Brandner et al., 4 it was observed that during exercise the SAP and DAP between the IBFR and HL protocols were similar, however the changes on the BP during the IBFR protocol were greater than the CBFR and LL protocols. The possible explanation is that for the IBFR protocol 130% of the rest pressure was used to promote restriction and only 80% for the CBFR, becoming evident that the percentage of pressure used is a regulator factor for the magnitude of the hemodynamic responses.
The training protocols did not promote the post-exercise hypotensive effect, with a similar response reported by Brandner et al. 4 that investigated the impact of intermittent and continuous BFR in normotensive individuals. Contrariwise, other studies that investigated the impact of continuous and intermittent BFR in normotensive male 5,6 and continuous BFR in women with hypertension 7 showed different results. The reason for these distinct outcomes may be related to the difference on the methods used on the studies.
The studies by Araújo et al., 7 performed with hypertensive women, Rodrigues Neto et al. 5 and Rodrigues Neto et al., 6 which investigated normotensive men, observed a hypotensive effect after BFR, however used protocols with higher volumes and multi-joint exercises. Higher training volumes and more complex exercises seem to be capable of increasing sympathetic and reducing parasympathetic activity changing the behavior of the hemodynamic variables during exercise and, consequently, provoking more significant decreases of blood pressure after exercise. 18 As limitations of this study, we can highlight the quantity of exercise performed that was only one for both the right upper limb (unilateral elbow flexion) and for the right lower limb (unilateral knee extension) and the protocols were equivalent, therefore the findings of this study cannot be extrapolated for other exercises.

CONCLUSION
Low load RE combined with continuous and intermittent BFR, on the upper and lower limbs, promoted similar changes on the hemodynamic variables. The RE with IBFR seems to be more suitable to be performed by clinical populations (i.e. people with hypertension and elderly) as it promoted lower elevations on hemodynamic variables during exercise. It is suggested that new studies carry out a resistance training program with continuous and intermittent BFR using different exercises (within the session) and with bilateral execution to verify changes in hemodynamics in patients with hypertension.
All authors declare no potential conflict of interest related to this article