Effects of Blood flow Restriction and Load on Mean Propulsive Velocity and Subjective Perceived Exertion During Squat and Bench Press Exercises

Abstract

Background:

The aim of this study was to determine the influence of different percentages of blood flow restriction (BFR) and loads on mean propulsive velocity (MPV) and subjective perceived exertion during squat (SQ) and bench press (BP) exercises.

Hypothesis:

Higher percentages of BFR will positively affect dependent variables, increasing MPV and reducing perceived exertion.

Study Design:

Cross-sectional study.

Level of Evidence:

Level 3.

Methods:

Eight healthy young male athletes took part. Two sets of 6 repetitions at 70% 1-repetition maximum (1RM), 2 sets of 4 repetitions at 80% 1RM, and 2 sets of 2 repetitions at 90% 1RM were performed randomly; 5-minute recoveries were applied in all sets. The varying arterial occlusion pressure (AOP) applied randomly was 0% (Control [CON]), 80%, and 100%.

Results:

No statistically significant differences in MPV were found during the BP exercise at any percentage of BFR at any percentage 1RM. During the SQ exercise, MPV results showed statistically significant increases of 5.46% (P = 0.04; η_p² = 0.31) between CON and 100% AOP at 90% 1RM. The perceived exertion results for the BP exercise showed statistically significant reductions of -8.66% (P < 0.01; η_p² = 0.06) between CON and 100% AOP at 90% 1RM. During the SQ exercise, the perceived exertion results showed significant reductions of -10.04% (P = 0.04; η_p² = 0.40) between CON and 100% AOP at 80% 1RM; -5.47% (P = 0.02; η_p² = 0.48) between CON and 80% AOP at 90% 1RM; and -11.83% (P < 0.01; η_p² = 0.66) between CON and 100% AOP at 90% 1RM.

Conclusion:

BFR percentages ~100% AOP at 90% 1RM improved acutely MPV (only in SQ exercises) and reduced acutely perceived exertion (in both exercises). These findings are important to consider when prescribing resistance training for healthy male athletes.

The benefits of resistance training (RT) are based on scientific evidence and are recognized widely in many domains related to physical activity and exercise. ³⁷ RT has developed greatly with the introduction of new methods and technologies such as blood flow restriction (BFR). ²³ BFR consists of fully or partially restricting blood flow by means of pneumatic cuffs placed on the most proximal part of the limbs, at a specific arterial occlusion pressure (AOP).^19,28 The BFR-based RT training methodology (BFR-RT) has become popular in recent years. Although some studies have reported differences in the improvements achieved in muscular strength, ²² gains in muscular hypertrophy by applying light loads (≈ 20-40% 1-repetition maximum [1RM]) appear similar to those obtained by applying traditional high-load training (≈ 60%-85% 1RM). ²⁸ It has been hypothesized that this could be due to the restriction of blood flow in the muscles during low-intensity training. This appears to mimic the local muscle physiological environment induced by training at higher intensities with greater metabolic stress, favoring hypertrophy similar to that which would occur at high intensities but with a lower training intensity. ¹⁷

This characteristic presents interesting practical applications when high-load RT is contraindicated for certain populations (eg, elderly people, patients with chronic diseases or recovering from musculoskeletal pathologies, etc). ²¹ Furthermore, the use of BFR-RT in the sporting environment has shown to greatly optimize performance in various sport disciplines.^6,16,36 Current BFR-RT prescription recommendations advise performing around 75 repetitions distributed in 4 sets (30-15-15-15 repetitions), with 40% to 80% AOP, at a controlled and uniform speed of execution in both eccentric and concentric phases. ²⁸

At this point, it is important to note the difference between using BFR as a method of strength training and using it as an external compression for acute performance enhancement.^11,44 In the latter respect, and especially in power and high-speed training where loads vary widely, ⁴⁰ the determining performance variable is the speed at which external resistance is mobilized. ²⁷ Since speed of execution has been highlighted as the key variable to measure RT intensity, ⁴¹ training that uses it as a method of control has become highly popular in recent years. ¹⁸ This approach is commonly known as velocity-based RT. ¹² Velocity-based RT has proven its importance in the physical preparation of athletes by monitoring and adjusting the degree of fatigue in real time.^2,25,31,47 In addition, it has also been reported that this type of training generates significant improvements in the rate of force development, which directly influences athletic actions such as jumping and sprinting. ¹⁴

Speed-control methods to stimulate strength seek to both improve and control sports performance instantaneously, dispensing with the need to perform multiple evaluation tests. ¹³ Mean propulsive velocity (MPV) is a variable used widely in this regard. MPV refers to the average velocity achieved by the displaced bar or weight from the beginning of the concentric phase until the acceleration of the bar is less than gravity (-9.81 m/s). ¹³ Based on a person’s functional capacity, ²⁷ MPV determines objectively the performance level, and even the fatigue level, recorded in each repetition or series. ¹⁸ It also helps optimize the instantaneous load and reduce overtraining. ²⁷

Fatigue can be expressed by various indicators, such as, objectively, through the velocity loss between successive repetitions in a same set. ³² It can also be expressed subjectively through a person’s perceived exertion (eg, heaviness of the movement), ²⁶ by assessing the rating of perceived exertion (RPE) through widely validated scales. ⁴ The use of these scales should be adjusted to intensities and loads to assess training progress. ²⁶ Their inclusion in RT is based on the functional link between physiological, perceptual, and performance responses.^26,39 This feature is in line with Borg’s principle, with the parallel exercise intensity increase and awarded score. ⁴ Intensity measurement units during RT should reduce variability and allow comparisons of measurements between different subjects. ³ The OMNI-RES scale was adapted to reduce variability and uncertainty when applying these scales in RT.^3,30 In recent years, this scale has undergone changes in terms of qualitative categories linked to numerical values. ³⁰

The effects of different BFR percentages on RPE and on certain variables related to execution speed are unknown. In previous work carried out by this research group, the acute effects of different percentages of BFR (40%, 60%, 80%, and 100% AOP) on MPV and maximum execution speed were assessed during squat (SQ) and bench press (BP) exercises with medium intensities (60% 1RM). ³⁴ It was from this work that the need arose to investigate whether the same effects would occur at higher intensities. Consequently, the aim of this study was to determine the influence of different BFR percentages (0%, 80%, and 100% AOP) on MPV and RPE, applying various intensities (70%, 80%, and 90% 1RM) during BP and SQ exercises.

Methods

This quasi-experimental study followed a repeated measures cross-sectional design, using nonprobability convenience sampling. Participant exclusion criteria consisted of (1) having arterial hypertension (resting systolic and diastolic blood pressure >160 and >105 mmHg, respectively); (2) a body mass index >35 kg/m²; or (3) having morphological or functional myocardial limitations (cardiomyopathies and congenital heart disease) or other cardiocirculatory pathologies that could hinder the correct performance of the test procedures and endanger the participant’s health.

Participants

The study participants were 8 healthy male athletes with over 3 years of RT experience and showing correct technical performance (age, 25 ± 5 years; body mass, 80 ± 10 kg; height, 178 ± 6 cm). They were recruited on a voluntary basis from among the students of the Degree in Physical Activity and Sport Sciences at the University of Alicante. Systolic and diastolic pressures taken at the humeral artery in the sitting and resting position were 139 ± 19 and 73 ± 8 mmHg, respectively. Heart rate was 69.74 ± 16.54 beats per minute and total occlusive pressure was 175.46 ± 20.73 mmHg for the humeral artery and 165.93 ± 18.50 mmHg for the femoral artery. The participants recorded a maximum repetition (1RM) and relative strength index of 88 ± 13 kg and 120 ± 5%, respectively in the BP exercise. For SQ, the recorded values were 92 ± 17 kg and 123 ± 1%. All participants stated that they did not take any substances or dietary supplements that could influence their physical performance. Furthermore, all participants were prohibited from taking drugs, medicines, and doping substances that could alter their performance in the tests and endanger their health. They were also asked not to have any food for at least 2 hours before the test in the interest of avoiding gastrointestinal problems.

Before starting the experimental procedures, all participants had the purpose of the study, the testing procedures, and the potential risks associated with their participation fully explained to them. Subsequently, each participant signed an informed consent form. The study experimental procedures complied with the ethical principles of research involving human subjects, as described in the 64th General Assembly of the Declaration of Helsinki (2013). Moreover, this study was approved by the University’s ethics committee (UA/2018-11-15).

Procedures

The entire experimental protocol of this study was conducted under stable environmental conditions of 20°C to 22°C and 55% to 65% relative humidity in the same time zone (16:00 UTC+1). Participants came to the laboratory on 10 separate occasions at least 48 hours apart (Figure 1). No adverse events were detected during the whole intervention process.

Figure 1.

Flowchart of the experimental design. 1RM, 1-repetition maximum; AOP, arterial occlusion pressure; BP, bench press; CON, control; h, hour; reps, repetitions; RPE, rating of perceived exertion; SQ, squat.

Premeasurement Sessions

In session 1, participants were given a health questionnaire and asked for their informed consent. The researchers took their body mass (Avery Ltd Model 3396 ABV) and height (Holtain Ltd) measurements as well as their resting blood pressure in a seated position (OMRON 705CP semi-automatic oscillometric monitor). The complete 100% AOP of the brachial and femoral arteries was then determined (Sonosite Titan Doppler ultrasound machine, Sonosite, Inc) using the following procedure ²⁰ : after lying supine on a stretcher for 5 min, the pulse was auscultated and detected using the Doppler probe in the brachial artery. The manufacturer reported a maximum waveform recording rate of 150 Hz with the L38/10-5 MHz broadband linear transducer for vascular tissues. A 57 × 9 cm pneumatic cuff (Komprimeter Rudolf Riester GmbH), located in the most proximal part of the arm, was progressively inflated in 25 mmHg ranges until the blood flow signal disappeared on the echo-Doppler. At this point, 100% of the AOP was recorded. Similarly, 100% AOP of the femoral artery was determined with consequent procedural differences: on 1 hand, in a prone stretcher position; on the other, a 96 × 13 cm pneumatic cuff was used, located over the inguinal area. ¹⁹ The cuff used was a straight, single chamber, manually inflatable cuff (not self-regulating) with a pressure adjustment in the same series in front of a full circumferential chamber.

Session 2 was used to familiarize the participants with BP and SQ exercises and the correct execution technique. Two certified specialists (NSCA-CSCS) oversaw the session, and the main objective was to improve the perception of movement speed. The session started with a warm-up consisting of 5 minutes on a treadmill at 10 km/h and 5 minutes of active joint mobility and dynamic stretching of the upper and lower limbs. Subsequently, participants performed 2 sets of 8 and 6 repetitions for each exercise with 3 minutes of recovery, using 20 kg and 30 kg loads in each set, respectively. ²⁷ Both exercises were performed with the Smith machine (Multipower Fitness Line) to allow a constant vertical movement of the bar throughout the execution. In both exercises, the eccentric phase speed was controlled and constant at an MPV <0.70 m/s, ²⁷ which corresponds to a moderate velocity. However, participants were strongly encouraged - via standardized means - to complete each concentric phase as fast as possible. MPV was recorded using a linear encoder (Chronojump) with a 1000 Hz sampling frequency. The average of the 3 best repetitions of each series were recorded for subsequent analysis.

The BP exercise began in the supine position on a flat bench with feet flat on the floor and hands gripping the bar and held slightly wider than shoulder width apart. ³² Bench positions and grip widths were measured and reproduced individually for each lift. During the eccentric phase, the bar path was a descent to the chest at the height of the intermammillary line at the controlled speed (0.70 m/s) and then a stop until the command was given to start the concentric phase. This momentary pause between the eccentric and concentric phases was applied to minimize the influence of the rebound effect and to allow for more consistent measurements. ³³ No barbell bouncing on the chest, shoulder lifting, or torso off the bench were allowed. In the SQ exercise, the participants began with their knees and hips fully extended in an upright position with feet shoulder-width apart and the bar resting on the trapezius. ³² The eccentric phase, also at the controlled speed (0.70 m/s), ended when the subjects lowered the bar until the upper part of their thighs was below the horizontal - parallel to the ground. ⁹ The reverse movement was then initiated (in this case, without a pause between the 2 phases) and the subjects ascended to the initial vertical position.

Session 3 began with the same warm-up as in session 2. Subsequently, the procedure to obtain the 1RM in the BP exercise was applied following the recommendations of Pareja-Blanco et al ¹³ and Sánchez-Medina and González-Badillo. ²⁷ The protocol was composed of sets of <5 repetitions; the initial protocol load was 20 kg and each set was progressively increased in 10 kg increments until the MPV was <0.8 m/s. Beyond this point, the load was adjusted individually with small increments of 2.5 to 5 kg until the load allowed a single repetition to be performed at a speed close to 0.16 ± 0.04 m/s. According to González-Badillo and Sánchez-Medina, ¹³ this speed corresponds to the 1RM in BP. The rest between sets varied from 3 to 5 minutes depending on whether the MPV was >0.68 m/s or <0.68 m/s, respectively. The measuring instrument used to record MPV was the same as in session 2. However, in this session, only the best repetition of each set was taken into account for each participant.

Experimental Sessions

Sessions 4 to 6 used the same warm-up as sessions 2 and 3, followed by 2 sets of 6 repetitions at 70% 1RM, 2 sets of 4 repetitions at 80% 1RM, and 2 sets of 2 repetitions at 90% 1RM; 5-minute recoveries were implemented in all performed series. In session 4, the experimental protocol described above was performed without applying any BFR (control [CON]). In session 5, an 80% AOP was applied. Finally, in session 6, the AOP was increased to 100%. Each participant performed the sessions and the intensities (% 1RM) within each session in a randomized order. In the recovery periods between sets, the BFR application was released to allow clearance of muscle metabolites.^28,42 In addition, the pressure of each AOP percentage was controlled to ensure stability by monitoring the cuff pressure during the performance of all sets. To estimate perceived exertion (ie, heaviness of the movement), RPE assessment was used by asking participants at the end of each set to score from 1 to 10, based on the Borg CR10 scale, CR 1 to 10. ⁴⁶ This assessment was established according to the difficulty of moving the load in the concentric phase of the exercise at maximum intentional speed: 1 corresponding to no difficulty and 10 to maximum difficulty.

Session 7 took place 1 week after the previous session and was aimed at obtaining the 1RM with the SQ exercise. The same warm-up and procedure were applied as in session 3, although in this case up to the load that allowed a single repetition to be executed at a speed close to 0.32 ± 0.03 m/s. According to Sánchez-Medina et al, ³² this corresponds to the 1RM in SQ. Sessions 8 to 10 used the same warm-up and procedure as sessions 4 to 6, but performing SQ instead of BP. In the same way as in sessions 6 to 8, each participant performed the sessions and the intensities (%1RM) within each session in a randomized order. No BFR (CON) was applied in session 8, 80% AOP in session 9, and 100% AOP in session 10. BFR application was also released during recovery periods and the pressure stability of each percentage AOP was monitored. To estimate perceived exertion (ie, heaviness of the movement), the same scale (RPE) and arrangement was applied as in sessions 4 to 6.

Statistical Analysis

All variables were expressed as means and standard deviations and complied with the normality assumption (Shapiro-Wilk test). To analyze the influence of the percentage AOP on the dependent variables analyzed (MPV and RPE), a repeated measures factorial analysis of variance (ANOVA) was performed. This analysis was performed with 2 intrasubject independent manipulated variables with 3 levels each. The first variable was percentage 1RM and its 3 percentages were 70%, 80%, and 90% 1RM. The second variable was the percentage AOP, also with 3 percentages: CON (0%), 80%, and 100% AOP. In the case of noncompliance with the sphericity assumption, the degrees of freedom were corrected using the Greenhouse-Geisser approximation. A Bonferroni post hoc test was performed to compare each percentage AOP. Effect size (ES) was expressed as partial eta squared (η_p²) values. This ES was classified as large (>0.137), moderate (from 0.137 to 0.06), and small (from 0.059 to 0.01). ⁵ The significance level was set at P < 0.05. All analyses were conducted using the version 25 of SPSS statistical package for social sciences (SPSS IBM Inc).

Results

The most relevant experimental data are summarized in Table. The values obtained for the dependent variables and their comparisons with the control group (ie, 0% AOP) are shown, and those statistically significant comparisons in levels 0.01 and 0.05 are highlighted. Next, the results are presented separately, first by dependent variable (ie, MPV and RPE) and then by exercise (BP and SQ).

Table 1.

MPV and RPE values in BP and SQ exercises

	MPV, m/s (Mean ± SD)		RPE, 0-10 scale (Mean ± SD)
Load and AOP Percentages	BP	SQ	BP	SQ
70% 1RM CON	0.62 ± 0.08	0.72 ± 0.06	5.87 ± 1.02	6.19 ± 0.82
70% 1RM 80% AOP	0.64 ± 0.07 (3.22%)	0.70 ± 0.06 (–2.77%)	6.19 ± 0.50 (4.91%)	6.21 ± 0.57 (1.80%)
70% 1RM 100% AOP	0.60 ± 0.08 (–3.22%)	0.71 ± 0.08 (–1.38%)	5.69 ± 0.79 (–3.55%)	5.80 ± 0.51 (–4.91%)
80% 1RM CON	0.51 ± 0.07	0.64 ± 0.04	6.88 ± 0.75	7.07 ± 0.61
80% 1RM 80% AOP	0.50 ± 0.08 (–1.96%)	0.63 ± 0.07 (–1.56%)	7.19 ± 0.65 (4.50%)	6.79 ± 0.42 (–3.96%)
80% 1RM 100% AOP	0.49 ± 0.06 (–3.92%)	0.64 ± 0.06 (0.01%)	7.00 ± 0.61 (1.74%)	6.36 ± 0.49 (–10.04%)*
90% 1RM CON	0.39 ± 0.10	0.55 ± 0.05	8.55 ± 0.94	7.86 ± 0.53
90% 1RM 80% AOP	0.39 ± 0.06 (–0.09%)	0.57 ± 0.06 (3.63%)	8.13 ± 0.81 (–4.91%)	7.43 ± 0.51 (–5.47%)*
90% 1RM 100% AOP	0.38 ± 0.07 (–2.56%)	0.58 ± 0.04 (5.46%)*	7.81 ± 0.40 (–8.66%)**	6.93 ± 0.57 (–11.83%)**

AOP, arterial occlusion pressure; BP, bench press; CON, control; MPV, mean propulsive velocity; RPE, rating of perceived exertion; SQ, squat; 1RM, 1-repetition maximum; (± X%), percentage difference of levels 80% or 100% AOP versus CON, in their respective %1RM.

*P < 0.05; **P < 0.01 (significant differences).

Mean Propulsive Velocity

Figure 2 shows the MPV results during the BP and SQ exercises. In the BP exercise, although slight variations were found in some comparisons of all intensities, no significant differences were identified at any percentage of 1RM for the different percentages of AOP. Regarding the SQ exercise, although slight variations at 70% and 80% 1RM were seen, the only significant differences were reported at 90% 1RM. In this sense, significant increases of 5.46% (p = 0.04; η_p² = 0.31) were found between CON and 100% AOP.

Figure 2.

MPV values (m/s) in BP and SQ exercises. 1RM, 1-repetition maximum; AOP, arterial occlusion pressure; BP, bench press; CON, control; MPV, mean propulsive velocity; SQ, squat. *P < 0.05 (significant differences).

Rating of Perceived Exertion

Figure 3 shows the RPE results obtained for BP and SQ exercises. In the BP exercise, while slight variations were found at 70% and 80% 1RM, the only significant differences were identified at 90% 1RM. In this regard, significant reductions of -0.74 points were reported between CON and 100% AOP (-8.66%; P < 0.01; η_p² = 0.06). In the SQ exercise, although no significant differences were seen at 70% 1RM, significant reductions were reported at 80% and 90% 1RM. Specifically, at 80% 1RM, a decrease of -10.04% (P = 0.04; η_p² = 0.40) was recorded at the 100% AOP versus CON comparison. At 90% 1RM, a significant reduction of -5.47% (P = 0.02; η_p² = 0.48) was found between CON and 80% AOP. A significant decrease of -11.83% (P < 0.01; η_p² = 0.66) was reported between CON and 100% AOP.

Figure 3.

RPE values in BP and SQ exercises. 1RM, 1-repetition maximum; AOP, arterial occlusion pressure; BP, bench press; CON, control; RPE, rating of perceived exertion; SQ, squat.*P < 0.05, **P < 0.01 (significant differences).

Discussion

The main objective of this study was to analyze the acute effect of different percentages of BFR on barbell displacement velocity as well as perceived effort at various intensities (% 1RM) during BP and SQ exercises. The findings of this study showed no changes at any percentage of 1RM and AOP in the BP exercise. In contrast, MPV production improvements were obtained in the SQ, although only at 90% 1RM and 100% AOP. However, with increasing AOP, the RPE values dropped significantly in both exercises, and more specifically at higher percentage 1RM and AOP. These findings suggest that the application of a BFR-based training program could delay the reduction in the production of the intrasets MPV during SQ exercise and reduce perceived effort during SQ and BP exercises.

Since the methodology used to improve hypertrophy through BFR may differ from that used to improve MPV, various protocols have been used in the literature to assess the effects of BFR during BP and to determine the most appropriate approach, if applicable.^34,43,44 For example, Wilk et al ⁴⁴ proposed the highest reported levels of BFR (applying 100% and 150% AOP), at an intensity of 60% 1RM, proposing sets to failure and performing >10 repetitions. However, the application of higher levels of occlusion did not produce significant improvements in mean velocity during BP. ⁴⁴ This could possibly be attributed to the use of a high number of repetitions up to failure. To investigate this, we can refer to another study by Wilk et al, ⁴³ which applied 70% AOP and evaluated its effect on mean velocity during BP at intensities ranging from 20% to 90% 1RM, performing only 2 repetitions in each set and, obviously, not to failure. Again, no significant improvements in mean velocity were observed, ⁴³ suggesting that the lack of improvement is not due solely to the number of repetitions performed. It would be advisable to consider alternative levels of occlusion in this case. In the present study, researchers observed similar results. Six repetitions at 70%, 80%, and 90% 1RM with higher BFR percentages (80% and 100% AOP) also failed to produce significant improvements in mean velocity during BP, indicating that higher occlusion may not be the optimal choice in this exercise. In a previous study by Serrano-Ramon et al, ³⁴ BFR of 40%, 60%, 80%, and 100% AOP were tested, performing 6 repetitions at 60% 1RM. Serrano-Ramon et al ³⁴ found that applying 80% AOP at 60% 1RM during 6 repetitions of BP was the only combination that showed small but significant improvements in MPV. ³⁴ Since this appears to be the only combination showing improvement, it would be reasonable to expect it to be the most suitable BFR methodology to increase intraset MPV during BP.

In this same line, we found only 1 study that applied BFR methodology to assess its effects on mean velocity during SQ ¹¹ ; Gepfert et al ¹¹ applied 2 percentages of BFR, 100% and 150% AOP, performing 3 sets of 3 repetitions at 70% 1RM. They found no significant changes in mean velocity with the application of 100% AOP, while they did find significant differences with 150% AOP. In the present study we did not analyze such high levels of BFR (ie, 150% AOP), but neither did we find significant differences in the MVP during the SQ exercise by applying 100% AOP at 70% 1RM. The only combination in which we found significant differences in MVP during SQ was applying 100% AOP at 90% 1RM. Therefore, in both studies, the only combinations that have shown positive results in mean velocity during SQ were the more intense combinations (ie, higher percentages of 1RM) and/or with higher BFR (ie, higher percentages of AOP). It seems reasonable to think that these more extreme combinations are required to favor an increase in MVP during SQ exercise.

On the other hand, RPE has been linked to factors related to exercise intensity, such as mobilized load (ie, %1RM),^30,38 or to BFR. ⁷ In the latter regard, a considerable number of papers have examined the effects of BFR on RPE.^7,24 However, most of these studies have used RT with BFR at light intensities (20%-50% 1RM). Overall, a systematic review by Miller et al ²⁴ indicated that low-load RT with BFR produced, at least during the initial stages of training (≤8 weeks), a greater RPE than traditional high-load RT (without BFR). Similarly, a meta-analysis by de Queiros et al ⁷ analyzed the effects of RT with BFR at low loads (<50% 1RM) versus RT without BFR, at low and high loads (<50% or >60% 1RM, respectively) on RPE and pain/discomfort. Their results also indicate that, in those sets that were not worked to failure (ie, with a pre-set number of repetitions), RPE was increased during RT with BFR (<50% 1RM; 50%-60% AOP in most cases) versus its equivalent in intensity but without BFR. ⁷

Our results showed reductions in RPE when applying BFR versus CON during both BP and SQ exercises. In addition, and similarly to MPV, most statistical significance appeared in the more extreme combinations (ie, more intense and/or with a higher percentage of AOP). In the case of the SQ exercise, there were some combinations that achieved significant reductions (5%-11%) in RPE: applying 100% AOP at 80% and 90% 1RM (versus CON) and applying 80% AOP at 90% 1RM (versus CON). However, the unique combination that achieved significant increases in MPV and significant reductions in RPE simultaneously was applying 100% AOP at 90% 1RM (versus CON). This suggests that this combination during SQ exercise may be the most appropriate in BFR-based RT methodology, as it achieves increases in MPV with simultaneous reductions in RPE. Concerning the BP exercise, we cannot draw a similar conclusion because we have not obtained any combination which increases MPV while achieving reductions in RPE. However, we can conclude that, by applying 100% AOP at 90% 1RM (ie, the most intense combination with the highest percentage of AOP), RPE was reduced significantly (≈10%) versus CON.

The differences found in our results with respect to the aforementioned literature, both in BP and SQ, may be due to variations in the protocols applied (eg, we performed <6 repetitions while others performed ≥15 repetitions; we performed shorter time under tension and higher intensities; we applied higher percentages of AOP; etc). Therefore, there was probably not enough time for the onset of the effects caused by continuous and prolonged BFR (eg, edema, muscle soreness, etc). ²⁸ Therefore, if these factors are not the main cause of the increase on MPV, a possible contributor could be the joint stability and sense of comfort provided by the external compression of the occlusive cuff. ¹⁵ This effect may be intensified with increased cuff pressure. ⁴⁵ Several studies have suggested that flossing bands (which may have a similar stabilizing effect to inflatable cuff) may increase jump performance.^8,10,15 In this sense, one of the most recent meta-analyses that has emerged on this subject concluded that these compressive bands could have a positive impact on power and jump performance. ²⁹ This argument could be reinforced by the results of our study, given that SQ is a more unstable exercise overall than BP. In fact, in the latter, the subject is even lying down and supported on a bench, which makes it necessarily more stable. It therefore seems reasonable to suggest that the greatest increases in MPV and reductions in RPE take place during SQ, since it is the exercise that requires the greatest demands on stability in this research. If this hypothesis is corroborated in future studies, we could begin to consider whether this type of training should be called BFR training or external compression training.

The main limitations of this study were the small sample size and that the findings can only be applied to healthy male participants, making it difficult to generalize the results. In this sense, the limited sample size of 8 athletes may have influenced the results, explaining the lack of significant statistical effects observed when applying BFR on MPV at different AOP percentages, particularly regarding BP exercise. In addition, the physical condition of the participants, the sport they practiced, or their experience in RT at high speeds could have influenced the reported results. Participants with greater or lesser physical condition or experience in performing power exercises could see their ability to apply force at maximum intentional speeds modified. ¹ Finally, although we have used the 100% AOP measurement protocols used most widely in the literature, the relative occlusion could have been influenced by measurement position. The estimation of the AOP in a supine position is the method used most widely to establish cuff pressures for BFR training. However, when resistance exercise is performed standing or sitting, occlusion pressures during the workout can vary significantly. ³⁵ In this regard, the use of continuous occlusion pressure monitoring devices (ie, Delfi tourniquet, or MadUp Pro device) may help to make the necessary adjustments in case of large differences between the estimated pressure (in supine) and the working pressure during the exercise. This is especially important when applying very high or total arterial occlusion pressures to prevent adverse effects.

Conclusion

According to the data obtained, applying BFR had no effect on MPV at any AOP percentage on the upper limbs during the BP exercise. However, in the lower limbs, MPV improvements were found when applying 100% AOP at 90% 1RM during the SQ exercise. In contrast, RPE showed significant decreases when applying 80% to 100% AOP at 90% 1RM during both exercises. Taken together, our results show that the combination of applying 100% AOP at 90% 1RM is able to increase MPV and reduce RPE at the same time during SQ exercise. These findings could be used by exercise professionals who work with BFR-based methodologies in RT.