Introduction
Resistance training has many known athletic benefits, including reducing the risk of injury, enhancing muscular endurance, improving power, promoting speed development, and increasing muscular strength. Although many forms of resistance training exist, weight training has long been a staple among coaches and athletes for eliciting improvements in muscular fitness.
Traditional weight training program design calls for the utilization of light weight and high repetitions for increasing muscular endurance (e.g., <60% 1 repetition maximum [1RM] for multiple sets of 10 or more repetitions), whereas increases in muscular size and strength are generally pursued with the use of heavy weight and a low number of repetitions (e.g., >70% 1RM for several sets of 6 repetitions or less) (1,6,11). However, present-day research has demonstrated that weight training with light weight and high repetitions can result in significant increases in muscle size and strength when it is used in conjunction with blood flow restriction (BFR). These observations have been made in healthy, untrained, and recreationally trained participants (2,31,32,39) and in athletic populations (3,30,36).
Blood flow restriction training (also known as occlusion training) is the act of reducing the amount of arterial blood flow to the working muscles while occluding venous return (8,25). This is achieved by placing a wrapping device around the proximal end of the muscles in which the restriction is desired. The resultant decreased delivery and cessation of return is believed to be responsible for many of the proposed mechanisms for the efficacy of BFR training in promoting muscular strength and hypertrophy. The most prevalent theories stem from the reduced oxygen availability and metabolite accumulation in the affected muscles. This low-oxygen high-metabolite environment has been demonstrated to increase the recruitment of high-threshold motor units (31,37), which are typically only recruited under heaving loading conditions (14,28). In addition, some research has indicated that there can be an exaggerated growth hormone release after BFR training (10,27,29), although the role played by systemic growth hormone in hypertrophy has been challenged in recent years (34).
However, these mechanisms cannot account for some circumstances in which BFR has been shown to be beneficial, as much of the BFR research uses modalities other than resistance training. In 2000, Takarada demonstrated that static BFR was effective in attenuation of muscle loss in bedridden patients recovering from anterior cruciate ligament surgery. Being nonambulatory negates the recruitment of any muscle fiber type, and metabolic build-up is negligible. A similar study conducted by Kubota in 2008 also demonstrated an offsetting of thigh muscle atrophy in movement-restricted participants receiving a BFR treatment (16). Abe et al. (4) observed increased muscular strength and hypertrophy by using BFR in combination with slow treadmill walking. Although Abe did not measure metabolites, Loenneke et al. (23) conducted comparable research in which lactate was assessed. Analysis revealed that slow treadmill walking using BFR did not result in metabolite accumulation. So, although increased motor unit recruitment and metabolite build-up may play a role in the positive muscular adaptations seen with BFR training, it is apparent that there are other mechanisms involved.
Loenneke et al. (18,20) have theorized that muscle cell swelling may be an important factor. The decreased arterial delivery and cessation of venous return during a BFR application lead to a pooling of blood in the muscles distal to the application site of occlusion. This pooling effect could cause a shift in intra- and extracellular fluids leading to an increase in muscle cell volume. Haussinger et al. (12) first theorized that cell swelling may induce an anabolic response, and follow-up work supports the concept (7,15). This mechanism may explain why BFR seems to attenuate muscle atrophy during times of immobilization where there is an absence of exercise and/or metabolite accumulation. It would appear that this may be the 1 consistent factor across all modalities of BFR training.
To obtain BFR, most research studies have used pneumatic wrapping devices, such as a KAATSU Master (Sato Sports Plaza Ltd., Tokyo, Japan), or modified blood pressure cuffs, which allow for precise control of the amount of applied pressure. Although pneumatic devices allow for control of the pressure during BFR training, generally, they are not practical for use outside of a clinical or laboratory situation because of being cost prohibitive and/or limited in accessibility. In 2009, Loenneke and Pujol (22) proposed the use of elastic knee wraps for BFR training (i.e., practical BFR), which would make the method a feasible option for general use. Quantification of the pressure exerted by a taut elastic wrap in a real-world setting is not possible; therefore, it was suggested that pulling the wraps tight to a moderate perceptive pressure (e.g., a 7 on a scale of 0 to 10) would be sufficient. This protocol has since been shown to be effective in occluding venous return while sufficiently reducing arterial delivery (35).
It is clear that the literature supports the efficacy of BFR training for promoting positive muscular adaptations across a variety of populations and modalities. However, few studies have used elastic knee wraps (17,21,23,24,36), and even fewer have used them outside of a laboratory setting with an athletic population (36). Additional research in this area will provide further insight into the use of practical BFR in those who are already well trained.
The purpose of this study was to examine the effects of a 7-week practical BFR protocol used in conjunction with a traditional weight training program on measures of muscular strength and size in collegiate American football players. The protocol used in this investigation was modeled after a practical BFR study conducted by Yamanaka et al. (36), which also used an American football team. This study was a field experiment conducted during the team's off-season, as a part of their strength and conditioning program. It was hypothesized that those who completed the traditional training program, in combination with the supplemental lifting protocols, under conditions of practical occlusion would experience greater gains in muscular strength and size than those in the other treatment groups.
Methods
Experimental Approach to the Problem
This investigation employed a pretest-posttest mixed model design with a training intervention. Participants were recruited from a National Collegiate Athletic Association (NCAA) Division II American football team, from which 72 players volunteered to take part. All participants completed a 7-week off-season football strength and conditioning program. Before the start of the program, and again on conclusion, the following dependent variables were measured: upper- and lower-body girths, and strength as determined by 1RM bench press and squat.
There were 4 groups of participants in this study. The football coaching staff was aware that the experimental design called for one of the group's training program to be modified in such a way that its members would not complete any high-intensity lifting. They expressed concern about restricting players who held the traditional strength and power positions (linemen and linebackers) from high-intensity work. Their concern was addressed by removing those positions from the initial selection pool and forming the modified group (M/S/R) from the remaining subset of players. Once the modified group was established, the linemen and linebackers were returned to the selection pool with the other remaining players and randomly assigned among the other 3 groups (H/S/R, H/S, and H). For a complete description of these groups, see Training Protocols and Groups.
Subjects
The football program was a part of the Intercollegiate Athletics Department at a midwestern regional university. Permission to conduct the study was granted by the university's institutional review board. The coaching staff of the football team agreed to the recruitment of participants from the team and allowing the necessary modifications to be made to the strength and conditioning program. Details of the study were verbally explained to the entire team by the principal investigator at a team meeting. Seventy-two team members volunteered to be participants. Each participant signed an informed consent document. All were deemed healthy and able to train by the university's medical and athletic training staff.
The off-season training program took place during an academic semester and lasted for 7 weeks, with 4 training days each week—2 upper-body days and 2 lower-body days. Players were assigned by their coaches to attend 1 of 3 training sessions each day, based on their class schedules. Training sessions were held at 7:15 AM, 1:30 PM, and 3:30 PM.
The study began with 72 participants (18 in each group). Because of non-BFR related injuries or lack of compliance with the protocol, 10 players were removed from the study. Complete data were collected on the 62 remaining participants (20.3 ± 1.1 year old, 99.1 ± 19.7 kg, and 7.1 ± 2.2 years of weight training experience).
Procedures
Pretests and Posttests
All participants attended pretest and posttest sessions for assessment of dependent variables. Both the pretests and posttests were split between 2 days. Pretest Day 1 was comprised of upper- and lower-body girths and 1RM bench press. Body mass was measured for descriptive and statistical purposes. This session was completed after 48 hours of rest. Pretest Day 2 followed the next day and consisted of the 1RM squat test. The same measures were again taken at the posttest sessions, which were completed at the conclusion of the program. Posttest day 1 took place after 48 hours of rest, followed by posttest day 2, taking place the very next day. All pretests and posttests took place during the participants' regular training session time. Figure 1 provides a schematic of the testing and training sessions.
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Figure 1: Testing and training schematic.
Body Mass and Girths
Body mass was measured with a Tanita WB-3000plus Digital Physicians Scale (Arlington Heights, IL, USA). The American College of Sports Medicine protocols for measuring circumferences were used for assessing arm and thigh girths (13). Chest girth was determined by placing the tape horizontally around the torso at the level of the nipple, and measurement was taken at the end of normal exhalation. All measurements, both pre and post, were assessed using a Gulick tape measure and were taken by the same investigator, whose test-retest reliability was 0.55% coefficient of variation (CV) for the arm, 0.47% CV for the thigh, and 0.48% CV for the chest.
1 Repetition Maximum Tests
Maximal strength for bench press and squat were assessed following procedures set forth by the football coaching staff. Players completed 1 warm-up set of 10 repetitions using approximately 40% of their estimated 1RM and a second warm-up set of 5 repetitions using approximately 60% of their estimated max. After adequate rest, players loaded the bar with approximately 80–85% of their estimated 1RM and completed 1 repetition. Weight was added with each subsequent 1 repetition set until the player could no longer complete a repetition correctly. The 1RM was determined as the last weight used in which the participant successfully completed the lift with proper form through the entire range of motion, as defined by National Strength and Conditioning Association (NSCA) (5). Conditions between the pre- and posttest 1RMs were made as identical as possible (see discussion above and Figure 1). Wearing a weightlifting belt was encouraged, but not required. Players who chose to wear a belt for a pretest 1RM also wore a belt for the posttest 1RM. The same was true for those who chose not to wear a belt. All 1RM tests, both pre and post, were supervised by the same members of our research team, each of whom is a NSCA Certified Strength and Conditioning Specialist (CSCS). Test-retest reliability as determined by our research team for the 1RM bench press was 0.62% CV and 0.35% CV for the 1RM squat.
Training Protocols and Groups
Each of the 4 groups completed a different training protocol and/or training intervention, an overview of which can be found in Table 1. Details of each can be found below and examples can be found in Tables 2 and 3.
Table 1: Groups, training programs, and protocols.*
Table 2: Representative lower-body day for each group: Total volume-load.*
Table 3: Representative upper-body day for each group: Total volume-load.*
Traditional High-Intensity Training Program (H)
In brief, this was a weightlifting program focused largely on increasing strength. It used sets, repetitions, and loading schemes of traditional high-intensity programs (i.e., multiple low-repetition sets with high %1RM). While the intricacies of the program changed over the course of the 7 weeks, at its foundation were lifts traditionally used in American football programs: bench press, overhead press, power cleans, squats, and variations of each. Auxiliary lifts, such as bicep curls, triceps extensions, calf raises, and abdominal work were also included. Training was split into alternating upper- and lower-body days, each being trained twice per week, although not always in the same sequence. There were 4 training days per week, occurring on Mondays, Tuesdays, Thursdays, and Fridays. Tables 2 and 3 provide representative workouts for lower- and upper-body days. The program followed this lifting format for the duration of the 7-week program.
Modified Training Program (M)
This protocol was identical to the traditional training program, with the exception that high-intensity bench press, squat, and their variations were excluded (Tables 2 and 3).
Supplemental 20% 1 Repetition Maximum Lifting Protocol (S)
Participants completed these sessions together, at the same time, at the conclusion of their training workouts. All sessions were supervised by the same 2 primary researchers to ensure compliance. The supplemental squats were performed at the end of lower-body training days, and the supplemental bench press was performed at the end of upper-body days. Barbell load was set at 20% of pretest 1RM. A list of each participant's barbell load was posted at each lifting station to ensure correct loads were used. Players completed 1 set of 30 repetitions followed by 3 sets of 20 repetitions, with 45 seconds of rest between each set (Tables 2 and 3). The pace of the concentric and eccentric phases of each repetition was set at 1.5:1.5 seconds. This cadence was guided by a series of ascending and descending tones that were played through the weight room's stereo system from a prerecorded .mp3 file. All 4 sets, including the rest periods, were incorporated into the .mp3 file and verbal instructions for the sessions. This provided consistency between all sessions throughout the duration of the program and allowed for the investigators to closely monitor the participants for compliance.
Practical Blood Flow Restriction (R)
Restriction of blood flow in the participants receiving the occlusion treatment was accomplished with the use of powerlifting elastic knee wraps with hook-and-loop closure (Grizzly Fitness, Kitchener, ON, Canada). The wrap dimensions were 7.6 × 167.6 cm (3.0 × 66.0 in) and were graduated every 1.3 cm (0.5 in) perpendicular to the edge with a silver permanent marker. For the BFR bench press, the wraps were applied to the proximal end of the upper extremities (above the bicep, below the deltoid). For the BFR squat, the wraps were applied at proximal end of the lower extremities (at the top of thigh, near the inguinal crease). The wraps were initially applied without tension, but secure enough to remain in place. Just before the start of the lifting session, the wraps were pulled to a 7.6 cm (3.0 in) overlap as measured by the silver markings and secured. This tension was maintained for the entire 4-set lifting session, including the rest periods. The wraps were removed immediately at the conclusion of the lifting sessions.
H/S/R Group
This group completed the traditional high-intensity training program (H) and the supplemental 1RM lifting protocols (S). They did so with the wraps in place, under conditions of practical BFR (R).
H/S Group
This group completed the traditional high-intensity training program (H) and the supplemental 1RM lifting protocols (S). However, they did not use the wraps; therefore, they did not receive the BFR treatment.
H Group
This group completed only the traditional high-intensity training program (H). They did not participate in the supplemental lifting sessions and at no time did they use the wraps.
M/S/R Group
This group completed the Modified Training Program (M). At the end of these sessions, they also completed the supplemental 1RM lifting sessions (S) and did so under conditions of practical BFR (R).
Training Sessions
To accommodate players' class schedules, the athletes were assigned by their coaches to attend 1 of the 3 training sessions each day. Training sessions were held at 7:15 AM, 1:30 PM, and 3:30 PM. Members of each training group were present during all training sessions.
Participants did not wear knee or elbow wraps during the workout sessions. In addition, they were instructed to refrain from any resistance training outside of football practice for the duration of the study.
Statistical Analyses
A 4 × 2 mixed-model multivariate analysis of covariance (MANCOVA), with training groups serving as the between-factor, pre- and posttests as the within-factor, and body mass as the covariate was performed using PASW Statistics 18. The level of significance was set at 0.05. Separate univariate 1 × 4 analysis of variance (ANOVA) tests were conducted on each dependent variable as a follow-up test for any significant main effects from the MANCOVA. The univariate follow-up ANOVA tests were also mixed model with training groups serving as the between-factor and pre- and posttests as the within-factor. Post hoc tests were conducted to examine any significant effects from the univariate ANOVAs.
Results
The means and SDs are listed in Table 4. MANCOVA results revealed a significant difference for the interaction on the dependent variables, Wilks' Λ = 0.606, F (15, 146.711) = 1.943, p = 0.023, multivariate ή2 = 0.154. To follow-up the significant MANCOVA on the interaction, separate univariate ANOVAs were conducted on each of the 5 dependent variables. Only one of the follow-up ANOVAs showed a significant effect. A significant interaction was found for 1RM squat, F (3, 57) = 6.460, p = 0.001, ή2 = 0.254 (Figure 2). To help interpret the interaction, a 1-way ANOVA was computed on the change scores for the 1RM squat. This ANOVA showed a significant difference between groups, F (3, 58) = 6.00, p = 0.001. Results of Fisher LSD post hoc tests revealed that the H/S/R group experienced greater gains in 1RM squat performance than did the M/S/R group (p < 0.000), the H/S group (p = 0.025), and the H group (p = 0.009).
Table 4: Girth and strength measures.
Figure 2: Group × time interaction for 1 repetition maximum squat. * = significantly different from the other 3 training groups (p ≤ 0.05).
MANCOVA results revealed no significant difference for the group factor on the dependent variables, Wilks' Λ = 0.75, F(15, 146.711) = 1.10, p = 0.360, multivariate ή2 = 0.093. MANCOVA results also revealed no significant difference for the time factor on the dependent variables, Wilks' Λ = 0.830, F(5, 53) = 2.172, p = 0.071, multivariate ή2 = 0.170.
Because the MANCOVA showed a nonsignificant main effect for group, follow-up analyses were not required. However, to better understand how current results compare to those of Yamanaka et al. (36), additional analyses were conducted on 1RM bench press performance and circumference measures.
For 1RM bench press, dependent t-tests were run to examine changes from pre- to posttest for the dependent variables, and a 1 × 4 ANOVA was conducted on change scores, which is a comparable analysis to the independent t-tests performed by Yamanaka et al. on percent change. Although the t-test on 1RM bench revealed that there was a significant increase across groups (t(1,61) = 6.713, p < 0.000), the ANOVA did not detect differences between the groups (F(3,58) = 1.687, p > 0.180).
Dependent t-tests on arm and thigh circumferences indicated a significant increase across groups (arm = t(1,61) = 2.04, p = 0.046; thigh = t(1,61) = 7.22, p < 0.000), but no change for chest girth (t(1,61) = 0.34, p = 0.739). The ANOVA did not detect differences between groups for any girth measurement (arm = F(3,58) = 0.946, p = 0.424; thigh = F(3,58) = 0.102, p = 0.958; chest = F(3,58) = 1.043, p = 0.381).
Discussion
The purpose of this study was to investigate the effects of a 7-week practical BFR protocol used in conjunction with traditional weight training on measures of muscular strength and size in collegiate American football players. We hypothesized that those who supplemented the traditional high-intensity strength training program with the low-intensity lifting protocol under conditions of practical occlusion would experience greater gains in muscular strength and size than those in the other treatment groups. The results partially support the hypothesis.
The primary results of this study were as follows: (a) H/S/R experienced significantly larger increases in 1RM squat than the other training groups; (b) although there was a significant increase in 1RM bench press across groups, the addition of the supplemental lifting protocol, with or without occlusion, made no difference in the extent of those gains; (c) although thigh and arm size increased significantly across groups, the addition of the supplemental lifting protocol, with or without occlusion, made no difference in the extent of those increases.
The supplementary low-intensity training protocol used in this study to examine the BFR treatment was a modification of that used by Yamanaka et al. (36), who also used a collegiate American football team as the testing population. Both the Yamanaka et al. study and this investigation used a training load of 20% 1RM with a set and repetition scheme of 1 set of 30 repetitions, followed by 3 sets of 20 repetitions, with 45 seconds of rest between each set.
The differences were that Yamanaka et al. (36) used a 5.0-cm wide elastic wrap (manufacturer not reported) and tightened to a 5.1 cm (2.0 in) overlap, whereas we used a 7.6-cm wide wrap and used a 7.6 cm (3.0 in) overlap to achieve the BFR. They used a cadence of 2.0:1.0 seconds for pacing the eccentric and concentric components of each lift, whereas we used a cadence of 1.5:1.5 seconds, based on work by Yasuda et al. (38).
Also, they performed both the BFR squat and bench press on the same day, as their 4-week program completed 3 total-body workouts per week (36). Our 7-week program used an upper- and lower-body split routine, with each being performed twice per week, for a total of 4 lifting days per week. Therefore, the BFR squat and bench press lifts were on separate days, each following the respective lower-body or upper-body workouts.
Finally, their study used 2 training groups, both of which completed the supplementary 20% 1RM lifting sessions, although only 1 received the practical BFR wrap treatment (36). We replicated this scenario with our H/S and H/S/R groups. However, we incorporated 2 additional groups in an effort to further clarify the potential effects of practical BFR training in a well-trained population. Yamanaka et al. reported significant differences between groups in 1RM bench press and squat performance gains, with those in the BFR treatment group experiencing larger increases. In addition, they also observed differences in chest size, with the BFR group again seeing greater increases. The results of this study only partially replicated the findings of Yamanaka et al.
Yamanaka at al. (36) reported that the BFR treatment group experienced significantly greater gains in 1RM squat than those of the non-BFR control group. This investigation replicated that finding. Univariate follow-up tests to the significant interaction showed a significant difference for 1RM squat, with the H/S/R group experiencing greater gains than the other training groups (Figure 2).
This disproportionate increase was likely a result of the use of practical BFR in conjunction with the low-intensity supplemental lifting protocol at the conclusion of the traditional high-intensity workout. A brief review of the training groups aids in understanding this interpretation. First, M/S/R also performed the supplemental lifts with the practical occlusion application (i.e., the wraps), but completed only the modified training program, which excluded any traditional high-intensity squat variations. This seems to indicate that performing low-intensity BFR after high-intensity training results in greater increases than can be expected when performing BFR in the absence of high-intensity training. Second, H/S completed the high-intensity training and the low-intensity supplemental lifts, but not under conditions of practical occlusion. Therefore, the occlusion application appears to provide an additional stimulus for strength gains beyond the low-intensity supplemental lifting protocol even when used in conjunction with high-intensity training. Finally, the gains experienced by M/S/R and H/S were the same as those seen by H, who completed only the traditional high-intensity workout. The lack of difference among these 3 groups further supports the concept that the additional gains seen by H/S/R are likely the result of the combination of high-intensity training followed by the low-intensity supplemental sessions under conditions of practical BFR.
As with the 1RM squat, Yamanaka et al. (36) reported significant increases in 1RM bench press performance, with the BFR treatment group experiencing greater gains than the non-BFR control group. This investigation did not support this finding. Because the MANCOVA showed a nonsignificant main effect for group, follow-up analyses were not required. But as previously noted, additional analyses were conducted to better understand how current results compare to those of the Yamanaka et al. study (see Results). Although the dependent t-test on 1RM bench revealed that there was a significant increase across groups, the ANOVA did not detect differences between groups. This indicates that in reference to upper-body strength, neither the supplemental lifting protocol nor practical BFR application provided any additional benefit beyond what was experienced with the traditional high-intensity training regimen.
One possible explanation for this is that the upper-body high-intensity workout had already provided a maximum stimulus for increasing strength and that the potential gains often seen with BFR training were attenuated accordingly. Wernbom et al. (33) noted in their review of resistance training that there appears to be a sigmoidal dose-response in reference to training volume, whereas gains in muscle mass seem to increase with greater volumes or durations of work, but that there is a point of diminishing returns. They go on to indicate that moderate volumes of work appear to result in the largest responses. Although Wernbom et al. are referencing muscle mass and not strength per se, it seems reasonable that a similar dose-response would exist with strength gains as strength is a property of the neuromuscular system. Therefore, it is possible that the volume of the upper-body high-intensity training protocol was near the peak of the dose-response curve and that the additional dose provided by the supplemental training volume and/or the BFR occlusion stimulus could not elicit further response.
Although the high-intensity workout may have provided sufficient stimulus for strength gains in H, H/S, and H/S/R, it does not explain the gains experienced by M/S/R, who only completed the modified training protocol before the BFR training. It is possible that the BFR application could account for the strength gains, which has been demonstrated previously in trained populations (3,30,36). However, in the absence of a non-BFR, modified training group with which to compare, it can only be speculated.
Another possibility is that although M/S/R did not perform any of the traditional “high-intensity” lifts, they still completed a substantial amount of total work. The overall volume of BFR training sessions can be quite high even though BFR training is often described as low-intensity work. Defining workout intensity by the percentage of the 1RM (%1RM) of a given lift for an individual is common and is often referred to as relative intensity (9). But, although BFR training typically uses a low relative intensity of 20–30% 1RM, the work volume for a session of BFR exercise can be substantial and possibly comparable to the work volume of a traditional “high-intensity” session. For example, a bench press 1RM of 100.0 kg would dictate a barbell load for a BFR session using 20% 1RM to be 20.0 kg. If the BFR protocol was identical to that used in this study, a total of 90 repetitions with that load would be performed, resulting in an exercise volume-load (repetitions × weight) of 1,800 kg. If a more traditional high-intensity workload of 80% of that same 1RM (80.0 kg) were used to complete a typical high-intensity workout of 4 sets of 6 repetitions, the total exercise volume-load would be 1,920.0 kg—only 120.0 kg more than the BFR session. Therefore, it is plausible that the volume-load completed by M/S/R was high enough on the dose-response curve that strength gains resulted, despite the absence of using a high relative intensity.
Although research generally indicates that traditional high-intensity programs are superior for strength gains, there is some work that suggests that using a low relative intensity along with higher repetitions may also be effective at promoting strength, provided enough volume is used, even in the absence of BFR (26). However, because total workloads for each participant were not calculated for this study, this remains speculative.
The possibility that the upper-body high-intensity training program alone may have provided a maximal strength gain stimulus is also supported by observations made during this study that seem to oppose those made by Yamanaka et al. (36) in their investigation. They stated that all participants in their study were able to complete every repetition in the supplemental protocols and that personal conversation with the participants after the sessions indicated that the players felt that the number of repetitions “was not sufficient for them to reach exhaustion.” Interestingly, our observations during this study were quite different. Although no data were collected on repetitions completed, we observed that some participants had to pause or skip a repetition during the supplemental lifting sessions. Personal discussions indicated that these participants were simply getting fatigued and needed a brief respite to continue. Although this was only occasionally seen during the squat exercise, it was more common during the bench press sessions. This was true for participants who were in both H/S and H/S/R (non-wrapped and wrapped), which indicates that the fatigue could not have been because of the use of the practical BFR wraps alone.
This is also supported by our observations that those in M/S/R did not skip repetitions during the sets, even though they were also using the elastic wraps in the same manner as H/S/R. Because M/S/R completed only the modified training program before BFR training (i.e., no high-intensity squats, bench press, or their variations), it suggests that the fatigue experienced by H/S and H/S/R was more likely a result of the high-intensity training program that they completed just before the supplemental training, rather than the extra lifting sessions and/or the BFR wraps. Although Yamanaka et al. (36) did not report the details of the strength and conditioning program used in their study, it seems reasonable to surmise that it was of a lower overall volume than the high-intensity training program used by H, H/S, and H/S/R in this investigation. The volume of the workout and BFR training protocol used by Yamanaka et al. may have been sufficiently low enough on the dose-response curve that the extra stimulus provided by the BFR wraps was able to produce an increased response.
In reference to the work volume-load of the lower-body sessions, H/S/R did experience a greater increase in 1RM squat compared with H and H/S. This suggests that the high-intensity lower-body training program did not provide a maximal stimulus for strength gains. Therefore, the volume was likely lower on the dose-response curve relative to the upper-body training, allowing for the addition of the practical BRF application to elicit a greater strength response.
Similar to Yamanaka et al. (36), this investigation employed the use of girth measurements in an effort to assess changes in muscular size, namely at the thigh, chest, and upper arm. The aforementioned study observed increases in chest girth but not thigh or arm girth. Thefindings of this investigation were contrary. As with the 1RM bench press, the MANCOVA revealed no interaction for group on circumferences, so additional analyses were conducted to better compare current results to those of Yamanaka et al. (see Results). The dependent t-tests on arm and thigh circumferences indicated a significant increase across groups, but no change for chest girth. The ANOVA did not detect differences between groups for any girth measurement. So, while there was no change in chest size, there were small but significant increases at the thigh and the arm across groups, but no differences among the treatments. However, the practical significance of these results for changes in girths becomes questionable when consideration is given to the magnitude of the changes, as can be seen in Table 4.
This study was not without limitations. Because of using elastic knee wraps in a practical manner to achieve BFR, knowing the precise pressure actually applied to each participant was not possible. Benefits from BFR occur when there is adequate pressure to occlude venous return, but yet only restrict arterial delivery (25). Wilson et al. (35) have shown that elastic wraps (7.6 cm wide) applied with a perceptive pressure of 7 on a scale of 0–10 are effective at allowing a restricted arterial flow while occluding venous return in the thigh muscle.
Perceptive pressure is a subjective measure and will likely differ among individuals and may even vary for each person on a day-by-day basis. Yamanaka et al. (36) used a 5.1 cm (2.0 in) overlap to achieve BFR in their study but did not report on the procedure used to determine that degree of tension. Before the start of our training program, we recruited 4 athletes in an effort to standardize the elastic wrap pressure to be used in the study. We explained to them the concept of the 0–10 scale of perceptive pressure and how to use it in reference to wrap pressure (35). We then applied a wrap to the upper leg with just enough tightness to remain in place (perceptive pressure = zero), and a note was made of the location of the end of the wrap. Then, the wrap was slowly pulled tight until the participant indicated that the tightness had reached a perceptive pressure of 7. The wrap was then secured in place. The difference between where the end of the wrap was before the tightening to where it was secured after the tightening (i.e., the overlap) was measured, on which the wrap was removed.
This procedure was repeated with every participant and each required a slightly different overlap to reach a perceptive pressure of 7. The overlaps were then averaged, with a result of approximately 7.0 cm (2.75 in). Following the same procedure on the arms, we found an average overlap of approximately 6.6 cm (2.60 in). We concluded that an overlap of 7.6 cm (3.0 in) for both the upper body and lower body during the study would likely be sufficient to obtain a perceptive pressure of 7 for most of the participants in the study. The use of a single overlap measure for both applications also simplified the procedures and reduced potential errors in applying and tightening the wraps.
Another potential limitation is that the participants in this study were well-trained, male, collegiate American football players. The results might not be generalizable to other athletic populations, non-athletes, or those who are weighttraining novices.
Future research should examine high-intensity programs of various work volumes and their relationship with the effects of concurrent practical BFR programs. This could provide additional insight into determining whether a dose-response does exist when the 2 are used in conjunction and if so, where the point of diminishing returns can be expected. If it is found that practical BFR, when used together with lower volumes of high-intensity work, can elicit strength gains that are similar to, or exceed those typically observed with traditional higher volumes of high-intensity work, then this could have implications for future program design. A lower overall training volume and/or lower external load may allow athletes to recover faster, reduce their risk of injury, and lessen their chance of overtraining. Taken together with an increase in strength, this could translate to improved athletic performance.
Investigating the dose-response in the context of in-season strength and conditioning programs would be especially relevant as these programs normally reduce volume as focus shifts from strength training to actual competition. This shift generally results in athletes experiencing declines in strength as the season progresses. An effective combination of low volume, high-intensity work and practical BFR may result in the maintenance or increase of strength during the competitive season, which is typically not experienced.
Also, limb size and possibly body composition appear to play a role in how much pressure is needed to achieve adequate BFR (19). Therefore, additional research should examine how to best individualize perceptive pressure when using practical BFR, for both the lower- and upper-body applications.
In conclusion, this study demonstrated that the use of a practical BFR program in conjunction with a traditional high-intensity off-season training program was effective in increasing 1RM squat performance in well-trained collegiate athletes.
Practical Applications
The results of this study indicate that practical BFR training can be effective in increasing 1RM squat performance when added to an off-season, high-intensity collegiate American football strength and conditioning program. Elastic powerlifting knee wraps are relatively affordable and easy to use compared with traditional BFR methods. This reduction in the cost and complexity typically associated with BFR training provides athletic programs, teams, coaches, and athletes an increased opportunity to incorporate BFR into their strength and conditioning programs.
Acknowledgments
The authors would like to thank the Emporia State University football team and coaching staff for their participation and dedication to this study. Also, we would like to thank the ESU Research and Grants Center and the ESU Teachers College for their help in funding this project.
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