The change in 1RM in bench press was significantly greater in the experimental group than in the control group, t(1, 30) = −3.859, p < 0.05. Likewise, the change in 1RM in squat was significantly greater in the experimental group as compared with that in the control group, t(1, 30) = 4.193, p < 0.05 (Table 3).
The change in the girth of the upper chest was significantly greater in the experimental group than in the control group, t(1, 30) = −5.102, p < 0.05. Additionally, the change in the girth of the lower chest was significantly greater in the experimental group as compared with that in the control group, t(1, 30) = −2.574, p < 0.05 (Table 4).
The change in girth of the right upper arm was not significantly greater in the experimental group than in the control group, t(1, 30) = 0.204, p > 0.05. The change in the girth of the left upper arm was significantly greater in the experimental group as compared with that in the control group, t(1, 30) = 2.385, p < 0.05. The change in the girth of the right lower arm was not significantly greater in the experimental group than in the control group, t(1, 30) = 1.338, p > 0.05. Likewise, the change in the girth of the left lower arm was not significantly greater in the experimental group as compared with that in the control group, t(1, 30) = 1.379, p > 0.05 (Table 4).
The change in the girth of the right thigh was not significantly greater in the experimental group than in the control group, t(1, 30) = −1.328, p > 0.05. Further, the change in the girth of the left thigh girth was not significantly greater in the experimental group as compared with that in the control group, t(1, 30) = −0.870, p > 0.05 (Table 4).
The purpose of this study was to investigate the effectiveness of 4 weeks of BFR training on muscular hypertrophy and muscular strength in NCAA Division IA collegiate football players. All the 32 subjects completed the study. This study was novel in that the subjects were more physically active than were most previous research samples (1,3,6–9,12–16,18,20–22,24–26,28,29). Moreover, the sample size of this study was greater than that of previous studies, which generally consisted of <20 subjects (1–3,8,9,14,18,20–22,24,26,27,29).
This study demonstrated that low-intensity resistance exercise (20% 1RM) combined with BFR resulted in greater muscular hypertrophy and significantly greater (p < 0.05) increases in muscular strength, whereas there were no significant changes in height and body mass, as compared with the control group (Table1). In terms of strength gains, the average percent increase in bench press was 7.0% in the BFR training group, which was significantly greater than the 3.2% increase in the control group (Table 3). Likewise, the 8.0% increase in the squat 1RM, on average, in the BFR training group was significantly greater than the 4.9% increase in the control group (Table 3). Therefore, although both groups showed significant changes after the 4-week period, the BFR training group had significantly greater (p < 0.05) increases in muscular strength. Because the subjects in this study were trained football players who had already achieved a high level of muscular strength, low-intensity (i.e., 20% 1RM) resistance training would not normally have produced muscular strength gains. The significant increases in strength and girth measurements in the control group are attributed to the regular off-season strength training program. This may indicate that short-term BFR training is effective in increasing strength among the athletic population when combined with high-intensity training.
The strength gains observed in this study were consistent with those reported by several researchers (1,3,9,18,25,27,28). Although previous studies had examined gains in muscular strength by measuring maximum voluntary contraction, isokinetic torque, 1RM, or a combination of those, muscular strength was assessed in this study through bench press and squat 1RM. More specifically, Yasuda et al. (29) who employed BFR training within the general population demonstrated higher EMG activity in the involved muscle group during low-intensity (i.e., 30% 1RM) bench press with vascular restriction. In addition, they indicated that the BFR training led to a hypoxic and acidic environment (29), resulting in lactic acid accumulation, which inhibits muscular contraction and recruitment of additional fast-twitch motor units to maintain force production (28). The additional fast-twitch fiber recruitment as a result of BFR training would be one of the factors that could potentially induce higher muscular strength. In fact, Takarada et al. (28) investigated integrated electromyogram (iEMG) activity to determine muscle fiber recruitment during BFR training and reported that there was almost equal iEMG activity between lower intensity BFR training and traditional high-intensity exercise. This finding could explain the underlying mechanism of the strength gains that occurred in our study.
In addition, increases in upper and lower chest girths were also observed, which revealed muscular hypertrophy (Table 1). Although the subjects in this study were trained athletes and had already achieved muscular hypertrophy in the chest area, greater muscular hypertrophy was observed in the chest girths of the subjects who were in the experimental group as compared with those in the control group. Interestingly, Yasuda et al. (29) showed that BFR bench press training significantly increased muscle activity, not only in the blood-flow restricted muscle (i.e., triceps brachii) but also the blood-flow nonrestricted muscle (i.e., pectoralis major). During bench press, the chest and triceps muscles are the primary muscles activated. Additionally, Yasuda et al. (29) documented elevated muscular activity in the pectoralis major muscle during the BFR training. It has been reported that BFR training induces acute changes in the redistribution of cutaneous blood circulation, resulting in greater girths (16). Although blood-flow redistribution after the BFR training could have increased the girth measures in our study, posttest measures were conducted 2 days after the last training session; thus, blood-flow changes were less likely to impact the observed outcomes.
To further extend our understanding of muscular hypertrophy because of BFR training, Madarame et al. (18) documented a crosstransfer effect as a result of BFR training. A crosstransfer effect occurs when muscular hypertrophy is seen not only in the trained limb but also in the untrained limb when combined with contralateral resistance training. In the study of Madarame et al. (18), adding lower extremity BFR training after regular upper extremity exercise induced greater hypertrophy in the upper extremity. Similarly, the subjects in this study performed squats immediately after bench press. Thus, the crosstransfer effect could also have played an important role in producing the observed hypertrophy of the chest in this study.
An interesting and novel finding of this study was that the 4 weeks of BFR training produced significant increases in chest girths but not in arm or thigh girths. This is contrary to the findings of previous research that has demonstrated significant changes in girths in all extremities after BFR training (1–3,6–9,13,17,18,20,22,24–29). Possible explanations for this difference may be (a) the variation in the type of subjects; (b) the number of exposures to BFR training; and (c) the types of exercise performed.
With respect to the variation in sample populations, the subjects in most previous studies that displayed hypertrophy with BFR training were healthy, untrained individuals (1,3,9,13,18,22,25,28,29), whereas this study examined physically trained individuals. For instance, the subjects in the study of Fujita et al. (9) were novice lifters. In terms of the number of training exposures, Takarada et al. (27) and Abe et al. (2) documented increases in muscular hypertrophy in both upper and lower extremities after a greater number of BFR training exposures. Specifically, the length of BFR training in the study of Takarada et al. (27) was 8 weeks with a total of 16 exposures to BFR training and in the study of Abe et al. (2), the training period was 8 days, providing a total exposure of 16 sessions of BFR training. In contrast, the training period of this study was 4 weeks with 12 exposures to BFR training, indicating that the number of exposure may not have been sufficient to produce hypertrophy in the upper and lower extremities as a result of the present intervention. Fujita et al. (9) documented significant hypertrophy in the quadriceps muscles after the same number of exposures to BFR training as in this study, yet, it is important to note that the subjects in the study of Fujita et al. (9) were from the nonathletic population.
Another possible explanation as to why there were significant changes in chest girths, but not in arm and thigh girths, might have been the differences in the type of exercises and exercise regimen performed in this study. In most previous studies, the subjects performed either biceps curls or knee extension and flexion, whereas the subjects in this study performed bench press and squat. Although increases in chest girths were observed in this study, another arm exercise may have been needed to observe muscular hypertrophy in the upper extremities in these trained athletes. Similarly, another lower extremity exercise could be added to enhance muscular hypertrophy in highly trained athletes.
The exercise protocol for BFR training in this study was 1 set of 30 repetitions of 20% predetermined 1RM, then 3 sets of 20 with each set separated by a 45-second rest period, which was consistent with that in several studies. All the subjects were able to complete all repetitions in this study, and according to brief conversations with the subjects after the training sessions, the number of repetitions was not sufficient for them to reach exhaustion. In fact, the BFR training study with elite rugby players by Takarada et al. (27) consisted of exercises until failure. The subjects in this study were trained athletes; therefore, the conventional BFR training regimen could have been modified by increasing the number of repetitions to perhaps produce greater increases in strength and girth measurements.
Lastly, the lack of significance in arm and thigh girths in this study may be because of the regular strength training that preceded each BFR training session. No other studies have been conducted to investigate the effectiveness of BFR training combined with regular high-intensity strength training. Therefore, the inclusion of regular strength training might have affected the results of BFR training in this study.
Several limitations did exist in this study. The first limitation was the number of exposures to BFR training. This study involved only 12 exposures to BFR training over a 4-week period, which was fewer than the previous studies (1–3,7,9,11,18,22,27,28). Additionally, there was no follow-up testing to see whether or not the observed increases in muscular strength and hypertrophy after BFR training were sustained. Further studies are warranted to observe the long-term effect of BFR training in trained athletes. As stated earlier, our results suggest that BFR training to failure be applied in future studies to maximize muscular hypertrophy and strength gains in trained athletes.
Another limitation of the study was that body water and body fat percentage were not measured. Specifically, body water and body fat measures can differentiate the changes in girth measures caused by increased protein synthesis from those caused by alterations in intercellular fluid levels and loss of body fat. True muscular hypertrophy is typically assessed using magnetic resonance imaging to assure that the girth measurements are not influenced by subcutaneous adipose tissue or intercellular fluid. In addition, even though the timing of the training sessions and tests were controlled, nutrition intake and hydration levels were not controlled. Although the magnitude of occlusion was controlled by following the same procedure across the subjects, pressure levels were not digitally measured due to the lack of an appropriate pressure control device. Lastly, the subjects of BFR training studies, including this study, have been limited to male subjects. Further research should encompass a variety of population to set recommendations to modify the traditional BFR training regimen.
In summary, BFR training in this study resulted in increased muscular strength and muscular hypertrophy among NCAA Division IA football players. However, future research is needed to reveal the potential advantages of BFR training in trained athletes.
The results of this study indicated that 4 weeks of occlusion training for bench press and squat can significantly improve muscular strength and muscular hypertrophy in NCAA Division IA collegiate football players when added to a traditional strengthening program. Although BFR training in this study showed improvements in measured outcomes, BFR training to failure along with multiple exercises per muscle group may produce greater outcomes in physically trained individuals. Occlusion training, therefore, can be used as a supplementary workout to regular strength and conditioning sessions during the off-season training period.
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Keywords:© 2012 National Strength and Conditioning Association
KAATSU; hypertrophy; athletes