The main findings of this study were that the protocol with higher BFR (20/120) and high load (70/0) induced a greater RPE response, whereas the LL-BFR protocols with higher BFR (20/80 and 120/0) induced higher PP and a lower feeling of pleasure, that is, “bad” perceived affect.
We observed higher RPE values in the 70/0 and 20/120 protocols than in the protocols with lower BFR (20/40 and 20/80). Moreover, the RPE in the 20/120 protocol was significantly increased as much as that in the 70/0 protocol from the second to fourth sets of exercise. RPE in response to HL seems to be intensity-dependent when exercise is not performed until muscular failure [32, 33]. For instance, Day et al. [33] reported a higher RPE value at 90% 1RM when compared with 70% and 50% 1RM in six exercises for the upper and lower body. When LL-BFR was compared with the HL protocol without muscular failure, studies have shown a higher RPE in favor of HL [11, 34]. Otherwise, when LL-BFR with partial BFR (~ 100 mmHg) at 30% 1RM and HL at 70% 1RM are performed until exhaustion, the RPE response is similar in both protocols [10]. Despite a similar RPE response found in our study between the 20/120 and 70/0 protocols, the magnitude of increase in 20/120 (ES: 5.4; 291%) was fivefold higher than that in HL (ES: 1.6; 48%). These findings highlight the pivotal role of the level of BFR on the RPE response, although the total training volume (TTV) in the 20/120 protocol was lower than that in all other protocols (p < 0.05).
When comparing the LL-BFR-induced RPE response with different degrees of BFR, previous studies have observed a dose‒response of BFR on RPE when the protocols were performed with volume matching [3, 35]. Mattocks et al. [3] reported higher RPE levels when participants exercised the upper arm at 30% 1RM with 90% AOP compared with 10–50% AOP across each set of exercise. In addition, a higher RPE response was observed when applying moderate BFR (70% and 80% of AOP) at 30% 1RM than when applying lower BFR (40% and 50% of AOP) [35]. Corroborating the abovementioned findings, we also observed significantly higher RPE during the 20/120 compared with the 20/40 and 20/80 protocols. For instance, in the 20/40 and 20/80 protocols, a BFR of ~ 87.1 ± 32.1 mmHg and ~ 161.3 ± 37.6 mmHg, respectively, was applied, while in the 20/120 protocol, a BFR of ~ 223 ± 57.0 mmHg was applied using a 5-cm wide cuff. In that regard, we may assert that during the 20/120 protocol, all participants initiated the exercise in complete arterial occlusion, and consequently, a higher RPE, as the degree of arterial occlusion exhibited in the 20/120 protocol may have contributed to a lower TTV, with 50% of participants failing to complete the last set of exercises.
To compare the RPE response in the 20/40 and 20/80 protocols, we observed a greater RPE value during the 20/80 protocol only in the third set of exercise (p = 0.028). We can argue that the exercise protocol (4 sets of 15 reps at 20% 1RM) may have blunted the increase in RPE across sets during the 20/80 protocol, divergent from other studies that have observed increases in RPE in all exercise sets (e.g., four sets − 1x30 + 3 x 15 reps at 30% 1RM and 90% of AOP) [3, 35]. Finally, we also found that the RPE significantly increased in 20/40 only during sets 3 and 4 (p < 0.0001), and the 20/40 protocol presented a lower RPE value than all other protocols (p < 0.05). Although the 20/40 protocol seems to be more tolerable, this BFR level when combined with 20% 1RM has been shown to be inefficient in yielding acute muscular responses beyond that of low-load resistance exercise (LL) alone [18]. LL-BFR-induced muscular adaptations have been shown to be effective when LL-BFR at 20% 1RM is combined with higher BFR (e.g., 60%-80%) (36). Conversely, increases in BFR seem secondary to exercise intensity when higher training loads are used (30% − 40% 1RM) [37]. Recently, a researchers group published a position stand on BFR exercise suggesting a large pressure range (40% − 80% of AOP) [38]. Thus, it is possible to prescribe LL-BFR protocols with the lowest pressure to attenuate the RPE, discomfort and pain; however, it is important to highlight that the BFR protocols must provide a minimum “threshold” stimulus to be effective training.
Regarding pain perception (PP), we observed greater PP in protocols with higher BFR (e.g., 20/80 and 20/120) compared with the 70/0 protocol in sets 3 and 4 (p < 0.001) and with the 20/40 protocol in sets 2, 3 and 4 (p < 0.0001). Some studies have found that hypoxia induced by LL-BFR yielded higher accumulation of metabolites (e.g., lactate, inorganic phosphate [Pi], and pH) [17, 39] and a reduction in tissue muscle oxygenation [TMO] when compared with low-load exercise without BFR (LL) [35, 18, 40] and similar or exceeded those from HL [39]. Thus, we suggest that the 20/80 and 20/120 protocols may have induced a greater accumulation of metabolites and a reduction in TMO [18]. Llet et al. [18] reported that TMO during exercise was significantly reduced across sets in LL-BFR and HL, with no significant change in LL. However, during rest intervals between sets, TMO was recovered to baseline level only for the HL, while it remained unchanged during the entire LL-BFR protocol. These findings support the contention that the HL protocol may cause smaller decreases in TMO during exercise and resting intervals due to relative local hyperoxygenation. Thus, one might speculate that the maintenance of ischemia during rest intervals in the 20/80 and 20/120 protocols would favor decreased metabolite removal and would create an environment for increased PP compared with the 70/0 protocol. Additionally, a higher reduction in TMO, deoxygenation and hypoxia-induced increase in accumulation metabolites in 20/80 (ES: 2.5; 245%) and 120/0 (ES: 3.9; 368%) compared with 20/40 protocol (ES: 1.5; 212%) could explain a higher PP with the increase of arterial occlusion pressure dose‒response pressure [18, 40]. We also observed that there was no significant difference in PP between 20/80 and 120/0. In this regard, we may speculate that blood flow to the working muscle at the 20/80 protocol could be closest to the arterial occlusion level, which could potentially be related to the behavior of perceptual responses.
Recent studies with BFR in different types of training (e.g., squat, treadmill) have reported increased RPE, fatigue and impaired mood state in athletes [24, 25]. Herein, our findings showed that immediately after performing the 20/120 and 20/80 protocols, the participants rated their feelings of affect (PA) as “fairly bad to very bad” (p < 0.0001), whereas after the 70/0 protocol, they rated themselves as “good”, and after the 20/40 protocol, they rated themselves as “fairly good to very good” (Table 4). The measurement of PA from 17 out of 22 participants from the 20/120 protocol (~ 77.2%) was rated as feeling of negative affect (displeasure), such as between “fairly bad to very bad”, with eight participants rating this protocol as “very bad” (~ 36.3%), while 10 out of 22 participants in the 20/80 protocol (~ 45.4%) rated it as “bad” (Table 4). Similar to PP, these results have reinforced the pivotal role that BFR level plays on PA (good/bad) evaluated by feeling scale (FS). Although almost half of the participants rated the 20/80 protocol as “bad”, more than half of the resistance-trained individuals (54.5%) rated this protocol as “neutral” (N = 4; 18.2%) and “fairly good to good” (N = 8; 36.3%). Given the comparable increases in strength and muscle hypertrophy observed between the 20/80 protocol and conventional resistance exercise (≥ 70% 1RM), we may suggest that this protocol could be feasible and incorporated into the routine training of resistance-trained individuals [2, 36, 14].
This is the first study that investigated the manipulation of different degrees of BFR with LL on perceived affect through FS (good/bad). Two other recent studies investigated the measure of affect with BFR [7, 26]. In the first study, the researchers reported an acute negative PA (“bad” feeling) and higher PP of BFR walking at 200 mmHg, as well as lower task motivation and enjoyment compared with walking alone [7]. Divergent from our study, the participants from Mok´s study underwent BFR with an absolute pressure (200 mmHg) during walking, and the authors did not report the cuff width. In the second study, with a similar protocol to ours, it was observed that four sets of LL-BFR at 20% 1RM, with 8 cm wide tourniquet cuffs wrapped placed on thighs, at 200 mmHg, resulted in lower affect, task motivation, enjoyment response, concurrently with higher PP and leg discomfort compared to the control-matched protocol [26]. Thus, it is important to highlight that regardless of cuff width, when arbitrary or absolute pressure is applied to the BFR protocol, it is possible that during exercise, some individuals reached arterial occlusion and then could have rated higher PP and PA levels.
Regarding the 70/0 protocol, only two out of 22 participants (9.8%) rated as “bad”. This finding was not surprising because the 70/0 protocol is part of the routine training of resistance-trained individuals. Interestingly, after the 20/40 protocol, participants rated PA as “good or very good”, with only one participant considering this training model “bad” (Table 4). Altogether, our findings suggest that the “good” feeling (PA) in resistance-trained individuals is related to the specificity of training (e.g., HL), and the feelings of pleasure and displeasure are directly related to the degree of restriction pressure used in the BFR protocol.
In conclusion, LL-BFR with a higher degree of BFR induced a similar RPE compared with HL and a higher PP compared with both LL-BFR with lower BFR or HL. In addition, LL-BFR with a higher degree of BFR induced lower affect (“bad feeling”) immediately after the exercise bout.