Effects of bilateral low-load resistance training with blood-flow restriction on post-activation performance enhancement in male collegiate athletes

Introduction

Post-activation performance enhancement (PAPE) is a practical strategy used to enhance muscular strength or power performance following the completion of conditioning activity (CA) in various sports, including athletic competitions and ball games (Dello Iacono, Martone & Padulo, 2016; Till & Cooke, 2009; Tsoukos et al., 2016). Previous research suggests that the potential mechanisms of PAPE may involve phosphorylation of myosin light chains (Hodgson, Docherty & Robbins, 2005; Smith & Fry, 2007), increased motor unit recruitment (Sale, 2002), and alterations in the angle of muscle fiber pennation (Blazevich & Babault, 2019). These physiological changes enhance force generation and power output. Although the exact biological processes remain incompletely understood, achieving an optimal PAPE effect requires a balance between fatigue and potentiation during conditioning activity (Jami et al., 1983; Rankin et al., 1988; Rassier & Macintosh, 2000; Vergara, Rapoprot & Nassar-Gentina, 1977). This balance is influenced by factors such as the individual’s physiological characteristics (e.g., muscle fiber composition, neuromuscular adaptations, and recovery capacity) (Chiu et al., 2003), the intensity and volume of conditioning activity, rest intervals (Wilson et al., 2013), and the athlete’s training status (Suchomel et al., 2016).

Resistance training (RT) protocols involving 1–5 repetitions at 80–90% of one repetition maximum (1RM) are commonly used to trigger PAPE (Seitz & Haff, 2016; Wilson et al., 2013). However, high-load (HL) exercises can lead to significant mechanical strain on the lower extremities making it unsuitable for athletes undergoing multiple training sessions per day or individuals undergoing rehabilitation (Haff & Triplett, 2016). These individuals typically exhibit lower neuromuscular efficiency and have a reduced capacity to recover from HL exercises compared to highly trained athletes (Chiu et al., 2004; Khamoui et al., 2009; Scott & Docherty, 2004). Furthermore, HL protocols often require heavy equipment, which can pose practical challenges in certain training environments. As such, HL training may not always be the most effective or feasible method for inducing PAPE, especially for those with limited training experience. Given these considerations, blood-flow restriction (BFR) training has gained significant attention in the scientific community within this context.

Blood-flow restriction (BFR) training involves applying a tourniquet or inflatable cuff to the limbs to partially obstruct venous return or reduce arterial inflow. This technique uses light loads, typically 20–40% of the one repetition maximum (1RM), which contrasts with traditional high-load resistance training (over 70% 1RM). The partial restriction of blood flow triggers metabolic stress and hypoxia, leading to adaptations similar to those achieved with high-load training, including increased motor unit recruitment and muscle hypertrophy (De Queiros et al., 2024; Loenneke et al., 2012b; Sato, 2005). Empirical studies have substantiated the efficacy of low-load resistance exercises in conjunction with BFR in sport science. For instance, Doma et al. (2020) showed that BFR during lunge exercises improved vertical jump height and power output. Similarly, Wilk et al. (2022) reported significant increases in power and bar velocity during bench press exercises with BFR. Furthermore, Miller et al. (2018) found that BFR, when combined with whole-body vibration or maximum voluntary contraction, enhanced jump performance (Miller et al., 2018). These findings suggest that BFR may augment PAPE through mechanisms such as metabolic stress and increased motor unit recruitment. While there is considerable research on PAPE of combining low-load resistance training with BFR, the back squat of a single session of BFR combined with low-load training on specific performance outcomes, such as vertical jump height (VJH) and force production, have not been fully explored.

This study aims to fill this gap by investigating the acute PAPE effects of BFR+low-load (LL) on explosive lower limb performance. Furthermore, by comparing peak and mean countermovement jump (CMJ) metrics, this study provides distinct insights into neuromuscular response, offering a methodological distinction from previous research that has typically focused on either peak performance or long-term outcomes.

Materials & Methods

Procedures

The experimental sessions are depicted in Fig. 1. Upon arriving at the laboratory, the previously described warm-up from the familiarization session was used on each trial. After 5 min of rest, baseline testing for CMJ were performed before the experimental sessions. Subsequently, one of the three trails were performed: (A) low-load resistance exercise at 30% 1RM back squat combined with BFR for four sets of 15 repetitions (BFR+LL): the pneumatic cuffs were inflated to estimated 80% of the participant’s individual arterial occlusion pressure (AOP) during each exercise set and deflated during the inter-set rest periods. (B) Low-load resistance exercise without BFR for four sets of 15 repetitions (LL): this condition followed the same exercise protocol but without the application of BFR. (C) Control condition involving passive rest (CON): no exercise and BFR was applied. Participants maintained a static standing position for a total of 360 s, divided into four sets of 45 s with three 60-second intervals. All squat repetitions were executed with a 2-second eccentric phase and a 1-second concentric phase. Between each set, a one-minute rest period was observed, during which subjects were instructed to remain standing without any movement. After each trial, participant completed three CMJ attempt at each assessment timepoint. The peak and average CMJ performance was recorded for further analysis.

Results

Statistical analyses showed significant condition × time interactions for VJH, RPP, FI, and RFD with detailed results provided in Table 2. Mean and peak absolute values for vertical jump parameters are shown in Tables 3 and 4, respectively, while percentage changes are illustrated in Fig. 2.

The two-way ANOVA revealed significant condition × time interactions for VJH (F (4.535, 63.50) = 16.94, p < 0.001), RPP (F(10, 140) = 11.76, p < 0.001) and FI (F10, 140 = 11.00, p < 0.001) (Table 2). Multiple comparisons analysis revealed that BFR+LL significantly (p < 0.05) improved VJH (46.93 ± 3.78 cm, ES = 0.76), RPP (61.13 ± 4.31 w/kg, ES = 0.42), and FI (235.0 ± 25.3 Ns, ES = 0.33) compared with CON (43.79 ± 4.13 cm, 59.78 ± 4.45 w/kg, 227.7 ± 25.4, Ns) and LL (44.37 ± 4.32 cm, 59.16 ± 4.66 w/kg, 228.0 ± 28.7 Ns) at CMJ-12 (Table 3). The percentage changes from baseline were 6.3 ± 2.2%, 3.0 ± 2.4%, and 3.9 ± 2.9%, respectively. However, there was a significant decline in performance (p <0.05) observed immediately after BFR+LL, with VJH (40.15 ± 3.87 cm, ES = −0.89), RPP (54.40 ± 4.55 w/kg, ES = −1.11), and FI (215.0 ±23.2 Ns, ES = −0.51) compared to CON (44.24 ± 4.61 cm, 59.47 ± 4.63 w/kg, 226.9 ± 28.7, Ns) and LL (39.90 ±4.88 cm, 56.74 ± 5.91 w/kg, 221.1 ± 28.8 Ns) at CMJ-0. The percentage changes from baseline were −9.1 ± 5.1%, −8.3 ± 4.3%, and 5.0 ± 2.9%, respectively.

There were no significant differences in RFD at any time points after the three protocols. Moreover, the peak CMJ performance was not different between baseline and either after CON, LL or BFR+LL (Table 4).

Discussion

This study aimed to investigate the effect of low-load resistance training combined with bilateral blood flow restriction on inducing post-activation performance enhancement (PAPE) in vertical jump performance. The key findings of this study revealed that BFR+LL resulted in improved vertical jump height (VJH), relative peak power output (RPP), and force impulse (FI) at the 12th minute after the completion of the protocol, despite a temporary decrease in these measures immediately after the protocol. Additionally, the study found no significant changes in the rate of force development (RFD) and no notable differences in peak countermovement jump (CMJ) performance across the three tested conditions.

Previous studies have shown that BFR combined with resistance exercise can enhance performance within 12 min post-exercise, depending on the training protocol and intensity. For example, Doma et al. (2020) observed improvements in jump height and power output with BFR during lunge exercises, while Wilk et al. (2022) reported increased power and bar velocity in bench press exercises (Doma et al., 2020; Wilk et al., 2022). Miller et al. (2018) also found positive effects of BFR combined with whole-body vibration or maximum voluntary contraction on jump performance (Miller et al., 2018). The mechanisms underlying post-activation performance enhancement (PAPE) following BFR+LL training remain unclear. While metabolites such as lactate and reactive oxygen species (ROS) are commonly proposed to play a role in potentiating performance, their precise contributions to the acute performance enhancement observed in this study are speculative. Lactate accumulation during BFR+LL training likely contributes to metabolic stress, which has been associated with short-term improvements in performance. However, the exact mechanisms by which lactate may enhance performance are still not fully understood. Similarly, while ROS are traditionally linked to long-term adaptations like muscle hypertrophy, they may also contribute to acute performance enhancement in BFR training through specific signaling pathways that support recovery and performance. The role of these metabolites in potentiating performance remains uncertain, and future research is needed to clarify these mechanisms. These mechanisms contribute to the acute performance enhancements observed post-BFR+LL training. While our study’s methodology did not directly allow us to verify the contributions of lactate and ROS to the PAPE effects, our findings suggest that the current unrestricted low-load resistance exercise protocol may not effectively improve CMJ performance. This could be due to the nature of the repetitions, which may not provide the necessary explosive load required to enhance vertical jump performance. Additionally, the current study employed a protocol of four sets of 15 repetitions, which induced a significant PAPE response in vertical jump performance. The observed effects may be linked to the alignment of the kinematic characteristics of the conditioning contractions with the performance measure (i.e., vertical jump), as studies suggest that the induction of PAPE is more effective when these characteristics are similar (Doma et al., 2019; Doma et al., 2016). However, as an inducing protocol, the use of multiple sets of 15 repetitions in this study was unavoidable for generating sufficient metabolic stress and muscle fiber recruitment. Future studies could explore alternative exercise schemes, such as varying repetition tempos or using higher-intensity protocols, to further optimize the induction of PAPE and maximize its effects on explosive performance. Consequently, by correlating these metrics with post-activation performance enhancement (PAPE), our study provides empirical support for the efficacy of BFR+LL training in eliciting PAPE. This offers valuable insights for athletes and coaches aiming to optimize training outcomes for explosive sports performance.

It is interesting to note that CMJ performance decreased following BFR+LL at CMJ-0 in the current study. This finding is consistent with previous studies that have reported a temporary decrease in performance after similar interventions. For example, Fowles & Green (2003) noted a diminution in muscle strength after a maximal voluntary contraction of the quadriceps muscle, highlighting the immediate impact of such exercises on muscle function. Teixeira et al. (2018) reported an increase in metabolic stress identified with blood lactate measurements and a decrease in muscle activation identified with electromyography (EMG) measurements after high-intensity resistance exercise. Similarly, Scott & Docherty (2004) observed a temporary decrease in vertical and horizontal jump performances in nineteen resistance-trained subjects after submaximal intensity (5 RM) deep squat exercises. The observed decrease in CMJ performance immediately after the BFR+LL protocol can be attributed to acute fatigue mechanisms. Central nervous system (CNS) fatigue, potentially associated with the accumulation of neurotransmitters such as serotonin and glutamate, along with peripheral factors, including disruptions in cross-bridge cycling, may have contributed to the temporary performance decrement. This mechanism aligns with findings from prior studies reporting neurotransmitter imbalance and altered muscle contraction kinetics post-exercise (Meeusen et al., 2006; Myburgh, 2004; Tornero-Aguilera et al., 2022). Additionally, peripheral nervous system (PNS) fatigue, which refers to fatigue originating from the peripheral nervous system, may involve disruptions in muscle contraction and cross-bridge cycling. The consistent application of BFR during each set of the low-load resistance exercise protocol might exacerbate this accumulation, further inducing PNS fatigue (Myburgh, 2004; Tornero-Aguilera et al., 2022). These fatigue mechanisms are consistent with prior studies that have reported short-term reductions in muscle performance following high-intensity exercises (Macdougall & Sale, 2014; Tornero-Aguilera et al., 2022). Hence, when administering PAPE protocols like BFR+LL, sufficient recovery time must be provided to mitigate these fatigue effects and optimize performance gains. This suggests that while BFR+LL can enhance muscle performance through PAPE in the post-exercise period, it may initially lead to a decrease in performance due to the acute onset of fatigue-related mechanisms (Tornero-Aguilera et al., 2022).

In the present study, RFD did not show any significant differences (p > 0.05), which contrasts with previous studies (Doma et al., 2020; Sun & Yang, 2023; Zheng et al., 2022). While it has been suggested that RFD may not always be a strong predictor of jump performance, there are several potential reasons for the lack of significant changes in our study. First, the RFD measurement protocol used may not have been sensitive enough to detect subtle changes in force development, particularly considering the low-load nature of the BFR+LL protocol, which may not provide sufficient neural responses necessary for a significant increase in RFD, as typically seen in higher-load resistance training. Previous studies have shown that RFD measurements can be influenced by factors such as task specificity and participant characteristics. Second, the BFR+LL protocol in our study, which combined low-load squats with blood flow restriction, might have induced different neural responses compared to the protocols used in prior studies. For instance, Doma et al. (2020) used lunge exercises with BFR, which likely engaged different muscle groups and movement patterns, potentially leading to different neural responses (Doma et al., 2020). These considerations help explain the lack of significant changes in RFD in our study. Recent research, including Miller et al. (2023), has indicated that the relationship between RFD and VJ height is not as strong as previously thought, suggesting other factors might be more critical in determining vertical jump performance (Miller et al., 2023). Nonetheless, the observed mean RFD values align with findings from several studies which have indicated a weak correlation between RFD and vertical jump outcomes (Haff et al., 2000; Marcora & Miller, 2000; Wilson et al., 1995; Young & Bilby, 1993). For instance, Miller et al. (2023) demonstrated that the relationship between RFD and VJH is not as strong as previously thought, suggesting that other neuromuscular factors might play a more critical role in determining vertical jump performance. Wilson et al. (1995) reported the absence of a significant link between RFD and countermovement jump (CMJ) performance, advocating concentric tests as more reliable for assessing RFD. Similarly, Haff et al. (2000) found no correlation between RFD and either CMJ or squat jump (SJ) performance among collegiate athletes. Such variations in findings could stem from methodological differences, participant gender (Marcora & Miller, 2000), or training status (Young & Bilby, 1993) across studies. These findings align with our observation that RFD did not show significant differences across the conditions tested in our study. Given these disparities and the consistent reports of poor correlations between RFD and vertical jump performance, it becomes imperative to approach RFD as a performance metric for vertical jumps with caution, especially in the context of male collegiate athletes. The apparent inconsistency in its reliability underscores the need for careful consideration of the factors that may influence the relationship between RFD and jump performance, suggesting that RFD may not always serve as a direct or reliable indicator of vertical jump capability (McLellan, Lovell & Gass, 2011).

Furthermore, the analysis of peak countermovement jump (CMJ) performance did not reveal any differences, echoing a broader dialogue within recent research about whether to prioritize peak or mean CMJ performance for post-intervention evaluation (Al Haddad, Simpson & Buchheit, 2015; Hetherington, 1973). Despite the varied applications of CMJ tests in recent studies, our results showed no significant distinctions between peak (effect size (ES) = 0.32, 95% confidence interval (CI) [0.05–0.65]) and mean (ES = 0.35, 95% CI [0.02–0.62]) CMJ height, indicating that both peak and mean measurements could be effectively used to monitor changes in CMJ performance. However, a meta-analysis by Claudino et al. (2017) pointed out that averaging CMJ parameters could potentially offer a more sensitive approach than focusing solely on peak values for tracking vertical jump performance, especially when increasing the sample size for such analyses. Given these insights, and to mitigate measurement inaccuracies while improving the precision of data, our findings advocate for the adoption of mean values as more reliable indicators for assessing neuromuscular status. Mean values offer a more stable assessment of VJ performance by mitigating the influence of outliers and single exceptional performances, ensuring a reliable indicator of consistent performance across multiple trials.

In summarizing our findings, it is crucial to acknowledge several limitations within our study. First, the investigation focused exclusively on the impact of blood-flow restriction combined with low-load (BFR+LL) resistance training solely on vertical jump performance. This narrow focus limits the applicability of our results to other sport-specific performance metrics, such as sprint speed and change-of-direction capabilities. Second, a significant limitation is the absence of a heavy load (HL) resistance training group, which precludes direct comparison between these two training modalities. While BFR+LL has shown promise as a practical alternative, particularly in contexts where high-load training is not feasible, the superiority or equivalence of BFR+LL to HL training cannot be concluded from our results alone. Future research should include HL training groups to provide a comprehensive evaluation of BFR+LL training’s relative effectiveness and to better understand the underlying physiological mechanisms. Another key limitation lies in the use of percentage changes in CMJ performance. While these changes provide a practical measure of performance enhancement, they may not fully capture the nuanced relationship between muscle strength and jump height. Chatlaong et al. (2024) highlighted the interpretive and statistical challenges associated with ratios or percentages when analyzing muscle strength relative to muscle size, which could also be relevant here (Chatlaong et al., 2024). Percent change may not be the most precise way to evaluate improvements in muscle performance, especially in strength and explosive power assessments. To better capture these effects, future studies could incorporate alternative metrics, such as absolute strength measurements or muscle cross-sectional area, which would offer a more comprehensive understanding of the relationship between muscle adaptations and performance outcomes. Lastly, the study’s generalizability is constrained by its small sample size and lack of gender diversity. Future research with larger, more gender-balanced cohorts is essential to elucidate potential sex-specific responses to PAPE following BFR+LL, thereby enhancing our comprehension of its effects across a broader athletic population.

Conclusions

We acknowledge that both blood-flow restriction (BFR) training and heavy load lifting have their own practical challenges and advantages. BFR training can be particularly useful in scenarios with limited access to heavy equipment or in specific rehabilitation contexts. Conversely, low volumes of heavy but non-fatiguing loads have been shown to be highly effective and are extensively used in both research and practical applications. Therefore, the choice between BFR and heavy load training should be guided by the specific needs and circumstances of the athlete. In conclusion, this finding underscores the potential of this training methodology as a viable strategy for enhancing explosive lower limb performance.

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