FormalPara Key Points

Previous literature suggests that vertical jump potentiation may be due to two primary factors including the characteristics of the individual and the design of the strength–power potentiating complex.

Subject characteristics that must be considered when seeking vertical jump potentiation are the individual’s relative strength, sex, muscle characteristics, neuromuscular characteristics, current fatigue state, and training background.

Aspects of the strength–power potentiating complexes that must be considered for vertical jump potentiation are the potentiating exercise, level and rate of muscle activation, volume load completed, the ballistic or non-ballistic nature of the potentiating exercise, and the rest interval(s) used following the potentiating exercise.

1 Introduction

Postactivation potentiation (PAP) is a topic that has become the subject of frequent investigation within strength and conditioning literature. PAP has been defined as an acute enhancement of muscle performance as a result of contractile history and is considered the basis of complex training [1]. Topics that have been investigated within the PAP literature include underlying physiological mechanisms, various potentiating stimuli, the rest interval following a stimulus, characteristics of the subjects, and the electromyography or muscle activation differences following a stimulus. Through the use of PAP, researchers have attempted to identify stimuli that will acutely improve the subjects’ performance (e.g., jumping, sprinting, agility, lifting, etc.). By identifying stimuli that may acutely improve performance, it may be possible to use PAP as a training stimulus. This review will focus on vertical jumping as the performance measure.

Previous research has indicated that the optimal conditions (i.e., type of exercise, exercise volume, exercise load, rest interval) for vertical jump potentiation are highly individualistic [2–6]. Thus, it appears that the characteristics of the subjects using various potentiation protocols may have a large effect on whether or not potentiation is realized. Specifically, previous research has indicated that the subject’s relative strength level, sex, muscle characteristics, and training background may alter the effect of PAP on subsequent performances [7–11]. Although some characteristics may have a greater impact on vertical jump potentiation, it is important to take as many of the subject’s characteristics into account as possible when considering the use of potentiation complexes within training or competition.

PAP is the basis of complex training. Complex training has been defined as a method of training that involves completing a resistance exercise before performing an exercise that is biomechanically similar [1, 10, 12]. It is believed that the use of complex training will allow participants to perform power exercises at a higher intensity [13–16], potentially leading to a greater chronic training stimulus if utilized repeatedly during specific blocks of training. Previous research has suggested that the enhanced training stimulus produced by complex training may result in superior performance gains longitudinally compared with normal training [14, 15, 17–19]. Protocols designed to produce a potentiated state have been termed strength–power potentiating complexes (SPPCs) [1, 7]. Specifically, SPPCs involve the performance of a high force or high power movement prior to a subsequent high power or high velocity movement (e.g., heavy back squats prior to drop jumps). An abundance of lower extremity SPPCs have been investigated with the intent to produce a potentiated state in which a subject can acutely improve their subsequent performance during various explosive movements such as jumping. However, it should be noted that different types of muscle actions during potentiation protocols may elicit varying effects on the subsequent explosive performances [8]. While some SPPCs have produced an enhanced jumping performance, others have not (Tables 1, 2, 3). There are a number of reasons as to why certain SPPCs may not produce an enhanced subsequent jumping performance, which makes designing an effective SPPC a trying task. In order to effectively design an SPPC, further understanding of jump potentiation is necessary.

Table 1 A summary of studies that have investigated the effects of various protocols on squat jump potentiation
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Table 2 A summary of studies that have investigated the effects of various protocols on countermovement jump potentiation
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Table 3 A summary of studies that have investigated the effects of various protocols on drop/depth jump potentiation
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Several underlying physiological mechanisms have been proposed to be components of the PAP phenomenon, including increased phosphorylation of myosin light chains [20–25], increased recruitment of higher order motor units [26–29], changes in the active muscle’s pennation angle [8, 30], and increased muscle stiffness [14, 31, 32]. Although several different underlying physiological mechanisms exist, it is possible that they interact concurrently to produce a change in subsequent vertical jump performance. However, it is possible that the subject’s characteristics and the design of the SPPC may alter the magnitude of the influence of a given underlying mechanism to a greater extent than another. For example, the use of heavier loads during an SPPC will likely promote the recruitment of higher order motor units as compared with lighter loads [33]. Ultimately, the combination of the subject’s characteristics and SPPC will affect the underlying mechanisms of potentiation that will produce a positive or negative change in the force production characteristics of the vertical jump (Fig. 1). It is clear that further understanding of how the subject’s characteristics and the design of the SPPC interact to produce a change in performance is needed.

Fig. 1
figure 1

Deterministic model for vertical jump potentiation. CON concentric muscle action, CSA cross-sectional area, ECC eccentric muscle action, ISO isometric muscle action, MU motor unit, MVC maximal voluntary contraction, PAP postactivation potentiation, Plyos plyometric exercise, RFD rate of force development, ROM range of motion, SPPC strength–power potentiation complex, SSC stretch-shortening cycle, WBV whole-body vibration

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One of the most common methods of assessing an athlete’s performance is the monitoring of vertical jump performance (i.e., squat jump, countermovement jump, or drop/depth jump) [34]. The squat jump, countermovement jump, and drop/depth jump have been previously described by Bobbert and colleagues [35, 36]. Briefly, a squat jump is a vertical jump in which an individual starts from a relatively low position (i.e., flexed hips, knees, and ankles), holds the position for a short period of time to reduce or eliminate the influence of the stretch-shortening cycle before explosively pushing into the ground to reach a maximum height. A countermovement jump begins from a standing position from which the athlete lowers quickly to a self-selected position before immediately extending their hip, knee, and ankle joints to achieve a maximum jump height. Finally, a drop/depth jump is typically performed from a raised surface or position where the individual falls (i.e., drops) due to gravity to land on their feet before performing rapid absorptive flexion followed immediately by explosive extension to achieve maximum jump height. While the drop and depth jump were grouped due to their similarity, it should be noted that each exercise has unique characteristics with the drop jump including a stiff landing, decreased contact time, and reduced power and jump height, while the depth jump includes increased compliance and contact time, but a greater power output and jump height [37]. Due to its use as a common performance test, vertical jump performance (e.g., height, peak power, rate of force development, etc.) appears to be a criterion measurement to determine whether or not performance increased, decreased, or was unchanged following different training interventions. Potentiation literature has followed suit as a number of studies have investigated the effect of various potentiation protocols on subsequent squat jump (Table 1), countermovement jump (Table 2), and drop/depth jump performances (Table 3). While many of the studies reported an enhanced vertical jump performance, others did not. In order to design an effective SPPC, practitioners must understand the factors involved within the SPPC, but also understand how these factors interact with the characteristics of the subjects using the SPPC. Therefore, the purpose of this review is to discuss previous PAP literature and propose a deterministic model for vertical jump potentiation.

2 Literature Search Methodology

Original and review journal articles were retrieved from electronic searches of PubMed and Medline (EBSCO) databases. Additional searches of Google Scholar and relevant bibliographic hand searches with no limits of language of publication were also completed. The search strategy included the terms postactivation potentiation, strength–power potentiating complex, complex training, vertical jump, squat jump, countermovement jump, drop jump, and depth jump. The last month of the search was August 2015.

3 Deterministic Model

There are two main factors that must be considered when the goal is to potentiate a vertical jump: the characteristics of the subject who is being tested and the design of the SPPC itself. Each factor will be discussed in more detail in the following sections. Using concepts from previous research that have examined vertical jumping, muscle function, and factors of PAP [8, 114, 115], the following deterministic model for vertical jump potentiation is proposed (see Fig. 1).

4 Subject Characteristics

The first half of the deterministic model focuses on the characteristics of the subjects that may affect the ability to potentiate a type of vertical jump. Previous research has indicated that characteristics that may alter the effect of PAP on subsequent jump performances include the subject’s absolute and relative strength, sex of the individual, their training background, and muscle characteristics [7–11].

4.1 Strength

Much of the existing potentiation literature has indicated that stronger subjects demonstrate a greater potential to use PAP more effectively to acutely enhance their performance as compared with their weaker counterparts [44, 48, 55, 81, 100, 116, 117]. Several studies indicated that individuals with greater relative strength levels may be able to dissipate fatigue faster when using SPPCs, allowing them to display an enhanced subsequent performance earlier as compared with weaker subjects [44, 48, 118]. Specifically, stronger and weaker subjects potentiated post-stimulus at 3 min compared with 5 min [44], immediately compared with 2 min [48], and 5 min compared with 15 min [118], respectively. Further research suggests that stronger subjects will develop fatigue resistance to high loads as an adaptation to repeated high load training [7]. Therefore, higher levels of relative strength may benefit an individual who is considering using SPPCs in their training programs. From a practical standpoint, practitioners should be aware that individuals with the ability to back squat at least twice their body mass have a greater potential to exhibit jump potentiation compared with weaker individuals [44, 47, 48, 119, 120]. Although there is evidence to counter the notion that greater relative strength levels relate to an individual’s ability to potentiate [93, 111, 121], Miyamoto et al. [122] reported that an individual can enhance their ability to potentiate after getting stronger. Additional research has indicated that the ability to squat 1.7 times one’s body mass [55] or 2.0 times one’s body mass [44, 47, 48, 119, 120] will result in a greater likelihood of potentiation during subsequent jump performance(s) and a greater magnitude of potentiation. Therefore, it appears that lower relative strength levels may result in decreased potentiation and a longer duration for potentiation to exceed the level of fatigue. However, this may be altered as relative strength levels increase, resulting in greater potentiation and a more rapid decrease in fatigue.

4.2 Sex

When designing an SPPC for athletes, practitioners should consider if the protocol can be beneficial for both male and female participants. From a fiber composition standpoint, previous researchers have indicated that no statistical differences existed between males and females in fiber-type distribution of the vastus lateralis muscle [123]. However, other researchers have indicated that men possess a greater percentage of type II fibers [124] and greater cross-sectional area of type II fibers compared with females [100, 124]. Because type II fibers are more likely to exhibit potentiation compared with type I fibers [24, 26, 124–129], it is possible that men are more likely to potentiate in response to an appropriate stimulus, but also display a greater degree of potentiation compared with women. However, the extant literature reveals mixed results. Some researchers have reported no statistical differences existed in lower body potentiation [3, 5, 85, 111], whereas other researchers have indicated that males and females display various potentiation differences, typically with men showing greater potentiation compared with women [107, 124, 130, 131]. It is unclear, however, whether or not these differences existed due to relative strength differences between men and women. Although the research that has investigated whether or not the sex of the subjects determines if potentiation may occur is inconclusive, there is little doubt that the vast majority of potentiation research has investigated SPPCs with male subjects. Thus, further research may be warranted to determine if the same potentiation protocols may be used effectively with male and female subjects.

4.3 Muscle Characteristics

An individual’s muscle characteristics may dictate whether or not they will enhance their jump performance following a potentiating stimulus. Although the existing literature investigating the influence of other factors on potentiation contains mixed findings, this does not appear to be the case with the information regarding the muscle characteristics of individuals. All of the existing studies support the notions that type II (fast twitch) muscle fibers are better able to express potentiation than type I (slow twitch) muscle fibers and that individuals who possess a greater percentage of type II fibers are more likely to potentiate and potentiate to a greater extent than those who are type I dominant [24, 26, 124–129]. Because the characteristics of the target muscles appear to be an important aspect to consider when designing SPPCs, the difficult task becomes identifying individuals who are type II dominant. However, several studies have reported that stronger individuals tend to have a greater percentage of type II muscle fibers [132–134]. Therefore, assessing muscular strength and possibly gaining strength may be beneficial prior to using SPPCs in order to ensure the effectiveness of the protocol.

As previously mentioned, the pennation angle of an individual’s active muscles may be considered as one of the primary mechanisms of PAP [8, 30]. The orientation of an individual’s fibers within a muscle may affect the transmission of forces to tendons and bones [135, 136]. Mahlfeld et al. [30] indicated that the pennation angle of the vastus lateralis was statistically decreased 3–6 min following three, 3-s maximal voluntary contractions (MVC). A second study reported changes in pennation angle for the rectus femoris and vastus lateralis following moderate intensity (i.e., three sets of ten repetitions at 75 % 1RM), high intensity (i.e., three sets of three repetitions at 90 % 1RM), and 1RM squat protocols [99]. However, their results indicated that minimal potentiation was observed with little change in vertical jump height, peak power, or mean power reported. It should be noted, however, that a statistically significant moderate relationship (r = −0.35) was reported between mean vertical jump power and vastus lateralis pennation angle 8 min post-stimulus. A decreased pennation angle may allow for a greater mechanical advantage leading to enhanced force transmission to the tendon and bone [135, 136]. However, it is possible that potentiating exercise may result in an increase in connective tissue/tendon compliance that may counter the increases in the transmission of forces due to decreases in pennation angle [137]. There is little doubt that further research on this topic is required; however, one cannot discount the individual variability of resting pennation angle, change in pennation angle, and connective tissue/tendon compliance following a potentiating stimulus and how this may affect performance within an SPPC.

4.4 Neuromuscular Factors

One element of the PAP phenomenon which is often alluded to, but rarely shown in complex human performance-based models, is reflex potentiation (RP). Reflex potentiation can appear as a result of increased sensory discharge sensitivity within type Ia afferents, decreased sensory discharge failure at type Ia afferents, or a preferential lowering of higher order motor unit activation thresholds [8, 138]. Such characteristics have been shown in a number of studies utilizing single joint MVC, with or without the addition of electrical stimulation (twitch interpolation) [139–141]. Although the reflexive contribution to the gross PAP state appears to be small, inhibition in the form of postactivation depression within such reflex pathways may have a significant negative impact upon movements reliant upon a stretch-shortening cycle (e.g., countermovement jump, drop/depth jump) [22, 140–147]. Although it is currently unclear whether muscular responses observed during single joint tasks would be elicited during multi-joint tasks due to the task dependency of the mechanical behavior of both uniarticular and biarticular muscles [148], RP would appear to be an important transient neuromuscular phenomenon which needs to be considered within the proposed deterministic model of vertical jump potentiation. As action type and movement specificity appear to affect motor unit recruitment and discharge rates differently [139, 141, 145, 149, 150], RP may therefore be produced at different degrees of magnitude. Maximal voluntary contractions, heavy load dynamic contrast external resistance, loaded and unloaded ballistic jumps, neuromuscular electrical stimulation, and whole-body vibration (WBV) may provide the central and peripheral nervous systems with varying degrees of challenges and unique ratios of PAP to fatigue [22, 139, 140, 142, 145, 147, 149–151].

Mechanistically, RP can be assessed by way of EMG, with both changes in reflex latency as well as frequency spectra characteristics following PAP [22, 140, 145, 146, 149, 152, 153]. Researchers have shown a lowering of the activation thresholds for sub-populations of higher order motor units during corrective reflexive tasks [8, 11, 33]. Such a phenomenon has led some researchers to suggest that increasing type Ia afferent spindle sensitivity prior to the performance of a lower extremity movement utilizing the stretch-shortening cycle could increase the resultant muscle activation within the same musculature [146, 149]. Such increased reflex activation in conjunction with the primary volitional activation could lead to greater force and rates of force development [22, 140, 144, 149, 150, 152]. The time course of RP, if present, appears to be correlated strongly with Hoffman reflex (H-reflex) up-regulation and/or depression following PAP activity [23, 27, 145, 146, 150]. The H-reflex is an externally induced reflex response from type Ia afferents in response to low–moderate intensity electrical stimulation [145, 146, 150]. As with fiber composition and training status, H-reflex patterns appear to be highly individualized with differences seen between endurance-trained versus strength/power-trained individuals [154–156]. In a previous review covering the PAP phenomenon, Tillin and Bishop [8] proposed that primary sites of PAP and concurrent fatigue were different based upon isometric versus dynamic-based interventions. The same authors proposed that MVC-based PAP interventions resulted primarily in peripheral-based PAP (at the site of the muscle) and central-based fatigue (within the brain and spinal cord). Heavy load and ballistic type movements were proposed to induce central-based PAP with peripheral fatigue. This would suggest that both modes of PAP could affect the central nervous system, but heavy load dynamic contrast external resistance and ballistic movements may have a greater relative impact upon RP [139, 144, 149, 151]. WBV has been proposed by some authors to bring about RP leading to improvements in countermovement jump height and power output [146, 147, 150, 157], while others suggest this is not the case [22, 142, 144]. An initial increase in type Ia afferent muscle spindle discharge has been shown followed by reduction and transient suppression following WBV exposure [22, 140, 144–146, 152, 153]. A supercompensatory rebound in Ia afferent activity could lead to increased alpha motor neuron discharge, decreased Ia afferent discharge failure, reduced sensitivity at the Renshaw cell (inter-neuron) level, or a reduction in the required descending drive from the primary motor cortex (M1) to maintain a similar force, or rate of force development level [140, 142, 145, 146, 150, 152].

Reflex potentiation coupled with reduced neural inhibition at the spinal cord level could result in greater alpha motor neuron firing frequency and motor unit synchronization [146, 149, 150]. Such transient effects in conjunction with increased phosphorylation of myosin regulatory light chains, localized muscle temperature, and inter- and intra-muscular coordination patterns would appear to account for the key neuromuscular factors behind the PAP phenomenon [22, 141–144, 150, 157]. As these factors appear to have different levels of susceptibility to facilitation and fatigue, and varying time courses of peak and plateaued effects, individualized ‘trial and error’ treatments may be warranted. In practice, utilizing SPPCs following or partly incorporated into ‘dynamic warm-up’ activities could transiently facilitate neural, myogenic, and metabolic/hemodynamic characteristics of PAP resulting in significant acute improvements in jump performance [22, 140–142, 144, 146, 147, 150, 157].

4.5 Training Background

The training background of subjects may also determine how they respond to various SPPCs. Several studies have examined the potentiation differences between athletes and non-athletes [116, 117, 158]. Chiu et al. [116] indicated that athletes improved their peak power to a greater extent than recreationally trained subjects during countermovement and concentric-only jump squats following five sets of one back squat repetition at 90 % 1RM. This may be due to the athletes developing resistance to high load fatigue as an adaptation to their training [7]. Similar results were found by Hamada et al. [158], who indicated that Canadian national team triathletes produced statistically greater peak torque during MVC in both the elbow extensors and plantar flexors as compared with sedentary subjects following maximal twitch contractions. A recent meta-analysis supports the findings of the above research, indicating that athletes displayed greater potentiation effects (d = 0.81) compared with trained subjects (d = 0.29) and untrained subjects (d = 0.14) [159]. Collectively, these studies indicate that potentiation favors athletes over non-athletes. Beyond performance measures, there is a paucity of research that has examined how various physical attributes differ between athletes and non-athletes in regard to potentiation. As shown here, the strength levels and muscle characteristics of an individual may dictate the ability of the subject to realize potentiation following a potentiating exercise. Thus, it should be noted that the training background of the subjects is just one of many factors that must be considered in regard to potentiation as indicated above (Fig. 1).

5 Strength–Power Potentiating Complex

The second portion of the proposed deterministic model focuses on the design of the SPPC. In order to design an effective SPPC, sport scientists and practitioners must consider all aspects that contribute to any variability that may affect an individual’s ability to potentiate. Specifically, sport scientists and practitioners should consider the choice of exercise(s) that is/are used as a potentiating stimulus, the volume load of the protocol, the muscle groups involved, the characteristics of the movement to be potentiated, the type of muscle action used during the stimulus and subsequent activity, the period of time between the conclusion of the warm-up and the subsequent performance, and the performance level of the athletes [9, 159–161]. The design of an SPPC ultimately produces a state of preparedness for subsequent activity. Preparedness may be defined as the summation of fitness and fatigue responses to a stimulus (fitness–fatigue relationship), where fitness includes the underlying mechanisms allowing performance and fatigue includes the factors that limit performance [162]. However, as displayed in Fig. 1, a number of factors within the SPPC itself can greatly affect whether or not the state of preparedness will lead to an enhancement or a decrement in performance. By taking into account as many aspects as possible, a sport scientist or practitioner may be able to more effectively design an SPPC.

5.1 Potentiating Exercise

Tables 1, 2 and 3 display the research that has examined the acute effects of many different types of exercise on subsequent squat jump, countermovement jump, or drop/depth jump performance. Although the exercise protocols may differ, the type of exercise typically falls within one of two categories: dynamic or static. Examples within the scientific literature that examined dynamic potentiating exercise include squatting movements, plyometrics, weightlifting movements, WBV, throwing implements, intermittent exercise, running and/or cycling, movements with weighted vests, leg press, and several miscellaneous exercises. In contrast, static potentiating exercise may include MVC, but also WBV. A recent review indicated that ballistic exercise as a potentiation stimulus may produce performance improvements of 2–5 % [163]; however, no further published information exists on any of the other outlined types of exercise. Practitioners designing SPPCs should consider how biomechanically similar the potentiating exercise and the subsequent exercise are in terms of the kinematic and kinetic variables associated with the movements and the muscle actions involved. For example, practitioners should choose a potentiating exercise in which the muscle actions and joint angles used are similar to those in the subsequent exercise [47].

5.2 Ballistic versus Non-Ballistic Movements

The nature in which the potentiating exercise is performed may alter the PAP effects displayed in subsequent performances. Previous research has indicated that ballistic movements produce greater muscle activation as compared with similar movements that are non-ballistic [164]. Further research has indicated that an exercise performed in a ballistic manner may produce greater power outputs than the same exercise performed in a non-ballistic manner [165]. Three studies have examined the potentiation differences between a ballistic exercise (i.e., hang clean or power clean) and a non-ballistic exercise (i.e., back squat) [3, 52, 166]. Although one study indicated that there were no differences in the potentiation effects between the hang clean and back squat [3], the remaining studies indicated that the hang clean [52]and power clean [166] produced statistically greater potentiation effects than the back squat. It should be noted that neither of these studies used the same absolute load between the exercises, which may effectively alter the necessary forces and rate of force production needed to complete the exercise, the individual’s level of fatigue, and exercise mechanics (e.g., muscle actions and joint angles). This in turn may lead to different degrees of potentiation. Recent research examined the differences in potentiation following the same potentiating exercise performed in either a ballistic or non-ballistic manner using the same absolute load [47, 48]. Collectively, the results indicated that ballistic concentric-only half-squats enhanced subsequent squat jump height, absolute peak power, and allometrically scaled peak power to a greater extent compared with concentric-only half-squats performed in a non-ballistic manner. For further information regarding the use of ballistic exercise within SPPCs, readers are directed to a recent review by Maloney and colleagues [163].

5.3 Volume Load

Previous researchers have indicated that the type, volume, intensity, and the duration of exercise and recovery may determine whether fatigue or potentiation is dominant over the other at various rest intervals [159, 167]. Thus, an aspect of each potentiation protocol that cannot be overlooked is the volume load completed prior to the subsequent vertical jump(s). Using the theoretical model of the interaction between fatigue and potentiation provided by Sale [11], Tillin and Bishop [8] expanded the model and indicated that two windows may exist to realize potentiation effects with regard to the volume load of the potentiating stimulus. If the volume load of the potentiating stimulus is low, but has sufficient intensity, it is likely that a decreased amount of fatigue will result and potentiation may be realized earlier (i.e., window 1). In contrast, if the volume load is high, greater fatigue may be present and a longer rest interval may be required to realize potentiation (i.e., window 2). Previous research has indicated that multiple sets of exercise produced a statistically greater effect size than a single set [159]. However, it should be noted that the volume load completed by the subjects must be large enough to stimulate the underlying mechanisms of PAP, but volume loads that are too large may result in excessive fatigue that may mask the potential benefits of PAP [168].

5.4 Rest Interval

Following a potentiation protocol, a state of both fatigue and potentiation is present [10, 11, 168, 169]. The interaction between fatigue and potentiation may be modeled acutely on the fitness–fatigue paradigm [170], where the subsequent performance(s) is/are the result of the interaction of fatigue and fitness after-effects that result following the potentiating exercise. In this case, the potentiating exercise raises the ‘preparedness’ (i.e., the difference between fitness and fatigue) of the subject for the subsequent performance(s) [7]. The rest interval length used within the SPPC may determine whether or not an enhanced performance is realized. Previous research has indicated that fatigue may dominate over potentiation in the early stages of recovery following the potentiating exercise [8]. Thus, if the rest interval is too short, fatigue may mask the benefits of potentiation [50, 171]. Conversely, if the rest interval is too long, the optimal potentiation effects may dissipate, which may lead to no changes in performance. In this regard, several studies indicated that fatigue dissipates faster than preparedness [128, 172, 173].

Previous research has indicated that potentiation effects may last from 2 to 20 min post-stimulus [100, 116, 125, 174]. Wilson and colleagues [159] indicated that the potentiation effects that existed between 3–7 min (d = 0.54) and 7–10 min were statistically greater than those that existed at rest intervals longer than 10 min (d = 0.02). A second meta-analysis supports these findings and indicated that a negative medium and a small effect size existed at rest intervals of 0–3 min and those >16 min, respectively [175]. In addition, positive medium and small effect sizes existed at rest intervals of 8–12 min and 4–7 min, respectively. Because the type, intensity, and duration of exercise may determine if fatigue or potentiation is dominant over the other [167], it is likely that each potentiation complex has an optimal rest interval where the greatest potentiation effects occur. However, practitioners should note that individualized rest periods may be needed in order to provide the optimal training stimulus [2–6, 48].

6 Conclusions and Practical Applications

The deterministic model proposed within this review may aid sport scientists and practitioners who hope to develop effective SPPCs for various populations. There are a number of factors that must be considered when designing an effective SPPC. Not only do sport scientists and practitioners have to consider the potentiating exercise and the subsequent exercise, but they must also consider the characteristics of the individuals who will use the SPPCs in training and/or competition. The subject characteristics that must be considered when seeking vertical jump potentiation are the individual’s absolute and relative strength, sex, muscle characteristics, neuromuscular characteristics, and training background. In addition, the aspects of the SPPC that must be considered for vertical jump potentiation are the potentiating exercise, volume load completed, the ballistic or non-ballistic nature of the potentiating exercise, and the rest interval(s) used following the potentiating exercise. The extent to which some of these factors affect one another may still be up for debate; however, the use of SPPC with certain subjects and the design of certain SPPC may be questioned given the findings of previous research. For example, using a specific SPPC with weaker subjects may not be ideal as the likelihood of producing an enhanced training response is less than that of stronger subjects who use the same protocols. Furthermore, during the development of an SPPC to elicit an enhanced countermovement jump performance, the practitioner should consider the inclusion of an eccentric muscle action, but should also consider the load and joint angles used with the potentiating exercise.

The design of SPPCs should be practical in nature with regard to the equipment needed and the rest interval required for the potentiation of a subsequent performance. A number of protocols within Tables 1–3 used WBV to enhance vertical jump performance; however, sport scientists and practitioners should question how economical the use of WBV on machines is in a practical setting. With regard to team sports using WBV, it is unlikely that an athletic department will allocate the necessary funds to purchase a sufficient number of WBV platforms to be used in training while free weights are already present. Practitioners must also consider the rest interval needed to realize potentiation using certain protocols. For example, meta-analyses have indicated that the optimal period to realize potentiation is 7–12 min post-stimulus [159, 175]. Even if the practitioners were to use the earliest rest interval of 7 min, it should be questioned whether an SPPC that requires individuals to wait 7 min before a subsequent performance occurs is actually practical. With athlete-training-time restrictions, such as the accountable hours enforced by the National Collegiate Athletic Association, practitioners who would like to incorporate PAP as a training tool must seek SPPCs that may be effectively implemented in training and that do not require excessive rest intervals that may take away from valuable training time. It should be noted that practitioners may decrease the necessary time needed to realize potentiation by improving their subject’s relative strength [44, 47, 48, 118, 122]. This may allow for the use of SPPCs within athletic events when time may be a limiting factor (e.g., track and field heats and attempts).