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Application of Methods of Inducing Postactivation Potentiation During the Preparation of Rugby Players

Seitz, Laurent B. MSc; Haff, G. Gregory PhD, CSCS*D, FNSCA

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Strength & Conditioning Journal: February 2015 - Volume 37 - Issue 1 - p 40-49
doi: 10.1519/SSC.0000000000000116
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Abstract

INTRODUCTION

There is a large and growing body of literature indicating that previous muscular contractions (i.e., potentiating stimulus) acutely increase the strength/power production in subsequent exercise(s) (23,38,40). This coupling of a potentiating stimulus with a strength/power performance is often referred to as a strength-power potentiating complex (SPPC) (36). These types of complexes have been shown to stimulate enhancements in vertical jumping (11,12,34), horizontal jumping (33), and sprint (10,29,35) performances, when applied between 4 and 18.5 minutes after the completion of a potentiating stimulus containing near-maximal back squats or power cleans. Similarly, previous studies report enhancement in bench press throw performance 7–8 minutes after the performance of a near-maximal bench press (15,25). The neuromuscular rationale underpinning the improvement of athletic performance after a potentiating stimulus has been referred to as postactivation potentiation (PAP). The proposed mechanisms responsible for PAP are thought to occur at the central (neural) and peripheral (muscle) level. At the central level, the performance of a potentiating stimulus may increase the excitation potential across the spinal cord, resulting in increased force generation capacity during a subsequent contraction (22). At the peripheral level, an increased phosphorylation of the myosin regulator light chains in response to the potentiating stimulus results in an increased sensitivity of the actin-myosin complex to calcium that is released from the sarcomplasmic reticulum (21,32,39). By increasing the sensitivity of the actin-myosin complex and releasing more calcium from the sarcoplasmic reticulum, there is a greater likelihood that there will be an increased interaction between myosin and actin (27,37). Specifically, an increase in the number and rate of myosin cross-bridges binding to the actin filament would occur and result in an increase in the amount of muscle tension developed (5,28,31), which could then stimulate a PAP response as indicated by increases in strength and power performance capacity.

The ability to stimulate a PAP response seems to be dependent on the intensity and type of potentiating stimulus used in the SPPC, the individual's strength level and the rest period between the potentiating stimulus and the subsequent performance exercise (38,40). From an applied perspective, SPPCs are often used in the training of athletes from a variety of sports including rugby in an attempt to optimize strength, power, and speed development, which are important qualities required for success, particularly in rugby (14,16,19,20,24,30). Support for this contention can be seen in the literature that indicates that these 3 qualities are major determinants in accessing higher divisions of play (14,16). Moreover, strength and speed have also been shown to discriminate between selected and nonselected players (20) and starters and nonstarters (19) in a rugby team, respectively. However, there is no consensus on how best to implement SPPC into a training prescription for rugby players. It is therefore the aim of this article to provide insights regarding the applicability of SPPC for the development of strength, power, and speed attributes in rugby players and how to best implement SPPC into a rugby-specific training intervention.

INTENSITY OF THE POTENTIATING STIMULUS

Examination of the scientific literature reveals that a broad range of loads has been used during potentiating stimuli designed to elicit a PAP response with rugby players. Protocols using traditional resistance exercise as potentiating stimulus have typically used heavy-loaded exercises including back squats (3 repetition maximum [3RM] or 87–91% 1RM) (6,13,25,26,34,35), power cleans (90% 1RM) (35), and bench presses (3RM, 87% 1RM, or maximal isometric efforts) (7,15,25). Lower loads in the bench press (65–68% 1RM) have also been used in an attempt to elicit PAP response (1,3). Additionally, there are limited studies looking at potentiating stimuli that contain accommodating resistance exercises but those present in the scientific literature have used 68% 1RM in the box squat loaded with an additional 6–20% 1RM coming from elastic band resistance (average total resistance of 81% 1RM through the entire range of motion) (4) and 65% 1RM in the bench press with an additional 12% 1RM coming from chain resistance (total resistance at lockout = 77% 1RM) (2).

In summary, PAP effects can be elicited among elite and subelite rugby players by the use of moderate to heavy traditional potentiating stimuli (3RM, maximal isometric efforts or 65–91% 1RM) including the back squat, power clean, and bench press exercises. Additionally, accommodating resistance exercises including box squat combined with elastic band resistance and bench press combined with chain resistance can also be used with loads ranging from 77 to 81% 1RM.

EXERCISE SELECTON

Examination of the scientific literature reveals that the type of exercise used as the potentiating stimulus can affect the magnitude of the PAP response during sprinting activities. Seitz et al. (35) compared the effects of potentiating stimuli, which contained 3 repetitions in a high force-low velocity movement (i.e., back squat) or 3 repetitions of an explosive movement (i.e., power clean), both performed at 90% 1RM, on the 20-m sprint performance of elite rugby league players. While both potentiating stimuli-elicited PAP, greater improvements in 20-m sprint time (3.1 versus 2.2%), velocity (3.2 versus 2.3%), and average acceleration (6.6 versus 4.6%) were observed after the potentiating stimulus that contained power cleans (Figure 1). Similarly, Esformes (15) compared the acute effects of performing a 7-s isometric bench press, a 3RM bench press, a 3RM concentric bench press, or 3RM eccentric bench press on bench press throw performance. The results showed that the isometric bench press was the only potentiating stimulus that induced statistically significant increases (2.8%) in subsequent bench throw performance.

Figure
Figure:
Twenty-meter sprint time effect size (A), velocity effect size (B), and average acceleration effect size. The 20-m sprint test was performed before and 7 minutes after the performance of either 3 back squats at 90% 1RM (white bar), 3 power cleans at 90% 1RM (black bar), and the control condition (no potentiating stimulus, rest; dashed bar). Both squats and power cleans potentiating stimuli elicited PAP effects. The power cleans induced greater PAP effects than the back squats. Adapted from Seitz et al. (35). PAP = postactivation potentiation. Adapted, by permission, from L.B. Seitz, G.S. Trajano, and G.G. Haff, 2014, “The back squat and the power clean: Elicitation of different degrees of potentiation,” International Journal of Sports Physiology and Performance 9(4): 643–649. http://dx.doi.org/10.1123/IJSPP.2013–0246. © Human Kinetics, Inc.

It seems that the power clean elicits a greater PAP response during sprinting activities when compared with the back squat. In addition, isometric bench press seems to be more effective than isotonic, concentric, and eccentric bench press to elicit PAP during bench press throw.

ACUTE INCREASES IN VERTICAL JUMP PERFORMANCE

There is a large body of literature reporting acute enhancement in the vertical jump performance of subelite and elite rugby players after the performance of a potentiating stimulus (4,13,25,26,34). Generally, it has been demonstrated in the scientific literature that when rugby players use SPPCs that utilize heavy-loaded (3RM or >87% of 1RM) back squats as a potentiating stimulus, resultant improvements in markers of vertical jump performance occur within a time frame of 3–12 minutes postpotentiating stimulus. For example, Crewther et al. (13) report statistically significant increases (3.0–3.8%) in countermovement jump height 4–12 minutes after the performance of a 3RM back squat with subelite rugby players. Similarly, Kilduff et al. (25) report that when a 3RM back squat is used as a potentiating stimulus, there is a statistically significant increase (6.8–8.0%) in jumping performance 8–12 minutes after the potentiating stimulus is completed. Although these studies suggest that the potentiating stimulus should use RM loads, 2 studies have demonstrated that intensities between 87 and 90% of 1RM can also be effective potentiating stimuli (26,34). Specifically, statistically significant improvement in peak power output, peak rate of force development, and jump height during countermovement jump were observed 8 minutes after the performance of 3 sets of 3 back squats at 87% of 1RM (26). Similarly, Seitz et al. (34) report that vertical jump peak power output (2.9–5.7%) and jump height (3.2–6.4%) are significantly improved 3–12 minutes after the performance of a potentiating stimulus, which uses 3 back squats performed at 90% of 1RM. Based on this evidence, it seems that heavy-loaded back squats that are used as potentiating stimuli during an SPPC can result in a PAP response as indicated by improvements in markers of vertical jump performance.

Although SPPCs are traditionally created with the use of exercises like the back squat, more recent research has suggested that back squats performed with accommodating resistances can be effectively used in an SPPC (4). Specifically, Baker (4) demonstrated that peak power output during a loaded squat jump is significantly improved (6.4–7.5%) approximately 90 seconds after the performance of box squats loaded with 68% 1RM with an additional 6–20% 1RM coming from elastic band resistance (average total resistance of 81% 1RM through the range of motion) in professional rugby league players. Similar improvements (5.9–6.2%) were found when analyzing the average power output data. Interestingly, this PAP effect was maintained across 3 sets of complexes. Based on this limited evidence, it is worth noting that using accommodating resistance exercises may be advantageous from a training perspective since PAP can be elicited with a considerably shorter rest period between the potentiating stimulus and the subsequent performance, and maintained across multiple sets of complexes. Although the use of accommodating resistance exercises seems to result in PAP responses, there is limited research that has validated these types of protocols and further research is required to truly understand how effective these methods are.

In conclusion, acute enhancement in the vertical jump performance of subelite and elite rugby players can be elicited after the completion of a potentiating stimulus consisting of traditional heavy (3RM or 87–90% 1RM) resistance exercise (i.e., back squat). Additionally, accommodating (i.e., box squats + elastic band resistance) resistance exercises can be used with lower loads (total load = 81% of 1RM) and result in acute statistically significant performance gains (Table 1).

Table 1
Table 1:
Acute increases in vertical jump performance

ACUTE INCREASES IN UPPER-BODY PERFORMANCE

Previous studies have also demonstrated that when subelite and elite rugby players use SPPCs that use the bench press as a potentiating stimulus, statistically significant improvements in markers of upper-body performance, as measured with the bench throw, occur 3–12 minutes postpotentiating stimulus (1–3,7,15,25). For example, peak power output during bench press throws has been shown to be improved (2.8%) 12 minutes after the performance of a 7-s isometric bench press (15). Isotonic potentiating stimuli can also be used to elicit upper-body PAP. Indeed, Kilduff et al. (25) report statistically significant improvement (0.8–5.3%) in bench throw performance 8–16 minutes after the use of 3RM bench press. Similarly, performing bench press between 65 and 87% of 1RM can also be effective to elicit PAP in the upper body as demonstrated by statistically significant improvement (3.6–4.5%) in bench press throws 2–3 minutes after bench press at 65–68% 1RM (1,3) and, 8 minutes after bench press at 87% 1RM (7). Similar to the application of accommodating resistance exercises with the lower body, a PAP response may also be induced in the upper body with shorter recovery intervals between the potentiating stimulus and the subsequent exercise. For example, Baker (2) observed statistically significant increases (4.8–7.7%) in peak power output during 3 bench press throws performed 90 seconds after 3 bench press 65% 1RM with an additional 12% 1RM coming from chain resistance (total resistance at lockout = 77% 1RM). Although accommodating resistance methods seem to offer a unique conditioning stimulus, much more research is needed to truly understand the effectiveness of this activity during SPPCs that are designed to enhance performance capacity of rugby players.

Acute enhancement in power output during bench press throw can be elicited in subelite and elite rugby players after the completion of heavy bench press (i.e., maximal isometric effort, 3RM, or 63–87% 1RM). In addition, accommodating resistance exercises (i.e., bench press + chain) can be used with lower loads (total load = 77% of 1RM) and result in acute statistically significant performance gains (Table 2).

Table 2
Table 2:
Acute increases in upper-body performance

ACUTE INCREASES IN SPRINT PERFORMANCE

To the best of our knowledge, only 3 studies have investigated the acute effects of performing a potentiating stimulus on the sprint performance with rugby players (6,13,35). In the study by Seitz et al., (35) elite rugby league players performed 20-m sprints before and 7 minutes after either 1 set of 3 back squats or 1 set of 3 power cleans at 90% 1RM. The results show a statistically significant potentiation effect after both the back squat and power clean potentiating stimuli as indicated by improved sprint time (2.2–3.1%), velocity (2.3–3.2%), and average acceleration (4.6–6.6%) over 20 m. Similarly, Bevan et al. (6) demonstrated statistically significant improvement (5.0–8.0%) in 5- and 10-m sprint performance after the completion of 1 set of 3 back squats at 91% 1RM in elite rugby players. The majority of the players displayed the greatest PAP effect 8 minutes after the potentiating stimulus. Conversely, in the study of Crewther et al., (13) sprint performance over 5 and 10 m was not statistically improved 15 seconds, 4, 8, 12, and 16 minutes after the performance of 1 set of 3RM back squats.

Based on the above studies, sprint performance of elite rugby players can be acutely improved if preceded 7–8 minutes earlier by a potentiating stimulus consisting of 3 back squats at 90–91% 1RM or 3 power cleans performed at 90% 1RM. Conversely, it seems that no improvement occurs 15 seconds to 16 minutes after 1 set of a 3RM back squat (Table 3).

Table 3
Table 3:
Acute increases in sprint performance

EFFECT OF STRENGTH LEVEL ON POSTACTIVATION POTENTIATION RESPONSE AND OPTIMAL REST

It is generally believed that the magnitude of PAP is influenced by the strength level of the individual with stronger individuals expressing a higher degree of potentiation during vertical jump (25,26,34), sprint (35), and bench press throw (25) performance. For instance, elite rugby union players displaying a greater absolute (25) and relative (25,26) 3RM back squat were shown to express a greater PAP effect on peak power output during a countermovement jump (r = 0.489–0.631, P = 0.029–0.009). Similarly, a very large statistically significant correlation was found between relative 1RM back squat and maximum PAP effect on absolute (r = 0.775, P = 0.002) and relative peak power output (r = 0.775, P = 0.002) as well as jump height (r = 0.740, P = 0.004) during a squat jump performed by elite rugby league players (34). With respect to sprint performance, Seitz et al. (35) found that stronger elite rugby league players were able to express a higher degree of PAP during a 20-m sprint performance, with the PAP magnitude being statistically significantly correlated to relative 1RM back squat (r = 0.56, P = 0.04) and relative 1RM power clean (r = 0.63, P = 0.02). Regarding upper-body performance, Kilduff et al. (25) found that elite rugby union players possessing a higher bench press 3RM displayed a greater PAP effect on bench press throw than their weaker counterparts (r = 0.631, P = 0.009).

In terms of optimal rest interval between SPPC, longer periods of rest are necessary to elicit PAP after the performance of potentiating stimuli using traditional exercises (4–12 minutes in the back squat, 3–16 minutes in the bench press, 7 minutes in the power clean). Potentiating stimuli using accommodating resistance exercise may allow PAP effect to appear after approximately 90 seconds of rest (2,4).

It is, however, worth noting that the temporal profile of PAP may be related to the individual's strength level. Specifically, Seitz et al. (34) have demonstrated that stronger elite rugby league players (back squat to body mass ratio >2) were able to express PAP during a vertical jump task earlier (i.e., 3 versus 6 minutes) in comparison to weaker players (back squat to body mass ratio <2). In addition, stronger players demonstrated PAP effects for a longer period after the performance of the potentiating stimulus than their weaker counterparts (i.e., 3–12 minutes versus 6–12 minutes).

In summation, stronger rugby players are able to express greater PAP response during vertical jump, sprint, and bench press throw performance than their weaker counterparts. The optimal rest interval between SPPC may depend on both the type of potentiating stimulus and strength level of the players: potentiating stimuli using accommodating resistance exercise may allow PAP effect to appear earlier when compared with potentiating stimuli using traditional exercises, and stronger players are able to express PAP earlier after the performance of the potentiating stimulus and for a longer period of time.

IMPLEMENTING STRENGTH-POWER POTENTIATING COMPLEXES

One could speculate that long-term SPPC training should result in greater training adaptations than more “traditional” training intervention since players should be able to train at higher power output during each session taking advantage of the PAP effects. The implementation of SPPCs in a program can be accomplished in many ways depending on the phase of the annual calendar and goal of the workout. SPPCs can be implemented during the precompetitive and competitive phases of the rugby season during which the development of strength and power should be the main emphasis of training (8). The strength and power exercises performed after the potentiating stimulus should be specific to rugby since the most effective mode of training is that which includes sport-specific exercises. The rationale behind this is that the more specific a training exercise to the competitive environment, the greater the transfer of the training effect between preparation training and actual competition (17,18). With this in mind, the potentiating stimulus can be paired with specialized preparatory exercises, specialized developmental exercises, and competitive exercises (9).

With respect to rugby, specialized preparatory exercises refer to exercises that train the same muscle groups as the competitive event but involve different movements (e.g., squat, bench press, deadlift, sled drag, push sled, etc.). Specialized developmental exercises train the same muscle groups and involve similar movements to the competitive event (e.g., sprint toward an opponent carrying a tackle pad and perform a tackle to stop him or sprint toward a tackle bag and perform a tackle). Finally, competitive exercises refer to exercises that are identical to the competition event (e.g., sprint toward a ball carrier to tackle him or sprint toward a defender while carrying a ball and try to score a try). Introduction of the ball or asking the players to make 1 or more change of directions will make these exercises even more specialized. The strength and conditioning coach could implement workouts including only 1 category of exercise (i.e., specialized preparatory exercises, specialized developmental exercises, or competitive exercises; Tables 4–6) or combining several categories of exercises (e.g., specialized preparatory exercises and competitive exercises; Table 7). From a periodization perspective, practitioners should start including specialized preparatory exercises in SPPCs early during the precompetitive phase of the season and move toward specialized developmental exercises in the later stages of this phase. Although specialized preparatory exercises and specialized developmental exercises can also be included during the competitive phase, a large emphasis should be given to competitive exercises. SPPCs can be advantageously implemented during congested training and playing schedules as they allow the stimulation of strength, power, and/or speed within the same session. Examples of SPPCs that can be implemented in the resistance training program of rugby players are provided in Tables 4–7.

Table 4
Table 4:
Example of SPPC implementation using specialized preparatory exercises within an upper/lower-body workout
Table 5
Table 5:
Example of SPPC implementation using specialized developmental exercises within a rugby-specific sprint workout
Table 6
Table 6:
Example of SPPC implementation using competitive exercises
Table 7
Table 7:
Example of SPPC implementation using DP and SP preparatory exercises, and competitive exercises within a full body workout

SUMMARY

The vertical jump, sprint, and upper-body performance of subelite and elite and rugby players can be acutely improved using PAP. Traditional (i.e., back squat, power clean, and bench press) and accommodating resistance exercises (traditional exercise with addition of chains or elastic bands) can be used as potentiating stimulus to induce PAP. Typically, the vast majority of protocols using traditional resistance exercise as potentiating stimulus used heavy intensities ranging from 87 to 93% of 1RM, whereas lighter intensities (77–81% 1RM) were used when using accommodating resistance exercise. In addition, while a long period of rest is necessary to elicit PAP after the performance of potentiating stimuli using traditional exercises (4–12 minutes in the back squat, 3–16 minutes in the bench press, 7 minutes in the power clean), it seems that potentiating stimulus using accommodating resistance exercise may allow a PAP effect to appear after approximately 90 seconds of rest. The degree of potentiation during jumping and sprinting activities is affected by the type of exercise used as potentiating stimulus. Heavy back squats seem to be more beneficial than plyometrics to elicit PAP during a jumping task and power cleans seem to elicit greater PAP effect during sprinting when compared with back squats. Finally, the level of PAP is also influenced by the strength level of the players with stronger players expressing higher degrees of potentiation than their weaker counterparts. In addition, stronger players are able to express PAP earlier after the performance of a potentiating stimulus and for a longer period in comparison with weaker players.

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Keywords:

postactivation potentiation; strength-power potentiating complex; rugby; vertical jump; sprint; squat

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