The precompetition preparation phase in sports performance is seen as vital in maximizing human performance. However, there has been a great deal of debate about what the best preparation strategy may be. The literature seems to agree that an active warm-up, involving rhythmic coordinated muscle actions, such as cycling or running, will increase performance (3–5,13,44) as long as sufficient warm-up intensity is used to raise the core temperature. However, the effects of other exercise modalities, commonly used as part of a pre-performance strategy, are much less certain. In particular, the stretch components routinely used as part of a preparation strategy have come under some scrutiny, with regard to their efficacy.
Active warm-up has traditionally been followed by a stretch component, thought to increase performance and decrease the likelihood of injury. This aspect of the preparation strategy is much debated, with the majority of the literature finding that the frequently used passive static stretches are linked to a decrease in a range of performance parameters. Decreases in strength (1,11,24,34), power (31,41), speed (15,16,35,42), jump performance (26,36), and agility (29) have been linked to the use of static passive stretching. These findings have lead to a re-evaluation of the preparation stretch component used as part of warm-up routines by many sports performers.
Recently, there has been a move toward the use of dynamic pre-performance stretches as part of athletes' preparation strategies. This has been because of an almost universal demonstration of increases in performance, when dynamic movements are used, compared with static stretches, in a range of high-intensity, short duration, performance, and muscular function tests (12,15–17,26,31,33,35,36,46,48). Interestingly, combining static and dynamic stretches as part of a warm-up has been explored but has been found to be inferior to just a dynamic stretch regime (15).
The specificity of the movements used and described as dynamic stretches has been examined. It seems that the use of faster stretches is linked to a greater increase in jump performance compared with slower movements (14). However, dynamic stretches performed in motion seem to be superior to stationary dynamic stretches with regard to increasing running speed (15,16), attributed to a rehearsal of the stretch-shortening cycle (SSC) actions, vital in sprint performance.
Another preparation strategy that has recently attracted a large amount of attention has been the phenomenon known as postactivation potentiation (PAP). This is defined as an excited or sensitive neuromuscular condition after intense loading (39). It is exemplified by the application of a preconditioning exercise, such as a heavy back squat, followed by a faster performance activity, such as a jump, commonly known as complex training. It is theorized that the preconditioning activity will increase the subsequent performance task, by increasing neural excitation (22), priming the motor system to a greater capacity. However, there is conflicting evidence with regard to the support of PAP as a training modality. Many studies have shown an increase in performance when a complex training protocol has been used (8,18–20,28,37,38,47,49); however, a large number of studies (2,10,21,27,30,43) have shown no effect on a performance task after a preconditioning activity. These contradictory findings can largely be attributed to differences in methodology; the optimal preconditioning exercise volume and intensity and the recovery time between the preconditioning and performance task have, as yet, not been established. It should be noted that most PAP studies have not established the effect on performance of the warm-up procedures they have used, concentrating on exploring the effect of the preconditioning exercise on performance tasks. This would seem to be a mistake because, commonly, athletes attempting to exploit the PAP phenomenon use an active warm-up, followed by a dynamic stretch, before a preconditioning exercise is employed. All 3 of these modalities have been shown to improve performance; therefore, the question arises as to how much does the preconditioning exercise actually contribute to the changes in performance reported by athletes and researchers alike.
Therefore, this study was designed to explore what affect a commonly used pre-performance preparation strategy would have on subsequent jump height performance. It specifically aimed to clarify which components of this preparation strategy would have the greatest effect on promoting performance. The magnitude of any performance increase linked to the active warm-up component, or the dynamic stretch component, or the preconditioning squat component has, as yet, not been established. It is hypothesized that the higher the intensity of the pre-performance preparation component the greater the jump height achieved.
Experimental Approach to the Problem
The effect of the different components making up a pre-performance preparation strategy was assessed by a randomized, counterbalanced, repeated measures designed study (Figure 1). Either squat jumps (SJs), or countermovement jumps (CMJs), or drop jumps (DJs) (independent variables) were performed in independent trials in the following order: after a 5-minute seated rest, after a standardized active warm-up, after a set of dynamic stretches, and after a standardized parallel squat (dependent variables). Subjects were required to perform the test intervention 4 times, with 3 days of rest between test sessions, with either a different jump assessed on each occasion, or a control condition, where no preparation strategy was employed. Trials took place at the same time of day to avoid any diurnal variations.
Sixteen healthy male subjects (age, 21.38 ± 0.52 years; height, 1.79 ± 0.07 m; and body mass, 75.1 ± 5.26 kg) were selected from a group of 30 collegiate athletes because of their superior CMJ performance. The subjects had a minimum of 2 years free weight squatting resistance exercise experience and all were familiar with the jump tests they were asked to perform. They were considered to be a well-trained group of athletes, competing in either team sports (rugby, football, basketball) or track and field at a semiprofessional/top collegiate level. Testing was conducted during winter, coinciding with the end of recovery phases in training, to prevent cumulative fatigue being a factor during testing. Subjects volunteered to take part in this study. The procedures were approved by a departmental committee for ethics. The subjects were asked to complete a health screen and were provided with written and oral information regarding the experimental protocol and possible risks of participation. Informed signed consent was then obtained from all subjects. Subjects were asked not to consume alcohol or perform any physical activity in the previous 24 hours before each trial. Subjects were required to use the same pre-performance routine they would normally employ before a competition; this included replicating nutrition, hydration, and sleep patterns; this was repeated for each test session. Subjects were required not to consume food or any caffeine products for 4 hours before testing but could consume water ad libitum. Testing was performed at 1400 hours (±1 hour) to replicate competition times for most subjects.
Familiarization and Maximum Squat Performance
Two familiarization sessions were performed. These consisted of a session practicing the data collection procedures, including the warm-up and jump protocols and the electromyography (EMG) setup. Session 2 established subject's 1 repetition maximum(1RM) for a parallel squat. To ascertain participant's 1RM, a 10-minute warm-up on a cycle ergometer (Monark Ergomedic 874E; Monark Exercise, Vansbro, Sweden) at a power output of 100 W was performed. This was followed by 8 unloaded squats to a depth where their thighs were parallel to the floor measured by a gravity-dependent goniometer (MIE Medical Research Ltd, Leeds, United Kingdom) reaching 0°. This position was recorded to standardize all subsequent squat depths performed. A bar was set on a stand positioned to allow subjects to touch their ischial tuberosities at the appropriate squat depth. The subjects then performed 3 squats with a 20-kg Olympic Bar (York, Performance Olympic Power Bar, United Kingdom); loading was than increased incrementally, until failure to perform a squat with good form to a parallel position. The heaviest load lifted correctly was used as a measure of 1RM. A qualified strength and conditioning coach supervised this and all subsequent exercise sessions. A mean of 147.5 ± 25 kg was recorded for participants 1RM.
The SJ was performed from a stationary position with a knee angle of 90° with hands placed on hips; knee angle was established using a universal goniometer (Baseline, Penkridge, United Kingdom) and correlated to a bar set at an appropriate height to reproduce the correct knee angle when subjects touched the bar with their ischial tuberosities (established during the familiarization process). The CMJ was performed with hands on hips with subjects having a self-selected squat depth, but with no pause between the downward and upward phases of the jump. The DJ was performed from a 0.2-m height with hands on hips, and the subjects were encouraged to jump as high as possible, with minimum ground contact time. Each jump type was performed 3 times with 1-minute seated rest between each repetition. The highest recorded jump, for each of the different jump types, was used for experimental analysis. The control condition consisted of performing the 3 jump types in a random order. This process was repeated 4 times, with a seated rest mimicking the rest periods employed between the individual components making up the preparation strategy employed in the intervention trials.
Performance Preparation Strategy
Jump height was assessed using a jump mat (just jump; Probiotics Inc, Huntsville, AL, USA) after a 5-minute seated rest. This was followed by an active warm-up, consisting of 10-minute cycle ergometry (Monark Ergomedic 874E, Monark Exercise) at a power output of 100 W; jump height was then measured after a standardized 5-minute seated rest. Subjects then performed 2 × 10 repetitions of specific dynamic stretches, consisting of a deep squat movement at a rhythm of 100 b·min−1 (adapted from Fletcher (14) set by a metronome; DM70 Digital Metronome; Seiko, Shanghai, China); jump height was then assessed after a 4-minute seated rest. Last, subjects performed parallel squats; 3 repetitions at 30% of their 1RM, followed by 3 repetitions at 70% of 1RM, finishing with 2 repetitions at 90% of 1RM; 2 minutes of seated rest was enforced between squats. After the last squat set, a 4 minute seated recovery was performed, before the last jump test.
The EMG analysis of the gastrocnemius, tibialis anterior, biceps femoris, and rectus femoris was performed using a Blue Tooth telemetry EMG system (Biometrics Ltd, Wales, United Kingdom). The EMG sites were shaved and cleaned with an alcohol swab (to reduce electrode impedance to <5 kΩ) with the reference electrode strap attached to the right ankle in a line with the lateral malleolus. Electrodes were attached to the skin, on the belly of each muscle, with the muscle under contraction, with a standardized interelectrode distance of 2 cm, aligned parallel to the direction of the underlying fibers (9). SX230 surface pre-amplified (1 k) electrodes were used at a sampling frequency of 2000 Hz. A main amplifier (0.3–1 k) was used with a common mode rejection ratio of >96 dB, with an input impedance of 10,000,000 (MΩ) and input referred noise of <5. A pre-amplified low-pass 8-order elliptical filter (550 Hz) was set with EMG measured using analogue inputs directly via a PC using a DLK900 Datalink and Datalink softwear (Biometrics Ltd). Raw EMG waveforms were rectified and averaged for the highest of each of the 3 jump types measured, with the whole of the jump movement analysed. EMG was synchronized with a Digital Camcorder (Sony HVR-HD 1000E; Sony Corporation, Tokyo, Japan) sampling at 100 Hz. This was used to establish which parts of the EMG trace represented the jump movements. The camera was mounted on a tripod recording movement in the sagittal plan set at a 10-m distance from the performers, at the height of each individual's greater trochanter when standing.
All data were considered to be normally distributed because the Shapiro-Wilk's test (<50 subjects) for normality was found to have an alpha level of p > 0.05. The control condition was examined with a 1 × 3-way repeated measures analysis of variance (ANOVA), designed to establish whether jump height changed significantly independently of any preparation strategy. The experimental interventions were examined with a 3 × 4-way repeated measures ANOVA; investigating differences between mean jump heights, measured after each preparation component for the 3 experimental conditions, designed to explore which elements of the preparation strategy significantly changed jump height from the initial baseline measure. A 3 × 4 × 4-way repeated measures ANOVA was used to explore differences between mean jump height, experimental conditions, and average EMG output, designed to establish whether any changes in jump height after different components of the preparation strategy were linked to changes in EMG output. After the ANOVAs, pairwise comparison post hoc tests were performed (Bonferroni). Statistical analyses were performed using SPSS version 16 for Windows (SPSS Inc, Chicago, IL, USA) with the alpha level set at p ≤ 0.05. Reliability of measures was assessed using an intraclass correlation coefficient (ICC) to compare repeated test measures. Reliability during the performance preparation trials was calculated for CMJ (ICC = 0.99), SJ (ICC = 0.98) and the DJ (ICC = 0.99). Variation in the control trial was calculated for the CMJ as 2.8% (ICC = 0.9), for the SJ 2.9% (ICC = 0.88) and the DJ 2.8% (ICC = 0.9).
The Control Conditions Jump Performance
When the jumps employed in the control condition were explored (Table 1), CMJ heights exhibited a main effect (F = 21.708, effect size = 0.745, p < 0.05). Post hoc analysis indicated that jump height was significantly (p < 0.05) higher for tests 2, 3, and 4 compared with the first CMJ measure; tests 2, 3, and 4 were not statistically different (p > 0.05). The same pattern of response was found for the SJs (F = 92.328, effect size = 0.758, p < 0.05) and the DJ tests (F = 17.601, effect size = 0.614, p < 0.05).
The Effect of the Individual Components of the Experimental Preparation Strategy on Jump Performance
When the effects of the different components, making up the pre-performance preparation strategy were examined (Table 2), CMJ heights were found to have a main effect (F = 32.205, effect size = 0.936, p < 0.01), indicating that jump performance significantly changed after each intervention. Post hoc analysis indicated that after the squat lift jump height was significantly (p < 0.01) greater than the other interventions. An order effect of the poststretch jump being significantly greater (p < 0.01) than the pre– and post–warm-up jumps and the post–warm-up jump height being significantly (p < 0.01) greater than the pre–warm-up jump was established. The same pattern of response was found for the SJs (F = 99.110, effect size = 0.934, p < 0.01) and the DJ (F = 98.961, effect size = 0.934, p < 0.01).
Jump Height Changes in Performance Comparing Jump Types
When the differences between jump heights were explored (Figure 2), a main effect (F = 5.206, effect size = 0.514, p < 0.05) indicated significant differences between the types of jumps used to measure performance. Post hoc analysis showed jump height changes were significantly greater (p < 0.05) for the CMJ and DJ compared with the SJ, but with no significant difference between changes in performance between the CMJ and DJ.
The Effect of the Individual Components of the Experimental Preparation Strategy on Average EMG Output
It should be noted that for clarity only significant EMG data have been reported in Table 3. The main effects of EMG indicated significant differences between the components making up the preparation strategy (F = 4.153, effect size = 0.714, p < 0.05). Post hoc analysis showed that there was a pattern of response where the average EMG increased after each individual component of the preparation strategy. In the CMJ, pre–warm-up to post–warm-up showed significant increases (p < 0.05) in bicep femoris activity, an increase maintained by the stretch and lift interventions. The stretch component caused significantly higher (p < 0.05) rectus femoris activity compared with post–warm-up values, whereas the squat lift significantly increased (p < 0.05) gastrocnemius activity in comparison with the poststretch measure. When the SJ was explored, rectus femoris activity significantly increased (p < 0.05) pre–warm-up to post–warm-up, maintained by the stretch component. The bicep femoris activity was significantly increased (p < 0.05) when the post–warm-up and poststretch conditions were compared (maintained by the lift intervention), whereas both the rectus femoris and gastrocnemius activity were significantly increased (p < 0.05) by the implementation of the squat lift intervention. In the DJ, the bicep femoris activity significantly increased (p < 0.05) from the pre– to post–warm-up, maintained by the stretch component and significantly increased (p < 0.05) after the lift intervention. When the post–warm-up and poststretch measures were compared, a significant increase (p < 0.05) in rectus femoris activity was shown, maintained by the squat lift exercise.
Figure 3 represents the raw data for the CMJ experimental condition. It shows that all subjects responded positively to the preparation strategy, with increases in jump height recorded after each of the different preparation components. However, it should be noted that though all subjects had substantial increases in jump height after the dynamic stretch component, subjects 7, 12, and 16 could be considered to be none responders to the lifting component, defined here as exhibiting ≥1 cm increase in jump height.
The results of this study show a stepwise increase in jump performances when the different components of the preparation strategy are employed. Jump height was significantly increased in all 3 vertical jump types measured when an active warm-up was employed (an average increase of 2.4%), a pattern of response expected and demonstrated in a number of previous studies (3–5,13,44). However, to understand the full implications of this performance change, a comparison with the control condition is appropriate. In the control condition, all 3 jump types exhibited significant increases in jump height from the first to second test battery (an average increase of 5.5%), but further jump tests (3 and 4) showed negligible variation from test 2. This was an unexpected finding, with the initial increase of control conditions in performance substantially greater than the initial performance changes linked to the active warm-up component of the experimental interventions. It could be that some residual fatigue was associated with the active warm-up component, blunting its potential positive effect on jump height. Fatigue was not a relevant variable in the control trial, where the initial jumps may have helped rehearse the motor skills tested, allowing the substantial increase in jump performance between tests 1 and 2. If this is the case, then any future studies, using active warm-up protocols as part of an investigation into PAP, need to make sure that their chosen warm-up methods do not cause an imbalance between stimulation and fatigue of the motor system in favor of fatigue.
The inclusions of a dynamic stretch component in the preparation strategy lead to a further increase (an average 4.8%) in the jump heights tested. The increase in performance linked to dynamic stretches has been shown in a number of studies (12,15–17,26,31,33,35,36,46,48).
When the last preparation component was employed, jump height was again significantly increased (average increase of 4%). This was assumed to be an example of PAP, where the heavy back squat was used as a preconditioning exercise enhancing the subsequent jump performance. This phenomenon has been demonstrated in a number of previous studies (8,18–20,28,37,38,47,49).
The mechanisms behind these performance changes have been explored in the past. The increase in jump height linked to the employment of an active warm-up is not surprising and well documented (3,44). This has been linked to a stimulation of blood flow and an improvement in the force-velocity relationship (3). This is thought to increase nerve receptor sensitivity and nerve impulse velocity, resulting in a more rapid and forceful muscle contraction (12). The EMG results from the present study support these postulations, indicating positive changes in muscle activation, with a significant increase in average EMG post–warm-up component.
The use of the dynamic stretch intervention further increased the preparation intensity and could have lead to heart rate and core temperature rising to a more optimal level, causing greater nervous system stimulation, resulting in the significant increase in average EMG in this and other studies (14). Importantly, Fletcher (14) found that dynamic stretches increased EMG and jump performance, but that bigger increases were linked to stretches of greater intensity and specificity, hence, the present studies used relatively fast velocity and specific movement pattern as a dynamic stretch. It should also be noted that heart rate and temperature changes were limited by employing a 4-minute rest before the jump tests. Therefore, the rehearsal of specific movement skills and/or PAP may help to explain the dynamic stretches effect on EMG and subsequent jump performance.
The jumps used after implementing the back squat component were preceded by a 4-minute rest period, again making it less likely that heart rate or core temperature increases could have caused the significant increases in jump height exhibited. Indeed, PAP is considered to be a non–temperature-related (4) occurrence. Therefore, of greater significance, may be muscle activation, exemplified by the average EMG recordings. There was a general pattern of a significant increase in EMG after each preparation component, with a stepwise increase in muscle activation after each intervention. The effect of PAP on the nervous system is unclear, with most studies not exploring the mechanisms behind changes in performance. Hodgson et al. (25) have postulated that PAP could cause synaptic modification at the spinal level because of an increase in motor neuron excitability; this may help explain the increases in average EMG found in the present study after both the stretch and squat lift components.
Interestingly, it has been theorized that it is vital for the dynamic stretch component to mimic the velocity and movement patterns of the performance task to maximize performance (14,15). This is supported by the findings in the present study, where although all the jump heights were enhanced, the CMJ and DJ changes in performance were significantly greater than the SJ changes. The stretch and lifts used in the present study used a similar movement pattern to the CMJ and DJ; an SSC was invoked in the dynamic stretch and back squat, as well as the CMJ and DJ. However, the SJ does not have the same eccentric component as the other jump tests, possibly explaining the lower increases in performance seen in this jump type. The EMG data also support the need for specific movements to prime subsequent performances. The bicep femoris and rectus femoris seem to be the muscles that exhibited average increases in EMG to a greater extent than the other muscles analyzed. These muscles are prime movers around the knee and hip in the squat action employed in the stretch and lift techniques in this study. They seem to be the muscles most stimulated, therefore it may be important that the priming exercise used to try to use PAP, needs to be as close as possible to the movement pattern of the subsequent performance task.
Although the present study has found evidence of the PAP phenomena, a number of studies present contradictory findings (2,10,21,27,29,43). Differences in the findings of PAP studies have often been attributed to methodological issues. With this in mind, the present study attempted to produce a PAP methodology supported by findings and recommendations from past literature.
Preconditioning activities employed in PAP studies have a symbiotic relationship between fatigue and potentiation. Although potentially enhancing potentiation and therefore performance, they will also have a fatiguing effect on skeletal muscle (7). It is therefore vital to examine the rest periods used after the preconditioning exercise; too short a recovery and muscular fatigue will prevent performance improvements, and too long and the stimulating effect of the conditioning exercise will be lost. This rest period has been explored and although there is some evidence that the optimal time frame is different for each subject (10), a number of studies have shown a 4-minute recovery to be optimal (6,28) and hence its use in the present study.
The preconditioning load needs to be optimal; PAP is most closely associated with type II muscle fibers (23); therefore, the preconditioning load has to be sufficient to activate substantial numbers of type II motor units. It is postulated that 90% of 1RM is used to optimize the development of PAP (45), an intensity that has been successfully employed in this and a number of previous studies (6,8,32).
Last, the type of subjects employed in PAP studies needs to be taken into account. It has been shown that stronger subjects (7,8,19) exhibit a greater propensity for PAP compared with fewer well-trained subjects with fewer nonresponders. Sale (40) hypothesized that this is because of trained individuals being able to activate the higher threshold, fast motor units, whose muscle fibers exhibit the greatest PAP. Therefore, the present study used a trained athletic population. However, when a Pearson's correlation was employed to see if there was a relationship between load lifted and the increase in jump performance, a nonsignificant R2 value of 0.12 showed no relationship between the squat load and the increase in jump performance. The lack of a relationship was also found by Mangus et al. (30) and McBride et al. (32) and could be because of the level of athletes studied. Although a trained population was used in this study, the loads employed (mean 135 kg) would indicate that they are not highly developed athletes. Whether the performance benefits observed here can be enhanced further through the use of a more trained population is still not clear and this may be worthy of future investigation.
This study aimed to investigate whether a pre-performance preparation strategy could enhance jump performance; the results indicate that all jump types were enhanced by the experimental protocol. Furthermore, the effect the different components making up this preparation strategy would have on jump performance was explored, to ascertain whether any component had a greater effect on performance, an aim believed to be unique among PAP studies. The results suggest that the dynamic stretch and the lift components had a greater positive effect on increasing jump height compared with the general active warm-up; however, the increases in performance linked to the stretch and the squat components are of the same magnitude. It therefore seems that to maximize performance, a preparation strategy, which not only employs an active warm-up, is required. The greater intensity and the specific movements employed in the dynamic stretch and the back squat components seem to be needed to cause an increase in motor neuron excitability in the specific muscles required for the subsequent performance task, demonstrated by the increases in EMG output, which seems to be linked to the increases in jump performances found in this study. Therefore, our original hypothesis seems to be correct, that higher intensity preparation components cause bigger increases in jump performance when compared with lower intensity components.
It seems that the use of a standardized pre-performance preparation strategy causes a greater increase in jump performance than a control condition, involving no preparation components. Furthermore, the more specific and the higher the intensity of the movements incorporated into the preparation strategy, the greater the increase in performance. Therefore, the results from this article suggest that if coaches/athletes wish to maximize high velocity/power performance a stepwise increase in intensity, as part of the warm-up process, should be employed. It is recommended that if coaches/athletes wish to try to use the PAP phenomenon (in a complex training strategy), the exercises used in the preparation strategy as part of the neuromuscular priming process should mimic the performance task as closely as possible. It should be noted that if the SSC is used in your performance task then the priming exercise should also use the SSC in a similar movement pattern.
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