The Effects of Plyometric Conditioning Exercises on Volleyball Performance with Self-Selected Rest Intervals

Abstract

Post-activation performance enhancement remains a topic of debate in sport science. The purpose of this study was to examine the effects of lower-body plyometric conditioning activity (CA) with a self-selected intra-complex rest interval on upper and lower-body volleyball specific performance. Eleven resistance-trained female volleyball players participated in the study (age: 20 ± 2 years; body mass: 67.8 ± 4.4 kg; height: 178 ± 6 cm; half back squat one-repetition maximum: 78.6 ± 10.2 kg; experience in resistance training: 5.5 ± 2.1 years and in volleyball training: 10 ± 2.3 years). Each participant performed a plyometric CA followed by two different sport-specific tests: an attack jump and a standing spike attack. The changes in jump height (JH), relative mean power output (MP) and ball velocity (BV) were analyzed before and after the CA with self-selected rest intervals. The applied plyometric CA with self-selected intra-complex rest intervals led to an insignificant decline in JH (p = 0.594; effect size [ES]: −0.27) and MP (p = 0.328; ES: −0.46) obtained during the attack jump as well as a significant decline in BV (p = 0.029; ES: −0.72) during the standing spike attack. This study showed that a plyometric CA with self-selected intra-complex rest intervals failed to elicit localized and non-localized PAPE effect in a group of sub-elite volleyball players.

1. Introduction

Since a slight augment of performance may be the worthwhile difference between winning and losing in sport, the pre-conditioning strategies for acute athletic performance enhancement are recently of great interest for coaches and sports scientists [1,2,3,4,5,6]. In addition to the ischemic preconditioning, acute caffeine ingestion, a post-activation performance enhancement (PAPE) is well-documented as an effective method of improving voluntary dynamic activities such as throwing, running or jumping in various athletes’ populations, i.e., track and field and team sports [7,8,9,10,11,12]. In practical terms, this method involves the complex execution of two similar exercises, with the first one being a high-intensity conditioning activity (CA), inducing PAPE, followed by an explosive movement. Due to the significant application of complex training by strength and conditioning coaches and athletes, the determination of the existence of non-localized PAPE effect is constantly gaining interest [13]. Thus, a research question arises: does the PAPE effect occur when the CA and subsequent explosive movement involve different muscle groups? There is strong evidence for a local PAPE effect [14,15]; however, some aspects may theoretically suggest that this phenomenon might be the more general effect due to an increase in muscle temperature and activation, an increase in circulating catecholamines after the brief bout of high-intensity exercise [16,17,18]. Therefore, to shed more light on this topic, it seems important to elucidate the existence of a non-localized PAPE effect.

Previous research indicates that the type of exercise used during the CA plays a critical role in eliciting PAPE [19]. Typically, moderate to heavy load CA resistance exercises are used to induce a PAPE effect. In addition, several studies have shown that plyometric exercises as a CA are also effective [20,21,22]. The performance enhancement after plyometric CA may be related to the lower threshold of motor unit recruitment than during slower, high-loaded resistance exercises [23,24] and might be less fatigable [19]. Furthermore, the advantage of plyometric CA is not needing equipment requirements [21]. Besides the type of exercises, the PAPE effect might be influenced by the load, volume and tempo of movement used during the CA, as well as the rest interval between exercises in the potentiation complex [19,25]. There is a consensus in the current evidence that the appropriate selection of mentioned variables creates the “window of opportunity” where the potentiation exceeds the fatigue at a certain time point, thus a performance improvement occurs. Such acute performance enhancement arises within a broad spectrum of intra-complex rest intervals; nevertheless, a large inter-individual variability due to the level of strength, muscle architecture and training background of the athletes exists [19].

Previously applied research protocols mainly fixed intra-complex rest intervals to single or various time points to verify the effectiveness of a particular CA [25,26] without allowing for adjustments based on the day-to-day variability, readiness to perform or perception of effort and fatigue. Do Carmo et al. [27] demonstrated that individually determined rest intervals were more effective than fixed intervals in enhancing countermovement jump performance among strength-trained males. While Santos et al. [28] did not find any differences in countermovement jump performance between 5 min, 10 min and self-selected intra-complex rest intervals among taekwondo athletes. However, to the best of the authors’ knowledge, no similar studies have appeared so far in team sports athletes, even though PAPE training protocols are commonly used in these sports [8,29,30]. Implementation of a self-selected approach combined with plyometric CA may be an attractive and easy solution to induce PAPE during a training session as well as before the competition: firstly, because of no equipment requirements during the CA and secondly, as it may become a time-efficient solution that avoids the need to set intra-complex rest intervals individually for particular PAPE protocols.

However, currently, it is unknown if athletes can effectively determine the moment in which potentiation overcomes fatigue and performance is enhanced. Based on the above and considering that the plyometric CA can effectively induce the PAPE phenomenon [19,20,21,22], the purpose of this study was to examine the effects of self-selected intra-complex rest intervals on upper and lower-body performance. Further, the second aim of this study was to verify the non-localized PAPE effect by assessing the impact of lower-body plyometric CA on upper-body performance. Since the existence of a non-localized PAPE comes down to purely theoretical speculation, we hypothesized that self-selected intra-complex rest intervals would significantly increase post-activation attack jump but not the standing spike attack performance.

2. Materials and Methods

2.1. Participants

Eleven female sub-elite volleyball players (2nd division polish league) with experience in resistance training participated in this study (

Table 1. Descriptive characteristics of the study participants.

Age [years] Body Mass [kg]	20 ± 2
	67.8 ± 4.4
Body Fat [%]	20.9 ± 4.4
Height [cm]	178 ± 6
Half Squat 1RM [kg]	78.6 ± 10.2
Experience in resistance training [years]	5.5 ± 2.1
Experience in volleyball training [years]	10 ± 2.3

1RM—one repetition maximum.

). Participants had at least 3 years of experience in resistance training and at least 6 years in volleyball training immediately before enrollment in this study. The experiment started 3 days after the last match in the season. The participants declared they were free from musculoskeletal disorders and provided written informed consent after they were informed about the purposes of the study, requirements and risks. The study protocol was approved by the Bioethics Committee for Scientific Research, at the Academy of Physical Education in Katowice, Poland (3/2021) and was performed according to the ethical standards of the Declaration of Helsinki, 2013. The statistical software (G*Power, Dusseldorf, Germany) was used to calculate the sample size. Given the related-samples Wilcoxon signed rank test, a small overall effect size (ES) = 0.85, an alpha-error <0.05 and the desired power (1-ß error) = 0.8, the total sample size resulted in 11 participants.

2.2. Procedures

The participants took part in a familiarization session and two experimental sessions within two weeks. All participants were tested within the same menstrual cycle (six participants were tested during the follicular phase of their menstrual cycle, whereas the remaining five players were tested during the luteal phase). To avoid the influence of circadian rhythm on performance, all study sessions were performed between 17:00 p.m. and 19:00 p.m. At first, the participants were familiarized with the experimental protocol and were subjected to anthropometric (stature, body mass analysis) measurements. The experimental sessions were performed in randomized order, 72-h apart, where each player performed a CA which consisted of 3 sets of 5 tuck jumps with a 60s rest interval followed by a lower-body (attack jump) or upper-body verification test (standing spike attack).

To verify the effectiveness of the plyometric CA with a self-selected intra-complex rest interval, the athletes performed single sets of 2 repetitions of sport-specific volleyball tasks: attack jump and standing spike attack, at baseline and after the CA. Differences in pre- and post-CA values in jump height (JH) and relative mean power output (MP) during the attack jump as well as ball velocity (BV) during the standing spike attack were assessed. To avoid fatigue, participants were instructed not to perform any additional resistance exercises within 72 h of the sessions. In addition, they were asked to maintain their normal nutritional and sleep habits throughout the study and not to take any additional supplements or stimulants for 24 h prior to the sessions.

2.3. Familiarization Session

All sessions were held in an indoor volleyball court. One week before the main experiment, participants conducted a standardized warm-up lasting approximately 10 min, which was repeated during the experimental sessions. The warm-up consisted of trunk forward and side-bends, alternating knee raises to the chest, forward and backwards walking lunges with overhead arm raises, followed by internal, external and lateral arm swings, slide steps and cariocas for each direction while jogging. Next, band pulls in front of the chest, external and internal shoulder rotations, side steps with a band, pogo jumps, squat jumps and lateral jumps were performed. Ten repetitions of all the warm-up exercises were performed. Following the warm-up, all participants performed 2 sets of 2 repetitions of the attack jump and standing spike attack.

2.4. Experimental Sessions

In a randomized order, 5 min. after an identical warm-up as in the familiarization session, the participants performed 2 different testing protocols, 72-h apart: where each player performed a baseline measurement of the (a) attack jump or (b) a standing spike attack (a single set of 2 repetitions), then after an additional 5 min. rest interval they performed a CA (3 sets of 5 tuck jumps with a 60 s rest interval) [20] followed by the (a) attack jump or (b) a standing spike attack performance evaluation after a self-selected rest interval. After completion of the CA routine, each participant rested in a sitting position and when they felt ready, reported their willingness to perform the attempt. One of the investigators was responsible for measuring the time of self-selected rest interval for each participant from the end of the CA to taking the attempt. The changes in JH, MP and BV were analyzed before and after the CA with self-selected rest intervals. The best repetition of each jump and spike was considered for further analysis.

2.5. Evaluation of Attack Jump Performance

In the attack jump test, the participants used an individually determined approach from 2 to 3 steps, performing a bouncing jump with an arm swing. This movement is followed by a quick upward vertical jump as high as possible, accompanied by a backward arm swing (photocells did not include the approach steps). Participants were instructed to perform the jumping procedure in a similar way to their technique during a volleyball game or practice. The jump performance was measured using Optojump photoelectric cells (Microgate, Bolzano, Italy). This device is an infrared platform with proven validity and reliability for assessing vertical jumps heights [31]. In the current study, the within-participants coefficient of variation for JH and MP measures was 3.2% and 5.8%. The device measures the flight time of vertical jumps with a sampling frequency of 1000 Hz. According to the manufacturer, the MP was calculated with the following formula:

$$P=g^2·T_f·\frac{\left(T_f+T_c\right)}{4·T_c}$$

$g$—gravity acceleration; $T_f$—flight time; $T_c$—contact time.

2.6. Evaluation of Standing Spike Attack Performance

The exercise protocol is based on the specific testing protocol for assessing spike speed in volleyball published by Palao and Valades [32]. In the standing spike attack test, the participants were instructed to hit the ball as hard as possible towards a delimited target zone, and BV was measured by a radar gun (Velocity Speed Gun, Bushnell; Overland Park, KS, USA) placed 2 m from the hitting zone [32]. The level of volleyball skills presented by sub-elite athletes allowed them to easily get the target without ball velocity decreases, using their typical technique. During the familiarization session, any problems with the accuracy were noticed, and the within-participants coefficient of variation for BV measures was 5.4% during the experimental trial. Radar gun displayed the fastest speed captured during the movement (attack). A standard ball used in training and competitions (Molten V5M5000) was used in this study.

3. Statistical Analysis

All statistical analysis were performed using SPSS (version 25.0; SPSS, Inc., Chicago, IL, USA) and were expressed as means with standard deviations (±SD), median and interquartile range. Moreover, the 95% confidence intervals for mean values between baseline (BA) and post-CA values were also calculated. The normality of data distribution was checked using Shapiro–Wilk tests. Due to the violated distribution of data, the related-samples Wilcoxon signed rank test was performed to assess differences between the BA and post-CA values of JH, MP, BV. Effect sizes (Hedges g) were reported where appropriate and interpreted as ≤0.20 “small”, 0.21–0.8 “medium” and >0.80 as “large”.

4. Results

The Wilcoxon signed-rank test showed no significant difference between BA and post-CA differences in JH (p = 0.594) and MP (p = 0.328) but there was significant decrease in BV following the CA in comparison to BA (p = 0.029) (

Table 2. Baseline and post-CA performance.

BA (95CI; Median [IQR])	Post-CA (95CI; Median [IQR])	ES	RE [%]
Jump Height [cm]
49 ± 5 (48.7 to 52.3; 46.5 [8.2])	47.4 ± 6.7 (42.9 to 51.9; 45.9 [6.3])	−0.27	−2 ± 19.2
Relative Mean Power Output [W/kg b.m.]
47. 3 ± 9.5 (40.8 to 53.6; 48 [17])	43.4 ± 7.2 (38.6 to 48.3; 43.2 [10.5])	−0.46	−5 ± 25
Ball Velocity [km/h]
72.9 ± 6 (68.9 to 76.9; 75 [7])	68.6 ± 5.9 * (64.7 to 72.6; 68 [10])	−0.72	−6 ± 7

BA—baseline; CA—conditioning activity; ES—effect size; RE—relative effect; CI—confidence interval; IQR—interquartile range; b.m.—body mass; * p < 0.05 significant different from the baseline.

). Moreover, individual choices of rest intervals during attack jump and spike attack complexes were presented in Figure 1.

5. Discussion

This study’s objective was to assess the effects of self-selected intra-complex rest interval on CMJ and standing spike attack performance after the plyometric CA. This study showed that a plyometric CA with a self-selected intra-complex rest interval failed to elicit localized and non-localized PAPE effect in a group of sub-elite volleyball players. Moreover, results of the present investigation showed a negative trend in the attack jump (decline in height by ~2% and in relative mean power output by ~5%), as well as a significant decrease of ball velocity during the standing spike attack (by ~6%).

Several reasons may explain the lack of performance enhancement observed in the protocol of this study. First, the participants in our study self-selected average intra-complex rest intervals of 262 ± 66 s for the attack jump and 197 ± 110 s for the standing spike attack (Figure 1); however, as shown by Seitz and Haff [19], intervals above 5 min are needed to enhance a greater PAPE effect than a shorter rest interval. In the case of the study by do Carmo et al. [27] in which the half squat exercise improved the countermovement jump performance with self-selected intra-complex rest intervals, the participants chose a longer rest interval time of 357 ± 164 s. It can therefore be assumed that the PAPE effect was not elicited because most likely fatigue exceeded the accompanying potentiation caused by the CA applied.

Secondly, this is the first study on female athletes using self-selected intra-complex rest intervals in PAPE protocols, while previous studies were carried out on males. Sex differences in muscle fatigue have been suggested before, with females generally exhibiting a greater relative fatigue resistance than males [33]. Therefore, females may also show a different level of perception of fatigue from males; however, this is speculation and therefore further studies are warranted. Third, the participants in the do Carmo et al. [27] study showed significantly higher levels of relative muscle strength (~2.4) than those in the Santos et al. [28] study (~1.9 kg/kg body mass (b.m.) as well as ours (~1.16 kg/kg b.m.) in the half back squat exercise. Seitz and Haff [19] showed that the level of muscle strength has a significant impact on the magnitude of the PAPE effect, stating that the stronger (above 1.75 kg/kg b.m. for men and 1.5 kg/kg b.m. for women in the back squat) show a greater response than the weaker ones (below 1.75 kg/kg b.m. for men and 1.5 kg/kg b.m. for women in back squat). It seems that the participants of this study failed to reach the moment in which the performance enhances after the CA.

This study raises another intriguing issue, the non-localized PAPE phenomenon. Our study, unlike the one of Cuenca-Fernandez et al. [13], showed a decrease in performance enhancement in the applied PAPE protocol. Cuenca-Fernandez et al. [13] found a slight increase in squat jump performance after an upper-body CA (bench press, 4 repetitions at 90%1RM). Of course, this result may also be related to a short intra-complex rest interval selected by the participants of our study. However, an alternative interpretation of the data could be provided. The reasons for these discrepancies can be found in the differences between the protocols. In our study, a CA involving the lower body was used, which resulted in a significant decrease in the performance of the upper body; the opposite was applied in the case of the Cuenca-Fernandez et al. [13] study. It seems possible that the intense activation of nonspecific muscle groups may impair performance, particularly when the CA engages such a large muscle area as the lower limbs before an upper-body explosive activity, as in our exercise protocol. Since the CA used in the present study decreased the capacity of the upper body, possibly by inducing fatigue, it cannot exclude that it could also cause potentiation. Nevertheless, due to the insufficient intra-complex rest intervals, augmentation of performance did not occur; therefore, this remains a problem to be resolved for further PAPE studies.

Even though plyometric CA with self-selected intra-complex rest interval might be an attractive approach to elicit PAPE due to easy practical application, it was ineffective on the participants of this study and in such a configuration. However, in light of the limitations of this study, appropriate caution is needed in interpreting the obtained results. First, there is no certainty that the applied CA would effectively induce the PAPE effect because there was no control group with fixed intra-complex rest intervals. Second, the sample size of this study was small; therefore, similar studies on large sample sizes are needed. Third, only a single PAPE protocol was investigated, so it cannot be ruled out that other CA might be effective. Fourth, the impact of the menstrual cycle on obtained results cannot be ruled out, since not all participants were in the same phase. As a final point, this finding has implications for the testing of female athletes and highly sport-specific tasks, thus the results of this investigation may not translate to alternative samples.

6. Conclusions and Practical Implications

The results of this study showed that the use of self-selected intra-complex rest intervals is not effective in inducing the PAPE effect in the group of sub-elite female volleyball athletes. Moreover, when self-selected intra-complex rest interval and plyometric CA involving the lower body is applied, upper-body performance might be impaired. These findings are of practical value as they suggest that the freedom to judge the moment to perform explosive tasks after a plyometric CA by the athletes is not recommended during PAPE training protocols.