Introduction

Volleyball has been an Olympic sport since the 1964 games in Tokyo. It is a game that is played between two teams, each comprising six court players. Volleyball is primarily based on repeated short high-intensity actions, which require well-developed energy systems that exist in muscle cells to replenish adenosine triphosphate (ATP; i.e., phosphagen system, glycolysis, and oxidative system; Smith, Roberts, & Watson, 1992), with a total match duration of 60 to 90 min. These short actions, which mainly occur during matches, are jumps, sprints, and dives (Puhl, Case, Fleck, & Van Handel, 1982), and volleyball players often perform changes of direction in a response to unpredictable stimuli (e.g., ball or opponent), which illustrates the intermittent nature of their efforts.

One of the main goals of the preseason training phase is to develop the physical condition in preparation for the impending competitive season (Jeong, Reilly, Morton, Bae, & Drust, 2011). In most team sports, this training phase ranges from 2 to 6 weeks before the athletes are required to compete on a weekly basis. Therefore, given the limited length of the preseason period, it is imperative that coaches plan an effective training program.

The theory behind triphasic training is that all dynamic muscle actions consist of three phases: eccentric, isometric, and concentric (Dietz & Peterson, 2012). The purpose of this training is to maximize sport performance by enhancing all three muscle actions to create a strong link between eccentric, isometric, and concentric phases (Dietz & Peterson, 2012). The first training phase focuses on time under tension by lengthening the duration of the eccentric portion of each repetition. The goal of this phase is to maximize force development by the potentiation of the contractile elements and the storage and use of elastic energy through a higher “preload” before the concentric phase (Schenau, Bobbert, & de Haan, 1997). The second training phase focuses on the isometric part of the muscle contraction. This type of training has been shown to be effective in improving isometric force production at the joint angle that the muscles were trained at (Tillin, Pain, & Folland, 2011). To maximize intermuscular coordination and force production, the last training phase (i.e., concentric) focuses on performing every repetition as fast as possible.

To the authors knowledge, there is no research that evaluates the impact of a triphasic resistance training program during the preseason period in elite athletes. Thus, the purpose of the present study is to assess the impact of a 6-week triphasic resistance training program during the preseason period in professional male volleyball athletes.

Methods

One week before and after the 6‑week training program, several tests and measurements were performed. The fundamental principle when sequencing various tests is that one test should not affect the performance of the following. Therefore, tests that might produce fatigue should be the last ones to be administered and vice versa (Haff & Triplett, 2015). On Monday, body composition, reactive strength, and change-of-direction speed (CODS) were assessed. On Tuesday, sprint speed was evaluated. On Thursday, maximal strength was tested, and finally, on Friday, aerobic and anaerobic capacity were assessed.

Subjects

Before their inclusion in the study, the experimental aims and procedures were explained to the participants, from whom written informed consent was obtained. The experimental protocol fitted the recommendations from the Declaration of Helsinki produced by the World Medical Association for research with humans (World Medical Association, 2008). In addition, all procedures adhered to established ethical standards for sports medicine (Harriss, MacSween, & Atkinson, 2019). Fourteen male elite volleyball players participated in this study (mean [± standard deviation] age: 28.88 ± 5.59 years; height: 192 ± 10 cm; body mass: 88.00 ± 14.54 kg). Athletes were in preparation for competing in three major competitions: the first Portuguese Volleyball Division, Liga UNA Seguros; the CEV Volleyball Challenge Cup; and the Portuguese Domestic Cup. All the participants were tested during the preseason phase and none of them had any disease or muscular injury during the intervention period.

Body composition

For body composition the following measurements were used: body weight, body skinfolds (triceps, biceps, subscapular, iliac crest, supraspinal, abdominal, front thigh, and medial calf), and body circumferences (upper arm relaxed, mid-thigh, and mid-calf). All measurements followed the International Society for the Advancement of Kinanthropometry (ISAK) guidelines (Marfell-Jones, Olds, Stewart, & De Ridder, 2006). Muscle mass was derived from the Lee et al. equation (Lee et al., 2000).

Reactive strength

For reactive strength, three trials were recorded for each jump (i.e., countermovement jump [CMJ], squat jump [SJ], and drop jump from a box of 50 cm [DJ50]) in free software, open hardware equipment (Chronojump Boscosystem, Barcelona, Spain), with a minimum of 60 s rest between trials. Previous research with adult male volleyball athletes showed greater reactive strength and jump height performances from box heights between 40 and 60 cm (Andrade et al., 2020). For this reason, a box height of 50 cm was chosen for the present study. In line with previous investigations, all subjects were instructed to perform maximal effort jumps with hands remaining on hips throughout the movement to limit the influence of the upper body on jump performance (Barker, Harry, & Mercer, 2018). For the CMJ test, the Bosco et al. procedures (Bosco, Luhtanen, & Komi, 1983) were followed, where athletes began in an upright position before execution of the vertical jump, which then started with a countermovement until the legs were bent down to 90°. For the SJ test, subjects were instructed to remain still in the squat position for 3 s, and to not perform a countermovement before jumping (McGuigan et al., 2006). For the DJ50 test, athletes started upright on the box with both hips and legs extended. Then, participants stepped off the box and were instructed to rebound as “fast and high” as possible upon touching with the contact mat before executing a controlled landing. The variables measured for these jump analyses were jump height from 50 cm (JH50), eccentric utilization ratio (EUR; i.e., the ratio between CMJ and SJ jumping heights), contact time from 50 cm (CT50), and reactive strength index from 50 cm (RSI50), calculated as jump height (JH) in meters divided by contact time (CT) in seconds. The best of three trials for each test was used for analysis.

Change-of-direction speed

For the CODS assessment, the T‑Test was performed on an indoor court, starting 0.3 m behind a pair of timing gates (WITTY System, Microgate, Bolzano, Italy) according to procedures previously published (Pauole, Madole, Garhammer, Lacourse, & Rozenek, 2000). Three trials were performed, with a minimum of 2 min rest between attempts. The best result was picked for analysis.

Sprint speed

Regarding sprint performance assessment, the athletes started in a two-point stance position, with the front foot behind a line 30 cm from the first gate. According to previous investigations, team-sport athletes reach maximum velocity during a 30- to 40‑m sprint (Rumpf, Lockie, Cronin, & Jalilvand, 2016). With this under consideration, it can be assumed that in this test, the subjects were in acceleration all the time. Single-beam postprocessing timing gates (WITTY System, Microgate, Bolzano, Italy) were placed using a tripod at a height of 1 m at the starting line and at 30 m. The result was expressed in seconds and the best of three trials was selected for analysis.

Maximal strength

Maximal strength was assessed via the one-repetition maximum (1-RM) test in the barbell back squat and the barbell bench press. The 1‑RM assessments were performed in a power cage using a 20-kg barbell. For each squat trial, subjects were instructed to perform the eccentric phase in a controlled manner until thighs were parallel to the ground. For the bench press, the eccentric portion of the lift finished when the barbell touched the athlete’s chest. Each participant performed a 1-RM back squat and 1‑RM bench press protocol according to NSCA guidelines (Haff & Triplett, 2015).

Aerobic and anaerobic capacity

The Yo-Yo Intermittent Recovery Test Level 2 (YYIRT2) was chosen because it provides an indication of both aerobic and anaerobic capacity (Bangsbo, Iaia, & Krustrup, 2008). The test was conducted according to established methods which consisted of repeated 2 × 20 m runs at a progressively increased speed (Bangsbo et al., 2008). The YYIRT2 was controlled by audio beeps from an iPhone device (Apple Inc., Cupertino, CA, USA) connected via Bluetooth to a portable speaker (JBL Xtreme, HARMAN International, Stamford, CT, USA) located immediately adjacent to the 20‑m running lanes.

Training intervention

Besides the usual volleyball practices completed five times per week, all subjects performed the training intervention for 6 weeks, each one comprised of three training sessions (i.e., 18 sessions in total). Training intensity for the back squat and the bench press was prescribed as a percentage of 1‑RM based on preintervention assessments. The intensity of the remaining exercises was prescribed based on a 1–10 scale in which a rate of perceived exertion (RPE) value corresponded to a number of repetitions in reserve (RIR; i.e., 10 RPE = 0 RIR; 9 RPE = 1 RIR, etc.; Zourdos et al., 2016). Training volume was manipulated by the number of sets and repetitions. All athletes were familiarized with the execution of all exercises. Nevertheless, an investigator was present at all training sessions to ensure that the execution of the exercises was correct. Each day comprised four groups of exercises (Table 1). The rest duration was 180 s, 120 s, 90 s, and 60 s between sets for the first, second, third, and fourth groups, respectively.

Table 1 Training program during the 6‑week intervention period
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Statistical analysis

Statistical analyses were performed using the Statistical Package for Social Sciences (v. 27.0; IBM Corp., Armonk, NY, USA). Intraclass correlation coefficients (ICCs) were calculated to determine the reliability of reactive strength, change-of-direction, and sprint testing methods within sessions. Interpretation of these values used Portney and Watkins (Portney & Watkins, 2009) ranges, whereby values of > 0.75 indicate good reliability, values ranging from 0.5 to 0.75 imply moderate reliability, and values < 0.5 suggest poor reliability. Variability in the data was assessed via calculation of coefficients of variation (CoVs); this analysis of absolute reliability provides information regarding within-trial variability expressed as a percentage. To assess differences between pre and post intervention measures, paired-sample t-tests were performed. Mean differences (MDs) and estimates of effect size (ES) were calculated using Cohen’s d with associated 95% confidence intervals (CIs) and interpreted using thresholds of 0.2, 0.5, and 0.8 for small, moderate, and large, respectively (Cohen, 1988). An ES of ± 0.2 was considered the smallest worthwhile effect, with an ES of < 0.2 considered to be trivial.

Results

All within-session measures of reliability are reported in Table 2. All parameters demonstrated good within-session reliability, ranging from 0.96 to 0.99 for all the variables. Of all tests, the DJ50 demonstrated the greatest variability within trials, with a CoV of 2.51% and 2.61% for JH50 and CT50, respectively.

Table 2 Within-session reliability (intraclass correlation coefficients [ICC] and coefficients of variation [CoV]) obtained from three repeated trials of the reactive strength, change-of-direction, and sprint performance tests
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Descriptive statistics for all body composition variables are shown in Table 3. Muscle mass (pre: 40.00 ± 4.74 kg, post: 41.16 ± 4.96 mm, p < 0.001, d = 0.25) significantly increased during the 6‑week training intervention, although the ES was small. Biceps skinfold (pre: 3.89 ± 1.23 mm, post: 3.43 ± 1.12 mm, p = 0.03, d = 0.41), subscapular skinfold (pre: 10.39 ± 4.65 mm, post: 9.54 ± 4.21 mm, p = 0.02, d = 0.20), abdominal skinfold (pre: 17.18 ± 10.54 mm, post: 13.32 ± 8.03 mm, p = 0.004, d = 0.43), sum of eight skinfolds (pre: 75.46 ± 34.13 mm, post: 64.39 ± 25.69 mm, p = 0.004, d = 0.38), and mid-thigh circumference (pre: 54.61 ± 4.60 mm, post: 55.51 ± 4.18 mm, p = 0.02, d = 0.21) all had significant pre- to postintervention differences with a small ES.

Table 3 Descriptive statistics (means ± standard deviations and 95% confidence intervals) for body composition variables pre and post training intervention
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Descriptive statistics for performance variables are in Table 4. Sprint performance (pre: 4.25 ± 0.29 s, post: 4.20 ± 0.29 s, p < 0.001, d = 0.18) increased during the 6‑week training intervention, although the ES was trivial. Regarding reactive strength, the SJ performance (pre: 43.32 ± 5.48 cm, post: 44.70 ± 6.44 cm, p = 0.02, d = 0.27) significantly increased from pre to post intervention with a small ES. Both lower (pre: 111.29 ± 25.77 kg, post: 129.71 ± 27.78 kg, p < 0.001, d = 0.71) and upper body (pre: 88.21 ± 15.01 kg, post: 95.25 ± 17.38 kg, p = 0.002, d = 0.45) maximal strength significantly increased from pre to post intervention with moderate and small ES, respectively.

Table 4 Descriptive statistics (means ± standard deviations and 95% confidence intervals) for performance variables pre and post training intervention
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Discussion

The aim of this study was to assess the impact of a 6-week triphasic resistance training program during the preseason period in professional male volleyball athletes. The main findings suggest that the parameters related to maximal strength performance improved over the intervention period.

The results of this study reveal that the triphasic training protocol can induce significant (p < 0.001) and small (d = 0.25) increases (1.18 kg) in muscle mass over a short 6‑week period. In addition, there was a small (d = 0.38) but significant (p = 0.004) decrease in the sum of eight skinfolds (−11.07 mm). This result is aligned with previous reports in the literature which showed that resistance training performed alongside technical and tactical sport-specific practices can produce increases in muscle mass and reductions in body skinfolds and body fat (Blazevich, Gill, Bronks, & Newton, 2003).

The only jumping variable that significantly improved during the 6‑week intervention was the SJ (p = 0.02) with a small ES (d = 0.27). The SJ test is typically used to measure an athlete’s explosive lower-body concentric power during the speed-strength spectrum (Markovic, Dizdar, Jukic, & Cardinale, 2004) and indicates that the triphasic resistance training program induced an improvement in the leg extensors’ concentric strength. In fact, lower limb maximal strength, assessed through the 1‑RM back squat, improved significantly (p < 0.001, d = 0.71) during the intervention period. Similar findings were found when the same type of training intervention was applied with basketball players during the same 6‑week duration (Russell & Brooks, 2013). The back squat has been shown to develop great lower body strength and power and is a good indicator of vertical jumping ability (Weiss, Relyea, Ashley, & Propst, 1997). The vertical jump component is critical for various volleyball actions such as blocks and spikes (Fuchs et al., 2019) and the results of this investigation provide evidence that the triphasic training is an effective resistance training program to induce positive changes in the 1‑RM back squat. Although nonsignificant, the EUR showed small (d = 0.38) reductions from pre to post intervention. The EUR (i.e., the ratio between CMJ and SJ jumping heights) provides insight into an athlete’s slow stretch-shortening cycle ability (McGuigan et al., 2006), and this type of training decreases this value mainly due to the increments in SJ performance. Therefore, this type of training can be useful for building the foundation for subsequent power and plyometric training regimens by augmenting lower body maximal strength and, therefore, prepare the elastic properties of both muscles and tendons.

The results of this study also underscored the fact that resistance training is not ideal to improve RSI in elite adult athletes. In general, elite adult athletes are more skilled and have higher levels of strength compared to their younger counterparts. Thus, after achieving specific strength standards, to improve their performance, elite athletes must shift towards a power-type training while maintaining their strength levels to improve fast stretch-shortening cycle (SSC) activities such as the DJ (Rebelo et al., 2022; Suchomel, Nimphius, & Stone, 2016).

There were also significant (p < 0.001) yet trivial improvements in sprint performance over 30 m. During the acceleration phase of a sprint, the force production is an important component (since this phase depends on mechanical power which is the product of force and velocity; Morin et al., 2012). Strength and conditioning professionals should be aware that despite the trivial training effect, strength training by itself can improve the initial phase of sprinting (Lockie, Murphy, Schultz, Knight, & Janse de Jonge, 2012). Moreover, during the acceleration phase of a sprint, an athlete needs to produce more horizontal force to propel himself (Nagahara, Mizutani, Matsuo, Kanehisa, & Fukunaga, 2018). However, the primary lower-body exercise used during the intervention period of this study was the back squat, which is an exercise that is performed in the sagittal plane and, therefore, is associated with vertical force production. Additionally, when the aim is to improve the acceleration phase of a sprint, strength and conditioning professionals should have the force-production vector in consideration while the strength program is being designed. Specific sprint training induces positive technical adaptations such as reduction of the ground contact time (Spinks, Murphy, Spinks, & Lockie, 2007), and, as can be seen in this study, the CT did not improve during the 6‑week training intervention. This might explain why there were trivial ES (d = 0.18) in the 30‑m sprint test, since there was no specific sprint training method applied.

Upper-body horizontal strength and power are also important physical components of a volleyball player, particularly for opposite hitters and right-side hitters (Gonçalves, Lopes, Nunes, Marinho, & Neiva, 2021). Various technical skills of the game, such as serves and spikes, require good amounts of upper-limb strength. Additionally, it is important to mention that arms can have a positive influence throughout the take-off on jumping during the game (Kitamura et al., 2017). In the present study, upper-limb maximal strength was tested through the 1‑RM bench press. The triphasic strength training intervention resulted in significant (p = 0.002), albeit small (d = 0.45), improvements in the 1‑RM bench press. Therefore, the triphasic strength training intervention seems to be effective in developing upper-body strength.

The T‑Test performance did not improve after the 6‑week resistance training intervention. Change-of-direction speed tasks typically require a quick shift from the eccentric to the concentric phase (Young & Farrow, 2006). Therefore, it is necessary a speed-strength stimulus (e.g., reactive strength) to observe improvements in this physical quality, as relationships of various CODS tasks with reactive strength tests have already been found (Young, Miller, & Talpey, 2015).

Resistance training may be a valuable form of training, as it improves anaerobic power and short- and long-term endurance capacity in elite athletes (Tanaka & Swensen, 1998). Nevertheless, a trivial ES was observed for the YYIET2, with statistical nonsignificance. It is worth noting that the focus of the volleyball sessions themselves was mainly on the tactical and technical elements of the game and no form of specific endurance training was performed. This could explain these results.

Although positive results were observed in some testing variables, it should be noted that the training intervention was completed during the preseason period, in which athletes are expected to significantly improve their conditioning after a period without competitions and/or training. Future studies should analyze whether this training methodology would have a different impact during the competitive period, where athletes are already at their expected peak in terms of their physical abilities. Another limitation of this study was the fact that all jumping tests were performed using a contact mat instead of a force plate. Despite the fact that contact mats are cheaper and easier to use than force plates, researchers should be warned that the flight times predicted from the contact mats are not always consistent when compared to the flight times estimated from the force plates (Whitmer et al., 2015). This study has no control group, and the sample size is small. However, all participants are elite athletes, which is an unusual sample to find in the scientific literature, as elite athletes are too valuable (economically and sportingly) to be studied.

Regarding this training methodology, it should be noted that during the last phase (i.e., concentric focus), the intention is to perform the exercise as fast as possible. Nonetheless, during the concentric part of the lift, there is always a deceleration portion throughout this section. This could explain the nonsignificant differences in the CMJ performance, for example. Keeping high power outputs during this last training phase was the goal. However, to accelerate the load through the full range of motion, future studies should implement this training methodology with techniques that can remove the deacceleration portion of the concentric phase of the lift. A technique that has been shown to increase peak power and peak force is the use of chains and elastic bands (Israetel, McBride, Nuzzo, Skinner, & Dayne, 2010). This is accomplished by altering the mechanical profile of an exercise, in particular the changes in the force-velocity curve.

The preseason period is a crucial phase of the season in which strength and conditioning coaches try to enhance physical performance and reduce the risk of injury. The literature shows the preseason period to be a time during which athletes are subjected to the highest workload; consequently, elevated injury rates have been observed in this period (Gabbett & Jenkins, 2011), including in elite male volleyball players (Timoteo et al., 2021). Therefore, an effective preseason training program can establish the basis for elite volleyball success during the in-season period. The results of this study reveal that triphasic resistance training is an effective method to apply during the preseason period of elite team sports, when proper exercise selection, volume, and intensity are prescribed.

Conclusion

One of the main goals of the preseason training phase is to develop the physical condition in preparation for the impending competitive season. The findings of this study suggest that in trained professional volleyball athletes, a short-term resistance training program following the triphasic method can increase maximal squat and bench press strength during the preseason period. Moreover, the explosive lower-body concentric power also improved during the 6‑week intervention. Strength and conditioning professionals should consider this type of training if the aim is to improve important physical aspects of elite volleyball athletes, such as maximal strength and concentric power. However, if the goals are to improve reactive strength and change-of-direction speed, then coaches must shift towards power-type and specific speed training to improve these stretch-shortening cycle activities.