Analyzing Targeted Muscle Strength: Impact on Speed, Endurance, and Performance in Female Volleyball

he influence of muscle strength on performance metrics in volleyball, addressing the need to understand how specific and non-specific strength training impacts athletic capabilities. A cohort of athletes underwent various strength tests, including squats (SQs), bench presses (BPs), and deadlifts (DLs), to assess their force and power during various forms of test. Lactate thresholds (LT 1and LT 2) were also measured to evaluate aerobic and anaerobic capacities. The median speed at LT 1was 1.80 m/s, and LT 2was determined at a mean velocity of 2.56 m/s. Notably, a correlation was found between SQ performance and total points scored (p= 0.040,r = 0.285), while upper body strength was strongly correlated with performance metrics, showing significant relationships with points scored (p= 0.0001, r = 0.690) and peak power during BPs (p= 0.0001, r = 0.587). The findings suggest that targeted strength training enhances physical capabilities and improves

m/s. Notably, a correlation was found between SQ performance and total points scored (p= 0.040,r = 0.285), while upper body strength was strongly correlated with performance metrics, showing significant relationships with points scored (p= 0.0001, r = 0.690) and peak power during BPs (p= 0.0001, r = 0.587). The findings suggest that targeted strength training enhances physical capabilities and improves technical and tactical performance in volleyball, highlighting the critical role of muscle strength in athlete selection and training strategies. Keywords:volleyball; exercise testing; muscular strength 1. Introduction Volleyball is a sport recognized for its dynamic nature and high physical demands. As a result, volleyball players have certain anthropometric and specific neuromuscular requirements, such as force development rate (FDR), muscle unit activation (MUA), and intermuscular coordination (IC). These qualities are directly linked to strength, speed, endurance, and other psychomotor qualities, all of which are essential during rapid move- ments, jumping, and landing. The influence of these characteristics is closely tied to muscle fibers. While volleyball may not be as metabolically demanding as other sports [1], it requires a higher force- to-weight ratio, which relies heavily on the nervous system, the degree of muscle fiber development [2], and energy availability. Several authors have published papers proving that strong muscles provide better support to joints and enhance stability [3], particularly in the shoulder and core, which are important during blocking and serving. However, according to Sheppard JM et al. [4], strength influences performance differently depending on the player’s position. The outside hitter requires both lower and upper body strength for powerful attacks and effective blocking. By contrast, the libero relies more on endurance and core strength to maintain consistent passing and defensive stability. Similar results were reported by Singh M. et al. [5] for the setter, which benefits from upper body strength Appl. Sci.2024,14, 10951.

Appl. Sci.2024,14, 10951 2 of 16 and shoulder stability for precise ball placement, while core strength supports efficient movement during quick transitions. For the middle blocker and the opposite hitter, most studies report high explosive power for effective blocking and attacking. As a result, most studies suggest that both specific and non-specific strength training are prioritized in weekly training cycles, tailored to the specific needs of each position [6]. Despite this broad understanding, there remains a lack of studies examining the precise interaction between strength, speed, and endurance in relation to volleyball perfor- mance across different player positions. While strength training is widely acknowledged as a fundamental component of physical preparation [7], studies that focus on the synergy between strength development, speed, and endurance within the context of specific vol- leyball skills are limited. Additionally, although the role of strength training in overall physical performance is well established, few studies address how strength impacts actual volleyball game performance in real-time, especially when considering both dynamic and static actions. Weldon A. et al. [7] emphasized the importance of muscle tissue recovery and the dominance of the parasympathetic nervous system [8] for effective athletic adaptation and injury prevention, further reinforcing the significance of strength development. In addition to strength training, other studies have also examined the effects of plyometric training on jump performance and the impacts of aerobic, general anaerobic, and specific anaerobic training, alongside training on different surfaces [9–12]. While each type of training influences performance to varying degrees, strength and power training consis- tently demonstrate the most significant effects [13]. However, research highlighting its direct impact on volleyball skills further supports this emphasis on strength and power training [14]. Some studies suggest the integration of conjugate training, which combines strength and power exercises to improve maximal and explosive power. Yet, according to Hody S. et al. [15], eccentric training has proven beneficial in enhancing muscle strength, particularly for high-intensity activities, while other studies have used a combination of exercises that target both maximal strength and explosive power, with an emphasis on movements that replicate jumping, blocking, and quick directional changes.

and power exercises to improve maximal and explosive power. Yet, according to Hody S. et al. [15], eccentric training has proven beneficial in enhancing muscle strength, particularly for high-intensity activities, while other studies have used a combination of exercises that target both maximal strength and explosive power, with an emphasis on movements that replicate jumping, blocking, and quick directional changes. While many studies have focused on isolated aspects of strength, endurance, and skill, there is a gap in the literature regarding how the integration of these qualities influences volleyball-specific actions such as passing, blocking, and serving. According to the litera- ture, strength and endurance influence skills like serving, passing, and blocking through the upper body muscles by affecting the force applied to the ball, and consequently its speed and trajectory [16]. These principles are particularly relevant for the outside hitter, who relies on upper body strength in attack, while along with setters, they benefit from arm and shoulder strength for precise ball control. The same principles are stated for passing and blocking [17]. According to Stojanovi´c N. et al. [18], during a pass, coordination and ball control are enhanced by the strength in the arms, shoulders, and core, with liberos and defensive actions depending on this for precise passes. By contrast, outside hitters and middle blockers rely on upper body strength to execute blocks, whereas endurance enables athletes to maintain effective technique throughout the match [19]. Similar findings have been reported regarding the role of strength in blocking effectiveness. While the vertical jump is driven by jumping ability, middle blockers and outside hitters rely heavily on upper body strength [20] to generate the force required to perform an effective block. However, few studies have simultaneously examined game and practice performance in conjunction with the development of key motor qualities and skills [4,21–23]. This is why our paper aims to explore the relationship between strength and specific performance, particularly how strength influences speed, endurance, and the interaction between speed and force during gameplay. Our hypothesis suggests that the results from strength assessments, particularly the one-repetition maximum (1RM), will provide a detailed

in conjunction with the development of key motor qualities and skills [4,21–23]. This is why our paper aims to explore the relationship between strength and specific performance, particularly how strength influences speed, endurance, and the interaction between speed and force during gameplay. Our hypothesis suggests that the results from strength assessments, particularly the one-repetition maximum (1RM), will provide a detailed understanding of each athlete’s physical profile. When integrated with short-distance speed and exercise capacity measurements, these factors are expected to determine the dynamic balance be- tween endurance, speed, and force application during gameplay. We propose that not only

Appl. Sci.2024,14, 10951 3 of 16 is the level of strength development crucial for optimizing volleyball performance but also the synergy between strength, speed, and endurance. This synergy impacts both dynamic and static game actions. 2. Materials and Methods We conducted an observational study at the Advanced Medical and Pharmaceutical Research Center (CCAMF) part of ”George Emil Palade” University of Medicine, Pharmacy, Science, and Technology of Targu Mures, Romania. This study complied with the execution principles established by the Ethics Committee and adhered to the Declaration of Helsinki regarding participants’ rights. 2.1. Study Period and Sample This study was carried out between July 2023 and September 2023. The study sample included 43 female athletes recruited from two (n = 2) volleyball clubs. The volleyball clubs were affiliated to Romania’s first and second volleyball leagues. To be included, athletes had to be active club members, be fully physically capable, be injury-free, and have participated in more than 90% of team practices over the last 30 days. The sample included athletes from various positions, with 9 outside hitters, 9 middle blockers, 7 liberos, 7 setters, 6 universal players, and 5 players in extreme positions, allowing for an analysis of strength training’s impact across different roles and performance levels. Power analysis was performed prior to the study to ensure an adequate sample size. Based on an effect size of 0.5, an alpha level of 0.05, and a target power of 0.80, the minimum required sample size was calculated. However, this study achieved a power of approximately 0.63 with 43 athletes, which is acceptable for detecting medium to large effects. To optimize the effect size, the study focused on selecting athletes with high performance consistency and training adherence. In addition, athletes’ specific playing positions (e.g., outside hitter, setter, libero) were taken into account, as these positions are known to require different physical attributes. The average duration of competitive practice for athletes in the study was 15 years. Before enrollment, both the clubs and the participants were informed about the methods, means, and objectives of the study, as well as the procedures regarding data storage

(e.g., outside hitter, setter, libero) were taken into account, as these positions are known to require different physical attributes. The average duration of competitive practice for athletes in the study was 15 years. Before enrollment, both the clubs and the participants were informed about the methods, means, and objectives of the study, as well as the procedures regarding data storage and their right to withdraw from the study at any time. The median age of the athletes was 22 years, with a minimum age of 16 and a maximum age of 31. The median height of the study sample was 179.5 cm, with a minimum height of 161 cm and a maximum height of 189 cm. Body weight ranged from 48.8 kg to 81.8 kg, with a median weight of 65.3 kg. The median wingspan was 185 cm, with a maximum reach of 231.8 cm while standing. The median active skeletal muscle mass was 32.2%, and the median fat mass was 27.95%. 2.2. Reliability of Measurements To ensure the precision and consistency of the data collected, reliability tests were incorporated into the study design. For strength metrics (e.g., 1RM and associated param- eters such as force, power, and velocity), inter-session reliability was evaluated during a preliminary phase involving a subset of five athletes who completed the same strength pro- tocol on two separate occasions, one week apart. The intraclass correlation coefficient (ICC) values for the key metrics—1RM load, relative power (W/kg), and velocity (m/s)—ranged between 0.91 and 0.95, indicating excellent reliability. Similarly, for speed and movement tests, test–retest reliability was assessed by having athletes complete two identical trials, separated by 48 h. The ICC values for time (ms), average velocity (m/s), and field-specific metrics (e.g., afv, aff) ranged from 0.88 to 0.93. These results confirm the consistency of the measurement tools and protocols used in the study. To further reduce measurement variability, all tests were conducted under standard- ized conditions by the same team of trained evaluators. For strength testing, the use of the Vitruve accelerometer ensured objective data collection, minimizing observer bias.

to 0.93. These results confirm the consistency of the measurement tools and protocols used in the study. To further reduce measurement variability, all tests were conducted under standard- ized conditions by the same team of trained evaluators. For strength testing, the use of the Vitruve accelerometer ensured objective data collection, minimizing observer bias.

Appl. Sci.2024,14, 10951 4 of 16 2.3. Tests and Measurements To test the study hypothesis, five different physical tests were conducted: strength testing, speed testing, field movement assessment, and lactate production measurement. These tests were statistically analyzed alongside the athletes’ game and match statistics. 2.4. Anthropometric Measurements Each participant underwent anthropometric measurements, which were conducted under standardized conditions in the morning, following a 12 h fasting period. The measurements included body weight (kg), height (cm), body fat percentage, and wingspan (cm) [24,25]. To ensure precision, each measurement was taken three times consecutively, and the procedure was repeated as necessary. Participants were required to wear minimal clothing, consisting of shorts and a sports top. The average of the three measurements for each variable was used for the statistical analysis, providing a more reliable value for each parameter. 2.5. Strength Test Strength was assessed using a one-repetition maximum (1 RM) protocol with pro- gressive loading [26], based on the athlete’s perception of effort. An Olympic barbell with free weights, along with the Vitruve accelerometer (SPEED4LIFTS S.L., Madrid, Spain), were used to determine the maximum load an athlete could lift in a single repetition. This allowed for the calculation of relative power (RP, W/kg), relative force (F, N/kg), and relative work (Wk, J/kg) at various load levels (kg). The strength assessment included three exercises performed in the following order: squats (SQs), bench presses (BPs), and deadlifts (DLs). For each repetition, the distance (cm) the weight traveled was measured to ensure accuracy and validate the execution of each lift. Additionally, acceleration (acc, m/s 2 ) and time (milliseconds, ms) were recorded to calculate velocity (m/s), power (W), and relative power (W/kg). Each participant began with a 10 min warm-up without external weight, followed by a set of free repetitions using a load of 0–70% of their estimated maximum. After the warm-up, the athlete performed a repetition at 50% of their maximum load to establish the range of motion (cm) for the lift. This distance was recorded, and subsequent repetitions with progressively increasing loads (from 50% to 100%) were considered valid if they matched the

a set of free repetitions using a load of 0–70% of their estimated maximum. After the warm-up, the athlete performed a repetition at 50% of their maximum load to establish the range of motion (cm) for the lift. This distance was recorded, and subsequent repetitions with progressively increasing loads (from 50% to 100%) were considered valid if they matched the established range of motion from the 50% repetition. All repetitions were monitored and recorded, but only the best attempt at each load was used for the analysis. If an attempt failed, the athlete was allowed one additional try. 2.6. Speed Test Speed was assessed over a 10 m distance [27,28] using a timing system from Micro-gate (Microgate SRL, Bolzano, Italy), equipped with three recording points, along with a sport speed radar (V-Maxx, TeamSports, Zielitz, Germany). The measurement began at 0 m, with intermediate recording points at 5 m and the final recording point at 10 m. Each participant completed three attempts, and the best time from these attempts was used for statistical analysis. The results were recorded in milliseconds (ms). The equipment recorded the maximum velocity (m/s), from which we calculated the following parameters: average velocity (av, m/s), force (F, N), and running power (rp, W). The calculations were performed using the appropriate formulas based on the recorded data.

Appl. Sci.2024,14, 10951 5 of 16 Equation (1): equations used to calculate Velocity (a.), Acceleration (b.), Force (c.), Power (d.) during the 10 m sprint. (a.)Velocity(m/s)= distance(m) time(s) (b.)Acceleration Γ m/s 2 Ë™ = Maximum velocity(m/s)−initial velocity(m/s) time(s) (c.)Force(N)=Body weight(kg)×acceleration Γ m/s 2 Ë™ (d.)Power(W)=Force(N)×maximum velocity(m/s) (1) Relative running power (rrp, W/kg) and relative running force (rrf, N/kg) were calcu- lated by dividing the power and force values by the body mass (km) of each participant. 2.7. Field Test Methodology Movement on the court was specifically monitored for attack and defense positions using the same equipment as in the 10 m speed test. Each athlete completed the course three times, with the best repetition used for statistical analysis. Athletes were coached to achieve their best time during each attempt. The total distance covered was 10.2 m, which included three recording points: the starting position, intermediate point 1 (3.30 m), intermediate point 2 (3.30 m), and the final point (3.80 m). This route followed an adapted Y-line [29] designed to test movement on the court, as illustrated in Figure.Appl. Sci. 2024, 14, x FOR PEER REVIEW 5 of 16 (�.) í µí±‰����í µí±–�� (m/s)= �í µí±–��í µí±Ž��� (m) �í µí±–�� (s) (�.) ������í µí±Ÿ��í µí±–�� (m/s 2 )= í µí±€��í µí±–��� �����í µí±–�� (m/s)âˆ’í µí±–�í µí±–�í µí±–�� �����í µí±–�� (m/s) �í µí±–�� (s) (�.) í µí°¹�í µí±Ÿ�� (N)=���� ��í µí±–í µí±”â„Ž� (kg) × ������í µí±Ÿ��í µí±–�� (m/s 2 ) (�.) í µí±ƒ���í µí±Ÿ (W)=í µí°¹�í µí±Ÿ�� (N) × ���í µí±–��� �����í µí±–�� (m/s) (1) Relative running power (rrp, W/kg) and relative running force (rrf, N/kg) were cal- culated by dividing the power and force values by the body mass (km) of each participant. 2.7. Field Test Methodology Movement on the court was specifically monitored for attack and defense positions using the same equipment as in the 10 m speed test. Each athlete completed the course three times, with the best repetition used for statistical analysis. Athletes were coached to achieve their best time during each attempt. The total distance covered was 10.2 m, which included three recording points: the starting position,

was specifically monitored for attack and defense positions using the same equipment as in the 10 m speed test. Each athlete completed the course three times, with the best repetition used for statistical analysis. Athletes were coached to achieve their best time during each attempt. The total distance covered was 10.2 m, which included three recording points: the starting position, intermediate point 1 (3.30 m), inter- mediate point 2 (3.30 m), and the final point (3.80 m). This route followed an adapted Y- line [29] designed to test movement on the court, as illustrated in Figure 1. The maximum velocity was measured at each intermediate point, from which we calculated the parameters average field velocity (afv, m/s), average field force (aff, N), av- erage field power (afp, W), relative field force (rmf, N/kg), and relative field power (rfp, W/kg), according to the equations outlined in Equation (1). The test began at the start line, where the athlete sprinted to point 1. From point 1, the athlete reversed direction and ran backward to point 2. Finally, the athlete sprinted forward to the finish line at point 3, cov- ering a total distance of 10.3 m. Figure 1. Illustration of the field test and the measuring point (1–3) during the field test. 2.8. Assessing Exercise Capacity: Lactate Threshold 1 (LT1) and Lactate Threshold 2 (LT2) Measurement Each athlete underwent a test to evaluate exercise capacity [30] and identify lactate thresholds 1 (LT1, mmol/l) and 2 (LT2, mmol/l). The test was conducted individually on a treadmill in an indoor environment at a stable temperature (22° Celsius). Athletes fol- lowed an adapted Bruce protocol, running in 3 min stages at speeds ranging from 3.5 to 16 km/h, with a 0% incline, until they reached and validated the LT2 value (LT2 = 4.0 mmol/l). The thresholds were determined by measuring lactate levels from capillary blood samples (LactatePro 2, Arkray, Kyoto, Japan), with LT1 set at 2.0 mmol/l and LT2 at 4.0 mmol/l. Using this protocol, we established exercise zones for each participant: aerobic (0–2 mmol/l), high aerobic (2–3.9 mmol/l), and anaerobic (>4.0 mmol/l). 2.9. Match

The study explores the relationship between muscle strength and performance in female volleyball athletes.