This study identified i) “high” correlations between FVtPpeak (W) and 20-m sprint (T5, T10, T20), and pro-agility shuttle, ii) “good” correlations between FVtPpeak (W.kg) and 5JTA, and iii) “fair” correlations between FVtPpeak (W) and 5JTA,between FVtPpeak (W.kg-0.67) and 5JTA, and 20-m sprint (T5, T10).
The findings of this study suggest that emphasizing leg power development in the youth volleyball population may improve sprint, horizontal approach, and agility. Moreover, our findings may be useful for youth volleyball coaches and strength conditioning coaches in determining which lower-body power tests should be prioritized when establishing an athletic testing battery for this population.
Relation between FVt and 5JT
We reported significant correlations between FVtPpeak (W, W.kg-0.67, W.kg) and 5JTA (Table 4). The 5JT(11) was applied in a previous study to assess the leg muscular power of young male volleyball players. Ben Ayed et al.(11) highlighted that the 5JT is an appropriate measure for assessing the power of volleyball players. Given the scarcity of equipments required to evaluate youth volleyball players' lower body strength and vertical jump, the 5JT provides an interesting way to quantify power as a horizontal approach(11). Vertical and horizontal leg hops, which are commonly considered as separate tasks with differing leg strength/power properties, are commonly compared, while authors have identified some similarities between them in previous studies (11, 45) (ie; short and maximum characteristic achievement).
The correlation involving muscle strength and performance assessment was acknowledged by Meylan et al.(45). The single-leg vertical and horizontal jump tests have a high correlation (r = 0.64) and a consistent variation of approximately 45%, (45). Spike jumps, jump setting, and blocking are only a few of the jumping techniques used in volleyball. Sprinting represents for a significantly larger proportion (i.e. 30%) of all movement distance in volleyball, especially in linear sprinting(1). Previous studies showed that the 5JT's explosive strength training might improve neuromuscular properties to increase muscular strength (23, 33, 34). It seems that the 5JT is an appropriate field test for determining soccer players' stride power (23, 33, 34). In fact, the power variables of jumps are associated with the 5JTA and 5JTLL (11). These findings appear to demonstrate that the 5JT provides adequate estimations of the lower limb muscular power (11, 23, 34, 43). The similarity of the bio-energetic and bio-mechanical parameters across FVtPpeak and 5JT contributes to the relationship between the two tests.. The 5JT is a performance of five alternating bounds that demands high neuromuscular coordination and technical ability (33), ), while the FVt is an assessment of pedaling with the legs in which one of the two legs is active while the other is passive (back pedal)(23). Additionally, various parameters, such as the ability to cycle, the pedaling velocity, motivation, and coordination between and within the muscle fiber contractions, can have an impact on the association between a field test (eg; 5JT) and the FVt (23). Furthermore, Diallo et al.(35) showed that the 5JT requires particular neuromuscular adaptations (motor coordination). Nevertheless, it is worth to notice that many factors can influence the different tests' performances. Our cycle ergometer protocol might be closer to the dynamics of muscle contraction and the times connected to the 5JT.
Potential mechanisms for improving jump performance in volleyball players involve more effective movements because the alterations in the temporal sequencing of muscle activation, the preferential recruitment of rapid motor units, and the enhanced nerve conduction velocity are characterized by stochastic, acyclic, and intermittent movement bouts, which are characterized by highly varied and unexpected movement patterns Adenosine triphosphate-phosphocreatine reserves, which are strongly tied to muscle volume, are actually what determines how well the Ppeak performs(21).Volleyball players must demonstrate a high level of speed, agility, upper and lower body muscle (2), power, as well as maximum aerobic power due to the physical demands of the activity and the length of a volleyball match, which may last up to 90 minute. (10, 20, 23).
The differences between young adults and youths may be partially explained by the significant recruitment of motor units from the neuromuscular system during diverse jumps (eg; attack against the net in volleyball) and intense brief repeated actions during a volleyball match(20), According to the latter, the increase in high velocity during the takeoff of a vertical jump associated with a force variable during the stretch-shortening cycle could explain for such muscular strength of the lower limbs (20). It is related to the volleyball player's attack movement (11, 46). In our investigation, the 5JT accurately reflects the lower limbs' "explosive" force.
Relation between the FVt and 20-m sprint
It has been previously revealed that performance in different types of jumps tests has positive relationships with faster linear and COD in athletic populations(7, 13, 21, 25, 47). The FVt, as a strength/power test, utilized the stretch-shortening cycle (SSC) capacities of the lower body, and this is an important quality for speed linear (eg; T5, T10, and T20). In line with all the cited findings about the importance of SSC, the current study identified “high” correlations between FVt (W) and T5, T10and T20 (Table 3). Volleyball imposes players to make quick actions/movements when responding to setting or preparing the attack approach (ie; side-out phase or break phase).
In volleyball, as a complex sport that relies on technical, tactical, and physical abilities, the periods of maximal bouts last only few seconds and are interrupted by rest or lower-intensity activity(2, 8, 19, 31, 48). The energy required during a single bout of brief (<10 s) dynamic maximal exercise must be provided through anaerobic pathways demands(2). Volleyball is a team sport characterized by intermittent efforts with periods of short duration (ie; 3-9 s), high-intensity activities, interspersed with relatively long periods (ie; 10-20 s) of recovery(8, 19). Actually, to measure the components of power/strength that are valid for sport, it is essential to reconstruct the activity of that sport as closely as possible(18-20, 24, 49). The energy requirements of volleyball are complex and difficult to quantify. Although previous research has shown that a strength and conditioning training programme improves jump performance in volleyball players, there is a significant gap in the literature regarding correlations between indicators of performance, specifically speed, horizontal jump approach, and Ppeak output in youth volleyball players(7, 13, 14, 48, 50).
Relation between the FVt and pro-agility shuttle
Previous studies revealed that a successful COD needs enhanced physical capacities of lower body strength and power(4, 7, 13, 15, 18, 21, 25, 32, 37, 45, 47). The results from the research of Banda et al.(13) confirmed that possessing a fitting level of lower-body power should assist an athlete in rapidly changing direction in reply to the demands of the competition. The authors mentioned that the value of lower-body power for COD speed was measured by pro-agility shuttle(13). Accordingly, this was supported by our results. In fact, “high” correlations were found between FVt (W) and pro-agility shuttle (r = -0.745), which represent the COD required in a volleyball match. This demonstrated that youth volleyball players should enhance their acceleration and COD performances on the court. Subsequently, the more developed these qualities are for youth volleyball players; the more likely they are to be successful(13).
Based on the time of each action spent on the court, volleyball drills can be classified as fast SSC exercises(51). Generally, exercises involving muscle power, linear sprint, agility, and COD speed benefit from the mechanical properties of the SSC(52). It has been highlighted that these types of exercises enhanced neuromuscular (eg; improved neural drive to agonist’s muscles) and/or mechanical/structural properties (eg; alterations to musculotendinous stiffness and architecture)(12). The alternating eccentric-concentric muscle work also leads to the accumulation of potential elastic energy through the series and parallel elastic components allowing more work to be performed in the concentric phase(52). These positive effects on neuromuscular and structural properties should have potential results in sports such as volleyball, which involves extensive movements, equivalent to different types of jump drills, COD, and linear speed. Accordingly, our data suggested that youth volleyball players should boost their SSC capacities of the lower-body to develop their agility, speed, acceleration, and horizontal approach performances. As significant procedures in volleyball competition, a suggested training modality included power, acceleration, and explosiveness (vertical and horizontal). The most common type of movement is linear sprint ability over short distances, which serves as the foundation for most speed training programs(7, 14).
The horizontal jump approach (ie; defensive and offensive volleyball skills) and speed tests impose great demands on the stretching and shortening abilities of the leg muscles. The relations between intrinsic muscle components (ie; elastic and contractile components) is one of the determinant factors of performance in jumps and linear sprints(14). Our findings are consistent with most previous publications(4, 7, 11, 18, 20, 46, 47), given the fact that some studies shared a good variance between horizontal and vertical jumps(45). In fact, the relationships between assessment of leg power to linear sprint speed were investigated in previous studies(7, 13-15, 32). McFarland et al.(15) determined a “good” negative correlation between 30-m sprint time and pro-agility shuttle with the CMJ (r = -0.50 to -0.75) and SJ (r = -0.50 to -0.68) among a group of soccer players. In contrast, the above-cited study reported a significant relationship between 10-m time and CMJH(15). The latter reported “fair” to “good” negative correlations between 10-m and 30-m sprint times to the CMJ (r= -0.48 and -0.57) and SJ (r= -0.44 and -0.55, respectively) among males at the same playing. Lockie et al.(7) identified limited relationships between performance in standing broad jump; which provided an indirect measure of horizontal power; and the 20-m sprint and pro-agility shuttle, which have an important implications for volleyball and strength and conditioning coaches for youth categories. In addition, the authors reported no significant relationships between standing broad jump with 0-10 m sprint interval in division collegiate volleyball players, and suggested that all jumps used in the study emphasized the SSC in the lower-body muscles power(7). Interestingly, even though the 10-m sprint distance is somewhat atypical to the distances volleyball players may need to cover during a match(8). Our study reported a “fair” negative correlation between the 5JT and the speed tests (Table 4). Several reasons can explain these correlations. For example, concentric power, as opposed to reactive power, may be more important for speed over short distances(53), and also small yet impactful difference in distance between the two tests. Future studies should investigate into how youth volleyball players optimise power qualities with shorter sprint acceleration distances and concentric power activity.
Study limitations
Our study has some limitations. The first has to do with the fact that it is observational. For example, as the number of recorded factors increases, the probability increases. Thus, at least one of the factors recorded was coincidentally strongly correlated with data output (54). Furthermore, observational studies must meet several criteria in order for their results to be more understandable and generalizable (54). Observational studies have been reported to provide information about 'real world' use and practice and help formulate hypotheses to be tested in follow-up experiments (54). A second limitation is related to possible sex and age differences in agile shuttle and coordination in 5JT. Ritzer et al.(55), indicated that female athletes had a higher rate of overuse injury than males, while male athletes had a higher rate of acute injury. In this study, overuse injuries were more likely to be frequent injuries than acute injuries, while acute injuries were more often new injuries. Attention to these differences between acute and overuse injuries can help inform improved athlete preparation (such as conditioning and strength training), treatment, rehabilitation, and schedules allowing for adequate rest time, which may reduce injuries and improve injury outcomes in high school athletics. A third limitation is that research on children can be disturbing for ethical reasons. As a result, underlying mechanisms are often proposed but not always proven. Fourth, our study focused primarily on the relationship between lower body strength in field and laboratory tests, not strength. Future studies of youth volleyball players may include examining strength/force protocol to investigate lower-body power. Finally, since we only study players from professional sports club 'youth division' teams, the sample is likely to be very homogeneous. Future studies should also consider testing multiple teams to increase the sample size of youth volleyball players and make the findings more replicable to a wider range of players.
To conclude, the present study identified significant relationships between the FVt and 20-m sprint, pro-agility shuttle, and 5JTA. The authors strongly suggest the use of the pro-agility shuttle and 5JT to evaluate lower limb explosive power in youth volleyball players. Further studies, concerning different sports games and the electromyography response of the muscles involved in jumping performance, are needed to confirm the use of the pro-agility shuttle, speed test, and the 5JT to determine which lower-body power tests should be prioritized when developing an athletic testing battery within this population.