In soccer, muscle strength and power constitute fundamental roles that influence player performance and match outcomes.1 Strength is crucial for executing movements such as dribbling, ball control, and powerful shots, enabling players to confront opponents and surmount physical challenges with efficiency.2 On the other hand, power, the capacity to generate strength quickly, is pivotal for sprints, jumps, and changes of direction, confering tactical advantages during the gameplay.3 Consequently, adequate strength and power development not only improves individual athletes’ performance, but also contributes to the collective success of the team, directly impacting results on the field. Recognizing this, a substantial portion of athletes’ physical preparation has been dedicated to refining these physical skills, resulting in changes in muscle morphology, especially in the lower limbs.4

Various methods have been employed to evaluate lower limb strength, one of which entails the utilization of isokinetic dynamometers.5 These devices provide accurate data regarding asymmetries in peak torque between limbs and muscular imbalances between agonists and antagonists, alongside measures of work produced.6 Such findings are instrumental in aiding healthcare professionals (medical team, physiotherapist, physical educator) and sports scientists in both physical preparation and injury prevention for these athletes.

Regarding the morphological aspects related to torque production, studies suggest a correlation between quadriceps muscle strength with morphological parameters, such as muscle volume,7 muscle thickness,8 and pennation angle of muscles like the Vastus Lateralis (VL).9 Furthermore, in soccer, the Countermovement Jump (CMJ) is commonly used to assess lower limb power parameters.10 A review by Ruiz-Cárdenas11 found that only the muscle thickness of the VL correlated with CMJ height (r = 0.28; p = 0.059). The authors concluded that the lower limb muscle architecture has a limited influence on jump performance, likely due to the predominance of neuromuscular components over metabolic aspects in single jumps.12 However, when assessing anaerobic power using the Wingate test,13 it was found that quadriceps muscle thickness, particularly of the Rectus Femoris (RF), is associated with peak and average power. It is noteworthy that anaerobic power assessments involving cycle ergometers may not accurately replicate actions performed during the game in team sports like soccer.

To address this limitation, Dal Pupo14 evaluated the validity and reproducibility of continuous jumps test over 30 s (CJ30s), which consist of maximal continuous vertical jumps performed for 30 s. The authors found that the CJ30s is a suitable method for assessing the anaerobic fitness (peak power, average power, and fatigue index) in athletes, especially those involved in stretch-shortening cycle activities. Nonetheless, to the best of our knowledge, no existing studies have investigated the relationship between quadriceps morphological parameters and anaerobic fitness as assessed by the CJ30s.

Therefore, the present study aimed to investigate the relationship between quadriceps morphological aspects and torque and power parameters assessed by the CJ30s in professional soccer players at the beginning of the season.

Table 1 presents the descriptive characteristics of the sample (mean, standard deviation, 95 % confidence interval, and minimum and maximum values) considering values ​​referring to the morphology of the players' quadriceps, assessed by means of ultrasound, torque parameters, assessed by means of isokinetic dynamometry, and anaerobic fitness, assessed by means of the continuous jump test (CJ30s).

Regarding the results of the general linear model results, we observed that MVQ exhibited a positive and statistically significant relationship with all torque parameters. Specifically, the associations were found withPTCon Extensors (p-value = 0.003), WCon Extensors (p-value = 0.013), PTEcc Extensors (p-value = <0.001), and WEcc Extensors (p-value = 0.004) (Table 2 and.Fig. 2). Notably, no other quadriceps morphology indicators were significantly associated with torque parameters in this sample of professional male soccer players.

Fig. 2.

Marginal means derived from the generalized linear models of the relationship between the MVQ and peak torque and work variables of knee extensors.

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As shown in.Table 3 and.Fig. 3, FL_VL and PA_VL were both positively and significantly associated with PPO (p-value = 0.003 and 0.030, respectively) and Av_P (p-value = 0.002 and 0.011, respectively). No other quadriceps morphology indicators were associated with anaerobic fitness outcomes in this sample of professional male soccer players.

Fig. 3.

Marginal means derived from the generalized linear models of the relationship between the PA_VL and FL_VL and PPO and Av_P of CJ30s.

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The aim of the current study was to evaluate the relationship between quadriceps morphological aspects in torque and anaerobic fitness parameters in soccer players at the beginning of the season. Our results indicated that MVQ was positively related with all torque parameters. In addition, both FL and PA of VL showed positive associations with peak power output and mean power obtained during the CJ30s.

Our findings showed a significant relationship between MVQ with torque and work (concentric and eccentric) of knee extensors, this result is similar to previous studies. Lanferdini,7 in cyclists, observed that the muscular volume of the right (r = 0.56) and left (r = 0.59) quadriceps presented positive and very strong correlations with the right and left maximal voluntary isometric contraction (MVIC), respectively. Hori22 also found a significant relation (r = 0.78) between MVQ and knee extensor isometric torque. This relationship can be expected, because the muscle size (i.e., muscular volume and/or cross-sectional area) is a primary determinant of maximal strength for different muscles.23 These results reinforce the clinical relevance of the importance of using different training strategies that promote increased quadriceps muscle volume to produce torque, neuromuscular work and consequent increase in performance.

A recent study (Lanferdini et al., 2025) 24 with athletes from various sports, such as soccer, futsal, American football, and basketball, showed a PA_VL like that observed in our study (20.69 ± 2.95 vs. 22.4 ± 3.5, respectively). Studies have shown a certain inconsistency in the relationship between the PA_VL and peak torque, with some studies finding a weak relationship,7,24 and other studies observing no relationship.25 Previous studies found no relationship between RF muscle fascicle length and isokinetic concentric peak torque,26 just as no relationship was observed between FL_VL and peak torque.27

However, Raj28 observed a relationship between FL_VL and vertical jump height, and Kumagai29 found a significant and negative correlation between 100-m sprint time and VL fascicle length. The FL can influence muscle contraction speeds, but not necessarily muscle strength, because if all sarcomeres shorten simultaneously, the cumulative shortening distance, and thus velocity, will be greater.30 These results are clinically relevant, since the inclusion of eccentric overloads in the knee extensors, as has already been observed for the hamstrings,31 could provide increases in fascicle length by adding sarcomeres in series, improving performance in activities involving power, such as jumping.

In the present study, the other morphological parameters of the quadriceps (echo-intensity, pennation angle, and muscle thickness) were not related to peak torque and work, although some studies have observed a positive relationship between quadriceps echo-intensity and MVIC,32 and rectus femoris pennation angle and muscle thickness are associated with peak torque in different isokinetic velocities,33 however, the samples tested in these studies were physically active men. Therefore, the characteristics of the sample and the training status may influence the results. In this sense, the athletes tested in the present study were in pre-season, and therefore the adaptations related to muscular strength may still be being developed, without significant morphological changes.

The peak power output and average power variables obtained in the 30CJ showed a significant relationship with FL and PA of VL. Some studies have found similar results, such as significant associations between the FL of VL34 and PA of VL35 with power obtained in the Wingate anaerobic test. Kordi36 found a high relationship between PA of the VL and peak power (r = 0.81) in a maximum sprint test on a cycle ergometer. According to the authors, this could be expected, since the PA is known to be related to muscle size indices, suggesting that a high PA is advantageous for neuromuscular power. This could explain the relationship observed in the present study in a test also using continuous vertical jumps, because power production is one of the main determining factors of performance.37 Furthermore, with a greater PA, force and, consequently, power, can be increased, as there is an increase in the number of sarcomeres in parallel that contract simultaneously to exert force.38

Activities that involve movements at high velocities can benefit from longer FL (i.e., a high number of sarcomeres in series) as this is associated with a high maximum contraction speed of the muscle fiber.38 This can be confirmed in the study by Methenitis39 in which performance in vertical jump tests (countermovement jump and squat jump) was positively related to the FL of the VL. The present study corroborates these findings because the peak anaerobic power was determined with the values ​​of the first four vertical jumps.

Finally, some limitations can be highlighted in this study. First, only one speed (60°/s) was used to evaluate isokinetic torque. It is recommended that other speeds be tested, since variables such as FL may present a better correlation with torque. Second, the athletes tested were at the beginning of the competitive season, so these analyses could be performed during the season or at the end, which may provide important results related to muscular adaptation in the quadriceps muscles and the relationship with physical performance. Also, no data were obtained on the athletes' training routines, which could interfere with the results of the results. Finally, we did not use limb dominance, but rather the right limb, to evaluate the US parameters. However, our study has strengths, as we evaluated 48 soccer players who compete at regional and national levels. Furthermore, we used standardized measures in the evaluations, as well as other measures that are little explored in this population, such as muscle morphology and anaerobic fitness using continuous vertical jumps.

From our findings it can be concluded that the muscular volume of the quadriceps is related to peak torque and concentric and eccentric work of the knee extensor muscles. Furthermore, the fascicle length and pennation angle of the vastus lateralis showed significant correlations with peak power output and average power during the CJ30s, representing anaerobic power and capacity, respectively.