The acute effects of dynamic and static stretching during warm-up on muscle architecture and performance in children

Abstract

Background

There is insufficient evidence regarding the acute effects of warm-up with dynamic stretching (DS) and static stretching (SS) on children.

Objective

The aim of this study was to explore how two common warm-up protocols—DS and SS—acutely influence muscle architecture and key physical performance, including explosive strength and flexibility, in children.

Methods

Twenty-one healthy children (age: 10.6 ± 0.73 years) voluntarily participated in this study. Each participant completed two warm-up sessions on separate days, consisting of 3 min of light jogging followed by either a DS or SS protocol. Assessments included biceps femoris muscle architecture (fascicle length, pennation angle and muscle thickness), 50-meter sprint (SPR50m), standing long jump (SLJ), and sit-and-reach (SR) tests. All variables were measured at four time points: before stretching, immediately after stretching, and at 10- and 30-min post-stretching.

Results

Results showed an increase in SPR50m, SLJ, and SR performance after warm-up with DS, lasting for 10 min (p < 0.01). SPR50m, SLJ, and muscle pennation angle decreased after SS (p < 0.05), while SR and muscle fascicle length increased (p < 0.05). Immediately after warm-up, SR and muscle fascicle length were higher in SS than DS (p < 0.05), while SPR50m, SLJ, and pennation angle were lower in SS (p < 0.01).

Conclusions

Similar to adults, warm-up with DS is more suitable for activities that require explosive power and strength in children. In contrast, when the primary goal is to improve flexibility, warm-up with SS can be selectively used. Therefore, the selection of warm-up stretching for children should be guided by the specific performance demands of the subsequent activities

Keywords

stretching warm up athletic performance muscle architecture

1. Introduction

In children's physical education classes, warm-up exercises are an essential component. Physical education teachers usually begin with light jogging to increase body temperature and enhance muscle cooperation.^1,2 They then incorporate stretching to improve joint flexibility and prevent sports injuries.^2-4 Static stretching (SS) has traditionally been a common part of children's warm-ups.^3,5 Studies have shown that SS alters the viscoelastic properties of the muscle-tendon unit (MTU), which helps decrease the risk of muscle injuries.⁶ Additionally, these changes can enhance the storage of elastic energy, thereby improving movement efficiency.⁶

However, with the advancement of research, many studies have concluded that SS has no impact on injury prevention.^4,7,8 Moreover, an increasing number of studies have highlighted its potential adverse effects on subsequent strength- and power-related activities.^4,9-11 These reductions may be attributed to various neural and peripheral mechanisms,¹² particularly a decrease in MTU stiffness.^13-15 Similarly, several studies on children and adolescents have reported that SS reduces explosive power,^2,16,17 speed,¹⁸ and agility.^2,16

Compared to SS, dynamic stretching (DS) has been increasingly recognized in recent years for its more positive role in warm-ups, especially in enhancing athletic performance. Research suggests that warm-up with DS significantly enhances strength,^4,19,20 sprint speed,^15,21,22 and jumping ability.^2,22 The reasons in which DS enhances such performance are believed to include increased muscular and body temperature,¹⁵ activation of the nervous system,²³ and decreased inhibition of opposing muscles.^19,22 However, most current stretching-related studies remain focused on young athletes or adult populations. In the limited research conducted on children, Lykesas et al.² demonstrated that, that, with a stretching duration of five minutes, warm-up with DS significantly enhanced performance in activities requiring greater lower-limb explosive force compared to SS. In contrast, Afroundeh et al.²⁴ found that, after five minutes of stretching, DS and SS had similar effects on such activities. Therefore, the acute effects of stretching on children's performance remain controversial.

Examining changes in muscle architecture can further elucidate the mechanisms underlying performance alterations following stretching, as muscle thickness (MT), fascicle length (FL), and pennation angle (PA) are key predictors of muscle force production. However, the changes observed in these parameters following acute stretching typically reflect short-term adjustments in muscle viscoelastic properties and passive tension, rather than actual anatomical remodeling.¹⁴ It has been reported that the remodeling of the MTU induced by stretching may require more than eight weeks or even longer to show significant changes.²⁵ Nevertheless, measuring these short-term effects holds significant value, as they reveal the immediate responses of muscles to stretching interventions. This helps in understanding the underlying mechanisms behind short-term changes in performance—such as flexibility and explosive power—and provides physiological support for optimizing warm-up strategies.

Given that children are still in the developmental age, their muscle architecture exhibit significant differences compared to those of adults.²⁶ Thus, studies conducted on adults may not be directly applicable to children. Currently, no studies have evaluated the acute effects of warm-up stretching on muscle architecture in healthy children. Hamstring injuries are among the most frequent sports-related injuries, with occurrence rates reaching up to 25%.²⁷ Approximately 83% of hamstring injuries affect the biceps femoris.²⁸ Therefore, the aim of this study is to compare the acute effects of two commonly used warm-up stretching (DS and SS) on the muscle architecture of the biceps femoris long head (BFLH), flexibility, explosive force, and athletic performance in children, as well as to examine the duration of these effects.

2. Methodology

2.1 Participants and setting

This study was conducted in a sports facility in Xiamen, Fujian Province, China. The facility is staffed with several professional physical education teachers who offer regular sports training and instruction. One of these teachers actively responded to the invitation from the first author's university and participated in this study.

Twenty-one participants (11 males, 10 females, age: 10.6 ± 0.73 years, height: 142.9 ± 3.64 cm, weight: 38.2 ± 4.46 kg) voluntarily participated in this research. All participants were fourth- and fifth-grade students from nearby elementary schools located near the sports facility and were engaged in extracurricular training for various sports within the facility. Participant recruitment was carried out with the assistance of cooperating Physical education teacher. Written informed consent was obtained from both the students and their guardians after providing a detailed explanation of the study. All research procedures and methodologies in this study adhered to the principles of the Declaration of Helsinki, and the ethics committee of the corresponding author's university approved this study (Approval number: 2021-094).

2.2 Experimental design

This study employed a randomized, counterbalanced crossover design. Before the formal experiment, participants underwent a familiarization process, during which they attended a training session to familiarize themselves with the warm-up protocols and testing procedures. During this period, a professional ultrasound physician used a surgical marker to draw a reference line along the muscle belly of the BFLH mid-region. This marker ensured that ultrasound measurements could be repeatedly taken from the same muscle location. Participants were instructed not to washing off that marker until experiment was completed. The formal experiment began after 24 h of rest following the familiarization session. Since all participants completed both stretching warm-up protocols (DS and SS), testing was conducted on two separate days with a 48-h interval between sessions. The study design is shown in Figure 1.

Figure 1.

Study design.

At the beginning of the formal experiment, the researchers and an ultrasound physician conducted baseline (pre-warm-up) measurements for each participant. Following this, each participant performed their first stretching protocol in a randomized order. The warm-up program followed the recommendations outlined in established children's warm-up guidelines and has been widely applied in physical education classes and training programs for children,^2,16 consisting of a 3-min light jog followed by 5 min of stretching exercises. Considering that a typical physical education class lasts approximately 40 min, testing was conducted at four time points: before warm-up, immediately after, and at 10 and 30 min post-warm-up.

During the waiting period between each testing time points, participants remained in a relaxed and natural state within the testing area under the guidance of the researchers. To minimize non-experimental variables, children were encouraged to stay quiet or engage in soft conversations, but were not allowed to perform vigorous activities, stretching, or additional physical exercises. Researchers used engaging prompts (such as timing cards) to remind participants of the time schedule and continuously monitored the scene to ensure the accuracy of testing times.

2.3 Warm up protocols

The warm-up protocol in this study consisted of 3 min of jogging followed by either DS or SS targeting the quadriceps and hamstrings. Given the participants’ age, the researchers simplified standard movement instructions to facilitate understanding and ensure consistent execution. Before the experiment, all participants received a standardized demonstration of the movements, accompanied by simple and clear verbal cues (e.g. “stand still—stretch—hold”) that replaced more technical terminology. During the experiment, researchers also provided on-site demonstrations to help participants maintain correct form and a consistent pace.

2.3.1 Dynamic stretching protocol

Participants were instructed to perform bilateral DS by actively moving their limbs at a controlled slow to moderate pace through their full range of motion. The stretching lasted approximately 5 min and included two exercises: the first was alternating lunges to target the quadriceps, and the second was alternating leg swings with forward steps to stretch the hamstrings. Each exercise was performed in 2 sets, with 10 alternating repetitions per set (5 repetitions per leg). A 30-s rest was given after each set, and the same pacing was maintained throughout. Before switching to the second exercise, participants rested for 1 min to ensure the quality of the stretching. The DS protocol is illustrated in Figure 2.

Figure 2.

Stretching protocols.

2.3.2 Static stretching protocol

Participants were instruc ted to perform bilateral SS by gradually extending the target muscles to their maximum range of motion without discomfort. The total duration of stretching was approximately 5 min and included two exercises: the first was a high-kneeling backward lean to stretch the quadriceps, and the second was a supine straight-leg raise to stretch the hamstrings. Each SS exercise consisted of two sets, with each set performed separately on both sides—holding the stretch for 30 s on one side before switching to the other side for another 30 s. A 30-s rest was provided between sets. After completing one stretching exercise, participants rested for 1 min before beginning the next SS exercise. The SS protocol is illustrated in Figure 2.

2.4 Measurement

During the testing phase, participants underwent ultrasound assessment of the BFLH, measuring MT, FL, PA. Additionally, they completed 50 meters sprint (SPR50m), standing long jump (SLJ) and sit and reach (SR) test.

2.4.1 Ultrasonography assessment

The ultrasound system used in this study was a portable doppler ultrasound device (Product model Z5, Shenzhen, Mindray Bio-Medical Electronics Co, Ltd, Shenzhen, China), along with a linear array probe (probe width: 3.5 cm, frequency: 7.5 MHz) to assess the muscle architecture of the BFLH. The same physician performed the same test procedure for each participant. During the testing process, all participants lay in a prone position with their knees fully extended and were verbally instructed to relax their muscles as much as possible. The length of the BFLH was defined as the distance from the ischial tuberosity to the superior edge of the fibular head. Based on the marked line, ultrasound scanning was performed at 50% of the BFLH length. To prevent muscle deformation, the probe was held with light contact, ensuring that the superficial and deep aponeurose remained as parallel as possible.

For each participant, three ultrasound images were captured and analyzed using image analysis software (Motic Images Plus 2.0, Motic, Hong Kong, China). The images were used to measure MT, FL, PA, and aponeurosis angle (AA) (Figure 3). The mean of these measurements was utilized for analysis. As the entire muscle fascicle was not fully visible within the probe's field of view, its length was estimated using a validated formula proposed by Blazevich et al.²⁹: FL = sin (AA + 90°) × MT/sin (180° − (AA + 180° − PA)).

Figure 3.

Ultrasound images obtained from the mid-region of the biceps femoris long head. AA, aponeurotic angle (the angle between the line marked as the aponeurosis and an intersecting horizontal line across the captured image); FL, fascicle length (The length of the muscle bundle path between the superficial and deep aponeurosis); MT, muscle thickness (The distance between the superficial and deep aponeuroses was measured, calculated as the average value of MT1 and MT2.); PA, pennate angle (the insertion of the muscle fascicle to the aponeurosis).

Before the formal experiment, the same ultrasound physician independently performed two separate BFLH ultrasound tests on four children not included in this study. The tests were conducted at least two days apart to evaluate the test-retest reliability of the ultrasound measurements.

2.4.2 Standing long jump

The SLJ test was used to assess lower limb explosive force. All participants performed two standing jumps, and the mean value was utilized for data analysis.

2.4.3 Sit and reach

The SR test was utilized to measure lower limb flexibility. Participants were instructed to keep their legs together, fully extend their knees, and place their feet against the measurement box. They then extended forward as far as possible and maintained the position for about 3 s. Each child performed two trials, and the mean value was utilized for data analysis.

2.4.4 50 meters sprint

The SPR50m was used to assess overall athletic performance, including lower limbs strength, agility, and coordination. Participants were directed to sprint at maximum speed from the starting line to the finish line. Given the high-intensity nature of this test, each participant completed it only once to prevent any potential impact on the results of subsequent tests.

3. Data analysis

To assess the test–retest reliability of the muscle architecture measurements, intraclass correlation coefficients (ICCs), standard error of measurement (SEM), and the corresponding relative SEM (%) were calculated. The Shapiro–Wilk test was used to assess the normality of the data. For each test variable, two-way repeated ANOVA (stretching type [DS and SS] × time [before warm-up, immediately after warm-up, 10 min and 30 min after warm-up]) were employed to determine if there was any significant difference (p < 0.05), followed by Bonferroni post-hoc analyses for all tested variables. For the effect size, partial eta-squared values (η²_p) were calculated to determine the effect size for repeated measures.

4. Results

4.1 Ultrasound measurement quality

The mean ICC was used to assess the consistency of the measurements. The results demonstrated good test–retest reliability. The ultrasound image analysis for PA, MT, and FL yielded ICC values of 0.87, 0.97, and 0.91, respectively. The SEM values for PA, MT, and FL were 0.70° (5.9%), 0.15 mm (1.0%), and 1.10 mm (1.9%), respectively, indicating low variability and good stability of the ultrasound-based assessments.

4.2 50 meters sprint

Significant main effects of stretching type and time, as well as their interaction (stretching type × time), were observed for SPR50m performance (stretching type: p < 0.01, η²_p = 0.71; time: p < 0.01, η²_p = 0.32; interaction: p < 0.01, η²_p = 0.82). The post-hoc test indicated a significant improvement in SPR50m performance after DS immediately, with the effect lasting for 10 min (p < 0.01, Table 1). As for SS, SPR50m performance significantly decreased after SS immediately (p < 0.01, Table 1). SPR50m performance after DS was significantly faster than after SS both after stretching immediately and 10 min (p < 0.01, Figure 4(a)).

Figure 4.

Time course effects of warm-up on 50 meters sprint (a), sit and reach (b), standing long jump (c), muscle fascicle length (d), pennate angle (e) and muscle thickness (f). * Indicates a significant difference (p < 0.05) from another stretching type at the same measure moment (before warm-up, immediately after warm-up, 10 min and 30 min after warm-up). ^# Indicates significant difference (p < 0.05) before warm-up protocol (baseline).

Table 1.

Changes in the architectural parameters, explosive force, flexibility, and athletic performance at before warm-up, immediately after warm-up, 10 min and 30 min after warm-up.

	Dynamic stretching protocol
Variables	Pre	Post	Post 10 min	Post 30 min
50 meters sprint (s)	10.62 ± 0.44	9.98 ± 0.32^a,b	10.17 ± 0.20^a,b	10.65 ± 0.46^b
Sit and reach (cm)	14.86 ± 1.61	16.60 ± 1.71^a,b	15.94 ± 1.79^a	14.93 ± 2.08^b
Standing long jump (cm)	143.33 ± 3.38	151.63 ± 4.74^a,b	147.82 ± 4.30^a,b	144.41 ± 6.51^b
Fascicle length (mm)	57.78 ± 4.46	58.99 ± 3.25	58.84 ± 5.37	57.12 ± 5.55
Pennation angle (°)	12.06 ± 1.13	11.59 ± 1.04	11.85 ± 1.11	11.91 ± 0.83
Muscle thickness (mm)	15.20 ± 1.05	15.16 ± 1.08	15.16 ± 1.10	15.18 ± 1.01
	Static stretching protocol
50 meters sprint (s)	10.60 ± 0.55	11.03 ± 0.39^a,b	10.53 ± 0.40^b	10.54 ± 0.44
Sit and reach (cm)	14.57 ± 1.68	17.91 ± 2.19^a,b	15.74 ± 2.40^a,b	14.73 ± 2.36^b
Standing long jump (cm)	142.39 ± 4.81	140.84 ± 4.56^a,b	140.45 ± 5.21	141.90 ± 3.62
Fascicle length (mm)	57.50 ± 6.53	61.44 ± 4.81^a,b	58.19 ± 5.01^b	57.64 ± 4.64
Pennation angle (°)	12.12 ± 1.73	10.01 ± 0.74^a,b	11.84 ± 1.33^b	12.09 ± 1.27
Muscle thickness (mm)	15.18 ± 1.01	15.21 ± 0.89	15.21 ± 0.79	15.16 ± 1.17

All values are mean ± SD.

Indicates significant difference (p < 0.05) was found compared with pre stretching protocol.

Indicates significant difference (p < 0.05) was found compared with 1 measure moment before.

4.3 Sit and reach

There were significant main effects (stretching type and time) and interaction (stretching type × time) for SR performance (stretching type: p > 0.05, η²_p = 0.01; time: p < 0.01, η²_p = 0.62; interaction: p < 0.05, η²_p = 0.12). The post-hoc test revealed a significant performance improvement after both stretching types, persisting for 10 min (p < 0.05, Table 1). SR performance after SS was significantly higher than DS when after stretching immediately (p < 0.01, Figure 4(b)).

4.4 Standing long jump

The main effects of stretching type, time and interaction (stretching type × time) for SLJ performance were observed (stretching type: p < 0.01, η²_p = 0.87; time: p < 0.001, η²_p = 0.28; interaction: p < 0.01, η²_p = 0.47). The post-hoc test showed a significant performance improvement after DS, sustaining for 10 min (p < 0.01, Table 1). A significant decrease of SLJ performance was only showed after SS immediately (p < 0.05, Table 1). SLJ performance following DS was significantly higher than SS both after stretching immediately and 10 min (p < 0.01, Figure 4(c)).

4.5 Muscle fascicle length

Significant main effects of stretching type, time, and their interaction (stretching type × time) on muscle FL were identified (stretching type: p > 0.05, η²_p = 0.02; time: p < 0.05, η²_p = 0.14; interaction: p > 0.05, η²_p = 0.05). The post-hoc test revealed a significant increase in FL after SS immediately (p < 0.05, Table 1). FL was significantly longer in SS compared to DS when after stretching immediately (p < 0.05, Figure 4(d)).

4.6 Pennate angle

The main effects of stretching type, time and interaction (stretching type × time) for the PA were observed (stretching type: p < 0.01, η²_p = 0.44; time: p < 0.01, η²_p = 0.65; interaction: p < 0.01, η²_p = 0.35). The post-hoc test indicated a significant decrease of PA after SS immediately (p < 0.01, Table 1). Immediately after stretching, PA after SS was significantly lower than DS (p < 0.01, Figure 4(e)).

4.7 Muscle thickness

There were no significant main effects (stretching type and time) and interaction (stretching type × time) for MT, as shown in Table 1 and Figure 4(f) (stretching type: p > 0.05, η²_p = 0.001; time: p > 0.05, η²_p = 0.001; interaction: p > 0.05, η²_p = 0.005).

5. Discussion

To the best of our knowledge, this is the first study to use ultrasound imaging to evaluate the effects of warm-up with SS or DS on muscle architecture (FL, PA, and MT) in healthy children. Furthermore, this study also assesses the acute effects of DS and SS on explosive force, flexibility, and athletic performance. The warm-up and stretching protocol used in this study—three minutes of light jogging followed by five minutes of SS or DS—is commonly applied in school physical education and youth sports training. However, stretching protocols with longer duration or higher intensity may lead to more significant changes in muscle architecture and performance.^4,23,30 Nevertheless, by employing a widely used and ecologically valid protocol, our study enhances the practical relevance of its findings and reflects the real-world conditions commonly encountered in youth athletic training environments.

Our results indicate that SS enhances flexibility but impaired subsequent athletic performance in children. For flexibility, some studies have suggested that DS and SS have similar effects on improving flexibility.³¹ However, more evidence indicates that DS is less effective than SS, both after a single warm-up session^2,32,33 and after long-term training.³⁴ These results may be related to the specific characteristics of each stretching type, as they exert different forces on muscle tissues. SS typically involves slowly and continuously lengthening the muscle and holding the stretch for an extended period. This sustained tension reduces muscle spindle sensitivity and the excitability of the stretch reflex, thereby decreasing protective muscle tone, which contributes to an increased range of joint motion.³⁵ However, this regulatory mechanism may also delay motor unit recruitment and reduce neural drive, impairing neuromuscular coordination required for tasks involving rapid muscle contractions,^35,36 and thus diminishing post-SS athletic performance.

In addition, a meta-analysis demonstrated that SS could induce acute changes in muscle architecture and reduce the stiffness of the MTU,³⁷ which may be another reason why SS enhances flexibility. MTU stiffness reflects the mechanical response of the entire muscle–tendon complex to external tensile forces and is modulated by multiple interacting factors, including muscle tissue properties, tendon characteristics, neural regulation, and the structural composition of connective tissues.^6,25,38,39 In this study, we observed a temporary increase in FL and a corresponding decrease in PA following SS. These structural changes may reflect adaptive adjustments in the viscoelastic properties within the MTU, indicating that stress relaxation occurred. This likely led to a temporary reduction in MTU stiffness, which in turn decreased passive joint torque and improved joint range of motion.^34,40 In contrast, DS relies on short-duration, repetitive stretching movements.^23,41 Due to its brief duration and the changing direction of stretching force along the limb's movement trajectory, it is less likely to induce structural changes in the MTU. However, while SS can effectively enhance flexibility, the reduced stiffness of the MTU may also weaken its elastic capacity, leading to a decrease in the amount of elastic energy available during rapid muscle contractions.^15,42 This may partially explain the impairment of lower-limb explosive power and athletic performance following SS.

Unlike our study, other research has found that SS has no effect on muscle architecture. Şekir et al.⁴³ conducted a six-week ankle joint stretching program, with each session lasting 240 s. Its results indicated that, regardless of acute or chronic effects, muscle architecture did not exhibit changes after SS. Similarly, Sa et al.⁴⁴ also found that there were no significant changes in fascicle length or pennation angle of the quadriceps and hamstrings after performing three sets of 30-s static stretching. We believe that the discrepancies between our findings and those of other studies may be attributed to multiple factors. Our warm-up protocol combined jogging and stretching. Jogging helps increase muscle temperature and reduces viscosity, which may enhance the effects of stretching.^1,2,45 Secondly, previous studies have reported that tendon stiffness increases with age.⁴⁶ Lambertz et al.⁴⁷ also found that passive muscle stiffness is associated with physical growth, as increases in body height are accompanied by greater passive muscle stiffness. Therefore, compared to adults, children exhibit lower MTU stiffness, making their muscle tissue more susceptible to temporary deformation during stretching. This may result in significant differences in muscle architecture (FL and PA) before and after stretching in children.

Our study also showed that DS did not affect muscle architecture in children, which is consistent with the findings of several previous studies.^48,49 Therefore, the improvement in explosive power and athletic performance after DS is likely not attributed to changes in muscle architecture. It may be attributed to various physiological factors. Studies have reported that DS increases muscle temperature, which has been shown to provide numerous benefits.^15,23 Elevated muscle temperature reduces lactic acid concentration in the blood and muscles while enhancing muscle force production and anaerobic capacity.⁵⁰ In addition, the acute effects of dynamic stretching may be related to post-activation potentiation, which temporarily enhances force output by increasing the rate of cross-bridge formation following prior muscle contractions.⁵¹ Therefore, warm-up with DS is more suitable for sports that require strength and explosive power in children.

Another interesting finding is that the enhancements in athletic performance and lower limb explosive force after DS lasted for more than 10 min. Similarly, the flexibility improvements after SS also persisted beyond 10 min, but neither lasted up to 30 min. In contrast, previous studies have shown that in adults, stretching exercises can typically produce effects that last for more than 120 min.^52,53 This discrepancy suggests that the post-stretching effects in children may diminish more quickly than in adults. As previously mentioned, stretching for up to 5 min in adults typically does not lead to significant changes in muscle architecture. Therefore, the more rapid decline in stretching effects observed in children may not be attributed to changes in muscle structure but is more likely related to the maturity of the nervous system. The immature state of the central nervous system in children—characterized by reduced muscle recruitment efficiency, limited neural drive, and less stable regulatory control—may further constrain neural adaptation.⁵⁴ This leads to a faster return of performance to baseline and a reduced maintenance of post-stretch neuromuscular effects. Overall, these physiological and neurodevelopmental differences may collectively lead to a shorter duration of performance enhancement, a faster return to baseline, and a higher sensitivity to stretching interventions in children.

Therefore, the findings of this study suggest that while SS can improve flexibility in children, DS demonstrates a more pronounced effect in enhancing explosive power and athletic performance—particularly important for rapid activation prior to physical education classes or training sessions. In this study, to control variables and eliminate exercise-related interference, participants did not engage in intense physical activity during the intervals between the four testing sessions. However, in real-world physical education settings, children typically begin moderate-to-high intensity exercise lasting approximately 30 min immediately after stretching. Although the duration of the intervention effect may be shorter in children compared to adults, the benefits of DS in practical contexts may be further amplified through mechanisms such as sustained elevation of muscle temperature and prolonged neural activation. Thus, in future practice, DS should be systematically incorporated into physical education and training programs.

Nevertheless, this study has several limitations. First, the long-term effects of stretching were not examined. Considering that children are undergoing rapid physical development; age-related physiological differences may limit the generalizability of the results. Second, several key physiological mechanisms, potentially underlying the effects of dynamic stretching—such as neural activation and changes in muscle temperature—were not directly assessed. Consequently, the exact mechanisms by which performance enhancements occur remain unclear. Third, all ultrasound measurements were performed in the prone position with the knee fully extended, which placed the BFLH under a degree of passive tension. This positioning may have exaggerated the relative changes observed. Finally, the study did not include a non-stretching control group, which may have introduced potential sources of bias or variability. However, the use of standardized assessment procedures ensures that the findings remain relevant and interpretable. Future studies are recommended to include a nonintervention control group to more accurately distinguish intervention effects from natural fluctuations or test-related influences.

6. Conclusion

Similar to adults, DS in children is more suitable for activities requiring explosive power and strength, while SS is more beneficial for flexibility-demanding activities. In addition, children may exhibit greater sensitivity to stretching stimuli, but also tend to recover more quickly. Considering that children's activities often require strength and explosive power, DS may be a more suitable component of warm-up routines for children. The effects of stretching for children do not last for 30 min, with DS generally having a longer-lasting effect than SS. However, DS does not alter muscle architecture, whereas SS can induce temporary changes in pennation angle and fascicle length.

Footnotes

Acknowledgments

The research team would like to thank all participants who participated in the study.

ORCID iDs

Zhiyu Tao

Yanyan Liu

Ethical approval

All research procedures and methodologies in this study adhered to the principles of the Declaration of Helsinki, and the Human Ethics Committee of Wenzhou University approved the study (Approval number: 2021-094). All participants received both a verbal explanation and written documents regarding the study. Prior to enrollment, their guardians provided informed consent by signing a consent form.

Author contributions

Concept: Zhiyu Tao; Experimental Design: Zhiyu Tao; Data Collection: Zhiyu Tao, Yanyan Liu, Zhixue Chen; Data Analysis: Zhiyu Tao, Yanyan Liu; Manuscript Writing: Zhiyu Tao.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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