Introduction

In the wrestling sport, every part of the wrestlers’ body makes direct contact with their opponent, and there are various movements in wrestling that require explosive strength, such as pushing, pulling, turning and throwing1. The hips and knees play an important role in wrestling. Therefore, promoting explosive strength in the lower limbs of wrestlers is of great significance to the improvement of wrestlers’ skills, and the development of scientific, efficient, and targeted training programs has become the focus of current research2.Adolescence is a critical period for the development of muscle strength and explosive power, with physiological changes in hormonal levels and neuromuscular adaptations influencing how female athletes respond to training3. This developmental phase presents unique opportunities for strength adaptations, making teenage female wrestlers a particularly interesting and relevant population for strength training studies. Moreover, there is a gap in research focusing on this specific demographic in wrestling, making this study an important contribution.

Explosive strength refers to the maximum amount of work done in a short period and is related to absolute force and speed of strength generation. Explosive strength is based on absolute strength and will increase with maximum strength in the early training or puberty stage4. When the maximum strength does not improve, low-intensity resistance training (LI-RT) can be carried out to promote the improvement of RFD5. Suga et al.6have shown that low-intensity resistance training (LI-RT), when combined with blood flow restriction (BFR), can effectively improve muscle strength and explosive strength, with positive impacts on both RFD and neuromuscular activity.Resistance training is an effective way to improve muscle strength by inducing muscle contraction and promoting an increase in muscle circumference and strength7,8,9. As a typical multi-joint movement, half-squat exercise (HSE) is commonly integrated into various resistance training programs to enhance lower limb strength10. Yuan et al.11 concluded that on the premise of athletes completing the half-squat movement at the fastest speed, the output power is the highest when 30%1RM resistance is applied. Tian et al.12 also reached the same conclusion. The above studies verify the effectiveness of the resistance training, but they are on the implementation of LI-RT. However, for wrestlers who belong to heavy athletics, only implementing LI-RT is less likely to increase maximum strength because it is insufficient to produce effective stimulus. Therefore, increasing the load of resistance exercise is the way to enhance the maximum strength of wrestlers. High-intensity half-squat training (HI-HST) is the traditional way of strength training, and the American College of Sports Medicine and the National Strength & Conditioning Association recommends a load of 70–80%1RM13.

Blood Flow Restriction Training (BFRT, also known as KAATSU training) restricts blood circulation during exercise, leading to an increased accumulation of metabolic by-products and acidity, which contributes to enhanced muscle fatigue and potentially greater training adaptations14. Studies have indicated that combining BFRT with lower intensity resistance training (20–40%1RM) can achieve results comparable to those of traditional high-intensity resistance training. This combination effectively increases metabolic stress, neural activity, and muscle fiber recruitment, enabling athletes to achieve higher output power in strength-based sports like wrestling15,16,17,18,19. Other studies have further demonstrated that BFRT specifically enhances the recruitment of type II motor units20, MANINI et al.21 research has also found that BFR combined with low-intensity resistance exercise creates local ischemia, leading to substantial recruitment of type II muscle fibers, which explains how BFR stimulation increases the recruitment of high-threshold muscle fibers. Additionally, the accumulation of metabolic byproducts in muscles stimulates the secretion of growth hormone (GH) and insulin-like growth factor-1 (IGF-1), hormones and growth factors that promote adaptation22. These physiological mechanisms further support the theory that resistance training combined with BFR can improve the training effect. In comparison, traditional high-intensity resistance training (HI-RT, 70–80%1RM) primarily promotes maximal strength and explosive strength through greater mechanical tension23. While HI-RT directly targets strength improvements, LI-RT combined with BFRT achieves comparable benefits predominantly through metabolic stress and neuromuscular adaptations. In wrestling, the ability to generate explosive strength rapidly can be effectively enhanced through low-intensity resistance training (LI-RT) combined with BFR, as this method induces higher-frequency impulses from the motor center to the motor units, promoting faster and more powerful muscle contractions24. In training practice, 30–50%1RM is the intensity range that can boost the rapid strength development of athletes. Based on the above, low-intensity blood flow restriction half-squat training (LI-BFR-HST) is proposed. LI-BFR-HST is a training program designed to enhance explosive strength and improve the rate of force development (RFD) in the lower limbs of teenage female wrestlers.

High-intensity half-squat training (HI-HST) and LI-BFR-HST can improve the lower limb strength theoretically, thus enhancing explosive strength. HI-HST provides high mechanical tension for lower limb muscles under high load training, focusing on training the maximum strength of muscles. By restricting blood circulation, LI-BFR-HST allows increasing muscle strength during LI-RT, thus promoting the development of rapid strength and explosive strength. Studies show that combining BFRT and traditional high-intensity resistance training (HI-RT) can realize the superposition of advantages and achieve a better effect. For example, after eight weeks of HI-RT combined with low-intensity BFRT, the performance of basketball players in accelerated running and run-up has been improved significantly25. Yasuda et al.26 concluded that HI-RT combined with low-intensity BFRT could improve muscle functional adaptability, and their effect on muscle circumference is similar to that of HI-RT alone and superior to that of low-intensity BFRT alone. Therefore, this paper believes that the combination of LI-BFR-HST and HI-HST (LI-BFR-HST & HI-HST) provides dual stimulation. LI-BFR-HST & HI-HST is more conducive to enhancing lower limb explosive strength, which is closely related to improvements in the rate of force development (RFD) in teenage female wrestlers.

Vertical jump ability is usually used to evaluate the level of lower limb explosive strength27,28, which is determined by the maximum strength, rate of force development (RFD), and the neuromuscular coordination between the upper and lower body29. Among vertical jumps, both squat jump (SJ) and countermovement jump (CMJ) are effective methods to evaluate the explosive strength of lower limbs. In addition, the rapid strength generation ability of muscles also plays a vital role in wrestling, which is mainly reflected by the peak torque at 180–300°/s angular velocity. Therefore, the isokinetic muscle force (IMS) of the knee joint (ω = 180 °/s) is selected as the indicator to evaluate wrestlers’ lower limb explosive strength and RFD, while the height and the peak RFD during the SJ and CMJ are used as indicators to assess to evaluate the lower limb explosive strength.

To sum up, this study takes teenage female wrestlers as research participants and implements a six-week group comparative training intervention. Based on the reviewed literature, we hypothesize that the combined LI-BFR-HST and HI-HST approach will produce significantly greater improvements in lower limb explosive strength than either LI-BFR-HST or HI-HST alone. Specifically, we predict that the combined training will result in: (1) greater increases in peak torque during isokinetic muscle strength testing of the knee joint at 180°/s; (2) higher vertical jump heights in both squat jump (SJ) and countermovement jump (CMJ) tests; and (3) superior improvements in peak rate of force development (RFD) during both jump tests. The effectiveness of LI-BFR-HST, HI-HST, and the combined approach on these specific performance metrics will be examined following the six-week intervention. This study aims to provide a scientific and efficient training program to enhance the athletic performance of teenage female wrestlers.

Study participants and methods

As shown in Fig. 1, the research mainly includes four parts: (1) division of groups, (2) design and implementation of intervention training, (3) measurement of indicators, and (4) analyzing the experimental results and obtaining optimal training programs.

Fig. 1
figure 1

The research framework (BFRT, blood flow restriction training; HST, half-squat training; BFR-HST, blood flow restriction half-squat training; BFR, blood flow restriction; without BFR, without blood flow restriction; LI-HST, Low-intensity half-squat training; RFD, rate of force development).

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Study participants

Twenty-four teenage female wrestlers were recruited as the research participants of this experiment. They were randomly assigned to three groups using a computer-generated random number table (simple randomization method): blood flow restriction training group (BFRT group), regular group (half-squat training group, HST group), and combination group (BFRT-HST group). Each participant was assigned a unique identification number, and these numbers were then randomly allocated to the three groups using Microsoft Excel’s random number generator function, ensuring eight participants per group. Baseline characteristics (age, height, weight, and BMI) of each group were statistically analyzed to verify no significant pre-intervention differences between groups, and the results are shown in Table 1.

Table 1 shows that the division of the group is random.

Table 1 Physical characteristics of participants.
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All wrestlers were healthy and had no history of injury or disease. They were informed of safety precautions and emergency plans for the test and volunteered to participate in the study. All participants signed informed consent forms prior to the test, and the informed consent was reviewed and approved by the Ethics Committee of Qingdao University Medical College. All methods in this study were conducted in accordance with relevant guidelines and regulations, including the Declaration of Helsinki.

Experimental design

The three groups were given intervention during strength training, respectively. Strength training includes half-squat, bench press, high pull, deadlift, pull-up, vaulting box, and core strength exercises. In this paper, the intervention was only carried out on the half-squat training because the half-squat movement has the strongest correlation and most direct influence on the increase of lower limb strength. The groups and their corresponding training programs are shown in Table 2.

To ensure that BFR was the independent variable, training loads were meticulously matched across all groups by controlling total volume load (sets × repetitions × intensity). The LI-BFR-HST and LI-HST groups adhered to identical low-intensity resistance training protocols (30% 1RM), with the sole difference being the application of BFR. Likewise, the HI-HST and BFRT-HST groups followed the same high-intensity training regimen (75% 1RM), maintaining consistency in training volume. Additionally, all groups underwent the same technical training, dietary regimen, and recovery schedule to eliminate potential confounding variables. These measures ensured that any observed differences in performance outcomes could be directly attributed to the application of BFR, rather than variations in training load or external factors.

Table 2 Design scheme of half-squat intervention training.
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In Table 2, “√” means that BFRT was implemented during training, and “–” means that BFRT was not implemented. The equipment used for BFR is KAATSU-Master (Sato Sports Plaza, Tokyo, Japan) (as shown in Fig. 2a) and a portable KAATSU device (YIJIAYUAN Sports Technology Development Co., LTD, Beijing, China) (as shown in Fig. 2b).

The pressure bandage (5 cm width) was tied to the upper 1/3 of the thigh and perpendicular to the longitudinal axis of the thigh. A pressure warm-up was performed before applying the training pressure. During BFRT, the binding pressure was set at 40 mmHg and the inflatable pressure at 180 mmHg. These pressure values were determined considering the relationship between limb circumference and blood flow restriction to identify optimal individualized restriction pressures, taking into account the interaction between blood pressure and lower limb circumference30,31,32. Wrestlers were required to complete half-squats with their lower limbs under pressure (as shown in Fig. 2c).

Fig. 2
figure 2

Examples of experimental instruments and training movement.

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The load intensity was set as 30%1RM, based on the optimal load range of BFRT proposed by Scott et al.33 As shown in Table 2, LI-BFR-HST was repeated 75 times while performing the lower limb in a pressurized state. The LI-BFR-HST was divided into four sets, 30 times in Set 1 and 15 times in Set 2–4, with an interval of 60 s between sets. The HST group set the load intensity of 75%1RM to perform HI-HST 36 times without BFR. The HI-HST was divided into four sets, 10 times in Set 1–2 while 8 times in Set 3–4, with an interval of 60 s between sets. Intervention training was performed three times a week for six weeks. The BFRT-HST group combined two training strategies, LI-BFR-HST and HI-HST, and wrestlers performed LI-BFRT-HS twice a week (on Monday and Wednesday) and HI-HST once a week (on Friday).

Essentials of half-squat training: ①The wrestlers stand on the Smith squat stand with their eyes flat and feet naturally apart. ②Squat down until the knee joint is at 90°, the wrestlers squat up at the fastest speed. The hips and knees must stretch coinstantaneous when squatting, and exertion is always maintained during the exercise. Test method: using Gymaware (Australia), a piece of linear sensing equipment, the 1RM value of the half-squat is measured by the incremental load test method34.

In addition to the half-squat, other strengths training of all wrestlers was entirely consistent, namely bench press, high pull, deadlift, pull-up, vaulting box, and core strength exercises. The training design scheme is shown in Table 3. The interval between each training is 180 s. In addition, according to the training plan of the wrestling sports teams, besides the strength training three times a week, there were also 4–6 times of technical and tactical training. The three groups had the same technical and tactical training, diet, rest time, and other conditions. The above designs ensured that the difference of half-squat intervention training is the only variable between groups. The effects of LI-BFRT-HS, HI-HST, and LI-BFRT-HS & HI-HST methods on wrestlers’ lower limb explosive strength and rate of force development (RFD) were analyzed respectively and compared effectively, and then, the optimal training program was selected.

Table 3 Training design scheme.
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In this paper, the indicators (be introduced in Section “Experimental test indicators”) were tested twice, respectively, before and after the six-week intervention training. The details, testers, and instruments of the two tests were the same to minimize equipment and human error. And the pre and post-tests were carried out 72 h after practice to ensure sufficient recovery time for wrestlers to avoid fatigue affecting the training effect.

Experimental test indicators

The effect of intervention training was quantified by comparing the changes of indicators in three groups before and after six-week training. The details of the indicators are described below.

Knee joint isokinetic muscle strength (Peak Torque)

The knee joint is one of the most complex joints in the body and the main weight-bearing joint in wrestling. Its main functional activity is flexion and extension, which is greatly affected by the surrounding flexion and extension muscle group reflecting muscle strength and explosive strength. In practice, the flexor and extensor muscles of the wrestlers’ knee joint are a pair of essential muscles that play a vital role in the maintenance of the wrestlers’ wrestling frame, the completion of the offensive and defensive movements, and the movement of the body’s center of gravity.

Isokinetic muscle strength (IMS) measurement is used to measure muscle strength and other parameters during the limbs’ isokinetic movement. It is used to judge the motor function of relevant muscles and joints. Since the limbs cannot produce the isokinetic movement on their own, it needs the help of the instrument. The instrument adjusts the limbs’ resistance to keep the limbs’ speed at a constant value when the limbs are moving autonomously. Torque, the product of the force applied by the moment arm, reflects the force of muscle contraction. Peak torque refers to the maximum torque value during muscle contraction and is the best indicator to reflect muscle capacity in IMS measurement. Knee joint movement takes the knee joint as the center, and the limbs flex and extend, so its speed is expressed as angular velocity. Faster angular velocity often requires greater, faster force. Therefore, the peak torque value at 180º/s angular velocity (ω = 180 º/s) is used as the indicator to evaluate the wrestlers’ muscles’ explosive strength and RFD. When the muscle force is strong, the resistance, the muscle load, and the muscle tension increase, as well as the peak torque value is higher, indicating that the more explosive the wrestlers’ muscles are, the faster they produce force.

The IsoMed 2000 isokinetic force testing system (Made in Germany) was used to measure the peak torque of the knee joint. Before the test, the wrestlers’ body should be placed on the seat, the upper body, hip, and thigh corresponding to the knee joint were fixed with a specialized belt. Adjust the rotation center of the knee joint to ensure that the length of the moment arm was combined with the rotation axis of the dynamometer. The upper part of the ankle joint was fixed with a gasket. During the test, wrestlers were required to perform knee joint extension and flexion at 180º/s angular speed. When the knee joint angle moved to 90°, wrestlers were required to exert maximum force. Finally, the peak torque values (ω = 180 º/s) of left and right knee joint flexion and extension were obtained, every wrestler would get four peak torque values.

Vertical jump height and peak rate of force development

Vertical jump height and peak rate of force development (PRFD) are representative indicators reflecting lower limb explosive strength. The RFD is the slope of the force-time curve of muscle under the isometric and dynamic rate of force development35, affected by both time and maximum force, reflecting the intensity of explosive strength and the ability of muscles to generate strength rapidly. Wrestlers have a lot of explosive movements such as pushing, pulling, turning, and falling in the competitive process, so RFD is considered one of the most critical indicators of wrestlers’ physical abilities. The higher the wrestler’s jump height and the PRFD during the vertical jump are, the stronger the wrestler’s lower limb explosive strength is.

The vertical jump test measures the height of the vertical jump and the PRFD during the vertical jump. The vertical jump test includes the squat jump (SJ) and countermovement jump (CMJ). The SJ test is divided into three steps: ① Make sure that the initial movement is the same as the half-squat, and the knee angle is 90º (joint angle meter can be used to assist measure). ②Make use of the muscle elasticity of the thigh and buttocks to jump to the limit height, apply force (explosive strength) at the moment of take-off, no countermovement. ③ Feet fall back to the ground, and ①-③ is a repeat. CMJ starts with a standing posture: ①Wrestlers crouches backward at the hips until the knees are at 90º. ② Use the countermovement to jump as high as possible. ③ Feet fall back to the ground, and ①-③ is a repeat. In addition, to limit arm swing, wrestlers were asked to jump with arms akimbo, and sufficient rest was taken between each jump practice to eliminate fatigue. The indicators were measured by a 400s performance force-measuring plate, which obtained the PRFD value when the jump height was read.

Statistical analysis

Descriptive statistics for all indicators and values are expressed as means ± standard deviation. Significant difference tests among multiple groups are performed using two-way repeated-measures analyses of variance (ANOVA). A paired T-test is performed within each group, and a one-way analysis of variance is performed between groups. Set the significance at p < 0.05. All p < 0.05 denotes the presence of a statistically significant difference.

Before selecting statistical methods, the normality of data distribution was assessed using the Shapiro-Wilk test. If the data followed a normal distribution, parametric tests such as ANOVA and t-tests were applied. If the data did not follow a normal distribution, non-parametric alternatives were considered, including Kruskal-Wallis tests instead of ANOVA and Wilcoxon signed-rank tests instead of paired t-tests.

Given the small sample size, effect sizes were calculated to supplement statistical analyses. Additionally, Cohen’s d was calculated to evaluate the magnitude of within-group pre-post changes, and η2 (Eta squared) was computed from ANOVA to estimate the proportion of variance in dependent variables explained by independent variables and their interactions. Effect sizes were interpreted according to conventional thresholds: small (d = 0.2, η2 = 0.01), medium (d = 0.5, η2 = 0.06), and large (d = 0.8, η2 = 0.14). These effect sizes provide additional insights into the practical relevance of the observed changes.

To reflect the change of indicators before and after intervention training more fairly and intuitively, the concept of “change ratio” is introduced, and the calculation formula is as follows:

$$\:change\:ratio=\frac{{Mean}_{post}-{Mean}_{pre}}{{Mean}_{pre}}\times\:100\%$$
(1)

Where, Meanpre represents the average value of the indicator of each group before intervention training, Meanpost\(\:{mean}_{post}\) represents the average value of the indicator of each group after intervention training. According to Formula (1), when the change ratio is greater than 0, the intervention training increases the indicator value of the group; otherwise, it decreases. The higher the change rate is, the higher the increment of the indicator is.

Data editing and collation were completed by Excel software. Statistical analyses were conducted with the Statistical Package for Social Sciences (SPSS) software (IBM SPSS v.22, Chicago, IL, USA).

Results and analysis

By comparing the changes of the indicators of the three groups (IMS of the knee joint, vertical jump height, and PRFD during vertical jump) before and after six-week training, this paper quantitatively analyzed the training effects of the corresponding training programs of each group and optimized the training programs.

Comparison of knee joint isokinetic muscle strength

The change and significance analysis results of IMS of the knee joint (represented by peak torque) at 180 º/s angular velocity are shown in Table 4.

Table 4 Comparison and significance analysis of peak torque (ω = 180 º/s).
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Analysis of Table 4 shows the following findings.

  1. (1)

    Results of ANOVA show that [group] has no significant effect on peak torques (ω = 180º/s) (main effect of [group], p > 0.05). The main effect of [time] on the peak torque (ω = 180 º/s) of right knee extension (F = 5.36, p < 0.05, η2 = 0.203, large effect) and left knee flexion (F = 8.35, p < 0.05, η2 = 0.284, large effect) is significant, indicating that intervention training has a considerable influence on the increase of peak torque value (ω = 180 º/s) of right knee extension and left knee flexion. Interaction [group]×[time] has a significant effect on peak torque (ω = 180 º/s) of right knee extension (F = 4.52, p < 0.05, η2 = 0.301, large effect), showing that different training methods of different groups have a significant effect on the increase of peak torque value of right knee extension.

  2. (3)

    The change rate of the same indicator in the BFRT-HST group is the highest among the three groups. The peak torque (ω = 180º/s) of right knee extension (Cohen’s d = 1.05, large effect) and left knee flexion (Cohen’s d = 0.70, medium to large effect) increased significantly in the BFRT-HST group (p < 0.05), indicating that the combined training of LI-BFR-HST and HI-HST has a better effect on the increase of IMS of the knee joint at ω = 180º/s than the single training method. However, the BFRT group (Cohen’s d = 0.37, small effect for right flexors; d = 0.23, small effect for left flexors) and HST group (Cohen’s d = 0.52, medium effect for right flexors; d = 0.41, small to medium effect for left flexors) do not show a significant increase after six weeks of training intervention, but they also produce some training effects.

  3. (4)

    The peak torque (ω = 180 º/s) of right knee extension in the BFRT group is almost unchanged (Cohen’s d = − 0.14, negligible effect), while the peak torque (ω = 180 º/s) of left knee extension in the HST group is slightly decreased (Cohen’s d = − 0.39, negative medium effect), which might be caused by fatigue not being completely relieved during the test.

  4. (5)

    The peak torques of ipsilateral flexion and extension show a great difference, which is consistent with the performance of the main flexor and extensor muscle group of Chinese wrestlers. The peak torque of the back muscle of wrestlers in China is greater than that of the knee joint, and the extension is greater than the flexion. Overall, knee flexor and extensor strength increase synchronously but show differential changes in ipsilateral flexion and extension. This phenomenon may be caused by the failure of balanced stimulation of the original dynamic muscles and antagonistic muscles of the lower limb joint, thus leading to the change of the joint muscle group cooperative contraction mode. However, individual differences cannot be ruled out.

Comparison of vertical jump height

The change and significance analysis results of vertical jump height before and after intervention training are shown in Table 5.

Table 5 shows that: (1) ANOVA shows that [group] has no significant effect on the vertical jump height (p > 0.05). However, [time] has a significant effect on SJ (F = 23.06, p < 0.05, η2 = 0.523, large effect) and CMJ height (F = 21.00, p < 0.05, η2 = 0.500, large effect), indicating that intervention training considerably increases SJ and CMJ heights. Additionally, the interaction of [group]×[time] significantly affects CMJ (F = 6.06, p < 0.05, η² = 0.366, large effect), demonstrating that different training methods significantly influence CMJ height improvements. (2) The change rates of SJ and CMJ in the BFRT-HST group are 13.2% and 9.7%, respectively, the highest among the three groups. The BFRT-HST group shows significant improvements in SJ (Cohen’s d = 2.04, very large effect) and CMJ (Cohen’s d = 1.21, large effect), suggesting that the combined training (LI-BFR-HST & HI-HST) is more effective than single training methods. The BFRT group demonstrates a significant improvement in SJ height (Cohen’s d = 1.27, large effect, p < 0.05), with an 8.5% increase, while the HST group significantly improves CMJ height (Cohen’s d = 0.72, medium to large effect, p < 0.05), with a 4.5% increase.

Table 5 Comparison and significance analysis of vertical jump height.
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Comparison of PRFD

Table 6 shows the change and significance analysis results of PRFD during take-off before and after intervention training.

Table 6 PRFD changes and significance analysis during take-off.
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As shown in Table 6: (1) ANOVA shows that [group] had no significant effect on PRFD (p > 0.05). However, [time] has a significant effect on PRFD of SJ (F = 5.95, p < 0.05, η2 = 0.221, large effect) and CMJ (F = 4.23, p < 0.05, η2 = 0.168, large effect), indicating that intervention training significantly improves PRFD during take-off. The interaction of [group]×[time] has no significant effect on PRFD.(2) The BFRT-HST group exhibits the highest change rates in PRFD for SJ (9.2%) and CMJ (8.0%) among the three groups. Specifically, the PRFD significantly increases in the BFRT-HST group after intervention (SJ: Cohen’s d = 0.69, medium effect; CMJ: Cohen’s d = 0.58, medium effect), indicating that combined training (LI-BFR-HST & HI-HST) is more effective than single training methods. In addition, the BFRT and HST groups also show beneficial training effects after six weeks. The BFRT group significantly increases SJ PRFD (Cohen’s d = 0.54, medium effect, p < 0.05, 9.2% increase), and the HST group significantly increases CMJ PRFD (Cohen’s d = 0.69, medium effect, p < 0.05, 4.8% increase). (3) It can be seen from Tables 5 and 6 that the increase of vertical jump height is positively correlated with the increase of PRFD during take-off, which is consistent with the results of previous studies36,37,38.

Summary

Table 7 summarizes the significance analysis results of IMS of the knee joint (peak torque), vertical jump height and PRFD changes in each group, before and after intervention training.

Table 7 Significance analysis results of each indicator in each group.
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The significance analysis results in Table 7 show that: (1) From ANOVA results, [group] has no significant effect on all indicators. In contrast, [time] has a significant effect on all indicators (p < 0.05). The interaction of [group]×[time] slightly affects the indicators. The above indicates whether the intervention training produces the main effect. (2) Two peak torque values increase significantly in the BFRT-HST group (p < 0.05), showing that LI-BFR-HST combined with HI-HST plays a vital role in improving IMS of the knee joint. Although the BFRT and HST groups show no significant increase, they also get some training effects. (3) The variation of jump height and PRFD at take-off are consistent. The SJ height and PRFD increase significantly in the BFRT group (p < 0.05), while the CMJ height and PRFD did not, indicating that LI-BFR-HST has a significant effect on the improvement of SJ capability. In contrast with the BFRT group, the CMJ ability improves significantly in the HST group (p < 0.05), while the SJ ability did not; Both SJ ability and CMJ ability improve significantly in the BFRT-HST group (p < 0.05). The above shows that the training mode of LI-BFR-HST & HI-HST fully combines the advantages of LI-BFR-HST and HI-HST.

In general, the training effect of the BFRT-HST group is markedly better than that of the BFRT group and HST group, and the implementation of intervention training plays a decisive role in the growth of each indicator. The combination of LI-BFR-HST and HI-HST improves the explosive strength of teenage female wrestlers’ lower limbs significantly. In addition, it promotes wrestlers’ ability to generate strength rapidly to some extent.

Discussion

This study explores the effects of different training methods on the explosive strength and rate of force development (RFD) of teenage female wrestlers through a group-controlled experiment and finds the optimal training program. During the research, some feasible training strategies are shared. The unsolved problems will be followed up in subsequent research.

Advantages of multi-mode resistance training

Multi-mode resistance training with a targeted combination of high- and low-intensity for lower limbs can effectively improve the IMS of the knee joints. Such beneficial effects are typically difficult to achieve through single-mode resistance training alone, especially for wrestlers who have been doing traditional muscle-building training for a long time. In summary, the advantages of multi-mode resistance training mainly lie in three points. First, compared with single high (or low) intensity resistance training, the alternating use of high-intensity and low-intensity resistance training can significantly increase the concentration of serum human growth hormone (HGH)39. Second, multi-mode resistance training is reported to result in higher muscular fitness of muscle groups40,41,42. Furthermore, studies have shown that multi-mode resistance training is highly effective for maximizing muscle strength39.

Our experimental results support the aforementioned statement, as demonstrated in Tables 4, 5 and 6. After six weeks of intervention training, the peak torque (ω = 180 º/s) of both right knee extension and left knee flexion in the BFRT-HST group increased significantly (p < 0.05). Specifically, right knee extension peak torque increased by 10.1%, and left knee flexion peak torque increased by 20.8%. Additionally, the height and peak rate of force development (PRFD) of the squat jump (SJ) and countermovement jump (CMJ) also showed significant improvement in the BFRT-HST group (p < 0.05), with SJ height increasing by 13.2% and CMJ height by 9.7%. PRFD improvements were also significant, with SJ PRFD increasing by 9.2% and CMJ PRFD by 8.0%.

These findings align with previous research. For example, Laurentino et al.43 reported significant improvements in knee extension strength following blood flow restriction training, observing a 6.3% increase in quadriceps cross-sectional area (CSA) after their eight-week intervention. In our study, we observed a 10.1% increase in right knee extension peak torque. The different results may be attributed to factors such as variations in the specific training protocol used or individual differences among participants. Similarly, Manimmanakorn et al.44 documented a 7.3% improvement in vertical jump height among netball athletes following BFRT protocols, whereas our combined approach yielded higher improvements (13.2% in SJ), suggesting that the multi-modal approach may be particularly effective for power development in wrestlers. Interestingly, our findings revealed differential adaptations between jump types (13.2% in SJ vs. 9.7% in CMJ), which contrasts with previous research showing more uniform adaptations across jump variants. This difference may reflect specific neuromuscular adaptations to our unique training protocol. Regarding power development, Scott et al.45 also reported that various blood flow restriction training methods can enhance explosive power metrics in athletic populations, supporting our findings on improvements in PRFD. The physiological mechanisms underlying these adaptations were explored by Takarada et al.46, who demonstrated that resistance exercise combined with blood flow restriction can effectively activate complementary adaptation pathways that enhance muscular function.

These results suggest that multi-mode resistance training (combining high-intensity with low-intensity) in the BFRT-HST group may have greater advantages compared to single LI-BFR-HST or HI-HST. LI-BFRT stimulates rapid strength development through low-load resistance training, while HI-HST stimulates neuromuscular adaptation through high-load resistance training. LI-BFR-HST & HI-HST combines the advantages of both and produces more favorable training effects, which could effectively enhance the lower limbs’ explosive strength and the RFD of lower limb muscle groups. Thus, LI-BFR-HST & HI-HST is significant in enhancing wrestlers’ actual combat level.

Effectiveness of blood flow restriction training

Muscles thickening and muscle strength growth are achieved through the division and hyperplasia of muscle satellite cells. To avoid muscles growing excessively, muscle satellite cells are generally in the resting phase of the cell cycle, during which they are usually dormant. Division and hyperplasia require the transition from the resting phase to the division phase47. The increase of hepatocyte growth factor (HGF) and the decrease of myostatin (MSTN) can accelerate this transition. Nitric Oxide (NO), a regulating messenger of HGF and MSTN, promotes HGF growth and inhibits MSTN secretion, thereby inducing the division of muscle satellite cells. Thus, the effect of muscles thickening and muscles strength growth can be achieved48.

The decrease of MSTN and the increase of NO and HGF in blood play a crucial role in muscle thickening and strength growth. However, BFRT demonstrates effectiveness in enhancing the concentration of NO, increasing the level of HGH, and inhibiting the secretion of MSTN. BFRT can cause local accumulation of lactic acid and metabolites, and form a local hypoxia environment, thus initiating the synthesis and secretion of NO synthetase (NOS)22. Drummond et al.49 stated that LI-BFR restriction training could change the mRNA expression of genes related to early muscle growth and protein conversion in human skeletal muscle after exercise. Takano et al.50 showed that short-term LI-BFR restriction training would gradually increase HGH concentration after exercise and reached its peak half an hour later, indicating that BFRT could significantly improve HGH level in the body. Zhao et al.51 concluded that for athletes, compared with traditional high-intensity resistance training, BFRT can more effectively promote the benign changes of hormones and bioactive factors related to muscle syntheses such as NOS and HGH. The increase of NOS and the down-regulation of MSTN expression after BFRT can eventually lead to the activation of muscle satellite cells. Meanwhile, BFRT can increase the concentration of HGH and insulin-like growth factor-1 in blood, promoting the proliferation and differentiation of muscle satellite cells. Ultimately, it encourages muscle thickening and muscle strength growth, thus conducive to explosive strength development52. In addition, BFRT is trained at light load intensity (20–40%1RM), which facilitates the ability of rapid strength generation.

Based on the above principles, LI-BFR-HST is designed in our experiment. Tables 4, 5 and 6 show that LI-BRF-HST (implemented in the BFRT group) and HI-HST (implemented in the HST group) produce similar training effects. Compared with HI-HST, LI-BFRT can achieve similar outcomes with HI-HST on the premise of decreased training load and reduced injury risk. On the other hand, it can improve the ability of lower limb rapid strength by reducing the training load. In conclusion, the LI-BFRT can be regarded as a more economical and effective training method.

Puberty is a critical period to increase muscles’ explosive strength

Puberty is a critical period for human growth and development. Exercise training during this period may be positively or negatively affected. Therefore, the growth and development characteristics of puberty must be followed in the design of intervention training programs. Muscle strength growth in female wrestlers occurs in late puberty (between the ages of 16–17), the second critical period of maximum strength growth53. During this period, the lower limb explosive strength usually increases with the increase of the maximum strength of the lower limb, while the ability of rapid strength generation is also in the development stage54. So it is important to design training programs that align with this critical period to optimize the development of lower limb strength effectively.

Teenage female wrestlers (around 17 years old) are taken as experimental participants in this experiment. Three experimental groups are designed: the BFRT group, the HST group, the BFRT-HST group, and three training methods LI-BFR-HST, HI-HST, and LI-BFR-HST & HI-HST are adopted, respectively. The results suggest that the training effect of the BFRT-HST group may be more beneficial than that of the BFRT group and HST group significantly. Therefore, this study suggests that LI-BFR-HST & HI-HST could be a promising training approach for teenage female wrestlers to improve their lower limb explosive strength and RFD generation ability.

Limitations

Due to experimental constraints, the BFRT-HST group followed a fixed weekly schedule—performing LI-BFRT-HST twice and HI-HST once. This distribution may have influenced training outcomes, as the relative contributions of intensity, volume, and BFR were not fully isolated. Additionally, the relatively small sample size (n = 8 per group) limits the statistical power and generalizability of our findings. Furthermore, the absence of long-term follow-up makes it difficult to evaluate the sustained effectiveness of these training strategies. Future studies should consider larger sample sizes, longer-term assessments, and additional training structures to better clarify the independent effects of each component.

Conclusions

The results of this study suggest that LI-BFR-HST & HI-HST is an effective training strategy to improve the knee flexion, extensor muscle rapid strength generation, and lower limb explosive strength of teenage female wrestlers. The results also confirm previous studies that LI-BFR-HST and HI-HST could achieve similar training effects. In addition, LI-BFR-HST & HI-HST can be used as part of training to develop lower limb explosive strength. This paper raises a scientific and efficient training method for the technical improvement of teenage female wrestlers and also provides some enlightenment for the explosive training of other athletes. However, further experiments are needed to confirm our results and better understand the adaptation produced by LI-BFR-HST & HI-HST in teenage female wrestlers.