Effects of blood flow restriction combined with electrical muscle stimulation on muscle functions and sports performance in male football players with knee osteoarthritis: a randomized controlled trial

doi:10.21203/rs.3.rs-4830944/v1

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Effects of blood flow restriction combined with electrical muscle stimulation on muscle functions and sports performance in male football players with knee osteoarthritis: a randomized controlled trial

https://doi.org/10.21203/rs.3.rs-4830944/v1

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The purpose of this study was to investigate the effects of combining BFRT with EMS on muscle functions and sports performance in football players with knee osteoarthritis (KOA). This parallel randomized controlled trial was conducted on 64 football players diagnosed with KOA at Chengdu Sport University. Participants were enrolled based on predefined eligibility criteria and randomly allocated to four groups: the control group (CTR, n = 16), BFRT-alone group (BFRT, n = 16), EMS-alone group (EMS, n = 16), and BFRT combined with EMS group (CMB, n = 16). Data were gathered via the 10-meter sprint, 20-meter sprint, countermovement jump (CMJ), and Illinois agility test (IAT) to assess sports performance. Additionally, peak torque (PT) was used to measure muscle strength, the root mean square (RMS) was used to assess muscle activation, and the cross-sectional area (CSA) was used to evaluate muscle volume. The data were statistically analyzed via SPSS software, and a p-value < 0.05 was considered significant. Following the 8-week intervention, the CMB group exhibited greater improvement in the 10-m sprint compared to the CTR group and demonstrated significant enhancements in the 20-m sprint, CMJ, and IAT, outperforming the other three groups (p < 0.05). To PT, the CMB groups demonstrated significant superiority over the other three groups, while the BFRT group exhibited greater improvement in PT than the EMS group (p < 0.05). Concerning RMS, the EMS and CMB groups showed significant improvements compared with the CTR and BFRT groups, whereas the improvement in the BFRT group was significantly greater than that in the CTR group (p < 0.05). For CSA, the BFRT and CMB groups presented notable advancements compared with the CTR and EMS groups (p < 0.05). In summary, the results suggest that BFRT combined with EMS can increase muscle strength in male football players with KOA through improving muscle volume and neuromuscular recruitment under low-intensity resistance training, thereby increasing explosive power and agility.

Health sciences/Health care/Therapeutics/Rehabilitation

Health sciences/Health occupations/Orthopaedics

Football

Knee osteoarthritis

Blood flow restriction

Electrical muscle stimulation

Muscle functions

Sports performance

Osteoarthritis (OA) is a common degenerative joint disease that can seriously affect the patient’s quality of life and burden the patient’s family and society¹. OA not only causes joint pain, stiffness, deformity, and dysfunction, but also significantly increases the risk of cardiovascular events, deep vein thromboembolism, hip fracture, and all-cause mortality². Currently, there are over 300 million OA patients worldwide³, and the overall prevalence of primary OA in individuals over 40 years old in China is as high as 46.3%⁴. Knee osteoarthritis (KOA) is a notably common type of OA, and its global incidence has increased significantly in recent years. KOA is defined as a degenerative disease caused by mechanical and biological damage to the homeostasis of articular chondrocytes, the extracellular matrix, and the subchondral bone of the knee joint, with joint pain, stiffness, swelling, and loss of major joint functions as the main symptoms⁵. Pain serves as the main symptom of KOA, diminishing a patient’s sports performance and muscle functions, as well as indirectly increasing the incidence of cardiovascular events⁶. The extensive physical activity in young patients surpasses the joints' capacity for repair and maintenance, subjecting the joints to an unfavorable biomechanical environment and hastening the degeneration of the articular cartilage⁷. Consequently, unlike the high incidence of late-stage OA in elderly individuals, early-stage OA is common in young individuals with exercise habits⁸.

Engaging in high-intensity exercise significantly increases the risk of injuries such as knee ligament tears, meniscal injuries, and fractures involving the articular surface, all of which are well-established risk factors for KOA, thereby accelerating joint deterioration and increasing the incidence of KOA^9,10. Specifically, athletes engaged in sports that subject the knee joint to substantial biomechanical stress, such as rapid acceleration and sudden deceleration, or those engaged in elite-level competitions over an extended period are more prone to developing KOA¹¹. Football is one of the sports that places the greatest biomechanical pressure on the knee joint¹². During football matches, professional players cover distances of up to ten kilometers or more, often accompanied by abrupt acceleration and abrupt stops, which can readily subject the knees to high-intensity pressure^13,14. Prolonged high-pressure exercise among football players can lead to secondary knee osteoarthritis, stemming from the intricate interplay of biological, mechanical, and biochemical factors^14,15. KOA is presently recognized as an occupational ailment among football players. The anterior cruciate ligament and meniscus are two common injuries in football, both of which play pivotal roles in the onset of KOA because of their association with an increased risk of bone marrow lesions in the knee joint, a precursor to KOA¹⁶.

The treatment of KOA can be divided into surgical and non-surgical approaches. Surgical treatments include arthroscopic procedures such as anterior cruciate ligament reconstruction, knee osteotomy, and meniscectomy¹⁷. For patients with advanced KOA suffering severe joint damage and pain, artificial joint replacement is generally considered the terminal treatment option¹⁸. Pharmacological treatments typically involve the use of acetaminophen, nonsteroidal anti-inflammatory drugs, glucosamine, diacerein, and traditional Chinese medicine. However, long-term use of these medications can lead to side effects such as liver and kidney damage, abdominal distension, and diarrhea¹⁹. Non-pharmacological treatments encompass exercise, physical therapy, and health education. Health education helps patients understand the disease process, prognosis, and treatment options for KOA. It also aims to prevent activities that exacerbate KOA symptoms, such as mountain climbing and squatting, while encouraging good lifestyle habits and self-management practices like weight control and regular exercise²⁰. Physical therapies, including transcutaneous electrical nerve stimulation (TENS), pulsed electromagnetic field therapy, ultrasound, and acupuncture, can alleviate symptoms and enhance the function of patients with KOA by reducing knee joint load, improving joint range of motion, and increasing neuromuscular control^21,22. The lack of targeted therapeutic rehabilitation training is often a factor leading to the further development of KOA²³, and exercise therapy has been listed as the preferred treatment for KOA by various guidelines²⁴. Exercise, with its broad applicability and ease of implementation, effectively enhances pain management and joint mobility without adverse reactions²⁵. Muscle weakness is an obvious characteristic of patients with KOA. Strength training is one of the most effective ways to combat muscle weakness, as it can significantly improve the strength of thigh muscles such as the quadriceps and promote the recovery of knee joint function²⁶. The American College of Sports Medicine (ACSM) recommends that resistance training to enhance muscle strength should involve a resistance load of at least 60%-70% of the single-repetition maximum load (1-repetition maximum, 1RM)²⁷. To increase muscle volume, a positive load of 70%-85% of the 1RM is suggested. However, this high load is often challenging to achieve for patients with knee osteoarthritis or those who have undergone early knee surgery. Therefore, exploring more effective rehabilitation strategies for knee joint diseases remains crucial.

Blood flow restriction training (BFRT), also known as KAATSU training, was invented by Yoshiaki Soto. This training involves using a compression cuff to apply pressure to the proximal end of a limb while performing low-load resistance exercises. BFRT has been shown to effectively promote muscle strength growth and muscle hypertrophy²⁸. When combined with low-load resistance training (30% 1RM), BFRT can achieve effects similar to those of high-load resistance training ²⁹. The mechanisms of BFRT include increased secretion of anabolic hormones, increased muscle protein synthesis signaling pathways, muscle tissue ischemia, and hypoxia, which lead to cellular hydration and swelling³⁰. While BFRT primarily induces muscle growth through metabolic stress and increased mechanical tension, its impact on neuromuscular function and muscle activation improvement is not significant³¹. Electrical muscle stimulation (EMS) is another treatment that uses low-frequency pulse currents to stimulate nerves or muscles, inducing passive muscle contraction to improve muscle function and treat neuromuscular diseases and injuries³². EMS can be divided into normal muscle electrical stimulation therapy and denervation muscle electrical stimulation therapy according to whether the muscles used have normal innervation, which can increase muscle strength and delay muscle atrophy, respectively³³. Owing to its noninvasiveness, practicality, and ease of operation, EMS is widely used in the rehabilitation field for conditions such as central or peripheral nerve injuries and musculoskeletal system diseases³⁴. Combining BFRT with EMS can help prevent muscle mass loss during limb disuse and enhance muscle strength and hypertrophy when incorporated into strength training^35,36.

The injuries sustained in football significantly impact athletes’ muscle function and sports performance, as well as pose a serious threat to their careers. While extensive research has focused on injuries among the relatively small number of professional football players, there has been limited focus on injuries affecting millions of amateur players. Thus, this study aimed to investigate the effects of combining BFRT with EMS on muscle strength, muscle activation, muscle volume, and sports performance. It was hypothesized that both modalities would increase muscle function and sports performance and that their combined use would additively augment the effects of sports performance indicators in amateur football players with KOA.

Participants

A total of 64 male football players from the Football Academy of Chengdu Sport University, all of whom were certified as second-level athletes by the General Administration of Sport of China, participated in this study. The first patient entered the study on March 19, 2023, enrollment was completed on December 1, 2023, and the last patient was assessed on January 5, 2024. This study confirmed that informed consent was obtained from all participants. The inclusion criteria required participants to be diagnosed with KOA via cartilage-sensitive magnetic resonance imaging (MRI) by a doctor to present non-specific symptoms including activity-related pain and effusion, etc., as well as no recent fresh, unscabbed open wounds. The exclusion criteria encompass participants with documented allergies to pressurized materials, inability to complete the required intervention exercises for personal reasons, intolerance to experimentally applied pressure or electrical stimulation intensities, and the incidence of other adverse reactions. Four participants withdrew from this study because of injury and competition tasks, leaving 60 participants who completed this experiment.

Study Design

The entire study was conducted at Chengdu Sport University (Chengdu, China). All procedures were reviewed and approved by the Ethics Committee of Chengdu Sport University and were conducted according to the principles of the Declaration of Helsinki. This study was registered with the Chinese Clinical Trial Registry with registration number ChiCTR2300072984 (29/06/2023). The experimental flow chart is shown in Fig. l, and the intervention and assessment schedules are presented in Table 1. The participants were randomly divided into four groups by the random number remainder grouping method, namely, the control group (CTR, n = 16), BFRT-alone group (BFRT, n = 16), EMS-alone group (EMS, n = 16), or BFRT combined with EMS group (CMB, n = 16). Operation steps: (1) 64 participants numbered 1 to 64. (2) The random number generator function in SPSS 22.0 (SPSS Inc., USA) software was used to generate random numbers so that each participant would obtain a random number. (3) The random number was divided by the number of groups four to find the remainder. If the remainder is 1, they would be assigned to the CTR group, if the remainder is 2, they would be assigned to the EMS group, if the remainder is 3, they would be assigned to the BFRT group, and if they are divisible, they would be assigned to the CMB group.

Intervention

The CTR group followed the RT program, which was conducted once daily over four days each week for eight weeks. The RT program performed the high-bar squat training at 25% 1RM. A metronome controlled the rhythm of the squat at 10 times/min (3 s concentric/3 s eccentric). In each set, the participants squat 30 reps in total and rest for 1 min after every 10 reps, and the total time for each set is 5 min. The participants repeat three sets with 2 min between sets. At the end of the second, fourth, and sixth weeks of intervention, the 1RM was reassessed periodically to adjust for exercise intensity appropriately. The BFRT group performed the same RT program as the CTR group did. According to the leg circumference inflated to the appropriate pressure (≤ 50 cm, 200 mmHg; 51–55 cm, 250 mmHg; 56–59 cm, 300 mmHg; ≥60 cm, 350 mmHg) ³⁷, a 5-cm wide tourniquet cuff (B-strong, USA) was placed at the groin crease during each set of squats. Each session comprised three cycles of 5 min of inflation and 2 min of deflation. The EMS group performed the same RT program as the CTR group and BFRT group did. Before performing the RT program, an exercise pointer was used to accurately locate the most obvious point of muscle contraction. Two negative electrodes (5×5 cm) were placed approximately 10 cm below the groin crease, and the other two positive electrodes (5×5 cm) were placed as close as possible to the movement points of the vastus lateralis and medial muscles. The electrical muscle stimulator (Twin Stim Plus: Tens Unit 7000, USA) was set to a duty cycle of 3 s ON (stimulation) and 3 s OFF (no stimulation), a pulse width of 400 µs, a stimulation intensity of 50 mA, and a stimulation frequency of 75 Hz ³⁸. The CMB group performed the same RT program as the other three groups did. BFRT and EMS were carried out simultaneously during the RT program in the same way as above. This study assigned code names to different groups to ensure that participants in each group were unaware of the names of the interventions involved.

The participants’ name, age, sex, and knee joint symptoms were recorded. All participants fully understood the entire trial process and the contraindications and indications for the use of the experimental equipment and signed informed consent forms. The participants gathered raw data on several parameters: the times for the 10-m sprint, 20-m sprint, and Illinois agility test (IAT); the height of the countermovement jump (CMJ); as well as measurements related to muscle, including peak torque (PT) for knee extension, root mean square (RMS) and cross-sectional area (CSA) of the rectus femoris (RF). Before the official intervention, the participants underwent 2 days of adaptive training according to their respective groups to familiarize themselves with the testing procedures and the interventions of each group. All interventions were conducted at the same time of day and at the same adequate temperature and relative air humidity ranges (26˚C-28˚C and 65–70%, respectively) in the Institute of Sports Medicine and Health at Chengdu Sport University. After the 8-week intervention, the participants were measured again for sports performance, muscle strength, muscle activation, and muscle volume.

Outcome measurement

Speed

To assess linear sprint ability, a telemetric photocell timing system (Witty System, Microgate, Italia) was used to evaluate the durations of the 10-m and 20-m sprints. The photocell gates were placed at a height of 0.3 m from the ground. The participants started each test with a standing split stance with the toes of the front foot 0.3 m behind the first gate and placed the other two gates at 10 m and 20 m, respectively. Each competitor selects a sprint start time and a full-load sprint in two tests. Three tests are conducted, with a 3-min rest between tests, and the shortest time is used as the final sprint time³⁹.

Jump

The CMJ was measured to evaluate jumping ability. The participants stood upright with arms on hips, hands on waist, and feet positioned hip-width apart. The participants were asked to perform a rapid downward movement at a self-selected depth and then a rapid upward movement to jump as high as possible⁴⁰. The CMJ height was measured using the Jump Tester (CSTF-ZT, Tongfang Health Technology, China). The participants were tested three times, and the best CMJ height was retained for analysis.

Agility

The IAT is a reliable and valid protocol for assessing the ability of male team athletes to change direction quickly⁴¹. The test was performed in an area of 10 × 5 m consisting of four cones, with another four cones placed in the center of the test area at a distance of 3.3 m from each other. The test began with participants lying face down with their hands at shoulder level. After the trial started, the participants began to run as fast as possible. When they crossed the finish line without knocking down any cones, the experiment was deemed complete, and the time was recorded. The test time was measured using the telemetric photocell timing system (Witty System, Microgate, Italia). Each participant performed three trials, and the shortest time was used for analysis.

Muscle Strength

The PT of knee extension was extracted with an isokinetic dynamometer (Con-Trex MJ, CMV AG, Switzerland). The participants were seated with the backrest at 90° and strapped across the chest, waist, and thighs. The dynamometer was aligned with the knee joint axis, and the participant's dominant leg was immobilized approximately 3 cm proximal to the medial malleolus. The method used to determine the dominance limb was self-report⁴². The test included concentric knee extension and flexion at 60°/s. Four warm-up repetitions with increasing intensity preceded five repetitions with the maximal effort to familiarize themselves with the procedure. Provide programmed verbal encouragement and visual feedback on real-time data during contractions to enable participants to contract as quickly and forcefully as possible.

Muscle Activation

Muscle functional activity was recorded via a wireless surface electromyography (sEMG) system (Myon 320, Schwarzenberg, Switzerland) while isokinetic strength testing was performed. The target muscle was the RF on the dominant limb. According to the surface EMG for non-invasive assessment of muscles (SENIAM) project recommendations, the electrodes corresponding to the vastus medialis were placed at 80% of the line between the anterior superior iliac spine and the anterior joint space of the anterior border of the medial ligament. The electrodes corresponding to the vastus lateralis muscle were placed 2/3 along the line from the anterior iliac superior to the lateral patella. The electrodes corresponding to the RF muscle were placed at 50% of the line between the anterior superior iliac spine and the upper part of the patella. Before electrode placement, specific areas were shaved, and the participants’ skin was cleaned with alcohol. The distance between the two bipolar Ag-AgCl surface electrodes was 20–30 nm. To process the raw data with a sampling frequency of 2000 Hz, the sEMG data were rectified, filtered, smoothed, and normalized via proEMG software (Myon 320, Schwarzenberg, Switzerland). The RMS standard value was selected as the time domain analysis index of the sEMG signal for statistical analysis.

Muscle volume

The muscle CSA of the RF was measured via real-time B-mode ultrasonography (CX50, Philips Medical Systems, Netherlands). During the ultrasound assessment, the patient was placed in a supine position with the hip and ankle joints in neutral positions and the knee joint fully extended. The probe was placed perpendicular to the skin without applying pressure, and the rectus femoris marking point was half the distance between the anterior superior iliac spine and the inferior edge of the patella⁴³.

Statistical analyses

Data were presented as the means ± standard deviations (SDs) with 95% confidence intervals (CIs) unless otherwise stated. A paired samples t-test was used to analyze the differences (Delta) in the data before and after the intervention. Possible differences between groups in the Delta changes in each outcome measure were tested through one-way analysis of variance. The Delta of the specific outcome measure was used as the dependent variable, whereas the intervention method served as the factor with four levels: CTR, BFRT, EMS, and CMB. If there was a significant F value, a Bonferroni post hoc analysis was conducted to evaluate the variation among the four interventions. Statistical significance was set at p < 0.05. All the statistical analyses were performed via SPSS Statistics version 24.0 (IBM Corp, Chicago, IL, USA).

Speed

The sprint performance data before and after the intervention were shown in Fig. 2A and 2B. No differences were observed for 10-m sprint and 20-m sprint times between the groups before the intervention. A within-group decrease in 10-m sprint time was observed only in the CMB group (p < 0.05) after the intervention. Similarly, the CMB group had a significant difference in the 10-m sprint compared with the CTR group (p < 0.05), whereas no significant differences were observed compared with the BFRT group (p = 0.068) and the EMS group (p = 0.095). Within-group decreases in 20-m sprint time were observed in the CMB group, the BFRT group, and the EMS group (all p < 0.05) after the intervention. Compared with the BFRT, EMS, and CTR groups, the CMB group presented significant differences in 20-m sprint time (all p < 0.05). Similarly, the BFRT group and the EMS group had greater decreases in 20-m sprint time compared with the CTR group (all p < 0.05). Notably, no significant difference between the BFRT group and the EMS group was observed (p = 0.076).

Jump

The jump performance data before and after the intervention were shown in Fig. 2C. No differences in CMJ height were observed between the groups before the intervention. Within-group increases in CMJ height were observed in the CMB group, the BFRT group, and the EMS group (all p < 0.05) after the intervention. Compared with the BFRT group, the EMS group, and the CTR group presented significant differences in CMJ height (all p < 0.05). Similarly, compared with the CTR group, the BFRT group and the EMS group presented greater increases in CMJ height (all p < 0.05). In contrast, no significant difference between the BFRT group and the EMS group was observed (p = 0.207).

Agility

The agility performance data before and after the intervention were shown in Fig. 2D. No differences were observed in the IAT time between the groups before the intervention. Within-group decreases in IAT time were observed in the CMB group, the BFRT group, and the EMS group (all p < 0.05) after the intervention. Compared with the BFRT group, the EMS group, and the CTR group presented significant differences in IAT time (all p < 0.05). Similarly, the BFRT group and the EMS group had greater decreases in IAT time compared with the CTR group (all p < 0.05). However, no significant difference between the BFRT group and the EMS group was observed (p = 0.778).

Muscle strength

The muscle strength data before and after the intervention were shown in Fig. 3. No differences were observed in the PT values between the groups before the intervention. Within-group increases in PT values were observed in the CMB, BFRT, and EMS groups (all p < 0.05) after the intervention. Compared with the BFRT group, the EMS group, and the CTR group presented significant differences in PT values (all p < 0.05). A greater increase in PT was also detected in the BFRT group than in the EMS group and the CTR group (all p < 0.05). Similarly, there was a significant PT change in the EMS group compared with the CTR group (p < 0.05).

Muscle activation

The muscle activation data before and after the intervention were shown in Fig. 4. No differences were observed in the RMS values between the groups before the intervention. Within-group increases in RMS values were observed in the CMB group, the BFRT group, and the EMS group (all p < 0.05) after the intervention. Compared with the BFRT group and the CTR group, the CMB group and the EMS group presented significant differences in RMS values (all p < 0.05), whereas there were no significant differences between the CMB group and the EMS group (p = 0.220). A greater increase in the RMS value was also detected in the BFRT group than in the CTR group (all p < 0.05).

Muscle volume

The muscle volume data before and after the intervention were shown in Fig. 5. No differences were observed in the CSA values between the groups before the intervention. Within-group increases in CSA values were observed in the CMB group, the BFRT group, and the EMS group (all p < 0.05) after the intervention. Compared with those in the EMS group and the CTR group, the CSA values in the CMB group and the BFRT group were significantly different (all p < 0.05), whereas there were no significant differences between the CMB group and the BFRT group (p = 0.525). Similarly, there were no significant differences between the EMS group and the CTR group (p = 0.789).

This study focused on male football players with KOA who are unable to perform high-load strength training. By choosing low-load resistance training combined with BFRT and EMS, this study explored whether the combination of BFRT and EMS can compensate for the lack of application effect of either intervention method and thereby improve the sports performance of football players with KOA. In addition, the effects of 8 weeks of BFRT, EMS, and BFRT combined with EMS intervention on muscle strength, muscle activation, and muscle volume in football players with KOA have also been reported.

Knee injury or surgery, aging, lower bone density, sex, and obesity are well-recognized risk factors for KOA⁴⁴. Engaging in continuous physical activity that can easily lead to knee injuries has been identified as a major risk factor for the early onset of KOA⁴⁵. A meta-analysis indicated that sports exerting excessive loads on the hip and knee joints substantially increase the risk of OA⁴⁶. Contact sports such as American football, ice hockey, and handball involve numerous high-impact movements that promote the development of KOA⁴⁴. Multiple epidemiological surveys have revealed that the knee joint is the most frequently injured site among football players. Injury history and insufficient hip control are common triggering factors for knee joint injuries. Furthermore, football is among the sports with the greatest biomechanical stress on the knee joint. Higher-level professional football players have a greater proportion of knee varus alignment than does the general population, and knee varus increases the risk of osteoarthritis and inflammation⁴⁷. The main activities in football include running, accelerating, decelerating, changing directions and jumping without the ball, dribbling, shooting, and confronting between players with and without the ball⁴⁸. Multiple studies have confirmed that KOA is the most common chronic injury among professional football players during and after their careers^49,50. In this study, BFRT and EMS were employed to improve sports performance after 8 weeks. After combining BFRT and EMS, low-intensity squat exercises can improve the speed, jump, and agility of football players with KOA who are unable to engage in high-intensity training. Importantly, this improvement in sports performance is notably superior to combining BFRT or EMS interventions alone. These results can improve the situation where knee osteoarthritis pain prevents football players from engaging in high-intensity strength training, affecting the contraction of lower limb muscles and causing abnormal knee joint movements during exercise."

The biomechanical changes caused by KOA symptoms in football cause a decrease in sports performance, including explosive power and agility, thereby affecting the results of teams and players in competitions. Muscles play important roles in maintaining the stability and flexibility of the knee joint. Changes in thigh muscle strength and muscle mass are also related to the incidence of KOA⁵¹. Currently, there are no drugs supported by high-quality evidence that can improve the clinical symptoms related to KOA and slow its progression. Therefore, it is crucial to find non-surgical and non-pharmacological methods that effectively improve thigh muscle function. Long-term KOA, neuromuscular diseases, and metabolic diseases all lead to a reduction in the CSA and muscle strength of the quadriceps and an increase in quadriceps intramuscular adipose tissue^52,53. These muscle changes lead to the deterioration of lower limb function and decreased exercise performance in KOA patients.

Although Kraemer et al.⁵⁴ have shown that traditional resistance training with a weight of ≥ 70% 1RM is sufficient to induce muscle hypertrophy and improve muscle strength effectively. This study took into account that KOA athletes generally suffer from knee joint pain during heavy weight resistance and selected only low-intensity (25% 1RM) squat training as a strength training method. The role of muscle growth in muscle strength is supported mainly by cross-sectional and retrospective studies. Although strong evidence demonstrating the necessity of increased muscle size for strength gains is lacking, cross-sectional data suggest that athletes have greater lean muscle mass than controls or non-athletes do⁵⁵. Takarada et al.⁵⁶ found that BFRT combined with low-intensity (50% 1RM) resistance training and high-intensity (80% 1RM) resistance training had similar effects on improving muscle strength and muscle circumference growth, and both effects were significant. It is better than low-intensity (50% 1RM) resistance training alone, and it is believed that training combined with BFRT can produce training effects similar to those of high-intensity strength training. Enhancing muscle strength relies not only on CSA enlargement but also on improved innervation and heightened recruitment of motor units. Thus, increasing muscle strength involves increasing muscle size and motor unit activation. The mechanism by which EMS promotes muscle strength growth is closely related to the stimulation intensity and stimulation frequency. Pantović et al.⁵⁷ showed that EMS has the same training effect as traditional high-intensity resistance training in improving muscle strength. EMS can improve the control of motor nerves by the central system and coordinate the agonist and antagonist muscles, thereby promoting the recruitment of motor units and activating more muscle fibers to improve muscle strength. These results revealed that 8 weeks of BFRT combined with EMS can effectively improve PT during knee flexion and extension, the cross-sectional area of the rectus femoris, and the degree of muscle recruitment. The intervention effect was better than that of BFRT or EMS alone. Therefore, this study confirmed that EMS combined with BFRT can improve thigh muscle strength deficits in KOA football players by enhancing muscle recruitment and increasing muscle CSA, effectively preventing further muscle strength loss.

The results of this study revealed that 8 weeks of BFRT combined with EMS resulted in significant changes in the CSA of RF compared with the EMS and low-intensity resistance exercise. Greater muscle size contributes to increased muscle strength, which is positively associated with various aspects of athletic performance. Maximal size and strength are associated with increased power and are associated with many factors related to sports performance, such as sprinting and jumping⁵⁸. These results also confirmed that 8 weeks of BFRT combined with EMS led to greater improvements in 10-m sprint, 20-m sprint, and CMJ performance than did the use of BFRT or EMS alone. The average sprint time in football is approximately 2 s, and the sprint distance is approximately 14 m, which means that athletes in football matches may not necessarily reach their maximum speed in a short sprint⁵⁹. Therefore, the ability to accelerate quickly to achieve high sprint speeds is an important component of a football player’s performance. Although the jumping ability of football is not as high as that of basketball and other sports, actions such as fighting for high-altitude balls and pitching and attacking goals also have certain requirements for jumping ability. In addition, jumping ability is an important indicator used to measure explosive power. Muscle strength and jumping ability demonstrated a notable positive correlation. Lamont et al.⁶⁰ showed that 6 weeks of resistance training can improve 30-cm depth jump performance. This study revealed that BFRT combined with EMS can improve the explosive power of football players with KOA under low-intensity resistance training. In addition to sprinting, football involves multiple continuous direction changes that require high agility. It consists of dynamic movements such as running forward and backward and moving in multiple directions⁶¹. Agility represents the ability to quickly and accurately change the direction of whole-body movement when stimulated⁶². Football players with KOA experience decreased sensitivity due to pain and other reasons, which is related to a decrease in neuromuscular recruitment. EMS has been widely used to improve neuromuscular recruitment. In traditional active training, the brain sends electrical pulse signals to motor nerves to cause muscle contraction. In contrast, the EMS sends electrical pulse signals from the electrical stimulator. The current is distributed and transmitted through the electrode patch, passing through the skin, reaching the nervous system, activating the motor nerves, and then controlling muscle contraction. Fil et al.⁶³ found that 4 weeks of EMS (30–35 Hz, 250–350 µs) can increase EMG electrical signals and muscle strength, thereby preventing muscle atrophy after stroke. This finding is consistent with our results. Both BFRT combined with EMS and EMS alone can improve neuromuscular recruitment of the rectus femoris and effectively shorten the duration of the IAT. These findings suggest that BFRT can improve the explosiveness and agility of football players with KOA to improve sports performance.

This study has several limitations. First, this study included only male football players with KOA, and the results of this study have a certain gender bias. As women's participation in multiple sports, such as football, increases annually, future studies can recruit female football players with KOA as subjects to clarify the intervention effects for subjects of different genders. Second, this study focused only on the effect on sports performance, but sports performance is usually negatively correlated with the injury rate. The injuries of the subjects in football during the intervention period can be recorded later to clarify the effect of BFRT combined with EMS on injury prevention.

BFRT combined with EMS for low-intensity squat training can increase muscle strength and improve the explosiveness and agility of football players with KOA by increasing muscle volume and improving neuromuscular recruitment.

Competing interests

The authors declare no competing interests.

Fundings

This study was supported by the Basic Cultivation Project of Sichuan Provincial Expert Workstation and Institute of Sports Medicine and Health of Chengdu Sports University (No: SCZJJCC-16), the China National Natural Science Foundation Cultivation Project of Chengdu Sport University (No: 23YJPY10), and the Key Laboratory of Sports Medicine of Sichuan Province and the State Sports General Administration of China (No: 2023-A022).

Author Contribution

Jinfeng Yang, Na Li, and Yuanpeng Liao conceptualized the study and its methodology. Jinfeng Yang, Xiao Peng, and Yunyan Zhou supervised the intervention. Jinfeng Yang, Na Li, Sheng He, and Jinqi Yang performed the data collection and curation. Jinfeng Yang, Na Li, and Jianxin Chen performed the data analysis. Jinfeng Yang, Na Li, Jinqi Yang, and Jianxin Chen interpreted the results and wrote the original manuscript. Jinfeng Yang, Na Li, and Yuanpeng Liao wrote and critically reviewed the final version. All the authors read and approved the final manuscript.

Acknowledgement

The authors would like to express their gratitude to the Football Academy and the Department of Sports Medicine and Health Football Team of Chengdu Sport University for their valuable assistance.

Data Availability

The datasets and materials used and analyzed in the current study are available from the corresponding author upon reasonable request.

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Effects of blood flow restriction combined with electrical muscle stimulation on muscle functions and sports performance in male football players with knee osteoarthritis: a randomized controlled trial

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Study Design

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Speed

Jump

Agility

Muscle Strength

Muscle Activation

Muscle volume

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Results

Speed

Jump

Agility

Muscle strength

Muscle activation

Muscle volume

Discussion

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Competing interests

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