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[Purpose] Understanding the neuromuscular cooperativeness functions when an athlete is fatigued is essential in preventing sports injuries and examining post-injury return standards. This study aimed to investigate the kinds of changes in neuromuscular cooperativeness before and after fatigue loading. [Participants and Methods] Fifteen female university athletes were examined for chronological changes in neuromuscular cooperativeness. Muscle fatigue loading was performed using BIODEX (180°/s) during knee flexion and extension exercises on one side. Surface electromyography of the rectus femoris and biceps femoris was performed on both sides before and immediately, 5 min, 10 min, and 15 min after loading. The switching silent period and pre-motor time were calculated from the electromyographic waveforms to indicate neuromuscular cooperativeness. [Results] The switching silent periods in the loading side immediately and 5 min after loading were significantly prolonged compared with that before loading. [Conclusion] Muscle fatigue loading instantaneously prolonged the switching silent period and decreased the neuromuscular cooperativeness. Furthermore, recovery generally occurred within 10 minutes after loading.

The purpose of the present study was to investigate the effects of using a combination of static stretching and aerobic exercise on muscle tendon unit stiffness and muscle strength in the ankle plantar-flexor muscles. Fifteen healthy males (23.3 ± 2.7 years, 170.3 ± 6.5 cm, 64.9 ± 8.7 kg) received three different interventions, in random order. Intervention 1 received 10 min of aerobic exercise after five cycles of one minute of static stretching. Intervention 2 received 10 min of aerobic exercise before the static stretching. Intervention 3 received 5 min of aerobic exercise both before and after the static stretching. The range of motion of ankle dorsiflexion, stretch tolerance, muscle tendon unit stiffness, peak torque of ankle plantarflexion, and the amplitude of electromyography were measured. In all interventions, the range of motion and stretch tolerance significantly increased (

To the best of our knowledge, most previous studies regarding the epidemiology of injuries in rugby union (rugby) players have focused on professional players. Therefore, data on injuries in collegiate rugby players in Japan is limited. The purpose of this study was to conduct a prospective injury survey of Japanese male collegiate rugby players over several years and to analyze the injuries that occurred during matches and training according to field position, type of injury, and mechanism of injury. This prospective study initially registered 128 rugby players from one university club. The occurrence of injuries was recorded by athletic trainers during the rugby seasons between 2017 and 2019. The total injury rate (IR) was 7.26 injuries/1000 player-hours (1000 PHs). The match IR (122.73 injuries/1000 PHs) was almost 31.9 times higher than the training IR (3.84 injuries/1000 PHs). Ankle sprains/ligament injuries (17.7%; 1.28 injuries/1000 PHs) were the most common injuries, in addition to acromioclavicular joint injuries in forwards and hamstring strain injuries in backs. The most common injury mechanism was tackling (16.4%). Injury characteristics differed according to field position; therefore, preventive measures according to field position are necessary. Moreover, the high number of tackle injuries suggests that improved tackle skills would help reduce injuries. The IR among Japanese collegiate rugby players was higher than that reported previously. Injury prevention training for collegiate players is necessary to reduce the number of injuries.

Head Injury Assessment (HIA) is the screening tool for head injury during a rugby game. The purpose of this study was to investigate the epidemiology of HIA in the Japan Rugby Top League (JRTL). The incidences of HIA, defined concussion (per 1,000 player-hours) and repeated concussions were evaluated in three seasons (2016-17, 2017–18, 2018–19; total 360 games). The HIA incidence rates were 12.7 (95% confidence interval 9.5–15.9), 20.8 (16.8–24.9), and 25.0 (20.5–29.5) in each season. HIA-1 criteria 2, which is applied for suspected concussion cases, was performed for 46 cases in the 2016–17 season, 81 cases in the 2017–18 season, and 88 cases in the 2018–19 season. The concussion incidence rates were significantly greater in the 2017–18 season (9.6/1000 player-hours, 95% confidence interval 6.8–12.4) and the 2018–19 season (14.4, 11–17.8) compared to the 2016–17 season (4.8, 2.8–6.8). The number of repeated concussion cases in the same season was 1 in the 2016–17 season and 4 in both the 2017–18 and 2018–19 seasons. This study confirmed significantly higher HIA and concussion incidence rates over time. Although the HIA system might have been established in the three seasons in JRTL, comprehensive management needs to be improved to prevent repeated concussions.

While previous research has identified the reasons for the concussion-reporting behavior of rugby union players, the influence of confounding factors such as concussion experience, education, and knowledge of concussion symptoms, any of which may have influenced the results, has not been considered. This study aimed to clarify the reasons for the reporting behavior of college rugby union players regarding suspected concussion symptoms by adjusting for confounding factors using the propensity score. A questionnaire about both concussion knowledge and concussion-reporting behavior was administered to 240 collegiate rugby union players. Of the 208 (86.7%) valid respondents to the questionnaire, 196 (94.2%) had experienced any one symptom of a suspected concussion, such as headache, at least once, and 137 (65.9%) reported symptoms to someone else. This study’s results revealed two important reasons for reporting symptoms: (1) the willingness of players to report experienced symptoms to someone else, along with realizing a concussion, and (2) the willingness of players to report suspected concussion symptoms, despite the absence of a doctor or trainer. These results suggest that providing educational opportunities to recognize suspected concussion symptoms and establishing a team culture of reporting physical problems to someone else is important for improving concussion-reporting behavior.

Japan has no streamlined concussion education for collegiate athletes, and guidelines vary by sport. In particular, research on knowledge of, and attitudes toward, concussion is necessary for the establishment of concussion education for Japanese collegiate athletes. The aim of the present study was to assess the knowledge of, and attitudes toward, concussion in Japanese male collegiate athletes and to investigate their experiences with suspected concussion symptoms. An online questionnaire was administered to 390 collegiate athletes participating in the following five sports with a high incidence of concussion: rugby union, soccer, basketball, American football, and judo. Of the 121 valid responses, 91 (77.1%) indicated that they had experienced suspected concussion symptoms at least once and 46 of these 91 respondents had not reported their symptoms of suspected concussion at least once. Athletes who had never experienced concussion symptoms were significantly less likely to recognize the symptoms of concussion (p < 0.001). Most athletes recognized headache and dizziness as suspected concussion symptoms. However, the recognition rate for several symptoms was lower than the prevalence of these symptoms as shown in previous studies. This suggests that educational initiatives might be important to bridge the gap between athletes' knowledge and understanding of frequently occurring concussion symptoms and to improve reporting behavior.

Background Increased strain of the iliotibial band (ITB) is a plausible contributing factor for the development of iliotibial band syndrome (ITBS). Although several studies have found relationships between the strain of the ITB and kinematic factors during running, the associations of the ITB strain with knee alignment and sex, which are considered intrinsic factors, are not well understood. Objective To clarify the sex differences in the ITB strain between genu varum and normal knee alignments in different postures. Design Observational cross-sectional study. Setting Laboratory research within a university. Participants Forty-four healthy recreational athletes (21 men and 23 women) volunteered for this study and were divided into four groups by sex and knee alignment: men with genu varum alignment, men with normal knee alignment, women with genu varum alignment, and women with normal knee alignment. Methods An ultrasound real-time elastography (RTE) unit was used for distal ITB strain measurements in weight bearing and for different non-weight-bearing: neutral, knee flexion, hip adduction, and hip adduction with knee flexion. Gender information and the intercondylar distance data were collected to divide the participants into two groups. Main outcome measurements Main Outcome was the ITB strain (strain ratio) measured by the RTE. Results There were no significant differences in neutral and hip adduction postures among the four groups. However, during weight-bearing, the women's genu varum group (6.91 ± 1.69; Mean ± SD) exhibited greater strain than both the men's normal group (3.50 ± 1.04, P = .005) and the women's normal group (4.42 ± 1.42, P = .048). In addition, there were significant positive correlations between the intercondylar distance and the ITB strain during weight-bearing (r = 0.315, P = .037). Conclusions The women's genu varum group exhibited a higher ITB strain during weight-bearing, which may be related to the high incidence of ITBS in women athletes. Furthermore, the changes in alignment and muscle activities during weight-bearing could influence the strain of the ITB. Level of evidence III.

The purpose of this study was to determine the factors related to the occurrence of concussion in rugby tacklers. Match video records showing tackles leading to concussion were used to identify injury-inciting events. Additionally, noninjury tackles by concussed tacklers (prior to concussion) and position-matched tacklers from the same matches were used as a control cohort. All tackles were coded according to the tackling characteristics. The odds ratio (OR) was reported by logistic regression. The results demonstrated that a side step of the ball-carrier reduced the risk of concussion for tacklers (OR = 0.13 [95% CI, 0.03-0.58]; P = .008). Conversely, the tackler's head/neck contacting the ball-carrier (OR = 18.62 [95% CI, 4.59-75.49]; P < .001) and not remaining bound to the ball-carrier since making initial contact (OR = 4.38 [95% CI, 1.69-11.34]; P = .002) were identified as risk factors for the concussion of tacklers. These results suggest that avoidance movements of the ball-carrier prior to tackling reduced the risk of concussion and that incorrect tackling techniques contributed to an increased occurrence of concussion. Furthermore, the probability of concussion for tacklers increased when their head was in front or to one side of the ball-carrier, and the direction of the tackle also affected the risk of concussion, especially from the side. Therefore, it is important to emphasize the tackler's head position in conjunction with the direction of tackle.

BACKGROUND: Chronic adaptations, including persistent sensorimotor deficits, remain in individuals with a history of ankle instability, resulting in altered postural control strategies during functional tasks such as gait, running, or landing. However, we do not know the contribution of the altered somatosensory input on postural control strategies during a dynamic balance task such as the Star Excursion Balance Test (SEBT). RESEARCH QUESTION: The purpose of this study was to characterize postural control strategies with and without disrupted somatosensory input during a dynamic balance task in people without chronic ankle sprain. METHODS: This study was a crossover study design. Twenty healthy young adults (10 men, 10 women; age = 23.9 ± 3.0 years, height = 174.2 ± 7.4 cm, mass = 71.2 ± 16.7 kg) performed the posteromedial reach test during the SEBT while standing on the ground and on foam. We measured the maximum reach distance (MRD); joint angles of the ankle, knee, hip, and trunk in the sagittal, frontal, and transverse planes; and position and displacement of the center of mass (COM) and center of pressure (COP) during the posteromedial reach task. RESULTS: The MRD was shorter when standing on the foam than on the ground (p < 0.001). There was a condition by phase interaction for ankle dorsiflexion; tibia internal rotation; and trunk flexion (p < 0.001; p = 0.03; p = 0.01, respectively). The COM and COP were positioned more laterally on the foam (p < 0.001). The COM and COP anterior-posterior displacements were more anterior during the foam condition (p = 0.017). SIGNIFICANCE: By using a foam pad to disrupt somatosensory information, participants demonstrated altered strategies to control the joint kinematics, COM, and COP, as a function of posteromedial distance. Ankle and trunk movement strategies may influence the posteromedial reach distance. This model may simulate changes that occur with chronic ankle instability.

The main purpose of this scoping review was to summarize the most common tasks and outcome measures in randomized control trials (RCTs) used to assess sensorimotor function following ankle sprain and chronic ankle instability (CAI). We also aimed to summarize the description of inclusion criteria used in articles. We searched for RCTs published between 2008 and 2018 using the following databases: MEDLINE, PubMed, SPORTDiscus, and Web of Science. Eligible studies included participants of either sex who had had at least one ankle sprain with/without subsequent CAI. All articles assessed sensorimotor function. The tasks, outcome measures, and inclusion criteria were categorized, and frequencies of use in each category were calculated. Of 272 publications, 31 met the eligibility criteria. The most common task was single-limb stance (58% of 31). The most common outcome measure was the posterior-medial reach distance of the Star Excursion Balance Test (SEBT) (13 of 16 articles, 81%). Different inclusion criteria for a history of ankle sprains or CAI were used. A wide range of sensorimotor assessments and inclusion criteria was used among studies involving individuals with a history of ankle sprain with or without CAI, which could make it difficult to compare and generalize study results. This scoping review provides a baseline for planning future studies exploring outcome measures to assess sensorimotor function of individuals with a history of ankle sprain with or without CAI.

Background/objective Anterior cruciate ligament injuries are prone to re-injury, and it is crucial to prevent the primary injury. One of the anatomical risk factors for anterior cruciate ligament injury is the posterior tibial slope angle. Investigating the characteristics of healthy individuals with respect to the posterior tibial slope angle is important to elucidate the risk of developing anterior cruciate ligament injuries. The purpose of this study was to determine the characteristics related to sex and of the posterior tibial slope angle in healthy Japanese subjects, and the effect of the dominant lower extremity. Methods Sixty-two knees of 31 healthy Japanese college students (15 males and 16 females) were included in this study. Magnetic resonance images of both knee joints of the subjects were measured using a 0.3 T scanner. The medial and lateral posterior tibial slope angles were measured from the obtained magnetic resonance images. Magnetic resonance images of the knee joint of the dominant lower extremity were used to compare differences in sexes between the medial and lateral posterior tibial slope angles. Bilateral knee joint magnetic resonance images were used to compare the dominant and non-dominant lower extremities. Independent t-tests were used to compare the differences regarding sex in the medial and lateral posterior tibial slope angles and to compare the dominant and non-dominant lower extremities. Results A comparison of the mean lateral posterior tibial slope angle showed that males had a 8.8 ± 1.7° angle, while females had a 10.3 ± 2.2° angle, which was significantly greater (p = 0.047). There was no significant difference comparing the posterior tibial slope angle between the dominant and non-dominant lower extremities (p = 0.430). Conclusions From the result of this study, the lateral posterior tibial slope angle was significantly higher in the female group than in the male group. However, both the medial and lateral posterior tibial slope angles were found to be unaffected by the dominant lower extremity.

Background: Rugby is a high risk of injury to the ankle, but epidemiological data on ankle injury is limited to specific competition levels and generations. This study aimed to clarify the epidemiological characteristics of ankle sprain by longitudinally investigating the incidence, severity and burden of ankle sprains in men's collegiate rugby players. Methods: The study recorded ankle sprains in rugby matches and training across three seasons from 2017 to 2019, investigating 128 male collegiate rugby players.Results: The incidence of ankle sprain was 1.21 injuries/1000 Player-hours (1000 PHs), and the risk of occurrence during matches (18.18 injuries/1000 PHs) was 25.6 times higher than during training (0.71 injuries/1000 PHs). Thus, it was thought that reducing the incidence of ankle sprains during matches would contribute greatly to reducing the loss of competition time due to injury of team members. The results suggested that the main injury mechanism was related to contact play and steps, and that contact skills and physical fitness characteristics were also involved in the risk of sprains. The incidence of ankle sprains in collegiate rugby players was higher than that reported in a previous study on professional-level players, and the rate of initial sprains was high in this study. Conclusions: This suggests that prevention of ankle sprains is important in university age rugby players.

Background: Neurocognitive function may be a risk factor for anterior cruciate ligament (ACL) injury by changing neuromuscular control such as muscle activities. However, the effect of differences in neurocognitive function on biomechanics and neuromuscular control related to ACL injury risk is not clear. The purpose of this study was to examine the effect of differences in neurocognitive function on biomechanics and neuromuscular control during an unanticipated side-step cutting motion. Method: The subjects were 15 collegiate female athletes who were divided into two groups using the Symbol Digit Modalities Test (SDMT). The experimental task was an unanticipated side-step cutting motion from a 30 cm high box. We calculated joint angles and moments using a 3-dimensional motion analysis system from the dominant leg, and measured muscle activities using a surface electromyography. We calculated the co-contraction ratio (CCR) as relative muscle activity of the quadriceps to the hamstring. Results: As a result, subjects with a lower SDMT score had significantly increased quadriceps activity before and after ground contact and decreased CCR only after ground contact. Conclusion: In the lower SDMT score group, the quadriceps showed stronger muscle activity than the hamstring during an unanticipated side-step cutting motion. This dominant quadriceps muscle activity has been reported to increase the load on the ACL, and there was a possibility of increasing the risk of the ACL injury. Considering these factors, subjects with lower neurocognitive function could have a high risk of ACL injury due to alterations in muscle activities surrounding the knee.

[Purpose] The aim of this study was to investigate the influence of baseline muscle tendon unit stiffness on static stretching. [Participants and Methods] Eighteen healthy males were divided into two groups according to their muscle tendon unit stiffness as follows: High (n=9) and Low (n=9). Flexibility assessment was performed before and after 10 minutes of static stretching. Alterations in range of motion, passive torque at the terminal range of motion, muscle tendon unit stiffness, muscle tendon junction displacement, and tendon length were examined. [Results] No significant interactions were found in all the measurements. After static stretching, the range of motion, passive torque, muscle tendon junction displacement, and tendon length increased, while muscle tendon unit stiffness decreased. There were significant differences in range of motion, muscle tendon unit stiffness, and muscle tendon junction displacement between the groups. [Conclusion] Ten minutes of static stretching increased the range of motion through a decrease in muscle tendon unit stiffness and an increase in tolerance in both groups. Differences in muscle tendon unit stiffness and muscle tendon junction displacement caused the differences in range of motion. Baseline muscle tendon unit stiffness had no effects on static stretching.

The purpose of this study was to describe the incidence, severity, mechanism, and intrinsic risk factors for knee injuries in Japanese collegiate rugby union players. Initially, 119 rugby union players from one university club were registered in this prospective cohort study. The occurrence of knee injuries was recorded by a team doctor and athletic trainers during the 2009-2012 playing seasons. The number of knee injuries recorded during these four seasons was 64. The incidence of knee injuries was significantly higher during matches (10.5 injuries/1000 player hours [ph]) than that during training (0.3 injuries/1000 ph). The most common match injury was the medial collateral ligament injury (4.4 injuries/1000 ph). The greatest severity and burden were observed for anterior cruciate ligament injuries (severity: 182.5 days, burden: 310.3 days/1000 ph). A majority of knee injuries were sustained during ruck/maul (26.6%) and step/cutting (20.3%). In addition, a history of injury (odds ratio [OR]: 3.3, 95% confidence interval [CI]: 1.3-8.4, p = 0.01) and rugby experience (

[Purpose] This study aimed to examine whether or not friction massage of the popliteal fossa would be effective for achieving dynamic changes in muscle oxygenation and ankle flexibility. [Subjects and Methods] Twelve healthy male university students participated. Before and after friction massage, dynamic changes in muscle oxygenation and ankle flexibility were measured by near-infrared spectroscopy to evaluate its efficacy. [Results] Oxygenated hemoglobin was significantly higher after as compared to before massage. The range of ankle dorsiflexion tended to increase after massage. [Conclusion] These results suggest that friction massage of the popliteal fossa stimulates venous return in the lower leg.

Takeuchi, K, Takemura, M, Nakamura, M, Tsukuda, F, and Miyakawa, S. Effects of active and passive warm-ups on range of motion, strength, and muscle passive properties in ankle plantarflexor muscles. J Strength Cond Res 35(1): 141-146, 2021-The purpose of this study was to examine the effects of active and passive warm-ups on flexibility and strength of calf muscles. Fourteen healthy males (age: 23.1 ± 2.6 years, height: 172.7 ± 5.6 cm, and body mass: 64.5 ± 7.0 kg) performed 3 types of warm-ups respectively for 10 minutes in a random order: an active warm-up by pedaling a cycling ergometer, an active warm-up doing repeated isometric contractions, and a passive warm-up in a hot water bath. To assess flexibility, range of motion (ROM) of ankle dorsiflexion, passive torque of ankle plantarflexion, and muscle tendon junction (MTJ) displacement were measured and then muscle tendon unit (MTU) stiffness was calculated. After the flexibility assessment, peak torque during maximum voluntary isometric contraction was measured to assess the isometric strength. These data were compared before and after each warm-up. As a result, all 3 types of warm-ups increased ROM (p0.05) and passive torque at terminal ROM (p0.01), but there were no significant changes in MTU stiffness or MTJ displacement. The active warm-up by pedaling a cycling ergometer increased peak torque during isometric contraction (p0.05), whereas the other warm-ups did not show significant alterations. In conclusion, the active warm-up with aerobic exercise increased flexibility and strength of the calf muscles.

Background/Aim During competitive diving, divers jump up from 1 to 3 m springboards or 5 to 10 m platforms and dive into the water. The impact forces are very large in the water entry phase, and, as such, microtraumatic injuries are common due to the tremendous physical stress placed on the diver. Low-back pain (LBP) is the most frequently reported symptom in divers. This study aimed to extract possible risk factors related to LBP from physical and technical characteristics in Japanese elite junior divers. Methods Eighty-three elite junior divers (42 men and 41 women) in Japan were included in this study. LBP was assessed by a questionnaire, interview and physical examination during a national training camp. Morphological data, physical fitness and diving skills were also evaluated. The factors related to LBP were extracted by using logistic-regression analysis and the forward-selection method (likelihood ratio). Results A total of 37.3% (31 reports) of back pain occurred in the lumbar region. Shoulder flexibility (OR 0.919; 95% CI 0.851 to 0.992) and age (OR 0.441; 95% CI 0.239 to 0.814) were recognised as factors related to LBP in male-elite junior divers, whereas only age (OR 0.536; 95% CI 0.335 to 0.856) was a factor in female-elite junior divers. Conclusions Our results suggest that shoulder flexibility is important for preventing LBP in elite-male junior divers, since they require full shoulder flexion during the water entry phase. Limited shoulder flexibility could cause lumbar hyperextension when adjusting for the angle of water entry.

In competitive diving, divers jump up from 1 or 3 m springboards or 5-10 m platforms and dive into the water. At the time of water entry, the force of impact is very large, which places tremendous physical stress on the diver. However, there are few investigations about injury occurrence in divers, especially during the junior period. Thus, this study aimed to describe the prevalence of injuries among elite junior divers over a 7-year period. One hundred and sixteen (60 male, 56 female) Japanese elite junior divers were included in this study. Parts of pain and injury incidence scene that the divers experienced were assessed by questionnaires during national training camps. Low back pain(LBP)was assessed by interviews, and physical examinations. The major findings were as follows: (1) Among all types of injuries, there was high prevalence of LBP (38.4%) in elite junior divers in Japan. (2) Most injuries occurred at the time of water entry.