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The magnitude of trunk acceleration reflects the ground reaction force. This study compared the frequency of high trunk accelerations during single-leg landing after an overhead stroke between junior and adolescent badminton players, and examined the difference in each directive magnitude according to age and landing leg. Thirty-eight female badminton players (17 junior and 21 adolescent athletes) played two singles games while wearing a tri-axial accelerometer on their upper back. The frequency and 95% confidence interval (CI) of single-leg landings that generated >4-G resultant acceleration, and each directive magnitude were calculated. A two-factorial analysis of variance (factor 1: group, factor 2: landing leg) was performed to determine the effects of age and different landing patterns. Frequency of single-leg landings following an overhead stroke in the adolescent athletes (mean, 1.71 cases/min; 95% CI, 1.59-1.83 cases/min) was higher than that in the junior athletes (mean, 1.13 cases/min; 95% CI, 1.01-1.25 cases/min). The adolescent athletes exhibited greater mediolateral acceleration in the movement towards racket-hand leg and anteroposterior acceleration in the movement towards the opposite leg than the junior athletes. This cross-sectional study suggests that the frequency and movement pattern associated with high-load landing in badminton games differ between junior and adolescent athletes.

Hamstring strain often occurs when an opponent unanticipatedly perturbs an athlete's movements. We examined the neuromuscular responses of hamstring and trunk muscles during unanticipated trunk perturbations in athletes with and without a history of hamstring strain injury. Male college athletes (11 with a history of a unilateral hamstring injury and 10 without prior injury) knelt while wearing a chest harness attached to a cable that was pulled backward. They were instructed to resist the force isometrically and maintain their position when the perturbations were applied. The pressure was released with or without a cue (CUE or NoCUE). We measured trunk acceleration, three-dimensional kinematic data, and surface electromyography (EMG) signals of the erector spinae, internal oblique, gluteus maximus, biceps femoris long head, and semitendinosus muscles. Maximum trunk acceleration and displacement were greater with NoCUE in both groups (p < 0.05). EMG amplitude did not differ after perturbation of any investigated muscle. The injured group demonstrated a delayed onset of the gluteus maximus and erector spinae muscles in NoCUE versus CUE stimuli (p < 0.05). Athletes with a history of hamstring strain injury exhibited a reduced neuromuscular coordination of the lumbopelvic muscles in response to unanticipated trunk movement.

In this study, we aimed to clarify the characteristics of neuromuscular function, kinetics, and kinematics of the lower extremity during sprinting in track and field athletes with a history of strain injury. Ten male college sprinters with a history of unilateral hamstring injury performed maximum effort sprint on an athletic track. The electromyographic (EMG) activity of the long head of the biceps femoris (BFlh) and gluteus maximus (Gmax) muscles and three-dimensional kinematic data were recorded. Bilateral comparisons were performed for the EMG activities, pelvic anterior tilt angle, hip and knee joint angles and torques, and the musculotendon length of BFlh. The activity of BFlh in the previously injured limb was significantly lower than that in the uninjured limb during the late-swing phase of sprinting (

BACKGROUND This study evaluated the status of sports participation and training frequency during school years to identify related factors for injuries in the general Japanese population. METHODS A total of 1,533 adult participants (762 males, 771 females) retrospectively completed a questionnaire assessing sports participation (single/multisport), training frequency (weekly days of sports participation), and injury history (acute and overuse) at each stage of school (elementary, junior high, and high school). RESULTS In total, 41.1% of participants reported playing multiple sports in elementary school; this rate decreased to 17.4% in junior high school and 8.9% in high school. Weekly days of sports participation were associated with almost all injuries at each age. Participants who still played multiple sports in junior high school had fewer overuse injuries in junior high school and high school (P = 0.017; odds ratio (OR) = 0.69; 95% confidence interval (CI) = 0.51-0.94; P = 0.006, OR = 0.66, 95% CI, 0.49-0.89, respectively). The ratio for sports sampling differed between elementary school and older ages. This trend was associated with the prevalence of overuse injuries. CONCLUSION Promoting sports sampling through junior high school ages and controlling the training frequency may decrease the occurrence of injuries in young athletes.

Yasuharu Nagano,1 Yui Shimada,2 Naoki Sasaki,1 Masaki Shibata1 1Faculty of Physical Education, Japan Women’s College of Physical Education, Tokyo, Japan; 2Faculty of Health Sciences, Tokyo Ariake University of Medical and Health Sciences, Tokyo, JapanCorrespondence: Yasuharu NaganoFaculty of Physical Education, Japan Women’s College of Physical Education, 8-19-1, Kitakarasuyama, Setagaya, Tokyo, 157-8565, JapanTel +81-3-3300-5437Fax +81-3-3300-5437Email nagano.yasuharu@jwcpe.ac.jpIntroduction: The purpose of this prospective cohort study was to investigate the prevalence and burden of “any physical complaint” in college female basketball athletes using a daily questionnaire.Methods: Fifty-four female college basketball players were recruited and followed up for 135 days using the Oslo Sports Trauma Research Centre questionnaire.Results: The questionnaire response rate was 96.4% (95% confidence interval: 95.7– 97.1). The average daily prevalenceof any problem was 44.4%, whereas that of substantial problems was 16.0%. The anatomical areas found to be most frequently affected by physical problems were the ankle (average daily prevalence: 14.5%, 95% confidence interval: 13.4– 15.7), lower back (14.4%, 95% confidence interval: 13.7– 15.2), and knee (9.6%, 95% confidence interval: 9.0– 10.2). The cumulative severity score, calculated by summing severity scores and dividing by number of respondents, showed that ankle, knee, and lower back problems exhibited greater relative burden.Discussion: Injuries common in basketball athletes, such as ankle sprain, anterior cruciate ligament injury, overuse knee pain, and low-back pain, are reflected in the present data.Keywords: epidemiology, sports injuries, overuse injuries, ankle, knee

Objectives Detection of the frequency or intensity of high-impact movements during volleyball match would help understand physical load causing the injuries. The present study aimed to classify different volleyball-specific high-impact movements based on the measurement of trunk acceleration in a volleyball match as a cross-sectional study. Methods Linear accelerations of six female volleyball players were measured during a single volleyball match. The instances at which >4G and >6G of resultant acceleration was generated were detected. Movements recorded with a synchronized video were also detected and categorized. Counts (cases) and frequencies (cases/min) of the detected movements were calculated, and the resultant and each directional acceleration among the top seven volleyball-specific detected movements were compared. Results For attackers, 361 and 97 movements were detected for the resultant acceleration thresholds over 4G and 6G, respectively. Landing, takeoff and running were the top three detected movements in both thresholds. Landing was the most frequently observed high-impact movement, and the ratio of landing over 6G was greater among all detected movements compared with the ratios of landing over 4G threshold. For receivers, 297 and 38 movements were detected for the resultant acceleration thresholds over 4G and 6G, respectively. Running, steps on the spot, and steps forward or backward were the top three detected movements. The top seven detected volleyball-specific movements generating over 4G were landing after blocking, landing after spiking, takeoff before spiking, takeoff before blocking, stationary steps during receiving, steps forward or backward during receiving and sidesteps during receiving. Resultant and vertical accelerations of landing after spiking were significantly greater than those of the other six movements (p < 0.001). Conclusions Using the results of present study, we were able to estimate the physical load causing injuries during a real volleyball match.

The purpose of the present study was to translate and modify the Oslo Sports Trauma Research Centre (OSTRC) overuse injury questionnaire into Japanese and validate it among Japanese athletes through a longitudinal survey. A modified back-translation method was used to translate the questionnaire from English to Japanese. The longitudinal survey was performed in 29 female college swimmers who were followed up for more than 24 consecutive weeks. The response rate to the 24 weekly questionnaires was 88.8% (95% confidence interval [CI]: 85.2-92.3). Internal consistency was measured by using Cronbach's alpha (0.73 (0.69-0.77)). The anatomical areas most frequently affected by overuse injuries were the lower back (average weekly prevalence: 27.6%, 95% CI: 25.1-30.1), shoulder (16.0%, 95% CI: 13.7-18.2), knee (9.9%, 95% CI: 7.7-12.0), and ankle (9.0%, 7.6-10.5). The severity score showed that knee (22.5, range: 6-65), ankle (21.5, range: 6-67), and lower back (20.7, range: 6-80) injuries had the greatest impact. The Japanese version of the modified OSTRC overuse injury questionnaire demonstrated reliability and validity based on the results of internal consistency and trend of injury of the swimmers. The participants in the present study did not have substantial injuries or time-loss injuries and continued practicing and competing, despite these minor injuries. Although knee and ankle injuries do not occur as often as lower back and shoulder injuries, these injuries often had a greater impact on swimmers when they did occur.

The purpose of this study was to measure the change in hamstring muscle thickness between contracting and relaxing conditions following a return to sports after a hamstring muscle strain and thereby evaluate muscle function. Six male track and field sprinters participated in this study. All had experienced a prior hamstring strain injury that required a minimum of 2 weeks away from sport participation. Transverse plane scans were performed at the following four points on the affected and unaffected sides under contracting and relaxing conditions: proximal biceps femoris long head, proximal semitendinosus, middle biceps femoris long head, and middle semitendinosus. The results demonstrated an increase in the thickness of the middle biceps femoris long head and middle semitendinosus regions on the unaffected side with contraction, whereas the affected side did not show a significant increase. The proximal semitendinosus muscle thickness was increased with contraction on both the unaffected and the affected sides. By contrast, the proximal biceps femoris muscle thickness did not show a significant increase on both sides. The results of this study show that evaluation of muscle thickness during contraction may be useful for assessing the change in muscle function after a hamstring muscle strain injury.

Introduction Raising awareness on a disorder is important for its prevention and for promoting public health. However, for sports injuries like the anterior cruciate ligament (ACL) injury no studies have investigated the awareness on risk factors for injury and possible preventative measures in the general population. The sources of information among the population are also unclear. The purpose of the present study was to identify these aspects of public awareness about the ACL injury. Materials and methods A questionnaire was randomly distributed among the general population registered with a web based questionnaire supplier, to recruit 900 participants who were aware about the ACL injury. The questionnaire consisted of two parts: Question 1 asked them about their sources of information regarding the ACL injury; Question 2 asked them about the risk factors for ACL injury. Multivariate logistic regression was used to determine the information sources that provide a good understanding of the risk factors. Results and discussion The leading source of information for ACL injury was television (57.0%). However, the results of logistic regression analysis revealed that television was not an effective medium to create awareness about the risk factors, among the general population. Instead “Lecture by a coach”, “Classroom session on Health”, and “Newspaper” were significantly more effective in creating a good awareness of the risk factors (p < 0.001).

The purpose of this study was to investigate the time series relationships between the peak musculotendon length and electromyography (EMG) activation during overground sprinting to clarify the risk of muscle strain injury incidence in each hamstring muscle. Full-body kinematics and EMG of the right biceps femoris long head (BFlh) and semitendinosus (ST) muscles were recorded in 13 male sprinters during overground sprinting at maximum effort. The hamstring musculotendon lengths during sprinting were computed using a three-dimensional musculoskeletal model. The time of the peak musculotendon length, in terms of the percentage of the running gait cycle, was measured and compared with that of the peak EMG activity. The maximum length of the hamstring muscles was noted during the late swing phase of sprinting. The peak musculotendon length was synchronous with the peak EMG activation in the BFlh muscle, while the time of peak musculotendon length in the ST muscle occurred significantly later than the peak level of EMG activation (p < 0.05). These results suggest that the BFlh muscle is exposed to an instantaneous high tensile force during the late swing phase of sprinting, indicating a higher risk for muscle strain injury.

The purpose of this study was to analyze the mechanism of anterior cruciate ligament (ACL) injuries among male and female high school students across several different sports to understand ACL injury trends. A total of 1000 cases involving high school students who suffered ACL injuries during school activities (soccer, basketball, volleyball, handball, and judo) and who received insurance benefits through the Injury and Accident Mutual Aid Benefit System, were included to clarify the various mechanisms of ACL injuries. The mechanism of ACL injury was divided into contact and non-contact injuries. Contact injuries were further divided into direct and indirect contact injuries. Non-contact ACL injuries were also further divided into landing injuries, which involved jump-landing movements, and cutting and stopping injuries, which involved movement with a change of direction and deceleration. Overall, 99.0% of judo ACL injuries were categorized as contact ACL injuries. With regards to ball sports, the number of non-contact ACL injuries among basketball, volleyball, and handball players was significantly higher than the number of contact injuries (67.0%, 86.5%, and 68.5% respectively). With regards to female soccer and basketball players, the number of indirect ACL injuries was higher than direct injuries (72.2% and 76.7%, respectively). Volleyball was associated with a higher rate of non-contact injuries. Soccer, basketball, and handball were associated with more or similar rates of indirect and non-contact injuries than direct injuries. Judo was associated with a higher rate of contact injuries.

Background: The risk of anterior cruciate ligament (ACL) injury is higher in female soccer players than in male soccer players. The most common reason for non-contact ACL injury has been found to be a cutting or stopping maneuver combined with deceleration and landing from a jump. In a previous study, there was no difference in the incidence of ACL injury between offensive and defensive players and in the risk of ACL injury between goalkeepers and other players. Recently studies reported that the most frequent injury situation was pressing in male players. However, the most common type of situation associated with ACL injury in female soccer players has not been clarified. Objectives: The purpose of the present study was to identify the most common type of situation associated with ACL injury in female soccer players. Methods: We handed out questionnaires to 80 female soccer players with a history of ACL injury (90 ACL injuries). The players were asked about the injury characteristics, injury circumstance, maneuver being performed when the injury occurred, and playing type associated with the injury. The players responded to the questionnaire under the guidance of the medical staff of each team. Results: The 80 female soccer players reported a total of 90 ACL injuries during soccer. Among 55 non-contact injuries, 29 (55%) occurred during a cutting maneuver and 22 (44%) occurred during pressing. On assessing the frequency distributions of playing type (pressing vs. others) and body contact (contact vs. no contact), we found that non-contact injuries at pressing were significantly more common than contact injuries at pressing (odds ratio: 3.03; 95% confidence interval, 1.11 - 8.25, P = 0.036) Conclusions: ACL injury often occurs as non-contact injury during pressing at the time of defense, regardless of the playing area, in female soccer players.

Osteoarthritis patients may exhibit different kinematics according to the disease stage. However, changes in the frontal and horizontal planes in each stage remain unclear. The purpose of this study was to investigate changes in the knee kinematic gait variables of osteoarthritis patients, including the frontal and horizontal planes, with respect to the severity of the disease.Forty-five patients with knee osteoarthritis and 13 healthy young subjects were recruited for the experiment. All subjects were examined while walking on a 10-m walkway at a self-selected speed. In each trial, we calculated the angular displacements of flexion/extension, abduction/adduction, and external/internal tibial rotation. We also measured muscle strength, range of motion (ROM), and alignment. We compared the differences in osteoarthritis severity and knee kinematic variables between osteoarthritis patients and normal subjects.The flexion angle at the time of foot contact was significantly less in patients with severe and moderate osteoarthritis than in normal subjects (both p0.01). The abduction angle at the 50% stance phase was significantly less in patients with severe osteoarthritis than in normal subjects (p0.05). The excursion of axial tibial rotation was significantly less in patients with early osteoarthritis than in normal subjects (p0.05).Osteoarthritis patients had different knee kinematics during gait, depending on the progress of osteoarthritis. Early-stage patients exhibit decreased axial tibial rotation excursion, while severe-stage patient exhibit increased knee adduction.

Objectives: To assess the relationship between dynamic knee motion in female athletes during landing after jumping and lower limb clinical physical measurements, considered risk factors for anterior cruciate ligament (ACL) injury. We proposed that (1) knee valgus and flexion angles during landing are correlated with clinical physical measurements; (2) combining these measurements enables prediction of the knee valgus and flexion angles during landing. Methods: Sixty-one female collegiate basketball athletes performed a continuous jump test; the peak knee valgus and flexion angles were measured. The Q-angle, the ranges of motion (ROMs) of hip internal rotation (IR) and external rotation (ER), as well as ankle dorsiflexion (DF), navicular drop, leg-heel alignment, and balance ability as assessed by the Star Excursion Balance Test (SEBT) were measured. Stepwise linear regression analyses were used to assess whether these factors can predict the peak knee valgus or flexion angle. Results: Increased ROM of hip IR and navicular drop predicted 7.9% of the peak knee valgus angle variance. Increased ROMs of ankle DF and hip IR, navicular drop, and anterior balance predicted 29.0% of the peak knee flexion angle variance. The knee valgus and flexion angles during the continuous jump test were slightly correlated with clinical physical measurements. Conclusions: Proximal and distal joint alignment and balance ability influence knee motion during landing. The relationship between knee motion during landing and these factors is weak; therefore, lower limb movement during landing is almost independent of clinical physical measurements, and knee movement should be evaluated by itself.

Tibial rotation during foot pronation has been proposed as a key factor in running related injuries. Precise analysis of knee motion during running, including the analysis of motion in the coronal plane, is difficult, and the effect of the wearing shoes on tibial rotation during running is unknown. Therefore, we aimed to determine the effect of wearing shoes in reducing tibial rotation during running. Fifteen healthy subjects (nine males, six females) participated in this study; 25 markers were secured on the left lower extremity of each subject. Three-dimensional kinematic data were collected using the MAC3D System (Motion Analysis Co.). The data were processed using the point cluster technique (Andriacchi et al. 1998, J Biomech Eng 120, 743). The subjects were required to run (a) barefoot and (b) while wearing athletic running shoes (Adidas Response Cushion). Tibial motion with respect to the femur was assessed in the stance phase. The internal/external rotation, adduction/abduction and flexion of knee ...

This study was designed to compare biomechanical characteristics of the knee joint for several athletic tasks to elucidate their effects and to examine what tasks pose a risk for ACL injury. Three athletic tasks were performed by 24 female athletes: single-limb landing, plant and cutting, and both-limb jump landing. Angular displacements of flexion/extension, abduction/adduction, and external/internal tibial rotation were calculated. Angular excursion and the rate of excursion of abduction and internal tibial rotation were also calculated. During plant and cutting, from foot contact, subjects rotated the tibia more rapidly and to a greater degree toward internal tibial rotation. Moreover, excursion of knee abduction is greater than that during single-limb landing. During both-limb jump landing, the knee flexion at foot contact was greater than for either single-limb landing or plant and cutting; peak knee abduction was greater than for either single-limb landing or plant and cutting. In plant and cutting, the risk of ACL injury is increased by greater excursion and more rapid knee abduction than that which occurs in single-limb landing, in addition to greater internal tibial rotation. Although single-limb tasks apparently pose a greater risk for ACL injury than bilateral landings, both-limb landing with greater knee abduction might also risk ACL injury.

The likelihood of sustaining an ACL injury in a noncontact situation is two to eight times greater for females than for males. However, the mechanism and risk factors of ACL injury are still unknown. We compared knee kinematics as well as electromyographic activity during landing between male and female athletes. Eighteen male athletes and nineteen female athletes participated in the experiment. The angular displacements of flexion/extension, valgus/varus, and internal/external tibial rotation, as well as the translational displacements of anterior/posterior tibial translation during single limb drop landing were calculated. Simultaneous electromyographical activity of the rectus femoris (RF) and hamstrings (Ham) was taken. During landing, internal tibial rotation of the females was significantly larger than that of the males, while differences were not observed in flexion, varus, valgus, and anterior tibial translation. Hamstrings/quadriceps ratio (HQR) for the 50 ms time period before foot contact was greater in males than in females. The mechanism of noncontact ACL injury during a single limb drop landing would be internal tibial rotation combined with valgus rotation of the knee. Increased internal tibial rotation combined with greater quadriceps activity and a low HQR could be one reason female athletes have a higher incidence of noncontact ACL injuries.

The purpose of this paper is to clarify gender specific differences in strategies adopted by athletes during a cutting maneuver, based on results of recent research. The experimental task selected for detection of the risk of an injury to the anterior cruciate ligament (ACL) during a cutting maneuver should also involve trunk control. An example of such a task is shuttle run cutting. Trunk control during this task can then be analyzed. Important factors for understanding the strategy adopted by female athletes during a cutting maneuver involve gender differences in trunk and knee kinematics and kinetics, and the athlete’s reaction to instruction. Both posture and reaction to instruction in female athletes during the cutting maneuver differ from those of their male counterparts. To decrease the risk of ACL injury, trunk position during the cutting task should be screened for forward and lateral inclination. A forward inclination of the trunk in female athletes can be achieved by improving hip and trunk muscle activity.

This study aimed to investigate the effects of forward trunk lean on hamstring muscle kinematics during sprinting. Eight male sprinters performed maximal-effort sprints in two trunk positions: forward lean and upright. A three-dimensional musculoskeletal model was used to compute the musculotendon lengths and velocity of the biceps femoris long head, semitendinosus, and semimembranosus muscles during the sprinting gait cycle. The musculotendon lengths of all the three hamstring muscles at foot strike and toe-off were significantly greater during the forward trunk lean sprint than during the upright trunk sprint. In addition, a positive peak musculotendon lengthening velocity was observed in the biceps femoris long head and semimembranosus muscles during the late stance phase, and musculotendon lengths at that instant were significantly greater during the forward trunk lean sprint than during the upright trunk sprint. The present study provides significant evidence that a potential for hamstring muscle strain injury involving forward trunk lean sprinting would exist during the stance phase. The results also indicate that the biceps femoris long head and semimembranosus muscles are stretched during forward trunk lean sprinting while contracting eccentrically in the late stance phase; thus, the elongation load on these muscles could be increased.

Context: The Foot and Ankle Ability Measure (FAAM) is a valid, reliable, and self-reported outcome instrument for the foot and ankle region. Objective: To provide evidence for translation, cross-cultural adaptation, validity, and reliability of the Japanese version of the FAAM (FAAM-J). Design: Cross-sectional study. Setting: Collegiate athletic training/sports medicine clinical setting. Patients or Other Participants: Eighty-three collegiate athletes. Main Outcome Measure(s): All participants completed the Activities of Daily Living and Sports subscales of the FAAM-J and the Physical Functioning and Mental Health subscales of the Japanese version of the Short Form-36v2 (SF-36). Also, 19 participants (23%) whose conditions were expected to be stable completed another FAAM-J 2 to 6 days later for test-retest reliability. We analyzed the scores of those subscales for convergent and divergent validity, internal consistency, and test-retest reliability. Results: The Activities of Daily Living and Sports subscales of the FAAM-J had correlation coefficients of 0.86 and 0.75, respectively, with the Physical Functioning section of the SF-36 for convergent validity. For divergent validity, the correlation coefficients with Mental Health of the SF-36 were 0.29 and 0.27 for each subscale, respectively. Cronbach α for internal consistency was 0.99 for the Activities of Daily Living and 0.98 for the Sports subscale. A 95% confidence interval with a single measure was ±8.1 and ±14.0 points for each subscale. The test-retest reliability measures revealed intraclass correlation coefficient values of 0.87 for the Activities of Daily Living and 0.91 for the Sports subscales with minimal detectable changes of ±6.8 and ±13.7 for the respective subscales. Conclusions: The FAAM was successfully translated for a Japanese version, and the FAAM-J was adapted cross-culturally. Thus, the FAAM-J can be used as a self-reported outcome measure for Japanese-speaking individuals; however, the scores must be interpreted with caution, especially when applied to different populations and other types of injury than those included in this study.

Background To prevent anterior cruciate ligament (ACL) injuries, knowledge regarding risk factors and prevention methods must be disseminated to the public. However, it is unclear how the general population obtains information about or recognizes risk factors for ACL injuries. Objective To identify the information sources and risk factor recognition level for ACL injury among the general public. Design Cross-sectional study. Setting Web-based survey. Patients (or Participants) 900 people who recognized “ACL injury”. The age and sex of participants were evenly distributed. Interventions (or Assessment of Risk Factors) Participants answered questions regarding their information sources and risk factors influencing ACL injury. Main Outcome Measurements Descriptive analyses of patient responses were performed, with each response characterized by percentage of participants and the 95% confidence interval (CI). Results As an information source, “television” was the most frequent (57.0% [53.8–60.2]). Other information sources were “injury of friends” (22.4% [19.7–25.2]), “coach” (16.6％ [14.1–19.0]), “internet” (16.3% [13.9–18.7]) and “newspaper” (9.3% [7.4–11.2]). Regarding risk factors of ACL injuries, the most frequent response was “increased weight” (80.3% [77.7–82.9]). “Knee valgus” and “knee varus” during landing were both considered risk factors (63.3% [60.2–66.5] and 62.9% [59.7–66.0], respectively). Additionally, decreased muscle strength of quadriceps and hamstrings were both recognized as risk factors (69.2% [66.2–72.2] and 68.9% [65.9–71.9], respectively). Conclusions Television, specifically news of an athlete9s injury, was the most frequent information source for ACL injury. Although knee valgus during landing and decreased muscle strength of the hamstrings are considered risk factors for ACL injury, this is not understood properly by the general public. It is clear that better education about risk factors and prevention methods for ACL injuries through media, such as television, is required.

Background Anterior cruciate ligament (ACL) injury is one of the most serious sports injuries. However, few studies have surveyed the details of ACL injury mechanisms in high school athletes. Objective To investigate the mechanisms of ACL injuries among 1,000 ACL injuries in high school athletes by retrospectively reviewing the Japan Sports Council notification data. Design Epidemiological survey and retrospective study. Setting Young athletes (15–18 years old) belonging to sports clubs (soccer, basketball, judo, handball, volleyball) in high school (10th–12th grade). These clubs had a high incidence of ACL injuries in young Japanese athletes. Patients (or Participants) We collected data on 100 ACL injuries for each sport and sex for 1,000 athletes with injured ACL. Interventions (or Assessment of Risk Factors) We divided these data according to mechanisms such as contact (direct and indirect) and non-contact (play- and surface-related). Indirect contact was defined as an external force applied to the athlete but not directly to the injured knee. External force was involved in the injury process. Main Outcome Measurements We compared the mechanisms of injury between sexes and specific sports. Results Non-contact injuries were greater than contact injuries in ball games, except in male soccer. Most judo players experienced contact injuries. Over half of contact injuries were indirect in ball games. Surface problems caused 2.4% of ACL injuries. Conclusions We clarified the mechanisms of ACL injuries in young athletes. Detailed investigations of ACL injury mechanisms and prevention programs are needed.

Background Anterior cruciate ligament and hamstring strain injuries occur during unanticipated cutting and stopping movements. Previous prospective studies showed that athletes with decreased trunk neuromuscular control are at increased risk of knee injury. Therefore, deficits in trunk neuromuscular control during unanticipated movements may result in injury. However, the modulations of the hamstring muscles to the unanticipated trunk perturbation are unclear. Objective To examine the neuromuscular responses of the hamstring muscles during unanticipated trunk perturbations. Design Descriptive laboratory study. Setting Male college athletes. Participants Eight male sprinters (age, 20.3±1.4 years). Intervention In the kneeling position, the participants wore a chest harness attached to a cable that was pulled backward as a resisting force at a constant level corresponding to 13% to 15% of each weight. The participants were instructed to resist the force isometrically. The force was released with cue (CUE) and without cue (NoCUE). Trunk acceleration and surface electromyography (EMG) signals of the erector spinae, gluteus maximus, biceps femoris, and semitendinosus muscles were measured. Main Outcome Measurements (1) Maximum trunk acceleration; (2) EMG activation in the 50-ms window before the perturbation; (3) onset time of the muscle response; and (4) phasic muscle activities after the perturbations. Results The maximum trunk acceleration was significantly greater during the NoCUE condition than during the CUE condition (p Conclusions The results indicate that the anticipation of perturbation decreased the hamstring muscle latencies and responses to control the trunk movement, suggesting that the central nervous system modulated the readiness of the trunk based on anticipatory information.

Objective The objective is to assess the in vivo knee secondary motions intrinsic to flexion in isolation from actual displacements during a landing activity. For this purpose a “static zero position”, which denotes the normal tibiofemoral position to the static flexion angle, was introduced to describe the intrinsic secondary motion. Methods The three‐dimensional motion data of the healthy knee were collected from 13 male and 13 female young adults by using an auto motion analysis system and point cluster technique. First, the relationship between flexion and secondary motion in the static state was determined during a single-leg quasistatic squat. The static zero position during a single-leg drop landing was then calculated by substituting the flexion angle into the flexion-secondary relational expression obtained. Results After the foot-ground contact, the estimated static zero positions shifted monotonically in valgus, internal rotation, and anterior translation in the case of both the male and female groups. For the time-course change, noticeable differences between the actual displacement and estimated static zero position were found from the foot-ground contact up to 25 ms after the contact for the valgus/varus and external/internal rotation, and between 20 and 35 ms after the contact for the anterior/posterior translation. Summary The static zero position demonstrated relatively modest but not negligible shift in comparison with the actual displacement. The intrinsic tibiofemoral motion, or baseline shift, would be worth taking into account when examining the fundamental function and injury mechanics of the knee during an impulsive activity.

Female athletes are considered to exhibit knee and trunk motion that is characteristic of anterior cruciate ligament (ACL) injury. The aim of this study was to examine the in vivo motion of the trunk and knee during a cutting manoeuvre and determine the relationship between them. All participants (10 male and 10 female college athletes) performed a shuttle run cutting task with the left limb. Trunk inclination (forward and lateral) and knee joint angles (flexion/extension, abduction/adduction, and internal/external tibial rotation) were calculated. Differences between the sexes and associations between knee motion and trunk inclination were examined. An increase in trunk forward inclination was strongly correlated with an increase in knee flexion angle and moderately correlated with a decrease in the excursion of internal tibial rotation. An increase in right trunk lateral inclination was moderately correlated with an increase in excursion of internal tibial rotation. The results also showed differences between the sexes in trunk forward inclination, lateral inclination, and knee flexion angle, but no such differences in knee abduction or internal tibial rotation. Trunk inclination is related to knee flexion and excursion of internal tibial rotation. Female athletes demonstrate a low trunk forward inclination and knee flexion angle, a posture that resembles that of ACL injury.

Background The hamstring muscles are susceptible to strain injury during sprinting, and the biceps femoris long head (BFlh) is reportedly the most frequently injured muscle. Therefore, elucidation of the risk factors is of particular concern for injury prevention. Objective To clarify the potential risk factors for the incidence of muscle strain injury in each hamstring muscle by comparing the time of occurrence of peak musculotendon length and electromyography (EMG) activation during the late swing phase of sprinting. Design Descriptive laboratory study. Setting Male college track and field athletes. Participants 13 male sprinters (age 20.2±0.6 years). Intervention Full-body kinematics and EMG of the BFlh and semitendinosus (ST) were recorded during overground sprinting at maximum effort. The hamstring musculotendon lengths were computed by using a three-dimensional musculoskeletal model. Main outcome measurements The time at the peak musculotendon length, in terms of percentage of the running gait cycle, was calculated and compared with that of the peak EMG activity. Results The peak length of the BFlh and ST was observed during the late swing phase, at 86.7% [2.5%] and 81.1% [2.5%] gait cycle, respectively (mean [SD]). A significant difference was observed in the time of the peak musculotendon length (P Conclusions The results indicate that the BFlh is exposed to instantaneous high tensile force during the late swing phase of sprinting, suggesting a higher potential risk for strain injury among the hamstring muscles.

Background Female basketball players are at a higher risk for injuries such as those of the anterior cruciate ligament (ACL). Therefore, preventing such injuries is essential for their health and the competition. Objective To assess the effect of an injury prevention training program on the incidence of injuries in female basketball players. Design Prospective intervention study. Setting Top-level basketball league in Japan. Participants A total of 1127 players from 12 top-league teams during 7 seasons. Interventions From the middle of the second (2007–2008) season, a 3-step injury prevention program was initiated. The program focused on strength, balance, jump-landing techniques, and basketball skills. Subjects were instructed to perform exercises in a neutral position and to avoid lumbar lordosis, rear axial weight bearing, hip adduction, and knee valgus. Main outcome measurements All injuries, including ACL injury and ankle sprain, occurring during the 7 seasons that caused a player to miss a current session and/or miss a subsequent session were recorded. Injury incidences were calculated in terms of per 1000 player hours (PH). Compliance with the program was also reported. Results During 7 seasons, 8,73,084 PH and 973 injuries were reported. The injury incidence was 1.11/1000 PH, which did not significantly change after the intervention. In each season, ankle or knee injuries were most frequent. 34 non-contact ACL injuries occurred, an incidence of 0.039/1000 PH. During 5 seasons after the intervention, the incidence of non-contact ACL injuries in the team conducting the prevention program was 0.032, while the team without the program had an incidence of 0.046. A total of 235 ankle sprains occurred, an incidence of 0.269/1000 PH. After the intervention, the incidence decreased to 0.19 in the 2011–2012 season. Conclusions The results show that the injury prevention program may decrease the frequency of non-contact ACL injuries and ankle sprains.

Background Some research studies have investigated the effects of anterior cruciate ligament (ACL) injury prevention programs on knee kinematics during landing tasks; however the results were different among the studies. Even though tibial rotation is usually observed at the time of ACL injury, the effects of training programs for knee kinematics in the horizontal plane have not yet been analyzed. The purpose of this study was to determine the effects of a jump and balance training program on knee kinematics including tibial rotation as well as on electromyography of the quadriceps and hamstrings in female athletes. Methods Eight female basketball athletes participated in the experiment. All subjects performed a single limb landing at three different times: the initial test, five weeks later, and one week after completing training. The jump and balance training program lasted for five weeks. Knee kinematics and simultaneous electromyography of the rectus femoris and Hamstrings before training were compared with those measured after completing the training program. Results After training, regarding the position of the knee at foot contact, the knee flexion angle for the Post-training trial (mean (SE): 24.4 (2.1) deg) was significantly larger than that for the Pre-training trial (19.3 (2.5) deg) (p < 0.01). The absolute change during landing in knee flexion for the Post-training trial (40.2 (1.9) deg) was significantly larger than that for the Pre-training trial (34.3 (2.5) deg) (p < 0.001). Tibial rotation and the knee varus/valgus angle were not significantly different after training. A significant increase was also found in the activity of the hamstrings 50 ms before foot contact (p < 0.05). Conclusions The jump and balance training program successfully increased knee flexion and hamstring activity of female athletes during landing, and has the possibility of producing partial effects to avoid the characteristic knee position observed in ACL injury, thereby preventing injury. However, the expected changes in frontal and transverse kinematics of the knee were not observed.

Background Female basketball players are at a higher risk of anterior cruciate ligament (ACL) injury than male players. Therefore, prevention of ACL injury in the former group is essential. Objective To assess the effect of an injury prevention training program on the incidence of ACL injuries in female basketball players. Design Prospective intervention study. Setting Top-level league in Japan. Participants Players from 12 top-league teams. The control season (2006–2007) included 158 players; the first intervention season (2007–2008), 168 players; the second intervention season (2008–2009), 174 players; and the third intervention season (2009–2010), 162 players. Interventions From the middle of the 2007–2008 season, a 3-step injury prevention program was initiated. The program focused on strength, balance, jump-landing techniques, and basketball skills. Subjects were instructed to perform exercises in a neutral position and to avoid lumbar lordosis, rear axial weight bearing, hip adduction, and knee valgus. Main outcome measurements Number and rate of ACL injuries during the four seasons and compliance with the program. Injury incidences were given in terms of per 1000 player-hours (PH). Results Seven non-contact ACL injuries were noted during the control season (0.059/1000 PH); 4, during the first intervention season (0.031/1000 PH); 10, during the second intervention season (0.073/1000 PH); and 2, during the third intervention season (0.016/1000 PH). During the second intervention season, the rate of ACL injuries in the teams that complied with the program was 0.053/1000 PH, while the rate in the teams that did not comply was 0.099/1000 PH. During the third intervention season, the rate of ACL injuries in the teams that complied was 0.011/1000 PH, while the rate in the teams that did not comply was 0.032/1000 PH. Conclusion The results show that the injury prevention program tended to decrease the frequency of ACL injuries.