The progress of human physical growth and functional development is not always consistent, and it depends on the different tempos and patterns of body parts, organs, and elements of physical fitness. When coaching and/or supporting young athletes, in addition to considerations of training efficiency, it is also important to consider the physical development of young athletes and their growth and development processes in order to avoid overloading parts of the body that have not fully developed due to their young age. Furthermore, since the speed and tempo of physical growth and development in young athletes differs from person to person it is desirable to avoid a coaching and/or support program that treats all athletes in a uniform manner. In other words, in this article I argue it is more beneficial to privilege considerations of biological maturity over chronical age.

In this article, we focus on the injury characteristics of youth athletes. First, we organize the physical characteristics of children during adolescent growth. Next, grasp the actual condition of injury of youth athlete in Japan. Finally, we summarize activities of sports organizations in Japan on injury prevention of youth athletes who are drawing the attention of sports orthopedic surgeons. During growth spurt phase, children have structurally fragile parts such as epiphysis and epiphyseal line, whose body structure is different from adults. The characteristic of sports injuries during the growth spurt phase occurs due to the fact that the growth of tissues such as the increase in bone mass and surrounding muscle tendons slightly lag against rapid bone growth. The sports injury is a summary of the traumatic injury in which the tissue is damaged by a major external force and the overuse injury in which the tissue gradually becomes damaged due to repeated minor external forces. Youth athletes often cause fractures and sprains in trauma and often develop osteochondrosis or stress fractures in overuse injury. In this study, individual body maturity is not taken into consideration, and it is caused by exercise practice in the physical disparity and over training due to load not matching body maturity. It is important in prevention of sports injuries to change the conditioning method, training and coaching method based on body maturity.

The number of anterior cruciate ligament (ACL) injuries in adolescents is rising. However, there is very little high-quality evidence to guide decision-making in management of pediatric ACL injuries. In October 2017, the International Olympic Committee hosted an international expert group, and the consensus statement on prevention, diagnosis and management of pediatric ACL injuries was posted. The consensus statement topics about 1) injury prevention and 2) high-quality rehabilitation were reported in this article. In addition, mechanism, risk factors, and effective preventive measures for ACL injuries in adolescent athletes were also reviewed. Stiff landings were associated with increased ACL injury risk for young female athletes, and the ACL injury risk could be reduced by neuromuscular control training program that targeted younger participants with high-compliance. Furthermore, we challenged to elucidate the movements requiring greater trunk accelerations and its frequencies during junior badminton games. ACL injuries in badminton have commonly occurred during single-leg landing after an overhead stroke in the backhand-side court. From our researches, the mediolateral physical demand and high-risk posture in the backhand-side court may be associated with a higher incidence of knee injuries during badminton games.

Osgood-Schlatter disease (OSD) is a well-documented clinical condition particularly in adolescent athletes. In recent years, the pathology and the factors associated with the onset has been clarified by applying the new evaluation tools and increasing in the longitudinal studies .On the other hand, there are few reports about the effect of the therapeutic exercises. Detection and intervention in early stage is required for the early return to sports. This article reviewed the scientific evidences about the pathology and the factors associated with the onset , diagnosis and treatment of OSD.

The current consensus on the pathophysiology of OSD is that it is a traction apophysitis of the proximal tibial tubercle resulting from repetitive microtrauma at the stage of relatively weak strength of the tibia tuberosity. Flexibility, muscle strength, growth, and kicking motions are factors that may cause OSD. These factors have generally been reviewed retrospectively and there have been a few prospective studies. For the early detection, it is important to imaging physical examinations such as pain regularly. Current treatment protocol for OSD is conservative, consisting primarily of rest, icing, NSAIDs, and therapeutic exercise. Although therapeutic exercise is the most important treatment that therapists and trainers associate with, the effects of exercises has not been established. In future, the appropriate treatment protocols especially therapeutic exercise according to pathological conditioning and the factors associated with the onset should be established.

Concussion is one of severe injuries in youth sports. Even though concussion has been considered as “mild” among sports-related head injuries and neglected the importance, recent studies clear the neurophysiological pathology. Most of the concussion improve in about 10 days, but it is reported some cases became repeated or chronic. Therefore, management of concussion requires proper evaluation and decision to graduated return to play/sports. According to epidemiological studies, sports with high incidence of concussion in adoselent are collision sports such as rugby, american football, and ice hockey. Especially in rugby, statistics show that one concussion occurred in every three games. In the soccer, the relationship between heading and concussion, and cognitive function has been suggested, but it remains unclear. In addition, it is reported that concussion is a problem with not only high incidence but also high recurrence rate and chronicity, suggesting a relationship with the long-term effects such as chronic traumatic encephalopathy (CTE). Regarding appropriate evaluation and management of concussion, injury assessment using Sports Concussion Assessment Tool (SCAT) and compliance with return to play strategy based on Graduated Return to Play/Sports protocol (GRTP/GRTS protocol) are necessary. In the future, more studies are needed to clear the effect of the concussion among adolescent, and the mechanism of long-term effects including after retirement.

The purpose of this study was to verify the reliability and the usefulness of a novel ankle plantar flexion strength test (Plantar flexion break test ; PFBT). 192 healthy volunteers were enrolled. All subjects were measured the ankle range of motion (dorsiflexion / plantar flexion), PFBT, and numbers of heel rising. The result of PFBT (positive / negative) was determined by ankle joint stability when maximum resistance was applied downward to calcaneus during maximum ankle joint plantar flexion in single leg standing position. The PFBT-positive group was significantly lower dorsiflexion range of motion and fewer numbers of heel rising than the PFBT-negative group (p<0.01). Although the reliability within the examiner of PFBT was almost perfect (κ=0.92), the reliability between examiners was fair (κ=0.37). PFBT is simpler than manual muscle test, but further verification is necessary due to the possibility of evaluating different muscle functions.

190 high school soccer players participated in this study and they were examined the relationship between the history of the lower extremity injuries ; thigh, hip joint, knee joint and ankle joint, and the score of each item of FMS and the difference between left and right.

Active Straight Leg Raise, Deep Squat, Trunk Stability Push Up were found to be significantly related to the history of the disorder. It is considered that decreases in hip joint flexibility, lack of coordination of the lower extremity, and core instability may be a factor of the lower extremity disorder.

The purpose of this study is to analyze daily variation of muscle strength of shoulder abduction in college baseball pitchers during pre-season. We continuously measured the shoulder abductor strength of pitchers in college baseball team. The mean abductor strength was 96±18 N on the first day, 101±16 N on the second day, 103±18 N on the third day, 108±16 N on the fourth day, and 113±17 N on the fifth day. A significant difference was observed between the first day and the fourth day, fifth day, and between the second day and the fifth day. The shoulder abductor strength of pitchers, therefore, varied daily during the pre-season.

The feet and toes of 110 collegiate-level baseball players were examined, and an analysis was performed to determine whether foot characteristics were correlated with throwing injuries of the shoulder and elbow.

A corn at the lateral side of the forefoot in the stance and lunge feet was significantly more prevalent in players with throwing injuries than in those without injuries. Compared with players without throwing injuries, those with throwing injuries tended to have a greater prevalence of varus deformities of the 4th or 5th toes of the stance foot, and of the 3rd to 5th toes of the lunge foot ; however, these intergroup differences were not significant.

These results suggest that players with throwing injuries could have instability during the pitching motion, with loading at the lateral side of the forefoot. The results also suggest that characteristic deformities of the foot and toes may be correlated with throwing injuries of the shoulder and elbow.

The Functional Movement Screen (FMS) has been utilized as a screening tool for detecting abnormalities such as asymmetries and compensations on movement patterns. Previous studies have reported that 14 points and under of the FMS composite score showed higher risk of severe sports injuries. Improving the FMS score is considered to be important for injury prevention. While the FMS has been considered to be a useful prediction tool for sports injury, it is still unknown whether exercises for mobility (MEx) influence the FMS score. The aim of this study was to determine the effects of MEx on the FMS score. Fifty-two collegiate American football players participated in this study. The inclusion criteria were as follows ; no orthopaedic injury history in latest 3 months, 2 points and under of the FMS mobility score (Shoulder Mobility Reaching ; SMR and Active Straight Leg Raise ; ASLR) in baseline test for the good mobility group (38 players), 3 points of the FMS mobility score for the poor mobility group (14 players). The FMS was measured at preseason as a baseline test and was retested after 12 weeks. Players performed the MEx for 12 weeks (3 times per week). For the poor mobility group, the FMS composite score, deep squat (DS), SMR and ASLR were significantly increased at 12 weeks. SMR and ASLR mainly require active mobility. The MEx affected not only the mobility items of the FMS but also DS which is a complex movement pattern required mobility and stability.

The running distance and speed of sevens rugby referees were recorded by Global Positioning System (GPS), and these data were compared to those of rugby players in order to investigate corresponding physiological load levels. Subjects were six rugby players who play in regional preliminaries of high school sevens rugby, and four referees who referee their matches. Running distance and speed during matches were recorded by GPS devices. At the same time, heart rate was recorded in order to determine exercise intensity. The results show that total running distance, mean speed, and exercise intensity were significantly greater in referees than in players. In conclusion, the physiological load of sevens rugby referees during matches is high, and it is clear that conditioning measures for referees are necessary for them to make accurate decisions during matches.

The purpose of this study is to investigate students’ sports background (sports and physical training), field practice experience as athletic trainer and their job expectations after graduation. The participants of this study are 343 students from sports based universities and physical therapy universities that offer a course for athletic trainer certification (JSPO-AT) in Japan. The responses of the two groups of students were compared and it was found out that both group have sports background experience, however, there were only over 30% of them who have physical training experience. Different trends on participants’ field practice experience as athletic trainer was noted as they differ in their place and frequency of practice per week. As to the job expectation after graduation, physical therapy university group has more expectation to be an athletic trainer than students from sports based university group.