Keishoku Sakuraba

Strength Deficits Identified With Concentric Action of the Hip Extensors and Eccentric Action of the Hamstrings Predispose to Hamstring Injury in Elite Sprinters

STUDY DESIGN Prospective cohort study. OBJECTIVES In this prospective cohort study of elite sprinters, muscle strength of the hip extensors, as well as of the knee extensors and flexors, was measured to determine a possible relationship between strength deficits and subsequent hamstring injury within 12 months of testing. The method used for testing muscle strength simulated the specific muscle action during late swing and early contact phases when sprinting. BACKGROUND There have been no prospective studies in elite sprinters that examine the concentric and eccentric isokinetic strength of the hip extensors and the quadriceps and hamstring muscles in a manner that reflects their actions in late swing or early contact phases of sprinting. Consequently, the causal relationship between hip and thigh muscle strength and hamstring injury in elite sprinters may not be fully understood. METHODS AND MEASURES Isokinetic testing was performed on 30 male elite sprinters to assess hip extensors, quadriceps, and hamstring muscle strength. The occurrence of hamstring injury among the subjects was determined during the year following the muscle strength measurements. The strength of the hip extensors, quadriceps, and hamstring muscles, as well as the hamstrings-quadriceps and hip extensors- quadriceps ratios were compared. RESULTS Hamstring injury occurred in 6 subjects during the 1-year period. Isokinetic testing at a speed of 60 degrees /s revealed weakness of the injured limb with eccentric action of the hamstring muscles and during concentric action of the hip extensors. When performing a side-to-side comparison for the injured sprinters, the hamstring injury always occurred on the weaker side. Differences in the hamstrings-quadriceps and hip extensors-quadriceps strength ratios were also evident between uninjured and injured limbs, and this was attributable to deficits in hamstring strength. CONCLUSION Hamstring injury in elite sprinters was associated with weakness during eccentric action of the hamstrings and weakness during concentric action of the hip extensors, but only when tested at the slower speed of 60 degrees /s.

Blood flow restriction by low compressive force prevents disuse muscular weakness

Repetitive blood flow restriction prevents muscular atrophy and weakness induced by chronic unloading. However, it was unclear which external compressive force for blood flow restriction was optimal to prevent muscular dysfunction. The present study was intended to investigate the effects of repeated muscle blood flow restriction at low pressure on muscular weakness induced by immobilization without weight bearing. Using casts, the left ankles of 11 healthy males were immobilized for 2 weeks. Subjects were instructed to walk using crutches with no weight bearing during the period. Subjects were divided randomly into two groups: a restriction of blood flow (RBF) group (application of external compressive force of 50 mm Hg) and a control (CON) group (no intervention). We measured changes in the muscle strength of the knee extensor-flexor and ankle plantar flexor. The percent changes in knee extensor torque at 60°/s under eccentric contraction in the RBF group were significantly smaller than in the CON group (-12.5±10.7% and -30.1±10.9%, p<0.05). The percent changes in knee flexor torque when performing an eccentric contraction at 60°/s, an isometric contraction, or a concentric contraction at both 60 and 300°/s in the RBF group were significantly smaller than those in the CON group (p<0.05). In conclusion, our results show that repetitive restriction of blood flow with 50 mm Hg cuff pressure to the lower extremity reduces muscular weakness induced by chronic unloading.

Snowboarding and Ski Boarding Injuries in Niigata, Japan

Background The purpose of this study was to compare the injury patterns and incidence of snowboarding and ski boarding injuries with that of alpine skiing in 2000 to 2005, as there are few previous studies comparing these 3 sports, especially in Asia. Hypothesis The injury patterns are different among the 3 snow sports. Study Design Descriptive epidemiology study. Methods The subjects were alpine skiers (1240 cases), snowboarders (2220 cases), and ski boarders (132 cases) who were injured in 2 ski resorts located in Niigata prefecture in Japan and visited the authors’ clinics in these ski resorts between 2000 and 2005. On visiting the clinics, patients completed a questionnaire reviewing the circumstances surrounding the injury event, and physicians documented the diagnosis. Results The injury rate, which was based on all purchased lift tickets, in snowboarding decreased gradually, although it was still 2 times higher than that of alpine skiing. Snowboarding and ski boarding had a higher fracture and dislocation rate. Both sports also had a 4 times higher rate of injuries because of jumping. The characteristics of ski boarding were a lower head and neck injury rate and collision injury rate than those of the other 2 snow sports, as well as a 2 times higher rate of fractures compared with alpine skiing injuries and a 1.4 times higher incidence than that of snowboarding injuries. Of the fractures caused by ski boarding accidents, 39.6% affected the lower leg bones. Conclusion Injury prevention strategies should focus on jumps for snowboarders and ski boarders.

Development of a baseball-specific battery of tests and a testing protocol for college baseball players.

Kohmura, Y, Aoki, K, Yoshigi, H, Sakuraba, K, and Yanagiya, T. Developments of a baseball-specific battery of tests and a testing protocol for college baseball players. J Strength Cond Res 22: 1051-1058, 2008-In this study, the relationship between the physical fitness of college baseball players found from 6 field tests and a performance evaluation by coaches was investigated. The purpose was to ascertain whether the results would be similar to those obtained in a previous study. The subjects of the study were 43 college baseball players (mean age, 20.7 ± 1.4 years; mean athletic career, 10.9 ± 2.6 years). Referring to the previous study, the field tests of physical fitness were composed of 6 items: throwing distance, back strength, medicine ball throwing, standing long jump, T-test, and base running. For capabilities in batting, fielding, and running, the coachs evaluation was expressed by T scores. The results of the analysis indicated that those players with high evaluation scores had significantly better test results in comparison with those players who were rated low in the evaluation. Although the multiple regression models of the previous study were associated with a middle goodness of fit, a significant correlation was found between physical fitness found in the field tests and performance. The results from a partial correlation analysis indicated a significant correlation between the following: batting evaluation with back strength (p < 0.01) and medicine ball throwing (p <0.01); fielding evaluation with throwing distance (p < 0.05); and running evaluation with medicine ball throwing (p < 0.01), standing long jump (p < 0.05), T-test (p < 0.01), and base running (p < 0.01). It is certain that the performance of college baseball players is related to their physical fitness.

Strength Training for the Intrinsic Flexor Muscles of the Foot: Effects on Muscle Strength, the Foot Arch, and Dynamic Parameters Before and After the Training

[Purpose] The purpose of the present study was to verify the effects of intrinsic foot flexor strength training. [Subjects] The subjects were 12 healthy males without motor system disease. [Methods] A training method that involved flexion of all toe interphalangeal and metatarsophalangeal joints against a 3-kg load was implemented and was performed for 200 repetitions once per day, three times per week, for a period of eight weeks. [Results] Significant changes were observed for intrinsic foot flexor strength scores, foot arches, vertical jumping, 1-legged long jumping, and 50-m dash time. [Conclusion] This muscle strength training method significantly improved muscle strength scores, foot arch shape, and movement performance.

Effect of isokinetic resistance training under a condition of restricted blood flow with pressure

BackgroundThe purpose of the present study was to investigate the effect of isokinetic training under the condition of restricted blood flow with pressure.MethodsThe subjects were 21 athletes at a university. They were classified into four training groups: group A (high speed under restricted blood flow condition with pressure); group B (low speed under restricted blood flow condition with pressure); group C (high speed without restricted blood flow condition); group D (low speed without restricted blood flow condition). The training session consisted of three sets of knee extension and flexion (repeated 10 times) using an isokinetic training machine (Biodex system 3). The training period was 4 weeks, with regular training sessions twice a week during this period. Before and after the training period, all of the subjects underwent measurements of quadriceps muscular strength of concentric contraction (CC) and eccentric contraction (EC) after isokinetic contraction as well as measurement of the thigh diameter. In addition, the group with restricted blood flow with pressure underwent magnetic resonance imaging (MRI).ResultsIn regard to quadriceps muscular strength before and after training, there was a significant difference between groups A and C at many degrees of velocity. For the muscular volume measurements by MRI before and after training, no significant difference was seen in group A or group B. A significant increase was not seen even when comparing groups A and B.ConclusionsIsokinetic resistance training with restricted blood flow with pressure had an effect on muscular strength improvement.

Properties of Force Output and Spectral EMG in Young Patients with Nonspecific Low Back Pain during Isometric Trunk Extension

[Purpose] To clarify the influence of nonspecific low back pain (NSLBP) on force fluctuation and the myoelectric data of back muscles during isometric trunk extension at low to high force levels. [Subjects] Fourteen male subjects with NSLBP and 14 healthy male control subjects participated in this study. [Methods] All participants extended their trunk isometrically maintaining 10 levels of target force [2, 5, 10, 15, 20, 30, 50, 70, 80 and 90% of maximal voluntary contraction (MVC) in a random order] for about 4 seconds with visual feedback. A force transducer and tri-axis force sensor were positioned at the 7th thoracic vertebra to measure force output and the direction of force. Myoelectric activities of the back muscles (longissimus thoracis, L2 level; multifidus, S1 level) were recorded by surface electromyography. [Results] Force output of NSLBP subjects fluctuated more than that of healthy subjects at 30% and 50%MVC. Higher median power frequency in the multifidus was observed in NSLBP subjects at moderate to high force levels. [Conclusion] These results show that the properties of force output in NSLBP subjects differ from those in healthy subjects, suggesting that the assessment of force fluctuation of back muscles at moderate force levels is a useful index for evaluating and discriminating NSLBP.

Pediatric orthopaedic injuries requiring hospitalization: epidemiology and economics.

Objective: This study aimed to identify the 10 most frequent pediatric orthopaedic injuries requiring hospitalization in the United States, the major causes of these injuries, and their economic burden to health care cost. Methods: The 2006 Kids’ Inpatient Database (KID) (age range, 0–20 years) was used to determine the 10 most frequent pediatric orthopaedic injuries requiring hospitalization. The injuries were identified by ICD-9-CM codes 800.0–999.9 and external cause of injury codes (E-codes). Discharges were weighted to produce national estimates according to average age at admission, hospital charges, and length of stay. Results: The 2 populations accounting for the highest total hospitalization charges (USD) for pediatric orthopaedic injury were young children with femur fractures (11 years of age, 20%,

Association between the stress fracture and bone metabolism/quality markers in lacrosse players

32 441 per visit) and adolescents with vertebral fractures (17 years of age, 8%,

Preliminary report: mitochondrial DNA 5178 polymorphism in male elite Japanese endurance runners

53 992 per visit). But the most common injuries requiring hospitalization were femur (11 years of age; 20%) and humerus (8 years of age; 18%) fractures. The most costly injuries, vertebral and pelvic injuries, were largely related to motor vehicle accidents (11.7% and 14.4%, respectively). In contrast, humerus and radius fractures had a high rate of playground-related injuries (21.9% and 11.3%, respectively). None of the causes accounted for more than 25% of the total incidence for the 10 most common injuries identified in this study. Conclusions: Identification of the patients responsible for the majority of the hospitalization charges for pediatric injuries will enable institutions to better plan their budgets on the basis of the local incidence.