Gravity stress and 30 N valgus stress may produce different effects with respect to medial elbow joint space gapping before pitching; however, 30 N valgus stress appears to induce greater mechanical stress, which may be preferable when assessing joint instability but also has the potential to be more aggressive. The present results may indicate that constraining factors to medial elbow joint valgus stress matched typical viscoelastic properties of cyclic creep.

Background:Landings in fatigue conditions are considered to be one of the factors that cause noncontact anterior cruciate ligament (ACL) injury. Additionally, it is known that fatigue alters lower extremity landing strategies and decreases the ability to attenuate shock during landing.Purpose:To determine characteristics of knee kinematics and shock attenuation during the landing phase of a single-leg vertical drop jump in a fatigued condition. The hypothesis was that knee kinematics during the landing phase of a single-leg vertical drop jump would demonstrate a significant difference between before and after fatigue.Study Design:Controlled laboratory study.Methods:Thirty-four college females participated in this experiment. They were randomly assigned to either the fatigue (n = 17) or control group (n = 17). The fatigue group performed the single-leg vertical drop jump before and after the fatigue protocol, which was performed on a bike ergometer. Knee kinematics data were obtained from the 3-dimensional motion analysis system. The ratio of each variable (%) was calculated, comparing the pre- to postfatigue protocol. Unpaired t tests were used to compare changes in kinematic variables between the fatigue-induced group and control group.Results:Peak knee flexion angular velocity increased significantly in the fatigue group (106.1% ± 8.0%) in comparison with the control group (100.7% ± 6.6%) (P < .05). However, peak knee flexion angle and acceleration had no differences between each group. Peak knee adduction/abduction angle, velocity, and acceleration also had no differences between each group.Conclusion:Fatigue decreased the ability to attenuate shock by increasing angular velocity in the direction of knee flexion during single-leg drop jump landing. These findings indicate the need to evaluate the ability to attenuate shock by measuring knee flexion angular velocity when fatigue is considered.Clinical Relevance:Measuring knee angular velocity during landings might be an important evaluation parameter in the consideration of the knee injury prevention.

We evaluated a range of physical characteristics related to hamstring injuries, as well as the Nordic Hamstring Exercise compliance rate, and whether this influenced the rate hamstring injury. Subjects comprised 259 male soccer players from seven high schools randomly clustered into two groups, a Nordic Hamstring Exercise group and a control group. Training and match time were logged, as well as details of hamstring injury, and subsequent time lost to hamstring injury recorded over a period of 27 weeks. The Nordic Hamstring Exercise compliance rate, injury rate per 10000 playing hours and time-lost-to-sport-injury rate were calculated. The relative risk and hamstring injury severity were also calculated. The hamstring injury rate was 1.04/10 000 h in the control group and 0.88/10 000 h in the intervention group. The relative risk for hamstring injury was 1.14. The time-lost to injury rate was 1116.3/10 000 h in the control group and 113.7/10 000 h in the intervention group; with relative risk 9.81. The Nordic Hamstring Exercise in high school soccer players significantly reduced hamstring injury severity compared to a control intervention. Our results indicate that the time-lost to injury rate should be taken into account when analyzing the severity of hamstring injury.

Background:Throwing athletes risk medial elbow injury from extreme valgus stress generated across the medial elbow during throwing. Braces have been developed to protect the elbow joint; however, no previous study has investigated the effects of elbow bracing on medial elbow joint space gapping associated with repetitive throwing.Hypothesis/Purpose:The purpose of this study was to investigate the effects of elbow bracing on medial elbow joint space gapping during repetitive throwing. Our hypothesis was that an elbow brace may reduce mechanical stress on the elbow by reducing medial elbow joint space gapping.Study Design:Controlled laboratory study.Methods:Twenty-five high school baseball players participated in this study. Each subject pitched 100 times under 2 conditions: control (without elbow brace) and elbow brace. The ulnohumeral joint space was measured ultrasonically before pitching and after every block of 20 pitches. Measurement of the ulnohumeral joint space was carried out using ultrasound with the forearm hanging by the side. Two-way repeated-measures analysis of variance and post hoc tests were used to compare ulnohumeral joint space with repeated pitching and between the elbow brace and control conditions.Results:In the control condition, ulnohumeral joint space after 60 pitches was significantly greater than that before pitching (P < .01). In contrast, in the elbow brace condition, ulnohumeral joint space was not significantly different after repeated pitching. When comparing these 2 conditions, ulnohumeral joint space in the control condition was significantly greater than that in the elbow brace condition after 60 pitches (P < .01).Conclusion:An elbow brace has the effect of preventing medial elbow joint space gapping with repeated throwing when determined ultrasonically by measuring the ulnohumeral joint space under gravity load.Clinical Relevance:An elbow brace worn during baseball pitching practice may help reduce mechanical stress on the elbow by reducing medial elbow joint space gapping.

[Purpose] To determine the relationship between low back pain and a range of demographic, environmental, and injury history factors to identify potential factors for the management of low back pain. [Participants and Methods] The participants were 123 elite high school male and female volleyball players. They answered an extensive questionnaire regarding demographic details, low back pain in the previous year, volleyball-specific movements, previous regional injuries, and years of volleyball experience. Questionnaire responses were analyzed. Data were analyzed using a multivariate logistic regression analysis using the presence and absence of low back pain within 1 year as the explanatory variable. [Results] Of the 123 volleyball players, 48.0% reported low back pain. The volleyball-specific movements that induced pain were diverse (e.g., spike, serve, and pass) with no common factor. The factors associated with low back pain were an ankle injury within the previous year and years of volleyball experience. [Conclusion] The associations found in this survey indicate that particular attention should be given to more experienced players with a history of ankle injury to manage low back pain in high school volleyball players.

Dynamic knee valgus during landings is associated with an increased risk of non-contact anterior cruciate ligament (ACL) injury. In addition, the impact on the body during landings must be attenuated in the lower extremity joints. The purpose of this study was to investigate landing biomechanics during landing with dynamic knee valgus by measuring the vertical ground reaction force (vGRF) and angular impulses in the lower extremity during a single-leg landing. The study included 34 female college students, who performed the single-leg drop vertical jump. Lower extremity kinetic and kinematic data were obtained from a 3D motion analysis system. Participants were divided into valgus (N = 19) and varus (N = 15) groups according to the knee angular displacement during landings. The vGRF and angular impulses of the hip, knee, and ankle were calculated by integrating the vGRF-time curve and each joint’s moment-time curve. vGRF impulses did not differ between two groups. Hip angular impulse in the valgus group was significantly smaller than that in the varus group (0.019 ± 0.033 vs. 0.067 ± 0.029 Nms/kgm, p<0.01), whereas knee angular impulse was significantly greater (0.093 ± 0.032 vs. 0.045 ± 0.040 Nms/kgm, p<0.01). There was no difference in ankle angular impulse between the groups. Our results indicate that dynamic knee valgus increases the impact the knee joint needs to attenuate during landing; conversely, the knee varus participants were able to absorb more of the landing impact with the hip joint.

Low back pain (LBP) is a typical symptom in volleyball players, yet associated physical function factors have not been identified. This study purpose is to determine the relationship between LBP and physical function factors in order to identify potential factors for the management of LBP. Participants were 123 male and female volleyball players of 15- to 17-year-olds who, completed a questionnaire regarding demographic details, presence of LBP, and years of volleyball experience. Participants were divided into 2 groups based on the presence of current LBP and evaluated on physical function tests. The results of the questionnaire response and physical function test were compared between the 2 groups. Data were analyzed using a multivariate logistic regression analysis with presence and absence of current LBP as the explanatory variable. 11.4% of all participants reported current LBP. Physical function factors associated with current LBP were a positive modified Thomas test, years of volleyball experience and reduced range of motion of shoulder horizontal abduction on the dominant hand side. The associations between physical function factors and LBP found in this survey suggest that attention should be given to more experienced players with decreased flexibility of hip and shoulder flexors on the dominant side in order to manage LBP in high school volleyball players.

Background: Medial elbow injury is common in baseball pitchers, with evidence of elbow valgus instability after only 60 consecutive pitches. However, the tissue-specific effects of repetitive pitching on medial elbow stabilizers are largely unknown. Purpose/Hypothesis: This study aimed to investigate changes in the ulnar collateral ligament (UCL) and forearm flexor-pronator muscles (FPMs) during repetitive pitching and factors that relate to identified change. We hypothesized that repetitive pitching would increase elasticity of the medial elbow stabilizers and therefore induce laxity. Study Design: Descriptive laboratory study. Methods: A total of 30 high school baseball pitchers participated (mean ± SD age, 16.6 ± 0.5 years). Each participant pitched 100 times (5 blocks of 20 pitches). The strain ratio, indicating elasticity in the UCL and FPMs, was measured using ultrasound before pitching and after every 20-pitch block. Data for each pitch block were compared using analysis of variance. Multiple regression analysis was used to investigate factors related to the change rate of the strain ratio. Results: The strain ratio of the UCL after 100 pitches was significantly less than that before pitching (before pitching, 4.83 ± 1.70; after 100 pitches, 3.59 ± 1.35; P = .013), but this was not the case for the FPMs (before pitching, 0.57 ± 0.24; after 100 pitches, 0.43 ± 0.18; P = .07). The ratio of the strain ratio in the UCL and FPMs (UCL/FPMs) before pitching (β = −0.385; P = .031) and the elbow flexion range of motion before pitching (β = −0.352; P = .046) were significantly and independently correlated with the change rate of the UCL. Conclusion: Elasticity significantly increased for the UCL, indicating laxity, but not for the FPMs after 100 pitches. Furthermore, the ratio of elasticity (UCL/FPMs) and the elbow flexion range of motion before pitching were significantly related to the change rate of UCL elasticity. Clinical Relevance: To reduce laxity of the UCL, pitchers should be limited to <100 pitches per game. Sustaining a lower level of relative FPMs to UCL elasticity at rest and maintaining a large muscle volume to avoid excessive elbow flexion range of motion may prevent UCL laxity that develops during repetitive pitching.