Ulnar collateral ligament (UCL) weakening or tears occur in 16% of professional baseball pitchers. To prevent players from sustaining a UCL injury, it is important to understand the relationship between the UCL properties and elbow stabilizers with the load on the UCL during pitching. Invitro studies showed that the ultimate external valgus torque of 34 Nm would rupture the UCL, which is in apparent conflict with the reported peak valgus torques in pitching (40-120 Nm). Assuming both observations are correct, the question rises why 'only' 16 out of 100 professional pitchers sustain a UCL rupture. Underestimation of the effect of other structures in in-vivo studies is most likely the explanation of this mismatch because the calculated in-vivo torque also includes possible contributions of functional and structural stabilizers. In-vitro studies show that the flexorpronator mass has the potential to counteract valgus torque directly, whereas the elbow flexorextensor muscles combined with the humeroradial joint might have an indirect effect on valgus torque by increasing the joint compression force. Accurate experimental electromyography data and a more detailed (musculoskeletal)mechanical model of the elbow are needed to investigate if and to what extent the structural and functional stabilizers can shield the UCL during pitching.

Upper extremity injuries are common in baseball. One of these is the ulnar collateral ligament (UCL) injury. In the field of sports injuries, most research focuses on average kinematics and kinetics between subjects, whereas focusing on within-subject variability appears to be more relevant for determining injury risk. We constructed a simple explanatory simulation model to illustrate the relationship between within-subject load variability and risk, illustrating how pitchers with a higher load variability are more likely to sustain an injury compared to pitchers with less load variability. Furthermore, the model comprises the (theoretical) effect of fatigue on load variability and injury threshold over time.

Medial elbow overuse injuries are rising in baseball. The external valgus torque magnitude is a possible risk factor for medial elbow injuries. The magnitude on its own cannot explain why one pitcher sustains an injury and another does not. Therefore, the aim of this study is to describe the within-individual external valgus torque variability and to determine whether the within-individual external valgus torque variability can be described by a Gaussian distribution. Eleven youth elite baseball pitchers threw twenty-five fastball pitches. Body kinematics were measured with VICON motion capture at 400 Hz. Elbow valgus torques of the total 270 pitches were calculated with a custom-made inverse dynamic model in Python. Visual inspection and the Shapiro–Wilk test were performed to test for the within-individual elbow valgus torque normality. The results showed that within-individual valgus torque variability was present in pitchers and differed among pitchers. Furthermore, it was shown that the within-individual valgus torque variability was normally distributed in nine out of eleven subjects. In conclusion, the presence of and differences in within-individual elbow load variability among baseball pitchers can be useful variables as they might be related to overuse elbow injuries.

Monitoring the performance and functional status of baseball pitchers’ upper extremity is important in maintaining the athlete’s health and performance. This study validated a Dutch translation of the original English Kerlan-Jobe Orthopaedic Clinic (KJOC) against the previously validated Disabilities of the Arm, Shoulder and Hand (DASH) and Western Ontario Shoulder Instability Index (WOSI) questionnaires in a group of talented juvenile Dutch baseball pitchers. Three times, from 2014–2016, 107 pitchers completed the Dutch KJOC, DASH and WOSI questionnaires. Participants’ questionnaire scores were analysed for the whole group and the symptomatic player subgroup separately. Internal consistency, construct validity and ceiling and floor effects were examined. Cronbach’s alpha was consistently above 0.8 for the three time periods for the whole group, and ranged between 0.62 and 0.86 for the symptomatic subgroup. Spearman’s rank correlation coefficients ranged from 0.47 to 0.67 for the whole group and 0.32 to 0.99 for the symptomatic subgroup. No floor effects were observed in the scores of the KJOC and only a ceiling effect for the whole group (15.2%) at one time period. The Dutch version of the KJOC has shown acceptable internal consistency and construct validity and can be used to assess overhead athletes’ shoulder and elbow functionality.

The purpose of the present study was to investigate the effect of an experimentally imposed kinetic chain disturbance in baseball pitching on ball speed and elbow kinetics. The experimental design consisted of two (within-subject) conditions. In one condition there was no manipulation (control condition). The other condition involved a manipulation of the kinetic chain by taping the pelvis and trunk. In both conditions, pitchers were instructed to throw fastballs until a minimum of 15 pitches were captured. Inverse dynamic solutions were used calculate the internal elbow moments of six elite youth baseball pitchers. The pitchers that were hampered in throwing fastballs, by the taped pelvis and trunk, showed significant lower ball speeds and peak internal varus moments compared to the pitchers that were allowed to throw without any hindrance.

BackgroundBaseball pitching performance can be mechanically explained by the summation of speed principle and the principle of optimal coordination of partial momenta. Impeding optimal energy generation or transfer by or between the pelvis and trunk segments could provide valuable insight into possible compensation or catch-up mechanisms that may manifest themselves based on these principles.AimThe aim of the present study was to explore the effects of experimentally impeding the mobility of and between the pelvis and trunk segments (1) on ball speed and mechanical peak joint power, and (2) on mechanical peak load of the elbow and shoulder joints at maximal external rotation (MER) during fastball pitching.MethodsEleven elite baseball pitchers (mean age 17.4, SD 2.2 years; mean pitching experience 8.9, SD 3.0 years) were instructed to throw at least 15 fastballs as fast and accurately as possible under two conditions. One condition involved impeding the mobility of the pelvis and trunk segments to hamper their ability to rotate independently, which consequently should affect the separation time, defined as the time interval between the pelvis and trunk peak angular velocities. In the other condition, pitchers threw unimpeded. Ball speed, mechanical peak joint power and peak net moment of the elbow and shoulder at MER were compared between conditions using Generalized Estimating Equations (GEE).ResultsIn the impeded pitching condition, the mean difference of the separation time was 12.4 milliseconds [95% CI (4.0, 20.7)] and for ball speed 0.6 mph [95% CI (0.2, 0.9)] lower compared to the unimpeded condition. Only the peak pelvic angular velocity, in addition to the trunk, upper arm and forearm, was 45 deg/s [95% CI (24, 66)] higher impeded condition. The mean differences of the joint power and net moments at the shoulder and elbow did not reach statistical significance.ConclusionIn elite adolescent baseball, the observed pitching performance after experimentally impeding pelvic and trunk mobility undermines a potential distal catch-up strategy based on the summation of speed principle. The increased peak pelvic angular velocity may indicate a compensation strategy following the optimal coordination of partial momenta principle to practically maintain pitching performance.

A common overuse injury in baseball pitching is the Ulnar Collateral Ligament (UCL) injury, due to high and repetitive loading of the medial side of the elbow. This repetitive loading (i.e. external valgus torque), caused by pitching a high number of balls in a practice session or during a game, is resisted by the UCL and counteracted by the elbow muscles. The elbow muscles have the potential to shield the UCL from the full external load and were active in all fifteen participants during pitching. To understand the injury mechanisms, we investigated the effect of repetitive pitching on the elbow load magnitude and variability. In addition, we explored whether repetitive pitching affects elbow muscle activation during pitching. On a group level, the linear mixed models showed no significant associations of repetitive pitching with valgus torque magnitude and variability and elbow muscle activity. Significant large differences exist between pitchers in their individual courses in elbow valgus torque and muscle activity with repetitive pitching. This shows the importance of individuality in relation to repetitive pitching. To arrive at effective elbow injury prevention in baseball pitching, individual characteristics of changes in elbow load and muscle activity in relation to the development of UCL injuries should be investigated.