Predicting Injury in Professional Baseball Pitchers From Delivery Mechanics: A Statistical Model Using Quantitative Video Analysis.

Baseball pitching imposes significant stress on the upper extremity and can lead to injury. Many studies have attempted to predict injury through pitching mechanics, most of which have used laboratory setups that are often not practical for population-based analysis. This study sought to predict injury risk in professional baseball pitchers using a statistical model based on video analysis evaluating delivery mechanics in a large population. Career data were collected and video analysis was performed on a random sample of former and current professional pitchers. Delivery mechanics were analyzed using 6 categories: mass and momentum, arm swing, posture, position at foot strike, path of arm acceleration, and finish. Effects of demographics and delivery scores on injury were determined using a survival analysis, and model validity was assessed. A total of 449 professional pitchers were analyzed. Risk of injury significantly increased with later birth date, role as reliever vs starter, and previous major injury. Risk of injury significantly decreased with increase in overall delivery score (7.8%) and independently with increase in score of the mass and momentum (16.5%), arm swing (12.0%), and position at foot strike (22.8%) categories. The accuracy of the model in predicting injury was significantly better when including total delivery score compared with demographic factors alone. This study presents a model that evaluates delivery mechanics and predicts injury risk of professional pitchers based on video analysis and demographic variables. This model can be used to assess injury risk of professional pitchers and can be potentially expanded to assess injury risk in pitchers at other levels. [Orthopedics. 2018; 41(1):43-53.].

Laboratory observation of localized onset of magnetic reconnection.

Magnetic reconnection is a fundamental process in plasmas that results in the often explosive release of stored magnetic energy, but the trigger for its onset is not well understood. We explore this trigger for fast reconnection in toroidal experiments using a magnetic x-type geometry in the strong guide-field regime. We find that the onset occurs asymmetrically: the reconnection begins on one side of the torus and propagates around approximately at the Alfvén speed. The fast reconnection occurs only in the presence of a global plasma mode, which breaks the axisymmetry and enables the current at the x line to decrease sharply. A simple semiempirical model is used to describe the onset's growth rate.

Experiments on the propagation of plasma filaments.

We investigate experimentally the motion and structure of isolated plasma filaments propagating through neutral gas. Plasma filaments, or "blobs," arise from turbulent fluctuations in a range of plasmas. Our experimental geometry is toroidally symmetric, and the blobs expand to a larger major radius under the influence of a vertical electric field. The electric field, which is caused by nabla B and curvature drifts in a 1/R magnetic field, is limited by collisional damping on the neutral gas. The blob's electrostatic potential structure and the resulting E x B flow field give rise to a vortex pair and a mushroom shape, which are consistent with nonlinear plasma simulations. We observe experimentally this characteristic mushroom shape for the first time. We also find that the blob propagation velocity is inversely proportional to the neutral density and decreases with time as the blob cools.