Arm Cocking And Upper Torso Rotation Patterns Associated With Elbow Varus Torque In Baseball Pitching

Abstract

PURPOSE To examine relationships among the shoulder horizontal abduction (HA) component of arm cocking, upper torso rotation, and the elbow maximum VT. METHODS A twelve-camera opto-electric system was used to collect kinematic data from 12 college and 8 high school pitchers. Joint kinematics and kinetics of three maximum effort strikes were averaged for each subject. A shoulder HA angle of zero meant that the upper arm was horizontal in the frontal plane. An upper torso angle of zero meant the lead shoulder was pointing directly towards home plate (throwing shoulder pointing towards second base). Subjects were divided into two groups based on the shoulder maximum HA angle achieved during arm cocking (high horizontal abduction HHA and low horizontal abduction LHA). Each group was then separated into high and low VT pitchers (top 5 and bottom 5). Two-way independent ANOVA (HA and VT) and independent t-tests were used to assess differences among pitchers (α=0.05). RESULTS Normalized elbow maximum VT varied substantially among all pitchers (1.2–4.6 % of body weight and height). No significant difference in VT was found between the HHA (3.21±0.81) and LHA (3.21±0.94) groups. However, the HHA group had significantly higher throwing velocity (80.7±3.2 mph) than the LHA group (75.9±3.2 mph). Two upper torso variables were assessed with respect to VT. First, high VT pitchers achieved a significantly greater upper torso maximum rotational angular velocity than low VT pitchers during the cocking phase (987±106°/s vs. 815±85°/s, respectively). Second, a univariate analysis revealed that high varus torque HHA pitchers achieved shoulder maximum HA at a significantly more open upper torso orientation (12.1±18.3°) than low varus torque HHA pitchers (−10.5±19.7°). CONCLUSIONS These results suggest that shoulder HA range of motion 1) may be an important factor in determining throwing velocity and 2) may have minimum influence on elbow VT. The elbow VT appears to be related to the timing of shoulder HA and upper torso rotation styles used during the arm cocking phase.