Kinematic Sequencing Of A Baseball Swing: Does Segment Order Influence Exit Velocity?

The proper kinematic sequence in a baseball swing is considered to occur when the first segment to reach maximum angular velocity is the hip, followed by the torso, arm, and finally the hand. Research is needed to assess the value of this order. PURPOSE: To test the effect of swing sequence on exit velocity in baseball players. METHODS: We captured average and peak exit velocity in 129 baseball players using a Trackman Launch Monitor. This served as our dependent variable. We assessed swing sequence using a K-Motion K-Vest, which captured segmental rotation velocities of the hip, torso, arm, and hand. Independent-samples t-tests compared outcomes of athletes whose swing was in the proper order to those whose swing was out of sequence. Players were also tested for isotonic power in 15 different exercises using a Proteus device to control for variability in strength between athletes. Linear regressions held significant confounders constant to isolate the effect of swing sequence on exit velocity. RESULTS: Subjects were 15.5 ± 3.0 years of age, height was 69.2 ± 3.9 in, and weight was 157.1 ± 34.7 lb. Rotational speed was 718.5 ± 104.1 °/s for the hip, 929.9 ± 147.1 °/s for the torso, 1,161.9 ± 150.4 °/s for the arm, and 1,518.3 ± 206.6 °/s for the hand. Average exit velocity was 74.8 ± 11.7 mph; peak exit velocity was 78.5 ± 9.6 mph. The ideal swing sequence was realized in 38.8% of players. Holding age, height, and weight constant, proper sequence did not affect average exit velocity (p = 0.532; 95% CI of β: -2.009, 3.872) or peak exit velocity (p = 0.710; 95% CI of β: -1.575, 2.305). Holding age, height, weight, and all significant exercise capacities constant, swing sequence did not predict average exit velocity (p = 0.576; 95% CI of β: -2.025, 3.623) or peak exit velocity (p = 0.755; 95% CI of β: -1.325, 1.822). Exit velocity was not related to hip or torso rotational speed (p > 0.100). Arm rotational speed was correlated with average (r = 0.410; p < 0.001) and peak (r = 0.386; p < 0.001) exit velocity. Hand rotational speed was correlated with average (r = 0.474; p < 0.001) and peak (r = 0.558; p < 0.001) exit velocity. CONCLUSIONS: Success in baseball batting is multifactorial. Exit velocity is one component of performance. Proper kinematic sequencing did not result in higher exit velocity in the present study. There may be other domains in which it predicts success.