Kinetic Analysis of Fingers During Aimed Throwing

Abstract

This study had two objectives: (a) revealing the difference in finger segments between the conventional and finger models during aimed throwing and (b) examining the central nervous system's timing control between the wrist torque and finger torque. Participants were seven baseball players. Finger kinetics was calculated by an inverse dynamics method. In the conventional model, wrist flexion torque was smaller than that in the finger model because of the error in ball position approximation. The maximal correlation coefficient between the wrist torque and finger torque was high (r = .85 ± .10), and the time lag at maximal correlation coefficient was small (t = 0.36 ± 3.02 ms). The small timing delay between the wrist torque and finger torque greatly influenced ball trajectory. We conclude that, to stabilize release timing, the central nervous system synchronized the wrist torque and finger torque by feed-forward adjustments.

Kinetic analysis of the wrist and fingers during fastball and curveball pitches

“…Based on the finger model in which the finger segment is considered rigid (Shibata et al, 2018), the kinematics and kinetics of fingers and wrist was calculated. Some mass parameters of the palm segment were modified.…”

“…l DIP and l PIP are calculated from the distal and medial phalange bone lengths, as reported in a previous study (Kong, Freivalds, Kim, & Chang, 2017). The rate of force at each position has been used to calculate the position of the COP in the finger model (Shibata et al, 2018). This data was captured from a force sensor buried in a wooden ball.…”

“…COM H represents the longitudinal COM of the hand segment (de Leva, 1996). COM F represents the longitudinal COM of the finger segment (Shibata et al, 2018). m H is the hand's total mass, 0.3 implies that the finger's mass is 30% of the hand's total mass, and 0.7 implies that the palm's mass is 70% of the hand's total mass.…”

“…The radius of gyration in the palm segment was set as 50% of the hand. The values for the moment of inertia and the radius of gyration in the finger segment were obtained from a previous study (Shibata et al, 2018).…”

“…Thus, it is considered that fingers will show adduction torque before ball release in curveball pitch to produce topspin. Also, Shibata, Inaba, Yoshioka, and Fukashiro (2018) reported that the wrist flexion torque and finger flexion torque during aimed throwing synchronized completely. Thus, we hypothesized that the wrist torque (flexion and ulnar) and finger torque (flexion and adduction) during fastball and curveball pitches would also synchronize completely.…”