Contact State between Fingertip and Ball before Ball-release Observed through Strain of Nails During Baseball Pitch

In order to observe the state of the contact and the release between ball and fingertips during baseball pitching, four strain gauges were affixed crosswise to the surface of each nail of participant's 2nd and 3rd fingers. Simultaneously, the angular velocities of the upper limb, trunk and lower limb were also measured with accelerometers and gyroscope sensors to observe the joint motion during pitching. Participants of this study pitched fastball and some breaking balls more than ten times toward the net located in 5 m forward. The similarity, difference and time lag of motions among fastball, slider and screwball pitches were clarified through analysis of angular velocities. The timings of ball-release in all trials were able to detect by observing the waveforms of strains of nails. The nails at ball-release of fastball pitches mostly showed compressive strains and the strains at N had similar tendency in all participants. In slider pitches, the large strains were found at portion W of nails of all participants. From these results, it became clear that baseball pitchers had the patterns of ball-release for each type of pitch, and had the timing of joint motions in accord with each ball-release.