Introduction The catcher should receive as much attention as a pitcher does in determining the factors involved in infield defense (Barzun, 1973). In a baseball game, catchers make more throws then other position player. Baseball coaches` main focus to maintain fast yet proper footwork, align the front shoulder with target, take out the ball quickly and pass it out in an actual situation (Fortenbaugh et al,.2010). Therefore, the aim of the present study was to investigate the lower extremity biomechanics involved forward stepping throwing and non-stepping movements in squatting postures. Methods Healthy college baseball catchers (n=12) were recruited for the study. An eight-camera Expert Vision Raptor motion analysis system (Motion Analysis Corp., Santa Rosa, CA, USA) was used to collect the position of the reflective markers at a sampling rate of 500 Hz. The tri-axial measurement of ground reaction force of catcher`s pivot foot is carried out with two force plates (1000 Hz) made by Kistler Instrument Corporation (Type 9281B: 2 sets, Kistler Instrument Corp, Winterhur, Switzerland). Results A number of significant differences were seen between the forward stepping throwing and non-stepping throwing, most notably ball speed (forward stepping throwing: 29.36.± 3.63 m s-1; non-stepping throwing: 25.734. ± 2.03 m s-1) (p = 0.000). In pivot foot, the adduction and abduction of knee and hip joint in non-stepping throwing were significantly greater than forward stepping movement (p=0.000). When forward stepping movement is performed, the upward-forward ground reaction force of the pivot foot is significantly greater than in non-stepping throwing (p = 0.000), and this difference continues to the stride period. Discussion In a previous study by Plummer and Oliver (2013), catchers passed the ball on knees. It was found that when lower limbs could not perform footwork, they were able to contribute little to energy generation in ball-passing movement, which put more loading on upper limbs and increased injury risk. Through forward stepping movement, this study identified that the greater upward-forward ground reaction force in the pivot foot appeared at the stride phase to push off and generate the driving force. Moreover, pervious investigators founded Weight-shift (forward stepping) throwing caused the flexion angle for greatest hamstring activation in the midst of the stride phase and pivot throwing occurred directly after the stride phase (Plummer and Oliver, 2014). To sum up, which is a possible reason for the higher ball speed and less injury risk in forward stepping movement. These information suggested helpful when training and developing efficient throwing mechanics.
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