INTERNAL ROTATION OF THE UPPER ARM: THE MISSING LINK IN THE KINEMATIC CHAIN
AbstractMany situations in sport demand that maximum speed be produced at the end of the most distal segment. An essential aspect in speed generation is that movement of each segment is exploited in order that maximum speed be generated from the "kinematic chain". A review by Putnam (1993) in discussing the sequencing of motion, while generally supporting the proximal-to-distal order of movement, also stated that internal rotation of the upper arm (UAIR) did not follow this timing pattern. Recent developments in computer software (Feltner and Dapena, 1989; Sprigings et al., 1994; Sakurai et al, 1993) have permitted the role of segment rotations about all their degrees of freedom to be calculated. Data collected by EIliott and colleagues c1early show the importance of UAIR in speed generation of the racket in a number if hitting sports. In the tennis serve approximately 54% of the forward racket velocity at impact can be attributed to this movement. In the forehand drive in tennis and squash approximately 30% of the forward racket velocity at impact could be accounted for through UAIR. These data also clearly show that UAIR is one of the last rotations to occur prior to impact, the majority of action occurring in the period 30 ms before and then after impact. This timing was generally corroborated by data from Rash and Shapiro (1995) on the quarter-back throw in American football and Feltner (1995) in the penalty throw in water polo. UAIR made a significant contribution to a number of hitting and throwing movement patterns, while also occurring very late in the temporal cycle where high end point velocities were desirable. As a link in the kinematic chain it must therefore be considered if three-dimensional movements involving the upper limb are to be understood. REFERENCES FELTNER, M. (1996). Three-dimensional kinematics of the throwing arm during the penalty throw in water polo, personal communication. FELTNER, M.E. & DAPENA, J. (1989). Three-dimensional interactions in a twosegment kinetic chain. Part I: General model, Int. J. Sport Biomech. 5: 403-419. PUTNAM, C. (1993). Sequential motions of body segments in striking and throwing skil/s : descriptions and explanations, J. Biomech. 26 (Suppl 1) : 125-135. RASH, G. & SHAPIRO, R. (1995). Athreedimensional dynamic analysis of the quarterbacks throwing motion in American football, J. of Appl. Biomech. 11 : 443-459. SAKURAI, S.1. KEGAMI, Y, OKAMOTO,A., YABE, K. & TOYOSHIMA, S. (1993). A three-dimensional cinematographic analysis of upper limb movement during fastball and curveball baseball analysis of upper limb movement during fastball and curveball baseball pitches, J ofAppl. Biomech. 9 (1): 47-65. SPRIGINGS, E., MARSHALL, R., ELLIOTT, B. & JENNINGS, l. (1994). A 3-D kinematic method for determining the effectiveness of arm segment rotations in producing racquet-head speed, J. Biomech. 27: 245-254.
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