THREE-DIMENSIONAL KINETIC ANALYSIS OF THE BASEBALL SWING ROBERT SHAPIRO (Department of Physical Education, Northern Illinois University, DeKalb, IL 60115, U.S.A.) NORMAN R. MILLER (Department of Mechanical Engineering, University of Illinois, Urbana, IL 61801, U.S.A.) Three-dimensional data collection and analysis techniques were developed to evaluate the dynamics of the baseball swing. The Direct Linear Transformation was utilized to obtain the three-dimensional spatial coordinates of points located on the bat. Four-by-four matrix techniques were used to determine the six parameters defining the location of the bat in space. A dual pass digital filter in conjunction with second order central differences were employed to smooth and determine time derivatives of the data. Results demonstrated the motion of the bat to be in two phases. The final action of the bat appeared to be caused by extension of the right forearm at the elbow rather than vigorous wrist action. Average impulsive forces were calculated to be of the order of 35OON. The major component, 93% to 99%, of the kinetic energy of the bat at contact was due to the linear motion of the bat. CONTRIBUTION OF GRAVITY AND CABLE PULL FORCES TO THE CYCLIC FLUCTUATlONS IN HAMMER SPEED IN THE COURSE OF A THROW J. DAPENA and T. BRANFF (Exercise Science Department, University of Massachusetts, Amherst, MA, U.S.A.) J. TIAN (Physical Education Department, Beijing Normal University, Beijing, China) The main factor for success in a hammer throw is hammer speed at release. This study investigates the process of hammer speed increase during the throw, and its causes. Kuznyetsov (1965) reported a general speed increase, with superimposed cyclic fluctuations. He found one local maximum and one local minimum in each turn, approximately at the low and high points of the orbit, respectively. In the present study, three competitive hammer throwers were filmed, and 3D kinematics and kinetics of the hammer head were derived. In all trials the component of gravity force tangential to the hammer path contributed little to the total tangential force. The study showed cable pull force, and not gravity, to be the main factor responsible for fluctuations in hammer speed. DYNAMIC LOAD DISPLACEMENT CHARACTERISTICS OF ATHLEI’IC SHOE MIDSOLE MATERIALS T. E. CLARKE and E. C. FREDERICK (NIKE Sport Research Laboratory, 156 Front St., Exeter, NH 03833, U.S.A.) This study compared the relative force attenuation and energy absorption of various midsole materials using a weighted shaft which was instrumented to provide data on load and displacement when dropped from a range of heights onto sample materials. The amount of energy absorbed was obtained for each drop on a given material through the use ofdynamic load displacement curves. The most important finding ofthis study was that materials which attenuate peak forces to a similar degree can have very different amounts of energy absorption. For example, three of the materials showed similar peak force attenuation, yet the amount of energy absorption measured as hysteresis ranged from 58.2 to 94.7%. Clearly, the ability to attenuate peak forces should not be the only criterion for choosing a midsole material because the amount ofenergy absorbed vs returned by the material may be a consideration, particularly in competition footwear. GENERAL VIEW ON SPORT BIOMECHANICS W~ODZIMIERZ S. ERDMANN (Biomechanics Laboratory, Colkge of Physical Education, Wiejska 1, 80-336 G&&k, Poland) This paper describes elemen ts of sport biomechanics. These are : (1) the sources of the competitor’s characteristics (environment, training), (2) the state of the competitor’s characteristics (general movement co-ordination, mechanical body build, general physical preparation and special tactical, technical, or physical preparation), (3) diagnostic, (4) selection, (5) competition-performance and elements which determine result (partner, opponent, circumstances, referee). The result obtained gives the appropriate place for each competitor. This information may be used as feedback for training and selection. Biomechanists possess research methods by which they can measure all the above elements and predict, with the help of modeling, the result of performance.