KINEMATIC AND KINETIC COMPARISON OF BASEBALL PITCHING FROM A MOUND AND THROWING FROM FLAT GROUND

G.S. Fleisig, R.F. Escamilla, S.W. Barrentine, N. Zheng, J.R. Andrews
American Sports Medicine Institute, Birmingham, AL 35205

Presented at the 20th Annual Meeting of the American Society of Biomechanics
Atlanta, Georgia. October 17-19, 1996

INTRODUCTION

The kinematics and kinetics of baseball throwing were compared between pitching from a mound and throwing from flat ground. Differences may help explain why most baseball throwing injuries involve pitchers. Results may also help determine the appropriateness of flat-ground throwing drills (such as long toss) for pitchers, as well as considerations for changing players between pitching and non-pitching positions.

REVIEW AND THEORY

Most overuse throwing injuries in baseball involve the pitcher. Consequently, previous motion analysis research in baseball throwing has focussed on the pitcher (Dillman et al., 1993; Elliott et al., 1986; Feltner et al., 1986; Fleisig et al., 1995; Fleisig et al., 1996; Pappas et al., 1995; Pappas et al., 1985; Sakurai et al., 1993; Vaughn, 1985; Werner et al., 1993). Conversely, minimal research has been published on baseball throwing mechanics utilized by non- pitchers (Atwater, 1979; Elliott et al., 1990; Hay, 1985), and no research has reported mechanics used by pitchers during flat ground drills. Although minimal scientific data are available, many baseball experts believe that throwing mechanics from a mound and from flat ground are similar; therefore, throwing from flat ground (in competition or practice) is appropriate training for a pitcher. The purpose of this study was to evaluate the hypothesis that minimal kinematic and kinetic differences exist between pitching from a mound and throwing from flat ground.

PROCEDURES

Twenty-seven healthy college baseball pitchers were tested. Their height was 1.84 ± 0.07 m, and their mass was 81.6 ± 8.8 kg. After providing informed consent, history, and physical information, each pitcher was tested in an indoor laboratory. Reflective markers were attached bilaterally to the distal end of the mid-toe, lateral malleolus, lateral femoral epicondyle, greater trochanter, lateral tip of the acromion, and lateral humeral epicondyle. A reflective band was wrapped around the wrist on the throwing arm and a reflective marker was attached to the ulnar styloid of the non-throwing arm. After stretching, the subject threw three balls from seven different conditions (i.e. 21 total trials). The conditions were: 100% effort from a standard- height 10" mound, 180' crow-hop throw, 120' crow-hop throw, 60' crow-hop throw, 75% effort from a 10" mound, 50% effort from a 10" mound, 100% effort from a 13" mound. Only data from the first four conditions listed were used for this study. The order of conditions was randomized for each subject, and warm-up time was provided before testing each condition. For all trials on a mound, the subject pitched from a portable pitching mound (B&P Sports Products Inc., Amelia, OH) towards a strike zone ribbon located over a home plate at a distance of 18.4 m (60.5 ft) from the pitching rubber. Velocity of the ball as it left the pitcher's hand was recorded with a Tribar Sport radar gun (Jugs Pitching Machine Company, Tualatin, OR).

Three dimensional coordinates during the second trial of each condition was determined with a four-camera 200 Hz automatic digitizing system (Motion Analysis Corporation, Santa Rosa, CA). Root mean-square error in calculating the three-dimensional location of markers randomly placed within the calibrated space was 1.0 cm. Using the digitized data, and published anthropometric data, 23 kinematic (Figure 1) and kinetic (Figure 2) parameters were calculated as previously described (Dillman et al., 1993; Fleisig et al., 1995; Fleisig et al., 1996). A one way repeated measures Analysis of Variance was performed, using a Bonferroni t- test to identify significant (p<0.05) differences between pitching from a mound (i.e. control group) and the other conditions.

Figure 1. Kinematic parameters: (a) elbow flexion; (b) shoulder external; (c) shoulder abduction; (d) shoulder horizontal adduction; (e) lead knee flexion; (f) forward trunk tilt; and (g) pelvis angular velocity ( P) and upper torso angular velocity ( UT).

Figure 2. Kinetic parameters: (a) shoulder forces; (b) shoulder torques; (c) elbow forces; and (d) elbow torques

Table 1: Mound pitching and flat ground throwing parameters. Angles, velocities, forces, and torques in deg, deg/s, N, and Nm, respectively, except where indicated.
* Significantly different (p<0.05) from pitching.

RESULTS AND DISCUSSION

Contrary to the belief that pitching and flat ground throwing mechanics are the same, several significant differences were found (Table 1). Throwing from flat ground corresponded with a shorter stride and less shoulder external rotation at foot contact. The drop of the mound appears to give the pitcher more time to stride forward a greater distance, and more time to externally rotate the shoulder. Arm and body motions and kinetics during arm cocking and acceleration were similar between mound and flat ground throwing.At the instant of ball release, a pitcher's trunk was more vertical when throwing from flat ground. However, relative to the throwing surface, the trunk angle was the same for 60' throwing from flat ground and pitching from a mound. This is because the trunk was 5ø less upright for pitching from the mound, but the mound was sloped 5ø downward. The trunk was 3ø more upright for the longer distance throws, which may help the athlete throw the ball with a slightly more upward trajectory in order to get more distance.

During arm deceleration, compressive forces generated at the elbow and shoulder to resist distraction were less in long distance flat throws than in 60' mound or flat throws. This may be related to the low incidence of throwing injuries in non-pitchers. Reduced deceleration forces in long toss support the concept that these are good training drills for pitchers. The biomechanics of these throws are similar to pitching; however, when converting from other positions or from flat ground training to pitching from a mound, an athlete should lengthen his stride and tilt his trunk forward.

REFERENCES

Atwater, A.E. et al. Exer Sport Sci Rev, 7, 43-85, 1979.

Dillman, C.J. et al. J Orthop Sports Phys Ther, 18(2), 402- 408, 1993.

Elliott, B. et al. J Human Mov Stud, 18(1), 1-23, 1990.

Elliott, B. et al. Int J Sport Biomech, 2(1), 20-28, 1986.

Feltner, M. et al. Int J Sport Biomech, 2(4), 235-259, 1986.

Fleisig, G.S. et al. Am J Sports Med, 23(2), 233-239, 1995.

Fleisig, G. S. et al. J Appl Biomech, 12(2), 207-224, 1996.

Hay, J.G. Biomechanics of Sport Techniques, Prentice-Hall, 1985.

McLeod, W.D. et al. Phys Ther, 66(12), 1901-1904, 1986.

Pappas, A.M. et al. Am J Sports Med, 23(3), 312-315,1995.

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Sakurai, S. et al. J Appl Biomech, 9(1), 47-65, 1993.

Werner, S.L. et al. J Orthop Sports Phys Ther, 17(6), 274-278, 1993.

ACKNOWLEDGEMENTS

The authors would like to thank B&P Sports Products for donating the mounds. The assistance in data collection and analysis provided by Andy DeMonia and Phillip Sutton is also greatly appreciated. In addition, the authors wish to thank the pitchers and coaches from the University of Alabama, the University of Alabama at Birmingham, and Samford University for their participation in this study.