This study investigated the relationship among hitting components and bat control during the normal and choke-up grip swings. Fourteen intercollegiate and professional baseball players were randomly assigned into five hitting groups. Within each group, the following four hitting components were computed to determine the relationship between bat control in two grip conditions (normal; choke-up): (1) Swing time (bat quickness), (2) stride time, (3) bat velocity, and (4) bat-ball contact accuracy. Results indicated significant differences (p =0.01) between choke-up and normal grips in swing time, stride time, and bat velocity. Players using the choke-up grip swing had significant less swing time and stride time than the normal grip swing. Results also indicated significant greater bat velocities (p = 0.01) with normal grip swings than the choke-up grip swings. In addition, further results indicated no significant differences (p = .90) between choke-up and normal grips in bat-ball accuracy. These findings suggest that the choke-up grip facilitates faster swing time and stride time without compromising bat velocity or contact accuracy.
Key words: bat control, bat quickness, stride time, accuracy.
Historically, since major league baseball established its modern day roots in the early 1900's, the best hitters in the game have studied hitting mechanics to improve their performances (Cobb, 1961; DeRenne, 2007; Gwynn, 1998; Lau, Glossbbrenner, & LaRussa; 1980; Williams, 1970). Though the early day great hall of fame hitters didn't have the advantages of present day high-technology and research-generated information, the majority of those hitters and those of present day agree that by studying and applying swing kinematics will create greater bat control during competition (Alston & Weiskopf, 1972; Cobb, 1961; DeRenne, 2007; Gwynn, 1998; Williams, 1970). From the one of games early great hitters TyCobb (1961), to modern era hall of famer hitter Ted Williams (1970), to eight time major league batting champion and hall of fame hitter Tony Gwynn (1998) and finally to major league home run king great Barry Bonds, these great hitters share in the belief that increasing bat control is essential for successful hitting (Cobb, 1961; Gwynn, 1998; Williams, 1970).
As intercollegiate baseball evolved in the 29th Century mainly from major league influences, hall of fame intercollegiate head coaches such as Rod Dedeaux (Division I Coach of the 20th Century), John Scolinos (Division II Coach of the 21st Century), Skip Berkman (Division I NCAA Coach of the 1990 Decade), Ron Polk (1978), Jerry Kindall (2000) and Tony Gwynn (1998); and intercollegiate hitting coaches Dr. Coop DeRenne, (2007), All-American Jerry Kindall (2000), and Tony Gwynn (1998) also recognize the importance of increasing bat control in various offensive situations (e.g., two-strikes on the hitter, hit-and-run play, hit to opposite field) (Delmonico, 1996). Yet, ask any of these great managers or hitters to define bat control, and there would no common answer. Furthmore, when these highly successful intercollegiate hitters and coaches discuss the topic of bat control, the majority agrees that choking up on the bat will increase bat control (Berkow & Kaplan, 1992; Delmonico, 1996; DeRenne, 2007; Gwynn, 1998; Kindall & Winkin, 2000; Polk, 1978; Stallings, J. & Bennett, B. [Eds.], 2003). If in the opinion of these intercollegiate coaches that choking up on the bat is a hitting technique used specifically in various game offensive hitting situations to increase bat control, then it is important for all collegiate hitters, coaches, and hitting coaches to understand what is bat control and how is it improved.
Anecdotal opinions from intercollegiate head coaches and hitting coaches, suggest that increased bat control is a result of choking up on the bat that may or may not aid in increasing bat speed, or bat swing time ("bat quickness ") (Delmonico, 1996; DeRenne, 2007; Gwynn, 1998; Kindall & Winkin, 2000; Polk, 1978; Stallings, J. & Bennett, B. [Eds.], 2003). In addition, intercollegiate hitters believe that as the bat travels through the swing’s range of motion with a choke-up grip, the bat feels lighter and more controllable (a potential psychological factor beyond the scope of this study) (Adair, 1990; Bahill & Karnavas, 1989; Delmonico, 1996; DeRenne, 2007; Gwynn, 1998; Kindall & Winkin, 2000) as compared to the normal grip swing with hands held down at the end of the bat.
Limited hitting research studies has been conducted over the past twenty-five years to determine bat control and associated factors (DeRenne, & Blitzbau, 1990; Escamilla, Fleisig, DeRenne, Taylor, Moorman, Imamura, 2009; Fleisig, Zheng, Stodden, & Andrews, 2002; McIntyre, & Pfautsh, 1982; Messier, & Owen, 1985; Messier, & Owen, 1986; Szymanski, D.J., DeRenne. C., & Spaniol, F.J., 2009). Based on limited research on bat control, the primary purposes of this study were to explore the relationship among hitting components (stride time, swing time, bat quickness, bat velocity, and bat-ball accuracy), and bat control during the normal and choke-up grip swings.
Fourteen adult baseball players (eight college and six professional players one year removed from college) volunteered to participate and were informed of all risks, hazards and benefits for this study. All participants provided written informed consent as approved by the university’s Office of Research Service’s Committee on Human Studies and the federally mandated Institutional Review Board. All participants were required (1) to be injury-free, (2) have a career batting average of least .300, (3) have choke-up grip hitting experiences at the youth, high school and collegiate levels, (4) and possess good hitting mechanics as determined by the players’ respective hitting coaches (DeRenne, 2007; Race, 1961; Welch, Banks, Cook, & Draovitch, 1995). The subjects had an average age, weight, and height of 22.2±2.3 y, 84.8±6.6 kg, and 180.6±3.7 cm, respectively. The college and professional participants were statistically equivalent to each other with respect to age, body mass, body height, bat characteristics, and temporal and kinematic parameters (Escamilla et al., 2009).
Pitched baseballs were assessed during the batting practice session by an electromagnetic radiation radar (CMI Model JF 100) with a transmission frequency of 10.525 GHz + 25 MHz (DeRenne, Ho, Blitzblau, 1990). Pitched ball velocities were recorded as the ball left the pitching machine. This radar gun has been reported to be a valid and reliable instrument to determine ball exit velocities and is accurate within ± 0.22 m/s (DeRenne et al., 1990).).
Two synchronized gen-locked 120 Hz video cameras (Peak Performance Technologies, Inc., Englewood, CO) were optimally positioned to view the hitter. To minimize the effects of digitizing error, the cameras were positioned so that the hitter was as large as possible within the viewing area of the cameras.
A 3-D video system (Peak Performance Technologies, Inc., Englewood, CO) was used to manually digitize data for all subjects. A spatial model was created, comprised of the top of the head, centers of the left and right mid-toes (at approximately the head of the third metatarsal), joint centers of the ankles, knees, hips, shoulders, and elbows, mid-point of hands (at approximately the head of the third metacarpal), and proximal and distal end of bat. All points were seen in each camera view. Each of these points was digitized in every video field.
Total body swing kinematics was calculated representing 59 measurements. The three most important swing kinematics that represented the total swing effects to be analyzed for swing grip differences were as follows: stride time, swing time (bat quickness), and estimated linear bat velocity at bat-ball contact.
The swing was defined by four events and three phases. The first event was “lead foot off ground”, which represented the beginning of the stride phase and was defined as the first frame in which the lead foot was no longer in contact with the ground. The next event was “lead foot contact with ground”, which represented the end of the stride phase and was defined as the first frame when the lead foot made contact with the ground. “Lead foot off ground” to “lead foot contact with ground” represented the time duration of the stride phase of the swing. The third event was “hands started to move forward”, which was defined as the first frame that both hands started to move forward towards the pitcher in the positive X direction. “Lead foot contact with ground” to “hands started to move forward” represented the time duration of the transition phase of the swing (transition between the stride phase and acceleration phase). The last event was “bat-ball contact”, which was defined as the first frame immediately before bat-ball contact. “Hands started to move forward to bat-ball contact” represented the time duration of the acceleration phase of the swing. Therefore, the “swing” was defined as from “lead foot off ground” to “bat-ball contact”, and consisted of stride, transition, and acceleration phases.
During the initial familiarization session, all players were given a preliminary choke-up questionnaire to provide background evidence of choking up on the bat during their respective youth, high school and collegiate careers. In order to participate in the choke-up hitting study, all players must have had answered the first three questions with a YES, indicating a substantial history of choking-up during their baseball careers. On question four, the players were asked to list the two top reasons why they decided to choke-up on the bat in competitive games. Bat control was listed by all 14 players (100%) as the number one reason for choking up in the games. The second highest reason was a tie: 50% indicated bat-ball contact accuracy was their second choice; and 50% indicated increased bat speed and bat quickness.
In addition, all players received batting practice instructions. At no time did the investigators reveal the purpose of the study to the players. They were told only that the study was a biomechanical hitting study to determine the mechanical commonalities of the 14 adult swing mechanics.
Bats were self-selected, and average bat weight was 8.5±0.3 N (30.6±1.1 oz) and average bat length was 84.8±1.3 cm (33.4±0.5 inch). The same bat was used for both grip swings. The players were randomly assigned into five hitting groups (4-groups of n =3; 1-group of n=2). Each group was randomized as to the order of group hitting and which bat grip to use. During warm-up, each player had two to-three rounds of hitting with each grip swing to become familiar with the speed and locations of the pitched balls, and the timing of the pitches from the pitching machine. Once the warm-up session was completed, the batting practice sessions commenced.
The first batting session was to determine the kinematic and temporal effects of the normal grip and choke -up grip swings. Each hitter rotated within his respective group until he completed 10 hard, full effort swings with a normal grip (hands as far down as possible on the bat); and 10 hard, full effort swings with a choke-up grip (hands 6.35 cm above the normal grip) as a pitching machine "pitched" baseballs to them. In each group, half the group were randomly assigned to hit with a normal grip first and the other half a choke-up grip first, to eliminate a potential timing confounder. The first three normal grip swings and three choke-up swings that met the following pitch and swing criteria were digitized for each hitter.
Pitches and swings were standardized according to the following criteria: 1) all pitches were between 32.6-33.5 m/s (73-75 mi/h); 2) the pitch had to be a strike on the inner half of the plate from waist to chest high on the hitter; and 3) all swings digitized and used as trials had to be a line drive hit to left-center outfield that carried in flight beyond a 68.6 m (225 feet) marker positioned in left-center field. From pilot data, hitting kinematic and temporal parameters from multiple swings by a hitter that met the above pitch and swing criteria were found to be remarkably similar between swings, typically varying less than 5-10% for each kinematic or temporal parameter.
The second batting practice session was conducted 48-hours after the first batting practice session in order to control fatigue. The purpose of this second batting practice session was to determine bat-ball contact accuracy performances of each player as the hitters executed normal and choke-up grip swings during a live practice simulated game. Along with the first batting practice session, this accuracy batting practice session represented a bat control measure. Specifically, each hitter was instructed to swing at ten acceptable strikes over the entire plate, (inside, down the middle and outside part of the plate; from knee to chest high) with each swing grip as to execute successful hits. Two rounds of five swings were performed by each hitter to control fatigue. A successful hit was defined as “putting the ball in play” with at least a normal or routine (1) groundball, (2) fly ball or (3) line drive. Unacceptable hits were as follows: (1) A swing and miss, (2) foul ball, (3) a weak pop-up, and (4) a weak groundball. As each hitter attempted to “put the ball in play”, they were instructed to swing accordingly with a “full” count of two strikes and three balls as live base runners were moving. In addition, if the pitch was a ball, they were instructed to take the pitch and swing only at acceptable strikes. Only swinging strikes counted against acceptable pitch strikes until each player accumulated ten acceptable swings from each grip. Again, the accuracy goal for each swing was to successfully put the ball in play. The four-man investigative team determined the following: (1) the first investigator determined if the pitch was acceptable within the 73-75 mph range and if the pitch was a strike or ball; and (2) the remaining three investigators determined the degree of accuracy and degree of hardness (e.g., no hit, weak hit, routine hit, hard hit) of each swing. The mean accuracy average of the three investigators was determined for each player's swing. The mean average was then converted into percentages, which were described as either a YES, successful; or a NO, unsuccessful swing/hit. Therefore, the resultant percentage describes the percentage out of ten swings that each player put the ball in play (see Table 1).
Table 1. Paired Sample T Test for Hitting Parameters in the Normal and Choke-up conditions (n = 14).
|Normal Grip||Choke-up Grip||p value|
|(Time from Lead Foot Off Ground to
Lead Foot Contact with Ground) (s) (% of Swing)
|p = .01|
|(Time from Lead Foot Off Ground to
Bat-Ball contact) (m/s)
|0.586±0.078*||0.535±0.083*||p = .01|
|Bat (distal end) Linear Velocity at
Bat-Ball Contact (m/s)
|Contact Accuracy Acceptable Hits Out Of
Ten Pitched Strikes (%)
|.63±.15||.64±.18||p = .90|
All data analyses were performed using SPSS, version 14.0 (Statistical Package for the Social Sciences, 2005). Kinematic and temporal data were averaged for the three normal swings and for the three choke-up swings and used in statistical analyses (Escamilla et al., 2009). Dependent (paired) t-tests were employed to test for differences in kinematic and temporal parameters and bat-ball accuracy between the normal grip and choke-up grip swings. In order to minimize the probability of making a type I error without increases the probability of making a type II error, the level of significance used was set at p < 0.01, resulting in an experiment-wise error of 0.31.
Temporal stride and swing parameters are shown in Table 1. The results of the dependent (paired) sample T-tests revealed no significant differences in bat-ball contact accuracy t(- .12) between the normal and choke-up conditions. Significant differences were found between stride time t(2.88) with the mean choke-up grip swing .039 seconds (10%) faster than the normal grip swing. Similar significant differences where found between swing time t(2.56) with the mean choke-up grip swing .051 (9%) seconds faster to the bat-ball contact. In addition, similar significant differences where found between bat velocity t(.289) with mean normal grip swing 3.0 m/s (10%) faster than the choke-up grip swing.
This study investigated the relationship among hitting components and bat control during the normal and choke-up grip swings. We found the choke-up grip facilitates faster swing and stride times without compromising bat velocity and bat control.
Two important findings in the present study were the significant reduced swing time (increased bat quickness) and stride phase time when using a choke-up grip swing. These results support the belief of many intercollegiate hitting coaches and players (Delmonico, 1996; DeRenne, 2007; Gwynn, 1998; Kindall & Winkin, 2000; Polk, 1978; Stallings, J. & Bennett, B. [Eds.], 2003) that using a choke-up grip results in a “quicker” bat during the swing (DeRenne & Blitzbau, 1990). When choking up, the hitters adjusted their swing mechanics for more bat control resulting in less stride time and increased bat quickness while not sacrificing a significant loss in bat velocity. In addition, the choke-up hitter may have better control the bat due to the smaller moment of inertia of the bat about the hands that choking up on the bat creates (Adair, 1990; Bahill & Karnavas, 1989; Fleisig et al., 2002).
Based on the results, the choke-up grip bat controlled swing may give hitters 0.039 seconds or 10% more time to decide whether or not to swing at a pitch. This may help the hitters to see the ball longer, due to the trunk being in a more open position and a smaller moment of inertia of the bat allow the choke-up hitter to have more time to “wait on the pitch”. Furthermore, the decrease in stride phase time using a choke-up grip may result in less total body movement for greater balance and possibly improved visual clarity (DeRenne, 2007), while maintaining the same stride length compared to the normal grip.
Choking up on the bat for more bat control allowed the hitters to reduce the moment of inertia of the bat about the hands (Adair, 1990; Bahill & Karnavas, 1989). That is, more of the bat mass was closer to the hands, so the summation of mass times distance squared (Σ (m·r2)) was reduced. Similarly, in golf, to increase club control and maximize the accuracy of pitching and chipping shots, professional golfers choke-down the grip-handle toward the shaft to produce a lower grip on the club and a slower/shorter backswing (Hume, Keogh, & Reid, 2005). In addition in assessing putting kinematics of low-handicap golfers versus high-handicap players, Paradisis and Rees (2002) reported that low-handicap players positioned their leading hand ~8cm further down the shaft of the club than the high-handicap players. In the present study, while the smaller moment of inertia in the choke-up group may lead to faster movements and to a diminished force production in accordance with the force-velocity relationship for muscle. This may be an important factor in helping to explain why linear bat velocity at bat-ball contact was less using a more controlled choke-up grip swing compared to a normal grip swing. It also may be that while choking up, the bat is “shorter”, thus, the distal endpoint of the bat is closer to the axis of rotation and traveling slower compared to the a normal grip swing. Therefore, the slower bat linear velocity at bat-ball contact when using the choke-up grip compared to the normal grip could be related to either or both of these factors.
Similar in tennis, (Chow, Carlton, Lim, Chae, Shim, Kuenster, and Kokubun, 2003) compared the pre-and post-ball and racquet kinematics of professional adult men and women (n=8) tennis players’ first and second serves. The results indicated a 24.1% decrease in post-impact ball speed from the first to the second serve. This finding was expected since the second serve is considered to be more accurate than the first serve because players are successful on a higher percentage of the second serves (Chow et al., 2003). More importantly, the second finding revealed that there were no significant differences between the pre-impact racquet head speeds of the first and the second serves. On the typical second serve, most elite players will use a sidespin “slice” serve increasing racquet control as a trade-off between ball speed and accuracy (Chow et al., 2003). In others words, it might have been expected that elite tennis players would have slowed down their racquet speed on the second slice serve to ensure greater accuracy. This did not happen. Therefore, there was a speed-accuracy trade-off between ball speed and accuracy, but not racquet movement speed and accuracy. Elite tennis players do not slow down their racquet swing when transferring from the first serve to the second serve. The authors also found no differences between racquet speed and accuracy as typically observed in motor tasks (Fitts, 1954).
In the current study, the choked-up bat velocities declined by a significant 10%; yet, the players’ swing times decreased by a significant 9%, which produced a quicker bat. Hence, as elite baseball hitters and tennis pros seek greater bat control when the hitters choke up and tennis pros serve the second serve, interestingly, both hitters and tennis pros swing just as hard and fast as with their normal swing respectively, with no trade-off between bat and racquet speeds and accuracy.
Furthermore, the current study is similar to the results of the pilot baseball swing study comparing the kinematic and temporal parameters of normal and choke-up grips swings reported by DeRenne & Blitzbau (1990). The result reported by DeRenne & Blitzbau (1990) of greater linear bat velocity at bat-ball contact using the normal grip may appear surprising to many collegiate head coaches and hitting coaches. Most collegiate coaches believe that a “quicker” and controlled swing using the choke-up grip equates to greater bat speed (Delmonico, 1996; DeRenne, 2007; Gwynn, 1998; Kindall & Winkin, 2000; Polk, 1978; Stallings, J. & Bennett, B. [Eds.], 2003). Although linear bat velocity was significantly less in the choke-up grip swing compared to the normal grip swing, and although the mass of the bat is the same between normal and choke-up grips, there are data that imply that choking up on a bat may affect the “effective mass” of the bat, resulting in less momentum (mass x velocity) with the choke-up grip (Fleisig et al., 2002). Therefore, using a choke-up grip for more bat control may result in decreased ball flight distance after bat-ball impact, which should be the focus of subsequent hitting studies.
Major league hall of fame hitters, hitting coaches, and managers (Alston & Weiskopf, 1972; Cobb, 1961; Lau, et al., 1998; Williams, 1970), and intercollegiate head coaches and hitting coaches believed that more bat control would produce greater bat-ball accuracy ((Delmonico, 1996; DeRenne, 2007; Gwynn, 1998; Kindall & Winkin, 2000; Polk, 1978; Stallings, J. & Bennett, B. [Eds.], 2003). ). This belief was supported in theory by Bahill’s and Karnavas’s (1989) baseball bat weights study. These investigators suggest that as hitters choke-up on the bat they will make the bat effectively shorter, move the center of mass closer to the hands thereby reducing the moment of inertia, in essence making the bat act like a lighter bat with greater accuracy. In contrast, the results of this study indicated that choking up on the bat did not increase bat-ball contact accuracy. Yet in essence, the hitters were as accurate choking up as with their normal grip swing.
In summary and most importantly, the results of this study suggest that choking up for greater bat control may increase the hitter’s confidence and execution knowing that is able to wait longer for the incoming pitch because he is quicker to the ball, and he is as accurate as his normal grip swing.
In conclusion, although time was not significantly different in the acceleration phase between normal and choke-up grips, the total time of the swing (from stride initiation to bat-ball contact) was significantly less with the choke-up grip, which supports the belief of many coaches and players that using a bat controlled choke-up grip results in a “quicker” overall swing. This “quicker bat" implies that with the bat controlled choke-up grip, a hitter can wait longer in order to determine how to handle the incoming pitch. In addition, because linear bat velocity was significantly less in the choke-up grip compared to the normal grip, there may be less momentum with the choke-up grip because of the differences in mass distribution of the bat with choking up, which may result in decreased ball flight distance after impact. A decreased flight distance (power) may not be so negative, since the hitter’s main goal is more solid contact accuracies.
Adair, R.K. (1990). The physics of baseball. New York, NY.: Harper & Row Publishers.
Alston, W. & Weiskopf, D. (1972). The complete baseball handbook. Boston: Allyn and Bacon, Inc.
Bahill, A.T. & Karnavas, W.J. (1989). Determining ideal baseball bat weights using muscle force-velocity relationships. Biological Cybernetics, 62, 89-97.
Berkow, I., & J. Kaplan (1992). The gospel according to Casey. New York: St. Martin’s Press.
Chow, J.W., Carlton, L.G., Lim, Y.T., Chae, W.S., Shim, J.H., Kuenster, A.F., & Kokubun, K. (2003). Comparing the pre-and post-impact ball and racquet kinematics of elite tennis players’ first and second serves: A preliminary study. Journal of Sport Sciences, 21, 529-537.
Cobb, T. (1961). My life in baseball: The true record. Garden City, NY: Doubleday Co.
Delmonico, R. (1996). Offensive baseball drills. Champaign, IL.: Human Kinetics.
DeRenne, C. (2007). The scientific approach to hitting: Research explores the most difficult skill in sport. San Diego, CA, University Readers.
DeRenne, C., & Blitzbau, A. (1990). Why your hitters should choke up. Scholastic Coach, Jan, 106-107.
Durocher, L. (1975). Nice guys finish last. New York, NY.: Simon & Schuster.
Escamilla, Fleisig, R.F., S., DeRenne, C, Taylor, M.K., Moorman, C.T., Imamura, R., et al. (2009). Effects of bat grip on baseball hitting kinematics. Journal of Applied Biomechanics, 25, 203-209.
Fitts, P.M. (1954). The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology, 47, 381-391.
Fleisig, G. S., Zheng, N., Stodden, D. F., & Andrews, J. R. (2002). Relationship between bat mass properties and bat velocity. Sports Engineering, 5, 1-8.
Gwynn, T. (1998). The art of hitting. Vancouver, BC, Canada: GT Publishing.
Hume, P.A., Keogh, J., & Reid, D. (2005). The role of biomechanics in maximizing distance and accuracy of golf shots. Sports Medicine, 35 (5): 429-449.
Kindall, J., & Winkin, J. (2000). The baseball bible. Champaign, IL.: Human Kinetics.
Lau, C., Glosssbrenner, A., & LaRussa, T. (1980). The art of hitting .300. New York, NY: E.P. Dutton.
McIntyre, D. R., & Pfautsh, E. W. (1982). A kinematic analysis of the baseball batting swings involved in opposite-field and same-field hitting. Research Quarterly in Exercise and Sport, 53, 206-213.
Messier, S. P., & Owen, M. G. (1985). The mechanics of batting: Analysis of ground reaction forces and selected lower extremity kinematics. Research Quarterly in Exercise and Sport, 56, 138-143.
Messier, S. P., & Owen, M. G. (1986). Mechanics of batting: Effect of stride technique on ground reaction forces and bat velocities. Research Quarterly in Exercise and Sport, 57, 329-333.
Paradisis, G. & Rees, J. (2002). Kinematic analysis of golf putting for expert and novice golfers: In: Hong, Y., editor. Proceedings of XVIII International Symposium on Biomechanics in Sports; 2002 Jul 23-26. Hong Kong. Hong Kong: Department of Sports Science and Physical Education, The Chinese University of Hong Kong, 2002: 325-8.
Polk, R. (1978). Baseball playbook. West Point, Miss.: Sullivan’s Printing.
Race, D.E. (1961). A cinematographic and mechanical analysis of the external movements involved in hitting a baseball effectively. The Research Quarterly, 32, 394-404.
Stallings, J. & Bennett, B. [Eds.] (2003). Baseball strategies: Your guide to the game within the game. Champaign, IL.: Human Kinetics.
Szymanski, D.J., DeRenne. C., & Spaniol, F.J. (2009). 1Contributing factors for increased bat swing velocity: A Brief Review. Journal of Strength and Conditioning Research (in press).
Welch, C. M., Banks, S. A., Cook, F. F., & Draovitch, P. (1995). Hitting a baseball: a biomechanical description. Journal of Orthopaedic and Sports Physical Therapy, 22, 193-201.
Williams, T. (1970). The Science of Hitting. New York, NY: Simon and Schuster.