Dec 6, 1998 - Eminent Scholar of Sports Medicine; Professor, College of Health and Human Sciences, Troy State. University, Troy, A1 ... ing of the mechanics and the stresses that result on the ..... shoulder and elbow were the great- est.
Biomechanics of Windmill Softball Pitching With Implications About Injury Mechanisms at the Shoulder and Elbow Steven W. Barrentine, MS Glenn S. Fleisig, PhD * james A. Whiteside, M D Rafael F. Escamilla, PhD james R. Andrews, M D
'
Underhand pitching has received minimal attention in the sports medicine literature. This veruse injuries caused may be due to the perception that, compared with overhead pitching, the underhand motion by the overhand creates less stress on the arm, which results in fewer injuries. The purpose of this study was to throwing motion in calculate kinematic and kinetic parameters for the pitching motion used in fast pitch sofiball. Eight men's baseball pitchfemale fast pitch soflball pitchers were recorded with a four-camera system (200 Hz). The results ing have been wellindicated that high forces and torques were experienced at the shoulder and elbow during the documented (3,13,16,17,25). To addelivery phase. Peak compressive forces at the elbow and shoulder equal to 70-98% of body dress this problem, several studies weight were produced. Shoulder extension and abduction torques equal to 940% of body have investigated the kinematics and weight x height were calculated. Elbow flexion torque was exerted to control elbow extension and kinetics during overhand pitching initiate elbow flexion. The demand on the biceps labrum complex to simultaneously resist (5,6,8,10,19,20,24).Forces produced glenohumeral distraction and produce elbow flexion makes this structure susceptible to overuse at the shoulder and elbow during injury. baseball pitching are equivalent to 80-120% of body weight (BW) for Key Words: biomechanics, underhand pitching, softball, shoulder, elbow compressive forces and 30 to 45% ' Biomechanist, American Sports Medicine Institute, Birmingham, AL BW for shear forces (8,lO-12,24). Smith & Nephew Chair of Research, American Sports Medicine Institute, 1313 13th Street South, Torques exerted at the shoulder and Birmingham, A1 35205 ' Eminent Scholar of Sports Medicine; Professor, College of Health and Human Sciences, Troy State elbow to generate the high velocities University, Troy, A1 during throwing are equivalent to Assistant Professor, Orthopaedic Surgery, Duke University Medical Center, Durham, NC 3-7% of body weight multiplied by Medical Director, American Sports Medicine Institute, Birmingham, AL height (BW X HT). Critical instances of the overhand pitching motion have been identified and related to NCAA softball tournament, Loosli et cluded that softball pitchers experiinjury mechanisms for rotator cuff a1 (14) attempted to quantify the fre- ence significant time-loss injuries as a tensile failure, subacromial impingequency of injury to underhand pitch- direct result of the underhand pitchment, and anterosuperior labrum ing motion. ers. Twenty of the 24 pitchers that tear at the shoulder (10). Injuries to softball pitchers have participated in the survey reported 26 Underhand pitching has received injuries, with 17 of these injuries inprompted investigations of the underlittle attention in the sports medicine volving the upper extremity. Eightyhand pitching motion. Based on literature. It has been noted that the three reported cases of fatigue fractwo percent of all time-loss injuries limited attention may be due to the (grade I1 and 111) involved the upper tures of the ulna, Tanabe et a1 (21) perception that the underhand moextremity. Almost one-half of all time- used high-speed cinematography and tion creates less stress on the arm loss injuries (five of 11) involved inju- computed tomography scans of six collegiate pitchers (three males, and, thus, fewer injuries occur (14). ries to the shoulder and elbow, inthree females) to analyze the underUsing a survey of eight collegiate soft- cluding bicipital and rotator cuff hand pitching motion and the resulttendinitis and strain. It was conball teams participating in the 1989
0
-
-
JOSFT Volume 28 * Number 6 December 1998
RESEARCH
-
STUDY
.. .
- - . . . . . . . . . . - . . - .-
. . .. . .
--
FIGURE 1. A view of laboratory set-up with a softball pitcher during testing.
ing effects on the ulna. The authors attributed the fractures to torsional stress exerted on the forearm as the arm pronated after release of the ball (21). The occurrence of injury to softball pitchers has also prompted the investigation of muscle firing patterns during the windmill fast pitch motion (15). The electromyographic activity of eight shoulder muscles for 10 collegiate pitchers were analyzed, and contributions to joint stabilization and arm velocity were determined. The dearth of research studies investigating the underhand pitching motion has limited the understanding of the mechanics and the stresses that result on the shoulder and elbow. Based on the results reported by Loosli et al, it is hypothesized that the stresses on the shoulder and elbow generated during underhand pitching are similar to the stresses experienced during overhand throwing. The purpose of this study was to calculate kinematic and kinetic parameters at the shoulder and elbow that occur during underhand windmill pitching in women's fast pitch softball. These results will be compared to values calculated for over-
hand throwing, with emphasis on the forces and torques experienced during the acceleration and deceleration phases. Critical instances of the pitching motion will be determined and used to investigate proposed mechanisms of overuse injuries.
METHODS Eight healthy female pitchers were used as subjects. A pitcher was considered healthy if she met three criteria: I) she was not currently injured or recovering from an injury at the time of testing; 2) she had not undergone surgery for at least 12 months prior; and 3) she felt that she was able to pitch with the same intensity as she would in a game environment. Six of the subjects were collegiate pitchers, and two subjects were former collegiate pitchers (competitive on semi-professional teams at the time of data collection). The average age was 21 (SD = 4) years, the average weight was 65 (SD = 5) kg, and the average height was 1.73 (SD = 0.08) m. A brief questionnaire was completed before the testing session concerning the medical history, pitching background, and the cur-
rent physical fitness level. Written consent was obtained from each s u b ject prior to testing. Height, weight, and length of the radius and humerus of the throwing arm were measured. The length of the humerus was measured from the lateral tip of the acromion to the lateral humeral epicondyle. The length of the radius was measured from the lateral humeral epicondyle to the radial styloid process. Each subject was then instructed to perform her normal warm-up routine that included stretching, throwing, and additional nonthrowing drills. Data collection and analyses consisted of a procedure similar to the method previously described (10,ll). Spherical (3.8 cm in diameter) reflective markers were used to identify anatomical landmarks for digitization. Markers were placed bilaterally on the distal end of the midtoe, 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 nonthrowing arm. A reflective band was also attached to the softball to determine the location of the ball. The testing set-up is shown in Figure 1. Ten trials were collected for each pitcher when throwing fastball pitches. All subjects threw to a strike zone net located behind a home plate placed 12.19 m from the pitching rubber. A threedimensional, automatic digitizing system (Motion Analysis Corporation, Santa Rosa, CA) was used to digitize the location of the reflective markers. Four electronically synchronized 200 Hz charged couple device cameras transmitted pixel images of the reflective markers directly into a video processor without being recorded onto video. Threedimensional marker locations were calculated with Motion Analysis Expertvision three-dimensional software that utilized the direct linear transformation method (1). Volume 28 Number 6 December 1998 JOSPT
RESEARCH
STUDY
The root mean square error in calculation of threedimensional marker location was determined to be less than 1.0 cm (11). A global reference frame was established using X, Y, and Z directions. The global X direction was defined as direction from the pitching rubber toward home plate. Global Y was a direction perpendicular to global X directed toward first base. Global Z was defined as a direction perpendicular to both global X and Y directed vertically. Local reference frames were established at the trunk, shoulder, and elbow (11). Anterior, superior, and lateral axes defined the trunk reference frame. The shoulder reference frame were defined by anterior, superior, and distal axes of the upper arm, while the elbow reference frame was defined by anterior, medial, and distal axes of the forearm. The locations of the midhip, midshoulder, elbow joint center, and FIGURE 2. Sequence of motion in windmill pitching: a-c) wind up, d-0 stride, g-j) delivery, k-I) follow through. shoulder joint center were calculated in each frame as described by Dillman et al (5). Midhip was determined to be the midpoint of a line segment between the two hip markers, and the midshoulder was established at the midpoint of a line segUnderhand Overhand ment between the two shoulder Parameter 2 SD Range markers. Digitized locations for the Stride throwing shoulder and elbow markLinear velocity of hips (dsec) 3.2 0.4 ers were translated to the estimated Delivery joint center location (11). Ball speed Shoulder flexiodaddudion (0-5090 of delivery) was recorded as it left a pitcher's 5260 2390 Shoulder flexion velocity ("/set) hand with a Jugs Tribar Sport radar Pelvidu~wrtorso rotation (50-75% of gun (Jugs Pitching Machines Comdelivery) Pelvis rotation velocity (O/sec) 430 140 640-660~~~ pany, Tualatin, OR). Upper torso rotation velocity (O/sec) 650 120 1170-1 220"eb Kinematic variables (angular disInternal rotation (75-100% of delived placement and velocity) at the shoulElbow extension velocity (O/sec) 570 310 2200-2440a99R der and elbow joints were calculated Internal rotation velocity ("/set) 4650 1200 6073-7550~~,~#~ as previously described (5,8,11,22). Instant at ball release Rotation of the forearm about the Ball speed (rn/sec) 25 2 34-38Follow through upper arm's long axis was used to Elbow flexion velocity (O/sec) 880 360 calculate shoulder external rotation. ." Uata - trom . ... . Shoulder flexion was calculated as tscamrlla et a1 (71. Data from Fleisig et a1 (1I). the angle between the upper arm Data from Fleisig et a1 (10). and the trunk in the sagittal plane. Data from Feltner and Dapena (8). Elbow flexion was defined as the anData from Werner et a/ (24). gle between the distal directions of Data from Dillman et a1 (5). the upper arm and forearm. Pelvis Data from Vaughn (22). orientation angle was defined as the TABLE 1. Maximum velocities during underhand and overhand pitching. -
'
JOSPT Volume 28 Number 6 December 1998
407
Parameter
Underhand
R
SD
h!kry Shoulder flexiodadduction (&SO% of delivewl Shoulder adductionlhorizontaladduction toque (%BW X HT) Shoulder internal rotation toque (%BW x Hn Shoulder medial force (%BW Pelvidu~wrtorso rotation (50-75% of delivery) Shoulder anterior force (%BW Elbow compressive force (%BW Elbow flexion torque (%BW X HT) Internal rotation (75-1 00% of delivew) Shoulder superior/compressive force (%BW Shoulder abduction toque (%BW X HT) Shoulder lateral force (%BW Elbow valgudvarus toque (%BW X HT) Elbow anterior force (%BW Elbow lateral/medial force (YoBW Shoulder extension toque (%BW x HT) Am deceleration/followthrough Shoulder extensionlhorizontal abduction torque (%BW X HT) Shoulder posterior force (%BW Shoulder compressive force (%BW Elbow compressive force (%BW Elbow extension toque (%BW
" Data irorn Fleisig et a1 ( 1 11. Data from Escamilla et a1 (12). Data from Fleisig et a1 (101. Data from Feltner and Dapena (8). Data from Werner et a/ (24). BW = Body weight. H T = Height.
TABLE 2. Magnitudes for kinetic data during underhandand overhand pitching.
angle between the pelvis line segment (lead hip to throwing hip) and the global Y direction in the global XY plane. Upper torso orientation angle was defined as the angle between the upper torso line segment (leading shoulder to throwing shoulder) and the global Y direction in the global XY plane. Linear and angular velocities and accelerations were determined with finite differences utilizing the fivepoint central difference method (18). Angular velocities of the pelvis and upper torso were calculated with a method published by Feltner and Dapena (9). Kinetic values (joint force and torque) were calculated with a previously described procedure that used kinematic data, docu408
mented cadaveric segment parameters, and inverse dynamics equations (9-11). The mass and the center of mass locations of the forearm and upper arm were determined using previously published cadaveric data (4). Kinetic values were reported as the force and torque applied to the forearm at the elbow and applied by the trunk to the upper arm at the shoulder (10). The force at the shoulder was separated into three components: anterior-posterior, superior-inferior, and medial-lateral. Torque at the shoulder joint was s e p arated into adductionabduction, external-internal rotation, and flexionextension. Force applied to the forearm at the elbow was separated
into three components: medial-lateral, anterior-posterior, and compressive. Elbow torque was separated into two components: flexion-extension and varus-valgus. Supination-pronation torque at the elbow could not be calculated with the methods available. Individual forces were divided by body weight (BW) and torques were divided by body weight and height (BW X HT)to normalize individual results and eliminate any effects due to the size of the subject. Temporal data were normalized by aligning the instant of foot contact and ball release for each subject. The timing of kinematic and kinetic data were reported as a percentage of the delivery phase completed, where 0% corresponded to the instant the front foot contacted the ground and 100% at the instant of ball release. Data for the three fastest pitches thrown by each pitcher into the strike zone were averaged. To simplify the interpretation of data, the pitching motion was separated into four phases: wind up, stride, delivery, and follow through (Figure 2). The wind-up phase was defined as the time from initial movement from the ready position until lead foot toe-off (Figure 2a-c). The stride phase was defined as the time from lead foot toe-off to lead foot contact (foot flat) with the ground (Figure 2d-0. The delivery phase was defined as the time from foot contact to release of the ball (Figure 2g-j). The final phase was follow through, which occurred from the instant of ball release until the forward motion of the throwing arm had stopped (Figure 2k-1). During the follow through, the forearm flexed at the elbow and continued to flex until the arm and forearm were decelerated. Means and standard deviations for all subjects were determined for 14 kinematic and kinetic parameters. The results were compared with overhand pitching data for qualitative analysis. The force and torque parameters were normalized Volume 28 Number 6 December 1998 JOSFT
tated toward third base and the humerus was flexed beyond 180" to an extended position. During the delivery phase, the ball was accelerated forward with a combination of trunk (pelvis and upper torso) rotation, arm (flexion and internal) rotation at the shoulder, and flexion at the elbow. The highest magnitudes for kinematic and kinetic parameters occurred during the delivery phase as the arm was accelerated (Tables 1 and 2). These occurred during an average time interval of 0.102 2 0.014 seconds for all subjects. From 0 to 50% of the delivery phase, a maximum adduction torque was exerted at the shoulder (Table 2, Figure 3). A maximum internal rotation torque was also exerted at the shoulder as forward flexion of the arm reached a maximum velocity greater than 5,000°/sec (Table 1, Figure 4). At approximately 45% of the delivery, a maximum medial (74% BW) force was produced at the shoulder. This was followed by a maximum anterior (38% BW) force at the shoulder which occurred at approximately 55% of the delivery. These forces were produced as the arm was adducted and flexed forward (Table 2, Figure 5). From 50 to 75% of the delivery, maximum pelvis rotation velocity was I 1 reached which was then followed by -14 0 25 50 7s 100 125 150 maximum upper torso rotation velocity (Table 1).As the humerus was REL PC Time (% pitch) flexed forward, the forearm extended FIGURE 3. Toques (% body weight x height)applied to the arm at the shoulder for A) adduction (+)/abduction at the elbow creating a maximum (-); B) internal (+)/external (-) rotation; and C) flexion (+)/extension (-) VS. time (% pitch). Graphs represent extension velocity of 570°/sec (Table mean and standard deviation data for all subjects. The instances of foot contact (FC) and ball release (REL) are 1, Figure 4). A flexion torque was shown. initiated at the elbow and reached a maximum at the end of the delivery phase (Table 2, Figure 6). During this time, a maximum compressive to body weight and height to allow phase, the arm was hyperextended at force (70% BW) was experienced at for comparison. the shoulder as the pitcher pushed off the elbow (Figure 7). This was folthe pitching rubber with the pivot foot lowed by a maximum superior force to initiate forward translation of the (98% BW) at the shoulder that ocRESULTS body. Emphasis on forward translation curred at approximately 77% of the During the wind-up and stride during the stride phase was illustrated delivery phase (Figure 5). phases of the motion, the majority of by the linear velocity of the hips (Table The last 25% of the delivery phase kinematic and kinetic parameters had 1). As the pitcher reached foot contact, was characterized by internal rotation low magnitudes. During the wind-up the trunk (pelvis, upper torso) was r e of the humerus, which reached a maxiJOSPT* Volume 28 * Number 6 - December 1998
RESEARCH
STUDY
velocity (880°/sec) was reached as the forearm continued to decelerate (Figure 4).
DISCUSSION The results of this study are compared with results from previous studies of overhand pitching in Tables 1 and 2. The purpose of the comparison is for qualitative analysis of the loads experienced during underhand pitching. Since baseball pitching studies used male subjects and the current study used female subjects, musculoskeletal and social differences between genders must be recognized. Typically, a female's upper torso and arms possess less muscle mass and strength than the male. At the elbow, the carrying angle is larg er, and there is often more ligamentous laxity in the female. Grip strength and hand sizes are usually less for women. While a starting baseball pitcher seldom pitches in a game without 3-4 days of rest, a female windmill pitcher may pitch 2 days in a row or twice in one day during a tournament. During overhand pitching, the stability of the glenohumeral joint is compromised when the humerus rotates internally and adducts horizontally while maintaining a position of 90" of abduction. his potential for 0 25 50 75 100 125 150 instability is magnified as the forces FC Time (% pitch) REL to resist glenohumeral distraction and anterior translation reach a peak FIGURE 4. Angular velocity ("/second) for A) shoulder flexion; Bj elbow extension (+)flexion (-); and after ball release during deceleration. C)shoulder internal (+)/external (-) rotation vs. time (% pitch). Graphs represent mean and standard deviation data for all subjects. The instances of foot contact (FC)and ball release (REL) are shown. Although the humerus is not held in an abducted position during underhand pitching, the motion does reAfter ball release, the arm and mum velocity (4,600°/sec) just prior to quire resistance to distraction while ball release (Table 1, Figure 4). During forearm were decelerated. A second also controlling internal rotation and peak extension torque (9% BW X this time, a maximum abduction elbow extension. The total circumHT) was exerted and a maximum torque (9% BW X HT) and a maxiposterior force (59% BW) was experi- duction of the arm about the glenomum extension torque (10% BW X humeral joint from the initiation of enced at the shoulder (Table 2, FigHT) were generated at the shoulder stride phase to completion of the ure 5). During the follow through (Table 2, Figure 3). Maximum lateral phase, a second peak elbow compres- movement is about 485". Of signififorce (47% BW) and valgus torque cance is that this windmill motion is (4% BW X HT) were generated at the sive force occurred (56% BW) as a performed rapidly with a softball that maximum extension torque (2% elbow. Just prior to ball release, elbow weighs 6% to 7 oz by design comBW X HT) was exerted (Figures 6 extension was terminated and elbow pared with the baseball weight of 5 and 7). A maximum elbow flexion flexion was initiated. Volume 28 Number 6 December 1998 JOSPT
RESEARCH
STUDY
stability by resisting the distraction of the humerus from the shoulder joint caused by the windmilling motion (23). Similar resultant forces resisting distraction at the shoulder have been calculated for overhand pitching (8, 10-12). A difference between the methods of pitching is the timing of the peak values for the resultant forces. The greatest resistance to distraction (compressive, superior forces) occurs during the delivery or acceleration phase for underhand pitching, while the greatest resistance during overhand pitching is produced in the deceleration phase (Table 2). The magnitude of the forces were similar, as normalized forces during underhand pitching were 80-95% of the normalized values determined for overhand pitching. Forces acting to resist distraction at the elbow were also similar with the magnitudes during underhand pitching equaling 67-79% of the values calculated for overhand pitching. Although the forces were slightly less during underhand pitching, many of the torques were equivalent or slightly greater. This is especially true for the extension (10% BW X HT) and abduction (9% BW X HT) torques exerted at the shoulder. Werner (23) concluded that a major contributor to ball velocity was ! I -100 J internal rotation of the humerus pro0 25 50 75 I00 125 150 duced by shoulder internal rotation FC REL Time (% Pitch) torque. In this study, internal rotaFIGURE 5. Forces (% body weight)applied to the a n at the shoulder for A) anterior (+)/posterior (-I; B) superior tion torque generated early in the (+)/inferior (-); and C) lateral (+)/medial (-) vs. time (% pitch). Graphs represent mean and standard deviation delivery phase was similar in magnidata for all subjects. The instances of foot contact (FC)and ball release (REL) are shown. tude to the torques calculated during overhand pitching (Table 2). The resulting internal rotation velocity oz. Most of the circumduction mopitching motion until just prior to was over 4,000°/sec which, although tion is performed with the elbow in ball release. This force corresponds smaller than overhand pitching, is a full extension, which accentuates the to the superior force calculated in high magnitude (Table 1). Maffett et centrifugal distraction force on the this study that reached a peak value a1 (15) observed high levels of activity glenohumeral joint. during the middle of the delivery for the pectoralis major and subscap In the first three-dimensional phase. Using the average weight of ularis, contributing to adduction and analyses of the windmill pitching mo- 635 N for all pitchers, the peak supe- internal rotation of the humerus durtion, Werner (23) observed a steady rior force of 98% BW equates to a ing windmill pitching. increase in the resultant force com625 N force acting on the shoulder. Although it is difficult to deterponent directed from the throwing As noted by Werner (23), this force mine how these forces and torques elbow to the shoulder during the had the effect of maintaining joint relate to the incidence of injury, the
JOSPT Volume 28 Number 6 December 1998
41 1
RESEARCH
STUDY
joint, it is speculated that the biceps tendon undergoes stretching and surface fibrillation. As discussed by Fleisig et al (10). during overhand pitching, the biceps brachii functions to provide elbow flexion torque and aids in resisting humeral distraction. With the attachment of the long head of the biceps brachii to the glenoid labrum, the contraction of the biceps brachii to control elbow extension creates tension on the biceps tendon labrum complex. At a similar time in the motion, compressive force is needed to resist distraction, which further increases the demand on the biceps labrum complex. This mechanism can be applied to underhand pitching during the delivery phase. Forces to resist distraction reach a peak at a time during delivery that elbow flexion torque is exerted to control elbow extension and initiate elbow flexion (Figures 5 and 6). The demand on the biceps la0 25 50 75 100 125 150 brum complex to both resist glenoFC REL humeral distraction and produce elTime (% pitch) bow flexion torque makes this structure susceptible to overuse inFIGURE 6. Toques (% body weight x heightJapplied to the foream at the elbow for A) extension (+)fixion (-), and B) varus (t)/valgus (-) vs. time (% pitch). Graphs represent mean and standard deviation data for all jury. Internal r o ~ t i o nof the husubjects. The instances of foot contad (FC) and ball release (REL) are shown. merus and pronation of the forearm further complicate the mechanism. Although not measured in the curtypes of injuries reported by Loosli et and 5). Maffett et al (15) concluded rent study, the torsional stress that a1 appear to be related to overuse that the high levels of activity for the occurs as the forearm is pronated and the accumulative stress at the pectoralis major and subscapularis through ball release has been related shoulder and elbow (14). Tendinitis, observed during early delivery also to stress fracture injuries to underrotator cuff and tendon strain, and contribute to the stabilization of the hand pitchers (21). ulnar nerve damage were the majoranterior capsule of the shoulder. DeSoftball pitchers often are reity of injuries reported for all grades spite the possibility of injury to these quired to pitch multiple games in of injuries. Similar to overhand structures, pain in the anterior shoulone day and or pitch consecutive throwing, the causes of these injuries der is often treated by injection of a days throughout the season. It would may be related to the mechanisms of steroid/analgesic mixture into the seem reasonable to speculate that, maintaining joint stability. bicipital tendon area. Unfortunately, A common complaint of softball repeated injections in the area of the even with perfect pitching mechanics, overuse type injuries will occur. pitchers is anterior shoulder discomanterior shoulder, with continued Loosli et al (14) reported that pitchfort near the origin of the long head pitching and without sufficient rehaers reporting grade I or I1 type injuof the biceps tendon. The diagnosis bilitation, may actually lead to weakries (did not result in missed games of bicipital tendinitis is often made ness, degradation, and even disrup o r practices) on average pitched with little consideration to the possition of the biceps tendon. more innings per season than uninbility of subscapularis or pectoralis The long head of the biceps tenjured pitchers. In the softball pitcher, don, by reason of its insertion into strain, which may occur as increased forceful deceleration of the upper shoulder extension is followed by the superior glenoid labrum, funcarm at or just prior to ball release, tions as a humeral head depressor large forces and torques produced during the delivery motion (Figures 3 normally. In the lax glenohumeral similar to baseball pitching, places a
-
Volume 28 Number 6 December 1998 0JOSPT
RESEARCH
0
25
FC
50
75
Time (% pitch)
100
12s
150
REL
FIGURE 7. Forces (% body weight) applied to the forearm at the elbow for A) medial (+)/lateral (-1; 8) anterior (+)/posterior (-); and C) compressive vs. time (% pitch). Graphs represent mean and standard deviation data for all subjects. The instances of foot contact (FC) and ball release (REL) are shown.
substantial burden on the posterior rotator cuff muscles (Figures 3 and 5). Maffett et al (15) have shown that, similar to baseball pitching, the teres minor is very active in decelerating the humerus. However, it was concluded that the stress on the teres minor is less during softball pitching because acceleration forces seem to be dissipated through contact of the arm against the lateral thigh. This JOSm Volume 28 Number 6 December 1998
conclusion does not appear to agree with the findings of this study. Using the average weight of 635 N and height of 1.73 m for all pitchers, torques applied at the shoulder to control adduction and flexion were equivalent to 100 Nm. These torques are required to decelerate the high rotational velocities achieved during delivery and to transfer momentum from proximal to distal segments
STUDY
down the throwing arm to the ball (2). Alexander and Haddow (2) analyzed the angular kinematics of the upper arm, lower arm, and hand of four skilled windmill pitchers. They observed a specific sequence of motions and concluded that the larger, more proximal segments attained peak acceleration before the more distal segments. After reaching peak velocity, the proximal segment was decelerated in order to transfer momentum to the distal segment. In the current study, this sequence was illustrated by the occurrence of peak flexion velocity of the humerus at the shoulder early in the delivery phase, which was followed by the generation of an extension torque at the shoulder to decelerate the humerus (Figures 3 and 4). A peak shoulder extension torque was reached as elbow flexion was initiated, enabling the momentum from the upper arm to be transferred to the lower arm. Werner (23) also observed a similar extension or negative "windmilling torque" just prior to ball release and believed the purpose was to control the windmilling motion. Posterior shoulder symptoms, which are usually present after pitching, appear to be the second most common site of pain and soreness in the female windmill pitcher. Eccentric loading and stretching of the posterior muscle girdle with overuse could significantly contribute to dynamic anterior instability of the humeral head. Ultimately, failure or insufficiency of the posterior support structures to keep the humeral head properly seated in the glenoid could propagate symptoms of posterior shoulder pathology. In baseball pitching, the production of varus torque to resist valgus motion often leads to elbow injury (10). Only occasionally does ulnar collateral ligament injury become apparent in the softball pitcher because only a small amount of varus torque is produced (Figure 6). Ulnar nerve neuritis does occur in windmill
RESEARCH
STUDY
pitching, although the cause is not the same as in overhand pitching. The injury in windmill pitching is attributed to poor mechanics and occurs as the medial elbow contacts the hip just before ball release.
CONCLUSIONS This study presented kinematics and kinetics for underhand pitching motion of eight collegiate fast pitch softball pitchers throwing the fastball pitch. Comparison of underhand and overhand pitching illustrated similar joint speeds and loads for each m e tion. One of the critical instances for underhand pitching wa. during the delivery or acceleration, where the forces to resist distraction at the shoulder and elbow were the greatest. This differed from overhand pitching, where the peak forces needed to resist distraction occurred during deceleration. Obvious differences, including gender, size and weight of the ball, and pitching environment (height of mound), prevent a direct comparison to overhand pitching; however, these results question the assumption that underhand pitching does not create significant stress on the shoulder and elbow. Further investigation is needed to fully determine the influence of underhand pitching on overuse injuries. Attention should be directed toward prevention of injury by teaching proper pitching mechanics, strengthening the shoulder and rotator cuff musculature, and regulating the number of pitches and mound a p pearances for the female fast pitch softball pitcher. JOSPT
ACKNOWLEDGMENTS The authors would like to thank Anthony DeMonia and Phillip Sutton for their assistance with data analysis and Dan Nichols for his assistance with illustrations. The authors would also like to thank Jennifer Hogan,
414
Cheri Kempf, and pitchers from Samford University and Troy State University for their assistance with this study.
REFERENCES 1. Abdel-Aziz Yl, Karara HM: Direct linear transformation: From comparator coordinates into objects coordinated in close-rangephotogrammetry. In: American Society of Photogrammetry, Symposium on Close-Range Photogrammetry, pp 1-19. Falls Church, VA: American Society of Photogrammetry, 1971 2. Alexander M, Haddow J: A kinematic analysis of an upper extremity ballistic skill: The windmill pitch. Can J Appl Sport Sci 7(3):209-2 17, 1982 3. Atwater AE: Biomechanics of overarm throwing movements and of throwing injuries. Exerc Sport Sci Rev 7:43-85, 1979 4. Clauser CE, McConville JT, Young JW: Weight, volume, and center of mass of segments of the human body. AMRLTR-69-70, Wright-Patterson Air Force Base, 1969 5. Dillman CJ, Fleisig GS, Andrews JR: Biomechanics of pitching with emphasis upon shoulder kinematics. J Orthop Sports Phys Ther 18(2):402-408, 1993 6. Elliott B, Grove JR, Gibson B, Thurston B: Threedimensional cinematographic analysis of the fastball and curveball pitches in baseball. Int J Sport Biomech 2(1):20-28, 1 986 7. Escamilla RF, Fleisig GS, Barrentine SW, Zheng N, Andrews JR: Kinematic comparisons of throwing different types of baseball pitches. J Appl Biomech l4(l):1-23, 1998 8. Feltner M, Dapena J: Dynamics of the shoulder and elbow joints of the throwing arm during a baseball pitch. Int J Sport Biomech 2(4):235-259, 1986 9. Feltner ME, Dapena J: Three-dimensional interactions in a two-segment kinetic chain. Part I: General model. Int J Sport Biomech 5(4):403-4 19, 1989 10. Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF: Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med 23(2): 233-239, 1995 11. Fleisig GS, Escamilla RF, Andrews JR, Matsuo T, Satterwhite Y, Barrentine SW: Kinematic and kinetic comparison between baseball pitching and football passing. J Appl Biomech 12(2):207-224, 1996
12. Escamilla RF, Fleisig GS, Alexander E, Andrews JR: A kinematic and kinetic comparison while throwing different types of baseball pitches. Med Sci Sports Exerc 26(5):Sl75, 1994 (abstract) 13. lobe F, Kvitne R: Shoulder pain in the overhand or throwing athlete: The relationship of anterior instability and rotator cuff impingement. Orthop Rev 18(9):963-975, 1989 14. Loosli AR, Requa RK, Garrick JG, Hanley E: Injuries to pitchers in women's collegiate fast-pitch softball. Am 1 Sports Med 20(1):35-37, 1992 15. Maffett M W, lobe FW, Pink MM, Brault J, Mathiyakom W: Shoulder muscle firing patterns during the windmill softball pitch. Am J Sports Med 25(3):369374, 1997 16. McLeod WD: The pitching mechanism. In: Zarins B, Andrews JR, Carson WG (eds), Injuries to the Throwing Arm, pp 22-29. Philadelphia: W.B. Saunders Company, 1 985 17. McLeod WD, Andrews JR:Mechanisms of shoulder injuries. Phys Ther 66(12): 1901-1904, 1986 18. Miller Dl, Nelson RC: Biomechanics of Sport-A Research Approach, Philadelphia: Lee & Febiger, 1973 19. Pappas AM, Morgan WJ, Schulz LA, Diana R: Wrist kinematics during pitching: A preliminary report. Am J Sports Med 23(3):312-3 15, 1 995 20. Sakurai S, lkegami Y, Okamoto A, Yabe K, Toyoshima S: A three-dimensional cinematographicanalysis of upper limb movement during fastball and curveball baseball pitches. J Appl Biol 9(1): 47-65, 1993 2 1. TanabeS, Nakahira 1, Bando E, Yamaguchi ti, Miyamoto H, Yamamoto A: Fatigue fracture of the ulna occurring in pitcherr of fast-pitch softball. Am J Sports Med 19(3):317-32 1, 199 1 22. Vaughn RE: Threedimensional kinematics of the baseball pitch. In: Terauds J, Barham JN (eds), Biomechanics in Sports 11, pp 72-78. Del Mar, CA: International Symposium on Biomechanics in Sports, 1985 23. Werner SL: Selected kinematic and kinetic parameters of the windmill softball pitch. Unpublished master's thesis, Indiana University, Bloomington, IN, 1987 24. Werner SL, Fleisig GS, Dillman CJ, Andrews JR: Biomechanics of the elbow during baseball pitching. J Orthop Sports Phys Ther 17(6):274-278, 1 993 25. Wilson FD: Valgus extension overload in the pitching elbow. Am J Sports Med 1 1(2):83-88, 1983
Volume 28 Number 6 December 1998 JOSPT
