Comparison of Windup and Stretch Pitching Biomechanics in Baseball With Implications for Safety and Performance

Abstract

Background:

Historically, it was assumed by some that high leg lift with windup pitching generated more ball velocity whereas pitching from the stretch was quicker to reduce the risk of base stealing but also more stressful on the arm. However, many now believe that velocity and stress do not differ between windup and stretch and always pitching from the stretch is simpler than mastering 2 techniques.

Purpose/Hypothesis:

The purpose of this study was to compare windup and stretch fastball pitching biomechanics. It was hypothesized that there would be statistically significant and clinically important differences in ball velocity, timing of angular velocities, joint kinetics, and pitching kinematics.

Study Design:

Controlled laboratory study.

Methods:

Fastball pitching biomechanics previously captured for 221 healthy baseball pitchers (105 professional, 52 collegiate, and 64 high school level) were analyzed. For each pitcher, data for 3 to 10 windup trials and 3 to 10 stretch trials were available. Ball velocity was recorded using a radar gun. A 12-camera, 240-Hz automated motion capture system was used to track 39 reflective markers attached to the pitcher. A total of 24 kinematic parameters, 4 temporal parameters, and 5 kinetic parameters were calculated. Data for each parameter were compared across the 2 techniques and 3 competition levels using 2-way repeated-measures analysis of variance (P < .01). Based on previous studies and the expertise of the investigators, the minimal clinically important difference (MCID) was set as 2° for angle measurements, 20 deg/s for angular velocities, 0.5 m/s for fastball velocity, and 0.3% body height × weight for normalized joint torque.

Results:

Fastball velocity was statistically greater from the windup than stretch for the collegiate subgroup but not for the other 2 levels. The collegiate level difference was below the MCID. Pitching from the windup generated greater front knee height and required more time from initiation of leg lift to front foot contact. From foot contact to ball release, there were 11 additional small, statistically significant differences between windup and stretch; however, each of these was well below the MCID.

Conclusion:

Pitching from the stretch was quicker and should be used with runners on base to prevent stealing. Pitching from the windup and stretch produced similar ball velocity, joint kinetics, and kinematics. Thus, pitchers may choose to use both techniques or stretch only based on comfort and personal preference.

Clinical Relevance:

The decision to pitch from both the windup and stretch or only from the stretch should not affect a pitcher's performance or joint stress (and injury risk).

Keywords

fastball velocity elbow shoulder injury kinematics kinetics timing

In baseball, a pitcher is allowed at any time to pitch from either the windup or the set position (also known as pitching from the stretch). In the windup technique, a pitcher initially stands with both feet (heels) on the pitching rubber with feet and shoulders facing the hitter (Figure 1A). The pitcher then steps backward or off to the side with his nonpivot foot (left foot for a right-handed pitcher) to begin the pitching motion (Figure 1B), followed by turning the pivot foot so the outside (lateral) edge of the foot is pressed against the pitching rubber (Figure 1C). When pitching from the stretch, the pitcher starts with the outside edge of his pivot foot against the pitching rubber (Figure 1C). The remaining motion of pitching looks similar between windup and stretch. The pitcher lifts his front knee (Figure 1D) and then strides toward home plate with his front leg while his hands swing apart and then up. After front foot contact (Figure 1E), the pitcher rotates his pelvis and then upper trunk to face home plate while the arm is cocked back into maximum external rotation (Figure 1F). The arm is rapidly rotated forward through ball release (Figure 1G) and shoulder internal rotation (Figure 1H). The pitching arm continues across the body while the back leg is lifted into the end of the pitch (Figure 1I).

Starting in the early 1900s, conventional thinking was that pitching from a windup is a more natural way to throw and that the higher leg kick creates more potential energy, which leads to greater ball velocity.² Furthermore, it was believed that greater potential energy in the windup produced by a higher leg lift may require less energy from the arm and thus less stress on the throwing elbow and shoulder.² In contrast, pitching from the stretch is a quicker motion and should be used when there are runners on base to prevent the base runners from stealing. However, the quicker motion from the stretch may require greater force and torque at the throwing shoulder and elbow to generate ball velocity. Thus, pitchers were taught to pitch from the windup without runners on base and from the stretch with runners on base. However, this thinking has been challenged since the 1980s, with widespread use of radar guns often showing similar ball velocities from the windup and stretch.

Although many pitchers still use both windup and stretch techniques, others (especially relief pitchers) pitch from the stretch only. The theory for always pitching from the stretch is that ball velocity does not differ between windup and stretch pitching and that it is simpler to master only 1 technique. Thus, some believe that pitching from the windup provides safety (less torque and force) and performance (greater ball velocity) advantages, whereas others believe that always pitching from the stretch eliminates neuromuscular learning of 2 different biomechanical techniques. Remarkably, although pitching biomechanics have been reported in hundreds of publications, comparison of windup and stretch biomechanics has been limited to 2 small-sample studies with few biomechanical variables. Dun et al² compared windup and stretch biomechanics using data from 28 professional pitchers. More recently, Scarborough et al⁷ studied differences in 10 amateur (6 collegiate, 4 high school) pitchers.

The objective of the current study was to compare windup and stretch fastball pitching biomechanics across a large sample of professional, collegiate, and high school baseball pitchers. It was hypothesized that there would be statistically significant and clinically important differences in ball velocity, timing, joint kinetics, and pitching kinematics between the windup and stretch techniques.

Methods

A retrospective analysis was conducted on pitchers tested between 2012 and 2022 by the American Sports Medicine Institute. The Ascension St Vincent's institutional review board determined that this retrospective study met exempt classification. Inclusion criteria were that a participant was an active high school, collegiate, or professional pitcher; self-reported as healthy; and threw fastballs from both the windup and stretch during testing. Exclusion criteria were history of elbow or shoulder surgery <1 year before testing, inability to pitch with 100% effort, or data available from <3 fastballs from the windup and <3 fastballs from the stretch. There were 221 pitchers who met the criteria, including 105 professional, 52 collegiate, and 64 high school athletes. All participants were male. There were significant differences in age, mass, and height between the 3 levels (Table 1).

Table 1

Demographic Differences Among Competition Levels^a

	Professional (n = 105)	Collegiate (n = 52)	High School (n = 64)
Age, y^b	22.2 ± 3.1	19.6 ± 1.2	16.2 ± 2.4
Mass, kg^b	94.1 ± 9.7	88.0 ± 10.7	79.8 ± 12.8
Height, m^b	1.90 ± 0.06	1.89 ± 0.06	1.84 ± 0.06

Data are reported as mean ± SD.

Significant difference (P < .05) across levels.

A total of 39 reflective markers were placed on each pitcher before testing. After unrestricted warm-up, the pitcher threw full-effort fastballs for data collection from a mound to a catcher or target strike zone above home plate at regulation distance from the pitching rubber (18.44 m). Fastball velocity was recorded using a radar gun (Stalker Sports Radar), while motion of the reflective markers was measured using a 12-camera, 240-Hz automated motion capture system (Motion Analysis Corporation). Each participant pitched 3 to 10 fastball trials from the windup and 3 to 10 from the stretch.

Motion data of the reflective markers were filtered using a fourth-order Butterworth low-pass filter with a cutoff frequency of 13.4 Hz.^1-5,8 Data capture was manually triggered near the time front foot leg lift was observed. Temporal parameters were calculated for each pitch as the times between initiation of leg lift (determined by lift of front heel) (Figure 1C), maximum front knee height (Figure 1D), front foot contact (Figure 1E), and ball release (Figure 1G). Total time was reported as the time from initiation of leg lift to ball release.

A total of 24 discrete kinematic parameters were calculated for each pitch. Maximum height of the front knee was reported as a percentage of the athlete's height. The remaining parameters were calculated as previously described.^1-5,8 At the time of front foot contact, stride length, front foot position, front foot angle, front knee flexion, pelvic angle, trunk axial rotation, upper trunk tilt, throwing shoulder abduction, throwing shoulder horizontal abduction, throwing shoulder external rotation, and throwing elbow flexion were analyzed. Maximum angular velocities were calculated for the pelvis, upper trunk, throwing shoulder internal rotation, and throwing elbow extension. Maximum external rotation of the throwing shoulder was also computed. At the time of ball release, front knee flexion, trunk forward tilt, trunk lateral tilt, throwing shoulder abduction, throwing elbow flexion, arm slot, and ball velocity were reported.

Five kinetic parameters were calculated at the throwing shoulder and elbow using the kinematic data, pitcher height, pitcher mass, and inverse dynamics equations.^1-5,8 Shoulder kinetic parameters were defined as torque or force applied by the trunk to the upper arm. Elbow kinetic parameters were defined as torque or force applied by the upper arm to the forearm. Joint torques were divided by body weight and by height to create normalized unitless variables.^1,4,8 Similarly, normalized forces were calculated by dividing joint force by body weight.^1,4 The kinetic parameters for the throwing shoulder were maximum values of proximal force, horizontal adduction torque, and internal rotation torque. The kinetic parameters for the throwing elbow were maximum values of varus torque and flexion torque.

Data for each kinematic, normalized kinetic, and temporal parameter were averaged for all windup trials and for all stretch trials for each pitcher. Data were then compared across the 2 techniques (windup, stretch) and 3 competition levels (professional, collegiate, high school) using 2-way repeated-measures analysis of variance. For any parameter with a significant interaction between technique and competition level, differences between techniques were assessed separately for each competition level using a paired t test. All statistical analyses were conducted using SPSS Version 27.0 (IBM Corp) with an a priori level of significance of α = .01.

The minimal clinically important difference (MCID) for angle measurements was set as 2°, as previous research has shown 2° to 7° within-pitcher variability when throwing fastballs.⁴ Similarly, the MCIDs for stride length, foot placement, and angular velocities were set as 1% body height, 2 cm, and 20 deg/s, respectively, based on within-pitcher variability previously reported.⁴ The MCID for maximum knee height was also set as 1% body height. The MCID for fastball velocity was set as 0.5 m/s.⁹ The MCID for normalized joint torque was set as 0.3% body height × weight, based on a previous study of fastball torque variability within professional pitchers.⁸ This is similar to the MCID set as 10% of maximum torque in a previous study of adolescent pitchers.⁶ The MCID for normalized shoulder proximal force was set as 10% body weight, which was about 10% of maximum force.⁶

Results

Temporal data are shown in Table 2. Time of initiation of leg lift was available for only a subset of pitchers (103/221) because data capture for the others started after this event. Times of maximum knee height, foot contact, and ball release were available for all pitchers. Pitching from the windup took more time from the initiation of leg lift to maximum knee height to foot contact. However, there was no difference in time from foot contact to ball release.

Table 2

Comparison of Time Between Pitching Techniques

	Mean		SEM
	Windup	Stretch	SEM
Time from initiation of leg lift to maximum knee height, s^a	0.955	0.610	0.047
Time from maximum knee height to foot contact, s^a	0.767	0.647	0.008
Time from foot contact to ball release, s	0.146	0.148	0.001
Total time (initiation of leg lift to ball release), s^a	1.894	1.425	0.057

Significant difference (P < .01) across levels.

Of the 24 kinematic parameters analyzed, 12 showed statistically significant differences between windup and stretch. Two of these parameters had significant interactions between technique and competition level. Specifically, fastball velocity and arm slot angle at ball release were significantly different between windup and stretch at the collegiate level, whereas no differences were found for the professional and high school levels. Of the 5 kinetic parameters, elbow flexion torque was the only one with a statistically significant difference. The mean and standard error of the mean are shown in Table 3 for all kinematic and kinetic parameters with statistically significant differences. Values for all kinematic and kinetic parameters are shown in Appendix Tables A1 and A2 (available in the online version of this article), respectively.

Table 3

Statistically Significant Differences (P < .01) in Kinematic and Kinetic Parameters Between Pitching Techniques

	Mean		SEM
	Windup	Stretch	SEM
Maximum knee height, % body height	61	47	1
Instant of front foot contact, deg
Knee flexion	42.2	42.8	0.2
Foot angle closed	8.6	9.3	0.2
Upper trunk tilt	8.1	7.6	0.1
Delivery
Maximum pelvic angular velocity, deg/s	569	561	2
Maximum shoulder external rotation, deg	159.1	159.9	0.1
Maximum upper trunk angular velocity, deg/s	1107	1103	1
Maximum shoulder internal rotation velocity, deg/s	6584	6653	24
Normalized elbow flexion torque, % body height × weight	3.42	3.38	0.01
Instant of ball release
Elbow flexion, deg	24.5	24.2	0.1
Trunk forward tilt, deg	34.5	35.0	0.1
Arm slot, deg (collegiate)	50.1	51.2	0.2
Ball velocity, m/s (collegiate)	35.5	35.2	0.1

Discussion

Although some people in baseball believe the windup can lead to greater fastball velocity, results from the current study did not support this hypothesis. The current study found no statistical difference across all pitchers. There was a small statistical difference at the collegiate level only, but it was less than the MCID. Dun et al² reported a small, statistically significant difference in fastball velocity between windup and stretch for professionals, but no such difference was found in the current study. Scarborough et al⁷ found no differences in pitch velocity between pitch techniques for collegiate and high school pitchers. Thus, there is no uniform consistency in statistically significant differences in ball velocity between windup and stretch across levels in the current study or across studies.

To prevent base runners from stealing, a pitcher wants to minimize the time from his first movement until the ball reaches the catcher's mitt. This includes the time from the pitcher's first movement until he releases the pitch combined with the time from when the ball is released until it hits the catcher's mitt. As expected, pitching from the windup involved a higher knee lift and took more time from initiation of leg lift until ball release. The difference in front knee height was the only kinematic difference above the MCID. As there was no difference in ball velocity, it can be assumed that time from ball release to the catcher's mitt was not different between windup and stretch pitching. Thus, the shorter time from initiation of leg lift to ball release when pitching from the stretch supports the belief that this is the preferrable technique for preventing stolen bases.

This study did not support the hypothesis that joint kinetics differ between pitching from the windup and stretch. The only statistically significant kinetic difference was normalized elbow flexion torque. However, the magnitude of this difference was 0.04% body height × weight, far below the MCID of 0.3% body height × weight. Furthermore, there were no statistically significant differences in elbow and shoulder torque in either previous study.^2,7 Thus, the belief that pitching from the windup is less stressful (and safer) than pitching from the stretch was not supported.

At the instant of foot contact, 3 of 11 kinematic parameters were statistically different between windup and stretch. However, these differences were well below the MCID. In fact, each angle parameter differed by <1°. Dun et al² analyzed 4 kinematic measurements at the instant of foot contact and found no statistical differences. Scarborough et al⁷ found no difference in stride length between the 2 techniques.

Between foot contact and ball release, maximum shoulder external rotation and 3 angular velocity parameters showed statistically significant differences between windup and stretch. At ball release, elbow flexion and trunk forward tilt showed statistically significant differences. Arm slot at ball release was statistically significantly different for collegiate pitchers. However, the magnitudes of these differences were very small, all well below the MCID.

A large sample size in a biomechanical study provides statistical power for finding significant differences. However, a large sample size also increases the possibility of finding small differences that are statistically significant but not clinically important. Because the sample size of the current study was larger than that of most biomechanical studies, statistical findings must be evaluated relative to the MCID. Although this study identified 13 statistically significant differences in pitching kinematics and kinetics between windup and stretch techniques, 12 of these were below the MCID. The only parameter above the MCID was maximum knee height, which occurred early in the pitch before front foot contact. There were no clinically important differences during the dynamic phase from foot contact to ball release. Thus, this study did not support the notion that pitching from the windup and stretch requires an athlete to master 2 different biomechanical patterns after foot contact.

As with all studies, there were limitations. One limitation was that we did not have data for the first movement (Figure 1A) for any windup pitches and had initiation of leg lift from the windup (Figure 1C) for only about half of the participants. This was because of the retrospective nature of the study and the fact that we had not anticipated analyzing biomechanics before maximum knee height when we captured the data. Although the current study clearly showed that pitching from the windup required significantly more time from the initiation of front leg lift, future research can quantify the difference in time required from the first movement. Another potential limitation was motion artifact of reflective markers, which must be considered for all studies involving human motion capture of superficial markers. To limit such error, we placed reflective markers on bony landmarks whenever possible. Within-pitcher variability with this method has previously been shown to be <2° for most parameters.⁴ This study tested differences between windup and stretch for a large group of healthy baseball pitchers, but future work is needed to answer some follow-up questions. For example, the current study did not look at various techniques for pitching from the stretch (such as slide step) and windup (such as hybrid windup), compare differences between left-handed and right-handed pitchers, or compare differences for pitches other than fastballs. Future research to address these issues is warranted. A comparison of windup and stretch pitching biomechanics at the youth level could add insight for young baseball pitchers at the start of their career. Epidemiologic research comparing injury rates between matched groups of windup and stretch pitchers versus stretch-only pitchers would also be valuable.

Conclusion

Based on biomechanical data from a large sample across different levels, pitching from the stretch was quicker and should be used with runners on base to prevent stealing. However, pitching from the windup and stretch produced similar ball velocity, joint kinetics, and kinematics. Pitchers could freely choose to pitch with both techniques or stretch only based on their comfort and personal preference, with no evidence that their decision will affect their performance or joint stress.

Supplemental Material

sj-pdf-1-ajs-10.1177_03635465241247543 – Supplemental material for Comparison of Windup and Stretch Pitching Biomechanics in Baseball With Implications for Safety and Performance

Supplemental material, sj-pdf-1-ajs-10.1177_03635465241247543 for Comparison of Windup and Stretch Pitching Biomechanics in Baseball With Implications for Safety and Performance by Glenn S. Fleisig, Jonathan S. Slowik, Charles B. Kutz and Rafael F. Escamilla in The American Journal of Sports Medicine

Footnotes

Submitted September 26, 2023; accepted February 20, 2024.

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

ORCID iD

Glenn S. Fleisig

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Supplementary Material

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