Current Workload Recommendations in Baseball Pitchers: A Systematic Review

Effect of Acute Workload on Physiology

Youth pitchers (age 9-14 years) demonstrated increased width of both the long head of the biceps and the infraspinatus tendon after 50 pitches in a single simulated game session. ³⁴ These changes in tendons measured via ultrasonography were not seen after 25 pitches. High school (age 14-19 years) pitchers demonstrated decreased voluntary activation of the infraspinatus muscle and decreased external rotational torque after 75 to 90 pitches in a simulated game session. Additionally, a decrease in pitch velocity was demonstrated during late inning (sixth inning) pitches. ¹⁶ Similarly, high school pitchers aged 16 to 18 years demonstrated an increase in shoulder flexion, extension, abduction, adduction, internal rotation, and external rotation weakness after a 100-pitch simulated bullpen session. ³² As seen in Tables 5 and 6, these changes can occur at pitch counts less than those recommended by baseball governing bodies.^3,24,40 Only 1 study was identified describing the acute physiologic changes associated with pitching workload in the professional athlete. MLB throwers demonstrated significant alterations in upper extremity arterial blood supply after a simulated game during a bullpen session (approximately 50 pitches). These arterial changes occurred only in pitchers without underlying anterior glenohumeral instability. ⁴

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Table 5

Current Single-Outing Pitch Count Recommendations by Organization

Age, y	Little League Baseball a	USA Baseball a	Baseball Canada a
7	50	50	No recommendation
8			No recommendation
9	75	75	75
10
11	85	85
12			85
13	95	95
14			95
15
16			105
17		105
18
<21		120	115

a

Values are pitch counts.

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Table 6

Current Recommendations for Days of Rest by Organization and Age Group ^a

	USA Baseball b							Little League b		Baseball Canada b
Days of Rest	7-8 y	9-10 y	11-12 y	13-14 y	15-16 y	17-18 y	19-22 y	<14 y	15-16 y	<11 y	<13 y	<15 y	<18 y	<21 y
0	1-20	1-20	1-20	1-20	1-30	1-30	1-30	1-20	1-30	1-25	1-30	1-35	1-40	1-45
1	21-35	21-35	21-35	21-35	31-45	31-45	31-45	21-35	31-45	26-40	31-45	36-50	41-55	46-60
2	36-50	36-50	36-50	36-50	46-60	46-60	46-60	36-50	46-60	41-55	46-60	51-65	56-70	61-75
3	NA	51-65	51-65	51-65	61-75	61-80	61-80	51-65	61-75	56-65	61-75	66-80	71-85	76-90
4	NA	≥66	≥66	≥66	≥76	≥81	80-105	≥66	≥76	66-75	76-85	81-95	86-105	91-115
5							≥106

a

NA, not applicable.

b

Values are pitch counts.

Effect of Acute Workload on Biomechanics

Adolescent pitchers (age 12-16 years) demonstrated a decrease in both trailing leg hip extension and ankle plantarflexion during the stride phase, a decrease in hip flexion and hip abduction at foot contact, and a decrease in ball speed at release after a simulated game session (approximately 90 pitches). ²² Gluteal and scapular muscle activation did not significantly change during a bullpen session (approximately 75 pitches) in a similar patient population (age 11.2 ± 0.8 years). ³⁰ Additionally, the same group of adolescent pitchers exposed to an 85-pitch workload simulated session of variable pitch type had no significant changes in pitching kinematics. Specifically, pelvic rotation, torso rotation, shoulder plane of elevation, and shoulder rotation, as well as muscle activation of bilateral pelvic and parascapular muscles, remained consistent across the throwing session. ²⁹ In the collegiate pitchers, forward trunk tilt became increasingly close to vertical at the moment of ball release during a 7- to 9-inning (approximately 105-135 pitches) simulated game session. ¹¹ In-game video recording of 11 collegiate pitchers found numerous kinematic changes over the course of a pitching outing (97.2 ± 16.1 pitches): decrease in maximum external rotation during late cocking phase, decrease in glove height during ball release, and decrease in glove height during follow-through. In the same population, throwers demonstrated additional kinematic changes during prolonged innings where they threw more than 15 pitches, including “increases in hip lean at hand separation, decreased stride length at foot contact, and increased hip flexion at maximum external rotation and ball release.” ¹⁷ MLB pitchers demonstrated kinematic changes during a 5- or 6-inning spring training appearance, including decreases in maximum shoulder external rotation and knee angle at ball release. These changes were associated with a 5-mph decrease in velocity from the first inning (90 mph) to the fifth inning (85 mph). ²⁸

Effect of Chronic Workload on Physiologic Parameters

Physiologic adaptations of the UCL have been shown to be correlated with increasing pitching workload, where pitchers throwing more than 67 pitches per outing, playing more than 5 innings per appearance, and having more than 5.5 years of pitching experience demonstrated significantly thickened UCLs. ² Furthermore, high school pitchers (age 16 ± 1 years; range, 14-18 years) throwing high volumes of pitches (>400 pitches per season or the highest volume tercile of pitchers) lost up to 13% of supraspinatus strength over the course of a single season. ²⁷ Additionally, high- and medium-volume pitchers failed to gain strength season-to-season, whereas low-volume (<130 pitches per season or the lowest volume tercile of pitchers) high school pitchers increased strength by 24%. ²⁷ Maintenance programs were not discussed in this study.

Range of motion (ROM) measurements in the above subset of high school pitchers were unaffected by high pitch volume. ²⁷ Freehill and colleagues ¹⁵ demonstrated similar findings in 6 collegiate pitchers (age 21.7 ± 0.7 years), with no association identified between single game and changes over the course of a season in upper extremity ROM changes and innings pitched, pitch count, or types of pitches thrown. In the lower extremity, no association was identified between cumulative pitching workload and hip ROM changes over the course of a collegiate baseball season in 12 college baseball pitchers (age 19.35 ± 1.4 years). ⁴⁵

Effect of Chronic Workload on Biomechanics

No studies were found that examined the influence of chronic workload (eg, over the course of a season or seasons) on pitching biomechanics.

Effect of Chronic Workload on Upper Extremity Pain

Two large, prospective cohort studies were identified regarding the association between pitching workload and shoulder and elbow pain in adolescent athletes (age 8-12 years). In the first study, Lyman and colleagues ²⁶ demonstrated increased odds of shoulder pain when athletes pitched more than 75 pitches in an outing, when compared with throwing fewer than 24 pitches (odds ratio [OR] = 3.22, P < .01). Additionally, increasing workload was associated with an increased risk of elbow pain, but results did not reach statistical significance. Finally, throwing more than 300 pitches in competition before a pitching outing was protective against elbow pain, whereas throwing more than 600 pitches was associated with an increased risk of pain.

In the second study, Lyman and colleagues ²⁵ reported similar findings between shoulder and elbow pain with increased pitch counts in youth baseball pitchers ranging from age 9 to 14 years, where throwing more than 100 pitches in an appearance increased risk of both elbow (OR = 1.44, P = .07) and shoulder (OR = 1.77, P < .01) pain.

Effect of Chronic Workload on Pitching Performance

Two studies attempted to associate exposure to a defined pitching workload and subsequent pitching performance at the professional level. Crotin et al ⁹ demonstrated that neither days of rest nor the ratio of pitching work to rest affected fastball velocity of young professionals. However, Bradbury and Forman ⁶ reported that earned run average (ERA) was adversely associated with increased pitches thrown in prior games. Those investigators demonstrated that a pitcher’s ERA increased with more pitches thrown in the prior appearance (0.007 earned runs per pitch) and with average workload in the prior 10 appearances (0.022 earned runs per pitch). ⁶

Effect of Chronic Workload on Injury Risk

In the adolescent population (age 9-14 years), injured pitchers (players with elbow or shoulder surgery or ending their career due to throwing injury) are more likely to cross the 100 innings per year threshold than their uninjured counterparts. ¹³ Pitchers requiring operative intervention on the shoulder or elbow threw more warm-up pitches (21 pitches control vs 34.1 injured, P < .01), more months per year (5.5 control vs 7.9 injured), more innings per appearance (4.3 control vs 5.6 injured), more pitches per appearance (66.2 control vs 87.8 injured), and more pitches per year than uninjured controls (1268 control vs 2562 injured). ³¹ Sueyoshi and colleagues ³⁸ demonstrated similar findings, with injured throwers again throwing more games per season, innings per game, and pitches per game than healthy throwers. Among Japanese Little League pitchers, injured pitchers were more likely to throw more than 100 pitches per week (24.5% injured vs 11.0% healthy). ⁴³ Finally, 85% of high school baseball athletes requiring UCL reconstruction exhibited increased or high-volume load in at least 1 of 3 categories: year-round throwing, seasonal overuse, and event overuse. ³³

A single study, performed by Erickson and colleagues, ¹⁰ examined the association between youth exposure to pitching workload and injury risk as a professional. The investigators found that players who had violated Little League pitch count recommendations of fewer than 85 pitches for players age 11 to 12 and fewer than 96 pitches for players age 13 to 16 were more likely to require UCL reconstruction during their professional career compared with professional throwers who adhered to pitch count recommendations as Little Leaguers (50% vs 1.7%, P = .009).

In professional pitchers, Whiteside et al ⁴² demonstrated that higher pitch counts per game and fewer days of rest between appearances increased the risk of UCL injury in professional pitchers. Conversely, Chalmers et al ⁸ reported that pitch counts per year were not statistically different between controls (2826 pitches) and throwers who required subsequent UCL reconstruction (2804 pitches). When broadening beyond UCL injuries, 2 studies from Karakolis and colleagues^18,19 demonstrated that no cumulative workload metric was a significant predictor for future injury including innings per season or year-to-year increases in innings pitched in professional baseball.

Youth/High School Pitchers

Eight studies^{10,13,27,31,33,34,38,43} reported on Little League and high school pitchers and demonstrated an association between increased pitch counts and shoulder or elbow pain and injury. Furthermore, Erickson et al ¹⁰ reported that increased in-game pitch counts as a Little Leaguer can also predispose to future UCL injury as a professional athlete. These results support the implementation of pitch count and rest recommendations by the USA Baseball Medical and Safety Advisory Committee ⁴⁰ to decrease the risk of injury. However, Olsen et al ³¹ found that the USA Baseball guidelines may be far too liberal. Those investigators reported that adolescent pitchers (age 14-20 years) who threw more than 80 pitches per game were at nearly 4 times increased risk of injury that would require surgery. The current USA Baseball recommendations suggest pitch count limits that significantly exceed this number, ⁴⁰ with pitchers who are 14 and 20 years of age being limited to a maximum of 95 and 120 game pitches per appearance, respectively. In addition, Popchak et al ³⁴ demonstrated acute physiologic alterations at the 50-pitch threshold in the youth (age 9-14 years) shoulder, demonstrating the potential for pathologic changes and injury to occur at a workload significantly below pitch count recommendations (Tables 5 and 6). Furthermore, McHugh et al ²⁷ reported decreased rotator cuff strength and muscular fatigue in 14- to 18-year-old pitchers throwing more than 400 pitches per season, a number attained by the majority of high school starting pitchers. This suggests that cumulative pitches over a season can have detrimental effects on a pitcher and should be included in pitch count recommendations as a result. Although these results demonstrate an association between pitch count and risk of shoulder and elbow pain and injury, several methodologic flaws limit the use of these conclusions. These studies were retrospective in nature and had significant recall bias and confounding variables present. As a result, high-level prospective studies are needed to demonstrate a causal relationship between pitch count and injury risk and to determine appropriate pitch count recommendations for Little League and high school baseball organizations.

Multiple studies also reported that pitching with arm fatigue is a significant factor associated with shoulder or elbow pain and injury, regardless of pitch count in youth players.^26,31 These results suggest that a player should be removed from a game or prevented from pitching, regardless of pitch count, if he or she complains of arm fatigue. This increased risk of injury is likely related to muscle fatigue, resulting in decreased dynamic stability provided by the arm and forearm musculature with excessive pitching. The dynamic stabilizers of the shoulder and elbow have been shown to weaken at the 75-pitch threshold in high school pitchers, ³² but dynamic stability is typically physiologically undetectable to the parent or the coach. As a result, the shoulder and elbow of the adolescent pitcher may be vulnerable to microtrauma and fatigue, which has been hypothesized to predispose to injury. For example, the flexor and pronator forearm muscles function as the primary dynamic stabilizers of the medial aspect of the elbow and decrease the forces placed on the UCL with excessive valgus force during pitching. ²³ However, with arm fatigue, the stabilizing effect of the flexor-pronator mass is likely decreased, resulting in increased tensile stress throughout the UCL. These studies demonstrate the limited utility of pitch count, as it is an absolute measure of workload that does not account for subjective feelings of arm fatigue or individual endurance levels. Future research is required to better understand the physiologic mechanisms (ie vascular, neuromotor, structural) that underlie this muscular fatigue and the resultant clinical effects.

A primary limitation on the use of baseball pitch counts for youth and high school players is the adherence of coaches, players, and parents to these recommendations. Several studies have obtained surveys of players and coaches and have demonstrated poor knowledge of and compliance with pitching guidelines.^{1,5,12,35,41,44} These surveys reported that the majority of youth players and coaches had little understanding of the USA Baseball pitch count and rest recommendations.^5,12 Furthermore, players and coaches also had opinions and actions regarding pitch counts and pitching injuries that were contradictory to the published literature.^1,5,12,35,41 These results suggest the importance of educating players, coaches, and parents about recommended pitch counts and rest days. Involved parties should also be aware of the injury implications associated with exceeding these pitching workload guidelines. Finally, players, coaches, and parents should be counseled regarding the increased injury risk when pitching with arm fatigue and pain. This awareness and compliance by athletes, coaches, and parents is critical to maintaining the health and performance of youth and adolescent pitchers.

College/Professional Pitchers

Overall, mixed results regarding pitch counts at the college and professional levels have been reported. Although Bradbury and Forman ⁶ and Whiteside et al ⁴² reported increased injury risk and worse performance with increasing pitches thrown compared with controls, Karakolis et al^18,19 and Chalmers et al ⁸ produced conflicting evidence. Furthermore, all of the evidence regarding college and professional pitchers, with the exception of 1 study, was level of evidence 3 and 4, with the majority of studies involving small cohorts of pitchers. This demonstrates the need for higher level prospective studies that can elucidate any deleterious effects of cumulative pitching workload in elite pitchers. Studies of this nature could further examine the benefit of pitch counts and cumulative workload on injury rates and performance in college and professional pitchers. Ultimately, higher quality research in this level of baseball pitcher will help to maintain the health, performance, and longevity of college and professional pitchers.

Although this conflicting evidence may suggest that developing athletes (Little League and high school) respond differently to musculoskeletal loads compared with elite athletes (college and professional), it may also be related to a survival bias. It is possible that the pitchers who attain collegiate and professional levels represent a cohort of players who have minimized physiologic and pathologic and performance changes with increasing pitching workload. These pitchers may have achieved their elite level of play due to an ability to avoid decreases in performance and injury with increasing stress and workload. Furthermore, these pitchers may have been able to train more and spend extra hours pitching as Little League and high school athletes without sustaining the detrimental effects often seen with high pitching volume. This training and durability advantage, compared with their teammates, could have allowed these pitchers to rise to the collegiate and professional ranks.

Another possible explanation for the difficulty in defining the relationship between workload and injury in the professional pitcher may be found in the work by Erickson and colleagues, ¹⁰ who demonstrate a correlation between Little League workload and professional UCL injury risk. Although this study had a significant risk of recall bias, it along with other physiologic studies demonstrated an association between long-term (>5.5 years of pitching experience) ² exposure to pitching workload and UCL thickening in younger populations. This may indicate that a professional pitcher’s risk of injury is likely a product of not only professional workload but also the cumulative, long-term stress imparted on the extremity over an athletic life time.

Interestingly, pitch counts in the acute settings noted above quantify only live, in-game (or simulated in-game) throws. Yet the upper extremity responds in a manner indifferent to the situation in which a force is applied: bullpen warm-up, between innings, or during a game. Consequently, the throw count (including bullpen warm-up, between-inning, and in-game pitches) experienced by the shoulder and elbow may be significantly distorted when quantified as only an in-game “pitch count.” Rather, the throw count, inclusive of bullpen warm-up and between-inning pitches, may better capture the cumulative workload imparted on the thrower. Furthermore, this suggests that bullpen warm-up and between-inning pitches should be included in the pitch count limits determined by baseball organizing bodies. This suggestion is supported by Crotin and colleagues, ⁹ who reported that injured professional baseball pitchers threw significantly more warm-up pitches than uninjured athletes.

Limitations

The studies that met our inclusion and exclusion criteria had significant limitations. Methodological designs were different in all studies with respect to data collection, limiting the comparison between studies and the ability to make conclusions regarding the results. Additionally, the majority of studies were level 3 and level 4 evidence, including case-control and/or retrospective studies, limiting the ability to demonstrate a causal relationship and questioning the overall quality of evidence summarized in this systematic review. Our review included a limited number of publications (n = 28), particularly at the college and professional levels (n = 12). Furthermore, given the age ranges for the players in the included studies, we combined Little League and high school players into a single cohort and combined collegiate and professional pitchers into a second cohort. However, this was a comprehensive review, and the limited quality of evidence points to the need for higher level prospective studies regarding safe and effective pitch counts at all levels of baseball. Multiple studies demonstrated kinematic and ROM changes with increasing pitch count.^{11,17,22,28,29,30} Although these changes may be significant, no existing literature suggests that these changes are injurious or detrimental to the pitcher. For example, Grantham et al ¹⁷ reported numerous kinematic changes over the course of a pitching outing, including decreased maximal external rotation during late cocking and decreased glove height during ball release and follow-through. Although these changes were significant, there is no reported literature to indicate that these kinematic changes will lead to pain, injury, or upper extremity abnormality. Furthermore, several different methods were used to collect and calculate pitch count and workload, with varying levels of accuracy. A prime example, as discussed above, is reporting only “in-game” pitches in a player’s final pitch count. As a result, the pitch count is an incomplete representation of the pitcher’s cumulative workload, as the pitcher will have thrown several warm-up pitches (on the field and in the bullpen) before an appearance and between innings. Finally, a few studies that discussed the injury or performance implications of pitch count monitoring were not found in our initial search results. These studies broached the subject of pitch counts but primarily addressed other related topics. Although the majority of these publications were found through “other sources,” as per the PRISMA guidelines, it is possible that a few publications were not included that met our criteria.