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Predictors of elbow torque among professional baseball pitchers
J Shoulder Elbow Surg (2019) -, 1–5
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Predictors of elbow torque among professional baseball pitchers Vincent A. Lizzio, MD, Caleb M. Gulledge, BS, D. Grace Smith, BS, Jason E. Meldau, MD, Peter A. Borowsky, BS, Vasilios Moutzouros, MD, Eric C. Makhni, MD, MBA* Department of Orthopaedic Surgery, Henry Ford Health System, Detroit, MI, USA Background: Overuse injuries of the shoulder and elbow continue to be prevalent in elite baseball pitchers. Pitch velocity has been shown to impact medial elbow torque in adolescent baseball pitchers. However, the determinants of medial elbow torque in professional baseball pitchers are not known. Purpose: To determine the influence of pitch type, velocity, and player characteristics on medial elbow torque in professional baseball pitchers. Methods: Professional baseball pitchers were recruited for participation. Height, weight, body mass index (BMI), and throwing arm measurements were obtained for all study participants. While wearing a gyroscopic sensor equipped with an accelerometer, participants were instructed to throw a standard, randomized sequence of fastballs, changeups, and curveballs. Elbow torque, arm slot, arm speed, shoulder rotation, and ball velocity were recorded for each pitch. A linear mixed model was used to evaluate the association of pitch type with each pitch parameter, adjusting for pitchers’ demographics. Results: A total of 12 professional baseball pitchers were included in this study. Among the pitch types, medial elbow torque was significantly higher in fastballs than in curveballs (P ¼ .001). An increased BMI value was independently associated with decreased elbow torque in pitchers (P ¼ .035). Conclusion: Fastballs place significantly higher torque on the medial elbow than do curveballs, which is consistent with previous studies done on high school and collegiate populations. Pitchers with a higher BMI experience significantly less torque across the medial elbow. Level of evidence: Basic Science Study; Kinesiology Ó 2019 Published by Elsevier Inc. on behalf of Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Pitching; ulnar collateral ligament; torque; biomechanics; Motus; baseball
Approval was received from the Henry Ford Health System Institutional Review Board Committee (no. 11756). *Reprint requests: Eric C. Makhni, MD, MBA, Department of Orthopaedic Surgery, Henry Ford Health System, 2799 W Grand Blvd, Detroit, MI 48202, USA. E-mail address: [email protected] (E.C. Makhni).
Overuse injuries of the shoulder and elbow, particularly ulnar collateral ligament injuries,8 are continuing to rise in youth and adult baseball pitchers.7,9,11,14 Risk factors that contribute to overuse injuries in pitchers include pitching in multiple leagues,17,25 pitching year-round,21-24 inadequate rest between seasons,23-25 pitching with high velocity,21,23 and pitching with poor mechanics.4,16,19 Unfortunately, despite widespread effort against these risk factors, shoulder and elbow injuries in throwers continue to increase.2,3
1058-2746/$ - see front matter Ó 2019 Published by Elsevier Inc. on behalf of Journal of Shoulder and Elbow Surgery Board of Trustees. https://doi.org/10.1016/j.jse.2019.07.037
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V.A. Lizzio et al.
Traditionally, off-speed and breaking pitches (such as the curveball [CB]) were demonstrated to cause the greatest amount of stress to the medial elbow.17,25 However, recent studies have contradicted this commonly held belief and have actually implicated fastballs (FBs) as the greatest stressor of the medial elbow.6,18,20 Understanding the relationship between pitch type and corresponding medial elbow stress is necessary in order to determine proper pitching guidelines for preventing overuse injury. The purpose of this study was to determine the relative medial elbow stress associated with common pitch types in a cohort of professional baseball pitchers. We hypothesized that medial elbow stress would be correlated with pitch velocity, thus being highest with FBs (as compared to CBs and changeups [CUs]). Moreover, we hypothesized that patients with small elbow circumferences would experience greater amounts of medial elbow torque than counterparts with larger elbows.
number or pitch type. Participants were then fitted with the appropriately sized sleeve equipped with the wearable sensor. Positioning of the sensor was periodically checked throughout the pitching session to ensure accurate placement over the medial elbow. All pitches were thrown from a mound toward a plate at a standard distance of 18.4 m. The pitching protocol used in this study was replicated from previously published studies that assessed elbow torque of various pitch types and consisted of a sequence of 5 FBs, 5 CBs, and 5 CUs in a standard, randomized order.18,20 Pitchers were instructed to throw at maximum effort throughout the duration of the pitching protocol. Participants were given 30-60 seconds of rest between pitches, a technique that has been shown to minimize fatigue and variations in pitching mechanics over a series of pitches.10 The study was aborted if pitchers reported fatigue or pain at any point in the data collection. For each pitch thrown, the instructor recorded the medial elbow torque, arm speed, arm slot, and shoulder rotation as measured by the sensor. In addition, a radar gun (Stalker Sport II; Stalker, Plano, TX, USA) was positioned directly behind the strike zone and used to record peak ball velocity in miles per hour (mph).
Methods
Statistical methods
Institutional review board approval was granted for this study (no. 11756). The study was entirely self-funded by the research institution and without involvement of the device manufacturer and vendor. Professional pitchers (class A) were recruited through conversation with the team’s front office staff. Inclusion criteria included baseball players who primarily self-identified as pitchers and were actively participating in competition. Players were excluded if they were not primarily pitchers, if they were not currently participating in competitive play, or if they did not feel that they could pitch with 100% effort. All participants completed an intake form that recorded age, injury history, and current injuries that involve the throwing arm. Several body measurements were collected from each pitcher, including height, weight, and body mass index (BMI). Throwing arm measurements, including total arm length, upper arm length, forearm length, and elbow circumference, were obtained with the arm in neutral rotation. Total arm length was determined by measuring the distance from the lateral aspect of the acromion to the most distal aspect of the fifth digit. Upper arm length was defined as the distance from the acromion to the lateral epicondyle of the humerus, and forearm length was defined as the distance from the lateral epicondyle of the humerus to the styloid of the radius. Elbow circumference was recorded by measuring the distance around the medial and lateral epicondyles with the elbow in full extension. The device used in this study consisted of a small, gyroscopic sensor equipped with an accelerometer (Motus Global, Rockville Centre, NY, USA). This wearable technology records peak elbow torque (newton-meters), arm speed (rpm), arm slot (degrees), and shoulder rotation (degrees). This device has been previously validated using high-speed motion analysis1 and proven to be reliable for throwers at various levels of competitive play.18,20 Per manufacturer instructions, the device was secured and positioned 1.5 inches distal to the medial epicondyle using a compression athletic sleeve. Pitchers were allowed to participate in warm-ups prior to the recorded pitching session (including stretching, jogging, and practice throws) and were not given any limitations on practice pitch
Descriptive statistics for characteristics of pitchers were calculated and presented as mean, standard deviation, and range. Linear mixed models were used to evaluate the association of pitch type with each pitch parameter, adjusting for pitcher demographics. The model included the intercept as random effect for individual subjects, pitch type as a repeated and fixed effect variable, and pitcher demographic variables as fixed covariates. Univariate analysis was first performed, and any variable with a P value less than .05 in the univariate analysis was considered to enter the multivariate model. The estimated least squares mean and standard error for categorical variables and the coefficient (b) for continuous variables were presented for those variables retained in the final model. The correlation between pitch velocity and elbow torque was quantified using Pearson correlation coefficient. Device precision was calculated by comparing the number of outlier measurements for elbow torque (defined as pitches more than 1.5 times the interquartile range, either above the third quartile or below the first quartile) to total pitches thrown for each pitch type. All analyses were performed using SAS (v 9.4; SAS Institute Inc, Cary, NC, USA).
Results A total of 18 professional baseball pitchers were evaluated for participation in this study. Six pitchers were excluded because of sidearm pitching mechanics, which impeded accurate data collection with the device. Thus, 12 pitchers were included for data analysis. The average age of the pitchers was 23.4 years (range 21-25 years), and the average height was 187.7 cm (range 175.3-200.7 cm). Nine of the pitchers were right-hand dominant (75%) and 3 were left-hand dominant (25%). Further data regarding pitcher demographic characteristics are described in Table I. No adverse events were experienced during the pitching sessions. All participants were able to securely and comfortably fit the sleeve and sensor directly onto the throwing arm.
Predictors of elbow torque among pitchers Table I
Pitcher demographic characteristics (N ¼ 12) Mean (SD)
Upper arm length, cm Forearm length, cm Total arm length, cm Elbow joint circumference, cm Height, cm Weight, kg BMI
34.4 27.4 77.9 30.2
(2.3) (2.5) (3.1) (1.2)
187.7 (6.1) 91.6 (8.4) 26.0 (2.2)
Range (minimum-maximum) 31.0-39.0 21.0-30.0 73.0-83.5 28.0-32.5 175.3-200.7 74.8-108.9 21.2-28.8
BMI, body mass index; SD, standard error.
The sleeve remained positioned correctly with each pitch type thrown (FB, CB, and CU). Under these conditions, the device was 89.5% precise in measuring elbow torque for FB, 100% precise for CB, and 91.7% for CU. On average, FBs produced the greatest torque on the medial elbow (54.3 7.0 Nm; Table II). In comparison, CBs produced 4% less torque on the medial elbow (54.3 vs. 52.1 Nm, P ¼ .001). There was no significant difference in medial elbow torque between FBs and CUs (54.3 vs. 53.4 Nm, P ¼ .112). Demographic and biomechanical factors that best predicted change in medial elbow torque included pitch type and BMI (Table III). Increased BMI was predictive for decreased medial elbow torque when controlled by pitch type (b ¼ –1.83, P ¼ .035). CB and CU were also found to independently predict lower medial elbow torque in the univariate analysis. However, a subsequent multivariate analysis found that CU did not significantly predict medial elbow torque (Table IV). The 3 pitch types were also evaluated to determine differences in ball velocity, arm slot, arm speed, and shoulder rotation (Table II). The mean arm slot in CBs was significantly greater than that for CUs (49.7 vs. 43.8 , P < .0001), and the mean arm slot in FBs was significantly greater than that for CUs (48.2 vs. 43.7 , P ¼ .001). There was no difference in arm slot between FBs and CBs (P ¼ .193). The average velocity was significantly higher in FBs (85.2 mph) when compared to CUs (77.9 mph, P < .0001) and CBs (73.1 mph, P < .0001), and the average velocity in CUs was significantly higher than the average velocity in CBs (P < .0001). There was no significant correlation between ball velocity and medial elbow torque, irrespective of pitch type (r ¼ 0.30, P ¼ .69).
Discussion Our study found that FBs produce the greatest amount of torque on the medial elbow when compared to CBs or CUs in professional baseball pitchers. We also found that BMI was the only demographic factor predictive of increased elbow torque.
3 The primary finding of this study is that FBs cause greater medial elbow stress than CBs in professional baseball players. This is consistent with previous studies that have evaluated medial elbow stress at other levels of competitive play. A study by Makhni et al18 compared elbow stress in high school and collegiate athletes using the same sensor and methodology and found the FB to produce greater stress when compared to the CB and CU. At this level of competition, the average torque for FB was 45.6 Nm and for CB it was 43.8 Nm (compared to 54.3 and 52.1 Nm, respectively, in our study). Okoroha et al20 performed a similar study in the youth and adolescent pitching population and again found the FB (47.3 Nm) to produce greater elbow torque than the CB (45.0 Nm) and CU (44.2 Nm). It is important to note that the differences in torque among pitch types, although statistically significant in all of these studies, is relatively small; because there is no established minimum clinically important difference for elbow torque, the clinical impact of throwing relatively more FBs than CUs is unclear in regard to elbow injury risk. Our finding that the FB, not the CB, places the greatest torque on the medial elbow is consistent with prior highspeed motion capture studies. Nissen et al19 used 3-dimensional ball marker analysis to assess the elbow valgus moment in 35 adolescent pitchers and found the FB to be more stressful than the CB (59.6 vs. 54.1 Nm; P < .001). This finding has since been corroborated at other levels of competition, including professional baseball pitchers, using gold standard high-speed motion analysis.12 In fact, a systematic review of biomechanical and EMG pitching studies found no evidence identifying CB as the most stressful pitch on the elbow.13 This laboratory finding is reflected by clinical evidence as well; most notably, a 10-year prospective study of youth baseball players found no evidence linking early or frequent use of the CB to elbow injury risk.11 Our study found that, after controlling for pitch type, BMI was the only independent demographic predictor of medial elbow torque, with larger BMI predicting decreased medial elbow torque. This is consistent with previous findings that BMI20 and weight18 have a protective effect for youth, high school, and collegiate pitchers. It is not clear why increased BMI is protective against medial elbow torque. One hypothesis is that a larger BMI correlates with greater dynamic stabilization at the elbow and protects the medial elbow from excessive forces. Unlike previous studies, however, our study found that increasing elbow circumference (a larger area for load distribution) did not independently predict lower elbow torque at this elite level of competition. There were significant differences in ball velocity among all 3 pitch types, with the FB exhibiting the fastest velocity and the CB exhibiting the slowest. Several studies have evaluated the effect of ball velocity on medial elbow torque and found conflicting results. A study by Hurd et al
4
V.A. Lizzio et al. Table II
Differences in pitch biomechanics among FB, CB, and CU Least squares mean (SE) FB : CB
Elbow torque, Nm 54.3 (2.1) : Arm slot, degrees 48.2 (2.4) : Arm speed, rpm 916.2 (17.8) : Shoulder rotation, 148 (2.7) : degrees Ball velocity, mph 85.2 (0.6) :
52.1 (2.2) 49.7 (2.4) 905.5 (17.2) 146.9 (2.6) 73.1 (0.8)
P value
.001 54.3 (2.1) .193 48.2 (2.4) .191 916.2 (17.8) .265 148 (2.7) <.0001
P value
FB : CU : : : :
53.4 (2.1) 43.8 (2.4) 914.2 (17.3) 146.4 (2.7)
.112 53.4 (2.1) .001 43.8 (2.4) .807 914.2 (17.3) .165 146.4 (2.7) <.0001
85.2 (0.6) : 77.9 (0.7)
CU : CB : : : :
P value
52.1 (2.2) .084 49.7 (2.4) <.0001 905.5 (17.2) .229 146.9 (2.6) .629
77.9 (0.7) : 73.1 (0.8)
<.0001
FB, fastball; CB, curveball; CU, changeup; SE, standard error. Bold values indicate P < .05.
Table III Independent predictors of medial elbow torque (univariate analysis) Upper arm length Forearm length Total arm length Elbow circumference Height Weight BMI Pitch type Fastball Curveball Changeup
Beta estimate
P value
0.79 0.19 0.97 –2.14 19.99 –0.34 –1.83
.411 .838 .145 .219 .592 .174 .035
Reference –2.19 –0.93
.005
BMI, body mass index. Beta estimate values denote the change in torque for every 1-unit increase in the independent variable. Bold values indicate P < .05.
used 3-dimensional motion analysis to evaluate 26 high school pitchers and found a strong association between peak pitch velocity and medial elbow adduction moment.15 However, a study by Post et al used similar technology to analyze 67 collegiate baseball pitchers and found no significant correlation between pitch velocity and elbow valgus stress.24 The correlation between velocity and elbow torque is reinforced by recent biomechanical studies using wearable technology.18,20 Interestingly, a study that compared the pitching mechanics of youth pitchers who developed elbow injuries against those who did not found that the average FB velocity was 6% higher for injured pitchers, providing clinical evidence that increased pitch velocity is a risk factor for elbow injury. The reliability of the wearable technology used in this population of professional baseball pitchers was slightly lower than what was previously reported for youth, high school, and collegiate pitchers.18,20 Unfortunately, this new electronic technology does not reliably detect measurements for the sidearm or submarine throwing motions. However, after excluding sidearm pitchers from analysis, the overall precision rate of the device in measuring elbow torque remained greater than 90%. This high reliability, along with
Table IV
Multivariate model for medial elbow torque
BMI Pitch type Fastball Curveball Changeup
Beta estimate
Standard error
P value
–1.83
0.86
.035
Reference –2.19 –0.93
d 0.66 0.59
d .001 .114
BMI, body mass index. Beta estimate values denote the change in torque for every 1-unit increase in the independent variable. Bold values indicate P < .05.
the validation of the sensor against the high-speed motion analysis (the current gold standard of biomechanical evaluation),1 demonstrates that wearable technology can be reliably used at all levels of competitive play and has practical implications for future methodology and analysis in the field of pitching biomechanics. Most notably, researchers can now bypass the use of high-speed motion analysis, which is not only expensive and cumbersome but also requires significantly more attachments to the pitcher that can interfere with native pitching mechanics. For example, a recent study by Dowling et al5 illustrated the practical use of wearable technology by quantitatively tracking medial elbow stress for various throws of an interval throwing program, a practice that is commonly used for preventing injuries or progressively increasing loads after injury.
Limitations This study has important limitations. The sensor used in this study, similar to 3-dimensional motion analysis, does not directly measure the force placed on the ulnar collateral ligament. For this reason, it is impossible to state with certainty that the ulnar collateral ligament is receiving the forces measured by the wearable technology. However, traditional studies assessing medial elbow torque during the throwing motion also rely on indirect measures of elbow torque, such as with high-speed motion analysis.12,15,19,24 Second, this study was done in a controlled, practice setting and not in a competitive game, where pitchers may demonstrate altered
Predictors of elbow torque among pitchers pitching mechanics in the presence of live batters, fatigue, stress, and weather conditions.
Conclusion This study found that FBs produce greater medial elbow torque than CBs in professional baseball players, and that increased BMI was an independent predictor of decreased medial elbow torque.
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Camp CL, Tubbs TG, Fleisig GS, Dines JS, Dines DM, Altchek DW, et al. The relationship of throwing arm mechanics and elbow varus torque: within-subject variation for professional baseball pitchers across 82,000 throws. Am J Sports Med 2017;45:3030-5. https://doi. org/10.1177/0363546517719047 2. Conte S, Camp CL, Dines JS. Injury trends in major league baseball over 18 seasons: 1998-2015. Am J Orthop (Belle Mead, NJ) 2016;45:116-23. 3. Conte SA, Fleisig GS, Dines JS, Wilk KE, Aune KT, PattersonFlynn N, et al. Prevalence of ulnar collateral ligament surgery in professional baseball players. Am J Sports Med 2015;43:1764-9. https://doi.org/10.1177/0363546515580792 4. Davis JT, Limpisvasti O, Fluhme D, Mohr KJ, Yocum LA, Elattrache NS, et al. The effect of pitching biomechanics on the upper extremity in youth and adolescent baseball pitchers. Am J Sports Med 2009;37:1484-91. https://doi.org/10.1177/0363546509340226 5. Dowling B, McNally MP, Laughlin WA, Onate JA. Changes in throwing arm mechanics at increased throwing distances during structured long-toss. Am J Sports Med 2018;46:3002-6. https://doi.org/10.1177/0363546518795892 6. Dun S, Loftice J, Fleisig GS, Kingsley D, Andrews JR. A biomechanical comparison of youth baseball pitches: is the curveball potentially harmful? Am J Sports Med 2008;36:686-92. https://doi. org/10.1177/0363546507310074 7. Erickson BJ. The epidemic of Tommy John surgery: the role of the orthopedic surgeon. Am J Orthop (Belle Mead, NJ) 2015;44:E36-7. 8. Erickson BJ, Chalmers PN, Axe MJ, Romeo AA. Exceeding pitch count recommendations in Little League Baseball increases the chance of requiring Tommy John surgery as a professional baseball pitcher. Orthop J Sports Med 2017;5:2325967117695085. https://doi.org/10. 1177/2325967117695085. 9. Erickson BJ, Chalmers PN, Bush-Joseph CA, Romeo AA. Predicting and preventing injury in Major League Baseball. Am J Orthop (Belle Mead, NJ) 2016;45:152-6.
5 10. Escamilla RF, Fleisig GS, Barrentine SW, Zheng N, Andrews JR. Kinematic comparisons of throwing different types of baseball pitches. J Appl Biomech 1998;14:1-23. 11. Fleisig GS, Andrews JR, Cutter GR, Weber A, Loftice J, McMichael C, et al. Risk of serious injury for young baseball pitchers: a 10-year prospective study. Am J Sports Med 2011;39:253-7. https:// doi.org/10.1177/0363546510384224 12. Fleisig GS, Laughlin WA, Aune KT, Cain EL, Dugas JR, Andrews JR. Differences among fastball, curveball, and change-up pitching biomechanics across various levels of baseball. Sports Biomech 2016; 15:128-38. https://doi.org/10.1080/14763141.2016.1159319 13. Grantham WJ, Iyengar JJ, Byram IR, Ahmad CS. The curveball as a risk factor for injury: a systematic review. Sports Health 2015;7:19-26. https://doi.org/10.1177/1941738113501984 14. Hodgins JL, Vitale M, Arons RR, Ahmad CS. Epidemiology of medial ulnar collateral ligament reconstruction: a 10-year study in New York State. Am J Sports Med 2016;44:729-34. https://doi.org/10.1177/ 0363546515622407 15. Hurd WJ, Jazayeri R, Mohr K, Limpisvasti O, Elattrache NS, Kaufman KR. Pitch velocity is a predictor of medial elbow distraction forces in the uninjured high school-aged baseball pitcher. Sports Health 2012;4:415-8. https://doi.org/10.1177/1941738112439695 16. Keeley DW, Hackett T, Keirns M, Sabick MB, Torry MR. A biomechanical analysis of youth pitching mechanics. J Pediatr Orthop 2008; 28:452-9. https://doi.org/10.1097/BPO.0b013e31816d7258 17. Lyman S, Fleisig GS, Waterbor JW, Funkhouser EM, Pulley L, Andrews JR, et al. Longitudinal study of elbow and shoulder pain in youth baseball pitchers. Med Sci Sports Exerc 2001;33:1803-10. 18. Makhni EC, Lizzio VA, Meta F, Stephens JP, Okoroha KR, Moutzouros V. Assessment of elbow torque and other parameters during the pitching motion: comparison of fastball, curveball, and change-up. Arthroscopy 2018;34:816-22. https://doi.org/10.1016/j. arthro.2017.09.045 19. Nissen CW, Westwell M, Ounpuu S, Patel M, Solomito M, Tate J. A biomechanical comparison of the fastball and curveball in adolescent baseball pitchers. Am J Sports Med 2009;37:1492-8. https://doi.org/ 10.1177/0363546509333264 20. Okoroha KR, Lizzio VA, Meta F, Ahmad CS, Moutzouros V, Makhni EC. Predictors of elbow torque among youth and adolescent baseball pitchers. Am J Sports Med 2018;46:2148-53. https://doi.org/ 10.1177/0363546518770619 21. Olsen SJ 2nd, Fleisig GS, Dun S, Loftice J, Andrews JR. Risk factors for shoulder and elbow injuries in adolescent baseball pitchers. Am J Sports Med 2006;34:905-12. https://doi.org/10.1177/0363546505284188 22. Oyama S, Sosa A, Campbell R, Correa A. Reliability and validity of quantitative video analysis of baseball pitching motion. J Appl Biomech 2017;33:64-8. https://doi.org/10.1123/jab.2016-0011 23. Petty DH, Andrews JR, Fleisig GS, Cain EL. Ulnar collateral ligament reconstruction in high school baseball players: clinical results and injury risk factors. Am J Sports Med 2004;32:1158-64. https://doi.org/ 10.1177/0363546503262166 24. Post EG, Laudner KG, McLoda TA, Wong R, Meister K. Correlation of shoulder and elbow kinetics with ball velocity in collegiate baseball pitchers. J Athl Train 2015;50:629-33. https://doi.org/10.4085/10626040-50.1.06 25. Yang J, Mann BJ, Guettler JH, Dugas JR, Irrgang JJ, Fleisig GS, et al. Risk-prone pitching activities and injuries in youth baseball: findings from a national sample. Am J Sports Med 2014;42:1456-63. https:// doi.org/10.1177/0363546514524699
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Predictors of elbow torque among professional baseball pitchers Vincent A. Lizzio, MD, Caleb M. Gulledge, BS, D. Grace Smith, BS, Jason E. Meldau, MD, Peter A. Borowsky, BS, Vasilios Moutzouros, MD, Eric C. Makhni, MD, MBA* Department of Orthopaedic Surgery, Henry Ford Health System, Detroit, MI, USA Background: Overuse injuries of the shoulder and elbow continue to be prevalent in elite baseball pitchers. Pitch velocity has been shown to impact medial elbow torque in adolescent baseball pitchers. However, the determinants of medial elbow torque in professional baseball pitchers are not known. Purpose: To determine the influence of pitch type, velocity, and player characteristics on medial elbow torque in professional baseball pitchers. Methods: Professional baseball pitchers were recruited for participation. Height, weight, body mass index (BMI), and throwing arm measurements were obtained for all study participants. While wearing a gyroscopic sensor equipped with an accelerometer, participants were instructed to throw a standard, randomized sequence of fastballs, changeups, and curveballs. Elbow torque, arm slot, arm speed, shoulder rotation, and ball velocity were recorded for each pitch. A linear mixed model was used to evaluate the association of pitch type with each pitch parameter, adjusting for pitchers’ demographics. Results: A total of 12 professional baseball pitchers were included in this study. Among the pitch types, medial elbow torque was significantly higher in fastballs than in curveballs (P ¼ .001). An increased BMI value was independently associated with decreased elbow torque in pitchers (P ¼ .035). Conclusion: Fastballs place significantly higher torque on the medial elbow than do curveballs, which is consistent with previous studies done on high school and collegiate populations. Pitchers with a higher BMI experience significantly less torque across the medial elbow. Level of evidence: Basic Science Study; Kinesiology Ó 2019 Published by Elsevier Inc. on behalf of Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Pitching; ulnar collateral ligament; torque; biomechanics; Motus; baseball
Approval was received from the Henry Ford Health System Institutional Review Board Committee (no. 11756). *Reprint requests: Eric C. Makhni, MD, MBA, Department of Orthopaedic Surgery, Henry Ford Health System, 2799 W Grand Blvd, Detroit, MI 48202, USA. E-mail address: [email protected] (E.C. Makhni).
Overuse injuries of the shoulder and elbow, particularly ulnar collateral ligament injuries,8 are continuing to rise in youth and adult baseball pitchers.7,9,11,14 Risk factors that contribute to overuse injuries in pitchers include pitching in multiple leagues,17,25 pitching year-round,21-24 inadequate rest between seasons,23-25 pitching with high velocity,21,23 and pitching with poor mechanics.4,16,19 Unfortunately, despite widespread effort against these risk factors, shoulder and elbow injuries in throwers continue to increase.2,3
1058-2746/$ - see front matter Ó 2019 Published by Elsevier Inc. on behalf of Journal of Shoulder and Elbow Surgery Board of Trustees. https://doi.org/10.1016/j.jse.2019.07.037
2
V.A. Lizzio et al.
Traditionally, off-speed and breaking pitches (such as the curveball [CB]) were demonstrated to cause the greatest amount of stress to the medial elbow.17,25 However, recent studies have contradicted this commonly held belief and have actually implicated fastballs (FBs) as the greatest stressor of the medial elbow.6,18,20 Understanding the relationship between pitch type and corresponding medial elbow stress is necessary in order to determine proper pitching guidelines for preventing overuse injury. The purpose of this study was to determine the relative medial elbow stress associated with common pitch types in a cohort of professional baseball pitchers. We hypothesized that medial elbow stress would be correlated with pitch velocity, thus being highest with FBs (as compared to CBs and changeups [CUs]). Moreover, we hypothesized that patients with small elbow circumferences would experience greater amounts of medial elbow torque than counterparts with larger elbows.
number or pitch type. Participants were then fitted with the appropriately sized sleeve equipped with the wearable sensor. Positioning of the sensor was periodically checked throughout the pitching session to ensure accurate placement over the medial elbow. All pitches were thrown from a mound toward a plate at a standard distance of 18.4 m. The pitching protocol used in this study was replicated from previously published studies that assessed elbow torque of various pitch types and consisted of a sequence of 5 FBs, 5 CBs, and 5 CUs in a standard, randomized order.18,20 Pitchers were instructed to throw at maximum effort throughout the duration of the pitching protocol. Participants were given 30-60 seconds of rest between pitches, a technique that has been shown to minimize fatigue and variations in pitching mechanics over a series of pitches.10 The study was aborted if pitchers reported fatigue or pain at any point in the data collection. For each pitch thrown, the instructor recorded the medial elbow torque, arm speed, arm slot, and shoulder rotation as measured by the sensor. In addition, a radar gun (Stalker Sport II; Stalker, Plano, TX, USA) was positioned directly behind the strike zone and used to record peak ball velocity in miles per hour (mph).
Methods
Statistical methods
Institutional review board approval was granted for this study (no. 11756). The study was entirely self-funded by the research institution and without involvement of the device manufacturer and vendor. Professional pitchers (class A) were recruited through conversation with the team’s front office staff. Inclusion criteria included baseball players who primarily self-identified as pitchers and were actively participating in competition. Players were excluded if they were not primarily pitchers, if they were not currently participating in competitive play, or if they did not feel that they could pitch with 100% effort. All participants completed an intake form that recorded age, injury history, and current injuries that involve the throwing arm. Several body measurements were collected from each pitcher, including height, weight, and body mass index (BMI). Throwing arm measurements, including total arm length, upper arm length, forearm length, and elbow circumference, were obtained with the arm in neutral rotation. Total arm length was determined by measuring the distance from the lateral aspect of the acromion to the most distal aspect of the fifth digit. Upper arm length was defined as the distance from the acromion to the lateral epicondyle of the humerus, and forearm length was defined as the distance from the lateral epicondyle of the humerus to the styloid of the radius. Elbow circumference was recorded by measuring the distance around the medial and lateral epicondyles with the elbow in full extension. The device used in this study consisted of a small, gyroscopic sensor equipped with an accelerometer (Motus Global, Rockville Centre, NY, USA). This wearable technology records peak elbow torque (newton-meters), arm speed (rpm), arm slot (degrees), and shoulder rotation (degrees). This device has been previously validated using high-speed motion analysis1 and proven to be reliable for throwers at various levels of competitive play.18,20 Per manufacturer instructions, the device was secured and positioned 1.5 inches distal to the medial epicondyle using a compression athletic sleeve. Pitchers were allowed to participate in warm-ups prior to the recorded pitching session (including stretching, jogging, and practice throws) and were not given any limitations on practice pitch
Descriptive statistics for characteristics of pitchers were calculated and presented as mean, standard deviation, and range. Linear mixed models were used to evaluate the association of pitch type with each pitch parameter, adjusting for pitcher demographics. The model included the intercept as random effect for individual subjects, pitch type as a repeated and fixed effect variable, and pitcher demographic variables as fixed covariates. Univariate analysis was first performed, and any variable with a P value less than .05 in the univariate analysis was considered to enter the multivariate model. The estimated least squares mean and standard error for categorical variables and the coefficient (b) for continuous variables were presented for those variables retained in the final model. The correlation between pitch velocity and elbow torque was quantified using Pearson correlation coefficient. Device precision was calculated by comparing the number of outlier measurements for elbow torque (defined as pitches more than 1.5 times the interquartile range, either above the third quartile or below the first quartile) to total pitches thrown for each pitch type. All analyses were performed using SAS (v 9.4; SAS Institute Inc, Cary, NC, USA).
Results A total of 18 professional baseball pitchers were evaluated for participation in this study. Six pitchers were excluded because of sidearm pitching mechanics, which impeded accurate data collection with the device. Thus, 12 pitchers were included for data analysis. The average age of the pitchers was 23.4 years (range 21-25 years), and the average height was 187.7 cm (range 175.3-200.7 cm). Nine of the pitchers were right-hand dominant (75%) and 3 were left-hand dominant (25%). Further data regarding pitcher demographic characteristics are described in Table I. No adverse events were experienced during the pitching sessions. All participants were able to securely and comfortably fit the sleeve and sensor directly onto the throwing arm.
Predictors of elbow torque among pitchers Table I
Pitcher demographic characteristics (N ¼ 12) Mean (SD)
Upper arm length, cm Forearm length, cm Total arm length, cm Elbow joint circumference, cm Height, cm Weight, kg BMI
34.4 27.4 77.9 30.2
(2.3) (2.5) (3.1) (1.2)
187.7 (6.1) 91.6 (8.4) 26.0 (2.2)
Range (minimum-maximum) 31.0-39.0 21.0-30.0 73.0-83.5 28.0-32.5 175.3-200.7 74.8-108.9 21.2-28.8
BMI, body mass index; SD, standard error.
The sleeve remained positioned correctly with each pitch type thrown (FB, CB, and CU). Under these conditions, the device was 89.5% precise in measuring elbow torque for FB, 100% precise for CB, and 91.7% for CU. On average, FBs produced the greatest torque on the medial elbow (54.3 7.0 Nm; Table II). In comparison, CBs produced 4% less torque on the medial elbow (54.3 vs. 52.1 Nm, P ¼ .001). There was no significant difference in medial elbow torque between FBs and CUs (54.3 vs. 53.4 Nm, P ¼ .112). Demographic and biomechanical factors that best predicted change in medial elbow torque included pitch type and BMI (Table III). Increased BMI was predictive for decreased medial elbow torque when controlled by pitch type (b ¼ –1.83, P ¼ .035). CB and CU were also found to independently predict lower medial elbow torque in the univariate analysis. However, a subsequent multivariate analysis found that CU did not significantly predict medial elbow torque (Table IV). The 3 pitch types were also evaluated to determine differences in ball velocity, arm slot, arm speed, and shoulder rotation (Table II). The mean arm slot in CBs was significantly greater than that for CUs (49.7 vs. 43.8 , P < .0001), and the mean arm slot in FBs was significantly greater than that for CUs (48.2 vs. 43.7 , P ¼ .001). There was no difference in arm slot between FBs and CBs (P ¼ .193). The average velocity was significantly higher in FBs (85.2 mph) when compared to CUs (77.9 mph, P < .0001) and CBs (73.1 mph, P < .0001), and the average velocity in CUs was significantly higher than the average velocity in CBs (P < .0001). There was no significant correlation between ball velocity and medial elbow torque, irrespective of pitch type (r ¼ 0.30, P ¼ .69).
Discussion Our study found that FBs produce the greatest amount of torque on the medial elbow when compared to CBs or CUs in professional baseball pitchers. We also found that BMI was the only demographic factor predictive of increased elbow torque.
3 The primary finding of this study is that FBs cause greater medial elbow stress than CBs in professional baseball players. This is consistent with previous studies that have evaluated medial elbow stress at other levels of competitive play. A study by Makhni et al18 compared elbow stress in high school and collegiate athletes using the same sensor and methodology and found the FB to produce greater stress when compared to the CB and CU. At this level of competition, the average torque for FB was 45.6 Nm and for CB it was 43.8 Nm (compared to 54.3 and 52.1 Nm, respectively, in our study). Okoroha et al20 performed a similar study in the youth and adolescent pitching population and again found the FB (47.3 Nm) to produce greater elbow torque than the CB (45.0 Nm) and CU (44.2 Nm). It is important to note that the differences in torque among pitch types, although statistically significant in all of these studies, is relatively small; because there is no established minimum clinically important difference for elbow torque, the clinical impact of throwing relatively more FBs than CUs is unclear in regard to elbow injury risk. Our finding that the FB, not the CB, places the greatest torque on the medial elbow is consistent with prior highspeed motion capture studies. Nissen et al19 used 3-dimensional ball marker analysis to assess the elbow valgus moment in 35 adolescent pitchers and found the FB to be more stressful than the CB (59.6 vs. 54.1 Nm; P < .001). This finding has since been corroborated at other levels of competition, including professional baseball pitchers, using gold standard high-speed motion analysis.12 In fact, a systematic review of biomechanical and EMG pitching studies found no evidence identifying CB as the most stressful pitch on the elbow.13 This laboratory finding is reflected by clinical evidence as well; most notably, a 10-year prospective study of youth baseball players found no evidence linking early or frequent use of the CB to elbow injury risk.11 Our study found that, after controlling for pitch type, BMI was the only independent demographic predictor of medial elbow torque, with larger BMI predicting decreased medial elbow torque. This is consistent with previous findings that BMI20 and weight18 have a protective effect for youth, high school, and collegiate pitchers. It is not clear why increased BMI is protective against medial elbow torque. One hypothesis is that a larger BMI correlates with greater dynamic stabilization at the elbow and protects the medial elbow from excessive forces. Unlike previous studies, however, our study found that increasing elbow circumference (a larger area for load distribution) did not independently predict lower elbow torque at this elite level of competition. There were significant differences in ball velocity among all 3 pitch types, with the FB exhibiting the fastest velocity and the CB exhibiting the slowest. Several studies have evaluated the effect of ball velocity on medial elbow torque and found conflicting results. A study by Hurd et al
4
V.A. Lizzio et al. Table II
Differences in pitch biomechanics among FB, CB, and CU Least squares mean (SE) FB : CB
Elbow torque, Nm 54.3 (2.1) : Arm slot, degrees 48.2 (2.4) : Arm speed, rpm 916.2 (17.8) : Shoulder rotation, 148 (2.7) : degrees Ball velocity, mph 85.2 (0.6) :
52.1 (2.2) 49.7 (2.4) 905.5 (17.2) 146.9 (2.6) 73.1 (0.8)
P value
.001 54.3 (2.1) .193 48.2 (2.4) .191 916.2 (17.8) .265 148 (2.7) <.0001
P value
FB : CU : : : :
53.4 (2.1) 43.8 (2.4) 914.2 (17.3) 146.4 (2.7)
.112 53.4 (2.1) .001 43.8 (2.4) .807 914.2 (17.3) .165 146.4 (2.7) <.0001
85.2 (0.6) : 77.9 (0.7)
CU : CB : : : :
P value
52.1 (2.2) .084 49.7 (2.4) <.0001 905.5 (17.2) .229 146.9 (2.6) .629
77.9 (0.7) : 73.1 (0.8)
<.0001
FB, fastball; CB, curveball; CU, changeup; SE, standard error. Bold values indicate P < .05.
Table III Independent predictors of medial elbow torque (univariate analysis) Upper arm length Forearm length Total arm length Elbow circumference Height Weight BMI Pitch type Fastball Curveball Changeup
Beta estimate
P value
0.79 0.19 0.97 –2.14 19.99 –0.34 –1.83
.411 .838 .145 .219 .592 .174 .035
Reference –2.19 –0.93
.005
BMI, body mass index. Beta estimate values denote the change in torque for every 1-unit increase in the independent variable. Bold values indicate P < .05.
used 3-dimensional motion analysis to evaluate 26 high school pitchers and found a strong association between peak pitch velocity and medial elbow adduction moment.15 However, a study by Post et al used similar technology to analyze 67 collegiate baseball pitchers and found no significant correlation between pitch velocity and elbow valgus stress.24 The correlation between velocity and elbow torque is reinforced by recent biomechanical studies using wearable technology.18,20 Interestingly, a study that compared the pitching mechanics of youth pitchers who developed elbow injuries against those who did not found that the average FB velocity was 6% higher for injured pitchers, providing clinical evidence that increased pitch velocity is a risk factor for elbow injury. The reliability of the wearable technology used in this population of professional baseball pitchers was slightly lower than what was previously reported for youth, high school, and collegiate pitchers.18,20 Unfortunately, this new electronic technology does not reliably detect measurements for the sidearm or submarine throwing motions. However, after excluding sidearm pitchers from analysis, the overall precision rate of the device in measuring elbow torque remained greater than 90%. This high reliability, along with
Table IV
Multivariate model for medial elbow torque
BMI Pitch type Fastball Curveball Changeup
Beta estimate
Standard error
P value
–1.83
0.86
.035
Reference –2.19 –0.93
d 0.66 0.59
d .001 .114
BMI, body mass index. Beta estimate values denote the change in torque for every 1-unit increase in the independent variable. Bold values indicate P < .05.
the validation of the sensor against the high-speed motion analysis (the current gold standard of biomechanical evaluation),1 demonstrates that wearable technology can be reliably used at all levels of competitive play and has practical implications for future methodology and analysis in the field of pitching biomechanics. Most notably, researchers can now bypass the use of high-speed motion analysis, which is not only expensive and cumbersome but also requires significantly more attachments to the pitcher that can interfere with native pitching mechanics. For example, a recent study by Dowling et al5 illustrated the practical use of wearable technology by quantitatively tracking medial elbow stress for various throws of an interval throwing program, a practice that is commonly used for preventing injuries or progressively increasing loads after injury.
Limitations This study has important limitations. The sensor used in this study, similar to 3-dimensional motion analysis, does not directly measure the force placed on the ulnar collateral ligament. For this reason, it is impossible to state with certainty that the ulnar collateral ligament is receiving the forces measured by the wearable technology. However, traditional studies assessing medial elbow torque during the throwing motion also rely on indirect measures of elbow torque, such as with high-speed motion analysis.12,15,19,24 Second, this study was done in a controlled, practice setting and not in a competitive game, where pitchers may demonstrate altered
Predictors of elbow torque among pitchers pitching mechanics in the presence of live batters, fatigue, stress, and weather conditions.
Conclusion This study found that FBs produce greater medial elbow torque than CBs in professional baseball players, and that increased BMI was an independent predictor of decreased medial elbow torque.
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
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