Predictors of throwing velocity in youth and adolescent

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Predictors of throwing velocity in youth and adolescent

Transcript Of Predictors of throwing velocity in youth and adolescent

J Shoulder Elbow Surg (2015) -, 1-7

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Predictors of throwing velocity in youth and

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adolescent pitchers

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15 Q2 Terrance Sgroi, DPT, MTCa, Peter N. Chalmers, MDb,*, Andrew J. Riff, MDb,

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16 Matthew Lesniak, DPTa, Eli T. Sayegh, BSc, Markus A. Wimmer, PhDb,

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Nikhil N. Verma, MDb, Brian J. Cole, MD, MBAb, Anthony A. Romeo, MDb

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20 Q1 aAccelerated Rehabilitation Centers Ltd, Chicago, IL, USA

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bDepartment of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL, USA

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cCollege of Physicians and Surgeons, Columbia University, New York, NY, USA

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Background: Shoulder and elbow injuries are a common cause of pain, dysfunction, and inability to play

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in overhead throwers. Pitch velocity plays an integral part in the etiology of these injuries; however, the

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demographic and biomechanical correlates with throwing velocity remain poorly understood. We hypoth-

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esized that pitchers with higher velocity would have shared demographic and kinematic characteristics.

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Methods: Normal preseason youth and adolescent pitchers underwent dual-orthogonal high-speed video

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analysis while pitch velocity was collected with a radar gun. Demographic and pitching history data

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were also collected. Kinematic data and observational mechanics were recorded. Multivariate regression

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analysis was performed.

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Results: A total of 420 pitchers were included, with a mean pitching velocity of 64 Æ 10 mph. After multi-

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and stride length (P < .001; R2 ¼ 0.016); in combination, these 4 variables explained 78% of the variance

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in pitch velocity. Each year of age was associated with a mean 1.5 mph increase in velocity; each inch in

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height, with 1.2 mph; separation of the hips and shoulders, with 2.6 mph; and a 10% increase in stride

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length, with 1.9 mph.

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Conclusion: Pitch velocity is most strongly correlated with age, height, separation of the hips and shoul-

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ders, and stride length.

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Level of evidence: Basic Science Study, Kinesiology.

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Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees.

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Keywords: Baseball; injury prevention; pitching; overhand throwing; motion analysis; ulnar collateral

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ligament tear; superior labral anterior-posterior tear

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This study was approved by the Institutional Review Board of Rush

Overhead throwing places substantial forces and torques 103

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University Medical Center: Protocol No. 13090101, Expedited Review

on the shoulder and elbow, with forces regularly exceeding 104

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Initial Approval Notification.

390 N and torques regularly exceeding 1000 Nm in pro- 105

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*Reprint requests: Peter N. Chalmers, MD, Department of Orthopaedic

fessional pitchers.13 These forces have been implicated in 106

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Surgery, Rush University Medical Center, 1611 W Harrison St, Chicago, IL 60612, USA.

the pathogenesis of shoulder and elbow injuries,5 which are 107

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E-mail address: [email protected] (P.N. Chalmers).

common in baseball pitchers.24,25 For example, superior 108

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1058-2746/$ - see front matter Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees.

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http://dx.doi.org/10.1016/j.jse.2015.02.015

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111 labral anterior-posterior tears are a common cause of

completeness with participants. A standardized physical exami-

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112 shoulder discomfort in pitchers and remain an unsolved

nation was performed. Passive glenohumeral rotation was

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113 problem, with rates of return to a preinjury level of play of

measured by a goniometer with the subject supine and the scapula

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114 22% to 60%.8,15,19,22

stabilized at neutral shoulder flexion, 90 shoulder abduction, and

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The neuromuscular and biomechanical factors that

90 elbow flexion. Total arc of motion, glenohumeral internal

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116 correlate with injury during overhead pitching have been

rotation deficit, and glenohumeral external rotation excess were

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117 previously studied,24,25,28 and velocity has been identified

then calculated from these measurements. These measurements

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118 as a primary factor.6,28 However, the demographic and ki- werAe lpl erfosurmbjeedctsin boththenuppuenr deexrtwreemntitiesv. ideo motion anal- 173

119 nematic factors that correlate with velocity remain only

ysis.3,7,16,18,24,25,29-31,33,36-39 With use of high-definition orthog-

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120 partially understood. Multiple prior kinematic and electro-

onal video cameras from the frontal and lateral views, subjects

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121 myographic analyses have been performed examining

were filmed at 210 Hz while pitching from a regulation practice

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122 normal youth, collegiate, and professional

mound appropriate for the subject’s level of play. Throwing ve-

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123 pitchers.1,2,6,10,12-14,17,21,32,36-39 These studies have focused

locity was measured with a radar gun (JUGS Sports, Tualatin, OR,

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124 on correlations between kinematic and kinetic fac-

USA), which per the manufacturer has an accuracy of Æ0.5 mph.

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125 tors.1,2,10,13,14,32,36-39 Very few studies have identified ki-

Filming took place after a full warm-up and once subjects felt

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126 nematic and demographic correlates with velocity. Those

ready to pitch at 100% velocity. All subjects pitched fastballs from

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127 studies that have been performed were conducted on small

the wind-up position over a regulation distance for their age at a

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128 groups of pitchers and did not incorporate demographic

strike zone target appropriately positioned and sized for their age.

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129 factors, which limits their generalizability.4,11,14,26,27,34,35,40 Fpiotrcheear’cshbepsittcehfefro,rtthweassirnegcolerdepditcfhor manoasltysriesp. resentative of the 184

130 A better understanding of the demographic and kinematic

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131 factors that correlate with velocity could provide therapists Data analysis

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132 and pitching coaches with areas on which to focus in

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133 training and pitcher development.

A standardized protocol was used to extract kinematic data from

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Our overarching goal was to perform a demographic and

video footage using commercial software (Dartfish Inc., Alphar-

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135 biomechanical analysis of the correlates with velocity in

etta, GA, USA). Only those kinematic variables shown previously

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136 overhead youth and adolescent pitchers. Our primary aim

to correlate with kinetic variables, as identified a priori, were

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137 with this study was to determine the demographic and

recorded (Table I). Observational mechanics were recorded once

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138 biomechanical factors that predict throwing velocity. We

for each pitch, with 2 study authors performing the measurements.

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139 hypothesized that pitchers with higher velocity would have

These were assigned a binary yes vs. no as previously described.9

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140 shared demographic and kinematic characteristics.

These included whether the subject (1) led with the hips, (2) had

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the hand on top of the ball during the stride phase, (3) had the arm

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in the throwing position at front foot contact, (4) had closed

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143 Methods

shoulders at the hand-set position, (5) had a closed foot orientation

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at front foot contact, (6) had separation of rotation in the hips and

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shoulders, and (7) was in the fielding position at follow-through.9

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145 This is a single-episode cross-sectional study. As many youth and

Separation of rotation in the hips and shoulders was defined as a

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146 adolescent overhand baseball pitchers as possible within our

binary yes in those pitchers in whom, during the cocking phase, a

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147 geographic area were recruited, and no a priori power analysis was

period could be identified during which the pelvis rotated to face

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148 cuonnddeurwcteendt. aAslltasnudbajredcitzsewd eervealcuuartrieonnt.lyExinclpurseiosenascorintetrriaaininincgludanedd home plate while the shoulders continued to face third base (for a 203

149 age <9 years; sidearm or ‘‘submarine’’ style pitching motion, as

right-handed pitcher). Pitchers in whom no such period could be

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150 the kinematic data obtained were thought to be incomparable to

identified were recorded as having a binary no for separation of

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151 the rest of the cohort; those who were not planning to pitch for

rotation of the hips and shoulders. All analyses were performed in

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152 their team that year; and those pitchers who did not think they

Excel X (Microsoft, Redmond, WA, USA) and SPSS 21 (IBM

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153 would be able to throw because of excess discomfort at the time of

Inc., Armonk, NY, USA). An independent observer who was not

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154 the evaluation. Pitchers who thought they were able to throw and

aware of the study hypothesis entered all data. Continuous data

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155 who had been throwing in practice were included even if they had

normality was evaluated with the Kolmogorov-Smirnov test. Ve-

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156 a history of injury or current discomfort within their arm. Par-

locity was compared between discrete groups by Student t test or Mann-Whitney U test as appropriate. Velocity was correlated with

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157 ticipants were unaware of the study hypothesis. In all cases, the

continuous variables by Pearson correlation coefficients. Because

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158 dominant extremity was measured.

multiple comparisons were performed before regression, P values

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159 160 Data collection

underwent Bonferroni correction, and values <.00147 were

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considered significant. Those variables that significantly corre-

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lated with velocity or those variables in which there was a sig-

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162 All pitchers completed a demographic survey, with the assistance

nificant difference in velocity between groups were then entered

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163 of their parents when possible. Data collected included age,

into a multivariate stepwise regression model to determine the

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164 height, and weight. Height and weight were used to calculate body

most important correlates. Within this model, P values < .05 were

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165 mass index (BMI). Surveys were administered in paper format in a

considered significant. From this model, correlation coefficients
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standardized fashion by 2 study authors and were reviewed for

and R values, as an estimation of percentage of variance in injury

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Velocity predictors

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Table I Demographic and kinematic correlates with throw velocity in miles per hour

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Type

Variable

Univariate analysis

Multivariate analysis

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Correlation P

R2

P

Coeff. SE

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Demographic

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Age Height

0.816 0.792

<.001 0.658 <.001 1.47 0.139 280 <.001 0.076 <.001 1.191 0.227 281

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Weight

0.732

<.001

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BMI

0.495

<.001 0.003

.024 À0.139 0.058 283

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Physical examination

ER-Dom

0.204

<.001 0.004

.006 0.05 0.022 284

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233 Wind-up

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Kinematics at front

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foot contact

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IR-Dom Arc-Dom GIRD GERE Max. knee height (% Ht) Stride length (% Ht) Elbow flexion Knee flexion Shoulder abduction

0.003 0.183 0.069 0.013 0.287 0.438 À0.084 0.318 0.07

.949

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<.001

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.166

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.791 <.001

0.004

288 .005 0.089 0.031 289

<.001 0.016 <.001 0.187 0.036

.09

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<.001 0.006

.001 0.083 0.022 291

.156

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Foot angle

À0.196

<.001 0.004

.003 0.036 0.012 293

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Kinematics at maximum Max. shoulder ER

0.132

.008

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shoulder ER

Max. shoulder abduction

0.117

.017

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Lateral trunk tilt

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Kinematics at ball release Elbow flexion

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Forward trunk tilt

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Knee flexion

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Lateral trunk tilt

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Observed mechanics

Leads with hips

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Hand on top of ball

0.152

.002

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À0.107

.03

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0.171

.001 0.002

.04

0.062 0.03

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0.07

.16

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À0.086

.082

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0.266

<.001

0.191

<.001

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NA

.139

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NA

.002

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Arm in throwing position at front

NA

.091

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foot contact

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Closed shoulders at hand separation NA

.001

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Foot closed

NA

.03

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Hip and shoulder separation

NA

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0.027 <.001 2.621 0.511 308

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Fielding position at follow-through NA

.411

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BMI, body mass index; ER, glenohumeral external rotation; Dom, dominant extremity; IR, glenohumeral internal rotation; Arc, glenohumeral rotational

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arc; GIRD, glenohumeral internal rotation deficit; GERE, glenohumeral external rotation excess; Max, maximum; % Ht, values expressed as a percentage of

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257 sFuobr juenctivhaeriiagthet;aCnoaelyffs,esc,oebfeficcaiuesnet mofucltoiprrleelactoiomnp;aSriEs,osntsanwdearredmerardoer,; NBAon, fneorrtoanpipcloicrarebcleti.on was performed and P values < .00147 were considered sig- 312

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nificant. For multivariate analyses, only those variables found to be significant in univariate analyses were included, and thus the traditional P value of

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.05 was used. P values identified as significant are marked in bold. R2 values > 0.01 are also marked in bold as these variables explained >1% of the

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variance in velocity.

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status explained by each variable, were determined. Only those

145.4 Æ 39.2 pounds, and mean BMI of 22.0 Æ 3.9. Mean 318

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variables with R2 values > 0.01 are discussed.

pitch velocity for the cohort was 64 Æ 10 mph.

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On univariate correlation analyses, pitch velocity signif- 320

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icantly correlated with the subject’s age, height, weight, 321

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BMI, glenohumeral external rotation in the dominant 322

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extremity, glenohumeral rotational arc in the dominant ex- 323

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Of the 429 pitchers recruited, 9 were excluded because they tremity, glenohumeral external rotation in the nondominant 324

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were no longer planning to pitch (3), threw with a sidearm extremity, and glenohumeral rotation arc in the nondominant 325

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or submarine style (2), had too much pain to pitch (1), or extremity (P < .001 in all cases; Table I). On univariate an- 326

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did not complete the demographic survey (3). A total of alyses of the kinematic analyses, pitch velocity significantly 327

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420 subjects were included for a 98% inclusion rate. Our correlated with 7 of the 15 measured variables: maximal knee 328

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cohort had a mean Æ standard deviation age of 14.7 Æ 2.6 height during the wind-up as a percentage of subject height, 329

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years, mean height of 67.5 Æ 5.3 inches, mean weight of stride length as a percentage of subject height at front foot 330

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print & web 4C=FPO

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344 Figure 1 Pitcher age significantly correlates with pitch velocity

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345 (P < .001; multivariate R2 ¼ 0.658). To simplify, mean velocity

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346 for each year of age is shown.

Figure 3 Clinical photograph demonstrating separation of

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rotation within the hips and shoulders; while the pelvis has rotated

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to face home plate (arrow), the shoulders still face third base. This

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observed mechanical factor was significantly correlated with pitch
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velocity on multivariate analysis (R ¼ 0.027; P < .001).

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print & web 4C=FPO

361 Figure 2 Pitcher height significantly correlates with pitch ve-

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362 locity (P < .001; multivariate R2 ¼ 0.076). To simplify, the full

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363 range of heights was divided into equally sized segments, and

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364 mean velocity for each of these groups is displayed.

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367 contact, knee flexion at front foot contact, foot angle at front

Figure 4 Clinical photograph demonstrating the measurement

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368 foot contact, forward trunk tilt at ball release, lead hip flexion

of stride length at the moment of front foot contact, which was

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369 at ball release, and lateral trunk tilt at ball release (P <.001 in

then normalized to the subject’s height. On multivariate analyses,

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370 all cases; Table I). Among the observed mechanics, subjects

stride length was significantly correlated with pitch velocity
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371 with a closed shoulder position at front foot strike had (P < .001; multivariate R ¼ 0.016).

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372 significantly higher velocity than those with an open shoulder

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373 position (P <.001; Table I). Those subjects with separation of pitch velocity. In multivariate analyses, each year of age was

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374 the hips and shoulders had significantly higher pitch velocity associated with a 1.5 Æ 0.1 mph increase in velocity (Fig. 1).

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375 than those without separation of the hips and shoulders Each inch in height was associated with a 1.2 Æ 0.2 mph

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376 (P < .001; Table I).

increase in velocity (Fig. 2). Separation of rotation within the

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377 On multivariate regression analysis, those variables with hips and shoulders was associated with a 2.6 Æ 0.5 mph in-

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378 R2 values > 0.01 (i.e., those variables that explained >1% of crease in velocity. Each increase in stride length by 10% of

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379 the variance in pitch velocity) included age (Fig. 1), height the subject’s height was associated with a 1.9 Æ 0.4 mph

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380 (Fig. 2), hip and shoulder separation (Fig. 3), and stride increase in velocity.

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381 length as a percentage of the patient’s height (P < .001 in all

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382 cases; Table I, Fig. 4). In combination, these 4 variables

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383 explained 78% of the variance in pitch velocity within our Discussion

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384 group; in total, all 11 variables with significant correlations

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385 with velocity on multivariate analysis explained 81% of the Shoulder and elbow injuries are common among baseball

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variance. Age alone accounted for 66% of the variance in pitchers,24,25 and operative treatment of these injuries does

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not predictably return players to painless pitching with

Stride length may play a similar role. Each increase in 496

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preinjury velocity and control.8,15,19,22 Whereas multiple stride length by 10% of the subject’s height was associated 497

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prior kinematic analyses have been performed to under- with a 1.9 Æ 0.4 mph increase in velocity. Whereas multiple 498

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stand the kinematic correlates with joint loads in kinematic factors, such as elbow flexion angle at various 499

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pitchers,1,2,6,10,12-14,17,21,32,36-39 fewer have analyzed cor-

points within the pitch and shoulder abduction angle within 500

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relates with pitch velocity and none have incorporated de- various points within the pitch, have been associated with 501

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mographic data.4,11,14,26,27,34,35,40 Our overarching goal

increased elbow valgus torque and shoulder proximal 502

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with this project was to perform a demographic and force,2,32,36-39 no previous studies have associated stride 503

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biomechanical analysis of those factors that correlate with length with increased stress on the arm. However, stride 504

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increased velocity in youth and adolescent pitchers using length is associated with increased velocity. As a result, 505

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video motion analysis.

pitching coaches could focus on stride length to improve a 506

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The 4 factors independently associated with an increase in pitcher’s velocity.

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velocity on multivariate regression analysis were age, height,

Several previous studies have been conducted to corre- 508

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hip and shoulder separation, and stride length as a percentage late factors identified in pitching motion analysis with pitch 509

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of the patient’s height. In combination, these factors velocity. Other studies performing similar analyses have 510

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explained 78% of pitch velocity variance. The covariance of correlated velocity with the kinematic variables shoulder 511

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age and pitch velocity is likely due to multiple factors. Older

external rotation,11,34,40 shoulder abduction,11,34 knee 512

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pitchers are more likely to have learned proper pitching flexion,34 trunk tilt,34 elbow flexion,34 trunk-pelvis separa- 513

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mechanics and are more likely to have the muscle develop- tion,26 pelvis orientation at maximal shoulder external 514

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ment to allow higher velocity pitching. After correction for rotation,35 and stride length.4 Several of these variables 515

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the remaining variables, each year of age was associated with were measured by our study and did not significantly 516

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a 1.5 Æ 0.1 mph increase in velocity.

correlate with pitch velocity. Multiple potential explana- 517

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The correlation between the pitcher’s height and pitch tions exist for the differences between our results and those 518

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velocity is likely due to the longer lever arm this allows

of the previous studies,4,11,14,26,27,34,35,40 including differ- 519

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subjects to use to transfer force onto the ball. Each inch in ences in the underlying population of patients (i.e., the 520

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height was associated with a 1.2 Æ 0.2 mph increase in evaluation of youth and adolescent pitchers in this study, 521

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velocity. Previous biomechanical analyses have normalized whereas other studies have largely analyzed elite collegiate 522

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force and torque for subject height, as taller subjects are and professional pitchers), differences in the methods of 523

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known to be able to exert more force and torque through the data collection (i.e., the use of video motion analysis 524

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upper extremity because of the longer lever arm.1,9 Sub- instead of a markered motion analysis), differences in 525

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sequent kinetic analyses of the pitching motion should sample size (i.e., the use of 420 pitchers instead of the 526

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normalize for subject height.

much smaller sample sizes of previous studies), and dif- 527

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Two kinematic factors correlated with pitch velocity: hip ferences in data analysis (i.e., the analysis of 1 pitch per 528

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and shoulder separation and stride length. In combination, subject instead of multiple pitches per subject as indepen- 529

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these 2 factors explain 4.3% of the variance in pitch ve- dent variables). One variable identified in our study and 530

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locity, suggesting that a pitcher with a short stride length also identified in multiple prior studies is proper timing of 531

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and without hip and shoulder separation would be able to pelvic and trunk rotation, allowing optimal summation of 532

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add 4.3% to the velocity by improving these aspects of the

speed.14,26,35

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mechanics (i.e., a 70 mph pitcher could increase to 73

Our study has several limitations. One limitation is the 534

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mph). Adding separation of the hips and shoulders alone use of a video motion analysis system instead of a tradi- 535

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added an average 2.6 Æ 0.5 mph. The importance of hip tional markered motion analysis system. Video motion 536

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and shoulder separation to pitch velocity relates to the analysis has been widely used for this purpose and is a 537

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‘‘summation of speed’’ principle,1 that is, the greatest

well-accepted method.3,7,16,18,24,25,29-31,33,36-39 However, 538

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transfer of force occurs when the subsequent segment be- the authors have not performed any validation or reliability 539

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gins rotating at the moment at which the prior segment studies with this methodology and are not aware of any 540

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reaches maximal angular velocity; therefore, proximal within the literature. An additional limitation is the use of a 541

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trunk rotation ideally begins at the moment of maximal single-episode study design. As a result, whereas the fac- 542

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angular velocity of the pelvis, which explains the critical tors identified in this study correlate with velocity, alter- 543

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importance of the core musculature for high-velocity ation of these factors would not necessarily improve 544

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pitching. This factor has been previously associated with velocity. Correlation does not imply causation. These fac- 545

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improved pitch efficiency (i.e., lower humeral rotational tors, in particular stride length and hip and shoulder sepa- 546

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torque and elbow valgus torque per velocity9) and thus ration, could be the result of increased velocity instead of 547

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could represent an avenue by which pitching coaches could the cause. In addition, many other unmeasured factors, such 548

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improve velocity by improving mechanics. This factor, as strength, could also influence velocity. Without a pro- 549

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dubbed the X-factor, has also been associated with spective longitudinal study to observe pitchers who expe- 550

increased club speed in golf.20,23

rience improvements in velocity, this limitation will remain.

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551 One additional limitation is the strong covariance of height

with arthroscopic fixation using a bioabsorbable tack. Arthroscopy

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552 and age. The multivariate regression model corrects for this

2006;22:136-42. http://dx.doi.org/10.1016/j.arthro.2005.11.002

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553 limitation, and although the whole model remains valid,

9. Davis JT, Limpisvasti O, Fluhme D, Mohr KJ, Yocum LA,

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Elattrache NS, et al. The effect of pitching biomechanics on the upper

554 interpretation of these factors as independent correlates can

extremity in youth and adolescent baseball pitchers. Am J Sports Med

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555 be more difficult.

2009;37:1484-91. http://dx.doi.org/10.1177/0363546509340226

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10. Dillman CJ, Fleisig GS, Andrews JR. Biomechanics of pitching with

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558 Conclusion
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emphasis upon shoulder kinematics. J Orthop Sports Phys Ther 1993;

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18:402-8.

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11. Escamilla R, Fleisig G, Barrentine S, Andrews J, Moorman C III.

Kinematic and kinetic comparisons between American and Korean

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560 Pitch velocity is most strongly correlated with age,

professional baseball pitchers. Sports Biomech 2002;1:213-28. http://

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561 height, separation of the hips and shoulders, and stride

dx.doi.org/10.1080/14763140208522798

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562 length. These factors have implications with regard to

12. Fleisig G, Chu Y, Weber A, Andrews JR. Variability in baseball pitching

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563 the etiology of injury in youth pitchers, the rehabilitation

biomechanics among various levels of competition. Sports Biomech

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2009;8:10-21. http://dx.doi.org/10.1080/14763140802629958

564 of these injuries, and the improvement in pitching

13. Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF. Kinetics of

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565 performance.

baseball pitching with implications about injury mechanisms. Am J

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Sports Med 1995;23:233-9.

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567 568
569 Acknowledgment

14. Fortenbaugh D, Fleisig GS, Andrews JR. Baseball pitching biome-

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chanics in relation to injury risk and performance. Sports Health 2009;

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1:314-20. http://dx.doi.org/10.1177/1941738109338546

15. Friel NA, Karas V, Slabaugh MA, Cole BJ. Outcomes of type II su-

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perior labrum, anterior to posterior (SLAP) repair: prospective eval-

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571 The authors wish to acknowledge Lisa Nold and the

uation at a minimum two-year follow-up. J Shoulder Elbow Surg

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572 athletic trainers at Accelerated Rehabilitation Centers

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