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Paper text:
nineteen of the subjects were collegiate athletes ( 16 baseball players , 3 non - throwing athletes ) .
prior to enrollment in the study , all participants were required to pass a throwing performance task ( supplementary note 17 ) in order to exclude poor throwers .
for all subjects , we collected weight , information on relevant injury / medical history , and basic anthropometric data ( height , segment lengths and circumferences , joint range of motion ) .
all subjects provided informed written consent in accordance with the harvard committee on the use of human subjects .
kinematic data were collected at 1000 hz using an eight - camera vicon t10s 3d infrared motion capture system ( vicon inc , centennial co , usa ) .
each subject had twenty - one passive reflective markers taped on the throwing arm and torso ( supplementary note 18 ) .
after the warm up period , subjects were tasked to throw a 144 g baseball at a 1m - radius target from 10 m away .
the subject then threw 8 - 10 normal pitches and 8 - 20 pitches using a donjoy shoulder stabilizer ( donjoy inc , vista , ca ) brace that restricts external rotational range of motion at the shoulder ( supplementary note 19 ) .
as a sham , data from an intermediate condition in which the brace was applied but not tightened were also collected ( supplementary note 8) .
ball release was timed using a synched flexiforce a201 force sensor ( tekscan inc , boston ma , usa ) collected at 1000 hz taped to the palmar side of the distal phalanx of the third digit and synched with a 30 hz canon vixia hv30 digital video camera ( canon inc , tokyo , japan ) . in order to filter
the kinematic data , a residual analysis of the entire throwing trial and the critical period during the humeral internal rotation motion was calculated in matlab ( version r2010b ) ( supplementary note 20 ) . a butterworth 2 order low - pass filter ( cutoff 25hz ) was applied and marker gaps up to 100 frames were interpolated using c - motion visual3d software ( v4 ) . for analysis , each motion was then subdivided into five standard phases of the throw : windup / stride , arm cocking , arm acceleration , arm deceleration , and follow - through .
joint euler angles were calculated and inverse dynamics analyses were performed using mass distribution data from dempster in visual3d .
joint angular velocities , moments , and power were calculated using each joint s instantaneous axis of rotation ( supplementary note 23 ) .
kinetic data were standardized to phase length , interpolated , and resampled using custom matlab code to yield comparable data across all trials and subjects ( supplementary note 21 ) .
individual subject means were compared across experimental conditions using repeated measures anova or manova where appropriate .
nineteen of the subjects were collegiate athletes ( 16 baseball players , 3 non - throwing athletes ) .
prior to enrollment in the study , all participants were required to pass a throwing performance task ( supplementary note 17 ) in order to exclude poor throwers .
for all subjects , we collected weight , information on relevant injury / medical history , and basic anthropometric data ( height , segment lengths and circumferences , joint range of motion ) .
all subjects provided informed written consent in accordance with the harvard committee on the use of human subjects .
kinematic data were collected at 1000 hz using an eight - camera vicon t10s 3d infrared motion capture system ( vicon inc , centennial co , usa ) .
each subject had twenty - one passive reflective markers taped on the throwing arm and torso ( supplementary note 18 ) .
after the warm up period , subjects were tasked to throw a 144 g baseball at a 1m - radius target from 10 m away .
the subject then threw 8 - 10 normal pitches and 8 - 20 pitches using a donjoy shoulder stabilizer ( donjoy inc , vista , ca ) brace that restricts external rotational range of motion at the shoulder ( supplementary note 19 ) .
as a sham , data from an intermediate condition in which the brace was applied but not tightened were also collected ( supplementary note 8) .
ball release was timed using a synched flexiforce a201 force sensor ( tekscan inc , boston ma , usa ) collected at 1000 hz taped to the palmar side of the distal phalanx of the third digit and synched with a 30 hz canon vixia hv30 digital video camera ( canon inc , tokyo , japan ) . in order to filter
the kinematic data , a residual analysis of the entire throwing trial and the critical period during the humeral internal rotation motion was calculated in matlab ( version r2010b ) ( supplementary note 20 ) . a butterworth 2 order low - pass filter ( cutoff 25hz ) was applied and marker gaps up to 100 frames were interpolated using c - motion visual3d software ( v4 ) . for analysis , each motion was then subdivided into five standard phases of the throw : windup / stride , arm cocking , arm acceleration , arm deceleration , and follow - through .
joint euler angles were calculated and inverse dynamics analyses were performed using mass distribution data from dempster in visual3d .
joint angular velocities , moments , and power were calculated using each joint s instantaneous axis of rotation ( supplementary note 23 ) .
kinetic data were standardized to phase length , interpolated , and resampled using custom matlab code to yield comparable data across all trials and subjects ( supplementary note 21 ) .
individual subject means were compared across experimental conditions using repeated measures anova or manova where appropriate .
although some primates , including chimpanzees , throw objects occasionally1,2 , only humans regularly throw projectiles with high speed and great accuracy . 
 darwin noted that humans unique throwing abilities , made possible when bipedalism emancipated the arms , enabled foragers to effectively hunt using projectiles3 . 
 however , there has been little consideration of the evolution of throwing in the years since darwin made his observations , in part because of a lack of evidence on when , how , and why hominins evolved the ability to generate high - speed throws4 - 8 . here , 
 we show using experimental studies of throwers that human throwing capabilities largely result from several derived anatomical features that enable elastic energy storage and release at the shoulder . 
 these features first appear together approximately two million years ago in the species homo erectus . given archaeological evidence that suggests hunting activity intensified around this time9 
 , we conclude that selection for throwing in order to hunt likely played an important role in the evolution of the human genus .