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1.1.
Foot position at stride foot contact
Fleisig, 1994
performed a kinematic analysis of the pitching technique of
72 baseballers and after consultation with pitching coaches
considered eight proposed mechanisms of 'improper mechanics'.
By accumulating this data, Fleisig was able to describe average
or normative values for each individual parameter. The pitches
of individuals were then compared to the accumulated means
for each of these parameters, and the kinetics calculated
to estimate variations associated with 'improper mechanics'
or deviations from these means. Of the originally considered
eight proposed mechanical faults, four were found to be associated
with increased kinetics at certain phases of the pitching
motion, including the positioning of the stride foot.
Fleisig, 1994
documented average stride foot placement to be 87% of body
height (measuring estimated centre of the stride ankle joint
back to the leading edge of the pitching rubber). This stride
was directed toward the plate within 10cm in either direction
in comparison to a line drawn from the centre of the trailing
ankle to the centre of the home plate. The stride foot was
found to be 'closed' or pointing toward the throwing arm side
at an angle of 15° ± 10° with reference to this line. (see
Figure 4 for an explanation of these terms).
Those pitchers who were found to deviate from these norms
toward open foot position and alignment showed increased kinetics
at the shoulder. For every extra centimeter the stride foot
lands toward the 'open' side, an extra 3.0N of maximum shoulder
anterior force was found during the arm cocking phase. Further,
if the stride leg was placed at an open foot angle, this too
increased the maximum shoulder anterior force during the cocking
phase at a rate of 2.1N per degree of open foot placement.
To place this data into some context, the maximum shoulder
anterior force found during the arm cocking phase was found
to be on average 350N, so if a pitcher were to place their
lead leg 10cm toward the open side and 10° further open, then
this would be associated with a 51N (or approximately 15%)
increase in shoulder anterior force during the arm cocking
phase. Interestingly, those pitchers who landed in a more
'closed' position (in terms of foot angle, and placement)
had no increase in stressful parameters demonstrated.
During the assessment of the injured throwing athlete, a routine
finding is reported shoulder pain during the arm cocking phase
of throwing (Andrews and Fleisig, 1998;
Curtis and Deshmukh, 2003;
Meister , 2000).
This can be associated with a positive Relocation Sign (Jobe,
et al., 1989),
and it has been suggested that this is indicative of subtle
anterior shoulder instability (Hamner et al., 2000).
Matsen amongst others believe that the primary restraints
to shoulder subluxation at extreme range of motion to be the
ligamentous structures (Matsen et al., 1991).
It would follow then that any increase in the amount of shoulder
anterior force during the arm cocking phase could be directly
associated with pathology at the ligamentous restraints such
as increasing anterior shoulder instability.
Montgomery
and Knudson, 2002
in an investigation of six professional baseball pitchers
found that increasing the stride length to 85-90% of their
body height to be associated with an increase in throwing
velocity in four of them. Contrary to some pitching instruction,
this was generally not associated with throwing the pitch
higher in the strike zone as only one of the pitchers showed
a weak trend (r = 0.54) towards doing so.
In a kinematic examination of 16 collegiate baseball pitchers
throwing a variety of pitch types (fastball, curveball, slider,
and changeup) Escamilla et al., 1998
found lead foot position to vary. This group found stride
length to be slightly lower than that reported by Fleisig,
1994
at 84% ± 5% for the fastball in comparison to 82% ± 4% for
the curveball. This is in distinction to the work of Elliot
et al. (1986)
who found no significant difference in their group of 8 International
level pitchers throwing fastball and curveball pitches (82%
± 2% and 81% ± 6% for the different pitches respectively).
Escamilla et al., 1998
also reported on the positioning of the lead foot angle for
each of the pitch types. They found that there were significant
differences during the fastball and curveball (0cm ± 10cm
versus -3cm ± 9cm); and the changeup and curveball pitches
(-3cm ± 9cm and -7cm ± 9cm). The position of the lead foot
was not significantly different for the slider (0cm ± 9cm).
Lead foot angle was not found to be statistically significantly
different for any of the trials at -8°±12°, -7°±11°, -14°±14°,
- 10°±11 for the fastball, changeup, curveball, and slider
respectively.
1.2.
Elbow flexion
Fleisig proposed that increased elbow flexion during the arm
cocking and acceleration phases would be associated with an
increase in kinetics, but his research did not bear out this
finding (Fleisig and Escamilla, 1996).
It would appear that this proposal is at least in part based
on the commonly held belief amongst pitching coaches that
"correct" mechanics are associated with maintaining
elbow flexion of less than 90° at the point of stride foot
contact (Figure 5). It
was indeed illuminating to then see the work of Werner who
analyzed the kinetics of forty professional pitchers during
Cactus League spring Training of 1998 (Werner et al., 2001;
2002).
Werner et al. (2001;
2002)
used three 120Hz cameras through at least 2 innings of pitching,
choosing the best fastball in terms of '…location, velocity,
and outcome' from this sample for analysis with an average
displayed ball velocity of 89 mph.
In one study Werner used shoulder joint distraction as a dependent
variable (Werner et al., 2001)
as it is proposed that longitudinal distraction of the glenohumeral
joint can be associated with pathology commonly seen in the
throwing athlete such as shoulder instability (Altchek and
Hobb,s 2001),
and traction injuries to the biceps anchor and superior labral
complex (Andrews et al., 1985;
Andrews et al., 1985).
Thirteen kinematic and kinetic variables were chosen as independent
variables for a step-wise regression analysis. A combination
of five of these parameters explained 72% of the variance
in shoulder distraction estimated during the throwing motion.
These parameters included elbow flexion at stride foot contact
and elbow flexion at ball release. This work infers that those
pitchers who have a more flexed elbow at the point of stride
foot contact and a more flexed elbow at the point of ball
release will have a reduction in the amount of peak longitudinal
distraction force at their shoulders during the throwing motion.
In a related study using similar materials and methods, Werner's
group (Werner et al., 2002)
performed a stepwise regression analysis with elbow valgus
as the dependent variable. Excessive elbow joint valgus force
during throwing is considered to be the primary cause of Valgus
Extension Overload (Andrews, 1985;
Andrews et al., 2001;
Cain et al., 2003;
Wilson et al., 1983)
- a spectrum of disorders including (but not limited to) attenuation
of the anterior band of the ulnar collateral ligament (UCL)
of the elbow, osteochondral damage to the postero medial olecranon
fossa, and osteochondral damage to the radio-capitellar joint.
Valgus Extension Overload is considered to be the most common
elbow injury suffered by skeletally mature throwing athletes
(Azar, 2003; Joyce et al., 1995; Pincivero et al., 1994). This study (Werner et al., 2002) found 4 independent variables were able to explain over
97% of the variance in elbow valgus, including elbow flexion
at the point of maximum valgus stress. Peak valgus stress
at the elbow occurs late in the cocking phase and very early
in the acceleration phase of throwing, and those who displayed
a greater amount of elbow flexion at this point in the throw
were associated with lower amounts of maximum elbow valgus
force during the throw (Werner et al., 2002).
Whilst it would appear then that the commonly held pitching
coach's maxim that the elbow should be flexed no more than
90° at the point of stride foot contact could bear re-examination,
this notion needs to be tempered in light of the findings
of Levin et al (Levin et al., 2004). This group investigated the amount of stress placed
at the UCL during valgus stress after progressive sectioning
of the posterior olecranon. Levin showed significantly more
strain occurred in the UCL at 90° than at 70° of elbow flexion
(Levin et al., 2004). The highest valgus stresses occur at late cocking and
early acceleration phases and perhaps assessment of elbow
flexion at this stage of the throw would be more appropriate.
In terms of pitching performance, one variable commonly sought
after is higher throwing velocity. Matsuo et al., 2001 examined 12 kinematic and 9 temporal parameters in a group
of 127 healthy college and professional pitchers (Matsuo et
al., 2001). These players had an average throwing velocity of 36.1
m·s-1 ± 1.9 m·s-1 for the group (80.75
± 4.2 mph). Matsuo et al. then compared the 12 kinematic and
9 temporal variables for the group who threw more than one
standard deviation greater than average (> 38.0 m·s-1,
>89 mph) with the group who threw less than one standard
deviation slower then the average (< 34.2 m·s-1,
<76.5 mph). One of the variables to show a statistically
significant difference between these two sub groups was the
timing of maximum elbow extension angular velocity during
the throw. Matsuo's group considered the throw from stride
foot contact until ball release, describing these two points
as 0% and 100% of the throwing cycle respectively. Intuitively,
one might expect the higher velocity group to display peak
elbow extension angular velocity at or very close to the point
of ball release. It was indeed surprising then to learn that
the high velocity group displayed the peak elbow extension
angular velocity to occur at 91.1% ± 1.9% of the throw duration,
whilst the slower throwing group displayed this event slightly
later at time = 93.0% ± 2.4% (Matsuo et al., 2001). Atwater, 1979 was amongst the first authors to propose a sequential
summation of kinetic links as being critical in the production
of velocity in the overhead thrower. She describes the sequential
nature of the acceleration of body segments moving from the
lower limbs through the trunk and then to the arm and hand.
This movement pattern typically shows each segment initially
lagging behind its preceding segment, and then accelerating
to even higher angular speeds whilst the preceding segment
lagged behind. This whip-like summation of angular velocities
requires extraordinarily precise timing, and the data of Matsuo
et al., 2001 would serve to underscore the delicacy of this balance.
The throwing motion has been modeled using a double pendulum
to estimate optimal conditions for throwing and striking (Alexander,
1991). Perhaps an alternate explanation for the seemingly counter-intuitive
finding of peak elbow extension velocity can be found in this
model. Whilst complex to describe mathematically, a double
pendulum can be constructed simply where two solid struts
(such as student's wooden rules) are connected at their end
and swung back and forth from one end (Cross, 2004). From this it can be appreciated that maximum linear
velocity of the distal end of the distal segment is not necessarily
associated with maximal angular velocity of the proximal segment.
Werner correlated elbow joint position and elbow kinetics
with an EMG analysis of the biceps brachii, triceps brachii,
and anconeus muscles in an investigation of seven healthy
college and minor league pitchers using a 2 camera 500 frames
per second analysis (Werner et al., 1993). The mean ball velocity for the subjects was 36.4 m·sec-1,
and the EMG data was captured using surface electrodes. Werner
showed a sequential activity of biceps followed by triceps
activity until the moment of maximal shoulder external rotation,
and thence activity in the anconeus muscle as the elbow continued
flexing during the first half of the acceleration phase (Werner
et al., 1993). Active elbow extension is thought to be principally
under the control of the triceps musculature, and secondarily
by the anconeus muscle (Basmajian and Griffin, 1972). The subsequent rapid elbow extension was not associated
with any appreciable increase in activity of either triceps
brachii or anconeus. The elbow flexion seen during the acceleration
phase was seen to be associated with a concurrent increase
in the amount of predicted elbow compressive force which peaked
at approximately 780N shortly before ball release (Werner
et al., 1993). The rapid elbow extension seen during the throwing motion
would therefore appear to be both a combination of active
elbow extension, and the mechanical conversion of angular
velocity of the more proximal segments (shoulder internal
rotation and horizontal adduction) into elbow extension.
In an investigation of the role of the triceps musculature
during throwing, Roberts reported on the preliminary work
of Dobbins who performed a radial nerve block (thereby rendering
the triceps brachii and wrist and finger extensors inactive)
and compared the kinematics of the throws performed prior
and subsequent (Roberts, 1971). Dobbins found that the timing of the onset of elbow
extension was unchanged after the radial nerve block, however
prior to extending the elbow 'collapsed' into a maximum elbow
flexion of 145° (from the pre-nerve block maximum of 90°).
On the sixth throwing trial after the nerve block was performed,
the subject was able to throw in excess of 80% of his original
velocity despite the absence of active triceps (and wrist
extensor) contribution. This work would suggest that part
of the role of the triceps musculature is to maintain elbow
flexion such that the moment of inertia of the rotating upper
arm is maximized (at 90° elbow flexion).
1.3.
Arm rotation
Investigations into the timing, magnitude, and duration of
arm rotation are shown to be related to performance and kinetics,
and are discussed below. It should be recalled that the amount
of arm rotation is usually being inferred from the positions
of skin markers on the ulna, humerus, and trunk. Commonly
this rotation (axial rotation of the humeral component in
comparison to the trunk) is termed "shoulder rotation",
however the components of this total arm rotation which occur
at the glenohumeral, scapulothoracic, acromioclavicular, and
sternoclavicular joints can only be guessed at. Accordingly,
for the purposes of this paper, this motion will be termed
"arm rotation".
1.3.1.
Early external rotation: In Fleisig's (1994) initial investigation he found the average amount of
arm rotation to be 53° ± 26° at the point of stride foot contact
(Figure 6). Those who
displayed an increase in the amount of arm external rotation
at stride foot contact also displayed increased kinetics at
the arm and elbow, and alterations in stride foot position.
An increase in the amount of arm rotation was shown to be
associated with increased shoulder anterior force during the
arm cocking phase at a rate of 1.3N/° of arm rotation. The
total shoulder anterior force during the arm cocking phase
was 350N, so an increase of say 40° would be associated with
an increase of 52N or almost 15%.
Increased
arm external rotation at stride foot contact was also shown
by Fleisig, 1994 to be associated with an increase in the amount of elbow
medial force at a rate of 0.7N/°. Elbow medial force averaged
a peak of 280N, so an increase of 40° of arm external rotation
at stride foot contact would be associated with 28N, or 10%
of the total medial elbow force. The passive restraints against
valgus stress at the medial elbow include the UCL, principally
its anterior band. During throwing, the load placed through
this structure is thought to approach its ultimate tensile
strength. Any further increases in the amount of valgus stress
through increased arm external rotation at stride foot contact
could place this structure at a heightened risk of tensile
failure.
Escamilla et al., 2002 evaluated kinetic, kinematic, and temporal values of 11
American and 8 Korean healthy professional pitchers during
trials of pitching a fastball including external rotation.
In this study, the Korean pitchers displayed reduced kinetics,
and approximately a 10% reduction in throwing velocity in
comparison to the American pitchers (37.1 ± 1.9 m·sec-1
vs. 34.9 ± 1.0 m·sec-1). In contrast to the findings
of Fleisig, 1994, one of the variables associated with reduced kinetics
at the shoulder and elbow was an increase in the amount of
arm external rotation displayed at lead foot contact.
1.3.2.
Late external rotation: A decreased amount of arm external
rotation at stride foot contact (beyond one standard deviation
from the group mean) was shown by Fleisig, 1994 to be associated with an increase in the maximum longitudinal
compressive force along the humerus during the cocking phase
at a rate of 1.5 N/°. The average maximum compressive force
along the humerus being 590N for the group, an increase of
40° then could be associated with an increase of 60N or over
10% of the total compressive force during the arm cocking
phase. It is thought that increases of longitudinal compression
during this phase could be associated with compression/rotation
injuries to the glenoid labrum, much in the manner of proposed
damage to the menisci of the knee during weight-bearing combined
with rotation.
A reduction in the amount of arm external rotation at stride
foot contact was associated with a reduction is stressful
kinetics at the elbow (Fleisig, 1994). It was shown that the elbow medial force (and varus
torque) was reduced at a rate of 0.8 N/° (0.2Nm varus torque)
(Fleisig, 1994). In our previous example of a 40° reduction in the amount
of arm external rotation at stride foot contact, this would
be associated with a reduction of 32N (over 10% of the total
valgus force).
1.3.3.
Total arm external rotation range: Very high figures -
up to 210° (Werner et al., 1993) are quoted for the total amount of arm external rotation
displayed during throwing (Figure
7). Feltner and Dapena, 1986, and Kreighbaum and Barthels, 1985 hypothesized that the arm external rotation displayed
during throwing with simultaneous EMG activity of the horizontal
adductors and internal rotators was due to the inertial lag
of the forearm as the proximal segments rotated toward the
contralateral (to the throwing arm) side. It is not surprising
then to learn of that there is no relation between the amount
of active external rotation range at the shoulder horizontal
abduction and adduction of the active arm external rotation
range and throwing skill or speed (Clements et al., 2001). Clinically, a more useful finding is the amount of passive
arm external rotation since it more closely reflects the nature
of the movement displayed in the throwing motion. Whilst many
authors (Baltaci et al., 2001; Bigliani et al., 1997; Brown et al., 1988; Crockett et al., 2002;
Ellenbecker et al., 2002;
Reagan et al., 2002)
have described a difference in the total range of external
and internal rotation in the dominant and non dominant arms
of high level baseball players, there are occasional exceptions
to this finding (Johnson, 1992).
The finding that increased range of external rotation is associated
with an increase in throwing speed was originally described
by Atwater, 1979
who investigated ranges of motion and throwing speed in a
group of varsity pitchers. Subsequently Wang et al., 1995
using 2 150Hz cameras examined fastball pitches of 3 pitchers
(2 college, 1 high school with an average release velocity
of 32.34 m·sec-1 ± 3.63 m·sec-1). This group showed a correlation
between the amount of maximum external rotation at the beginning
of the acceleration phase and ball release velocity, with
the Pearson r value measuring 0.86. This work was further
expanded in the investigation of Matsuo who found an increased
maximum displayed shoulder external rotation range (from 166.3°
± 9° to 179° ± 7.7°) to be associated with higher throwing
velocities in his group of 127 healthy college and professional
pitchers (Matsuo et al., 2001).
Baseball
players have regularly been shown to have both an increased
passive range of external rotation in their dominant arm,
and a reduction of passive range toward internal rotation
(Donatelli et al., 2000;
Ellenbecker et al., 2002).
It has been suggested that those in whom the lost range of
internal rotation exceeds their gained external rotation are
at a greater risk of subsequent shoulder labral injury (Burkhart
et al., 2003c)
and that remediation (Burkhart et al., 2003b)
and prevention (Burkhart et al., 2003b)
of this lost range of motion is curative and preventive of
these injuries.
During the investigation of Werner et al., 2001,
the amount of shoulder distraction at the point of maximum
external rotation was found to be proportional to the total
external rotation range displayed. Werner's group (2001)
investigated the total shoulder distractive force as a dependent
variable in their regression analysis as it was thought to
relate to the potential for pathology at the rotator cuff
and glenoid labrum (Werner et al., 2001).
Shoulder distractive forces ranging from 83% to 139% of body
weight (108% ± 16%) were found for the group of forty professional
pitchers playing in the Cactus League of 1998, which was in
line with other reported data (Feltner and Dapena, 1986;
Fleisig et al., 1995)
regarding the maximum distractive force at the shoulder during
throwing. Shoulder joint distraction during the follow-through
phase where the biceps is acting forcefully to decelerate
the extending elbow has been theoretically implicated as a
potential source of traction injury to the biceps anchor at
the superior glenoid labrum (Andrews et al., 1985).
More recently in a cadaveric study of tension on the proximal
long head of biceps at the glenoid labrum, arm external rotation
in abduction (in a simulated position of arm cocking) was
shown to be associated with markedly higher amounts of strain
in the proximal long head of biceps than in any of the other
simulated throwing positions (Pradhan et al., 2001).
In the examination of American and Korean pitchers by Escamilla
the Korean pitchers were shown to have a reduction in maximum
arm external rotational range of motion during arm cocking
(180 ± 10° vs. 165 ± 10°), and this was associated with a
reduced kinetics at the shoulder and elbow, and reduced ball
velocity (Escamilla et al., 2002).
When considering the total amount of arm external rotation,
and the contribution of the glenohumeral joint, the amount
of individual humeral torsion needs to be factored into the
equation. The degree of humeral torsion an individual displays
has been shown to be associated with the total range of external
rotation as well as the propensity for anterior dislocation
(Crockett et al., 2002;
Kronberg and Brostrom, 1990;
1991;
1995;
Kronberg et al., 1993;
1990;
Osbahr et al., 2002;
Reagan et al., 2002).
Pieper in a study of 51 male National Level Handball players
found a variation in the side to side values of humeral torsion
when measuring with longitudinal X-Ray analysis (Pieper, 1998).
Interestingly of his sample the 13 who were presently complaining
of shoulder pain had an average reduction of humeral torsion
of 5.4° on their dominant side, whilst the remaining 38 healthy
players had an average increase of 14.4° of humeral retrotorsion.
Similar conclusions were reached by Osbahr et al., 2002
who used longitudinal X-Ray to find a 10° increase in retroversion
of the dominant side humeral head of 19 male college baseball
pitchers. This figure concurs with the findings of Crockett
who used CT to investigate the humeral torsion and glenoid
version in 25 professional baseball pitchers and 25 non-throwing
controls (Crockett et al., 2002).
This group showed an average increase of 17° in the retrotorsion
of the dominant arm's humeral head in the pitchers that was
not found in the controls. This increased humeral retroversion
was found to be associated with an increase in humeral external
rotation when measured at 90° of abduction, and would clearly
influence the amount of arm rotation which is occurring at
the glenohumeral joint. This work suggests that the increased
arm external rotation and concomitant reduction in internal
rotation (which has often been ascribed to capsular and muscular
adaptive changes) may well be partly bony in origin, and a
requisite for healthy performance of the extreme range of
external rotation seen in throwing athletes.
1.4.
Horizontal abduction and adduction
1.4.1. Horizontal adduction: Published data show the maximum
horizontal adduction a pitcher displays to be in the order
of 14° ± 7° (Fleisig, 1994).
Pitching coaches will often see an excessive amount of arm
horizontal adduction as a mechanical fault, sometimes describing
this pattern as 'leading with the elbow'. Fleisig, 1994
found the maximum horizontal adduction range displayed to
be proportional to the maximum elbow medial force during arm
cocking phase at a rate of 2.4 N/°. Since the total amount
of elbow medial force during the arm cocking phase was 270N
in Fleisig's study, an increase of 7° horizontal adduction
would be associated with an 18N or 7% increase in this force.
1.4.2.
Horizontal abduction: Escamilla et al's (2002)
investigation of differences between a group of American and
Korean pitchers showed the higher velocity American pitchers
to have an increase in the amount of horizontal abduction
at stride foot contact (23 ± 12° vs. 14 ± 9°, Figure
8).
It
has been theorized that an increase in the amount of shoulder
horizontal abduction range during the arm cocking phase is
associated with a propensity for shoulder pathology. Jobe
deemed this to be 'hyperangulation' and thought that it would
be coupled with attenuation of the shoulder anterior capsular
structures, and therefore anterior shoulder instability (Jobe
and Pink, 1996).
These workers state that this is seen with a throwing pattern
of the hand not being "on top of the ball" as is
thought to be preferred by pitching coaches.
Burkhart's group (2003a)
believe that in the presence of a tight and thickened postero-inferior
glenohumeral capsule, horizontal abduction combined with external
rotation as is shown in the arm cocking phase will be associated
with a postero-superior translation of the humeral head relative
to the glenoid such that it no longer contacts the posterosuperior
glenoid labrum. These researchers feel that the normal contact
of the trapped posterosuperior glenoid labrum in this position
increases tension in the anterior glenohumeral capsule in
a cam like manner, thereby enhancing glenohumeral stability
and so the failure of this mechanism during postero-superior
translation leads to a failure of the shoulder's normal stability
apparatus.
1.4.3.
Timing of horizontal abduction and arm external rotation:
It is seen that during the arm cocking and subsequent acceleration
phases, the arm moves from horizontal abduction to adduction
and from extremes of external rotation to internal rotation
with extremes of external rotation displayed during concomitant
shoulder horizontal adduction (Figure
9). Clinically, it is commonly seen that the amount of
painless passive external rotation available when measured
at 90° of arm abduction will be reduced with increased arm
horizontal abduction. Whilst this has not been formally investigated
it would seem rational to suggest that shoulder pain would
be present in those individuals who aberrantly 'leave' their
arm too long in horizontal abduction during the external rotation
phase of arm cocking via a similar mechanism perhaps through
attenuation of the anterior capsular structures.
1.5.
Arm abduction
Atwater was the first to propose that across all the throwing
and striking sports, the amount of arm abduction at release/impact
stayed relatively constant at 90° with apparent variations
being due to trunk inclination (Atwater, 1979).
This has only recently been partially challenged by Matsuo
who analyzed a group of 2 submarine type pitchers, 2 sidearm
type pitchers, and a control group of 13 ¾ arm style pitchers
(Matsuo et al., 2000).
Matsuo found the submarine style pitchers to abduct their
arms to less than 75° during the arm acceleration phase, and
that this style of throwing was associated with an increased
maximum shoulder anterior force in comparison to the ¾ arm
style pitchers (Matsuo et al., 2000).
This is a significant finding, as it has been suggested by
some pitching coaches that submarine style pitching whilst
generally capable of lower velocity than ¾ style pitching,
is less stressful on the arms of those performing it, and
has been recommended to injured pitchers as a way of extending
their careers. The sidearm pitchers were noted to have an
increased medial elbow force in comparison to the ¾ arm style
pitchers, and this would appear to concur with the majority
of opinion of pitching instructors (see Figure
10).
Matsuo et al., 1999
modeled the effect of varying the amount of arm abduction
at ball release (through the ranges 50° to 130°) during the
throw for a number of kinetic and performance variables. This
group found that wrist velocity was at a maximum when the
shoulder was at 90° abduction at ball release. Elbow varus
torque was at a minimum at 80° of arm abduction at release,
while peak shoulder anterior force was minimized at 110° arm
abduction at release. Shoulder compressive force was at its
lowest at 130° arm abduction at release, increasing with all
lower values investigated. This work was complemented by a
subsequent investigation of eleven professional pitchers by
Matsuo et al., 2002
where a two camera videotape analysis was conducted calculating
elbow varus torque and peak wrist velocity. Subsequently these
values were recalculated with theoretically varied levels
of arm abduction. Each pitcher was found to have optimized
their level of arm abduction to minimize the amount of elbow
varus torque and maximize the peak wrist velocity. More recently,
this work was followed up with a 4 camera, 200Hz investigation
into 33 healthy college pitchers upon whom a two-way analysis
of variance was performed examining the effects of trunk tilt
and arm abduction on elbow varus torque through modeling predicted
forces across a range of trunk inclination and arm abduction
angles (Matsuo et al., 2006).
In the simulated overhand and three-quarter arm conditions
(see section 7 for and explanation of these terms) elbow varus
torque was minimized with arm abduction of 90°, while overall
varus torque was minimized at 100° of arm abduction with a
contralateral trunk tilt of 10°. During ipsilateral trunk
tilt conditions the optimum angle of arm abduction in terms
of minimizing elbow varus torque was generally 100° or greater.
Werner's group (2001)
found the amount of arm abduction at stride foot contact to
be 109° ± 33°, with Flesig's (1994)
investigation showing lower values. Fleisig reported arm abduction
at ball release to be approximately 95°, and most authors
show the arm to slightly abduct from the time of stride foot
contact until maximum external rotation, then to slightly
adduct until ball release, and then there is a sharp abduction
during the decelatory phase until maximum internal rotation
of the arm is reached. Increasing the amount of arm abduction
was shown by Werner et al., 2002
to be contributory to increasing the amount of valgus stress
at the elbow. In contrast to these findings, Escamilla's (2002)
investigation of a group of American and Korean pitchers showed
the lower velocity (and reduced kinetics) Korean group to
have an increase in the amount of arm abduction at stride
foot contact (94 ± 11° vs. 104 ± 7°). These findings should
be considered in light of Matsuo's (2002)
more recent modeling work in which arm abduction angle and
trunk inclination were found to be interdependent and analyses
examining only one aspect may be therefore be superficially
confounding only.
1.6.
Lead knee position
At the point of stride foot contact, the lead knee has been
reported to be in varying amounts of flexion, and then move
toward more flexion, extension, or not at all (Figure
11). In Matsuo's (2001)
previously described investigation of a high and low velocity
pitching group, the higher velocity group displayed both a
slower rate of knee flexion on landing, and a higher rate
of subsequent knee extension. Pitching coaches will occasionally
describe this behavior as 'firming up the front side', and
have been reported as claiming that those throwers who allow
their 'front side to soften' (by letting their lead knee move
toward more flexion during the acceleration and release phases)
are not throwing to their highest potential velocity. In agreement
with these findings, Escamilla et al., 2002
showed a reduction in the amount of knee flexion at release
(37 ± 14° vs. 48 ± 16°) in the higher velocity group of American
pitchers in comparison to their Korean counterparts.
In an investigation of kinematic differences between pitch
types (fastball, curveball, changeup, and slider) thrown by
16 college pitchers, Escamilla et al., 1998)
showed the changeup pitch to have the greatest excursion of
knee flexion from stride foot contact to ball release, and
the lowest ball velocity across all pitch types.
MacWilliams et al., 1998
investigated the ground reaction forces during pitching for
one high school and six collegiate pitchers. This group placed
a force platform immediately in front of the pitching rubber
(underneath the stance leg of the pitcher) and another at
the site of stride foot landing. This enabled them to record
the magnitude and directions of the 'push off' and 'landing'
forces during pitching. They also measured wrist linear velocity
(a good correlate of ball speed). They found that ground reaction
force directed toward the plate was highly correlated with
throwing speed (r² = 0.82) indicating that those who pushed
hardest toward the plate (from their stance leg) and therefore
were also able to decelerate most strongly with their landing
leg also displayed the highest linear wrist velocities. The
results of this study contrast somewhat with the findings
of Elliot et al., 1988
who examined 8 International level pitchers whilst throwing
fastball and curveball pitches using a force platform analysis
of the push-off leg. In the data from the 3 highest velocity
pitchers, it was found that the timing of the force pushing
toward the plate was later in the pitch cycle but of a similar
magnitude to those three who threw slowest.
1.7.
Pelvic and trunk orientation
Whilst there appear to be no strictly held definitions, it
would seem that pitchers are classified in terms of their
degree of forearm inclination at release from vertical, and
the extent and direction of trunk sideflexion. Those who display
significant trunk sideflexion away from the throwing arm side
with a concomitant vertically oriented forearm at release
will be termed 'Overhand' throwers. If the same pitcher were
to have their trunk vertically oriented and the forearm almost
horizontal at release then they are termed 'Sidearm' pitchers.
The majority of pitchers display mechanics somewhere between
these two extremes with a trunk inclined slightly toward the
contralateral (to the throwing arm) side and the forearm in
between the extremes of vertical and horizontal. This style
is termed a 'Three-Quarter arm' throwing. Less commonly, a
thrower will inclined their trunk toward the throwing arm
side delivering the ball from a lower height. These throwers
are termed 'Submarine' style pitchers. (See Figure 12 for an explanation of these terms).
Matsuo et al., 2000
investigated the kinematics and kinetics of two sidearm and
two submarine pitchers. This group found that the sidearm
style of throwing was associated with an increase of peak
medial elbow force which concurs with the majority of opinion
of pitching instruction. Perhaps more surprisingly given the
weight of opinion of pitching instructors, the two submarine
style throwers were found to show an increase in the maximum
amount of shoulder anterior force.
In an effort to determine if variation in trunk sideflexion
influences the optimal angle of arm abduction in terms of
the sum of minimum torque squared required, Matsuo et al.,
2003
using a 4 camera 200Hz analysis investigated the kinematics
of seven professional pitchers (throwing with an average velocity
of 38.0 ± 1.3 m·sec-1). After determining the kinematics
for each of the pitchers, torque squared was recalculated
considering variations in trunk tilt angle for seven cases
(-20°, -10°, 0°, 10°, 20°, 30°, and 40°) and for 6 different
angles of arm abduction at release (70°, 80°, 90°, 100°, 110°,
and 120°) giving 42 possible combinations for each individual.
For these subjects, Matsuo found that for contralateral trunk
tilt (10° to 40° conditions) optimal arm abduction angle varied
from 90° to 105° whilst in the ipsilateral conditions, torque
squared decreased as arm abduction as shoulder abduction increased,
although the optimal abduction angle was not found in the
ranges of arm abduction studied (Matsuo et al., 2003).
It was concluded that on average ipsilateral trunk tilt was
associated with greater requirements of torque squared than
for the contralateral conditions, and that the optimal condition
(in terms of minimum torque squared) was in the condition
of 100° of shoulder abduction and 30° of contralateral trunk
tilt. However the authors hastened to point out that two of
the seven subjects did not fit this pattern in that altering
their kinematics toward this condition increased their torque
squared, suggesting that other factors (they put forward trunk
inclination and elbow extension angular velocity as possible
candidates) may be significant contributors. A subsequent
investigation (Matsuo et al., 2006)
using similar methodology and 33 college pitchers (average
ball release velocity 36.8 ± 0.9 m·sec-1) which again modeled
varied kinematics across the same combinations of 42 variables
and compared varus torque as a dependent variable showed similar
results in that peak elbow varus torque varied according to
both arm abduction and trunk inclination angles. In this investigation,
peak elbow varus torque generally displayed a minimum shifted
toward greater arm abduction angles as trunk tilt angle increased
ipsilaterally. Again, there were individual differences between
subjects however this data showed a shoulder abduction angle
minimizing elbow varus torque depending on the trunk tilt
angle with minimum varus torque at approximately 90° of arm
abduction in the cases of contralateral trunk tilt in the
order of 20° to 30° - the trunk inclination generally described
as overhand and three-quarter pitchers, and in accordance
with the general teaching of pitching coaches.
In an EMG investigation into muscular activity during throwing,
Hirashima et al., 2002
showed activity of the external oblique muscle contralateral
to the throwing arm prior to the ipsilateral external oblique.
This pattern of muscle activity during the axial rotation
phase of trunk movement is thought to be best disposed to
assist in the transfer of torque from the lower limb to the
upper limb. Activity in the rectus abdominus was only seen
immediately prior to release suggesting active trunk flexion
activity occurred quite late in the propulsive phase. In their
investigation of 127 college and professional pitchers, Matsuo
et al., 2001
looked at kinematic differences between the groups which threw
at 1 standard deviation above and below the sample mean. Among
their results was the finding that higher velocity throwers
tended to display an increased forward trunk tilt at the moment
of ball release. As rectus abdominus is considered to be a
primary trunk flexor, it would appear that this EMG activity
seen by Hirashima et al., 2002
late in the throwing cycle is significant in the generation
of ball speed.
Stodden et al., 2001
investigated aspects of trunk and pelvic positioning in the
horizontal plane during pitching for a group of 19 elite level
subjects (7 professional, 9 college, 3 high school). Each
of the participants displayed a variation of at least 1.8
m/sec (approximately 4.0 mph) in their trial of 10 maximal
effort fastball pitches averaging 35 ± 2 m·sec-1 (78.3 ± 4.5
mph). The variables studied were pelvic orientation and upper
torso orientation (in the horizontal plane) at maximum knee
height; stride foot contact; instant of maximal arm external
rotation; and at the instant of ball release. They also considered
pelvic and upper torso angular velocity (in the horizontal
plane) during the arm cocking and arm acceleration phases.
This data was then analyzed using a mixed model analysis including
all 12 pelvis and trunk related variables, of which 5 were
found to be associated with variations in velocity. Principal
findings were that during the higher velocity trials, subjects
displayed a more 'open' pelvis and upper torso at the point
of maximum arm external rotation, and a more open pelvis at
the point of ball release. It was also shown that the higher
velocity throws were made with higher pelvic angular velocities
during the arm cocking phase and higher upper torso angular
velocities during the arm acceleration phase. Whilst this
work was limited to the horizontal plane, Matsuo et al., 2001
in their investigation of pitchers throwing more than one
standard deviation above and below the mean velocity of the
group of 127 pitchers considered variables in the horizontal
and sagittal planes. Matsuo et al., 2001
investigated maximum pelvis linear velocity, maximum pelvis
and upper trunk angular velocity (in the horizontal plane),
trunk forward tilt angular velocity, and forward tilt at the
instant of ball release. With the exception of linear pelvic
velocity, these entire trunk related variables were of higher
magnitude in the high velocity group. However, only forward
trunk tilt at the instant of ball release (36.7° ± 6.7° in
contrast to 28.6° ± 11.1°) reached statistical significance.
In accordance with these findings, Escamilla et al., 2002
in their investigation of a group of American and Korean pitchers,
showed the higher velocity American group to have a higher
pelvic angular velocity during arm cocking (660 ± 60°/s vs.
610 ± 55°/s), and an increase in forward trunk tilt at ball
release (32 ± 8° vs. 26 ± 9°).
In a 2001 investigation into 9 pitchers separated into low
and high skill level by an experienced coach, Murata, 2001
looked at the amount of non-throwing shoulder movement. Using
a two camera, 200Hz analysis, a marker was placed over the
acromion process of the non-throwing arm, and its three dimensional
motion recorded from stride foot contact until ball release
and normalized as a function of body height. The skilled group
of four pitchers threw their fastballs at 38.22 ± 1.02 m·sec-1
in comparison to the less skilled group who threw at 35.96
± 1.45 m·sec-1. The skilled group of throwers were found to
have a reduction in the amount of non-throwing shoulder movement
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