Download gluteal muscle group activation and its relationship with pelvis and

GLUTEAL MUSCLE GROUP ACTIVATION AND ITS
RELATIONSHIP WITH PELVIS AND TORSO KINEMATICS
IN HIGH-SCHOOL BASEBALL PITCHERS
GRETCHEN D. OLIVER
AND
DAVID W. KEELEY
Department of Health, Kinesiology, Recreation, and Dance, University of Arkansas, Fayetteville, Arkansas
ABSTRACT
INTRODUCTION
Oliver, GD and Keeley, DW. Gluteal muscle group activation and
its relationship with pelvis and torso kinematics in high-school
baseball pitchers. J Strength Cond Res 24(11): 3015–3022,
2010—The purpose of this study was to examine the activation
patterns of the gluteal muscle group and their relationship to pelvis
and torso kinematics throughout the high-school pitching motion.
A single group, repeated-measures design was used to collect
gluteus maximus and gluteus medius muscle activity through
surface electromyography for the preferred and nonpreferred
sides during the various phases of the pitching motion. In addition,
data describing the kinematics of the pelvis and torso were
collected at foot contact, maximum shoulder external rotation, ball
release, and maximum shoulder internal rotation. For all pitchers,
preferred gluteus maximus activity was observed to be in excess of
100% of their maximum voluntary isometric contraction throughout the stride and arm-cocking phases of the pitching motion. The
observed means for the preferred gluteus medius, nonpreferred
gluteus maximus, and nonpreferred gluteus medius, although
different in magnitude, were similar in pattern. From the conclusion
of the stride phase, through the conclusion of the arm-cocking
phase, muscle activity increased for all pitchers. In examining the
relationship between the rate of axial pelvis rotation and gluteal
activity, several significant relationships were observed. In
contrast, no significant relationships were observed with gluteal
activity parameters and the rate of axial torso rotation. However,
because the pitching motion progresses sequentially from the
pelvis to the torso, variability in pelvis rotation may be directly
related to variability in torso rotation. The findings from this study
indicate that during the baseball pitch, there is a need for greater
control of gluteal activation throughout the pitching motion.
I
KEY WORDS electromyography, kinetic chain, overhead
throwing
Address correspondence to Dr. Gretchen D. Oliver, [email protected].
24(11)/3015–3022
Journal of Strength and Conditioning Research
Ó 2010 National Strength and Conditioning Association
t has become evident in the literature that control of the
pelvis and torso plays a major role in not only athletic
performance but also in injury prevention (17,22,31,32).
Core stability is critical in allowing for optimal transfer
of forces generated from the lower extremity to the upper
extremity (26). It has been defined by Pope and Panjabi (24)
that core stability is the function of the lumbopelvic-hip
complex to both prevent collapse of the vertebral column
and return it to natural stability. When discussing the lumbopelvic-hip complex, we include the gluteal muscle group.
As described by Baechle et al. (4), Kibler et al. (18), and
Putnam (26), it is the premise that the core, or lumbopelvichip complex, essentially allows proximal stability for distal
mobility. Structurally, the lumbopelvic-hip complex is the
area encompassing the pelvis and supporting the torso. The
foundation of stability for the pelvis is fundamentally supplied
through activity in the gluteal muscle group. The gluteal
muscle group acts to stabilize the torso over a leg that is
planted and allows for transference of power for any forward
leg movements (25,26,30,32).
From a functional biomechanics perspective, Putnam (26)
described the appropriate timing and momentum of the
larger more proximal segments (trunk) as being summated by
the speed principle. Essentially, a segment initiates its
movement when the adjacent proximal segment reaches
its maximum angular velocity (e.g., the shoulder reaches its
maximum angular velocity just before the elbow reaching its
maximum angular velocity). When examining activities such
as kicking, jumping, and the tennis serve, the pelvis and torso
segments have been shown to have the largest contribution to
the body’s total angular momentum (5,8,25). Similarly, these
segments have been shown to contribute approximately 50%
of the kinetic energy during the act of throwing (29).
In baseball, many studies have examined the upper
extremity and the stresses about the shoulder (1,3,9–11,30),
whereas others have focused on the lower extremity (19,20).
In investigating pelvis and torso kinematics, it has been found
that lower values of lumbar flexion and rotation are indicative
of a more open torso position during the pitch (22), and that
decreases in forward trunk tilt result in pitchers throwing
with a more upright posture (9). Unfortunately, the manner
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Glut Muscle Activity Relationship With Torso and Pelvis
would be significantly related to the kinematics of the trunk
and pelvis and that the nature of those relationships would be
dependent on the function of each individual gluteal muscle.
METHODS
Experimental Approach to the Problem
Figure 1. Position and orientation of electromagnetic markers affixed to
subjects during testing.
in which the kinematics of these segments may be affected by
core, or the true lumbopelvic-hip complex activity, has yet to
be thoroughly researched. Furthermore, it is not currently
known as to what role the gluteal muscle group plays with
the movements of the pelvis or torso throughout the pitch
cycle. Thus, it was the purpose of our study to examine the
activation patterns of the gluteal muscle group and their
relationship with pelvis and trunk kinematics during the
pitching motion of high-school baseball pitchers. It was
hypothesized that the observed patterns of gluteal activation
A single group, repeated-measures design was used to collect
gluteus maximus and gluteus medius muscle activity for both
the preferred and nonpreferred legs throughout the stride,
arm-cocking, arm acceleration, and arm deceleration phases
of the pitching motion. In addition, data describing the
kinematics of the pelvis and torso were collected at the points
of foot contact, maximum shoulder external rotation, ball
release, and maximum shoulder internal rotation. The data in
the current study were collected in a manner such that
subjects threw a series of maximal effort fastballs to a catcher
located the regulation distance from the pitching mound
(18.44 m) and those data from the fastest pitch passing
through the strike zone were analyzed (15,27). Subsequent to
data collection, both surface electromyographic (sEMG) and
kinematic data were analyzed using a series of descriptive
statistics to identify outliers and determine the nature of the
distribution before testing for the presence of relationships.
The nature of the distribution was analyzed using the
Shapiro–Wilk statistic (W-statistic, p . 0.05).
Once the data were deemed to be normally distributed,
testing for relationships was conducted by calculating the
Pearson product moment correlation coefficients to examine
the relationship between gluteal activity and both pelvis and
torso kinematics. In the current design, electromyographic
data were the independent variables, whereas the kinematic
data describing torso and pelvis kinematics were the
dependent variables. These variable assignments are consistent with the opinion that because the pitching motion can be
viewed as the sequential activation of body segment through
TABLE 1. Sequencing of angle decompositions used to describe pelvis and torso orientation throughout the pitching
motion.*
Body segment
Pelvis
First rotation
Second rotation
Third rotation
Thorax
First rotation
Second rotation
Third rotation
Axis about which rotation was performed
Resulting angle
Z
X’
Y$
Flexion (2)/extension (+)
Left lateral tilt (2)/right lateral tilt (+)
Right axial rotation (2)/left axial rotation (+)
Z
X’
Y$
Flexion (2)/extension (+)
Left lateral tilt (2)/right lateral tilt (+)
Right axial rotation (2)/left axial rotation (+)
*Prime (’) and double prime ($) notations are used to represent previously rotated axes. Each time the local coordinate system is
rotated, all axes within that system are rotated (i.e., 2 When an initial rotation occurs about the Z-axis, both the Y-axis and Z-axis are also
rotated producing 3 new axes; X’, Y’, and Z’. Subsequent rotations will then be about these axes.)
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Board, and before participation,
the approved procedures, risks,
and benefits were explained to all
subjects and their parents who
then signed the appropriate
paperwork to provide consent
for testing.
Procedures
Subjects reported for testing
before engaging in resistance
training or any vigorous activity
that day. Location of right and
left gluteus maximus and right
Figure 2. Mean and SD for preferred gluteus maximus activity (filtered % maximum voluntary isometric contraction
and left gluteus medius was
data) throughout the stride, arm-cocking, arm acceleration, and arm deceleration phases of the pitching motion.
identified through palpation.
Before testing, the identified
locations for surface electrode placement were shaved,
a linked system, alterations in gluteal activity throughout the
abraded, and cleaned using standard medical alcohol swabs.
pitching motion may result in changes to pelvis and/or torso
Subsequent to surface preparation, adhesive 3M Red-Dot
kinematics.
bipolar surface electrodes (3M, St. Paul, MN) were attached
over the muscle bellies and positioned parallel to muscle fibers
Subjects
using techniques described by Basmajian and Deluca (6). In
Twelve high-school male pitchers (age: 16.3 6 1.1 years;
the current study, the selected interelectrode distance was
height: 176.6 6 7.8 cm; and mass: 76.4 6 7.4 kg) regardless of
25 mm (16). Surface electrodes were used because they have
throwing arm dominance volunteered to participate in the
been deemed to be a noninvasive technique that is able to
current study. All subjects had recently completed their
reliably detect surface muscle activity (6,14,16).
competitive spring baseball seasons and were thus deemed
To transmit sEMG data to The MotionMonitorTM motion
appropriately conditioned for competition. Additional critecapture system (Innovative Sports Training Inc, Chicago IL),
rion for participation included recommendation of their
a Myopac Jr 10-channel amplifier with a common mode
respective coaching staff, multiple years (up through the
rejection ratio equal to 90 dB and set at a gain of 2,000 (RUN
current season) of pitching experience, and freedom from
Technologies Scientific Systems, Laguna Hills, CA) was
injury throughout the current baseball season.
employed. Throughout all testing, sEMG data were sampled
Data collection sessions were conducted indoors at the
at a rate equal to 1,000 Hz. Filtering of all sEMG data was
University of Arkansas Health, Physical Education, and Recrecompleted using standard band-pass filtering techniques with
ation building and were designed to best simulate a competitive
band-pass filters set at cutoffs of 20 and 350 Hz, respectively.
setting. All testing protocols used in the current study were
Additionally, all sEMG data were notch filtered at frequenapproved by the University of Arkansas Institutional Review
cies of 59.5 and 60.5 Hz,
respectively (7).
Once all electrodes had been
secured, 3 manual muscle tests
(MMT) were conducted for
each muscle. These MMTs
were conducted using techniques described by Kendall et al.
(16) and used to identify the
approximate maximum voluntary isometric contraction
(MVIC) for each muscle. All
MMTs consisted of a 5-second
isometric contraction for each
muscle, with the first and last
seconds of each contraction
Figure 3. Mean and SD for preferred gluteus medius activity (filtered % maximum voluntary isometric contraction
removed so as to obtain steady
data) throughout the stride, arm-cocking, arm acceleration, and arm deceleration phases of the pitching motion.
state results. Each MMT was
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Glut Muscle Activity Relationship With Torso and Pelvis
attached to a stylus and used to
digitize the palpated position of
various bony landmarks (23).
To accurately digitize the selected bony landmarks, subjects
stood in the neutral anatomical
position while digitization was
being completed.
Throwing kinematics for
right-handed subjects were calculated using the standards and
conventions for reporting joint
motion recommended by the
International Shoulder Group of
the International Society of BioFigure 4. Mean and SD for nonpreferred gluteus maximus activity (filtered % maximum voluntary isometric
mechanics (33,34). Raw data
contraction data) throughout the stride, arm-cocking, arm acceleration, and arm deceleration phases of the pitching
motion.
describing sensor orientation
and position were transformed
to locally based coordinate systems for each of the respective
conducted to establish baseline readings for each particbody segments. Euler angle decomposition sequences were
ipant’s maximum muscle activity to which all sEMG data
used to describe the position and orientation of the both the
could be compared. Before MMT conduction, the approved
pelvis and trunk relative to the global coordinate system (33,34).
testing protocol was explained to all subjects to ensure their
The use of these rotational sequences allowed the data to be
full understanding.
described in a manner that most closely represented the
In addition to sEMG data, kinematic data describing the
clinical definitions for the movements reported (23). Angle
movements of the pelvis and torso were collected throughout
decomposition sequencing for the pelvis and torso, and
the phases of the pitching motion. Kinematic data were
definitions of the movements they described are shown in
collected using The MotionMonitorTM motion capture
Table 1. Throwing kinematics for left-handed subjects were
system (Innovative Sports Training, Chicago IL). Before
calculated using the same conventions; however, it was
completing test trials, subjects had a series of electromagnetic
necessary to mirror the world Z-axis so that all movements
sensors attached to the medial aspect of the torso and pelvis
could be calculated, analyzed, and described from a right-hand
at the C7 and S1 locations, respectively (21). Sensors were
point of view (34).
affixed using double sided-tape and then wrapped using
Once all initial setup and pretesting had been completed,
flexible hypoallergenic athletic tape (Figure 1). After the
subjects were allotted an unlimited time to warm-up. Subjects
attachment of the electromagnetic sensors, a third sensor was
were allowed to perform their own specified precompetition
warm-up routine but were
asked to spend the latter portion of that warm-up time
throwing from the indoor
pitching mound to be used
during the test trials. After
completing their warm-up and
gaining familiarity with the
pitching surface, each participant threw a series of maximal
effort fastballs for strikes toward
a catcher located the regulation
distance from the pitching
mound (18.44 m). For the
current study, those data from
the fastest pitch passing
Figure 5. Mean and SD for nonpreferred gluteus medius activity (filtered % maximum voluntary isometric
through the strike zone were
contraction data) throughout the stride, arm-cocking, arm acceleration, and arm deceleration phases of the pitching
selected for detailed analysis
motion.
(15,27).
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TABLE 2. Mean (6SDs) for pelvis and torso kinematics at selected instances throughout the pitching motion.
Pelvis lateral flexion (o)
Pelvis axial rotation velocity
(os21)
Torso flexion (o)
Torso lateral flexion (o)
Torso axial rotation velocity
(os21)
Foot contact
Maximum external rotation
Ball release
Maximum internal rotation
25 (617)
367 (6146)
212 (614)
678 (6148)
26 (617)
1019 (6449)
25 (611)
206 (6148)
16 (617)
26 (612)
432 (6155)
27 (68)
215 (611)
705 (6190)
218 (68)
224 (67)
1277 (6548)
227 (614)
230 (68)
237 (6144)
RESULTS
Statistical Analyses
Data analysis for the current study was conducted using the
statistical analysis package SPSS 11.5 for Windows (SPSS,
Chicago, IL). For the fastest strike thrown by each
participant, mean and SD for all sEMG and kinematic
parameters were calculated. Once these measures of central
tendency were calculated, a series of descriptive statistics
were conducted to identify the presence of outliers and to
determine the nature of each of the distributions in terms of
both skewness and kurtosis. Once the data were deemed to
be normally distributed through the calculation of Shapiro–
Wilk statistic (W-statistic, p . 0.05), Pearson product
moment correlation coefficients were then calculated to
identify the possible relationships between gluteal activity
and throwing kinematics. For the current study, although
the data were derived from the same group of subjects at
multiple intervals, the level of significance was retained at
p # 0.05 as each phase of the pitching motion was analyzed
as an independent interval. With regard to the observation
of correlation power for the current study, significance was
indicated by an observed power $ 0.80.
Gluteal Activation
The mean magnitudes of preferred gluteus maximus activity
throughout the movement analysis are shown in Figure 2. For
all pitchers, preferred gluteus maximus activity was observed
to be in excess of 100% of their MVIC throughout the stride
and arm-cocking phases of the pitching motion. From the
end of the cocking phase (maximum external shoulder
rotation) through the remainder of the movement, mean
preferred gluteus maximus activity decreased to levels less
than 100% of mean MVIC levels.
The observed means for the preferred gluteus medius
(Figure 3), nonpreferred gluteus maximum (Figure 4), and
nonpreferred gluteus medius (Figure 5), although different
in magnitude, were similar in pattern. From the conclusion
of the stride phase, through the conclusion of the armcocking phase, muscle activity increased for all pitchers.
From this point, through the remainder of the pitching
motion, muscle activity decreased to levels that remained
fairly constant.
TABLE 3. Calculated Pearson product moment correlation coefficients (r) between preferred gluteal activity and both
pelvis and trunk kinematics.*
Preferred gluteus maximus activity
Preferred gluteus medius activity
Variable
FC
MER
REL
MIR
FC
MER
REL
MIR
Pelvis lateral tilt (o)
Pelvis axial rotation (os21)
Torso flexion (o)
Torso lateral tilt (o)
Torso axial rotation (os21)
0.346
0.106
20.118
20.335
0.048
0.285
0.730†
20.470
20.585
0.439
0.507
0.831†
20.178
20.343
0.390
0.517
0.086
20.494
20.092
0.332
0.207
20.341
0.046
20.428
20.279
0.071
20.824†
0.443
20.051
20.703
0.433
20.647
0.299
20.382
20.286
0.104
20.254
0.374
20.422
20.119
*FC = foot contact; MER = maximum external rotation; MIR = maximum internal rotation; REL = ball release.
†Significant difference at p # 0.05.
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Glut Muscle Activity Relationship With Torso and Pelvis
TABLE 4. Calculated Pearson product moment correlation coefficients (r) between nonpreferred gluteal activity and both
pelvis and torso kinematics.*
Nonpreferred gluteus maximus activity
Nonpreferred gluteus medius activity
Variable
FC
MER
REL
MIR
FC
MER
REL
MIR
Pelvis lateral tilt (o)
Pelvis axial rotation (os21)
Torso flexion (o)
Torso lateral tilt (o)
Torso axial rotation (os21)
20.178
20.047
0.034
20.319
20.086
20.171
20.550
0.058
20.248
20.164
20.197
0.837†
0.440
20.291
20.444
20.126
20.283
0.193
20.046
20.133
0.011
0.437
20.034
20.288
0.318
0.107
0.794†
20.064
20.088
0.346
0.048
0.779†
20.051
20.127
0.634
0.015
0.249
20.081
20.156
0.227
*FC = foot contact; MER = maximum external rotation; MIR = maximum internal rotation.
†Significant difference at p # 0.05.
TABLE 5. Calculated Interclass correlation coefficients (Pearson) between pelvis kinematics and torso kinematics.*
Pelvis lateral tilt (o)
Pelvis axial rotation (o/s)
Variable
FC
MER
REL
MIR
FC
MER
REL
MIR
Torso lateral tilt (o)
Torso axial rotation (os21)
0.803†
0.153
0.759†
0.211
0.717
0.121
0.566
0.075
0.132
0.857†
0.189
0.917†
0.086
0.953†
0.109
0.956†
*FC = foot contact; MER = maximum external rotation; MIR = maximum internal rotation.
†Significant difference at p # 0.05.
DISCUSSION
Pelvis and Trunk Kinematics
Results of pelvis and trunk kinematics are given in Table 2.
Throughout pitching motion, both the pelvis and the torso
remained tilted laterally toward the glove hand with a slightly
higher angle of lateral tilt being observed for the torso. Also,
throughout the movement, both the pelvis and the torso
rotated forward toward the plate with the velocity of axial
torso rotation slightly exceeding the velocity of axial pelvis
rotation. In addition, both peak axial rotation velocity and
minimum axial rotation velocity for the pelvis preceded that
of the torso.
Correlation
Correlation coefficients were computed to see if a possible
relationship between gluteal activities throughout the phases
of the pitching motion were related to pelvis and trunk
kinematics at specific instances during the pitching motion.
Pearson product moment correlation coefficients are shown
in Table 3 (preferred gluteal activity/pelvis and trunk
kinematics), Table 4 (nonpreferred gluteal activity/pelvis
and torso kinematics), and Table 5 (dependent variable
Interclass Correlation Coefficients).
3020
the
Typically the gluteus maximus acts to extend the hip and then
allows for external rotation of the hip. The greater activation
of the gluteus maximus on the preferred or drive leg indicated
that it was active in externally rotating the drive hip
throughout the arm-cocking and acceleration phases. From
a kinematic chain standpoint, this increased activation may
result in an increased rate of axial pelvis rotation throughout
these phases. This is evident in the positive relationship
(r = 0.730, p # 0.05 at maximum external rotation; r = 0.831,
p # 0.05 at release) between the rate of axial pelvis rotation
and preferred gluteus maximus activity at the points of
maximum external shoulder rotation and ball release.
In a similar fashion, the gluteus medius acts as an internal
rotator of the hips. As the nonpreferred leg (plant leg) was
planted, the magnitude of gluteus medius activation increased.
After foot contact, nonpreferred gluteus medius activity increased to a level near 145% of MVIC. This, coupled with the fact
that the rate of axial pelvis rotation peaked just before release
indicates that the nonpreferred gluteus medius may not simply
function as a pelvic stabilizer throughout these phases, but may
also function to allow for increased internal hip rotation during
the arm-cocking and acceleration phases of the pitching motion.
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This is supported further by the observed positive relationship
between axial pelvis rotation and nonpreferred gluteus medius
activity (r = 0.794, p # 0.05 at maximum external rotation; r =
0.779, p # 0.05 at release). Also throughout the arm-cocking
phase, preferred gluteus medius activity was observed to be
inversely related to the rate of axial pelvis rotation (r = 20.824, p
# 0.05 at maximum external rotation). This again indicates that
the role of the gluteus medius may be twofold, with it serving as
both a pelvic stabilizer and an internal hip rotator with the latter
action possibly being directly related to the ability of a pitcher to
control the rate of axial pelvis rotation.
In examining the rate of axial torso rotation, no significant
relationships were observed between any gluteal activity
parameters and the rate of axial torso rotation. However, because
the pitching motion progresses sequentially from the pelvis to the
torso (1), variability in pelvis rotation may be directly related to
variability in torso rotation. The interclass correlation coefficients
calculated between the 2 dependent variables support this notion
and indicate that the rate of axial torso rotation may be directly
related to the rate of axial pelvis rotation.
PRACTICAL APPLICATIONS
The findings from this study indicate that during the baseball
pitch, there is a need for greater control of gluteal activation
throughout the pitching motion. These findings may have
implications for future injury prevention mechanisms within
the pitching cycle. Furthermore, it can be inferred that the
activation of the gluteal group may have a greater influence on
the entire pitch vs. only trunk and pelvic control.
It has been previously suggested that throughout the
pitching motion, kinematic alterations in the actions of
proximal segments may result in kinematic alteration in
the actions of distal segments (1,27) as in the actions of the
pelvis could alter the actions of the torso. It has also been
suggested that baseball pitchers who exhibit difficulty in
controlling the rate of trunk rotation may increase their
risks for injury (1). The results of the current study
indicate that the pattern of gluteal activity observed
throughout the pitching motion is directly related to the
rate of axial pelvis rotation, and indirectly related to the
rate of axial torso rotation. Thus, to better control the rate
of both axial pelvis and torso rotation, high-school
pitchers should focus on specific training techniques that
will allow for the use of both the preferred and
nonpreferred gluteal musculature in an appropriate
manner throughout the pitching motion. By doing so,
pitchers of this age may be able to better control both the
rate and timing of axial rotation during pitching, and
possibly decrease the risks of developing overuse injuries,
such as to the elbow and shoulder that are commonly
associated with poorly controlled trunk kinematics
throughout the pitching motion. In an attempt to train
the gluteal muscle group, athletes should focus on
adequately training their core musculature through isometric exercises that address not only the abdominals but
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also the gluteal muscle group. Protocols such as the ones
developed by Szymanski and Fredrick (28), Hendrick (13),
Akuthota and Nadler (2), and Handzel (12) are great
adjuncts to baseball training regimens.
ACKNOWLEDGMENTS
The authors would like to thank Bob Carver and his support
of the throwing biomechanics research being conducted at
the University of Arkansas, Priscilla Dwelly, Hiedi Hoffman,
and Jackie Booker for their aid in data collection, and the
coaches, the players, and their parents without whose
participation, this study would not have been possible. No
authors received financial support for this study.
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