1. ORIGINAL RESEARCH
The Relationship Between Anterior Glenohumeral Laxity
and Proprioception in Collegiate Baseball Players
Kevin G. Laudner, PhD, ATC,*† Keith Meister, MD,† Satoshi Kajiyama, MS, ATC,*
and Bria Noel, ATC*
Objective: To determine if a relationship exists between anterior
glenohumeral (GH) laxity and proprioception.
Design: Cross-sectional study.
Setting: University biomechanics laboratory.
Participants: Thirty asymptomatic collegiate baseball players.
Independent Variables: Anterior GH laxity.
Main Outcome Measures: Proprioception (active joint position
sense) at positions of 75 degrees of external rotation, 30 degrees of
external rotation, and 30 degrees of internal rotation were measured
using an isokinetic dynomometer. Anterior GH laxity was measured
using an instrumented arthrometer.
Results: Linear regression analyses showed that there were no
relationships between anterior GH laxity and active joint position
sense at 30 degrees of GH internal rotation and 30 degrees of GH
external rotation (r = 0.21, P = 0.13). However, there was a moderate
positive relationship between anterior GH laxity and joint position
sense at 75 degrees of shoulder external rotation (r = 0.56, P = 0.001).
Conclusions: These results suggest that shoulder proprioception in 75
degrees of external rotation decreases as anterior GH laxity increases.
These results may prove beneficial in the prevention, evaluation, and
treatment of various shoulder injuries associated with GH laxity.
Key Words: shoulder, throwing athlete, instability, sensorimotor
(Clin J Sport Med 2012;22:478–482)
INTRODUCTION
During the late cocking phase of the throwing motion,
the glenohumeral (GH) joint has been shown to produce up to
310 N of anterior force.1
These large forces are believed to
result in microtrauma that over time may cause adaptive
changes, such as increased laxity of the anterior GH soft tissue
restraints.2,3
This increased laxity may partially explain the
increased GH external rotation repeatedly seen in the throwing
arm of baseball players compared with the nonthrowing arm.4,5
Although this increased laxity among baseball players is com-
mon, excessive laxity may have several detrimental effects in
regard to shoulder dysfunction and injury.6,7
Furthermore, this
increase in GH laxity is hypothesized to affect the propriocep-
tive abilities, such as active joint position sense, of the athlete.8,9
As stated previously, the throwing motion places
a tremendous amount of force on the shoulder joint. Therefore,
it is imperative that both the dynamic and static restraints form
a synergistic phenomenon to provide the appropriate amount of
functional stability. More specifically, baseball players require
optimal joint position sense in an effort to repetitively maintain
proper throwing mechanics over the course of a game, season,
and career. As this joint position sense decreases, so does
the body’s ability to maintain correct biomechanics during
the throwing motion placing various structures, including the
shoulder, at an increased risk of injury.
Several studies have reported that patients diagnosed
with shoulder instability also present with decreased pro-
prioception.8–11
Other studies have noted similar deficiencies
in the dominant shoulder of various asymptomatic overhead
athletes.12–14
However, no data are currently available detail-
ing the effect of adaptive GH laxity among asymptomatic
baseball players and proprioceptive alterations. Therefore,
the purpose of this study was to determine the strength of
the relationship between anterior GH laxity and active joint
position sense in the throwing arm of asymptomatic baseball
players. Identifying such a relationship may be beneficial for
clinicians in the prevention, evaluation, and treatment of var-
ious shoulder injuries associated with increased GH laxity.
METHODS
Participants
Thirty collegiate baseball players (age = 20.2 ± 1.4
years, height = 185.0 ± 5.0 cm, mass = 88.9 ± 9.7 kg) par-
ticipated in this study. This group consisted of 13 pitchers and
17 position players. At the time of testing, no subjects pre-
sented with any recent upper extremity pain or discomfort
within the past 2 years and no subject had any history of
upper extremity surgery or neurological disorder that may
have affected their proprioceptive sense.
Each subject voluntarily attended 1 testing session in
the biomechanics laboratory at Illinois State University. All
participants provided informed consent as mandated by the
Submitted for publication March 21, 2012; accepted June 26, 2012.
From the *School of Kinesiology and Recreation, Illinois State University,
Normal, Illinois; and †Texas Metroplex Institute for Sports Medicine and
Orthopedics, Arlington, Texas.
Supported by a grant from the Illinois Association for Health, Physical
Education, Recreation and Dance.
Investigation was performed at Illinois State University, Normal, Illinois.
Corresponding Author: Kevin G. Laudner, PhD, ATC, Illinois State
University, School of Kinesiology and Recreation, Campus Box 5120,
Normal, IL 61790 (klaudner@ilstu.edu).
Copyright © 2012 by Lippincott Williams & Wilkins
478 | www.cjsportmed.com Clin J Sport Med Volume 22, Number 6, November 2012

2. Illinois State University Institutional Review Board before
testing (IRB number: 2009-0279). All testing was performed
by the same investigators, and no testing was performed after
an extensive throwing session.
Instrumentation
The Biodex System 4 Quick Set (Biodex Medical, Inc,
Shirley, New York) was used to measure shoulder proprio-
ception. This device uses a specialized software package,
combined with a dynamometer containing strain gauges,
potentiometer, and remote range of motion set switches, along
with several limb attachments, for testing, rehabilitation, and
diagnostic purposes of a variety of joints and muscle groups.
The LigMaster arthrometer (Sport Tech, Inc, Charlottes-
ville, Virginia) was used to measure anterior GH laxity. This
device uses a modified Telos GA-II/E stress system and
specialized software to calculate a force–response curve, which
provides the total amount of soft tissue compression and stiff-
ness of the joint restraints. The software is then capable of
calculating the amount of joint displacement (in millimeters).
Previous studies have shown the LigMaster to have both excel-
lent within-session reliability [intraclass correlation coefficient
(ICC) = 0.84, standard error of the mean (SEM) = 0.53 mm]
and between-session reliability (ICC = 0.83, SEM = 0.43 mm)
when measuring anterior GH laxity.15
Procedures
Shoulder proprioception was assessed by measuring
active joint position sense of the throwing shoulder. Each
subject was seated in an upright position on the Biodex
system with their shoulder in approximately 90 degrees of
abduction and the elbow in 90 degrees of flexion. The
dynamometer axis was aligned with the GH joint axis using
an imaginary line running up through the humerus toward the
center of the shoulder (Figure 1). The shoulder was randomly
positioned in target positions of 75 degrees of external rota-
tion, 30 degrees of external rotation, and 30 degrees of inter-
nal rotation.16
For these positions, the subject was blindfolded
and passively placed in the appropriate amounts of rotation,
as determined by the Biodex software. The subject was
then asked to concentrate on this target position for 10
seconds.13,16,17
After the 10-second concentration period, the
test arm was passively moved away from the target position.
Each subject was then asked to actively move their shoulder
back to the target position. Practice trials were provided
before data collection to ensure all subjects were comfortable
with these testing procedures. The absolute amount of error
between the target position and the replicated position was
used to determine accuracy of active joint position sense.
A total of 3 repetitions for each target position were collected,
with the average of these trials used for data analyses.
Anterior GH laxity was measured with the throwing
arm in an externally rotated position. For this measurement,
each subject was seated with the shoulder in 90 degrees of
abduction and 90 degrees of external rotation, while the
elbow was positioned in 90 degrees of flexion and full
pronation. Twelve decanewtons of anterior force was then
applied to the posterior proximal humerus (Figure 2) at a rate
of approximately 1 daN/s. Glenohumeral laxity was deter-
mined by taking the difference in displacement between the
inflection point, which is calculated by the LigMaster soft-
ware as the end of soft tissue compression and the initiation of
humeral head translation, and the final amount of displace-
ment recorded at 12 daN of anterior force.15
Statistical Analysis
A linear regression analysis using SPSS (Version 18.0;
SPSS, Inc, Chicago, Illinois) was used to determine if a relation-
ship existed between anterior GH laxity (independent variable)
and the 3 proprioception shoulder positions (dependent varia-
bles). An alpha level of 0.05 was set before all analyses.
RESULTS
The mean and standard deviation for anterior GH laxity
was 14.1 ± 6.0 mm. The means and standard deviations for
amount of error from the target position for 30 degrees of
FIGURE 1. Shoulder proprioception measurement. FIGURE 2. Anterior GH laxity measurement.
Clin J Sport Med Volume 22, Number 6, November 2012 Relationship Between Laxity and Proprioception
Ó 2012 Lippincott Williams Wilkins www.cjsportmed.com | 479

3. internal rotation, 30 degrees of external rotation, and 75
degrees of external rotation are shown in the Table. Indepen-
dent t tests showed that there were no differences in propri-
oception or GH anterior laxity between pitchers and position
players (P . 0.36). There were no relationships between
anterior GH laxity and active joint position sense at 30
degrees of shoulder internal rotation (r = 0.21, P = 0.13)
and 30 degrees of shoulder external rotation (r = 0.12, P =
0.26) (Table 1). However, there was a moderate positive rela-
tionship between anterior GH laxity and joint position sense
at 75 degrees of shoulder external rotation (r = 0.56, P =
0.001) (Figure 3). Post hoc statistical power was calculated
and showed that external rotation at 75 degrees was shown to
have strong power (0.51), suggesting the clinical usefulness
of this finding.
DISCUSSION
Throwing athletes may present with increased anterior
GH laxity as a result of microtrauma accumulated during the
late cocked position of the throwing motion, which primarily
consists of GH abduction and external rotation.1
Both
increased anterior GH laxity and decreased proprioception
have been associated with several shoulder injuries.6–10
The
results of this study suggest that as anterior laxity increases,
active joint position sense diminishes when at the larger
degrees of shoulder external rotation.
Active joint position sense is a critical function during
the throwing motion. This ability allows the athlete to
accurately replicate various positions, like the late cocked
position, throughout the throwing motion in an attempt to
maximize performance and minimize the risk of injury.
However, previous research has shown that the shoulder
external rotators of the throwing arm among baseball players
have neuromuscular imbalances.18
The relationship shown in
the current study between decreased active joint position sense
at 75 degrees of shoulder external rotation and increased GH
laxity support these previous findings. However, the findings
of this study did not show a significant relationship when at 30
degrees of shoulder external rotation. This is most likely due to
the increased tension placed on the static restraints and poten-
tially increased activity of the mechanoreceptors at the higher
range of shoulder external rotation.19
Previous investigations
have shown that mechanoreceptors are not sufficiently stimu-
lated during the early ranges of motion.19,20
Our results did not show a significant relationship
between anterior GH laxity and joint position sense at 30
degrees of shoulder internal rotation. This was not surprising,
considering our laxity test position of 90 degrees of shoulder
abduction and external rotation followed by an anteriorly
directed force has been shown to stress the anterior inferior
GH ligament21,22
while internal rotation stresses the posterior
capsule and ligaments.21,22
Future research should investigate
the effect of both increased and decreased laxity of the pos-
terior soft tissue restraints and their effect on internal rotation
joint position sense.
These findings may be extremely important in the
prevention, evaluation, and treatment of shoulder injuries
related to anterior GH laxity among baseball players.
Decreased joint position sense during the later degrees of
shoulder external rotation among players with increased
anterior GH laxity could result in a pathological cycle
ultimately resulting in injury. Lephart et al11
described this
pathological cycle between excessive shoulder laxity and
decreased proprioception and neuromuscular control. These
authors proposed that as laxity increases, proprioception and
the resulting neuromuscular control are diminished, resulting
in a vicious cycle until instability develops. In the case of
throwing athletes, such as baseball players, if joint position
sense is decreased due to increased anterior GH laxity, then
the ability to accurately externally rotate the shoulder during
the late cocking phase of the throwing motion may be
reduced. If shoulder external rotation is excessive during this
late cock position, the amount of microtrauma to the anterior
inferior GH ligament may be increased, leading to an
increased risk of instability and injury.
These findings may also be clinically significant among
other overhead athletes who present with increased anterior
GH laxity, such as tennis, volleyball, and softball players.
These athletes perform similar motions to the baseball throw,
often requiring a large amount of shoulder external rotation
before ballistic internal rotation resulting in powerful throws,
TABLE. Descriptive Statistics for Absolute Joint Position Sense
Error
Shoulder Test
Position
Mean ± Standard
Deviation, Degrees r
Confidence
Interval P
Internal rotation
at 30 degrees
4.8 ± 2.1 0.21 20.06-0.21 0.13
External rotation
at 30 degrees
5.6 ± 2.5 0.12 20.11-0.22 0.26
External rotation
at 75 degrees
5.4 ± 2.7 0.56* 0.09-0.32 0.001
*Statistically significant correlation (P , 0.05).
FIGURE 3. Linear relationship between GH laxity and pro-
prioception at 75 degrees of external rotation.
Laudner et al Clin J Sport Med Volume 22, Number 6, November 2012
480 | www.cjsportmed.com Ó 2012 Lippincott Williams Wilkins

4. serves, or spikes of the ball. Swimmers may also present with
increased anterior GH laxity,23
which may be accentuated
during the recovery phase of the swimming motion as the
hand and arm leave the water in preparation for internal rota-
tion back to the catch phase.
It is also worth noting that although a moderate
relationship did exist between anterior GH laxity and
decreased proprioception at 75 degrees of shoulder external
rotation, we cannot definitively conclude that increased laxity
causes decreased joint position sense nor vice versa. How-
ever, based on previous research that has shown increased
attenuation of the soft tissue restraints, which house the
mechanoreceptors, to diminish sensory output and ultimately
decreased propriocption,8–11
it is reasonable to conclude that
the increased GH laxity most likely lead to the decreased
active joint position sense in the current study.
As with any study, this investigation has several
limitations. Firstly, although the regression analysis showed
that 56% of the error variance in active joint position sense at
75 degrees of shoulder external rotation was explained by
anterior GH laxity, there is still a large percent of error
variance not explained by this laxity. The target positions for
measuring active joint position sense were at 30 degrees of
shoulder internal rotation and 30 degrees and 75 degrees of
external rotation. These positions most likely created various
amounts of tension to the GH soft tissue restraints between
participants. For example, 75 degrees of shoulder external
rotation for one subject may be near their end range of
motion, while this may be in the mid-range of motion for
another. Therefore, we cannot conclude that this position
stressed the ligament equally among all subjects. As such,
some subjects may have had more mechanoreceptor activa-
tion and thus increased active joint position sense than others.
Future research should look at the relationship between GH
laxity and joint position sense with the shoulder at the
individual end range of motion for each subject. Other
potential causes of this variance may be due to the
contribution of proprioceptive input from other static
restraints, such as the superior and middle GH ligaments,
and dynamic restraints, such as the pectoralis major and long
head of the biceps brachii. Most likely, there were also
individual differences in proprioceptive ability between
subjects adding to variance. Secondly, we only tested the
throwing shoulders of each subject. There may be differences
in proprioception among dominant and nondominant limbs,
although we are unaware of any research to date that has
investigated this possibility. Thirdly, our active joint position
sense task was conducted in a slow and controlled manner
and cannot be compared with the ballistic rotational speeds
created during the throwing motion. Finally, we tested
proprioception in a seated position, which may have affected
the baseball players’ proprioception. These athletes typically
are neuromuscularly trained to perform the throwing motion
through a creation of forces in the lower extremity, which are
ultimately transferred to the upper extremity and more spe-
cifically the throwing arm. It is also worth mentioning that
although the use of an arthrometer to measure laxity was not
a limitation of our study, clinicians may not have access to
such equipment. In this situation, the clinician must rely on
their training and experience to measure laxity using standard
special tests to determine laxity.
CONCLUSIONS
The results of this study show that there is a moderate
relationship between increased anterior GH laxity and
decreased active joint position sense at 75 degrees of shoulder
external rotation. Therefore, clinicians may use anterior GH
laxity measurements as a partial predictor of active joint
position sense. However, because the subjects used in this
study were asymptomatic, a pathologic laxity threshold for
determining insufficient proprioception was not appropriate.
Regardless, these results suggest that it may be important to
recognize those players with increasing laxity and incorporate
proprioceptive training before the development of injury. As
such, these results may prove beneficial in the prevention,
evaluation, and treatment of various upper extremity injuries
associated with anterior GH laxity.
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