Current Reviews in Musculoskeletal Medicine (2020) 13:155–163

https://doi.org/10.1007/s12178-020-09615-1

INJURIES IN OVERHEAD ATHLETES (J DINES AND C CAMP, SECTION EDITORS)

Step by Step Guide to Understanding the Kinetic Chain Concept

in the Overhead Athlete
Todd S. Ellenbecker 1 & Ryoki Aoki 2

Published online: 14 March 2020

# Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract
Purpose of Review The purpose of this review will be to provide both a historical and recent review of the role of the kinetic chain
for the overhead athlete. The kinetic chain concept will then be applied to clinical exercise modifications and integrations for
prevention and treatment of shoulder injury.
Recent Findings The primary conclusion reached through this review is the important role the lower extremity, trunk, and
scapular region play in the development of optimal terminal segment acceleration in the overhead throwing and serving motion.
Failure of any links in the kinetic chain has implications for shoulder and elbow injury in the overhead athlete. Modifications of
traditional shoulder exercises emphasizing activation of the scapular stabilizers and core musculature alongside concomitant
rotator cuff activation are recommended and supported in EMG research.
Summary Future research is needed to further identify risk factors and rehabilitation and prevention strategies and key clinical
tests for the overhead athlete. The goal is to elucidate the important role the kinetic chain plays in both performance enhancement
and injury prevention for the overhead athlete. Understanding the key role all segments of the kinetic chain play in the complex
biomechanical segmental rotations required for high-level throwing and serving will assist clinicians who work with overhead
athletes.

Keywords Kinetic chain . Upper extremity . Shoulder . Rehabilitation

Introduction Relevant Historical Concepts of the Kinetic

Chain
This article will briefly review some of the initial historical
concepts of the kinetic chain to provide an overview of more The kinetic chain or kinetic link principle provides both the
specific discussion of the relevancy of the kinetic chain bio- framework for understanding and analyzing human move-
mechanical studies in throwing and the tennis serve. This will ment patterns as well as the rationale for the utilization of
be followed by discussion regarding the application of the exercise conditioning and rehabilitation programs that empha-
kinetic chain in first evaluation of the throwing athlete, as well size the entire body, despite a target joint or anatomical struc-
as in designing and integrating concepts of the kinetic chain in ture being injured. The kinetic link principle describes how the
the design and implementation of rehab programs for the over- human body can be considered in terms of a series of interre-
head athlete with shoulder and elbow injury. lated links or segments. Movement of one segment affects
segments both proximal and distal to the first segment.
This article is part of the Topical Collection on Injuries in Overhead Kibler [1] refers to the kinetic link system as a series of se-
Athletes quentially activated body segments. The kinetic link principle
is predicated on a concept developed and described initially by
* Todd S. Ellenbecker Hanavan [2], who constructed a computerized form of the
ellenbeckerpt@cox.net adult human body. This computerized form comprises conical
links that include the lower extremities, torso, and upper ex-
1
Rehab Plus Sports Therapy Scottsdale and ATP Tour, Scottsdale, AZ, tremities. In reference to upper extremity skill performance,
USA work in the upper extremity segments is transmitted to the
2
MGH-IHP, Boston, MA, USA trunk and spine via a large musculoskeletal surface. There is
156 Curr Rev Musculoskelet Med (2020) 13:155–163

an exchange of forces across this musculoskeletal surface, demonstrate decreased joint loads, maximum velocity,
which results in the generation of massive amounts of energy and m aximal force prod uction during throwing.
[2]. Dysfunction of kinetic chain during throwing increases
Davies [3] described how the upper extremity can be stress placed on distal segments and can result in shoulder
viewed as a series of links. The links proposed by Davies and elbow pathologies.
[3] include the trunk, scapulothoracic articulation, Dysfunction of the kinetic chain will reduce efficiency
scapulohumeral or glenohumeral joints, and distal arm re- of throwing and will increase the risk of injury in shoulder
gions. Each of these links can be considered independent and elbow [7, 8, 10, 11•]. The hip/trunk area contributes
anatomically and biomechanically, but with reference to approximately 50% of the kinetic energy and force to the
human function must be considered a unit. entire throwing motion; thus, the force and power genera-
Similar to the descriptions of the kinetic link by tion in this area is compromised by altered kinematic in
Hanavan [2] and Davies [3], the literature has described this area, resulting in increased stress in distal segments.
the concept of proximal-to-distal sequencing [4, 5]. Robb et al. [12] found that decreased hip ROM in the
While ultimately utilized in the biomechanical analysis of dominant side hip compared with non-dominant side is
human movement, the proximal-to-distal sequencing mod- highly correlated with shoulder injury and poor throwing
el has relevance in exercise both for rehabilitation and per- mechanics. Kibler et al. [7] proposed that inadequate hip
formance enhancement. The terms kinetic link, proximal- ROM and poor balance may significantly affect an ath-
to-distal sequencing, summation of speed principle [4], and lete’s ability to transfer energy along the kinetic chain,
Plagenhof’s [5] concept of acceleration-deceleration all at- resulting in dysfunctional movement and increased stresses
tempt to describe the complex interaction of the body’s on the shoulder and elbow, and several studies have shown
independent segments working together to form a se- a correlation between poor lower extremity balance and
quence or unit of functional segments. overhead injuries including UCL tear [7, 10, 13•, 14•, 15•].
The goal of nearly all sport-related activities such as The trunk is the vital structure to deliver the force produced
throwing, serving, and kicking a ball is to achieve maxi- by the lower limbs to the upper limbs. Proper trunk movement
mal acceleration and the largest possible speed at the end is important during throwing, as it is integral to the transfer of
of the linked segments [4]. The concept ideally states that energy to distal body segments during the throwing motion.
motion should be initiated with the more proximal seg- Previous studies using mathematical modeling showed that a
ments, and proceeds to the more distal segments, with reduction in trunk kinetic energy development increased the
the more distal segment initiating its motion at the time demand in the distal segment to maintain the same energy ball
of the maximum speed of the proximal segment. Each release, resulting in increased stress placed in the shoulder and
succeeding segment would generate larger endpoint elbow joints [11•, 16•, 17•, 18•].
speeds than the proximal segment. This proximal-to- The scapula and glenohumeral joints are the key in facili-
distal sequencing has been demonstrated in research by tating energy transfer produced by lower limbs and trunk.
examining the linear speeds of segment endpoints, joint Kibler et al. [19] calculated that a 20% decrease in kinetic
angular velocities, and resultant joint moments [6]. energy delivered from the hip and trunk to the arm requires
a 34% increase in the rotational velocity of the shoulder to
generate the same amount of force to the hand. Deficits of
Biomechanics of the Kinetic Chain strength and mobility in these areas can negatively impact
in the Throwing Motion shoulder kinematics which would increase injury risk in the
shoulder and elbow [10, 19].
The overhead throwing motion is developed and controlled
through a sequential body position and motion, involving
sequential activation, both in onset timing and peak acti- Biomechanics of the Kinetic Chain
vation transferring from the lower extremities to upper ex- in the Tennis Serve
tremities [7, 8]. Although the throwing motion is an ex-
tremely rapid movement occurring within only 0.145 s, Proximal-to-distal sequencing has been reported in the histor-
the effective synchronous sequencing of the body seg- ical literature on the tennis serve [5, 20–22]. Closely analyzing
ments is vital to maximize the efficiency of the kinetic the literature in upper extremity throwing or striking sports
chain [9]. Sciascia et al. [8] suggested that the kinetic chain shows a modification of the proximal-to-distal pattern. This
is influenced by multiple factors including core strength, modification occurs when the human body exploits the bene-
hip strength and range of motion (ROM), scapular kine- fits of long-axis rotation of the humerus (internal rotation) and
matics, shoulder strength and ROM, knee, and ankle mo- forearm (forearm pronation) to maximize endpoint speed [6].
bility, and efficient kinetic chains have been shown to Research has demonstrated consistently that peak internal
Curr Rev Musculoskelet Med (2020) 13:155–163 157

rotation of the shoulder (humerus) follows the movement of Additionally, there is a 63% greater incidence of shoulder
the wrist and hand [6, 21, 22]. Additionally, the peak speed of injury in this population, as compared with those players
pronation has been found to occur immediately prior to ball who did not have a history of tennis elbow.
contact on the tennis serve and forehand groundstroke sug- Another classic foundational study of the total arm strength
gesting that this long-axis rotation does not conform to tradi- concept is that by Strizak et al. [29]. These researchers incor-
tional explanations of proximal-to-distal sequencing porated the isometric strength of the forearm (pronation and
(Marshall & Elliot, 2000). supination), wrist (radial, ulnar deviation, and flexion and ex-
Additionally, Kibler [19] provided an objective analysis of tension), and metacarpal phalangeal (MCP) joints (flexion and
force generation during a tennis serve. Fifty-four percent of extension) to create a total arm strength index. This index was
the force development during the tennis serve comes from the compared among three groups: (1) a normal, uninjured, non-
legs and trunk, with only 25% coming from the elbow and tennis-playing control population, (2) healthy recreational ten-
wrist. Non-optimal performance and increased risk of injury nis players, and (3) recreational tennis players with tennis
occur in tennis and other sport activities when individual’s elbow. Results of this study showed significantly greater
attempt to utilize the smaller muscles and distal arm segments dominant-arm total arm strength relative to body weight in
as a primary source for power generation [1, 20]. the control group and tennis-playing group, but no significant
Finally, research from the Sydney Olympics, where the difference in the tennis elbow study population [29]. The find-
highest level tennis players from around the world competed ing of greater “total arm strength”: in both the control popu-
and were analyzed in competition, revealed some very clini- lation and in healthy tennis players and lack of this finding in
cally applicable information relative to the tennis serve and the the injured group supports the use of “whole extremity” or in
kinetic chain. Servers were broken down into two categories this application “total arm strength” rehabilitation and condi-
based on the amount of leg drive (knee flexion) utilized during tioning programs.
the loading or cocking phase of the tennis serve [23, 24]. More recently, Alizadehkhaiyat et al. [30] measured EMG
Minimal “leg drive” servers had 7.6° of knee flexion com- activity and fatigue response in a population of 16 patients
pared with those with more optimal “leg drive” (14.7°) and with tennis elbow and 16 control subjects. Similar to the older
had significantly larger anterior shoulder forces and elbow study by Strizak et al. [29], five forearm muscles and two
varus torques measured at the stage of maximal external rota- shoulder muscles were measured bilaterally. All control sub-
tion during the cocking phase of the tennis serve. Values for jects showed a dominance difference effect in all muscles
anterior shoulder force (shoulder internal rotation torque) and tested; however, the tennis elbow patients did not show a
elbow varus torque at MER in the serving motion were shown dominance effect for any muscle tested. In fact, deficits of
to be greatly increased when the lower body contribution to 25 to 35% in strength were documented in the patients with
the serving motion was decreased. Similar to the mathematical tennis elbow compared with the control subjects. Similar find-
modeling research from Kibler [19], this study shows how ings were reported by Lucado et al. [31] in a group of female
non-optimal contribution from the lower body kinetic chain tennis players with lateral epicondylitis. Players in their study
segments creates concomitant increases in shoulder and elbow with lateral epicondylitis had significantly decreased lower
loading which would potentially increase injury risk. trapezius strength compared with a control population that
was asymptomatic. Day et al. [32] also reported unilateral
weakness of the scapular musculature (middle trap, lower trap,
Application of the Kinetic Chain to Evaluation and serratus anterior) in patients with lateral epicondylitis. The
of the Overhead Athlete decrease in local and proximal muscle strength found in these
studies shows the important of a kinetic chain “total arm
Application of the kinetic link system in a clinical or rehabil- strength” approach to rehabilitation in patients with upper ex-
itative way has led to the development of the total arm strength tremity injury. This concept is prevalent today in upper ex-
(TAS) concept [25, 26]. This concept is predicated on the tremity rehabilitation and is reflected in the large emphasis in
kinetic link system as well as demonstrated by the close clin- both shoulder and elbow rehabilitation in trunk and scapular
ical relationship between shoulder and elbow injuries in sport. stabilization exercise and evaluation inclusion for the over-
Classic research by Priest and Nagel [27] studied 84 world head athlete.
class tennis players and reported that 74% of men and 60% Extensive evaluation of the scapulothoracic joint is indicat-
of women had a history of shoulder or elbow injury in the ed as an essential part of the kinetic chain in the overhead
dominant arm that affected tennis play. Injuries to both the athlete. Kibler [33, 34] has provided the early foundational
shoulder and elbow of the dominant arm were reported by emphasis regarding the role of the scapula in the overhead
21% and 23% of the men and women, respectively. Another athlete as well as provided an evaluation scheme to identify
study by Priest et al. [28] surveyed 2633 recreational tennis scapular dyskinesis [34]. The use of repeated shoulder eleva-
players and found an incidence of tennis elbow of 31%. tion with or without loading is an essential part in any
158 Curr Rev Musculoskelet Med (2020) 13:155–163

evaluation of the overhead athlete and can identify unilateral

scapular pathology for both preventative screening and clini-
cal evaluation. Despite the recent study by Plummer et al.
[35•], where similar incidences of scapular pathology were
visually identified in patients with shoulder pathology (67%
in flexion, 67% in abduction) and in controls (61% in flexion
and 52% in abduction), scapular evaluation has been found to
be a valuable inclusion in the evaluation of patients with upper
extremity dysfunction. In fact, a recent systematic review and
meta-analysis by Hickey et al. [36•] concluded that athletes
with scapular dysfunction are 43% more likely to develop
shoulder pain than athletes without scapular dysfunction.
The use of the Kibler scapular dyskinesis test alongside tests
like the scapular assistance [37] and scapular retraction test
provides a battery of examination methods to screen this im-
portant articulation in the overhead athlete [38•].
Evaluation of the elite-level tennis player for prevention
of injury and recognition of injury risk has resulted in the
development and implementation of an instrument called
the High Performance Profile (HPP) by the US Tennis
Association [39], as well as the ATP Performance and Fig. 2 Y balance test
Injury Prevention Screening PIPS tool [40]. This instru-
ment has been utilized to screen elite-level tennis players and 55% and can serve to facilitate preventative hip and
resulting in published descriptive profiles showing the core training programs to improve hip and core stability
identification of core and lower body weakness on tests [40, 41, 42•].
like the one-leg stability test (Fig. 1), and abdominal brac- Garrison et al. [10] found a decreased score on the Y bal-
ing and bridging core tests in elite players [40, 41, 42•]. ance test (Fig. 2) for both the stance and stride lower limb in
Surprisingly, among healthy, uninjured competing tennis baseball players with confirmed UCL tears. The Y balance
players, the number of failed one-leg stability tests indicat- score is reflective of lower extremity strength and neuromus-
ing hip weakness has been reported to range between 45 cular control. Thus, a lower score on the Y balance test may
indicate a deficit in balance, strength, and neuromuscular con-
trol in the lower extremities. In baseball, the deficit in neuro-
muscular control and strength at the trunk and lower extrem-
ities would negatively impact the ability to transfer energy into
the upper extremities, resulting in increased stresses placed on
the shoulder and elbow which would potentially increase in
injury risk.
Another key measure for the kinetic chain in throwing ath-
lete is hip rotation range of motion. Prior studies have
established normative data for the key movements of hip in-
ternal and external rotation range of motion in elite-level ten-
nis players [40, 41, 43] and in youth, collegiate, and profes-
sional baseball players [12, 43, 44•, 45•]. Limitation in hip
rotation ROM can have consequences and affect upper ex-
tremity loading during the throwing motion and negatively
impact performance and elevate injury risk. Therefore, a
screen of prone hip internal rotation (IR) ROM has been reli-
ably utilized to assess hip rotation range of motion in overhead
athletes [43, 46] (Fig. 3).
The inclusion of lower body and core screening tests is an
important part of the comprehensive evaluation of an over-
head athlete. The key tests for inclusion recommended by
Fig. 1 One-leg stability test to assess hip and core stabilization these authors would include the one-leg stability test, Y
Curr Rev Musculoskelet Med (2020) 13:155–163 159

upper extremity activation and performance, and the applica-

tion and use of unstable surfaces. These exercises create fur-
ther challenge for the athlete performing the traditional
glenohumeral and scapulothoracic exercise patterning with
the added requirement of enhanced core activation through
the unstable surface and bilateral extremity activation. Myers
et al. [48] applied the advanced thrower’s ten exercises char-
acterized by a sustained isometric contraction and bilateral
extremity involvement in a randomized clinical trial. They
found these exercises to improve strength and muscle endur-
ance by 10–14% in a pre-/post-testing paradigm. While these
Fig. 3 Prone hip internal rotation range of motion measurement exercises did not increase strength and endurance to a greater
extent than traditional exercises, the bilateral activation and
balance, and core series including abdominal and extensor- increased involvement of the core and lower extremity mus-
based tests to determine competency in this important part of culature during the performance of these exercises are clini-
the kinetic chain. Failure of these kinetic chain tests can guide cally recommended.
exercise prescription for both prevention and treatment of up- Figures 4 and 5 show two examples of the sustained hold
per extremity injuries in the overhead athlete. bilateral exercises recommended by Wilk et al. [47]. The 90/
90 external rotation exercise (Fig. 4a–c) starts with both arms
in 90° of external rotation with resistance applied by an elastic
band or tubing. While holding one extremity in an isometric
Application of the Kinetic Chain: Upper external rotation position as pictured, the contralateral extrem-
Extremity Rehabilitation Concepts ity performs 10–15 repetitions of slow controlled external ro-
for the Overhead Athlete tation. Upon completion of those extremity repetitions of ex-
ternal rotation, the contralateral extremity is then moved
Following the use of a comprehensive evaluation of the upper through 10–15 repetitions of external rotation. Finally, one
extremity and other key components of the kinetic chain for set of 10–15 repetitions is completed using a reciprocal acti-
the throwing athlete, several modifications to traditional exer- vation pattern (one rep left with isometric hold right, then one
cise programs can be undertaken to provide greater activation rep right with isometric hold left) to provide greater endurance
of the kinetic chain and incorporate proprioceptive and core training. Figure 5 a, b, and c show how the same patterning
challenges to the athlete while performing upper body can be used while the athlete is positioned over a physio ball
exercise. using the movement of prone horizontal abduction.
Wilk et al. [47] have recommended a more advanced form DeMay et al. [49] has demonstrated the effects of combin-
of upper extremity exercises that are characterized by bilateral ing different weight-bearing postures and positions on lower

Fig. 4 Bilateral sustained isometric 90/90 external rotation exercise: each Sustained hold 90/90 START. b Sustained hold R shoulder isometric. c
limb performs 90° abducted external rotation while the contralateral limb Sustained hold L shoulder isometric
maintains an isometric 90/90 position with scapular retraction. a
160 Curr Rev Musculoskelet Med (2020) 13:155–163

Fig. 5 Prone horizontal abduction sustained isometric exercise: each limb START. b Sustained hold R shoulder isometric. c Sustained hold L
performs horizontal abduction while the contralateral limb maintains an shoulder isometric
isometric position with scapular retraction. a Sustained hold horiz ABD

trapezius muscle activity during upper extremity shoulder ex- studies [50, 51•] have both advocated conscious correction
ercises. Their study has shown that unilateral stance and other and use of visual and tactile feedback to enhance muscle ac-
postures have an effect (both unilateral stance and bilateral tivation of the scapular stabilizing musculature during shoul-
stance) on lower trapezius muscle activation. Figure 6 shows der rehabilitation exercise. These studies demonstrate the im-
a unilateral stance external rotation exercise on a stability portance of using proper body positioning and especially
trainer that can be used to augment a traditional exercise for scapular positions to enhance muscular activation of the im-
external shoulder rotation in the overhead athlete. The use of portant scapular stabilizers that are a critical part of the kinetic
perturbation exercise is also added to provide additional chal- chain in the overhead athlete.
lenger to the athlete. Figure 7 shows the application of a core
challenge through the use of a side plank posture for the side
lying external rotation ball drop plyometric. Elastic resistance
is added to provide additional overpressure and challenge to
Summary
the exercise where 30–45 s time intervals are applied to foster
A review of the classic and more recent biomechanical studies
local muscular endurance.
on the throwing motion and tennis serve demonstrates the
A final component worth discussing regarding the use of
important interaction between segments of the kinetic chain
any kinetic chain exercise is the use of visual and tactile feed-
for optimal performance and injury prevention. A comprehen-
back to the athlete through clinical exercise supervision. Two
sive evaluation program for the overhead athlete that includes
key tests and measures to assess hip and core function is ad-
vocated. Finally, the inclusion of evidence-based modifica-
tions to traditional shoulder rehabilitation exercises can be
used to engage surrounding portions of the kinetic chain for
the overhead athlete.

Fig. 6 90/90 external rotation exercise with unilateral stance and distal Fig. 7 Side lying plank plyometric ball drop with band loop external
arm segment perturbation rotation loading
Curr Rev Musculoskelet Med (2020) 13:155–163 161

Compliance with Ethical Standards throwing motion, the role of the kinetic chain in throwing,
and the clinical evaluation and management of abnormal
throwing mechanics and related injury. Understanding the
Conflict of Interest Todd S. Ellenbecker & Ryoki Aoki declare that they
proper mechanics of the overhead throwing motion and the role
have no conflicts of interest.
of the kinetic chain in throwing is important when evaluating
overhead throwing athletes. When evaluating an overhead
Human and Animal Rights and Informed Consent This article does not throwing athlete, observation of overhead throwing mechanics
contain any studies with human or animal subjects performed by any of and examination of the kinetic chain and shoulder should be
the authors. performed. Level of evidence: Level 5.
14.• Kantrowitz DE, Trofa DP, Woode R, et al. Athletic hip injury in
Major League Baseball pitchers associated with ulnar collateral
ligament tear. Orthorp J Sports Med. 2018. https://doi.org/10.
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aim of this study was to characterize the prevalence of There was no significant difference in left-handed pitchers for
scapular dyskinesis in participants with shoulder pain as IR (p = 0.80, ES = 0.11) and ER (p = 0.56, ES = 0.15). When
compared with a matched control group without shoulder comparing youth with collegiate, IR increased in the stance
pain on prevalence of scapular dyskinesis. The scapular (2°) and stride (5°) hip, and an increase in the stance (5°) and
Curr Rev Musculoskelet Med (2020) 13:155–163 163

stride (5°) hip were present for ER as well. From collegiate to 48. Myers NL, Toonstra JL, Smith JS, et al. Sustained isometric shoul-
professional, IR increased in the stance (4°) and stride (3°) hip der contraction on muscular strength and endurance: a randomized
whereas a decrease in the stance (9°) and stride (12°) hip was clinical trial. Int J Sports Phys Ther. 2015;10(7):1015–25.
present for ER. The data suggests an increase in passive ROM 49. DeMay K, Danneels L, Cagnie B, et al. Kinetic chain influences on
from youth to collegiate and a decrease from collegiate to pro- upper and lower trapezius muscle activation during eight variations
fessional level. Level of evidence: cross-sectional study; Level 4. of a scapular retraction exercises in overhead athletes. J Sci Med
45.• Oliver GD, Weimar WH. Hip and shoulder range of motion in Sport. 2013;16:65–70.
youth baseball pitchers. J Strength Cond Res. 2016;30(10):2823– 50. DeMay K, Danneels L, Cagnie B, et al. Conscious correction of
7. https://doi.org/10.1519/JSC.0000000000000796 The purpose scapular orientation in overhead athletes performing selected shoul-
of this study was to measure and evaluate bilateral hip and der rehabilitation exercises: the effect on trapezius muscle activa-
throwing shoulder rotation PROM in youth baseball pitchers, tion measured by surface electromyography. J Orthop Sports Phys
to determine if there is any correlation between the throwing Ther. 2013;43(1):3–10.
shoulder and stance hip rotation PROM. Twenty-six youth 51.• Staker JL, Evans AJ, Jacobs LE, et al. The effect of tactile and
baseball pitchers were recruited and measured for bilateral verbal guidance during scapulothoracic exercises: an EMG and
hip and shoulder PROM. The youth baseball pitchers in this kinematic investigation. J Electromyogr Kinesiol. 2019. https://
study displayed similar PROM patterns as collegiate and pro- doi.org/10.1016/j.jelekin.2019.07.004 The purpose of this study
fessional baseball pitchers. Youth baseball pitchers in this study was to determine if clinician guidance changes scapulothoracic
presented strong relationships between hip and shoulder muscle activity and kinematics compared with unguided
PROM. Level of evidence: case-controlled study; Level 3. shoulder exercises with electromyographic (EMG) sensors
46. McCulloch PC, Patel JK, Ramkumar PN. Asymmetric hip rotation placed on serratus anterior, upper, and lower trapezius. The
in professional baseball pitchers. Orthop J Sports Med. 2014;2(2). study found that verbal and tactile guidance during exercises
https://doi.org/10.1177/2325967114521575. significantly increases shoulder muscle activity and improves
47. Wilk KE, Yenchak AJ, et al. The advanced throwers ten exercise lower trapezius/upper trapezius muscle recruitment. Level of
program: a new exercise series for enhanced dynamic shoulder evidence: case-controlled study; Level 3.
control in the overhead throwing athlete. Phys Sports Med.
2011;39(2). https://doi.org/10.3810/psm.2011.11.1943. Publisher’s note Springer Nature remains neutral with regard to jurisdic-
tional claims in published maps and institutional affiliations.