Rehabilitation Exercise Progression for the Gluteus Medius Muscle With Consideration for Iliopsoas Tendinitis An In Vivo Electromyography Study

Abstract

It is common for hip arthroscopy patients to demonstrate significant gluteus medius muscle weakness and concurrent iliopsoas tendinitis. Restoration of gluteus medius muscle function is essential for normal hip function.
A progression of hip rehabilitation exercises to strengthen the gluteus medius muscle could be identified that minimize concurrent iliopsoas muscle activation to reduce the risk of developing or aggravating hip flexor tendinitis
Descriptive laboratory study.
Electromyography (EMG) signals of the gluteus medius and iliopsoas muscles were recorded from 10 healthy participants during 13 hip rehabilitation exercises. The indwelling fine-wire EMG electrodes were inserted under ultrasound guidance. The average and peak EMG amplitudes, normalized by the peak EMG amplitude elicited during maximum voluntary contractions, were determined and rank-ordered from low to high. The ratio of iliopsoas to gluteus medius muscle activity was calculated for each exercise. Exercises were placed into respective time phases based on average gluteus medius EMG amplitude, except that exercises involving hip rotation were avoided in phase I (phase I, initial 4 or 8 weeks; phase II, subsequent 4 weeks; phase III, final 4 weeks).
A continuum of hip rehabilitation exercises was identified. Resisted terminal knee extension, resisted knee flexion, and double-leg bridges were identified as appropriate for phase I and resisted hip extension, stool hip rotations, and side-lying hip abduction with wall-sliding for phase II. Hip clam exercises with neutral hips may be used with caution in patients with hip flexor tendinitis. Prone heel squeezes, side-lying hip abduction with internal hip rotation, and single-leg bridges were identified for phase III.
This study identified the most appropriate hip rehabilitation exercises for each phase to strengthen the gluteus medius muscle after hip arthroscopy and those to avoid when iliopsoas pain or tendinitis is a concern.

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The American Journal of Sports
http://ajs.sagepub.com/content/39/8/1777
The online version of this article can be found at:
DOI: 10.1177/0363546511406848
2011 39: 1777 originally published online May 12, 2011Am J Sports Med
Marc J. Philippon, Michael J. Decker, J. Erik Giphart, Michael R. Torry, Michael S. Wahoff and Robert F. LaPrade
Tendinitis : An In Vivo Electromyography Study
Rehabilitation Exercise Progression for the Gluteus Medius Muscle With Consideration for Iliopsoas
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Rehabilitation Exercise Progression for
the Gluteus Medius Muscle With
Consideration for Iliopsoas Tendinitis
An In Vivo Electromyography Study
Marc J. Philippon,
*
yz
MD, Michael J. Decker,
§
PhD, J. Erik Giphart,
y
PhD, Michael R. Torry,
||
PhD,
Michael S. Wahoff,
{
PT, SCS, and Robert F. LaPrade,
yz
MD, PhD
Investigation performed at the Steadman Philippon Research Institute, Vail, Colorado
Background: It is common for hip arthroscopy patients to demonstrate significant gluteus medius muscle weakness and con-
current iliopsoas tendinitis. Restoration of gluteus medius muscle function is essential for normal hip function.
Hypothesis: A progression of hip rehabilitation exercises to strengthen the gluteus medius muscle could be identified that min-
imize concurrent iliopsoas muscle activation to reduce the risk of developing or aggravating hip flexor tendinitis
Study Design: Descriptive laboratory study.
Methods: Electromyography (EMG) signals of the gluteus medius and iliopsoas muscles were recorded from 10 healthy participants
during 13 hip rehabilitation exercises. The indwelling fine-wire EMG electrodes were inserted under ultrasound guidance. The aver-
age and peak EMG amplitudes, normalized by the peak EMG amplitude elicited during maximum voluntary contractions, were
determined and rank-ordered from low to high. The ratio of iliopsoas to gluteus medius muscle activity was calculated for each exer-
cise. Exercises were placed into respective time phases based on average gluteus medius EMG amplitude, except that exercises
involving hip rotation were avoided in phase I (phase I, initial 4 or 8 weeks; phase II, subsequent 4 weeks; phase III, final 4 weeks).
Results: A continuum of hip rehabilitation exercises was identified. Resisted terminal knee extension, resisted knee flexion, and
double-leg bridges were identified as appropriate for phase I and resisted hip extension, stool hip rotations, and side-lying hip abduc-
tion with wall-sliding for phase II. Hip clam exercises with neutral hips may be used with caution in patients with hip flexor tendinitis.
Prone heel squeezes, side-lying hip abduction with internal hip rotation, and single-leg bridges were identified for phase III.
Conclusion/Clinical Relevance: This study identified the most appropriate hip rehabilitation exercises for each phase to
strengthen the gluteus medius muscle after hip arthroscopy and those to avoid when iliopsoas pain or tendinitis is a concern.
Keywords: hip rehabilitation; electromyography; gluteus medius muscle; iliopsoas muscle
The gluteus medius muscle is one of the strongest lower
extremity muscles.
22
Appropriate strength of the gluteus
medius muscle has been positively linked to improved per-
formance.
1,14,19
A weak or fatigued gluteus medius muscle
results in excessive pelvic rotation and femoral internal
rotation,
23
consequently leading to pain or injury.
3,15,17,18
Proper strength and conditioning of this muscle is also
important because it influences hip,
2
knee,
3,15,16
and lower
back
17
function. Physical examination of patients with hip
pain often reveals weakness or inhibition of the gluteus
medius muscle and this strength loss increases after hip
surgery. Further, we have often found gluteus medius
muscle weakness to be accompanied by iliopsoas muscle
tendinitis and believe that these clinical entities may be
functionally linked.
Iliopsoas pain or tendinitis is common during postoper-
ative rehabilitation.
21
Although there is limited evidence,
it is plausible that the rehabilitation exercises addressing
gluteus medius weakness may also aggravate an inflamed
iliopsoas muscle. The selection of the appropriate exercises
*
Address correspondence to Marc J. Philippon, MD, Steadman Phil-
ippon Research Institute, 181 W Meadow Dr, Suite 1000, Vail, CO 81657
(e-mail: mjp@sprivail.org).
y
Steadman Philippon Research Institute, Vail, Colorado.
z
Steadman Clinic, Vail, Colorado.
§
Alignmed, LLC, Santa Ana, California.
||
Illinois State University, School of Kinesiology, Normal, Illinois.
{
Howard Head Sports Medicine, Vail, Colorado.
One or more authors has declared the following potential conflict of
interest or source of funding: This study was funded by the Steadman
Philippon Research Institute. The Steadman Philippon Research Institute
is a 501(c)(3) non-profit research organization funded in part by private
donations and corporate support from the following entities: Smith &
Nephew Endoscopy, Arthrex, Siemens Medical Solutions USA, Ortho-
Rehab, Ossure, Alignmed LLC, Opodix, Linvatec, and SBi. Neither the
donors nor the corporate sponsors to the Institute played a role in this
investigation. Individual authors have received royalties from Smith &
Nephew, Bledsoe, DonJoy, Arthrosurface, and SLACK Inc; are paid con-
sultants for Smith & Nephew and Arthrex; and/or hold stock or stock
options with Smith & Nephew, Arthrosurface, Hipco, and MIS.
The American Journal of Sports Medicine, Vol. 39, No. 8
DOI: 10.1177/0363546511406848
Ó 2011 The Author(s)
1777
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to strengthen the gluteus medius muscle, while reducing
activation of the iliopsoas muscle, is difficult because the
relative activation of these muscles during the perfor-
mance of hip rehabilitation exercises is currently
unknown. Therefore, our purpose was to investigate glu-
teus medius and iliopsoas muscle activity during hip reha-
bilitation exercises and design a continuum of gluteus
medius muscle exercises for progressive strengthening
that also recognizes iliopsoas muscle activation. Our
hypothesis was that a progression of hip rehabilitation
exercises to strengthen the gluteus medius muscle could
be identified that minimized concurrent iliopsoas muscle
activation.
METHODS
Participant Preparation
Ten healthy individuals (5 males, 5 females; age, 28.7 6
2.0 years; height, 1.72 6 0.04 m; weight, 67.4 6 4.3 kg) par-
ticipated in this study. All participants provided written
consent before participation, in accordance with the Insti-
tutional Review Board at the Vail Valley Medical Center.
Muscle activation of the gluteus medius and iliopsoas
muscles was measured during the performance of 13 hip
rehabilitation exercises. With use of a sterile technique,
fine-wire electrodes (0.07-mm Teflon-coated, nickel-
chromium alloy wire, VIASYS Healthcare, Madison, Wiscon-
sin) were placed intramuscularly via a 25-gauge needle into
the muscle bellies of the gluteus medius and iliopsoas
muscles. The intramuscular electrodes were inserted under
ultrasound guidance to ensure correct placement into the
muscle and for patient safety. The gluteus medius electrodes
were inserted approximately 1 inch distal to the midpoint of
the iliac crest. The iliopsoas electrode was inserted 2 finger-
breadths lateral to the femoral artery and 1 fingerbreadth
below the inguinal ligament. A radiologist who was blinded
to the study confirmed the locations of the electrodes from
inspection of the digital ultrasound pictures. The electro-
myography (EMG) signals were collected at 1200 Hz and
preamplified at the skin surface (Bagnoli-8, DelSys, Boston,
Massachusetts; common mode rejection ration [CMRR] .84
dB; input impedance .10 MO).
Experimental Protocol
The testing session began with a series of 3 isometric max-
imum voluntary contractions (MVC) for each muscle. The
3-second maximum contractions were interspersed with 3
to 5 seconds of rest. The MVC for the gluteus medius was
measured with the participant standing with slight hip
external rotation and abducting the hip as hard as possi-
ble. The MVC for the iliopsoas was measured with the indi-
vidual sitting on the edge of a table with full hip and knee
flexion and flexing the hip as hard as possible. The exam-
iner provided manual resistance and the consistency of the
participant effort was measured with a hand-held force
transducer (MicroFET2, Hoggan Health Industries, West
Jordan, Utah). The MVC trial was accepted if the 3 peak
forces fluctuated less than 5%.
The 13 exercises included the double-leg bridge, single-
leg bridge, prone heel squeeze, supine hip flexion, side-
lying hip abduction with internal rotation, side-lying hip
abduction with external rotation, side-lying hip abduction
against a wall, traditional hip clam, hip clam with hip in
neutral, resisted terminal knee extension, resisted hip
extension, resisted knee flexion, and stool hip rotation.
All exercises were completed in a slow, controlled manner
with the aid of a metronome to minimize EMG amplitude
variations attributable to differences in speed while per-
forming the exercises. The exercise order was randomly
selected for each individual, and each participant per-
formed 2 trials with 5 repetitions each.
The double-leg bridge began with the participant in the
supine position on an examination table with the feet flat
on the table and the knees and hips flexed to accommodate
the position of the feet. The participant extended the hips
and knees until the hips were in a neutral position and
the knees were flexed near 90° (Figure 1A). The partici-
pant then returned to the starting position by flexing at
the knees and hips.
The resisted terminal knee extension exercise started
with a bolster under the distal tibia and the knee flexed
to approximately 30°. The participant extended the knee by
contracting the knee extensor muscles while the examiner
provided resistance to the back of the knee (Figure 1B).
The examiner maintained resistance on the back of the
knee to flex the knee back to the starting position while the
participant resisted with the knee extensor muscles.
The resisted knee flexion exercise began with the leg
straight and resting on the examination table. The partic-
ipant flexed the knee by contracting the knee flexor
muscles while the examiner provided resistance to distal
end of the tibia (Figure 1C). The examiner maintained
resistance on the distal end of the tibia to extend the
knee back to the starting position while the participant
resisted with the knee flexor muscles.
The resisted hip extension exercise began with the knee
flexed to 90°, with the thigh resting on the examination
table. The participant extended the hip by contracting
the hip extensor muscles while the examiner provided
anterior resistance to the distal end of the posterior thigh
(Figure 2A). The examiner maintained resistance on the
distal end of the posterior thigh to flex the hip back to
the starting position while the participant resisted with
the hip extensor muscles.
The traditional hip clam exercise began from the side-
lying position with the non–test side on the examination
table with the hips and knees flexed to 45°. While the
inside of the heels remained in contact and in line with
the participant, the test leg performed hip abduction and
external rotation (Figure 2B). The participant returned
to the starting position by adducting and internally rotat-
ing the hip.
The hip clam with the hip in neutral began from the
side-lying position, with the non–test side on the examina-
tion table with the hips in neutral and the knees flexed to
90°, positioning the feet behind the participant. While the
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inside of the heels remained in contact, the test leg per-
formed hip abduction and external rotation (Figure 2C).
The participant returned to the starting position by
adducting and internally rotating the hip.
The stool hip rotation exercise was performed while
standing, and the knee of the test leg resting at 90° with
approximately 20% body weight on a rolling stool with
the hip externally rotated 30° (Figure 2D). The hip was
internally rotated through a 60° range of motion ending
at 30° of internal rotation (Figure 2E). The participant
returned to the starting position by externally rotating
through a 60° range of motion and ending at 30° of external
hip rotation.
The prone heel squeeze was performed with the partici-
pant prone on an examination table with the hips slightly
abducted, the knees flexed to approximately 70°, and the
inside of the heels touching together. The participant
pressed the heels together and slightly lifted the knees
off the table (Figure 3A). The position was held for 3 sec-
onds and then the participant slowly returned to the start-
ing position.
The side-lying hip abduction with internal rotation
exercise began from the side-4 lying position with the
non–test side on the examination table, the lower back in
a neutral position, and the hip of the test leg internally
rotated approximately 15°. Maintaining hip internal rota-
tion, the participant performed 30 ° of hip abduction (Fig-
ure 3B) and then returned to the starting position by
lowering the leg (hip adduction) to the starting position.
The side-lying hip abduction with external rotation exer-
cise was performed identically to the leg raise with internal
rotation, except the hip of the test leg was externally
rotated approximately 15° (Figure 3C).
The side-lying hip abduction against a wall exercise
began from the side-lying position with the non–test side
on the examination table, with the lower back and hips
in a neutral position and the backside of the body adjacent
to a wall. Maintaining neutral lower back and hip posi-
tions, the participant performed 30° of hip abduction while
the heel was continuously pressed into the wall via hip
extension (Figure 3D) and then returned to the starting
position by lowering the leg (hip adduction) and maintain-
ing constant heel pressure against the wall.
The single-leg bridge was performed identical to the
double-leg bridge exercise, but the hip of the non–test leg
was in neutral and the knee was extended throughout
both phases of the exercise (Figure 3E). Care was taken
to visually ensure that the hips remained level throughout
the performance of the exercise.
The supine hip flexion exercise began with the partici-
pant supine on the examination table with both legs
extended and lying flat on the table (Figure 4A). The hip
and knee of the test leg flexed while the heel moved prox-
imally on the table (heel slide). When the hip and knee
attained approximately 45° of flexion (Figure 4B), the
heel was lifted off of the table while the hip continued to
flex to 90° of flexion (Figure 4C). The participant returned
to the starting position by extending the hip to 45° and
allowing the heel to contact the table. The heel moved dis-
tally along the table while the hip and knee extended to
neutral positions.
The resisted terminal knee extension exercise, hip exten-
sion exercise, and knee flexion resistance exercise were
each performed with the participant prone on the examina-
tion table. The examiner provided moderate resistance
throughout the range of motion of each exercise.
For the purpose of recording the motions and to sepa-
rate the EMG signal into the 5 repetitions per trial and
Figure 1. Exercises recommended for phase I rehabilitation
after hip arthroscopy: A, double-leg bridge; B, resisted termi-
nal knee extension; C, resisted knee flexion.
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into the concentric and eccentric phases of each exercise,
kinematics were concurrently collected of the performed
exercises. Fifty-three retro-reflective markers were
attached to select anatomic landmarks in a modified Helen
Hays marker set.
11
A 10-camera motion analysis system
(Motion Analysis, Santa Rosa, California) captured 3-
dimensional marker trajectories. These marker trajecto-
ries were low-pass filtered at 10 Hz with a fourth-order
Butterworth filter and the marker that most appropriately
delineated the motion repetitions and phases was selected
for each exercise.
Analysis
All EMG data were processed with a 50-millisecond, root-
mean-square (RMS) moving window (1-millisecond incre-
ments) using custom software (MATLAB, The MathWorks,
Natick, Massachusetts). Maximum EMG reference values
that represented 100% MVC were calculated from the
MVC trials for each muscle by averaging the peak EMG
signal of the 3 MVC repetitions. The EMG data measured
during the rehabilitation exercises were analyzed to deter-
mine average and peak EMG amplitudes for each repeti-
tion and expressed as a percentage of the reference value
(% MVC). The peak EMG amplitude elicited from each
rehabilitation exercise categorized the intensity of muscle
activation as minimal (0%-20% MVC), moderate (21%-
50% MVC), or high (.50% MVC).
4
Descriptive statistics were calculated for peak and aver-
age EMG amplitudes for each phase of each exercise across
the 5 repetitions. These values were used to determine an
exercise continuum of gluteus medius muscle activation
and the activation ratio between the iliopsoas and the glu-
teus medius muscles. Exercise continuums were designed
for peak and average gluteus medius activation during
the concentric and eccentric phases.
4,5
Within each contin-
uum, muscle activity was rank-ordered by exercise and
regression analysis determined whether a significant lin-
ear increase was present (P  .05). The 4 regression anal-
yses (peak and average gluteus medius activation,
concentric and eccentric phase) were then incorporated
into an overall continuum with equal weighting given to
average and peak EMG amplitudes, and to concentric
and eccentric phases. The exercise that consistently eli-
cited the greatest EMG activity for the gluteus medius
muscle represented the top-ranking exercise.
An activation ratio was calculated for each hip rehabil-
itation exercise by dividing peak iliopsoas EMG amplitude
(% MVC) by the peak gluteus medius EMG amplitude (%
MVC). The higher the ratio, the higher the iliopsoas mus-
cle activation was in relation to the gluteus medius activa-
tion. Ratios greater than 1.0 indicated that the iliopsoas
muscle was activated more than the gluteus medius mus-
cle. Exercises were placed into respective time phases
based upon average gluteus medius EMG amplitude,
Figure 2. Exercises recommended for phase II rehabilitation
after hip arthroscopy: A, resisted hip extension; B, traditional
hip clam; C, hip clam with the hips in neutral; and D and E,
stool hip rotations (D, internal rotation end point; E, external
rotation end point).
Figure 3. Exercises recommended for phase III rehabilitation
after hip arthroscopy: A, prone heel squeeze; B, side-lying
hip abduction with internal rotation; C, side-lying hip abduc-
tion with external rotation; D, side-lying hip abduction against
the wall; and E, single-leg bridge.
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except that exercises involving hip rotation were avoided
in phase I.
RESULTS
Group means and standard errors for average and peak
EMG amplitudes for the gluteus medius and iliopsoas
muscles during the 13 hip rehabilitation exercises are
reported in Table 1. Peak gluteus medius muscle activity
ranged from 16% to 73% MVC and average gluteus medius
muscle activity from 3% to 35% MVC. The single-leg
bridge, the prone heel squeeze, and the side-lying hip abduc-
tion whether performed with internal hip rotation, against
a wall, or with external hip rotation were considered to
have high peak gluteus medius muscle activation (.50%
MVC). All other exercises demonstrated moderate gluteus
medius activation (21%-50% MVC) except the resisted
knee flexion and terminal knee extension exercises, which
demonstrated minimal activation (20% MVC).
Peak iliopsoas muscle activity ranged from 3% to 48%
MVC, while average iliopsoas activity ranged from 1% to
18% MVC. Supine hip flexion, side-lying hip abduction per-
formed against the wall, side-lying hip abduction with
external rotation, and hip clam exercises demonstrated
moderate iliopsoas muscle activation (.20%). All other
exercises demonstrated minimal iliopsoas muscle activity.
All regression analyses demonstrated a significant
increase in gluteus medius activation among the rank-
ordered exercises (P \ .05). The rank orders based on the
average and peak activations and the concentric and eccen-
tric phases were incorporated into an overall continuum
for gluteus medius muscle activity (Table 2). The side-lying
hip abduction performed with hip internal rotation and
prone heel squeeze had equal average rankings. The
higher rank was given to the side-lying hip abduction per-
formed with hip internal rotation because it had the great-
est peak gluteus medius EMG activity. Figure 5
demonstrates the peak and average muscle activation lev-
els for the gluteus medius for both the concentric and
eccentric phases of the exercises in the final rank-order.
The activation ratio for each exercise in final rank-order is
graphicall y illustrated in Figure 6. The activation ratio
ranged from 0.1 to 5.3. The prone heel squeeze, single-leg
bridge, and the side-lying hip abduction with internal rotation
had the lowest ratios of 0.1 (activation of the g luteus medius
muscle 10 times greater than the iliopsoas muscle). The
supine hip flexion exercise showed the greatest ratio (5.3).
DISCUSSION
A continuum of hip rehabilitation exercises was identified
based on in vivo gluteus medius muscle activation in healthy
individuals. In addition, supine hip flexion, side-lying hip
abduction with external hip rotation, and the hip clam exer-
cises were identified to also activate the iliopsoas muscle con-
siderably and should be avoided in the face of concurrent hip
flexor irritation. Therefore, the rank order for the remaining
exercises was found to be (from low activation to high activa-
tion): resisted terminal knee extension, resisted knee flexion,
stool hip rotations, hip clams with a neutral hip, double-leg
bridges, resisted hip extension, side-lying hip abduction
with heel against the wall, prone heel squeeze, side-lying
hip abduction with internal hip rotation, and single-leg
bridges. These exercises can be designated into a typical
phase I through III postoperative rehabilitation program.
Figure 4. Supine hip flexion exercise: A, initial position; B,
intermediate position following the heel slide; and C, final
position.
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The rank-ordered exercises are discussed here in the
context of hip rehabilitation following hip arthroscopy.
The goals of phase I of postoperative rehabilitation are to
ensure mobility of the joint and to minimize general mus-
cle atrophy, while also protecting the integrity of the
repaired structures of the joint. The goals of phase I were
TABLE 1
Peak and Average (With Standard Error in Parentheses) EMG Amplitudes for the Gluteus Medius and Iliopsoas Muscles
During the Concentric and Eccentric Phases of 13 Hip Rehabilitation Exercises
a
Concentric Phase Eccentric Phase
Exercise Muscle PA AA PA AA
Single-leg bridge GMD 72.5 (18.4) 35.1 (10.7) 51.1 (3.8) 24.0 (8.1)
ILI 6.3 (1.3) 2.5 (0.5) 6.0 (0.5) 2.1 (0.4)
SL hip abduction–IR GMD 65.8 (16.8) 33.3 (8.6) 44.1 (3.1) 20.1 (4.8)
ILI 9.2 (2.7) 3.6 (1.0) 10.3 (1.7) 3.3 (1.3)
Prone heel squeeze GMD 55.2 (15.2) 27.2 (8.4) 54.7 (4.7) 30.9 (9.0)
ILI 8.6 (4.6) 2.3 (0.8) 2.9 (0.2) 1.4 (0.3)
SL hip abduction–wall GMD 58.1 (12.9) 31.4 (7.1) 43.3 (2.6) 20.5 (4.2)
ILI 21.1 (6.4) 7.8 (3.0) 15.2 (1.6) 6.3 (2.5)
SL hip abduction–ER GMD 55.4 (14.1) 23.3 (5.6) 39.4 (3.6) 12.7 (2.9)
ILI 29.2 (8.0) 16.0 (5.6) 23.8 (2.4) 11.2 (2.9)
Resisted hip extension GMD 39.6 (6.3) 23.3 (3.3) 39.1 (1.7) 15.7 (2.4)
ILI 15.1 (4.8) 4.4 (1.1) 18.0 (2.3) 3.9 (1.0)
Traditional hip clam GMD 43.4 (13.0) 16.7 (4.3) 32.3 (3.4) 11.2 (2.9)
ILI 22.9 (4.4) 11.9 (2.6) 17.7 (1.0) 8.0 (2.2)
Double-leg bridge GMD 26.2 (7.7) 10.8 (2.8) 21.7 (1.7) 8.3 (2.0)
ILI 12.8 (5.0) 3.0 (1.0) 9.7 (1.0) 2.7 (0.8)
Hip clam–neutral GMD 28.4 (8.6) 12.5 (3.6) 17.9 (1.5) 6.3 (1.9)
ILI 18.0 (3.9) 7.8 (2.6) 14.3 (0.6) 4.8 (0.8)
Stool hip rotations GMD 22.9 (8.9) 6.7 (2.0) 21.7 (2.0) 7.9 (2.2)
ILI 12.4 (3.9) 3.4 (0.8) 11.7 (1.2) 3.5 (0.8)
Resisted knee flexion GMD 17.3 (4.3) 8.9 (2.4) 15.6 (1.2) 7.5 (1.8)
ILI 10.7 (3.1) 4.1 (1.2) 10.7 (1.0) 3.7 (0.9)
Supine hip flexion GMD 23.8 (13.5) 3.3 (0.8) 17.9 (2.9) 3.1 (0.7)
ILI 45.1 (11.0) 17.5 (3.9) 48.4 (5.3) 14.6 (4.3)
Resisted knee extension GMD 19.7 (4.9) 7.1 (2.0) 15.5 (1.3) 5.2 (1.1)
ILI 9.6 (3.7) 3.5 (1.2) 8.6 (1.2) 3.8 (1.7)
a
EMG, electromyography; GMD, gluteus medius muscle; ILI, iliopsoas muscle; PA, peak amplitude; AA, average amplitude; SL, side-
lying; IR, internal rotation; ER, external rotation.
TABLE 2
EMG Amplitude Ranks and Final Rank Order for Gluteus Medius Muscle Activation and
Final Rehabilitation Phase Assignment
a
Concentric Phase Eccentric Phase
Rehabilitation
Final Rank Exercise PA AA PA AA Phase
1 Single-leg bridge 1 1 2 2 III
2 SL hip abduction–IR 2 2 3 4 III
3 Prone heel squeeze 5 4 1 1 III
4 SL hip abduction–wall 3 3 4 3 II
5 SL hip abduction–ER 4 5 5 6 II
6 Resisted hip extension 7 6 6 5 II
7 Traditional hip clam 6 7 7 7 II
8 Double-leg bridge 9 9 8 8 I
9 Hip clam–neutral 8 8 11 11 II
10 Stool hip rotations 11 12 9 9 II
11 Resisted knee flexion 13 10 12 10 I
12 Supine hip flexion 10 13 10 13 I
13 Resisted knee extension 12 11 13 12 I
a
EMG, electromyography; PA, peak amplitude; AA, average amplitude; SL, side-lying; IR, internal rotation; ER, external rotation.
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early gluteus medius muscle reactivation and avoidance of
hip external rotation past 45° to protect capsular repair or
plication. Phase I ranges from the first 4 weeks after sur-
gery up to 8 weeks for a concurrent microfracture proce-
dure. During this phase, exercises to facilitate muscle
activity initially include isometrics, resisted terminal
knee extensions, and resisted knee flexion. These exercises
activate the gluteus medius minimally according to our
data. Exercises can be progressed by adding double-leg
bridges because of their controlled motion, moderate acti-
vation of the gluteus medius, and low iliopsoas activation.
After hip arthroscopy, hip extension and hip external rota-
tion are typically restricted during this phase and patients
are on crutches or partially weightbearing; therefore, exer-
cises that require these motions or weightbearing are
avoided during this phase.
In phase II (typically starting at week 5 or 9 after sur-
gery), the focus is on muscular stabilization of the hip
under relatively controlled conditions. The goals of phase
II were the addition of hip rotation exercises (short exter-
nal rotators) and to further develop gluteus medius muscle
strengthening to aid with activities of daily living. Stool
hip rotations can be initiated, because the patients are
now fully weightbearing. Hip clams either with neutral
or flexed hips and resisted hip extension are now started
to generate more gluteus medius muscle activation,
because hip external rotation and hip extension are
allowed starting in phase II. However, caution should be
exercised in cases where hip flexor tendinitis is present.
Increased gluteus medius activation may be provided by
side-lying hip abduction exercises with wall sliding.
Phase III exercises are designed to fully regain strength
in the hip joint musculature and to work on global lower
extremity strength. The goals of phase III were to work
on a full return of gluteus medius muscle functioning
with a plan to return to full sports or labor activities and
normalize cocontraction of the hip abductors and adductors
to avoid imbalance. Prone heel squeezes, side-lying hip
abduction with internal rotation, and single-leg bridges
can be started to activate the gluteus medius highly while
minimally activating the iliopsoas muscle. During this
phase, closed chain exercises such as various forms of
squatting, leg presses, and lunges are initiated to
strengthen the entire lower extremity.
One of most common exercises for strengthening the
gluteus medius muscle is hip abduction, either standing,
side-lying, or with some other variation.
2,8,10,15
The varia-
tions to the side-lying hip abduction exercise in the current
study with hip internal rotation, hip external rotation, or
sliding along a wall demonstrated high EMG activation
(.50% MVC of peak activation), supporting that these
Figure 5. Peak (A) and average (B) electromyography (EMG)
amplitude (%maximum voluntary contractions [MVC]) and stan-
dard errors recorded from the gluteus medius muscle during
the concentric and eccentric phases for 13 hip rehabilitation
exercises in the rank order of increasin g activity. ER, external
rotation; ext, extension; IR, internal rotation; SL, sidelying.
Figure 6. Activation ratio for the 13 hip rehabilitation exer-
cises calculated by dividing the iliopsoas peak activation by
the gluteus medius peak activation for each exercise. A
higher activation ratio indicates relatively increased iliopsoas
activation. ER, external rotation; ext, extension; IR, internal
rotation; SL, sidelying.
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are all good exercises to exercise the gluteus medius. The
variations of internal or external hip rotation may change
the mechanical advantage of the hip abductor muscles. The
gluteus medius muscle is made up of 3 parts of nearly
equal volume with 3 distinct muscle fiber directions and
separate innervations.
7,9
Thus, by rotating the hip, at least
1 portion of this muscle will have a mechanical advantage
to perform hip abduction. However, during external hip
rotation while performing hip abduction, the iliopsoas is
much more activated and therefore this exercise should
be avoided when flexor tendinitis is present.
The stool hip rotation exercise stimulated moderate glu-
teus medius muscle activity during both internal and
external hip rotation. With the pelvis stabilized and the
hip in neutral, the anterior and posterior portions of the
gluteus medius muscle internally and externally rotate
the femur relative to a stationary pelvis.
6
Conversely, the
gluteus medius muscle can also rotate the pelvis about
a transverse axis relative to a fixed femur.
9,20
Both of these
scenarios function to produce hip internal or external rota-
tion. However, the production of these rotary hip motions
when the pelvis is stationary would likely require lower
gluteus medius muscle activation because the mass of the
leg is considerably less than the upper body, and may
explain why the stool hip rotation exercise only demon-
strated gluteus medius muscle activity of 22% MVC. In
addition, the smaller hip rotator muscles should be active
during this exercise as well. This exercise may be the
most appropriate at the beginning stages of rehabilitation
when strengthening exercises are initiated.
Gluteus medius muscle activation was consistently the
lowest during the supine hip flexion exercise. This exercise
was performed in the sagittal plane with the patient
supine and was primarily controlled by the hip flexors.
The heel-sliding component required slight pressure of
the heel into the examination table and consequently eli-
cited moderate levels of gluteus medius muscle activation.
Core stabilization concurrent with hip flexion is the focus
of this exercise and large gluteus medius muscle activation
was not expected. This exercise provided a good reference
for the activation levels of the iliopsoas during the gluteus
medius exercises. For instance, the average iliopsoas activ-
ity during the side-lying hip abduction with the hip exter-
nally rotated was almost the same as during the supine hip
flexion exercise (16% vs 18% MVC, respectively, for the
concentric phase), while most other exercises were half
that activation or less.
This study also determined that iliopsoas activation was
increased for some hip strengthening exercises during the
early phase of rehabilitation, and therefore may poten-
tially aggravate any concurrent hip flexor tendinitis.
Supine hip flexion, the side-lying hip abduction performed
with external rotation, hip clams, and the side-lying hip
abduction performed against the wall demonstrated mod-
erate iliopsoas activation. Iliopsoas muscle activation was
elicited because these exercises either required hip flexion
or hip external rotation. It is unlikely that the performance
of these exercises after hip arthroscopy will cause hip
flexor tendinitis; rather, it is more probable that this clin-
ical issue would be present before surgery from the altered
movement patterns used to compensate for hip pain or
mechanical range of motion constraints.
12,13
In this study, the rehabilitation exercises were pre-
sented in the context of hip arthroscopy. However, these
data may also provide useful information for nonoperative
treatment or rehabilitation after other hip surgical proce-
dures. These other procedures may impose different func-
tional limitations and timing restriction (eg, different
restrictions on weightbearing) and, therefore, the exercises
may be assigned to other phases of the rehabilitation pro-
gram. However, the progression of muscle activation
remains applicable to the exercises as described. Another
limitation of this study is that the data were collected
using healthy individuals, who may or may not exhibit
the same muscle activation patterns as the patients under-
going the rehabilitation protocol after arthroscopy. It is
possible, particularly in early rehabilitation, that activa-
tion patterns may be altered. However, especially in the
later rehabilitation phases, the patients’ function is nearly
normal and activation patterns should become normal as
well. A study in patients postoperatively would elucidate
this issue and is recommended for future study.
SUMMARY
We identified a continuum of gluteus medius muscle acti-
vation for 13 common hip rehabilitation exercises and eval-
uated concurrent iliopsoas activation in light of iliopsoas
tendinitis, which is often present after hip arthroscopy.
Based on these data, we identified resisted terminal knee
extension and resisted knee flexion for early phase I and
double-leg bridges for later in phase I. For early phase II,
resisted hip extension and stool hip rotations, and later
the side-lying hip abduction exercise with wall sliding,
were identified as appropriate exercises. Hip clam exer-
cises with hip extension can be used with caution in case
of hip flexor tendinitis. Prone heel squeezes, side-lying
hip abduction with internal hip rotation, and single-leg
bridges are recommended for phase III.
ACKNOWLEDGMENT
We thank Tyler Anstett, Jacob Krong, and Daniel Peterson
for their invaluable assistance with this project.
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