Research Review By Dr. Shawn Thistle ©

Date Posted:

Sept. 2009

Study Title:

Gluteal muscle activation during common therapeutic exercises

Authors:

Distefano LJ, Blackburn JT, Marshall SW, Padua DA

Author's Affiliations:

Departments of Human Movement Science, Epidemiology, Exercise and Sports Science; University of North Carolina, USA.

Publication Information:

Journal of Orthopaedic & Sports Physical Therapy 2009; 39(7): 532-540.

Background Information:

Most manual therapists are well aware that proper gluteal muscle function is crucial for proper human movement (not to mention athletic performance). In the existing literature, weakness of the gluteal muscles has been associated with many lower extremity issues including patellofemoral pain syndrome (see Related Reviews below), iliotibial band friction syndrome, chronic ankle instability, and ACL sprains.

Functionally, weak gluteal muscles (we are speaking here about gluteus maximus [Gmax] and gluteus medius [Gmed]) may influence lower extremity joint loading patterns and dynamic control. Most commonly, gluteal weakness causes impaired control of dynamic knee valgus which results from hip internal rotation and adduction.

Further, weakness or inhibition of the Gmax can lead to hamstring substitution in hip extension, perhaps leading to premature fatigue, reactive shortening etc. (RRS Clinical Note from Shawn: If you’ve ever have a patient with chronic “tight” hamstrings, investigate their Gmax function – they may have what I call “lazy butt syndrome” – I’m pretty sure there is no reference for this, just an observation).

Since the Gmax and Gmed resist the above mentioned injurious motions and mechanisms, identifying appropriate and effective rehabilitation exercises to improve the function of these muscles is paramount. Such exercises should form a cornerstone of many lower extremity rehabilitation and injury prevention programs.

The literature to date has shown that such programs effectively improve strength and faulty movement patterns while reducing injury risk.

Therefore the goal of this laboratory study was to quantify and compare the EMG signal amplitude of the gluteal muscles during the performance of a variety of commonly used rehabilitative exercises. The overall goal was to establish a set of core exercises that efficiently activate the Gmax/Gmed muscles.

Pertinent Results:

See “Study Methods” below for detailed descriptions of the exercises:
  • there was a significant difference noted among the 12 exercises for Gmed activity (p < 0.0001)
  • the side-lying hip abduction exercise produced the highest EMG activation for Gmed (16% greater than the other “top tier” exercises), greater than both clam exercises, the 3 lunge variations, the forward hop and transverse hop
  • the single-limb squat also produced high Gmed activity
  • a significant difference was also noted among the 12 exercises for Gmax activity (p < 0.0001)
  • the single-limb squat and single-limb deadlift produced significantly higher Gmax activation than the lateral band walk, clams, forward and transverse hops
  • Gmax activity during the transverse lunge was higher than the lateral band walk
  • in a reliability analysis across 4 repetitions of each exercise, the ICC values for Gmed ranged from 0.93-0.98 with a standard error of measurement on EMG of 6-8%; for Gmax the ICC ranged from 0.85-0.98 with SEM of 5-9% - taken together this suggests moderate to high reliability across trials for both muscles
Previous literature on this topic has suggested that 50-60% MVC is required to achieve muscle strength gains – using this threshold, the exercises were divided into “tiers” of effectiveness:
  • Top Tier Exercises: single-limb squat and deadlift strongly activated the gluteal muscles, while the side-lying abduction, lateral band walk, and sideways hop strongly activated the Gmed

Clinical Application & Conclusions:

This study incorporated a number of exercises of variable difficulty, all of which used only body-weight, segment weight or tubing as resistance, making them easily applicable in many settings. It is one of the few studies that has investigated more advanced exercises that can be incorporated into advanced, later-stage rehabilitation or preventive programs.

The results suggest a “top tier” of 5 exercises that as a whole are most effective: the single-leg squat and deadlift strongly activate the Gmax and Gmed, while side-lying abduction, lateral band walks, and sideways hops strongly activate the Gmed. It is within reason that the addition of external weight to these exercises would further increase muscle activity.

The gluteus medius muscle concentrically abducts the hip, stabilizes the pelvis isometrically, and eccentrically controls hip adduction and internal rotation. The exercises mentioned here adequately incorporate these tasks. Further, exercises that involved single-limb support and large ranges of motion through hip flexion/extension stimulate the Gmax effectively.

Clinicians employing a comprehensive approach to many lower extremity conditions can utilize the information from this study to effectively design rehabilitation or preventive exercise programs.

Study Methods:

EMG was utilized in this study, and is frequently used to compare muscle activation levels between exercises (with the assumption that higher signal amplitude on EMG represents higher muscle activation).

In this study, 21 healthy subjects (average age 22, 9 males and 12 females) participated. Subjects were recreationally active (60 minutes of activity, 3 times per week) and had no current, symptoms, history of ACL injuries or recent (within 2 years) lower extremity surgery. They had to be able to perform all 12 exercises without pain.

After a short warm-up, subjects performed 8 repetitions of 12 exercises (they were allowed to practice before testing and the exercises were performed in random order) while surface EMG recordings were obtained from the Gmax/Gmed muscles. Two minutes of rest was permitted between exercises. With the exception of the multi-planar hop, exercises were performed with a metronome (both concentric and eccentric phases lasted 2 seconds). Maximum voluntary isometric contractions were also recorded to normalize the EMG data.

EXERCISES:
  1. Hip Clams - Two variations of this exercise were performed, using different degrees of hip flexion (60° or 30°). Clams were performed with subjects positioned side-lying on the floor, with their knees flexed 90°. Subjects abducted the top (dominant) knee off of the bottom knee while keeping their heels together and the ASIS facing forward.
  2. Side-Lying Hip Abduction - Subjects were positioned side-lying on the floor, in a starting position of full knee extension and neutral hip position. Subjects slowly abducted the hip of the top (dominant) limb, while keeping the knee in extension, the tibia and femur in a neutral transverse plane position, and the bottom limb stationary. Subjects stopped at 30° of hip abduction and slowly returned to the starting position
  3. Single-Limb Squat - Subjects started by balancing on their dominant lower extremity, with their knee and hip flexed approximately 30° and their hands on their hips. Subjects slowly lowered themselves toward the ground, using their ankle, knee, and hip joints, until they could touch their contralateral middle finger to the outside of their dominant foot without reaching with their shoulder. Subjects then returned to the starting position and were instructed to keep their knees over their toes to prevent a knee valgus position
  4. Single-Limb Deadlift - Subjects balanced on their dominant limb, with their knee and hip flexed approximately 30° and their hands on their hips. Subjects slowly flexed their hip and trunk and touched their contralateral middle finger to the ground beside their support foot, and returned to the starting position. Subjects were instructed to keep their knee flexed 30° when reaching for the desired level, to enable primarily trunk and hip flexion, and to keep their knees over their toes.
  5. Lateral Band Walks - An elastic band (resistance, 2.04 kg/30.5 cm of expansion) was tied around the subjects’ ankles while they stood upright with their feet together During the exercise, the subjects maintained their knees and hips in 30° of flexion. Subjects kept their hands on their hips and began with their feet together. Next, subjects sidestepped, leading with their dominant limb, a distance of 130% of their shoulder width (indicated by floor markings), assumed a single-limb stance on the dominant limb, and adducted their non-dominant limb to replicate the starting position. All subjects were instructed to keep their toes pointed straight ahead and their knees over their toes
  6. Multiplanar Lunges - Lunges were performed in the sagittal, frontal, and transverse planes. All 3 lunges started with the subjects standing with their feet near each other and hands on their hips. All lunges were performed with the dominant limb, keeping the trunk in an upright position, so that the knee and hip of the dominant limb flexed to 90°. This prevented the knee from moving anterior to the foot, and the knee of the non-dominant limb was maintained above the ground. Subjects were instructed to keep their knees over the toes for all lunges. Subjects lunged forward, sideways (towards their dominant side), and rotated towards their dominant side. During the transverse-plane lunge, subjects rotated 135° on their non-dominant limb towards their dominant side. Subjects twisted and lunged forward in this direction with consecutive motion.
  7. Multiplanar Hops - Similar to the lunges, hops were performed in the sagittal frontal, and transverse planes. Subjects started in the same position of the lunges and hopped in the desired direction off the non-dominant limb and landed on the dominant limb. The same directions used for the multiplanar lunges were used for the multiplanar hops as the subjects jumped forward, sideways, and rotated 135° toward the ipsilateral side. All jumps were performed off of the subjects’ non-dominant limb, landing on the dominant limb, and subjects jumped a distance of half of their body height in the appropriate direction. Subjects were instructed to land “as softly as possible,” with their knees flexed, and to keep their knees over their toes. They were also told to stabilize their body and balance upon landing for 3 seconds.

Study Strengths / Weaknesses:

This study was generally well done, but a few limitations should be kept in mind when interpreting and applying these results:
  • while EMG is a valuable tool, there are inherent limitations to its use as a sole indicator of muscle activity – cross-talk between muscles is an example which surface EMG is particularly prone
  • only healthy subjects were used for this study – the results may differ slightly if a clinical population was studied
  • EMG studies also rely on the assumption that high signal = high levels of motor unit activity needed for strength gains to occur
  • surface EMG data collection can be problematic during dynamic tasks – kinetic and kinematic data collection could have strengthened these results