Exercise to maximize hip musclse activation

Hip muscle activation and knee frontal plane motion during weight bearing therapeutic exercises.

Lubahn AJ, Kernozek TW, Tyson TL, Merkitch KW, Reutemann P, Chestnut JM. Int J Sports Phys Ther. 2011 Jun;6(2):92-103.

원문 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3109897/?tool=pubmed

As the kinetic chain concept has taken hold throughout the sports medicine community, it has become more and more important for the clinician to understand how to treat not only the injury itself, but accurately treat and identify discrepancies of the entire kinetic chain. Weakness of the hip musculature has been a common finding among athletes with knee injuries. Therefore, research identifying the most effective exercises to activate the hip musculature is of critical importance. The purpose of this study was 2-fold. First, to determine which of 3 exercises (double-leg squat, single-leg squat, front step-up) most effectively activated the hip musculature and allowed maintenance of a neutral frontal plane knee alignment. Second, to determine what effect a medial pull applied to the knees would have on gluteus maximus and gluteus medius activation, while attempting to maintain neutral frontal plane knee alignment. In this study, 18 healthy females participated (18 to 26 year old). For the double-leg squat a green theraband was placed around both knees, while a load of 15% body weight was applied in a medial direction to the knee via a cable column machine for the single-leg squat and front step-up. Hip muscle activation during the trial was measured with surface EMG. Frontal plane knee alignment was measured with high speed cameras. Data was collected from each participant’s dominant leg, which was defined as the leg that they used to kick a soccer ball. Each participant executed five repetitions of each exercise in the weighted and un-weighted conditions while keeping pace with a motronome set at 40 beats/minute. Each repetition lasted a total of 3 seconds. The participants were allowed to rest 10 to 15 seconds between reps and 45 to 60 seconds between each exercise. For the single-leg squat and front step-up exercises the subjects were allowed to use a vertical pole to maintain their balance.

Figure 1. Participant shown with marker set used for motion capture. Rigid shells with retroreflective markers were placed on the thigh and shank to measure peak movement of the varus/valgus knee motion during each exercise.

Figure 2. Participant performing a double-leg squat exercise.

Figure 3. Participant performing a double-leg squat exercise with medial knee resistance via a resistance band. Arrow depicts direction of pull on the knee.

Figure 4. Participant performing a front step-up exercise.

Figure 5. Participant performing a front step up exercise with an applied resistance to the knee via a cable column. Arrow depicts direction of pull on the knee.

Figure 6. Participant performing a single-leg squat exercise.

Figure 7. Participant performing a single-leg squat exercise with an applied resistance to the knee via a cable attached to a weight stack. Arrow depicts direction of pull on the knee.

The results of this study show that the single-leg squat, regardless of condition, elicited the highest muscle activation for both the gluteus maximus (47.4% maximum voluntary isometric contraction [MVIC]) and gluteus medius (65.6% MVIC). A previous study (Andersen, 2006) has stated that muscles must reach 40 to 60% of maximal effort in order for adaptive strength changes to be reached. The single-leg squat clearly reaches that, but the double-leg squat and front step-up fall short. With that being said, the authors don't rule out continuing to utilize the double-leg squat and front step-up in rehabilitative efforts. They(the double-leg squat and front step-up) suggest using these exercises to train the gluteal muscles for endurance. By utilizing these exercises in this manner, the patient should be able to limit the amount of excessive internal rotation that occurs at the hip while running, which can lead to patello-femoral pain syndrome. Adding a medial pull to the double leg squat exercise did increase the amount of muscle activation by 6% MVIC, but it did not increase with the single-leg squat exercise. A muscle activation decrease of 11.9% MVIC was seen in the gluteus medius during the loaded single-leg squat trial. Although, there was a pronounced decrease in muscle activation comparing the unloaded to the loaded gluteus medius trial, the muscle activation during the loaded condition was still better than the front step-up and double leg squat by 8% and 30% MVIC, respectively.

Table 1.

Two-way analysis of variance results and means (SD) for integrated gluteus maximus electromyography (EMG) during exercises with and without an applied load to the knee.

Exercise Type	No Applied Load Mean (SD)	Applied Knee Load Mean (SD)	Exercise Main Effect Mean (SD)
Double Leg Squat	21.7 (15.8)	27.7 (20.3)	24.7 (18.1)
Step-Up	36.4 (18.6)	34.4 (11.6)	35.4 (15.1)
Single Leg Squat	47.4 (21.2)	40.0 (17.6)	43.7 (19.4)
Load Main Effect Mean (SD)	35.2 (18.5)	34.0 (16.5)

Main Effect of Exercise (Double-Leg Squat, Step-Up, Single-Leg Squat) p = 0.000

Main Effect of Load (No Applied Load, Applied Load) p = 0.019

Interaction Effect of Exercise and Load p = 0.001

*Note: Data are expressed as a percentage of maximum voluntary isometric contraction (% MVIC * sec).

Table 2.

Two-way analysis of variance results and means (SD) for integrated gluteus medius electromyography (EMG) during exercises with and without an applied load to the knee.

Exercise Type	No Applied Load Mean (SD)	Applied Knee Load Mean (SD)	Exercise Main Effect Mean (SD)
Double Leg Squat	20.8 (14.7)	23.7 (16.3)	22.5 (15.5)
Step-Up	48.2 (20.4)	45.2 (21.7)	46.7 (21.1)
Single Leg Squat	65.6 (23.8)	53.7 (27.6)	59.7 (25.7)
Load Main Effect Mean (SD)	44.9 (19.6)	40.9 (21.9)

Main Effect of Exercise (Double-Leg Squat, Step-Up, Single-Leg Squat) p = 0.000

Main Effect of Load (No Applied Load, Applied Load) p = 0.019

Interaction Effect of Exercise and Load p = 0.001

*Note: Data are expressed as a percentage of maximum voluntary isometric contraction (% MVIC * sec).
 

Table 3.

Two-way analysis of variance results and means (SD) for peak gluteus maximus electromyography (EMG) during three different exercises with and without an applied load to the knee.

Exercise Type	No Applied Load Mean (SD)	Applied Knee Load Mean (SD)	Exercise Main Effect Mean (SD)
Double Leg Squat	22.0 (16.6)	25.8 (18.7)	23.9 (17.7)
Step-Up	33.5 (13.4)	37.8 (11.4)	35.7 (12.4)
Single Leg Squat	40.5 (16.8)	36.7 (11.2)	38.6 (14.0)
Load Main Effect Mean (SD)	32.0 (15.6)	33.4 (13.8)

Main Effect of Exercise (Double-Leg Squat, Step-Up, Single-Leg Squat) p = 0.000

Main Effect of Load (No Applied Load, Applied Load) p = 0.042

Interaction Effect of Exercise and Load p = 0.087

*Note: Data are expressed as a percentage of maximum voluntary isometric contraction (% MVIC).

Table 4.

Two-way analysis of variance results and means (SD) for peak gluteus medius electromyography (EMG) during exercises with and without an applied load to the knee.

Exercise Type	No Applied Load Mean (SD)	Applied Knee Load Mean (SD)	Exercise Main Effect Mean (SD)
Double Leg Squat	17.6 (10.4)	18.7 (11.1)	18.2 (10.8)
Step-Up	43.5 (14.4)	43.8 (20.1)	43.7 (17.3)
Single Leg Squat	47.5 (13.2)	40.0 (13.8)	43.8 (13.5)
Load Main Effect Mean (SD)	36.2 (12.7)	34.2 (15.0)

Main Effect of Exercise (Double-Leg Squat, Step-Up, Single-Leg Squat) p = 0.000

Main Effect of Load (No Applied Load, Applied Load) p = 0.019

Interaction Effect of Exercise and Load p = 0.026

*Note: Data are expressed as a percentage of maximum voluntary isometric contraction (% MVIC).

Table 5.

Two-way analysis of variance results and means (SD) for peak knee abduction angles (degrees) during exercises with and without an applied load to the knee.

Exercise Type	No Applied Load Mean (SD)	Applied Knee Load Mean (SD)	Exercise Main Effect Mean (SD)
Double Leg Squat	−4.1 (3.5)	−6.0 (2.6)	−5.1 (3.1)
Step-Up	−4.2 (3.8)	−10.2 (2.9)	−7.2 (3.4)
Single Leg Squat	−5.6 (4.0)	−9.2 (3.5)	−7.4 (3.8)
Load Main Effect Mean (SD)	−4.6 (3.8)	−8.5 (3.0)

Main Effect of Exercise (Double-Leg Squat, Step-Up, Single-Leg Squat) p = 0.011

Main Effect of Load (No Applied Load, Applied Load) p = 0.000

Interaction Effect of Exercise and Load p = 0.016

*Note: Data are expressed in degrees. Negative numbers depict knee abduction or valgus angles and positive numbers represent knee adduction or varus angles.

The authors believe that the load applied might have been too great and that postural compensations occurring during the exercises could possibly account for this decrease in muscle activation. This study also demonstrated that there is a significant increase knee abduction angle during each exercise whether there is medially directed load or not. This is important to note because the gluteal muscles help maintain proper frontal plane knee alignment which has been linked to ACL injuries, patello-femoral pain syndrome and iliotibal band syndrome. This study is clinically important for several reasons. First it clearly shows that of the 3 exercises the single-leg squat is the most effective exercise for recruiting the gluteus maximus and medius. By virtue of having increased muscle activity, as well as an increased knee abduction angle to work against, it is conceivable that the individual might be able to improve their knee mechanics during athletic activity and thus prevent future knee injuries. Once the exercises that best activate the hip musculature have been identified, the clinician can then institute them into training programs that focus on preventing knee injuries that result from overuse, deceleration and cutting. Are you addressing the hip in your injury prevention programs and if so, what types of outcomes are you seeing? What has and hasn't worked for you?

Written by: Mark Rice
Reviewed by: Stephen Thomas

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