Reliability and Validity of Hip Stability Isometric Test (HipSIT): A New Method to Assess Hip Posterolateral Muscle Strength.

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RELIABILITY AND VALIDITY OF HIP STABILITY ISOMETRIC TEST (HipSIT): A

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NEW METHOD TO ASSESS HIP POSTEROLATERAL MUSCLE STRENGTH

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Gabriel Peixoto Leão Almeida, PT, PhD Student1,2

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Helena Larissa das Neves Rodrigues, PT Student2

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Bruno Wesley de Freitas, PT2

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Pedro Olavo de Paula Lima, PT, PhD1,2,

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1Physical

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Fortaleza, CE/ Brazil.

Therapy Department, School of Medicine, Federal University of Ceará,

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2Knee

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This study was approved by the Ethics Committee at the Federal University of Ceará

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with protocol number 1.000.404

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This research was supported by PIBIC/CNPq. The funder had no role in study

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design, data collection and analysis, decision to publish, or preparation of the

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manuscript.

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--

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Corresponding author:

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Gabriel Peixoto Leão Almeida.

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Alexandre Baraúna Street, 949 – 1º andar – Rodolfo Teófilo;

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Postal Code: 60430-160; Fortaleza, CE, Brazil;

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Telephone: 55 85 33668632

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E-mail: [email protected]

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Manuscript word count: 3230

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Abstract word count: 248

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Research Group, University of Ceará, Fortaleza, CE/ Brazil.


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ABSTRACT

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STUDY DESIGN: Cross-sectional study.

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BACKGROUND: The HipSIT evaluates the strength of the hip posterolateral

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stabilizers in a position that favors greater activation of the gluteus maximus and

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gluteus medius and lower activation of the tensor fascia lata.

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OBJECTIVES: To check the validity and reliability of the Hip Stability Isometric Test

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(HipSIT) and to evaluate the HipSIT in women with patellofemoral pain (PFP).

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METHODS: The HipSIT was evaluated with a hand-held dynamometer. During

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testing the participants were side-lying, with the legs positioned at 45° of hip flexion

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and 90° of knee flexion. Participants were instructed to raise the knee of the upper

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leg while keeping the heels in contact. To establish reliability and validity, 49 women

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were tested, with the HipSIT, by 2 different evaluators on day one, and then again 7

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days later. The strength of the hip extensors, abductors, and external rotators were

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also evaluated. Twenty women with unilateral PFP were also evaluated.

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RESULTS: The HipSIT has excellent intra- and inter-rater reliability. The standard

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error of measurement was .01kgf/kg, and the minimal detectable change was .027

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kgf/kg. The HipSIT showed good validity in the isolated hip abduction, external

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rotation and extension (P < .01). Women with PFP showed a 10% deficit in the

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HipSIT results for the symptomatic limb (P = .01).

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CONCLUSION: The HipSIT showed excellent inter- and intra-rater reliability,

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moderate-to-good validity in women, and was able to identify strength deficits in

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women with patellofemoral pain.

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Keywords: hip, muscle strength dynamometer, reproducibility of results, validation

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studies.

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INTRODUCTION Studies3,

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have reported that excessive hip internal rotation and

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adduction range of motion (ROM) can be prevented by proper alignment of the lower

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limbs during daily activities and sports. The ability to maintain proper alignment

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depends on the strength and proper activation of the hip abductor, external rotator,

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and extensor muscles3, 8, 9. Weakness of these muscles in the lower limbs are found

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in different conditions such as osteoarthritis,5, 12 knee arthroplasty,23 patellofemoral

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pain (PFP),25,

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femoroacetabular impingement (FAI),20 ankle sprain,11 and low back pain,7 among

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others.

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anterior cruciate ligament injury,13 iliotibial (IT) band syndrome,21

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Hip abductor, external rotator, and extensor muscle strengths are evaluated

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separately.25, 31 However, the movements of the human body are three-dimensional

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(3D), and this method of evaluation does not reproduce the functional demands of

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the hip stabilizer muscles. Furthermore, proper implementation of isolated hip

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muscle strength testing requires repetitive training, testing, rest periods, and

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positioning adjustments for the tests.12, 23, 25 Clinically, these tests provide valuable

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information, but they are tiring for the patient, and their execution is time-consuming.

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The Hip Stability Isometric Test (HipSIT) was developed to allow a three-dimensional

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evaluation of gluteal muscle strength, which makes it more functional when

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compared to the uniplanar assessment of the hip muscles.

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Selkowikz et al.27 evaluated the electromyographic activity of the gluteus

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maximus (Gmax), gluteus medius (Gmed), and tensor fascia lata (TFL) in 11

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exercises. The authors found that the clam exercise produced the greatest

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electromyographic activation of the gluteus complex in relation to the TFL. This

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exercise is performed with the subject in the lateral decubitus position, lower limbs in


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45° of hip flexion and 90° of knee flexion. The individuals are instructed to separate

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their knees while maintaining contact between their heels, moving the superior hip

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into abduction, external rotation, and extension.27,

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based on the body’s position in the clam exercise.27, 33

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The HipSIT was developed

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A functional, reliable, valid, and quick test to assess the strength of the hip

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abductors, external rotators, and extensors could help clinicians and researchers in

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clinical decision making. The HipSIT offers a unique assessment of the strength of

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the entire posterolateral hip musculature without the need to evaluate each muscle

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alone. Thus, the objectives of this study were: 1) to assess the intra- and inter-rater

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reliability of the HipSIT and to evaluate its validity by comparing with isolated

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strength tests of the hip abductor, extensor, and external rotators, and 2) to

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determine whether the HipSIT can detect hip strength asymmetries in young female

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athletes with PFP.

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METHODS

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Participants

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This study was a cross-sectional analysis of 49 physically active women

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(Table 1). Recreational physical activity was defined as any physical activity in which

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a participant was engaged for at least 30 minutes per day or for at least 150 minutes

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per week.22 This group was selected to evaluate intra- and inter-rater reliability and

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the validity of the HipSIT. Data were reported according to the Guidelines for

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Reporting Reliability and Agreement Studies (GRRAS).14 In addition, the HipSIT was

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applied to 20 young female athletes with unilateral PFP. The inclusion criteria for the

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group with PFP were the following: pain specifically located around the

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patellofemoral joint; reproduced or reported pain with at least two of the following


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going up or down stairs, squatting, kneeling, sitting for prolonged periods, isometric

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contraction of the quadriceps, jumping, running, and pain on palpation of the lateral

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and/or medial facet of the patella; report of insidious onset of pain lasting at least

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three months; pain level of at least three on the visual analog scale (VAS) of pain

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during the last week2; and reporting a maximum of 86 points on the Anterior Knee

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Pain Scale (AKPS). The AKPS value was used to exclude patients with PFP without

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clinically relevant reduction of functional capacity and the minimal detectable change

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for the scale is 13 (maximum = 100 points).32 In both study groups, participants with

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the presence of trauma or surgery of the lower limbs and lower back, pain during

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testing, and neurological disorders that compromised the tests were excluded.

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All participants were from 18 to 30 years of age and were available for testing

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at the Human Movement Analysis Laboratory, Federal University of Ceará. Prior to

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participation, the objectives, procedures, and risks of the study were explained to

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each participant. This study was approved by the Ethics Committee at the Federal

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University of Ceará with protocol number 1.000.404. All of the participants provided

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written informed consent before participating in the study.

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Instruments

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An evaluation form containing questions related to anthropometric and clinical

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features, sporting activities, and injury history was administered. The Lower

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Extremity Functional Scale (LEFS)19 was applied to the population without PFP, and

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the AKPS10, 19 was applied to the population with PFP to assess the functional status

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of the lower limbs of the participants. The strength of the hip muscles was evaluated

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using a hand-held dynamometer (Nicholas Manual Muscle Tester; Lafayette

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Instrument Company, Lafayette, IN, USA).


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Lower Extremity Functional Scale was developed based on the model

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suggested by the World Health Organization (WHO). There are five possible

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responses (0–4) for each of the 20 questions, with possible scores from 0 (worst) to

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80 (best). This scale was culturally adapted to Brazilian Portuguese with excellent

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reliability and validity for knee injury patients.19

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Anterior Knee Pain Scale assesses pain and symptoms in patients with PFP.

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This scale was translated and culturally adapted to the Brazilian Portuguese

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language,10 and the score ranges from 0 (worst) to 100 (best).

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Muscle strength was evaluated using the hand-held dynamometer. This

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instrument has been widely used to measure muscle strength because of its ease of

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use. Studies have shown that this equipment has excellent intra- and inter-rater

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reliability and validity compared with the gold standard isokinetic dynamometer. 18, 28

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This method has good-to-excellent intra-rater and inter-rater reliability for

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measurement of hip strength.1, 26 The positioning of the hand-held dynamometer in

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this study was based on parameters established in the literature.1 Muscle strength

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(kgf) data were normalized by the body mass (kg) of each participant (strength

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[kgf]/body mass [kg]).

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Procedures

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The women participated in two sessions of data collection. In the first session,

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they completed the evaluation form and the specific questionnaires. In addition,

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HipSIT and isolated hip abductor, external rotator, and extensor muscle strengths

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were evaluated. In the first session, HipSIT was evaluated by two blinded evaluators

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(1A and 2). In the first session, the sequence of evaluation of the hip muscles was


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randomized using Random Allocation Software (v. 1.0.0). Participants were again

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evaluated with the HipSIT by only one evaluator (1B) after a week.

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To mitigate the influence of the rater, a strap was used for all tests.

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Participants were instructed to push the dynamometer as hard as they could for 5

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sec. They performed one practice trial, rested for 30 seconds, and then performed

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the measured trials. Two tests were performed with a 30 seconds rest between each

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trial. Mean values were calculated for each participant. Participants rested for one

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min before changing the muscle group. When compensation was identified, values

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were discarded, and a new evaluation was done after 20 sec.1

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The two researchers have three years of experience in measuring muscle

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strength of the lower limbs with the hand-held dynamometer. Before starting the data

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collections, the researchers held meetings to standardize verbal stimuli and

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positioning. The evaluators were blinded to the results of the HipSIT between

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themselves (inter-rater reliability) and between a first and second evaluation (intra-

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rater reliability). For HipSIT evaluation of patients with (PFP), the evaluator was

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blinded in relation to the symptomatic and asymptomatic limb.

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The HipSIT was performed with the participant in side-lying, with both legs

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positioned at 45° of hip flexion and 90° of knee flexion, with the limb to be tested

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superior to the opposing limb (Figure 1). The participant was instructed to lift the

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knee of the superior leg while keeping the heels in contact, such that the hip was in

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20º of abduction. The center of the dynamometer was laterally positioned 5 cm

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above the knee joint interline. After positioning, the proper performance of the test

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was demonstrated and the participant was asked to perform the movement with the

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greatest possible force by separating the knees without the feet losing contact.


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Isometric hip abductor force was measured with participants in side-lying, with

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the lower hip and knee positioned at 45º of flexion. The tested hip was abducted

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(20º) and extended (10º), and with neutral rotation (absence of internal or external

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rotation), the knee was extended. The dynamometer was positioned 5 cm proximal

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to the lateral malleolus midpoint.

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Isometric hip extensor force was measured with subjects in a prone position.

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The not to be assessed limb was fully extended, while the assessed limb was in 10º

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of hip extension, 10o of hip external rotation, and 90º of knee flexion. The

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dynamometer was positioned over the posterior thigh, 5 cm proximal to the popliteal

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crease.

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Isometric hip external rotator force was tested with participants in the sitting

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position, with the hip and knees flexed to 90º. The dynamometer was positioned over

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the distal-medial tibia, 5 cm proximal to the medial malleolus midpoint. Straps were

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used to prevent subjects from adducting the hip.

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The isometric hip posterolateral complex force consisted of the sum of the

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force values of the three hip stabilizer muscles, divided by 3 ([abductors + extensors

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+ external rotators] ÷ 3).1, 16

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Insert Figure 1

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Statistical analysis

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The normality of distribution of the data was determined by using the Shapiro-

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Wilk test. Descriptive statistics (mean and standard deviation) were used to describe

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the anthropometric and clinical characteristics and the outcome variables. The first

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step of the analysis was to calculate intra- and inter-rater reliability, which was done


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through the degree of consistency for intraclass correlation coefficients (ICC 2,1).

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Analysis of variance (ANOVA) was used to compare the means found in the three

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evaluations of the HipSIT that each subject was submitted (1A, 1B and 2).

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Reliability coefficients were interpreted as follows: < .69 indicated poor inter-

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rater reliability; .70–.79 indicated fair inter-rater reliability; .80–.89 indicated good

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inter-rater reliability; and .90 to 1.0 indicated excellent inter-rater reliability.6 We used

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three measures of agreement: the Bland and Altman plots, the standard error of

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measurement (SEM), and the minimal detectable change (MDC) with 95%

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confidence intervals (CI). The SEM was calculated by dividing the standard deviation

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(SD) of the mean differences between the two measurements by the square root of 2

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(SD differences ÷ √2), and the MDC was calculated using the formula of MDC = 1.96

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x √2 x SEM. The SEM reflects the absolute error of the instrument, and the MDC

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reflects the smallest within-person change in a score that can be interpreted as a

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‘‘real’’ change, above the measurement error of an individual. 30 Limits of agreement

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(LOA) were calculated as the SD of the individual differences between raters

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multiplied by 1.96. Both the SEM and MDC were also presented as percentages by

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dividing SEM and LOA by the average score of HipSIT 1A and 1B (subsequent

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week).

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Validity was analyzed using Pearson’s correlation coefficient to check the

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strength of the relationship between the HipSIT results for the force of the abductors,

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external rotators, extensors, and posterolateral complex of the hip, with coefficient

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values set as follows: < .5 indicated poor validity, .5–.75 indicated moderate-to-good

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validity, and > .75 indicated excellent validity. The Bland-Altman plots were designed

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in order to assess the agreement between HipSIT and other measures of hip

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strength.


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The PFP group was used to verify differences in HipSIT between the

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symptomatic and asymptomatic limbs. It was not used for comparisons between

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groups. The same statistical procedures were performed in patients with PFP by

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considering two assessments in sequence of the HipSIT. Finally, the paired t-test

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was used to compare HipSIT results between limbs with PFP and limbs without PFP

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in young female athletes. Significance was established at the 5% level for all

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statistics. Calculations were performed using SPSS version 17.0 for Windows

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(SPSS, Inc., Chicago, IL, USA).

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RESULTS

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Reliability and validity of the HipSIT

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The anthropometric and clinical features of the 49 women evaluated to

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analyze the reliability and validity of the HipSIT are presented in Table 1.

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Insert Table 1

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Insert Figure 2

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The values from the HipSIT of each subject are shown in Figure 2. HipSIT 1A

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represents the values obtained for first evaluator, HipSIT 2 shows the values

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obtained for the second evaluator and HipSIT 1B represents the third evaluation

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(retest) performed after one week by the first evaluator. Forty-nine subjects

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performed the HipSIT 1A and 2, and 46 performed HipSIT 1A and 1B. Analysis of

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variance (ANOVA) did not find significant differences between the three evaluations

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(P = .58).

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The intra- and inter-rater reliability of the HipSIT showed excellent reliability

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indices. The ICC2,1 intra-rater was .981 (CI 95%, .966–.99) and the inter-rater was

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.981 (CI 95%, .967–.989). The LOA ranged from -.047 to .025 (kgf/kg) for the intra-

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rater and inter-rater, as shown by the Bland and Altman plots (Figure 3). The SEM

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was .013 kgf/kg (4.7%), and the MDC was .036 kgf/kg (13.2%).

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Insert Figure 3

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The validity of the HipSIT with the isolated tests for abduction, external

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rotation, and extension of the hip showed good validity, with Pearson’s correlation

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coefficients equal to .535 (P < .01), .536 (P < .01), and .514 (P < .01), respectively.

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The validity of the HipSIT for the average of the three muscle groups assessed was

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.65 (P < .01) (Figure 4). The Bland-Altman plot between the HipSIT and the other

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variables of hip strength presented a mean difference from .04 to .12 (kgf/kg) (Figure

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5).

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Insert Figure 4

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Insert Figure 5

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HipSIT in women with patellofemoral pain

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The anthropometric and clinical features of young female athletes with PFP

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are shown in Table 2. The HipSIT showed excellent reliability indices between the

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first and second evaluation (ICC = .991 [CI 95%, .978–.997]) in women with PFP.

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The LOA ranged from -.030 to .039 (kgf/kg). The SEM was .012 kgf/kg (4%), and the

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MDC was .034 kgf/kg (11.4%). Compared to the limb with no PFP, the limb with PFP

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showed a 10% deficit in the results obtained in the HipSIT (P = .01) (Table 2).

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Insert Table 2

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DISCUSSION

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The results from this study supports that HipSIT is a valid test for evaluating

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the muscle strength of the posterolateral hip stabilizers, presented excellent intra-

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and inter-rater reliability, moderate-to-good validity in measurements of isolated

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muscle strength. The differences found between the HipSIT and the isolated hip

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strength tests are within clinically acceptable values as demonstrated by the Bland-

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Altman plot.

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The measurement of strength with the hand-held dynamometer is widely used

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in scientific research and clinical practice because it is easy to handle, is portable,

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and has good reliability and good validity compared with the isokinetic dynamometer,

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which is considered the gold standard for evaluations of strength.28 Studies15, 18 have

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shown that the hand-held dynamometer has good-to-excellent reliability for

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assessing the strength of the lower limb muscles, especially the hip muscles. The

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HipSIT also provides excellent levels of intra- and inter-rater reliability to assess the

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strength of the hip muscles. The SEM and MDC presented similar values for the

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populations with and without PFP. These parameters help in the evaluation,

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interpretation, and monitoring of the evolution when using the HipSIT as a measure

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of outcome.

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The physical position adopted in the HipSIT was based on the clam exercise

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and is suitable to evaluate the function of the Gmax and Gmed as hip stabilizers,

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decreasing the influence of the TFL,4,

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muscle of the hip.27 In this position, there is high electromyographic activity of the

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Gmax and Gmed muscles, with low electromyographic activity of the TFL.27 Willcox

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and Burden33 evaluated the electromyographic activity of the Gmax, Gmed, and TFL

27, 33

which is an important internal rotator


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using the clam exercise at three different degrees of hip flexion: 0°, 30°, and 60°. It

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was found that, in all three positions, the electromyographic activity of the Gmax and

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Gmed was higher than of the TFL. Moreover, Berry et al.4 compared the Gmax,

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Gmed, and TFL in subjects performing side stepping with a resistive band around

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the ankle while maintaining a standing position and in a squat. In the squatting

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position, the activation of the Gmax and Gmed was superior to the TFL. Therefore,

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the literature supports the use of the position adopted in our study.

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HipSIT is more practical for assessing the strength of the stabilizing muscles

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because it considers muscular action as 3D. Besides being a reliable test, it proved

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to be a valid test when compared with isolated measures of the extension,

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abduction, and external rotation of the hip and with the average of these three

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evaluations. However, HipSIT evaluates three hip muscle groups in concomitance;

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therefore, a deficit in only one muscle group may not be detectable because of the

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overlap of strength of the other muscle groups. For example, if the patient has

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weakness of the hip abductors and has adequate or superior strength of the external

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rotators and extensors, the HipSIT presents symmetrical data between the limbs.

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The differences found between the HipSIT and the isolated hip tests may be due to

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the changes in the patient's position during the isolated tests, because this

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influences the activation and the lever arm of the muscles.

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Weakness of the hip muscles has been associated with PFP. 25 We found a

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strength deficit of 10% in the HipSIT results for the limb with PFP compared to the

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limb without PFP. This is similar to findings in previous studies, 16, 24 where deficits

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ranged from 12%–27% in abductors, 7%–52% in extensors, and 5%–36% in external

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rotator muscles.


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The limitations of this study serve as guidance to determine future studies.

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Although evaluators were blinded to the symptomatic and asymptomatic limbs in

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patients with PFP, just knowing who has PFP can be considered a bias. Another

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limitation is that it was only evaluated in women, so it is unknown if the same results

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would be observed in men. Prospective cohort studies need to elucidate the HipSIT

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relationship with the development of lower limb injuries, especially PFP and injuries

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to the anterior cruciate ligament. The relationship of the HipSIT with biomechanical

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changes of the lower limb has not yet been evaluated. Such information can guide

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preventive and therapeutic approaches to lower limb injuries.

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CONCLUSION

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The HipSIT was found to have excellent intra- and inter-rater reliability in

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assessments of the hip muscles strength in women; good validity for measures of

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strength in the extensors, external rotators, and abductors of the hip; and the ability

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to identify strength deficits in women with PFP. In conclusion, the HipSIT can be

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widely used in clinical practice and scientific research because it is reproducible,

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valid, more functional and faster than other tests for analyzing each isolated plane of

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hip movement.

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KEY POINTS

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Findings: The Hip Stability Isometric Test was found to be a method with excellent

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reproducibility and good validity for measuring the strength of the extensor, external

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rotator, abductors, and posterolateral hip complex.

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Implications: The HipSIT is a more functional way of evaluating the strength of the

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hip-stabilizing muscles and is faster than assessing these muscles in three isolated

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planes of motion.

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Caution: We cannot determine a cause-and-effect relation of the HipSIT and injuries

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or infer its relationship with biomechanical abnormalities of the lower limbs.

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486

487

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Figure 1. Hip Stability Isometric Test.

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489 490

Figure 2. Crude data from the HipSIT 1A (first evaluator), HipSIT 2 (second

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evaluator) and HipSIT 1B (subsequent week for first evaluator). The horizontal axis

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shows each individual and the vertical axis show the recorded strength (kgf/kg) for

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each session.

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Figure 3. Bland and Altman plots for intra-examiner (A) and inter-examiner (B).

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HipSIT 1A (first evaluator), HipSIT 2 (second evaluator) and HipSIT 1B (subsequent

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week for first evaluator).

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499 500

Figure 4. Correlation between hip stability isometric test with A) hip abductor

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isometric test with (r = .535, P < .01); B) hip extensor isometric test (r = .514, P

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