Evaluation of Hip Muscles using Torque and Power- Velocity Relationships in Chronic Low Back Pain Subjects

Research Article

Phys Med Rehabil Int. 2015; 2(7): 1059.

Evaluation of Hip Muscles using Torque and Power- Velocity Relationships in Chronic Low Back Pain Subjects

Lemaire A1,2*, Lisembart A¹, Ritz M² and Rahmani A¹

¹LUNAM Université, Université du Maine, Laboratoire "Motricité, Interactions, Performance" EA4334, France

²Centre de l’Arche, Pôle Régional Spécialisé en Médecine Physique et Réadaptation, France

*Corresponding author: Lemaire A, Département STAPS, University of Maine, Avenue Olivier Messiaen 72085 Le Mans, France

Received: August 17, 2015; Accepted: September 22, 2015; Published: September 25, 2015


The aim of the present study was to evaluate hip muscles in chronic low back pain (CLBP) patients, thanks to the torque- and power-velocity relationships and to determine whether a possible imbalance can be related to the trunk muscles. Twelve CLBP patients and fifteen healthy subjects (Control Group, CG) participated to the study. CLBP and CG performed isokinetic trunk and hip flexions and extensions at several velocities. Mechanical parameters, such as theoretical maximal isometric torque (T0) and maximal power (Pmax) were extrapolated from torque- and power-velocity relationships. T0 and Pmax, were significantly higher in CG than CLBP (p<0.05), whatever the considered movement, showing a muscle weakness in CLBP. A significant difference was obtained between the two lower limbs for CLBP when considering Pmax during hip extension. Although no relationship was clearly observed between hip weakness and trunk weakness for CLBP, results obtained for CLBP could be attributed to a deconditioning syndrome and to muscle inhibition typically observed in these subjects. This study shows the importance to take hip muscle rehabilitation into account in CLBP support.

Keywords: Hip; Trunk; Low back pain; Isokinetic; Torque- and powervelocity relationships


CG: Control Group; CLBP: Chronic Low Back Pain; e: Extension; f: Flexion; Pmax: Maximal Power; Ppeak: Instantaneous Peak Power; T0: Theoretical Maximal Isometric Torque; Tpeak: Peak Torque


Chronic low back pain (CLBP) is characterized by a strength imbalance between trunk flexor and extensor muscles [1-3]. This imbalance is responsible for significant functional impairment [4-7] which should be treated with a complex rehabilitation program [8]. Trunk rehabilitation is essential for CLBP subjects [1,3]. Nevertheless, other muscles should be considered. In a previous study [9], observed relationships between lower limb and pelvis movement in CLBP. Indeed, people with low back pain who play rotation-related sports are able to move their lumbopelvic region with a greater extent and earlier during lower limb movements than people without low back pain. Recently, focusing our attention on the leg extensor muscles, we observed higher torque (19.2%) and power (19.8%) productions in healthy subjects compared with CLBP patients [10]. Even if no relationship was revealed between the weakness of the leg extensor muscles and the trunk imbalance in CLBP patients, it can’t be denied that these two statements are probably linked, and can be explained by a CLBP inactivity, a fear relative to daily activity movements, and finally to the CLBP deconditioning syndrome.

These previous studies suggest that lower limb and pelvis muscles must be considered in the management of CLBP rehabilitation. Some previous studies focused on lower limbs in CLBP [9-11]. However, to the authors’ knowledge, no study focused on hip muscles assessments, which are anatomically directly linked to the trunk muscles. Indeed several hip flexor and extensor muscles have their proximal insertions on the trunk [12]. Deconditioning syndrome that occurs on trunk muscles and its consequences on muscle properties [13] would also have an impact on hip muscles. This impact could probably also be linked to low back pain, since these muscles have an important postural and dynamic role especially at the lumbar spine [14].

The aim of the present study was then i) to evaluate hip flexor and extensor muscles torque production capacity using torque- and power-velocity relationships in both CLBP and healthy subjects, and ii) to determine whether a possible imbalance between the two sides in CLBP hip muscle strength can be related to the trunk muscles.



Twenty-seven subjects signed an informed consent to participate in this study. A control group (CG) was composed of fifteen healthy males with no prior history of low back pain. Healthy subjects were recruited in the rehabilitation centre or from a call for volunteers, and should respect the anthropometric characteristics (40.5 ± 5.0 years, 1.8 ± 0.6 m, 72.4 ± 8.7 kg) of the low back pain patients to allow group’s comparison. To also avoid any bias in the study, subjects of control group were not involved in any physical training.

Chronic Low Back Pain (CLBP) group was composed of twelve subjects (42.4 ± 7.4 years, 1.7 ± 4.5 m, 91.8 ± 29.6 kg) involved in a five weeks multidisciplinary rehabilitation program. This program was proposed by The Centre de l’Arche (Le Mans, France), following the Lombaction’s protocol from Angers (France) hospital. All the CLBP patients were recruited by the head clinician in charge of CLBP program of the rehabilitation center following the low back pain definition proposed by the French Society of Rheumatology (i.e., back pain for at least 3 months) [15]. For the present study, inclusion criteria for the CLBG patients were presence of chronic pain defined as a daily or almost daily pain for at least six months and a lumbar or lumbosacral pain before the start of the treatment. Selected patients had reported lower back pain for at least five years and had not been free of pain for a year. None of the subjects had any hip or lower limb injury or surgery, and no other associated pathology (e.g., multiple sclerosis, Guillain-Barre, muscular dystrophy, pelvic inflammatory disease). They were able to exert a maximal effort on isokinetic device. The rehabilitation program proposed at the Centre de l’Arche does not take into account current daily pain as an exclusion criterion. For the present study, exclusion criterion was a history of spine surgery. Testing was carried out in accordance with the ethical standards laid down in the 1964 Helsinki Declaration. Since the two groups presented a significant difference in weight values, results were normalized relatively to the subjects’ body weight in order to allow comparison between groups.


The protocol of the present study was carried out during three different sessions on three following different days. Both groups performed the same protocol. Trunk flexions and extensions were tested on day 1 and 2 respectively, as recommended by Ripamonti et al. [16]. Assessment of hip flexions and extensions was performed on the third day. Each measurement was done within a week following the admission of the CLBP patients in the CLBP program. To limit errors due to faulty equipment and inherent wrong measurement, all the measurements were realized by the same highly qualified investigator.

Trunk flexion and extension measurements: Trunk flexions and extensions were both conducted on a Biodex® isokinetic dynamometer (Model 900-240, Biodex Corporation, Shirley, NY, USA). Subjects were seated on a chair, with the dynamometer aligned bilaterally with the anterior superior iliac crests at the mid-axillary line of the trunk. The upper body was then strapped to the back of the chair equipped with three fixable pads at the head, the dorsal region and the bottom of the back. Legs were also strapped and positioned on the footrest with a maximal knee angle of 15 degrees to minimize leg involvement in trunk movements [17]. Subjects were asked to hold the trunk strap with their hands, without contracting the upper limbs. Upper limb muscles activity was not controlled by any device but one experimenter made sure that subjects did not use their upper limbs as an extra help to produce force. If any arm movement was observed, the trial was not recorded and was repeated after a rest period of at least 4 minutes. Once the subject position was properly established, mechanical stops were positioned to allow a range of motion of 60 degrees (from 90 to 30 degrees relatively to the horizontal axis). This amplitude was selected to prevent subjects working in non-conventional zones. This amplitude was recorded by the computerized monitor after the Biodex lever arm had been placed in front of the 90 and 30 degrees graduations around the rotation axis.

Trunk extensors and flexors were assessed on two different days. On the first day, flexor muscles were evaluated, whereas the extensor muscles were assessed at the same time on the following day. After a period of standardized warm-up (10 minutes warm-up on a cycle ergometer (50 watts at 50 to 60 rpm) each subject performed sub maximal trunk flexions and extensions before the testing session. During the test, subjects performed five contractions [18] at 120, 105 and 90 deg.s-1 and three at 75, 60 and 45 deg.s-1. Only the concentric part of the movement was considered. At a given preset velocity, subjects were asked to perform the concentric contraction as rapidly and forcefully as possible, and to return to their initial position without any effort during the eccentric phase (isokinetic velocity was then fixed at 300 deg.s-1). A one-second break was set between two consecutive contractions to avoid any possible influence of the eccentric part of the movement. A 4 minutes rest period was observed between two preset-velocity trials. Verbal encouragements were given to the participants during all trials.

Hip flexion and extension measurements: Hip flexions and extensions were conducted using a calibrated Biodex System 4 dynamometer (Biodex Medical Systems, Inc., Shirley, NY). The motor axis was aligned with the major trochanter of the femur. Subjects were lying on their back on the dynamometer with an angle of 15 degrees at the hip joints to prevent lordosis. Subjects were fastened with belts at the chest, pelvis and thigh to minimize the contribution of the body parts that were not supposed to be involved in the movement. Subjects had to keep their hands crossed on the chest. The thigh of the tested hip was attached to the level arm of the Biodex (Figure 1). The tested hip was attached to the lever arm of the dynamometer. If any compensation with the back was observed, the trial was not recorded and was repeated after a rest period of at least 4 minutes. The range of motion during hip flexions and extensions evaluation was fixed at 75 degrees, with a starting position corresponding to the leg extended at an angle of 15 degrees relatively to the hip joint (0 degree corresponding to a complete hip extension). The final position of the leg was defined for an angle of 90 degrees at the hip joint.