Research Review By Dr. Demetry Assimakopoulos©

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Date Posted:

November 2013

Study Title:

Improvements in hip flexibility do not transfer to mobility in functional movement patterns

Authors:

Moreside JM & McGill SM

Author's Affiliations:

Dalhousie University, Halifax, Nova Scotia; University of Waterloo, Ontario, Canada.

Publication Information:

Journal of Strength & Conditioning Research 2013; 27(10): 2635-43.

Background Information:

Two of the most frequently cited goals for patient/client care in rehabilitation and fitness settings are improvement in hip flexibility, and an increase in core strength/coordination/control. The perception is that attaining these goals will prevent injury. However, it is uncertain as to whether or not these changes in flexibility and strength are transferred to the overall function of the individual, as little evidence exists, showing that combined improvements in hip mobility and core endurance are reflected in day-to-day functional activity. It may not be enough to just increase the capacity of the patient/client by achieving these gains. It might actually be necessary to also focus on changing the preferred movement pattern that produces a given movement. This study sought to understand just that: establish if improvements in passive hip ROM and core endurance would result in changes in hip and spine motion during the performance of functional movements.

Pertinent Results:

The 24 accepted individuals were assigned to 1 of 4 groups for the duration of the 6 week protocol:
  1. Hip stretching only
  2. Hip stretching and hip/spine dissociation exercises
  3. Core endurance and hip/spine dissociation exercises
  4. Control
Group 1 and 2 experienced an increased range of motion in hip extension, internal rotation and external rotation. However, there were no significant increases in hip extension or rotation utilized during dynamic/active activities. Actually, the average peak active hip extension decreased an average of 2.2° and 0.8° in groups 1 and 2, respectively.

Similarly, there was no evidence of increased hip ROM being utilized during the elliptical and twist/reach trials. Rather, total hip rotation decreased by 2.3° and 1.6° in groups 1 and 2, respectively while using the elliptical. The twist and reach trials saw similar results for groups 1 and 2: a decrease of 4.6° and a very small increase of 0.4°, respectively.

Lumbar rotation associated with active hip extension was the only instance where lumbar motion changed significantly across groups, post-intervention. The largest change was experienced by group 2, who received both stretching and hip/spine dissociation exercises. They decreased their active lumbar rotation from approximately 8.3° to 4.2°. Group 2 also experienced a 7° decrease in side-bending during the twist and reach maneuver.

Conversely, group 1(stretching only group) experienced an increase in lumbar extension during the active hip extension trials; they demonstrated an average of 9.2° of lumbar extension while actively extending their hips pre-trial, and increased this amount to 15.1° post-trial.

Group 3 showed the most consistent increase in active/dynamic hip ROM overall. In 7 out of the 8 hip ranges of motion measured, group 3 demonstrated increased dynamic ROM utilized, with 6 out of the 8 measuring higher than groups 1 or 2 post-intervention.

Clinical Application & Conclusions:

Large increases in passive hip extension were achieved with training, but did not cross over to functional activities, such as active hip extension or lunging. The two stretching groups averaged less hip extension post-intervention while performing a lunge, hip extension and while performing elliptical training activities, although, not significantly so. Both stretching groups decreased the amount of hip extension utilized during active hip extension activities, while at the same time, increasing the associated lumbar extension after the 6 week trial. In these individuals, while they may have been trying to increase absolute hip extension ROM, they did not have the ability to differentiate between hip and spinal motion during the active hip extension task (in spite of performing exercises which were supposed to train this).

In addition to having difficulty separating hip extension from lumbar spine extension, many of the participants also had difficulty constraining total lumbar sagittal motion during functional tasks post-training. However, all intervention groups showed less lumbar rotation during the active hip extension maneuver.

This study appears to be one of the first to suggest that increasing a patient’s capacity by increasing the available ROM of a joint as well as core strength may not translate into function, or change a ‘default’ movement pattern. While stretching and core endurance protocols are incorporated into many rehabilitation and training programs, the evidence of whether or not measured improvements transfer into day-to-day function is lacking. In this study, large improvements in passive hip extension and rotation did not result in greater use of the newly-established ROM into functional activities that challenge these motions.

The results shown by group 3 (core stabilization group) indicate that improving proximal stability might increase distal mobility to a greater extent than simple stretching and hip/spine dissociation exercises (1). In spite of improved core endurance resulting in decreased lumbar rotation during a hip extension maneuver, no reduction in total flexion/extension movement during other activities was found.

Many of the subjects had difficulty differentiating hip motion from spinal motion when doing an active hip extension maneuver. Thus, it may be necessary to practice producing peripheral joint motion on a stable trunk (such as a bird dog). Overall, a successful stretching or core endurance program may require simultaneous movement re-patterning (through practicing the desired movement), to ensure the increase in mobility or core endurance is incorporated into the functional movement pattern of the individual.

Study Methods:

250 potential male participants between the ages of 19-30 were screened for hip range of motion deficits. Included individuals were those who demonstrated hip mobility less than the 50th percentile, ideally in both extension and total rotation (IR plus ER of the hip), based on the normative data published previously by this group (2). Accepted individuals were assigned to one of 4 groups for the duration of the 6 week protocol:
  1. Hip stretching only
  2. Hip stretching and hip/spine dissociation exercises
  3. Core endurance and hip/spine dissociation exercises
  4. Control
To determine if changes in total hip range of motion transferred to changes in functional movement, both hip and spinal motion were monitored during 4 activities, including:
  1. Active hip extension in upright standing: specifically, given to observe peak ROM, together with any associated spinal extension and/or rotation.
  2. Forward lunging from the standing position: floor was marked at a distance 1.5x the shin length in front of the left foot. Instructions were to step forward with the left foot until their toe reached the marker, and to lunge forward into left hip flexion and right hip extension. They were to maintain full right knee extension. The researchers wanted to see the peak sagittal motion of the hip and back.
  3. Standing twist and reach: participants were asked to reach for a pole positioned at their side. They were asked to touch a small knob attached to the pole at waist height with their left hand, should the knob be on their right side, and with their right hand, should the knob be on their left side without moving their feet. The researchers were attempting to focus on hip and lumbar rotation with associated hip/spine flexion, and lumbar side-bend.
  4. Exercising on an elliptical trainer.
These dynamic activities were performed with minimal guidance, other than to make sure to keep the body erect at all times. Each action was performed twice.

All included participants were measured before and after the 6 week protocol. Each activity challenged either rotation or extension of the hip and/or spine during a functional activity. Foot and hand position were standardized. The researchers measured various outcomes depending on the task, including dynamic hip flexion/extension and rotation, and peak lumbar spine flexion, extension, rotation and side bending.

The participants also exercised on an elliptical trainer for 30 minutes at a speed between 40-70 cycles per minute. They utilized a 66 cm stride length at a speed 30% faster than the self-selected speed of the participant, with their hands holding onto the oscillating handles. Four cycles were captured for analysis.

Motion was captured at a frequency of 60 Hz. Reflective markers were attached to the shin, thigh, foot, hand, upper arm and overlying the midline of the posterior pelvis, T12 and forehead. The data was processed to determine 3-dimensional lumbar and hip angles relative to the pelvis. Symmetry was assured for the elliptical and twist trials; the right leg was used for the analysis. Joint angles at the hip joint for the forward lunge and hip extension were calculated at the moment of peak joint motion. For instance, in the left forward lunge, spine and right hip angles were measured at the moment of peak hip flexion. Also, during the right hip extension trial, angles were calculated at the moment of peak right hip extension.

Repeated measures ANOVA were performed for each dependent variable (relevant spine and hip angles), for pre/post treatment within each condition and between subject grouping factors. Paired t-tests were conducted on individual pairs of pre and post results, with Boneferroni adjustments.

Study Strengths / Weaknesses:

Strengths:
  1. Movements that were measured pre and post were standardized for each included individual, and were measured kinematically.
  2. Established and recent normative data from this research group were used to establish cut-off points for inclusion of individuals in this study.
Weaknesses:
  1. Small, apparently healthy subject cohort.
  2. Only males were included in this study.
  3. The hip/spine dissociation and core strength exercises were not described in this study, making it difficult to replicate.

Additional References:

  1. Kibler WB, Press J, & Sciascia A. The role of core stability in athletic function. Sports Medicine 2006; 36: 189-198.
  2. Moreside JM. & McGill SM. Quantifying normal 3D hip ROM in healthy young adult males with clinical and laboratory tools: Hip mobility restrictions appear to be plane-specific. Clin Biomech 2011; 26: 824-829.