Overview:

Testing hip flexion and extension is becoming more popular. Largely because of the increase in hip arthroscopies. More research is available although it is often contradictory. 

Femoroacetabular Impingement (FAI):

Casartelli et al.(2012) described decreased isokinetic (and isometric strength tested on a isokinetics machine) muscle strength of the hip flexors in patients with femoral acetabular impingement syndrome (FAI), compared with controls. However, Diamond et al. (2015) and Brunner et al. (2016) did not find a difference. 

Falls:

Borges et al. 2015 showed that strength around the hip does not fall as rapidly when aging as strength around the knee (strength fell by on average 10% less in the hip).

Positioning:

These movements can be performed in either the lying, or standing positions.  

The hip has the same degrees of freedom (movements) as the shoulder, however, unlike the shoulder the hip is bound tightly to the pelvic girdle making it much more stable. This stability gives the hip virtually no intrinsic motion. This limits the hips motion in each plane. This stable configuration reduces the possible contraindications and compensations (posterior tilt in flexion) are limited and easily identifiable. The bony landmarks are easy to find and the range of motion can be used without limitation as injury is unlikely.

The actions of the hip muscles are complex and often change in relation to demands. Any functional motion requires a coordinated effort by several muscles which may participate in many different actions together or individually. The function of some muscles (Medial gluteal is a good example as the posterior section rotates the hip inwards whilst the anterior section can rotate it outwards) changes depending on hip position and whether the position is weight bearing or not.

Lying position:

The supine position has obvious limitations in that the leg can not cross the hips anatomical neutral position. This means extension is tested from flexion - back to neutral - and vice versa. This obviously leaves a significant section of the range of motion not tested at all. Even adding prone testing does not resolve this problem.

Having said that it is still the position used in the majority of the literature as it offers good stabilisation and controls the effects of gravity and limb pendular forces well.

Overall the most stabilised position for testing flexion but it limits extension unless the subject can get very close to the edge of the bed. Best for flexion research poor for extension.

 

hipflexlying

To view a set up video see below

Standing position:

It is claimed that the standing position is more functional and involves the use of gravity. If the knee is allowed to flex the resulting gravitational moment of the leg is lower than if the knee was fully extended and rectus femoris contraction may result in variations of the strength curve. However, flexion of the knee is recommended, although only passively against gravity if for no other reason than to avoid sciatic nerve traction.

Mohammad (2015) has shown that testing in standing is both reliable and for men at least offers more accurate measurements of strength at higher speeds.

In the standing position (see below) stabilization is difficult if not impossible (and probably undesirable). Testing in this position is more functional than that in the seated position and allows the investigation of extension. It is claimed that this is more functional and involves the use of gravity. Best for athletes.

hipflexstanding

To view a set up video see below

Stabilisation:

Lying: In the lying position stabilisation normally only involves a pelvic strap to prevent the torso from influencing the results and a leg strap for the opposite (non tested) leg.

Standing: Stabilistion in the standing position is not normally required as this is the most functional position.

Attachments:

The thigh stabiliser pad is normally used and should be positioned just proximal to the knee joint (see below).

hipflexlyingpositionpad

Axis of rotation:

The instantaneous axis of rotation is simply straight across from the greater trochanter to the axis of the dynamometer (as seen as the red line).

Anatomical zero:

With leg straight (as in standing).

Range of motion:

Unfortunately there is great discrepancy concerning the normal ROM of the hip in the saggital plane. A good example of this is Boone and Azen (1979) who found normal hip extension to be 10 degrees, whereas Dorinson and Wagner (1948) found it to be 50 degrees. The point of maximal isokinetic strength is another area of contentious debate. Callahan et al (1988), in a very comprehensive study, suggested that 45 degrees hip flexion is the point of maximum efficiency (for flexion and extension). Consequently, strength measurements should be made from 0 degrees flexion to 75 degrees flexion (and obviously back for extension). 

Gravity correction:

As the lever arm can be very long and heavy in these movements setting of gravity correction is essential.

Speeds:

Debate rages on this, however, slower velocities tend to be more comfortable but higher velocities are more reliable and offer a better insight into ratios.

Dos Santos Andrade et al. (2015) found ICC for peak torque in flexion and extension ranging from 0.55 to 0.76 (high reliability) at 150º/s. These were higher than the results at 30º/s

Mohammad (2015) also found high correlations at 180º/s again these were higher than the results at 60º/s

It seems the weight of modern evidence (on a new style dynamometer) is to use higher speeds.

Hip Flexion / Extension Protocols:

Muscles involved:

        Rectus femoris, psoas major, glute major and hamstrings

 

Strength Test Protocols General Patients Athletes Research
Contraction Cycle con/con con/con 

con/con

con/ecc 

con/con

ecc/ecc

Speed/s 30 up to 180 30/60/90 30-300 30-500
Trial Repetitions 0 0 3
Repetitions 10 10  10 5
Sets 3 4 up to 9
Rest between sets 20-30 secs 20-30 secs  20-30 secs 20 secs
Rest between speeds 2 minutes 2 minutes

2 minutes 

2-5 minutes
Rest between sides 5 minutes 5 minutes 

5 minutes 

5 minutes 
Feedback  nil nil  nil  nil 

 

Endurance Test Protocols General Patients Athletes Research
Contraction Cycle con/con con/con 

con/con

con/ecc 

con/con

ecc/ecc

Speed/s 90 60 90-300 90-500
Trial Repetitions 0 0 0
Repetitions Max Max Max Max
Sets 1 1 1
Rest between sets N\A N/A N/A N/A
Rest between speeds 10-15 mins 10-15 mins  10-15 mins 10-30 mins
Rest between sides 5 mins 5 mins  5 mins  5 mins 
Feedback  nil nil  nil  nil 

 

Strength Exercise Protocol General Patients Athletes
Contraction Cycle con/con con/con con/ecc
Speed/s 30 up to 180 30 up to 180 30-300
Trial Repetitions 0 0 0
Repetitions 10 10 14
Sets 6 6 up to 12
Rest between sets 30-60 secs 30-60 secs 30 secs
Rest between speeds 2 mins 2 mins 2 mins 
Rest between sides Nil Nil Nil 
Feedback bar bar bar

 

Endurance Exercise Protocol General Patients Athletes
Contraction Cycle con/con con/con con/con
Speed/s 120-180 90 90-300
Trial Repetitions 0 0 0
Repetitions Max Max Max
Sets 1-3 1 1-3
Rest between sets 5-10 mins N/A 5-10 mins
Rest between speeds 10-30 mins N/A 10-30 mins 
Rest between sides Nil Nil Nil
Feedback bar/pie chart bar/pie chart bar/pie chart

 

Notes:

Test the uninvolved or dominant limb first.

Stabilisation difficult.

 

Interpretation:

In the hip it is normal to look at the ratio between the right and left sides there should be a 0-10% difference between the sides. Anything beyond this would indicate a muscle imbalance which would be best corrected.

Eccentric results are generally 30% higher than concentric within the same muscle.

Concentric/concentric ratio; flexion/extension 0.60% this means the flexors are only 60% of the extensors or the other way around is the extensors are 40% stronger than the flexors

Angle of peak torque for flexion and extension is 45 degrees flexion according to Callahan et al (1988),

Labral Tear:

The curve will reach a peak before the point where the labrum inhibits the muscles. The inhibition is due to the pain but once beyond the range where the affected part of the labrum is stressed the torque will return giving a second peak. This M shaped curve can be biased towards the beginning or end of the curve dependent on where the damage is.

Please note absence of a curve does not necessarily indicate a normal labrum.

Concentric hip flexion shown.

Hiplabrumflex

Normative values:

Smith et al. (1981) Age Sex Machine ftlbs peak ftlbs peak
speed deg/s 22-24 m   Flexion Extension
30       128.3 204
180       83.9 149.8
           
Poulmedis et al. (1985) 28 M      
30       132 198.4
90       95.1 153.4
180       70.1 119.5
           
Nicholas et al. (1989) non trained        
30 20-30 M   77 98
30   F   55 83
           
Tippett (1986) 20 M      
60 dominant       105 200
60 non dominant       118 191
           
Alexander (1990)   M      
180 concentric     145.3 230.1
180 eccentric     177.7 268.5
180 concentric F   107 171.1
180 eccentric     129.8 205
           
Tippett (1986) 20 M      
240 dominant       69 173
240 non dominant       70 174
           
           
Biodex Values N/A M Biodex PTBW Goal PTBW Goal
45 supine       40-52 63-82
300       10-13 34-44
    F      
45       38-50 57-77
300       7-9 28-37
flexion/extension ratio %  

Dominant

flex/ext%

Smith et al (1981) M 24yrs  
30   0.64
180   0.59
     
Alexander (1990) M 22yrs  
30 concentric   0.74
30 eccentric   0.75
180 concentric   0.59
180 eccentric   0.66
30 concentric F 20yrs 0.79
30 eccentric   0.74
180 concentric   0.65
180 eccentric   0.65
     
Poulmedis (1985) m 28yrs  
30   0.66

 Hip flexor and extensor concentric strength (based on Cahalan et al 1989)

 

Female

Male

 

20-40 yrs.

40-81 yrs.

20-40 yrs.

40-81 yrs.

Flexion

       

30/sec

91

67

152

113

90/sec

70

46

126

84

Extension

       

30/sec

110

101

177

157

90/sec

97

70

163

132