Overview:

Testing of the trunk is limited on the 3 largest dynamometers on the market at the moment to flexion and extension of the lumbar spine. There have been trunk machines in the past which offered rotation and side flexion but they appear to have been phased out.

CSMI/Cybex offer a standing unit which attaches onto the Norm base and offers excellent stability and range of motion. A version of this unit (almost an identical version) is also produced by Con-Trex. Biodex have produced a unit which tests in the seated position.

Debate still rages as to whether the seated unit is a suitable test of the lumbar spine with articles appearing on both sides of the argument. As most people will simply have the one which comes with their machine often the point is academic as most machines are not purchased specifically for their back module. If you were to look for a machine specifically for lumbar spine testing then a standing unit would still be the first choice.

CSMI/Cybex have also had various lift testing units and the latest incarnation is based off the cable system on the latest Norm.

Testing Positions:

The standing position for trunk sagital plane testing is considered to be the gold standard of trunk measurement. The normal lumbar biomechanical actions are duplicated during both test and exercise. The system permits the natural reversal of the natural lumbar lordotic curve during flexion and then the return to lordosis during extension and even an increased lordosis during hyper-extension. This is thought to prevent abnormal stresses passing through the spine during isokinetic activity. More importantly the normal biomechanical functioning facilitates a natural set of contractile activity within the spinal muscular groups.

During the motions of flexion and extension there has been much debate int he literature as to the affect of the kinetic chain state. It is commonly accepted that a change in kinetic chain state has been found to affect the performance of the lumbar spine muscle groups under isokinetic conditions. A closed lower extremity results in higher figures in both flexion and extension peak torque outputs when compared to the seated position. Lumbar muscle torque production decreases as the lower extremity kinetic chain becomes more open i.e. a seated test with fixed feet will give an intermediary result between the highest expected figure in standing and the lowest expected figure in sitting with no foot support.

Standing position:

To view a set up video see below

Angular velocities:

The traditional velocity spectrum for flexion and extension in the trunk is 30-150 degrees per second. Studies have suggested that testing across a velocity spectrum is not necessary in the spine because physiological overflow readily occurs between the velocities (Timm,1987) with no statistically significant difference between single and multi- speed protocols observed (Timm, 1995)

Test range of motion:

Although there have been prescribed ranges of motion for trunk flexion and extension many studies have shown these to be not only arbitrary but not to reflect any definitive physiological requirement enabling an accurate test outcome. The accepted methods for testing the spine are normally deemed to be independent of spinal range of motion. Current convention is to test through a spinal range of motion that is comfortable and functional for the subject.

Interpretation:

Average performance deficit (APD).

APD is a method of spinal data interpretation that has demonstrated high levels of intra and inter-rater reliability. This method is practical because it based on reference criteria of 100% as being normal spinal muscle function (Timm, 1989). In this test 4 maximal repetitions are performed at each test speed with a 20 second rest interval between speeds. The procedure requires tests performed at 5 different speeds (30, 60, 90, 120 and 150). A final set of 20 repetitions is performed at 150 degrees per second. The formula for data interpretation can be seen next.

 

 Speed  30 60  90  120 150
  PT%BW PT%BW AP%BW AP%BW AP%BW
  TW%BW TW%BW TW%BW TW%BW TW%BW
          ER

Key:
PT%BW = Peak torque to body weight
AP%BW = Average power to body weight
TW%BW = Total work to body weight
ER = Endurance ratio

APD analysis

APD = 100% - average performance ratio

APR = (PT%BW 30 + PT%BW 60 + AP%BW 90 + AP%BW 120 + AP%BW 150 + TW%BW 30 + TW%BW 60 + TW%BW 90 +TW%BW 120 + TW%BW 150 + ER 150) / 11

This gives a percentage figure for APR which is subtracted from 100 and this number is the deficit in performance.

Muscle performance index (MPI)

MPI is a robust method for interpretation of spinal flexion and extension. MPI can be adapted to any testing protocol that uses 2 or more test speeds. The MPI is a comparative method for data analysis which makes it appropriate for patients with spinal problems as an increase in score from a retest indicates improvement whilst a decreased score indicates regression (Jerome et al, 1991). As with ADP MPI also uses a minimum of 4 maximal test repetitions at each speed and a minimum rest interval of 20 seconds between speeds.

MPI equation

MPI = (peak torque at the slowest test speed + peak torque at the next slowest test speed + average power at the fastest test speed + average power at the next fastest test speed + total work at the slowest test speed + total at the next slowest test speed + total work at the fastest test speed + total work at the next fastest test speed) / 8

Normative Values:

Age Range

Gender

Flexion

Extension

10-19 F 98 118
M 108 131
20-29 F 94 112
M 103 122
30-39 F 90 105
M 98 118
40-49 F 85 101
M 94 112
50-59 F 82 97
M 90 108
60-69 F 78 92
M 86 103
70-79 F 74 87
M 82 97