Modified stabilization methods appear to be a valid and reliable substitute when standard method equipment is not available. These modified techniques may be utilized by clinicians of different sizes and in different settings. Many rehabilitation settings do not have tables that allow a belt to be wrapped under its surface, eliminating the possibility of using the original testing methods. Alternative methods, such as those used in this study, therefore, can be implemented reliably.
The ICCs for flexion and extension are considered moderate to excellent, respectively.17
Other studies' ICC values are higher because researchers used multiple measurements for each test.14,15
To prevent fatigue from interfering with the participants' best effort, time was measured only once for each method at weekly intervals. ICCs using average measures are consistently higher than those measures using single measurements.18
The authors of the current study are aware of only one other study that has investigated the correlation between the ST methods and any modification.16
Inter‐rater reliability for the modified testing procedures using a clinician in the same manner as the current study was 0.97 for extension and 0.93 for flexion. Correlation of endurance times for this modified testing16
with the ST procedure was 0.90 and 0.84 for extension and flexion, respectively. A limitation in the Reiman et al. study16
was that the clinician providing stabilization was always larger than the participant.
Concurrent validity of the MOD tests with the ST test was determined by the correlation between the extension and flexion times, respectively. The absolute value of validity is an accurate indicator of the extent of validity determined as follows: correlation coefficients >.80 indicate high validity, values between .60 and .80 indicate good validity, values between .40 and .59 indicate moderate validity, and values <.40 indicated poor validity.19
Thus, the values from this study show that modified methods are valid measures as efficient as compared to the gold standard (use of belts) and, therefore, may be used instead.
The reliability reported in the current study was lower than previously reported values.14
The testing method in the McGill et al study used only five participants tested consecutively for 5 days and then once 8 weeks later.14
The current study involved more participants (n=28) and fewer test sessions, which is more likely representative of clinical situations.
Although the clinician who provided stability is not the same as a static belt, no resistance on the part of the clinician was required. The clinician simply lay over the lower extremities (or sat on the feet in the case of flexion) and remained stationary, using his/her body mass as a stabilizing force throughout
the test. Neither the clinician nor the participants reported any adverse effects of this method. All of the participants subjectively reported that they were stabilized equally during all sessions.
There are a number of limitations in this study that warrant mention. Although these modified testing methods appear to be acceptable alternatives to the ST testing procedure in a normal, asymptomatic population, their applicability in LBP subjects is unknown. Trunk extensor20
muscle endurance times in subjects with LBP are less than those in the normal healthy population and it is unknown whether this would impact the reliability or validity of the methods. Trunk muscle endurance testing methods have been implemented in different LBP populations.22‐24
It remains to be determined whether the modified procedures will compare favorably in a symptomatic population.
The criterion for test termination for measuring flexion endurance was previously established as deviating from the 60‐degree angle.14,15
The authors of the current study determined, with pilot testing, that reliability was lower using the criterion of breaking the 60‐degree plane in any manner compared to the subject's breaking the plane by contacting the pre‐fabricated wedge. We believe the latter more clearly defines test termination. In pilot testing, it was often difficult to ascertain if the subject broke the 60‐degree plane throughout the entire spine. Many subjects would lose lumbar lordosis, yet appear to maintain the 60‐degree angle and not contact the wedge. Due to this potential complication in test termination criterion, which was also encountered by Chan,15
the authors decided on the termination criterion being when the subject contacted the prefabricated wedge. Although reliability was lower than the initial standardization studies,14
it was still high. The different criterion for test termination may be a factor for the differences seen between the current results and those of Chan14
and McGill et al.15
These modified techniques were found to be reliable methods of testing trunk endurance, allowing for potential use in research to determine normative values for different populations. Future research regarding modified endurance testing methods should investigate the size relationship between the clinician and testing participant in different populations. Determining the ratio of clinician to participant size needed for sufficient stabilization in order to achieve reliable outcomes could provide additional information.