Reliability of a test measuring transversus abdominis muscle recruitment with a pressure biofeedback unit

There are indications that segmental stabilising exercises (SSEs) are effective in the treatment of low back pain. The evaluation of successful training in SSE performance in patients requires a reliable outcome measure. The PRONE test gives an indication of the activity of the transversus abdominis muscle. Performed in prone lying using a pressure biofeedback unit, it has been used as an aid to training and to assess the subject's ability to perform SSEs correctly.

To evaluate inter-observer and test-retest reliability of the PRONE test.

Repeated measures by three observers on 2 days.

Department of Physical Medicine and Rehabilitation, Ludwig-Maximilian University, Munich, Germany.

Forty nurses (39 females and one male), aged between 24 and 62 years, with at least one episode of low back pain.

During the test, movement of the abdominal wall was monitored by measuring a change in pressure during muscle contraction termed 'abdominal hollowing'. Defined observation and palpation criteria were verified by the observers to ensure correct execution of the test.

Participants were tested on two separate days. On the first day, Observer A performed two similar test sets, each with four exercises. On the second test day, Observers B and C conducted one test set each.

This study found an intra-class correlation coefficient (ICC) of 0.47 [95% confidence interval (CI) 0.20 to 0.67] for inter-observer reliability, and an ICC of 0.81 (95% CI 0.67 to 0.90) for test-retest reliability. Kappa values and the limits of agreement were also calculated with similar results.

For this subject group, the PRONE test had relatively low inter-observer reliability but, as may be expected, higher test-retest reliability. It is suggested that by providing visual feedback, the PRONE test may enhance patients' insight into their deep abdominal muscle recruitment and thereby increase their motivation to exercise.