A clinical test of the function of the deep abdominal muscles was compared to a laboratory electromyographic (EMG) investigation of the contribution of transversus abdominis (TrA) to stability of the lumbar spine during limb movement. The two different functions of TrA were evaluated in 15 subjects. The subject group included six subjects with chronic low back pain and nine subjects with no history of low back pain so that the resultant recordings were spread over a wide range for each test. The clinical test involved quantification of the ability of the subjects to specifically displace the anterior abdominal wall in a way consistent with the function of the muscle. This was evaluated by use of a device designed to measure pressure reduction as the abdomen lifted off a transducer in the prone position. The laboratory test involved determination of the onset of contraction of TrA associated with rapid upper limb movement, measured using fine-wire EMG electrodes. The parameter evaluated was the latency between the contraction of TrA and the prime mover of the limb. Data were analysed both as absolute values and as ordinal data of a three-rating scale derived from criteria based on current knowledge of the response to both tests. No significant correlation was found between the absolute magnitudes of the pressure and timing data, however, comparison of the rating scale data indicated a significant relationship between the tests and associated high level of agreement between the two measures. The results of the study indicate that a reduction in the ability to draw in the abdominal wall is related to changes in the coordination of TrA, although the magnitude of the changes were not correlated. The degree of causality between these co-varying but independent manifestations of the function of TrA is uncertain.