SUMMARY. The brachial plexus tension test (BPTT) is used clinically to test the dynamics of the neural tissues of the upper quadrant. The upper trapezius muscle and the nerves of the brachial plexus share common anatomical locations and are jointly affected by BPTT movements. This study investigated the relationship between the BPTT, upper trapezius muscle activity and range of neural tissue extensibility in asymptomatic subjects. Normal male subjects with greater and lesser neural tissue extensibility were tested. Results revealed that those with lesser neural extensibility exhibited significantly greater upper trapezius muscle activity during discrete BPTT stages. There was no difference between groups in the levels of pain perceived with the test. These results suggest that asymptomatic neural tissues are protected from stretch by muscle activity not solely mediated by pain but also possibly mediated by stretch receptors in neural structures. Copyright 1997 Harcourt Publishers Ltd.