Diagnostic catheters based on fiber Bragg gratings (FBG's) are proving to be highly effective for measurement of the muscular activity associated with peristalsis in the human gut. The primary muscular contractions that generate peristalsis are circumferential in nature; however, it has long been known that there is also a component of longitudinal contractility present, acting in harmony with the circumferential component to improve the overall efficiency of material movement. While detection of the circumferential contractions has been possible using solid state, hydraulic, and pneumatic sensor arrays in the oesophagus and anorectum, there have been relatively few reports on the measurement or inference of longitudinal contractions in humans. This is partly due to the lack of a viable recording technique suitable for real-time in-vivo measurement of this type of activity over extended lengths of the gut. We report on the development of, and latest results from, catheter based sensors capable of detecting both forms of muscular activity. Results from validation trials of both circumferential and longitudinal FBG catheters during simultaneous recording and video analysis in lengths of excised mammalian colon are given. Preliminary data from human clinical trials in patients with functional gastrointestinal disorders of the colon are also presented demonstrating the ability of the fiber optic catheter technology to provide high resolution data from the complex and convoluted regions of the human gut below the stomach.