MEASUREMENT OF SOFT-TISSUE STRAIN IN RESPONSE TO CONSECUTIVELY INCREASED COMPRESSIVE AND DISTRACTIVE LOADS ON A FRICTION-BASED TEST-BED

Purpose: To abstract the essential elements of chiropractic prone leg checking and subject them to controlled, experimental parametric testi ng. Design: Controlled, objective, repeated-measure analysis of the dy namic response of leg positions to distractive and compressive loading conditions. Setting: Research laboratory in a chiropractic college. P articipants: Twenty-five compression and 30 distraction subjects, most of whom were male, asymptomatic chiropractic students. Intervention: The subjects were lowered to the prone position on a table optimized t o detect dynamic leg positions, with separate sliding segments support ing each leg. A trial consisted of a 2-min control run, followed by tw o 2-min experimental runs in which compressive or distractive loads we re applied incrementally to the table-leg segments. Main Outcome Measu re: An optoelectric system measured realtime absolute and relative leg positions. Results: Right legs showed a greater average response than left legs under both distractive and compressive loads, and tended to respond more proportionately to incremental load increases. The avera ge response to compression exceeded the response to distraction. Both legs showed a greater average response in the second half of the trial s. Correlation of weights with responses was about four times greater in traction than compression. Conclusion: The functional short leg is confirmed as a stable clinical reality, a multitrial mean of unloaded leg positional differences. The prone leg check may be a loading proce dure, albeit unmeasured, that detects non-weight-bearing, functional a symmetry in loading responses. These probably reflect differences in l eft-right muscle tone, joint flexibility and tissue stiffness. The rel atively nonmonotonic, nonlinear quality of left leg responses is consi stent with asymmetric neurological responses.