AIMSPrevious studies using isolated strips of human detrusor muscle identified adjustable preload tension, a novel mechanism that acutely regulates detrusor wall tension. The purpose of this investigation was to develop a method to identify a correlate measure of adjustable preload tension during urodynamics. METHODSPatients reporting urgency most or all of the time based on ICIq-OAB survey scores were prospectively enrolled in an extended repeat fill-and-empty urodynamics study designed to identify a correlate of adjustable preload tension which we now call dynamic elasticity. Cystometric capacity was determined during initial fill. Repeat fills to defined percentages of capacity with passive emptying (via syringe aspiration) were performed to strain soften the bladder. A complete fill with active voiding was included to determine whether human bladder exhibits reversible strain softening. RESULTSFive patients completed the extended urodynamics study. Intravesical pressure (p(ves)) decreased with subsequent fills and was significantly lower during Fill 3 compared to Fill 1 (P=0.008), demonstrating strain softening. Active voiding after Fill 3 caused strain softening reversal, with p(ves) in Fill 4 returning to the baseline measured during Fill 1 (P=0.29). Dynamic elasticity, the urodynamic correlate of adjustable preload tension, was calculated as the amount of strain softening (or its reversal) per %capacity (average p(ves) between fills/%capacity). Dynamic elasticity was lost via repeat passive filling and emptying (strain softening) and regained after active voiding regulated the process (strain softening reversal). CONCLUSIONSImproved understanding of dynamic elasticity in the human bladder could lead to both improved sub-typing and novel treatments of overactive bladder. Neurourol. Urodynam. 36:1086-1090, 2017. (c) 2016 Wiley Periodicals, Inc.