BARTIK, L.; UDOVICH, J.; RAGHUNAND, N.; GMITRO, A.F.; JOB, C.; KLEE, V.; WEINSTEIN, R.B.; Univ. of Arizona, Tucson: Simultaneous measurement of muscle force and 31P-magnetic resonance spectroscopy indicates a rapid recovery of inorganic phosphate in ghost crab extensor carpopodite.

Ghost crabs exercising to fatigue at a speed faster than their maximum aerobic speed (MAS) on a motorized treadmill exhibit a decline in arginine phosphate and a partial re-synthesis of arginine phosphate occurs during the first 2 minutes of recovery. We developed an optical force transducer to measure in vivo force production of the extensor carpopodite muscle during 31P-magnetic resonance spectroscopy (31P-MRS) to examine the time course of changes in high energy phosphates during stimulation. The apodeme of the extensor carpopodite was attached to a force beam to allow measurement of isometric force production. A reflected laser beam monitored deflection of the force beam. The optical force transducer produced a linear relationship between force input (14 to 1030 mN) and voltage output of a photo-sensing diode. The carpopodite extensor was stimulated in vivo at 3.0 Hz with a duty factor of 23% at 24C in the magnet. This stimulation protocol was selected to mimic a locomotor speed of 160% MAS. Peak force declined rapidly during the first minute of stimulation and was approximately 10% of its initial value after 4 minutes. At the end of the stimulation period, there was a decline in arginine phosphate and an accumulation of inorganic phosphate, a postulated causative agent of fatigue. The arginine phosphate and inorganic phosphate returned to their pre-stimulation levels within 2 minutes of recovery. The results of our in vivo 31P-MRS study suggests that fatigue from exercise at 160% MAS is correlated with an accumulation of inorganic phosphate in the extensor carpopodite and that recovery of inorganic phosphate is rapid. Supported by University of Arizona Prop. 301/Optics.