Isometric contractile properties of the superficial (SDF) and deep digital flexor (DDF) muscles of the horse have not yet been reported. Our data along with muscle architectural characteristics may be used to explain the function of the SDF and DDF muscles in the horse, and provide essential information for computer model simulation studies. The right fore SDF and DDF muscles were tested in 4 adult Thoroughbred horses under general anesthesia. Ulnar and median nerves were instrumented with bipolar cuff electrodes for electrical stimulation, and the humerus was fixed to a rigid frame. The insertion tendons of SDF and DDF muscles were freed from the carpal retinaculum and severed distally. Each tendon was then connected with a metal clamp to a force transducer in line with an air cylinder and linear potentiometer for muscle pre-loading and force recording. Threaded pins were inserted through the radial and metacarpal condyles and attached to the frame to maintain isometric conditions. In all 4 horses, each muscle was incrementally pre-loaded and supramaximal stimulation conditions were identified after separate and combined stimulation of ulnar and median nerve. Passive and active forces and muscle elongation were then measured after supramaximal dual nerve stimulation (3 sec, 50 Hz). When ulnar and median nerves were electrically stimulated, a voltage of 2.5-5.0 V proved supramaximal with respect to force developed in SDF and DDF muscles. The median nerve elicited significantly greater forces in the DDF than SDF muscle. Dual supramaximal nerve stimulation of SDF and DDF resulted in peak isometric forces of 649 ± 95 N and 1467 ± 107 N respectively. Both ulnar and median nerve supply motor innervation to SDF and DDF muscles, but motor function of the DDF appears to be primarily mediated by median nerve activity. Measured peak isometric forces in both muscles were remarkably lower than predicted. Moreover, in-vivo peak isometric contraction occurred only after significant muscle preloading. One might speculate, that the discrepancy between observed and estimated muscle forces is not primarily experimental protocol related but rather to the muscle architecture (particularly regarding the number of muscle fibers working in series) and dynamic changes occurring during contraction. Elucidation of the exact mechanisms will require further investigation.
In-vivo study on forelimb superficial and deep digital flexor muscle isometric force characteristics in Thoroughbred horses.
ZARUCCO, Laura;
2000-01-01
Abstract
Isometric contractile properties of the superficial (SDF) and deep digital flexor (DDF) muscles of the horse have not yet been reported. Our data along with muscle architectural characteristics may be used to explain the function of the SDF and DDF muscles in the horse, and provide essential information for computer model simulation studies. The right fore SDF and DDF muscles were tested in 4 adult Thoroughbred horses under general anesthesia. Ulnar and median nerves were instrumented with bipolar cuff electrodes for electrical stimulation, and the humerus was fixed to a rigid frame. The insertion tendons of SDF and DDF muscles were freed from the carpal retinaculum and severed distally. Each tendon was then connected with a metal clamp to a force transducer in line with an air cylinder and linear potentiometer for muscle pre-loading and force recording. Threaded pins were inserted through the radial and metacarpal condyles and attached to the frame to maintain isometric conditions. In all 4 horses, each muscle was incrementally pre-loaded and supramaximal stimulation conditions were identified after separate and combined stimulation of ulnar and median nerve. Passive and active forces and muscle elongation were then measured after supramaximal dual nerve stimulation (3 sec, 50 Hz). When ulnar and median nerves were electrically stimulated, a voltage of 2.5-5.0 V proved supramaximal with respect to force developed in SDF and DDF muscles. The median nerve elicited significantly greater forces in the DDF than SDF muscle. Dual supramaximal nerve stimulation of SDF and DDF resulted in peak isometric forces of 649 ± 95 N and 1467 ± 107 N respectively. Both ulnar and median nerve supply motor innervation to SDF and DDF muscles, but motor function of the DDF appears to be primarily mediated by median nerve activity. Measured peak isometric forces in both muscles were remarkably lower than predicted. Moreover, in-vivo peak isometric contraction occurred only after significant muscle preloading. One might speculate, that the discrepancy between observed and estimated muscle forces is not primarily experimental protocol related but rather to the muscle architecture (particularly regarding the number of muscle fibers working in series) and dynamic changes occurring during contraction. Elucidation of the exact mechanisms will require further investigation.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
