Effect of Intermittent Passive Stretching on Serial Sarcomere Loss Caused by Electrical Stimulation in Rabbit Triceps Surae Muscles

Abstract

Most individuals with Cerebral Palsy suffer from muscle spasticity. These involuntarymuscular contractions are caused by lesions in the brain which develop intohypoextensibility of joints. In a previous study, Tabary and Tardieu found a 25% lossof serial sarcomeres in guinea pig Soleus over 12 hours of electrical stimulation1. Thusthe hypoextensibility seen in patients may be caused by a decrease in serial sarcomerenumbers due to the chronic electrical stimulation. A current method of treatment forspastic Cerebral Palsy patients includes a passive stretch protocol adapted for eachpatient. In order to observe the effect of passive stretching treatments we conducted anexperiment on a New Zealand White Rabbit animal model (n=4). The experimental legs’Medial Gastrocnemius, Plantaris, and Soleus muscles were electrically stimulated atthe tibial nerve for 10 hours (20 Hz, 1.5-4.5 V). The stretch protocol employed includeda 5 min stimulation free passive stretch period every 55 minutes that dorsi-flexed andplantar-flexed the ankle joint alternatively for 2 seconds. The contralateral leg was usedas a control where the tibial nerve was transected to prevent any stimulation cross-overeffects. At the end of the experimental period, rabbits were euthanized and the hindlimbs were prepared for analysis through a muscle fixation and connective tissuedigesting process. Fascicles were then teased out from the target muscles and mountedon slides. Fascicle lengths were measured by a camera and software system andsarcomere lengths were examined through laser diffraction. Results showed a 9.42.8%serial sarcomere loss in the Medial Gastrocnemius, a 3.53.3% loss in the Plantaris,and a 14.710.6% loss in the Soleus. These results indicate that serial sarcomere loss isnot eliminated, but prevented to a certain extent.