2. Department of Biomechanics, Medicine and Rehabilitation of the Locomotor Apparatus, University of São Paulo, Brazil.
3. Ribeirão Preto of School Medicine, University of São Paulo, Brazil.
Background: The responses to the use of neuromuscular electrical stimulation (NMES) technique, once or twice a day, are not well described in literature. In this direction, we measured the biomechanical properties and morphological responses of NMES, applied once or twice a day to the gastrocnemius muscle of female rats after cast immobilization in comparison with both sham control and immobilized control groups.
Methods: Eighty Female Wistar rats (Body mass±SDg; 210±10g) were divided into five groups: Control (CG); Immobilized (IG); Immobilized then freed (IFG); Immobilized and subjected to NMES once a day (1ESIG) and another twice a day (2ESIG). All groups that suffered cast immobilization were kept in a shortened position for fourteen days, and then NMES was applied once or twice a day for ten consecutive days. The assessments included the mechanical properties of load and elongation at the limit of proportionality, as well as the resilience obtained from the load versus elongation graph. The crosssectional area (CSA), the different fiber type proportions and the perimisial connective area were measured.
Results: There was restoration of load at the limit of proportionality (LLP), but not resilience, in the 1ESIG and 2 ESIG, as well as restoration of atrophy (CSA) of type I (TIF), type II ad (TIIadF) and type IId (TIIdF) fibers in the 1ESIG, but not in the 2ESIG. An induction of the TIIcF proportions in the 1ESIG and 2ESIG, and a reduction of the TIIad in the 1ESIG were verified.
Conclusions: The muscle remobilization intensity can, influence the recovery responses postimmobilization either positively or negatively, for it was observed that NMES once a day can recover most mechanical (except resilience) and structural parameters of gastrocnemius muscle after casting, whereas twice daily, promoted deleterious effects to the much clearer muscles. Moreover, the animals` free movement allowed them to identify their own mobilization limits, which did not cause neither mechanical nor structural overload in the evaluated muscles.
Keywords: Immobilization, gastrocnemius muscle, electric stimulation, skeletal muscle