Effect of neuromuscular electrical stimulation on rat skeletal muscle architecture

Neuromuscular electrical stimulation (NMES) is a rehabilitation application frequently used in the clinic to improve muscle strength and function. However, the effect of NMES applied at different muscle lengths on muscle architecture is unknown. The aim of this study was to investigate the effects of NMES applied at medium and long muscle length on skeletal muscle architecture. Twenty-four rats were randomly divided into four groups (two NMES groups and two control groups). NMES was applied to the extensor digitorum longus muscle at long muscle length (170 in plantar flexion) and medium muscle length (90 in plantar flexion). A control group was formed for each NMES group. NMES was applied for 10 minutes a day, 3 days a week for 8 weeks. After eight weeks, muscle samples were removed at the NMES application lengths and examined macroscopically and microscopically using a transmission electron microscope and streo-microscope. Architectural features of the muscle including pennation angle, fiber length, muscle length, muscle mass, physiological cross-sectional area, fiber length/muscle length, sarcomere length, sarcomere number and muscle damage were then evaluated. An increase in fiber length and sarcomere number and a decrease in pennation angle were observed in both lengths (p<0,05). In the long muscle length group, muscle length increased (p<0,05), but diffuse muscle damage was observed. These results suggest that NMES intervention at long muscle length can increase muscle length but also cause muscle damage. Furthermore, the greater longitudinal increase in muscle length may be the result of a continuous cycle of degeneration-regeneration.