Non-invasive isometric force measurement of plantar flexors in rats

Introduction: Isometric muscle force measurement is a sensitive marker for motor function recovery in rat nerve repair models. Current methods of eliciting maximal isometric force with nerve stimulation cannot provide longitudinal data. Methods: We developed a novel method for measuring isometric muscle force with a device designed to allow minimally invasive nerve stimulation and measurement of plantar flexion force. This indirectly elicited muscle force was compared with muscle force elicited by direct muscle stimulation in 3 surgical models. Results: The force measured after sciatic nerve transection and repair followed a parabolic trend. There was a postinjury decrease in force that continued until postoperative day 42, after which the force increased with time, indicating muscle reinnervation. Conclusions: This approach can track longitudinal changes in force in the most common animal model for studies of clinically relevant problems in the peripheral nerve field.