Low levels of anterior tibial loading enhance knee extensor reflex response characteristics

Abstract

We examined whether neuromuscular reflexes were altered with anterior loads applied to the tibio-femoral joint. A ligament testing device was modified by attaching a reflex hammer to a steel mounted frame to illicit a patellar tendon tap, while anterior directed loads displaced the tibia on the femur. Five trials were acquired while anterior-directed loads (20, 50, 100 N; counterbalanced) were applied to the posterior tibia between 20 N pre (20 N Pre) and post (20 N Post) baseline conditions on two different days. Surface electromyography (sEMG) recorded mean quadriceps ( Q) and hamstring ( H) reflex time ( R Time = ms) and reflex amplitude ( R Amp = %MVIC). A load cell on the anterior tibia measured the timing (KE Time = ms) and amplitude (KE Amp = N) of the knee extension force, and was used to calculate electromechanical delay (EMD = ms) and peak knee extension moment (KE Mom = N m/kg). Data from 19 recreationally active subjects revealed good to excellent response consistency between test days and between baseline conditions for R Time, R Amp, KE Time and KE Amp. With anterior tibial loading, R Time was faster at 50 N vs. 20 N Post, and R Amp was greater at 20 N Pre vs. 20 N Post ( Q and H) and at 50 N vs. 100 N ( Q only). KE Mom was greater at 20 N Pre and 50 N vs. 20 N Post, and EMD was shorter at 50 N vs. 20 N, 20 N Pre and 20 N Post. These results suggest that knee extensor reflex responses are enhanced with low (50 N) but not moderate (100 N) anterior loading of the knee.