Inhibition of Knee Sensory Receptors does not affect Quadriceps Muscle Activity at Different Conditions of Patellofemoral Loading

Sensory receptors within joints provide the central nervous system (CNS) with information about the stress and strains in joint structures such as ligaments and menisci. How these joint sensory afferents are used by the CNS to generate motor commands is still poorly understood. In this study, we evaluate the hypothesis that the role of joint sensory afferents depends on the level of joint loading. To this end, we assessed the effect of temporarily inhibiting joint sensory receptors on quadriceps muscles activity during locomotion in the rat before and after paralysis of vastus lateralis, a perturbation that causes medial loading in the patellofemoral joint. The CNS compensated for the loss of vastus lateralis by gradually increasing the activity of vastus intermedius and rectus femoris over five weeks of adaptation. This strategy limits patellofemoral joint loading, suggesting that the CNS regulates internal joint stresses and strains. However, the temporary inhibition of knee sensory receptors did not cause significant changes in quadriceps muscle activity, both before and at any time point after paralysis. We therefore found no evidence for the existence of fast feedback loops mediated by joint sensory afferents, that depends on patellofemoral joint loading. Additional work is needed to investigate whether joint sensory afferents mediate long-term adaptation to joint stresses and strains.