Effect of knee joint angle on motor unit synchronization

Abstract

Activity of the vasti has been argued to vary through knee range of movement due to changes in passive support of the patellofemoral joint and the relative contribution of these muscles to knee extension. Efficient function of the knee is dependent on optimal control of the patellofemoral joint, largely through coordinated activity of the medial and lateral quadriceps. Motor unit synchronization may provide a mechanism to coordinate the activity of vastus medialis (VMO) and vastus lateralis (VL), and may be more critical in positions of reduced passive support for the patellofemoral joint (i.e., full extension). Therefore, the aim of this study was to determine whether the degree of motor unit synchronization between the vasti muscles is dependent on joint angle. Electromyographic (EMG) recordings of single motor unit action potentials (MUAPs) were made from VMO and multiunit recordings from VL during isometric contractions of the quadriceps at 08, 308, and 608 of knee flexion. The degree of synchronization between motor unit firing was evaluated by identification of peaks in the rectified EMG averages of VL, triggered from MUAPs in VMO. The proportion of cases in which there was a significant peak in the triggered averages was calculated. There was no significant difference in the degree of synchronization between the vasti at different knee angles (p ¼ 0.57). These data suggest that this basic coordinative mechanism between the vasti muscles is controlled consistently throughout knee range of motion, and is not augmented at specific angles where the requirement for dynamic control of stability is increased. ß

Influence of knee alignment on quadriceps cross-sectional area

“…The quadriceps femoris, a knee extensor muscle, plays the most important role in leg muscle training and functions to stabilize the patella, as well as to flex the knee joint (Mellor and Hodges, 2006;Panagiotopoulos et al, 2006). Imbalance between the vastus medialis (VM), which pulls the patella inward, and the vastus lateralis (VL), which pulls the patella outward, may cause patellofemoral pain syndrome (PFPS) (Fredericson and Yoon, 2006;Sakai et al, 2000).…”

The Effects of a Neoprene Knee Sleeve on Subjects With a Poor Versus Good Joint Position Sense Subjected to an Isokinetic Fatigue Protocol

“…The cutaneous stimulation of this tape seems even to have an impact on muscle recruitment. 27 In the present study, there was a decrease of proprioceptive input, caused by fatigue influencing the muscle and joint mechanoreceptors. The NKS stimulates the mechanoreceptors of the skin and gives proprioceptive input.…”

Task-Dependent Intermuscular Motor Unit Synchronization between Medial and Lateral Vastii Muscles during Dynamic and Isometric Squats

“…Differences in muscle force levels were addressed above and did not seem to modify our results significantly. The effect of knee flexion angle and respective Vastii muscle length on IMUS between VM and VL has been investigated by Mellor & Hodges [ 33 ]. Since synchronization was shown to be independent of the knee flexion angle, we assume that different squatting depths in this study did not influence coherence.…”