Muscular coactivation

Abstract

The objective of this study was to quantify the coactivation patterns of the knee flexor and extensor muscles as part of continued efforts to identify the role of the antagonist muscles in maintaining joint stability. The simultaneous EMG from the flexor and extensor muscles of the knee were recorded during maximal effort, slow isokinetic contractions (15 deg/sec) on the plane parallel to the ground to eliminate the effect of gravity. The processed EMG from the antagonist muscle was normalized with respect to its EMG as agonist at maximal effort for each joint angle. The plots of normalized antagonist EMG versus joint angle for each muscle group were shown to relate inversely to their moment arm variations over the joint range of motion. Additional calculations demonstrated that the antagonist exerts nearly constant opposing torque throughout joint range of motion. Comparison of data recorded from normal healthy subjects with that of high performance athletes with hypertrophied quadriceps demonstrated strong inhibitory effects on the hamstrings coactivations. Athletes who routinely exercise their hamstrings, however, had a coactivation response similar to that of normal subjects. We concluded that coactivation of the antagonist is necessary to aid the ligaments in maintaining joint stability, equalizing the articular surface pressure distribution, and regulating the joint's mechanical impedance. The reduced coactivation pattern of the unexercised antagonist to a hypertrophied muscle increases the risk of ligamentous damage, as well as demonstrates the adaptive properties of the antagonist muscle in response to exercise. It was also concluded that reduced risk of knee injuries in high performance athletes with muscular imbalance could result from complementary resistive exercise of the antagonist muscle.

Effects of Fatigue Induced by Prolonged Gait When Walking on the Elderly

“…During Loading, the ankle should act as rigid block to support and transfer ground reaction forces to the entire lower limb. Therefore, since lower levels of coactivation implies stiffness in the lower joint [13,14], we can suggest that at MIN20 these subjects have a less stable joint in comparison to MIN1, indicating a higher fall risk. Hence, even with an increase of VL activation during Loading (maintaining joint preparation to counteract ground reaction forces), fatigue can become dangerous, since the coactivation in the ankle results in a reduction of joint stiffness.…”

“…There is no standard value for this variable; however, increased values represent higher energy consumption [3] and a decreased capacity in controlling movement [12]. In addition, lower coactivation scores have been found to represent a reduction in joint stability [13,14].…”

Influence of wearing an unstable shoe construction on compensatory control of posture

“…The decreased antagonist co-activation was a surprising finding since "Freezing degrees of freedom" has been described as a primitive strategy when mastering a new skill (Baratta et al, 1988;De Luca & Mambrito, 1987) and because it has been shown that subjects use co-contraction control to offset the effects of destabilising forces (Burdet et al, 2001). The higher activity of GM when WUS could be associated with the lower levels for leg antagonist coactivation as there is evidence that the level of inhibition of the antagonists increases in proportion to the level of motor activity in the agonists (Lavoie et al, 1997).…”

Understanding the Effect of High-Cut Shoes, Running Shoes and Prophylactic Supports on Ankle Stability When Performing a “V”-Cut Movement

“…39,40 This is an important factor influencing dynamic joint stability to protect the lateral ankle ligaments from excessive inversion due the experience of rapid loading. 39,40 Such activation may have stiffened the joint so that it barely experienced inversion which is represented by the slight everted magnitude experienced at the rearfoot.…”