(J. Basmajian, Motor learning and control: a working hypothesis, Arch. Phys. Med. Rehabil. 58 (1977) 38–41) :  Muscle co-activation is the simultaneous activity of various muscles acting around a joint. It has been suggested that muscle co-activation indicates the achievement of a motor skill with the progressive inhibition of muscular activity that is not related to the task

( W. Solomonow, B. Baratta, B. Zhou, H. Shoji, W. Bose, C. Beck, R. D’Ambrosia, The synergetic action of the ACL and thigh muscles in maintaining joint stability, Am. J. Sports Med. 15 (1987) 207–213)Coactivation is also related to joint stability

( K. Falconer, D. Winter, Quantitative assessment of cocontraction at the ankle joint during walking, Electromyogr. Clin. Neurophysiol. 25 (1985) 135–149.)( D.A. Winter, Biomechanics and Motor Control of Human Movement, Wiley, New York, 1990. ) co-activation is considered as an important factor which contributes to the inefficiency of human movement

The methods used to examine co-activation vary from advanced mathematical models

The methods used to examine co-activation :simple electromyography (EMG) measurements

The ideal method to quantify muscle co-activation is to estimate the muscular forces exerted by all muscles that surround a joint