QUANTIFICATION OF QUADRICEPS AND HAMSTRING ANTAGONIST ACTIVITY

The coactivation of hamstrings and quadriceps, and its relation to kne e joint stability and cruciate ligament loading, have been extensively examined over the last decades. The purpose of this review is to pres ent findings on the quantification of antagonist activation around the knee. Coactivation of the quadriceps and hamstrings during many activ ities has been examined using electromyography (EMG). However, there a re several factors that affect antagonist EMG activity, such as the ty pe of muscle action, velocity of the movement, level of effort and ang ular position. Furthermore, the antagonist EMG can be affected by meth odological factors which relate to the data recording, analysis and qu antification of the signal. Research has demonstrated that the effect of cross-talk on the hamstrings and quadriceps antagonist EMG depends on electrode size and location, fat layer of the muscles and the techn ique used to reduce it. There is an inconsistency as to the method use d to normalise antagonist EMG depending on the type of movement examin ed. This makes comparisons between studies difficult and, therefore, f urther research is recommended. The antagonist function is better repr esented when the antagonist moment exerted is known, however, the dire ct measurement of antagonist moments or forces is very difficult. Few studies have used mathematical models to determine the moment or force distribution around the knee, including antagonist forces. This can b e attributed to the complexity of the anatomy and function of the knee joint. Despite this, in vivo and in vitro experiments have demonstrat ed that quadriceps contraction near full extension induces significant ly higher anterior shear forces when compared with the forces exerted when the hamstrings act as antagonists. thus indicating the important rule of antagonist activity in knee joint stability. However, the magn itude of this contribution to the force distribution around the knee i n many activities is unclear.