Muscular strength is generally measured using either of the following methods، one repetition maximum (1- RM) of a weight-lifting exercise، a resisted maximal effort and portable or laboratory-based dynamometry. The 1- RM method refers to measurements of maximum strength using a strength training device such as a barbell or stationary weight-lifting machine. Dynamometry can be divided into two separate methods according to the muscle action involved. Isometric dynamometers assess the force exerted during static muscular actions typically associated with the back، legs and upper limb، e.g. hand (grip). The classical method of recording isometric muscle strength was cable tensiometry، later replaced by use of load cells and force transducers. In experimental studies، maximal voluntary contraction (MVC) is employed as the criterion for muscle strength، typically registered using strain-gauge assemblies. Such devices are relatively inexpensive and convenient to use in and out of the laboratory. Hand grip dynamometers are possibly the most widespread devices for measuring strength however there is concern regarding the strength in the muscle involved in isometric gripping and the generalisation to large muscle group or whole-body strength.The main limitation of such dynamometers is that they do not replicate sport specific activity. Dynamic strength assessment is the preferred method when assessing athletic performances opposed to isometric testing because of the large neural and mechanical differences between isometric and dynamic muscular action. This recommendation is supported by a number of studies that have found a poor association between isometric strength and dynamic performance in strength-based activities.Isokinetic dynamometry is used to assess dynamic muscle action whereby the velocity of limb movement is held constant throughout the range of movement and the resistance applied is equal to the muscular torque during the movement. Such a device allows accurate measurement of torque throughout many limb movements under concentric and eccentric muscle actions. With the subject maintaining a static position، the dynamometer also allows measurement during isometric muscle action. In order to measure absolute strength it is advised that a relatively low velocity is used to allow for production of maximal torque throughout the movement. The protocol used to establish maximum torque can vary، but this function is most often evaluated following several submaximal repetitions and from the first two or six maximal repetitions. Although such dynamometers allow for isolation of specific muscle groups through a single joint motion، they are limited in their representation of typical sports activities. In this paper some important isokinetic parameters relevant to soccer will be discussed.
