Hamstring injuries are one of the most common injuries in sports that involve sprinting or abrupt decelerations, as when kicking the football, because the muscle moves in an eccentric motion to stop the acceleration. In football, hamstring injuries have been shown to account for up to 37% of muscle injuries (Ekstrand, Hägglund, & Waldén, 2011). Therefore, determining risk factors associated with this injury is essential to design preventive strategies.

One of the factors associated with an increase in the risk of injury, is having low strength levels or significant muscle imbalance (for example, having a greater flexion strength rather than knee extension). In fact, the highest incidence of hamstring injuries has been shown to occur during the second half of a match, when the muscles are fatigued and generate lower strength levels. Thus, it is best to assess athletes’ hamstring strength after matches throughout the season to understand which athletes reach higher levels of fatigue and/or residual muscle damage, which could lead to a greater risk of injury.

Traditionally, the most accurate method for evaluating knee flexion strength (that is, of the hamstring muscle) has been by using complex dynamometers. However, in recent years, a very useful isometric strength test of the posterior chain, known as the McCall test, author of the first validation study of this test, has become more popular (McCall et al., 2015). In this test, the athlete lays down on his back and places his heel on a force plate (which may be placed high, giving the knee a greater degree of flexion, or closer to the ground with less knee flexion). From this position, the athlete will perform an isometric contraction, trying to extend the hip and flex the knee, thus activating the posterior chain, without lifting the hip off the ground (Figure 1).