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Soccer is the most popular sport worldwide, with 275 million participants of either sex and of all ages. 1 In general, sports participation generates a physically active lifestyle. However, the beneficial health effects of sport are tempered by the risk of injury. 2 Unfortunately, soccer has a high injury rate, with male amateur soccer players being particularly prone to injury. 3-7 Of all players, 60-100% sustain at least one injury per soccer season. 8 9 In terms of incidence rates in amateur players, soccer leads to 21.9 injuries per 1000 match hours and to 3.4 injuries per 1000 training hours. 3 7
Hamstring injuries, defined as any physical complaint affecting the posterior side of the upper leg irrespective of the need for medical attention or time loss from soccer activities, 10 are the most common soccer-related muscle injury. 11 12 They account for 13-17% of all soccer injuries and require extensive treatment and long rehabilitation periods, leading to absence from training and matches for up to 90 days. 8 7 12 13 Hamstring injuries also have a high recurrent rate, varying from 12% to 33%. 12-15
Of a number of potential risk factors for hamstring injuries, such as age, previous hamstring injury, muscle architecture, fatigue, flexibility, core stability and strength, flexibility and strength are considered important modifiable risk factors. 16-18 Biomechanical analyses have shown that hamstring ruptures typically occur in the latter part of the swing phase during sprinting. 19 20 Before the foot hits the ground, the hamstring is (sub)maximally stretched over the knee joint, but at the same time it has to counter isokinetic forces from the preswinging leg. The higher the sprinting velocity, the greater these forces are. 19 20 The vulnerability of the hamstring to injury during this phase of sprinting is associated with inadequate eccentric strength of the hamstring. 21-23
Exercises to increase eccentric muscle strength, such as the Nordic hamstring exercise or hamstring curl, have shown to reduce the rate of hamstring injury by 65-70%, and particularly recurrent injuries, in professional soccer players. 24-26
Male amateur soccer players form the largest subgroup of soccer players worldwide, with the incidence of injury increasing with higher levels of play. 3 4 Strategies to prevent hamstring injuries, such as the Nordic...