The Effect of Full Range Nordic Hamstring Curls During Pre-Activation Warm-Up Sessions on Hamstring Eccentric Strength, Neural Activation and Athletic Performance in English Academy Soccer

Background: It has been widely reported in the scientific literature that hamstring injuries are an issue in professional soccer. These injuries generally occur at long muscle lengths and joint angles similar to those observed during sprinting. Factors affecting the incidence of hamstring injuries are numerous but one highly researched modifiable factor is eccentric hamstring strength. The Nordic Hamstring Exercise (NHE) is a commonly researched and implemented exercise to improve eccentric hamstring strength because of its ease to administer using no equipment. NHE programmes have been shown to be effective at improving strength and reducing hamstring injuries but commonly have high workloads which produce high levels of muscle soreness, resulting in low compliance and thus are not practical in professional soccer.

Aims: The aim of the study was to assess the assisted NHE when used as part of a pre-activation warm up on hamstring muscle strength and neuromuscular activation, and in turn, the effect on soccer-specific performance. The theory behind the use of the assisted NHE was that anecdotally the full range of movement of the NHE is not commonly completed (i.e., chest to the floor). Thus, the traditional NHE does not train the hamstring muscles at long lengths specific to those in sprinting.

Method: Sixteen full time academy footballers (aged 17 ± 2 years, height 183 ± 7 cm, mass 72.3 ± 9.0 kg) undertook a crossover design study in which firstly the players completed a six-week control period during which the players undertook a soccer-specific training programme. Testing was undertaken before and after the control period to establish any changes in eccentric strength, muscle contractile properties, and sprint and jump performance. Players subsequently undertook a six-week intervention period where players continued to take part in a soccer-specific training programme with the addition of the assisted NHE during the pre-activation warm up. The testing battery was repeated pre- and post-intervention to establish any changes due to the intervention.

Results and conclusions: A significant change was observed from the intervention in eccentric strength in the right limb but not in the left limb (+34N, p = 0.034; ES: 0.66 & +15N, p = 0.471). These changes were smaller in magnitude than previously seen in the literature, likely due to differences in volume. Muscle contractile properties showed no significant changes; however, significant changes were observed in 10m sprint (-0.02 secs, p=0.005; ES: -0.16), 30m sprint (-0.09 secs, p≤0.001; ES: -0.61), SJ (+3.5cm, p=0.008; ES: -0.12) and CMJ performance (+3.3cm, p=0.006; ES: 0.00) after the intervention. Therefore, the assisted NHE intervention may not have been provided enough stimulation to promote similar changes hamstring muscle contractile and strength improvements in both limbs. However, there may have been more significant changes that occurred at longer muscle lengths, in turn changing the tension length relationship of the hamstring muscles and thus resulting in the significant improvements in sprint and jump performance