Effects of Nordic Exercises on Hamstring Strength and Vertical Jump Performance in Lower Limbs Across Different Sports

Nordic exercises are widely used to improve physical performance and prevent injuries; however, their applicability across different sports remains unclear. Objective: This study examined the effects of Nordic exercises on the lower limbs and their relationship with absolute strength and vertical jump performance across various sports disciplines (soccer, athletics, basketball, sport climbing, cycling, and taekwondo). Methods: We conducted a quasi-experimental study involving 122 athletes (mean age 18.2 ± 3.2 years), who were not in pre-competitive or competitive periods, distributed across the following disciplines: soccer (n = 24), sprinting/athletics (n = 20), sport climbing (n= 20), basketball (n = 24), taekwondo (n = 14), and cycling (n = 20). Participants were randomly assigned to a control group (CG), n = 57, with regular training and an experimental group (EG), n = 65, that performed Nordic hamstring exercises (NHEs). The effects of a 7-week NHE program were assessed on absolute strength (measured with a dynamometer) and vertical jump performance (Vert). A mixed-design repeated measures ANOVA was used, considering the factors time, group, and sport discipline, with a significance level set at p < 0.05. Results: Both groups (CG and EG) presented homogeneous baseline values for absolute strength (dominant and non-dominant sides) and vertical jump (p > 0.05). The EG exhibited significant gains in dominant-leg strength (from 12.4 kg to 14.5 kg), non-dominant side strength (from 11.1 kg to 13.8 kg), and vertical jump (from 42.4 cm to 45.8 cm), with statistically significant differences between pre- and post-tests (p < 0.01). No relevant changes were observed in the CG. The repeated measures ANOVA confirmed a significant time × group effect in all three variables (p < 0.01), although no significant time × sport × group interaction was found. The largest strength gains occurred in strength were observed in sport climbing, basketball, and athletics and in vertical jump in soccer. Conclusions: Absolute strength improvements were most notable in sport climbing, basketball, football, and sprinting. Vertical jump performance improved notably in soccer, sprinting/athletics, climbing, and basketball. These results justify incorporating NHEs into youth athletes’ training, tailored to the specific demands of each sport.