The effect of volume equated 1- versus 2-day formats of Nordic hamstring exercise training on fitness in youth soccer players: a randomised controlled trial

Purpose: This randomised controlled trial examined the effect of an 8-week volume-equated programme of Nordic hamstring exercise (NHE) training, executed at frequencies of 1- or 2-days per week, on fitness (10 m and 40 m sprint, ‘505’ change of direction [COD] and standing long jump [SLJ]) in male youth soccer players (mean age: 16.4 ± 0.81 years). Method: Players were divided into an experimental group (n=16) which was further subdivided into 1-day (n=8) and 2-day (n=8) per week training groups and a control group (n=8). Results: There were significant group-by-time interactions for 10-m sprint (p<0.001, η2=0.120, d=1.73), 40-m sprint (p=0.001, η2=0.041, d=1.26) and COD (p=0.002, η2=0.063, d=1.01). The experimental group demonstrated a ‘very large’ effect size (d=3.02) in 10-m sprint, and ‘large’ effect sizes in 40-m sprint (d=1.94) and COD (d=1.84). The control group showed no significant changes. There were no significant differences between the 1-day and 2-day training groups. In three of the four tests (40 m, COD, SLJ) the 2-day group demonstrated larger effect sizes. Ratings of perceived exertion (RPE) were significantly lower in the 2-day group (p<0.001, d=3.46). Conclusion: The NHE increases fitness in youth soccer players and there may be advantages to spreading training over two days instead of one.