Soccer players' physical performance adaptations with four weeks isometric versus dynamic contrast training: a randomized controlled trial

This randomized controlled study aimed to compare the effects of isometric contrast training (ICT) versus dynamic contrast training (DCT) on the physical performance of soccer players. Tier 3 male soccer players (age: 22.8±1.7 yrs) were randomly assigned to ICT (n=10), DCT (n=10), and control group (CG; n=10). Intervention groups performed similar lowload ballistic exercises, although the ICT and DCT incorporated push-isometrics or dynamic resistance high-load exercises, respectively. Aside from interventions, the off-season soccer training load was the same for control and intervention groups. Before and after 4-week of intervention, data were collected for 10 m, 20 m, and 40 m linear sprints, change of direction speed (CODS), countermovement jump (CMJ), standing long jump (SLJ), and 300-yard shuttle run test (SRT). After adjusting for baseline differences, statistical analysis revealed significant differences in all performance variables (p<0.001-0.018). Compared to controls, both intervention groups improved 40 m linear sprint, CODS, CMJ, and SRT (all p<0.05), and ICT also improved 10 m and 20 m linear sprint, and SLJ (all p<0.05). Relatedly, ICT improved 10 m linear sprint (p=0.001) and SLJ (p<0.001) when compared to DCT. In conclusion, soccer players improve physical performance with contrast training, particularly after ICT.