The effects of acute static and dynamic stretching on spring-mass leg stiffness

This study investigated the effect of brief static and dynamic stretching on spring-mass leg stiffness in a vertical bilateral hopping task.

38 men and 18 women were randomly assigned to either a natural (NAT; n = 27), or maximal (MAX; n = 29) hopping group. NAT bounced at their self-selected stiffness and MAX were instructed to bounce as stiffly as possible. Hopping was performed at 2.2 Hz on a force plate. After each of four treatment conditions (no stretch, 30 s stretch, multiple (4 × ) 30 s stretch, and dynamic stretch), subjects completed three × 30 s bouts (2 min rest periods) of hopping, in a counterbalanced crossover design. Stretches were performed on: gluteals, hamstrings, quadriceps and calves. Spring-mass leg stiffness was calculated as the ratio of peak vertical force to vertical displacement during ground contact.

The results revealed that men displayed greater leg stiffness than women (mean difference: 6.04 kN m^-1; 95% likely range: 1.94-10.13 kN m^-1), and that MAX produced higher stiffness values than NAT (mean difference: 10.93 kN m^-1; 95% likely range: 6.84-15.03 kN m^-1). Although there were no significant effects of treatment (p = 0.85) or time (p = 0.54) on leg stiffness, there was a significant treatment × time interaction (p = 0.015). Nevertheless, post hoc analyses were unable to identify where those differences were.

Relative to controls, the results of this study showed that brief static stretching or non task-specific dynamic stretching does not affect spring-mass leg stiffness during vertical bilateral hopping.