Acute effects of stretching on leg and vertical stiffness during treadmill running

The implementation of static (SS) and dynamic (DS) stretching during warm-up routines produces significant changes in biological and functional properties of the human musculoskeletal system. These properties could affect the leg and vertical stiffness characteristics that are considered important factors for the success of athletic activities. The aim of this study was to investigate the influence of SS and DS on selected kinematic variables, and leg and vertical stiffness during treadmill running. Fourteen males (age: 22.58 +/- 1.05 years, height: 1.77 +/- 0.05 m, body mass: 72.74 +/- 10.04 kg) performed 30-s running bouts at 4.44 m[BULLET OPERATOR]s-1, under three different stretching conditions (SS, DS, and no stretching). The total duration in each stretching condition was 6 min and each of the four muscle groups was stretched for 40 s. Leg and vertical stiffness values were calculated using the "sine-wave" method, with no significant differences in stiffness found between stretching conditions. After DS, vertical ground reaction force increased by 1.7% (p < 0.05), which resulted in significant (p < 0.05) increases in flight time (5.8%), step length (2.2%), and vertical displacement of the center of mass (4.5%) and a decrease in step rate (2.2%). Practical durations of SS and DS stretching did not influence leg or vertical stiffness during treadmill running. However, DS appears to result in a small increase in lower-limb force production which may influence running mechanics.