Introduction: Stiffness is a mechanical properties of viscoelastic structures which researchers have believed it has three important function in body mechanism: it adjusts rate of force development in system, determine force storage capability for stretch-shorten cycle, and determine system resistant against perturbations (system stability). Therefore, stiffness can effects on body mechanics during activities. Whole body vibration training (WBVT) is an exercise-therapeutic modality which acts by transition of oscillating mechanical stimulation to whole body and stimulation of muscles through the muscle spindle reflexes. Previous studies have reported improvement in muscles function, position sense, balance and reduction in pain after WBVT in a wide range of people. However, the acute effects of WBVT still is not well defined and regarding the role of leg stiffness in sports performance and injuries, the question arise if acute WBVT can effect on lower extremity stiffness. The purpose of this research was to examine acute effects of WBVT on lower limb stiffness during hopping.
Methodology: Twenty athletic girls voluntarily participated in this research. Participants did preferred, maximum, and 2.2 Hz hopping (15 jumps per hopping) on force plate barefoot and with hands on waist, before and after a session of acute WBVT with 30 Hz frequency and 10 mm amplitude. The Ground Reaction Forces (GRF) during hopping were be recorded with 500 Hz frequency. The five middle preferred, maximum, and 2.2 Hz hopping were selected and lower limb stiffness were calculated by dividing maximum vertical GRF on the vertical displacement in center of mass.
Results: The results of paired sample t test showed there is significant increase in lower limb stiffness during preferred, maximum, and 2.2 Hz hopping after one session of acute WBVT (P ≤ 0.05).
Discussion: Possibly, acute WBVT can increase lower limb stiffness by effects on muscle spindle and Golgi tendon organ, and therefore, it has positive effects on athletics performance, especially during explosive performances.