The Acute Effects Of Whole Body Vibration On Hamstring Flexibility

Abstract

The use of whole body vibration (WBV) platforms has been shown to increase flexibility in acute and chronic exercise studies. However, the vibratory settings used in these studies have varied considerably in terms of the frequency, displacement, and platform type. PUROPSE: The purpose of this study is to find the optimal frequency and displacement of WBV that elicits the greatest increase in hamstring range of motion on a triplanar WBV platform. METHODS: Six male (25 + 6 yrs) and 5 female (22 + 2 yrs) participants volunteered for this study. Participants attended a total of nine days, with each day used to examine the effects of a unique WBV setting on hamstring flexibility. Conditions were combinations of 4 frequencies (30, 35, 40, and 50Hz) and Low vs. High Amplitudes (2 vs. 5mm), with one day during which stretching was performed with no vibration (NV). During training participants were instructed to bend forward at the waist keeping their knees at a 180 degree angle in an attempt to maximally stretch the hamstring muscle group. Flexibility was assessed using a modified sit and reach test, before vibration (pre), immediately after vibration, one minute post, two minutes post, and five minutes post vibration. A two-way repeated measures ANOVA (condition × time) controlling for pre-test measures, was used to analyze the data. RESULTS: The repeated measures analysis revealed no significant differences for stretching condition (F(8, 8) = 2.21, p =.141) or for time (F(3,3) =.932, p =.522) however, power levels were.484 and.115, respectfully for the full model. Separate ANOVAs comparing selected stretching conditions over time revealed a significant main effect for condition (F(1,8)= 6.23, p=.037) but not for time. Post hoc analyses revealed that 50 Hi elicited a significantly greater improvement than NV, (p=.040). CONCLUSION: Acute stretching of the hamstrings musculature during WBV resulted in a significant increase in hamstring flexibility over stretching without vibration. The setting 50 Hi condition proved to be the best setting to elicit positive changes in hamstring flexibility. These findings should be considered preliminary, due to the low sample size in this preliminary study.