miércoles, 12 de octubre de 2011

International Journal of Exercise Science

Esteban Martínez1, Iván Chulvi-Medrano2
1Physiotherapist (Master Physical Activity and Health), 2PhD Sports Science.

In recent years, whole body vibration (WBV) has become the subject of a great deal of research into improving physical capacity and post-activation potential  so muscle spindle sensitivity can be increased (4). Typically, WBV is achieved by the subject squatting on a platform while the platform oscillates at different intensities and amplitudes. Previous reports have shown that WBV produces pre-conditioning effects that lead to an increase in power and flexibility (2), but controversial data exists that show no positive effect if it is not used in a controlled manner (6) and it has been suggested that the frequency may affect output (5).
The purpose of this study was to investigate the effects of a single session of whole-body vibration at two different frequencies on isometric lumbar extension (ILE), isometric deadlift (ID), posterior leg flexibility (PLF) and core muscle endurance test (CMET). 
Participants.  23 physically fit and healthy subjects (26.39±4.45) from NOWYOU personal training studio were recruited for the experimental session 30 Hz WBV or 50 Hz WBV. Protocol. Each subject complete two trials, i) 30 Hz (3 sets of 30 seconds 2mm amplitude); ii) 50 Hz (3 sets of 30 seconds 2mm amplitude) in squat position using a commercial platform of WBV (PowerPlate Pro 5, Tecnosport) . Isometric strength measurement for lower limb and lumbar was taken using a load cell and following the ASEP recommendation for muscular assessment. All signals were acquired in digital form. All records of force (kg) were stored on a hard drive for later analysis. Flexibility was tested with ‘sit and reach’, which was performed using the procedures outlined in the ACSM manual. Core test was assessed  using the prone bridge adapting the advice outlined in the original work of (3) for the side bridge.
Statistical Analysis.
The peak of the three trials on each test was stored on a hard drive for subsequent analyses. Peak data force, heart rate, flexibility and time endurance core test for both trials were compared using repeated ANOVA measures. The changes in the different physical capacity parameters for all groups were analyzed by repeated ANOVA measures. Contrast analysis was used to assess between-and within-group difference. All statistical treatment was made with SPSS 17.0.
The 23 subjects completed the study protocol without adverse effects. Statistical analysis revealed that no changes occur in any capacity after single exposure WBV (p>0.05). ID doesn’t increase in any conditions (p>0.05) baseline values (69,6 ± 30,26Kg), post30Hz (72,51± 26,81  Kg), post50Hz (73,25 ± 26,83 Kg). After WBV mean values of peak in (ILE) don’t increase significantly for baseline values (50,77± 21,81 Kg), post30Hz (53,89 ± 24,94 Kg), post50Hz (53,89 ± 24,94 Kg). The mean sit-and-reach test maintain without significative changes (p>0.05) baseline values (2,42 ±6,76 Cm), post30Hz (4,45 ± 6,68 Cm), post50Hz (5,55 ± 6,30 Cm). No significative changes found (p>0.05) in (CMET), baseline values (57,73 ± 15,15 sec), post30Hz (62,20 ± 19,81 sec) and post50Hz (63,56 ± 22,95sec).
Our research shows that a single session of WBV doesn’t enhance average values in physical capacity in any conditions. This data is different from previous reports. For example, it has found that in golfers the flexibility and power output increases after a WBV (50 Hz; 2mm; 30 sec) warm-up (1). Protocol differs for our research because they use 8 exercises with WBV while our study only uses the squat position. This data suggests that the amount of exercise can be an important variable to achieve a postactivation potential. Recently, similar results are reported (2), who found an interesting warm-up effect (for flexibility and dynamic strength) post WBV protocol that was similar to ours (near 30 Hz in a squat position 170-175º knee extension) but these researchers prolonged the WBV for a total of 6 minutes, which was superior to our exposure. Thus, time of exposure can be an important variable for a warm-up which will lead to deep changes.
The results of the current study show that WBV is an ineffective method to acutely increase lower-limb muscular force production and flexibility.  
  1. Bunker DJ, Rhea MR, Simons T, Marin PJ. The use of whole-body vibration as a golf warm-up. J Strength Cond Res 25 (2):293-297, 2011.
  2. Jacobs PL, Burns P. Acute enhancement of lower-extremity dynamic strength and flexibility with whole-body vibration. J Strength Cond Res 23 (1): 51-57, 2009.
  3. McGill SM, Childs A, Liebenson C. Endurance times for low back stabilization exercises: clinical targets for testing and training from a normal database. Arch Phys Med Rehabil 80: 941-914, 1999.
  4. Rittweger, J. Vibration as an exercise modality: How it may work, and what its potential might be. European Journal of Applied Physiology 108(5), 877-904, 2010.
  5. Turner AP, Sanderson MF, Attwood LA. The acute effect of different frequencies of whole-body vibration on countermovement jump performance. J Strength Cond Res 25 (6):1592-1597, 2011
  6. Wilcock IM, Whatman Ch, Harris N, Keogh JWL. Vibration training: could it enhance the strength, power, or speed of athletes? J Strength Cond Res 23 (2): 593-603, 2009.

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