Recent years have seen an increasing popularity of whole body vibration (WBV) as an exercise modality. As a consequence there is an increased need for greater understanding of the effects of the addition of vibration to exercise. The effects of WBV on the musculoskeletal system have been the subject of much research in the last decade and have been summarised in recent reviews (Cochrane, 2011; Rittweger, 2010; Rauch, 2009). Studies on the effects of vibration are essentially split into two categories, those on occupational vibration and those on vibration as an exercise modality. Typically occupational vibration is much higher frequency (100 Hz) with exposure over longer durations e.g. hours each day (Griffin, 1990). Vibration for exercise purposes is typically much shorter in duration e.g. minutes on a few days per week, with much lower frequencies and amplitudes (Dolny and Reyes, 2008). To date there have been few studies investigating the effect of WBV on tissue blood flow and oxygenation parameters. Nakamura et al. (1996) was one of the first researchers to report that vibration exercise has different blood flow responses to occupational vibration, in that blood flow is increased to the digits of the hand. Laser Doppler studies have shown that application of both local vibration (Maloney-Hinds et al., 2008) and WBV during isometric weight-bearing exercise (Lohman III et al. 2008) significantly increased skin blood flow without subsequent vasoconstriction during the recovery period. Kerschan-Schindl et al. (2001) reported a 100% increase of blood flow in the popliteal artery (from 6.5 to 13 cm s1), corresponding to Lythgo et al. (2009) who found an increased mean blood cell velocity in the femoral artery following WBV. However, previously Hazell et al. (2008) reported no difference in the femoral artery from WBV in addition to Button et al. (2007) who found local vibration did not affect blood flow.
Cardinale et al. (2007) investigated the effects of vibration during a static squat on vastus lateralis and gastrocnemius oxygenation, however no statistically significant results were found. More recently Coza et al. (2011) investigated gastrocnemius muscle oxygenation during heel raise exercise in arteriolar occluded (AO) conditions with respect to performance and recovery, both of which are dependent on blood flow.
Near Infra-Red Spectroscopy (NIRS) has been shown to provide valid, non-invasive measurements regarding tissue oxygenation parameters (Boushel et al., 2001; McCully and Hamaoka, 2000; Suzuki et al., 1999) and provides information on combined arteriolar, capillary and venular haemoglobin concentrations (Quaresima et al., 2001). The signal obtained is therefore dependent on both oxygen delivery and rate of use. The aim of this study was therefore to assess the acute effects of WBV vibration during dynamic exercise on NIRS-derived muscle oxygenation parameters.
This study was carried out in accordance with University Ethics Guidelines and the ethical standards of the Declaration of Helsinki. All participants gave informed consent and received familiarisation of the procedure before data collection. Twenty physically active subjects (14 male, 6 female, age 29 [+ or -] 10.4 years, height 1.75 [+ or -] 0.09m, weight 76.2 [+ or -] 17.15 kg, BMI 24.8 [+ or -] 4.3), with no recent history of lower limb musculoskeletal disorders were selected for inclusion in the study.
All heel raise exercises were performed on a Power Plate[R] pro6 (Power Plate International Ltd) whole body vibrating platform (40Hz 1.9mm vertical displacement), with either no vibration (NVIB) or vibration (VIB) being utilised in ten alternating sets of 15 heel raises. The initial set for each subject was randomised (i.e. VIB or NVIB). The exercises were completed using a metronome operating at 1Hz to ensure all exercises were completed at the same pace. The subjects were instructed to move at a pace of 0.5Hz i.e. one second up on to toes to maximum heel raise and one second down to complete flat foot and to ensure each repetition was a full heel raise i.e. as far up onto their toes as possible. Subjects were also instructed to keep a slight bend on their knees to prevent excessive transmission to their heads. During straight leg heel raise activity although the soleus muscle contributes to the movement, the prime activity comes from the gastrocnemius which is mechanically better positioned to generate full power while the knee is extended compared to when flexed (Baechle and Earle, 2008; Palastanga et al., 2004).
Data collection and processing
Tissue oxygenation parameters were obtained using a NIRO 300 (Hamamatsu Photonics, Japan), the emitter and recording sensor were placed on the right lateral gastrocnemius with the central distance between the emitter and detector 1/3 of the distance between the head of the fibula and the calcaneus. A constant distance of 4cm was maintained between the emitter and the detector. Analogue output to a USB AD board allowed synchronous oxygenation and motion data capture. One retro-reflective marker was placed on the right lateral malleolus and tracked for 60 seconds at 20Hz to determine baseline activity, ankle motion and recovery period (Oqus3, Qualysis SB, Sweden).
Marker motion was tracked and all synchronous data exported in c3d format for subsequent analysis in Visual3D (C-Motion). Motion data was filtered (6Hz, 4th order low pass Butterworth filter), maximal and minimal vertical displacements were defined from which vertical ankle displacements were derived as well as total exercise time. Voltage calibration was used to convert oxygenation signals to appropriate values; these data were then smoothed using a 0.2Hz 4th order lowpass Butterworth filter. All signals were baseline corrected relative to the first 5 seconds of data prior to initiation of the exercise. Maximal or minimum values during the exercise period were used to determine absolute concentration changes for deoxyhaemoglobin ([DELTA]HHb), oxyhaemoglobin (DELTA]O2Hb), total haemoglobin (DELTA]cHb), and tissue oxygenation index (TOI, the ratio of oxygenated to total tissue haemoglobin) and normalised tissue haemoglobin index (nTHI, the relative concentration of total haemoglobin).
Mean values of the five VIB and five NVIB repetitions were determined for each participant and group...