Analysis and modelling of muscles motion during whole body vibration

The aim of the study is to characterize the local muscles motion in individuals undergoing whole body mechanical stimulation. In this study we aim also to evaluate how subject positioning modifies vibration dumping, altering local mechanical stimulus. Vibrations were delivered to subjects by the use of a vibrating platform, while stimulation frequency was increased linearly from 15 to 60Hz. Two different subject postures were here analysed. Platform and muscles motion were monitored using tiny MEMS accelerometers; a contra lateral analysis was also presented. Muscle motion analysis revealed typical displacement trajectories: motion components were found not to be purely sinusoidal neither in phase to each other. Results also revealed a mechanical resonant-like behaviour at some muscles, similar to a second-order system response. Resonance frequencies and dumping factors depended on subject and his positioning. Proper mechanical stimulation can maximize muscle spindle solicitation, which may produce a more effective muscle activation

Bone metabolism and fracture risk during and after critical illness.

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In the unloaded lower leg, vibration extrudes venous blood out of the calf muscles probably by direct acceleration and without arterial vasodilation

Purpose During vibration of the whole unloaded lower leg, effects on capillary blood content and blood oxygenation were measured in the calf muscle. The hypotheses predicted extrusion of venous blood by a tonic reflex contraction and that reactive hyperaemia could be observed after vibration. Methods T welve male subjects sat in front of a vibration platform with their right foot affixed to the platform. In four intervals of 3-min duration vibration was applied with a peak-to-peak displacement of 5 mm at frequencies 15 or 25 Hz, and two foot positions, respectively. Near infrared spectroscopy was used for measuring haemoglobin oxygen saturation (SmO2) and the concentration of total haemoglobin (tHb) in the medial gastrocnemius muscle. Results Within 30 s of vibration SmO2 increased from 55 ± 1 to 66 ± 1 % (mean ± SE). Within 1.5 min afterwards SmO2 decreased to a steady state (62 ± 1 %). During the following 3 min of recovery SmO2 slowly decreased back to base line. THb decreased within the first 30 s of vibration, remained almost constant until the end of vibration, and slowly recovered to baseline afterwards. No significant differences were found for the two vibration frequencies and the two foot positions. Conclusions T he relaxed and unloaded calf muscles did not respond to vibration with a remarkable reflex contraction. The acceleration by vibration apparently ejected capillary venous blood from the muscle. Subsequent recovery did not match with a reactive hyperaemia indicating that the mere mechanical stress did not cause vasodilation

Passive vibration on the legs reduces peripheral and systemic arterial stiffness

Intermittent leg exercise (10 × 1-min sets) with whole-body vibration (WBV) decreases brachial-ankle pulse-wave velocity (baPWV)1 and leg PWV (legPWV) but not aortic PWV.2 As baPWV is an index of systemic arterial stiffness3 mainly influenced by aortic PWV (∼58%) and legPWV (∼23%),4 previously published results1, 2 suggest that WBV affects baPWV through peripheral but not central PWV. The post-exercise decrease in PWV is associated with vasodilation in the exercised limb.5, 6 Similarly, intermittent WBV (3 × 3-min sets)7 or passive vibration (PV)8 has been shown to increase blood flow in the vibrated limb after only 1-min post vibration. Interestingly, 10 min of continuous PV was found to increase arm skin blood flow after 5-min post vibration,9 indicating a direct relationship between the duration of exposure and vasorelaxation. We hypothesized that PV on the legs may decrease legPWV and baPWV more than aortic PWV. The purpose of our study was to examine PWV responses following continuous PV of lengthy duration