Failure of the vasculature to respond to metabolic needs of the bone might predispose to bone disease. Alterations in vascular function and in intraosseous angiogenesis may be  contributory. Several studies suggest a correlation between bone perfusion and bone density. Studies used different methodologies and are, therefore, difficult to compare. In one study, magnetic resonance imaging was used to obtain an indirect measure of bone marrow perfusion at the level of the lumbar spine. Bone marrow perfusion was correlated with bone mineral density in postmenopausal but not in premenopausal women. In another study, decreased bone marrow perfusion was associated with progression of collapse of fractured vertebra in patients with osteoporosis. Perhaps “bone vascular disease” contributes to osteoporosis.

One might further speculate that interventions that improve bone vascular function may have a beneficial effect on bone structure. The anatomic structure of blood small blood vessels within the bone is similar to the structure of blood vessels in other tissues. These vessels may be  susceptible to the same genetic and environmental risk factors. If bone vascular disease and, thus, alterations in perfusion were a cause of excessive bone loss, atherosclerosis risk factors
should also increase the risk for osteoporosis. Indeed, smoking, diabetes mellitus, elevated low-density lipoprotein cholesterol, reduced high-density lipoprotein cholesterol, and  hyperhomocystinemia are associated with increased cardiovascular risk and reduced bone mineral density. Both the risk for cardiovascular disease and the risk for osteoporosis increase sharply after menopause. A study in rabbits suggests that experimental “postmenopause” through oophorectomy leads to changes in bone vascular function. In this study, oophorectomy increased the responsiveness of isolated vascular rings from small bone arteries to norepinephrine and to endothelin. However, whether vascular damage to the bone vasculature explains the association between osteoporosis and cardiovascular risk factors in humans is unknown. Interestingly, treatment of some cardiovascular risk factors appears to have a beneficial effect on osteoporosis. For example, smoking cessation leads to an  improvement in markers of bone turnover within a 6-wk period. Lipid-lowering therapy
increases bone mineral density. Thiazide diuretics appear to lower the bone fracture rate. Moreover, beta blockers appear to do the same. Finally, estrogen replacement therapy improves bone density and endothelial function in humans.

If bone perfusion has an important effect on bone density, could an increase in bone perfusion also increase bone density? How can bone blood flow be increased? In this issue of the American
Journal of Physiology-Regulatory, Integrative and Comparative Physiology, Stewart reviewed the literature on bone perfusion and bone mass. The few available publications seem to suggest that increased venous pressure and increased perfusion tend to increase bone mass. They reasoned that an increase in leg and, perhaps, bone perfusion may contribute to the recently
described increase in bone mass with whole body vibration. To address this issue, they assessed changes in leg hemodynamics and fluid shifts using strain-gauge and impedance  plethysmography before and during whole body vibration. The vibration was elicited by placing the subjects on a vibrating platform. Whole body vibration increased blood flow to the lower body while subjects were in the supine position. Furthermore, the intervention reversed the decrease in leg blood flow in the upright position. Finally, leg vibration shifted the microvascular filtration relation to higher pressures, both in the supine and in the upright position. The shift is probably explained by improved lymphatic drainage. Thus whole body vibration substantially altered leg hemodynamics. The study by Stewart necessarily has some limitations.

The authors did not measure bone perfusion directly. It is difficult to know whether the change in leg blood flow is associated with a change in bone perfusion. I would suggest comparing “cheap” leg blood flow measurements with “costly” more direct measurements of bone blood flow in future studies. It would be tremendously helpful to have inexpensive methods that could be used to obtain hemodynamic measurements that are relevant for bone hemodynamics. Furthermore, the authors did not provide data linking changes in hemodynamics and bone turnover. Perhaps more questions were raised than answered. Nevertheless, the study is of importance because it may generate interest in studying the interaction between bone and the cardiovascular system. Promising clinical and epidemiological data linking vascular disease and osteoporosis ought to be supported by solid physiological work. Equally important, the study suggests that even in the era of molecular medicine, a simple and “old-fashioned” physiological method is still useful to raise new scientific hypotheses. A final question for those who will not be interested in bones: Do good vibrations add to angiogenesis elsewhere?

Good vibrations and strong bones? is a post from: Vibrating Exercise

SHAKE, RATTLE, AND roll have now entered the osteoporosis quietness with two papers on the clinical effect of whole body vibration in the March issue of JBMR. Besides, we can already see these products at scientific meetings. To what extent does the present knowledge address the potential for such approaches in the prevention of fractures?

GOOD VIBRATIONS
Clinical studies have been based on animal experiments that have shown a positive effect on bone strength and mass of various forms of loading. The basis of these experiments is the concept that trabecular bone adapts to its mechanical environment—Wolff’s law. Support for these experiments has also come from epidemiological findings that greater physical activity–mechanical stimulation is associated with greater bone mass, and in some studies, fewer fractures.

The question of the ideal form of stimulation has been addressed in animal studies.  High – frequency (30 Hz), lowmagnitude (200
strain) signals stimulated large increases in cortical bone in turkeys. However, higher amplitude and lower frequency was not anabolic in that model. In a longer-term study in sheep over 1 year, daily 20-minute sessions of high-frequency mechanical stimulation of sheep produced a 35% increase in BMD. This kind of vibration
may also affect the sarcopenia that occurs at the same time as bone loss with aging. Other animal studies have shown similar results. Low-magnitude mechanical loading became osteogenic when rest is inserted between each load cycle.  Effects of loading frequency on mechanically induced bone formation and periosteal osteogenesis suggested a complex interaction between  extracellular fluid forces and cellular mechanics in mechanotransduction, best predicted by a
mathematical model that assumed that (1) bone cells are activated by fluid shear stresses and (2) stiffness of the bone cells and the extracellular matrix near the cells increases at higher loading frequencies because of viscoelasticity. These animal experiments have formed the scientific basis for studies in humans.

SHAKING ALL OVER
In humans, extremely low-level, high-frequency mechanical accelerations have been shown to be readily transmitted into the lower appendicular and axial skeleton of the standing
individual. In a recent study, 21 male and 35 female volunteers (age, 19–38 years) were randomly assigned to a vibration or control group. Individuals stood on a vibration platform that was either stationery or oscillated in an ascending order from 25 to 45 Hz, corresponding to maximum vertical accelerations from 2g to 8g, for 4 minutes/day, 3–5 times/week, over an 8-month period. Although there was no effect on bone mass, serum markers, or other performance and balance tests, there was an increase in vertical jump height in the vibration group. In this issue, Verschueren report on a 6-month study of whole body vibration in older women with respect to hip density, muscle strength, and postural control. The 70 volunteer women, 60–70 years of age, who were healthy and had a BMD T score
2, were randomized to a control group with no organized training; resistance training knee extensor by dynamic leg press and leg extension exercises or whole body vibration, where the subjects performed the same exercises for 20 minutes/day on a vibration platform that had a vibration frequency of 35–40 Hz and peak acceleration of 2.3–5.1g. The vibration training improved the isometric and dynamic muscle strength by 15% and 16%, respectively, and increased BMD by 0.93%. No hip BMD change was observed in the resistance training or the age-matched controls. Serum markers of bone turnover did not change in any groups. The authors concluded that whole body vibration training might be a feasible and effective way to modify well-recognized risk factors for falls and fractures in elderly women.

Also in this issue, Rubin et al. report another trial for 1 year in 70 healthy women who were 3–8 years postmenopausal (mean age, 57 years). Those randomized to the vibration platform were exposed to a peak vertebral acceleration of 0.2g at a frequency of 30 Hz. Compliance was not good as in many other exercise (and pharmacologic) interventions, and the intention-to-treat analysis did not show an The authors have no conflict of interest. effect. In an analysis limited to those in the highest quartile of compliance (86% compliant), vibration subjects gained 0.04% in femoral neck BMD, whereas placebo subjects lost 2.13% over 1 year in the femoral neck. The corresponding figures for the lumbar spine were 0.1% and 1.6%. Interestingly, the lower body weight (65 kg) women experienced the greatest benefit: a 3.4% increase in the highest
compliance group and a 2.7% increase in the mean compliance group. The authors concluded that these preliminary results indicate a potential for a noninvasive mechanical mediated intervention for osteoporosis that is perhaps more effective in lighter women, who are at greatest need of intervention.

How shall interpret these trials? First, there are differences in age. The study by Torvinen et al. had younger and perhaps more healthy participants. The greater benefit in lighter individuals in the Rubin study could explain some of these differences. Although there were differences in study duration, these overlapped and do not seem to explain any of the differences reported. The Torvinen study used a short exposure period (4 minutes) for each treatment and somewhat greater loads, although at similar frequency. None of the studies showed any differences in bone turnover markers, but there were observable differences in muscle strength (e.g., jump height). These possibilities require examination in further studies with respect to study sample age and weight, as well as vibration exposure and amplitude.

Any side effects? Vibration of the human body has been proposed from epidemiological studies to cause back pain. However, no such major side effects were reported from these studies, and whole body vibration exercise has been proposed for treatment of chronic low back  pain. Another possible safety aspect is that the displacement could be large enough for the patient to fall, but this was not reported in these studies. What could be the biological mechanisms of this whole body vibration?

The vibration is sufficiently low to be unappreciable by the participants, so it seems unlikely to be a direct effect of the mechanical strain. It could be an indirect effect through amplifying of signals by intramedullary pressure or through fluid flow in the bone tissue. For the  neuromuscular or muscular effects, stimulation of the skeletal muscular pump has also been proposed to affect circulatory flows and flow through the bone tissue. However, these
potential mechanisms still need to be fully studied. How do these effects compare with published studies on pharmacologic interventions?

Leaving aside any potential muscle or balance effects, the net benefit versus placebo ranged from 1.55% to 2.2% and up to 3.4% in those of lower weight and best compliance. These effects over 1 year are difficult to compare with pharmacologic studies over 2–3 years, but in a bisphosphonate study with a 1-year endpoint, the difference from placebo was 2.4%. This comparison might suggest somewhat similar benefit, provided that good compliance can be
achieved. However, it is recognized that change in BMD cannot be easily translated to fracture reduction. Thus, the burning question is what fracture reduction could be achieved with whole body vibration. A tantalizing possibility is that there could be an interaction between whole body vibration and pharmacologic treatment.

Could whole body vibration enhance the effect of an anabolic agent or an antiresorptive? In one study in rat tail, there was a synergistic effect of parathyroid hormone (PTH) and mechanical stimulation on trabecular bone formation. It remains to be seen whether similar  interactions could be seen in humans, where no major effect on bone turnover from whole body vibration has been observed. A further development in the future might be shock wave treatment, which in animals, has been shown to be positive with increased bone mass in  fractured limbs.

WHAT’S SHAKING?
What are the requirements to bring this equipment to the market place? Vibration platforms are regarded as “devices” and not a pharmaceutical intervention; therefore, they are subject to different regulatory criteria for safety and efficacy. Therefore, for considerations of clinical application, it is important to determine what kinds of data are needed to support vibration as a valid and rational treatment option. Should BMD change be sufficient or should we require
fracture reduction data ? Is analysis by compliance reasonable in light of our judgments about other randomized placebo controlled trials, where intention to treat (ITT) is and should remain the gold standard? Although vibration platforms seem to be relatively safe, it will be important to establish their antifracture and BMD efficacy as well as their safety in larger and more adequately powered randomized double-blinded controlled trials.

Whole Lotta Shakin’ Goin’ On is a post from: Vibrating Exercise

Vibration is a mechanical stimulus characterized by an oscillatory motion. The biomechanical variables that determine its intensity are the frequency and amplitude. The extent of the oscillatory motion determines the amplitude (peak to peak displacement, in mm) of the vibration. The repetition rate of the cycles of oscillation determines the frequency of the vibration (measured in Hz). Vibration has been studied extensively for its dangerous effects on humans at specific amplitudes and frequencies. On the other hand, recent work has suggested that low amplitude, low frequency mechanical stimulation of the human body is a safe and effective way to exercise musculoskeletal structures. In fact, increases in muscular strength and power in humans exercising with specially designed exercise equipment have been reported.

In particular, the effects of whole body vibrations (WBVs) have been studied with subjects exercising on specially designed vibrating plates producing sinusoidal vibrations. The exercise devices currently available on the market deliver vibration to the whole body by means of oscillating plates using two different systems: (a) reciprocating vertical displacements on the left and right side of a fulcrum; (b) the whole plate oscillating uniformly up and down. WBV exercise devices deliver vibrations across a range of frequencies (15–60 Hz) and displacements from ,1 mm to 10 mm. The acceleration delivered can reach 15 g (where 1 g is the acceleration due to the Earth’s gravitational field or 9.81 m/s2). Considering the numerous combinations of amplitudes and frequencies possible with current technology, it is clear that there are a wide variety of WBV protocols that could be used on humans. Vibration exercise is quite a new topic in sport science. Many athletes and fitness and rehabilitation centers are using vibration in their exercise programs, but current knowledge on appropriate safe and effective exercise protocols is very limited, and claims made by companies and pseudo-experts can be misleading.

The purpose of this review is to analyze the potential mechanisms by which muscles respond to vibration and to summarize current knowledge of the effects of vibration on human strength and power performance.

IS VIBRATION A NATURAL STIMULUS?

During all sporting activities our bodies interact with the external environment and experience externally applied forces. These forces induce vibrations and oscillations within the tissues of the body. Tissue vibrations can be induced from impact related events where either a part of the body or sporting equipment in contact with the body collides with an object. Examples of this are the impact shocks that are experienced through the leg when the heel strikes the ground during each running stride or the impact shock that occurs when a racquet is used to hit a ball. The initial impact causes vibrations within the soft tissues, after which the tissues continue to oscillate as a free vibration—that is, vibrating at their natural frequency, with the amplitude of these vibrations decaying because of damping within the tissues. Tissue vibrations can also be induced when the body experiences more continuous forms of vibration, such as may occur through the legs during skiing across a groomed slope or through the arms during bike riding. A continuously oscillating input force drives the soft tissue vibrations to be at the same frequency as the input force, but the amplitude of the vibrations will be greatest if the natural frequency of the tissues is close to that of the input force (resonance); however, the amplitude of these larger amplitude vibrations can be reduced by damping from the tissues. Therefore we can expect to experience soft tissue vibrations in all sporting activities, and the amplitude and frequency of these vibrations is partly determined by the natural frequency and damping characteristics of the tissues.

The body relies on a range of structures and mechanisms to regulate the transmission of impact shocks and vibrations through the body including: bone, cartilage, synovial fluids, soft tissues, joint kinematics, and muscular activity. Changes in joint kinematics and muscle activity can be controlled on a short time scale and are used by the body to change its vibration response to external forces. It has been proposed that the body has a strategy of ‘‘tuning’’ its muscle activity to reduce its soft tissue vibrations in an attempt to reduce such deleterious effects. This idea would predict that the level of muscle activity used for a particular movement task is, to some degree, dependent on the interaction between the body and the externally applied vibration forces. It has been proposed that vibrations could be used as a training aid. However, prolonged exposure to vibrations has been shown to have detrimental effects on the soft tissues, including muscle fatigue, reductions in motor unit firing rates and muscle contraction force, decreases in nerve conduction velocity, and attenuated perception.  The natural frequency of a vibrating system depends on its stiffness and mass. Within the skeletal muscles, each cross bridge between the actin and myosin myofilaments generates some stiffness, and so the tissue stiffness (and therefore natural frequency) can be increased with increases in muscle activity. Indeed, studies have shown that increases in the natural frequency of whole muscle groups do concur with the joint torques developed by the muscle and typically range between 10 and 50 Hz for the lower extremity muscles (zero to maximal activity). Muscles can also damp externally applied vibrations, and, indeed, more vibration energy is absorbed by activated muscle than by muscles in rigor, suggesting that the active cross bridge cycling is an important part of the damping process. Studies have shown that the damping coefficients of whole muscle groups increase with muscle activity, supporting the idea that the cross bridge mechanisms are important. A maximally activated muscle can damp free vibrations so that the tissue oscillations are virtually eliminated after a couple of cycles.18 It is thus possible that muscles are activated to minimize the vibrations that occur within the tissues, but does this actually happen during WBV exercise?

VIBRATION AND MUSCLE ACTIVATION: THE MUSCLE TUNING HYPOTHESIS

Evidence for muscle tuning requires information on the nature of the input force, the vibration response of the tissue, and the level of muscle activity. These can be difficult to measure because vibrations induced in the tissues can cause movement artifacts, which may interfere with measurement of muscle activity. Nonetheless, in a study of hand held vibrating tools, it was found that activation of the triceps brachii was greatest between vibration frequencies of 8 and 16 Hz, coinciding with the resonant frequencies measured at the wrist and elbow (10–20 Hz). In a similar experiment, vibration was recorded directly from the soft tissue groups in the lower extremities while subjects stood on a vibration platform. The natural frequencies for the tissues for each posture were determined by measuring the vibration response to a complex vibration covering a range of frequencies and therefore accounted for changes in resonance that occurred with altered limb posture and muscle activity. The vibration response of the soft tissues was measured for a range of input vibration frequencies (10– 65 Hz), and it was found that most vibration damping occurred at the resonant frequencies of the tissues, concurring with the highest levels of muscle activity. The responses of the lower extremities to continuous vibrations or sequences of single, impact-like input were similar. This suggests that the body has a strategy to minimize its vibrations regardless of the mode of the input force. These studies support the muscle tuning paradigm, but these concepts should be tested further. For instance, the effect of the amplitude of the input vibrations on the tuning response has not yet been determined. Is there minimum amplitude below which the body is not triggered to respond?

At high vibration amplitudes, the maximum damping from the tissues will not be as effective at dissipating the vibration energy. We do not yet know the most effective range of vibration amplitudes that can be applied safely while eliciting a significant tuning response. Training protocols and sporting equipment that cause specific alterations in muscle activity during exercise may have important implications for athletic training, rehabilitation after injury, and competitive performance. For instance, the hardness of a shoe midsole causes changes in the time to peak impact force at heel strike. This time and the associated loading rate are a correlate of the major frequency content of the impact force; impact forces that drive the soft tissues of the lower extremity closer to resonance cause increases in muscle activity and vibration damping from those tissues. It is conceivable that different types of equipment may be designed in future: training equipment, which promotes increased muscle activity, and competition equipment, which reduces the muscle activity required for vibration damping and thus allows more of the muscle activity to be used for the sporting task. Vibration platforms are the most recent example. They have been developed with the idea of promoting muscle activity, hence providing an effective training stimulus. Are they effective?

METABOLIC EFFECTS OF VIBRATIONS

The possibility of using vibrations as an effective training tool can be considered a recent idea. However, it should be noted that early work by Whedon reported some positive effects of oscillating beds on plaster immobilized patients. The possibility of using vibration in an athletic setting was introduced relatively recently by Russian scientists, who developed specific devices to transmit vibratory waves from distal to proximal links of muscle groups, mainly during the performance of isometric exercises. Recently many studies have been conducted with the aim of understanding the acute and chronic responses to WBV training (WBVT). WBVT has been shown to cause clear metabolic responses similar to other forms of exercise. In a study by Rittweger, WBVT to exhaustion with an extra weight showed an O2 uptake of less than 50% of VO2MAX.

An acute reduction in vertical jump was observed, suggesting that vibration exercise to fatigue can impair neuromuscular performance. The early impairment of muscle performance was shown to be recovered 20 seconds after the end of the fatiguing vibratory exercise. Another experiment conducted by Kerschan-Schindl showed a significant increase in muscle blood volume in the calf and thigh and a significant increase in mean blood flow velocity in the popliteal artery after vibration exercise on a vibrating plate (26 Hz, 3 mm amplitude). The mean blood flow measured by Doppler ultrasound increased from 6.5 to 13 cm/s, and this acute  response was attributed mainly to the effect of vibrations in reducing the viscosity of blood and increasing its speed through the arteries. The above studies seem to indicate that WBVT may represent a mild form of exercise for the cardiovascular system. However, owing to the relatively low level of stimulation, it is unlikely that an athletic population could benefit from such a training stimulus if the aim is to improve cardiovascular performance. However, elderly people could make use of this form of exercise when other solutions are not possible. Also, because of its reported beneficial effects in reducing low back pain, pain sensation, and pain related limitation, it may be a viable alternative for a patient who cannot run and/or lift weights. However, the extensive literature on the dangerous effects of WBV on the spine (for a review, see Cardinale and Pope) suggests that more, well controlled, long term intervention studies are needed before WBVT can be prescribed for patients with low back pain.

ACUTE EFFECTS OF VIBRATION ON NEUROMUSCULAR PERFORMANCE

Most of the studies so far conducted have focused on the acute and chronic effects of WBVT on neuromuscular performance. In our studies, WBV exercise has been shown to acutely enhance strength and power capabilities in well trained people. Acute application of five minutes of WBVT at 26 Hz and 10 mm peak to peak amplitude were in fact shown to shift the force-velocity and power-velocity relations to the right in the vibrated legs of well trained volleyball players.1 Finally, WBVT applied for a total of 10 minutes (26 Hz, 4 mm) was shown to improve vertical jumping ability, increase concentrations of testosterone and growth hormone, and decrease cortisol concentrations in recreationally active people. The results of this preliminary study have been used by many companies to advertise WBVT as a way to boost anabolic hormones, reduce stress, and accelerate muscle remodeling. For this reason, it is important to recognize that the study has many limitations, the primary one being the absence of a control condition. Also, not all studies have shown acute increases in strength/power performances and hormone concentrations. Torvinen, for example, have shown acute increases in knee extension maximal strength and vertical jumping height after four minutes of WBVT when a relatively large amplitude was applied (4 mm) with a tilting plate as compared with no significant acute effects when low amplitude whole plate oscillation (2 mm) was applied. Results from our laboratory have also shown that, when vibration duration is relatively long (seven minutes), an acute decrease in vertical jumping ability is observed even in well trained subjects.

Recent work from De Ruiter in which subjects exercised on a vibrating plate for  one minute (frequency 30 Hz, amplitude 8 mm) with two minutes rest in between, showed an acute reduction in maximal voluntary knee extension force. Also, in their well controlled study, the authors showed that vibration depressed voluntary activation of the leg extensor muscles up to 180 minutes after the exercise bout. Finally, Di Loreto et al have recently shown that 10 minutes of WBVT at 30 Hz with a relatively small amplitude did not produce any change in the serum concentrations of growth hormone, insulin-like growth factor 1, and free and total testosterone.

At this stage, owing to the differences in WBVT protocols used in the different studies, it is difficult to ascertain the acute effects of the WBVT intervention on the neuroendocrine and neuromuscular systems. However, it is important to consider that a certain degree of muscle activation is needed from lower limb muscles to damp the vibrations originated by vibrating plates. In fact, this extra muscle activity results in a greater rate of oxygen uptake during exposure to vibrations. It should be remembered that, according to the muscle tuning theory, the magnitude of the muscular response is related to the interaction between the amplitude and frequency of the vibration input and the intrinsic neuromuscular properties. It is possible that many studies have failed to show any positive effect of vibration because the applied vibrations did not stimulate the target muscles at their resonant frequencies. It should also be noted that most of the studies have focused on leg extensors, while neglecting plantar flexors which have been shown to increase their electromyographic activity up to five times the baseline values with vibration. It is clear that more studies are needed to ascertain the influence of the above variables on humans.

CHRONIC EFFECTS OF VIBRATION ON NEUROMUSCULAR PERFORMANCE

Chronic studies seem to provide more supportive evidence for the possibility of using WBVT effectively in different populations. A few weeks of training seem to produce conflicting results.

In our study in 10 days of WBV (26 Hz, 10 mm, total exposure time 100 minutes) resulted in an increase in average jumping height (+11.9%) and power output during repeated hopping in active subjects. No change was observed in counter movement jump performance. Five training sessions of five minutes each (30 Hz, 8 mm amplitude, total exposure 25 minutes) did not affect maximal voluntary contraction and voluntary activation of leg extensors in untrained students.34 The same authors also analyses the effects of 11 weeks of WBVT on maximal voluntary contraction measured with an isometric leg extension task (maximal voluntary contraction), maximal force generating capacity, and stimulated maximal rate of force rise. The results showed no change in all variables except for an increase in stimulated maximal rate of force rise in the group undergoing WBVT detected at week 14. The subjects in this study were exposed to WBVT three times a week starting with five sets of one minute each with one minute seated rest in between.

Exercise duration was progressively increased up to eight sets of one minute each. However, even if the total exposure time to WBVT was relatively high (169 minutes), it is important to note that the training period was not continuous because of two weeks of non-training allowed between week 5 and week 7 of the study. Nine days of WBVT have also been recently shown to have no effect on jumping ability, sprinting, and agility tests in sport science students. In the light of the above, it seems clear that, when WBVT is performed with small amplitudes for a short time by physically active people, it is unlikely to produce significant improvements in force and power generating capacity of the lower limbs. However, when resistance exercise is performed on a vibrating plate, it seems that even physically active people can improve vertical jumping ability more than by resistance exercise alone.

When standing on a vibrating plate, young healthy people generate relatively low force levels in their lower limbs compared with their maximal voluntary capacity. Hence, even if the vibration stimulation can increase their muscle activity, it is likely that this would not be enough to produce any significant change in their ability to forcefully activate their muscles. So, if well trained populations use vibration exercise with the aim of improving neuromuscular performance, an optimal amplitude and frequency should be coupled with an optimal level of muscle activity on which the vibration stimulation can be superimposed. Of course, this should be the aim of future studies and for this reason we have recently patented an exercise device able to allow the user to perform vibration exercise while controlling the level of force and muscle mechanics. On the other hand, sedentary, injured, and elderly people with impaired muscle activation capabilities may benefit from currently available WBVT applications. In this case the results seem to be more encouraging.

In fact, Torvinen showed a net improvement of 8.5% in vertical jumping ability after four months of WBVT performed with static and dynamic squatting exercises with small vibration amplitudes (2 mm) and frequencies ranging from 25 to 40 Hz in sedentary subjects. A 12 week WBVT program (frequency 35–40 Hz and amplitude 2.5–5 mm) induced a significant enhancement in isometric, dynamic, and explosive strength of knee extensor muscles in healthy, untrained, young adult women. Also, vertical jump improved only in the group undergoing WBVT and not in the group performing conventional resistance exercise. However, it should be noted that the resistance exercise program in this study was of relatively low intensity (started with a load of 20 repetition maximum and reached 10 repetition maximum in the last four weeks) and the exercises (leg press and leg extensions) were performed to failure and not with explosive movements, reducing the possibility of such a program producing significant changes in explosive measures. The same authors also showed that 24 weeks of WBVs were effective in producing a rightward shift in the force-velocity relation of knee extensor muscles and an increase in fat-free mass in untrained female subjects.

Despite not being significantly different from the standard training groups, the results observed by both Delecluse  and Roelants  highlight the possibility that long term program of WBVT may produce significant improvements in muscle function of the leg extensors in untrained subjects. As more supportive evidence, a recent study from the same group7 showed that WBVT was superior to a low intensity resistance training program in improving isometric and dynamic muscle strength in middle aged and older women (58–74 years). The WBVT program was also effective in increasing bone mineral density of the hip even though the improvement was very small (+0.93%) and within the error of measurement used for establishing bone mineral density.

Finally, Torvinen  have shown that eight months of WBVT with small amplitude (2 mm) improved vertical jumping ability in young healthy sedentary subjects compared with a control group, but did not change dual energy x ray  absorptiometry derived bone mineral content measures, markers of bone turnover, and postural sway. The latest results support our idea that the current technology/methods of use of WBVT (standing on a vibrating plate with low force generation in the lower limbs) are unlikely to produce significant improvements in performance in well trained athletes and physically active young subjects, and, even if they do, conventional resistance exercise should still be superior. However, this technology may be of benefit to the elderly or in rehabilitation programs, as little effort is required and there is no complicated technique to master. Special populations in particular seem to benefit from acute bouts of WBVT. Unilateral chronic stroke patients, for example, have been shown to improve postural stability after a few minutes of WBVT at 30 Hz and 3 mm amplitude. Also, heart transplant patients seem to be able to exercise on vibrating plates with no adverse events. Furthermore, owing to the potential of this intervention to stimulate bone remodeling, it is possible that WBVT may be a possible non-pharmacological intervention for the prevention of osteoporosis, but more evidence needs to be gathered with well controlled studies.

CONCLUSIONS

The current evidence indicates that WBVT may be an effective exercise intervention for reducing the results of the ageing process in musculoskeletal structures. It would also appear that vibration may be an effective countermeasure to microgravity and disuse. However, it is important to conduct further studies to understand the neurophysiological mechanisms involved in muscle activation with vibration in order to be able to prescribe safe and effective WBVT programs. Not only the optimal frequency and amplitude need to be identified but also the level of muscle activation that would benefit more from vibration stimulation. Considering current WBVT technology, it is possible to confirm that the procedure seems safe when subjects stand on vibrating plates for a relatively short time with knees semi-flexed to limit transmission of vibrations to the head. However, when vibration transmission frequency is too high, some can experience motion sickness-like symptoms. As we know from occupational medicine that prolonged exposure to WBVT can have major negative effects on health, proper care should be taken when exercise programs are prescribed so as to guarantee safety.

Whole body vibration exercise: are vibrations good for you? is a post from: Vibrating Exercise

Remember the vibrating belts of mid-century “reduction machines” that were supposed to effortlessly trim your waistline? If you thought they looked silly, wait until you see what’s shaking now in the fitness industry. New “whole body vibration” machines showing up in some swank health clubs and rehabilitation facilities are generating ripples of curiosity — and concern. No Washington area gyms are among the early adopters.

The training method, pioneered in the 1970s by Russian Olympic sports trainers looking to boost muscle strength, flexibility, range of motion and more, involves standing on what looks like a high-end bathroom scale with handlebars. But even on a bad day, your home bathroom scale won’t bounce like this. Step up, flip the switch and, instantly, you’re all aquiver. If there’s anyone in the room you want to impress, it’s too late now. Reading the roster of vibration proponents, though, might stop your laughter. Lance Armstrong, who claimed his fifth consecutive Tour de France bicycle race win last July, owns one body-shake device, called the Galileo, says its marketer, Orthometrix. So do nearly all the German Olympic training centers, the company says. The maker of a competing body-shake product, the Power Plate, counts among its users the Tampa Bay Buccaneers football team, the New York Mets baseball club and the Anaheim Mighty Ducks hockey squad. Garrett Giemont, the Tampa Bay Buccaneers’ strength and conditioning coach, says he has players use the Power Plate not to replace standard conditioning, but to loosen and massage sore muscles the day after a game. “I call it a tool in my toolbox,” he said.

But it may not be just world-class athletes who can benefit from vibration exercise. Scientists are exploring a range of possible therapeutic applications that, if shown effective, could literally shake up the way we get fit, recover from illness and injury and manage chronic health conditions. For example, some research suggests vibration may help build bone — a finding that could lead to an alternative treatment for the 44 million Americans who, according to the National Institutes of Health, have either osteoporosis or low bone mass, which is a precursor for the brittle bone disease. Studies may also one day confirm whether vibration could help relieve arthritic and postoperative pain, control incontinence, restore blood flow to the extremities or activate the muscles of people with multiple sclerosis. While there have been some high-quality human studies showing the technologies’ benefits, as a whole the body of research is inconsistent and not comprehensive enough to permit broad conclusions. And hopes of benefit are offset by a nagging concern: Too much body rattling is a proven health hazard, particularly for people with long-term exposures, like truck drivers and jackhammer operators.

Shake Your Booty

Exactly how mechanical vibration might produce benefits for the body scientists don’t know. Human research into the technique is relatively new. The prevailing theory is that vibration stimulates the body’s natural stretch reflex, much as when a doctor taps a patient’s patella with a reflex hammer and elicits a knee-jerk reaction. Vibration causes the muscles to flex and relax involuntarily. Repeated rapid muscle contraction boosts blood flow to the muscles, bones and tissues and can even make you break a sweat. The potential bone-building effects of vibration made national headlines in August 2001 when the journal Nature published a sheep study led by Clinton Rubin, director of the Center for Biotechnology at the State University of New York at Stony Brook. Adult female sheep exposed to gentle vibrations for 20 minutes a day increased bone density in their hind legs by 34 percent over a year, compared with a control group, the study found.

The findings aroused enormous interest. “I got thousands if not tens of thousands of e-mails asking, ‘Should I be standing on my washing machine?’” Rubin recalls. Some scientists speculate that vibration could be a particularly useful tool for older or obese individuals, who have trouble doing traditional weight-bearing exercise, or people who cannot tolerate pharmaceutical treatment. For now, however, much of the medical evidence supporting vibration therapy is anecdotal. Clifford Rosen, a past president of the American Society for Bone and Mineral Research and scientist at The Jackson Laboratory in Bar Harbor, Maine, has two women patients with low bone density who have been using a vibration platform for two years. Both women — a 38-year-old with a muscle disorder and a 41-year-old who’s been unable to tolerate drug treatment — have seen their bone density stabilize since beginning vibration treatment, he said. “I think it’s a great option for some people,” Rosen says.

Diane Kelly, a chiropractor in Arnold, says she’s also seen good results since putting patients, including some who found traditional exercise painful and difficult, on a Power Plate she bought in October for between $9,000 and $10,000. One patient, a 69-year-old retired nurse, couldn’t walk up stairs previously without having to stop, grab the railing and rest, Kelly said. Vibration training, she said, “strengthened her back and it gave her endurance so she could climb up stairs without panting.” Patrick Jacobs, an assistant professor and researcher with The Miami Project to Cure Paralysis at the University of Miami School of Medicine, has been using the Galileo for the past several months with able-bodied people to better understand the effects of vibration on flexibility and muscle strength. If his initial studies go well, he hopes to use the device with people with spinal cord injury. He wants to know, for example, whether patients who retain some degree of sensation and motor control can optimize use of their afflicted limbs through vibration training. Jacobs and research colleagues presented results of the initial studies at last week’s annual meeting of the American College of Sports Medicine in Indianapolis. One study found that vibration increased heart rate response, flexibility and muscle power in healthy adults; the other revealed significant neural changes in healthy subjects after vibration, findings that have promising implications for people spinal cord injury, said Kristina Beekhuizen, one of the researchers.”I was very, very impressed with our preliminary results,” said Jacobs. Neither Jacobs and colleagues nor the university has any financial stake in the Galileo or Orthometrix.

Feeling the Burn

One aspect of whole body vibration is likely to have broad appeal: Compared with traditional forms of exercise, vibration training requires relatively little exertion. I agreed to try out two models — the Galileo, used primarily by rehab facilities, physical therapists and medical research institutions, and the Power Plate, which dominates the sports and fitness market. First, Bruce Harvey, a sales manager for Orthometrix Inc., gave me a demonstration of the Galileo at the company’s headquarters in White Plains, N.Y. The Galileo vibrates in a unique teeter-totter motion within a range of 5 to 30 hertz (more on this below). That’s mild compared with other machines on the market. The model I tried had an oscillating plate barely large enough to accommodate my size 8-1/2 feet and a digital pad to adjust the speed and duration of the exercise. You simply stand with knees slightly flexed on the oscillating plate, heels lifted a bit, and let your muscle reflexes do the work. Depending on the vibration frequency selected, you may need to grab on to the handlebars to steady yourself. Changing your body position targets other muscle groups: A deep squat with legs slightly apart concentrates on the calves and quadriceps. “So the entire body is being exercised depending on which muscle you tense,” explains Reynald Bonmati, founder, chairman and chief executive of Orthometrix Inc., maker of Galileo.

Afterward, I felt as if my legs were weightless. But I also wondered whether some stiffness in my shoulder the following day resulted from all that shaking. Harvey said the platform’s teeter-totter motion was probably not responsible. “There’s absolutely no transmission of the vibration up to the shoulders,” he said. A few weeks later, personal trainer Chris Imbo of New York’s tony Casa Fitness took me through the paces on the Power Plate, which the club installed for its members about six months ago. The vibrating plate on this unit moves in an up-and-down pattern and is roomy enough for the largest feet. That machine vibrates within a much higher range, starting at 30 hertz and topping out at 50 — the number of times a hummingbird flaps its wings in a second. Having a better idea of what to expect, I enjoyed the machine’s pulsing action at the lower frequency. But at full tilt, it felt as if I were being whipped to a froth. A day later, my glutes and quadriceps definitely felt the burn, the same as I’d have felt after weight training.

Bad Vibes

If all this sounds good, consider what else we know about vibration. For decades, biomechanical engineers have reported on the occupational hazards associated with driving big rigs and using vibrating hand tools, jobs that involve long-term exposure to intense vibration. Jackhammer operators are prone to a circulatory condition called Reynaud’s syndrome that can numb fingers and damage blood vessels, say scientists at the University of Tennessee’s Institute for the Study of Human Vibration. The institute studies medical risks tied to job-related vibration exposure, not vibration as exercise. Bus and truck drivers’ chronic exposure to whole body vibration can lead to lower back problems. And studies suggest women who operate heavy machinery while pregnant may be at greater risk of miscarriage than women who don’t. The risk of harm, say researchers, is dependent on the duration, frequency and magnitude of the exposure. Typically, vibration exercise is performed in short spurts. It takes 10 to 15 minutes to complete an entire workout, whether you’re using it for rehab or exercise, and that’s often repeated a couple times a week. Truck drivers, by contrast, often are exposed to jarring motion for hours at a time, day after day. Frequency refers to the number of vibrations, or oscillations, per second. At 25 hertz, the targeted muscles receive 25 cycles of vibration per second, making them contract and relax as many times in the same period. Oddly, scientists have found the most troublesome vibration frequencies for the human body occur at the “slower” range of 4 to 8 hertz in the vertical position and 1 to 2 hertz in the side-to-side and front-to-rear directions. Magnitude is the so-called G-force, or acceleration, of the movement, and there is wide disagreement about the safe level. Vibration plates made for exercise and physical training deliver more than 8 g of force, says Rubin, the SUNY Stony Brook researcher. He insists that’s far too much.

In a study published in the March 2004 issue of the Journal of Bone and Mineral Research, Rubin and colleagues found that exposing postmenopausal women to low-magnitude vibration — less than 0.3 g — for brief periods while they are standing can inhibit bone loss in the spine and thighbone. “We are arguing that mechanical signals can be very beneficial to the skeleton,” he says. “But just like any other drug or any other intervention that causes a response, there can be too much of a good thing.” Using the commercially available vibration platforms for fitness, he said, “is jumping off your refrigerator.”

Makers of vibration platforms reject that analogy, insisting the devices are safe. “A professional athlete is not going to jeopardize their career by using something that is not safe and effective for them,” said Chris Camacho, director of athletic and physiological applications at Power Plate North America in Culver City, Calif. Orthometrix executives likewise dismisses Rubin’s concerns. “If it’s good for muscle, believe me it’s good for bone,” said Bonmati, the company’s chairman. But few rigorous long-term safety studies have been published on the training method in humans. Studies on the method’s effectiveness also fall short. Of the dozens published to date, few compare the method, long-term, against a control group or more traditional training. When randomized controlled trials have been conducted, they have produced conflicting results, especially concerning bone mass and strength, notes Pekka Kannus, chief physician of Finland’s UKK Institute, which conducts health and exercise research. Accordingly, many U.S. health and fitness experts urge caution. “The evidence is equivocal regarding the benefits of vibration training,” states William P. Ebben, a clinical assistant professor in the exercise science program at Marquette University in Milwaukee.

Going Slow

For those who’d like to still like to try whole body vibration, Rodney Corn, an educator with the National Academy of Sports Medicine, has this advice: Go easy and consult with your doctor first. Whole body vibration is not recommended for people with fresh fractures or new implants, people with epilepsy, individuals prone to blood clots and women who are pregnant. If you want to buy your own machine, start saving. Commercial units cost around $10,000 (Power Plate recently cut the price on most models to $8,500). The company’s looking to roll out a home unit by year’s end for around $3,000. Galileo has no home unit yet. Or then again, maybe you can pick up one of those old jiggly belt things at an antique store or garage sale for a fraction of the price.

Karen Pallarito, a former health reporter for Reuters, is a freelance writer in Westchester County, N.Y.

Whole Body Vibration: Does it Work? is a post from: Vibrating Exercise