body vibration frequencies

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MED SPORT 2003;56:287-92

The acute effects of two different wholebody vibration frequencies

on vertical jump performanceM. CARDINALE1, J. LIM2

1School of Medical Sciences, College of Life Sciences and Medicine, University of Aberdeen,Aberdeen, Scotland, UK

2

Department of Health and Physical Education, Northern State University, Aberdeen, SD, USA

Mechanical stimulation in the form ofvibration has been recently shown toproduce specific adaptive responses inhumans.1-9 It has been hypothesized that alow-frequency, low-amplitude vibratory stim-ulation it is a safe and effective exercise inter-

vention. A single session of 5 min of wholebody vibration (WBV) has been shown toinduce a shift of the force-velocity and pow-er-velocity curve to the right in well trainedfemale volleyball players.3A single session of10 min divided in 2 sets of 5 bouts of 60 s

WBV with 60 s rest in between sets has been

shown to improve vertical jumping perfor-mance and determine an increase in testos-terone and growth hormone production in

well-trained individuals.10 Recent evidencefrom Torvinen et al.5 suggests that short-timeexposure to WBV cab lead to an improve-

ment in vertical jump performance and forcegenerating capacity in lower limbs. On theother side, prolonged administration has beenshown to induce fatigue and inhibit neuro-muscular performance.1, 8, 11Although vibrationis being employed from athletes in their train-ing regimes, it is still unclear how it is possi-ble to effectively use this novel exercise inter-

vention. Few studies looking at the acuteeffects of WBV have shown contradictoryresults. In particular, the effect of different

vibration frequencies on neuromuscular per-

Address reprint requests to: M. Cardinale, phD, Universityof Aberdeen, College of Life Sciences and Medicine, Schoolof Medical Sciences, Human Physiology Building, Foresterhill,

AB25 2 ZD Aberdeen, Scotland (UK).E-mail: [email protected]

Aim.Vibration exercise is a novel exercise intervention, which is applied in athletes and generalpopulations with the aim of improving strength and power performance. The present study wasaimed to analyse the adaptive responses to different whole body vibration frequencies.

Methods.Fifteen untrained subjects were randomly assigned to a 5 min whole body vibration (WBV)training session on a vibrating plate producing sinusoidal oscillations at 20 Hz (low frequency) and40 Hz (high frequency) with constant amplitude. Squat jump, countermovement jump and sit andreach test were administered before and after the WBV treatment.

Results. Low frequency WBV stimulation was shown to significantly increase hamstrings flexi-bility by 10.1% (p


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CARDINALE THE ACUTE EFFECTS OF TWO DIFFERENT WHOLE BODY VIBRATION FREQUENCIES ON VERTICAL JUMP

formance is still unclear. Therefore, the pur-pose of this study was to analyse the acuteeffects of 2 different WBV frequencies on ver-tical jump and flexibility.

Materials and methods

Subjects

Fifteen subjects (2 women and 13 men)voluntarily participated to the study. Theywere all involved in recreational sport activ-ities. They were randomly divided into 2groups: a high frequency group (HFG) and a

low frequency group (LFG). Subjects withprevious history of fractures or bone injurieswere excluded from the study. The HFG wasconstituted from 7 subjects (age: 20.40.5

years, height: 1.790.05 m; weight: 789.4kg). Eight subjects were assigned to the LFG(age: 212.2 years, height: 1.760.1 m; weight:75.218.2 kg). The protocol was approvedby the local ethics committee.

Procedures

The subjects were familiarized with the

protocol and the WBV treatment the daybefore the experimental trial. At the beginningof the experimental session anthropometricmeasures (height and weight) were recordedtogether with the age of the subjects.Following this phase a 10 min standard warmup consisting of running, jumping and stretch-ing exercises was performed. After the warmup, the subjects performed the followingstests: sit and reach test (S&R), squat jump(SJ), and counter movement jump (CMJ).Between groups comparison did not reveal

statistically significant differences at baselinefor all the measured variables.

Sit and reach test was performed on a sit andreach box in which subjects were seated withtheir heels firmly planted against the heelboard, and feet approximately 1 foot apart.Testing procedures have been described else-

where.12 Three trials were performed and thebest one was used for statistical analysis.

Vertical jumping tests were conducted ona resistive platform 13 connected to a digitaltimer (accuracy0.001s) (Ergojump, Psion XP,MA.GI.CA. Rome, Italy) which was recordingthe flight time (tf) and contact time (tc) of

each single jump. In order to avoid unmea-surable work, horizontal and lateral dis-placements were minimised, and the hands

were kept on the hips through the tests. Therise of the center of gravity above the ground(h in meters) in was measured from flighttime (tf in seconds) applying ballistic laws:

h=tf2g8-1 (m) [1]

where g is the acceleration of gravity (9.81ms-2).

Two different jumping tests were per-formed: squat jump (SJ), in which subjects

were jumping from a semi-squatting position

without counter movement and countermovement jump (CMJ) in which subjects

were allowed to perform a counter move-ment with lower limbs before jumping. Threetrials for each test were performed, the bestresult was considered for statistical analysis.

Treatment procedures

Subjects were exposed to vertical sinu-soidal WBV using the device called NEMESLC (Ergotest, Greece). The frequencies used

288 MEDICINA DELLO SPORT Dicembre 2003

TABLE I. Data are expressed as meanSD.

Parameter Pre Post Significance

20 Hz group

Squat jump (cm) 242.5 253.1 p


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THE ACUTE EFFECTS OF TWO DIFFERENT WHOLE BODY VIBRATION FREQUENCIES ON VERTICAL JUMP CARDINALE

in this study were 20 Hz for the LFG and 40Hz for the HFG (Peak-to-peak displace-ment=4 mm; theoretical acceleration=6.4 g(20 Hz) and 25.7 (40 Hz) g, where g is equalto 9.81 ms-2). The subjects were exposed to5 bouts lasting 60 s each of WBV while stand-ing on the vibrating plate in semi-squattingposition. Sixty s rest in between each bout

was allowed. Sixty s following the last bout

of WBV testing took place again.

Statistical methods

Conventional statistical methods usedincluded mean, standard deviation and pairedand unpaired Students t-test. The level ofsignificance was set at p


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They reported a significant marked reduc-

tion in vertical jump 6, 14 and maximal kneeextensors force 11 following WBV exercise

with similar protocols.Five minutes of WBV with a low frequen-

cy (20 Hz) were shown to acutely enhanceneuromuscular performance as measured by

vertical jumping ability. This observation isalso consistent with previous findings 1-3, 5

which found acute improvements in verticaljumping ability and force-generating capac-ity in humans following 4 to 5 min WBV atfrequencies ranging from 15 to 30 Hz.

Any acute effect of WBV training was

expected to be of neural origin. In particular,the role of agonist/antagonist muscle activi-ty in the modulation of joint stiffness hasbeen hypothesized to be the responsible foracute adaptive responses.15 In this study dif-ferent vibration frequencies were shown tohave different effects on knee joint stiffnesssince the change in vertical jumping ability

was parallel to the change in hamstrings flex-ibility. During vibration the body and theskeletal muscle undergo to small changes inmuscle length. The peculiar characteristicsof the vibratory stimulus determine an acti-

vation of Ia afferent fibers.16 Mechanical vibra-tions applied to the muscle itself or the ten-don elicit a reflex muscle contraction namedtonic vibration reflex (TVR).17 This reflex con-traction is caused by an excitation of musclespindles leading to an enhancement of theactivity of the Ia loop.18, 19 Facilitation of theexcitability of spinal reflexes has been shownto be elicited through vibration to quadri-ceps muscle.20 Lebedev and Peliakov 21 alsosuggested that vibration may elicit excitatoryflow through short spindle motoneurons

connections in the overall motoneuroninflow. The neural circuitry involved in thetonic vibration reflex has been quoted to besimilar to the one observed for the tendon tapreflex. It then involves the activation of thehomonimous motor units and the decrease inexcitability of the motor neurons innervat-ing the antagonist muscle through the recip-rocal-inhibition circuit. Since no EMG mea-surement was performed in this study, it wasnot possible to measure the actual effect of

vibration on agonist and antagonist muscles

acting on the knee joint. However, the

changes in vertical jumping ability and thecorrespondent changes in hamstrings flexi-bility seem to suggest that vibration exerciseis capable of acutely affect joint stiffness.

Vibrations are perceived not only by spin-dles, but also by the skin, the joints and sec-ondary endings. All those structures contributeto the facilitatory input to the -system 22, 23

which in turn affects sensitivity of the pri-mary endings. Hollins and Roy24 found thatsinusoidal stimuli ranging from 10 to 100 Hz

with a small amplitude applied to the leftindex fingerpad were perceived by Meissner

and Pacinian afferents and were able to trig-ger spindle activation. The modulation ofneuromuscular response to vibration is thennot only to be referred to spindle activation,but to all the sensory systems in the body.

Various parameters can affect the synergies inthe sensory system and determine specificresponses. Vibration is thought mainly toinhibit the contraction on antagonist musclesvia Ia inhibitory neurons.25 However thereis also some evidence that vibrations can pro-duce also coactivation. Rothmuller andCafarelli 16 applying vibrations to the patellartendon and measuring biceps femuris coac-tivation have observed this phenomenon.

Jones and Hunter 26 also found an increasedcoactivation when applying vibrations. Thisphenomenon has been attributed to centralmechanisms increasing presynaptic inhibi-tion of Ia afferents transferring the inhibitionto antagonist motoneurons.16 This has beenobserved when vibrations were applied infatiguing conditions or when vibration wascausing fatigue.

Individual fitness status should also be con-

sidered when developing vibration exerciseprotocols. As supportive evidence, well-trained individuals showed an acute improve-ment in force-generating capacity2, 3 anduntrained subjects showed an acute decreasefollowing similar vibration exercise proto-col.11 In our study, untrained individualsshowed acute improvement in vertical jump-ing ability and hamstrings flexibility follow-ing low frequency vibration exercise andacute decrease in vertical jumping and ham-strings flexibility following high-frequency

290 MEDICINA DELLO SPORT Dicembre 2003


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THE ACUTE EFFECTS OF TWO DIFFERENT WHOLE BODY VIBRATION FREQUENCIES ON VERTICAL JUMP CARDINALE

vibration exercise. The muscle-tendon com-

plex acts as a low pass filter and is able toattenuate vibration transmission to the spin-dles. Those capabilities of the musculo-tendinous units have been clearly identifiedin the lower limbs while running. In fact,impact forces during running have beenfound to produce vibrations, which are trans-mitted to the body at a frequency compo-nent between 10 and 20 Hz.27 The soft tissuesof the lower limb damp those vibrations com-ing from heel contact changing their stiff-ness. The adjustment of the stiffness of thelower limbs based upon the shock wave

received is also based on the sensory receptorsin the muscle itself, in the tendons (Golgi ten-don organs), but also in the joints, ligamentsand in the skin. In our opinion the muscletuning hypothesis underlined by Nigg and

Wakeling 27 and Wakeling and Nigg 28 is to beconsidered also as the possible adaptiveresponse to the application of vibrations.Different individuals can adapt to different

vibration frequencies since they possess dif-ferent bandwith properties of their spindles,different amounts and location of mechano-ceptors and proprioceptors, different visco-elastic properties of the muscle tendon com-plex and different percentages of type IIfibers. Previous authors have reported thata frequency below ~20 Hz induces musclerelaxation, whereas at frequencies above ~50Hz severe soreness may emerge in untrainedsubjects.9 The enhancement of performanceobserved with low frequency stimulationcould be due to several aspects. First, it ispossible that the low frequency stimulationused in our study was not strong enough tocause muscle fatigue and was triggering a

limited TVR. Also, relaxation of hamstringsmuscles, as shown by an increase in flexi-bility, would have facilitated vertical jumpingability, which is characterised by high-speedknee joint rotation. Second, it is likely that thehigh frequency treatment elicited a strongTVR, increasing the neuromuscular activa-tion of the lower limbs in order to damp the

vibratory waves transmitted to the body.Stressful vibratory stimulation could in factincrease co-contraction of the hamstrings.Our results seem to support this view. As

previously suggested,15when the vibration

stimulus does not produce fatigue and is ofrelatively short duration can determine anincreased excitatory state of the CNS andfacilitate force-generating capacity in humans.On the other hand, when the opposite occur(vibratory stimulus is too stressful causingfatigue), force generating capacity is impaired.Considering the background of our subjects(untrained individuals) it should not be farfetched to suggest that a good progressionprogram with vibration exercise should start

with the use of lower frequencies of stimu-lation. Moreover further studies are needed inorder to elucidate the exact neurophysio-logical mechanisms involved in the adaptiveresponses to vibration exposure in differentpopulations. Vibration exercise its a novelform of exercise and only few studies havebeen so far conducted on combining differ-ent frequencies/amplitudes of stimulation.The results of our study suggest that untrainedindividuals are able to increase force-gener-ating capacity acutely with low-frequency

vibration stimulation. The main conclusionof the present study suggests that future workis needed in order to develop safe and effec-tive protocols for vibration exercise in dif-ferent subjects and in different muscle groups.

Acknowledgements.The authors would like toacknowledge Gordon Smith, Leanne Cairns, Iain Haslam,

Alan MacKenzie and Randawa Gurneelam for technicalassistance.

Riassunto

Gli effetti acuti di due diverse frequenze di vibrazio-ne sulla prestazione di salto verticale

Obiettivo. Lutilizzo delle vibrazioni come mezzo diallenamento rappresentano una novit nel campodellattivit fisica. Le vibrazioni sono, infatti, utilizza-te da atleti e non atleti con lobiettivo di migliorare leprestazioni di forza e potenza. Lo scopo di questostudio consiste nellanalizzare le risposte acute a 2diverse frequenze di vibrazione.

Metodi. Sedici soggetti sedentari sono stati asse-gnati in maniera random a diversi trattamenti di 5min di vibrazioni applicate a tutto il corpo per mez-zo di una pedana vibrante che produceva oscillazio-ni sinusoidali alle frequenze di 20 Hz (bassa fre-quenza) e 40 Hz (alta frequenza). Laltezza di salto ver-ticale misurata mediante lesecuzione dello squat jump

Vol. 56, N. 4 MEDICINA DELLO SPORT 291


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e del counter movement jumpe la flessibilit dei

muscoli ischio-crurali mediante il test del sit and reachvennero verificate prima e dopo il trattamento inentrambi i gruppi.

Risultati. Il gruppo sottoposto al trattamento conbassa frequenza dimostr un miglioramento statisti-camente significativo del 10,1% (p

body vibration frequencies

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