A Comparison of the Physiologic Effects of Acute Whole-Body Vibration Exercise in Young and Older People

Article Outline

• Abstract
• Methods
  • Vibration and Load
  • Participants
  • Study Design
  • The Physical Activity Questionnaire and Anthropometric Measures
  • V̇o2, Heart Rate, Blood Pressure, and Rating of Perceived Exertion
  • Statistical Analyses
• Results
• Discussion
  • Study Limitations
• Conclusions
• Acknowledgments
• References
• Copyright

Abstract 

Cochrane DJ, Sartor F, Winwood K, Stannard SR, Narici MV, Rittweger J. A comparison of the physiologic effects of acute whole-body vibration exercise in young and older people.

Objective

To examine the acute physiologic effects of acute whole-body vibration (WBV) exercise in young and older people.

Design

Every participant performed 9 conditions in a static squat position, consisting of no vibration and WBV at 30Hz and 3 loads corresponding to (1) no load (0% body mass), (2) load of 20% body mass, and (3) load of 40% body mass. A Jendrassik voluntary contraction was also performed with no vibration and WBV at 30Hz with no load and 20% body mass.

Setting

Laboratory facilities at a university in the United Kingdom.

Participants

Healthy young people (n=12; 6 men, 6 women; mean age, 21.5y) and 12 healthy older people (6 men, 6 women; mean age, 69.2y) from the local community.

Interventions

Not applicable.

Main Outcome Measures

The Physical Activity Questionnaire, anthropometric measures, counter-movement jump, and isometric maximal voluntary contraction with the Jendrassik maneuver were assessed in both groups. Oxygen uptake (V̇o₂), blood pressure, heart rate, and rating of perceived exertion (RPE) were recorded during WBV and load conditions as the outcome of the study.

Results

Both vibration and load were associated with an increase (P<.001) in V̇o₂ for older and young groups. WBV elicited the equivalent of a .35 metabolic equivalent (MET) increase in V̇o₂, with additional loads of 20% and 40% body mass increasing V̇o₂ by 0.8 and 1.2 METs, respectively. Additionally, there was an interaction effect of vibration and group in which the WBV-related V̇o₂ increase was less in the old compared with the young. Both vibration and load caused an increase in heart rate, blood pressure, and RPE (all P<.001); however, there were no significant group differences between young and older groups. The Jendrassik maneuver elicited an increase in V̇o₂ by 27.6% for the old and 33% for the young group (P<.001); however, there was no significant difference between groups.

Conclusions

V̇o₂ significantly increased in both the older and young people with vibration and additional load and when the Jendrassik maneuver was superimposed with vibration and load. However, the elicited increase in V̇o₂ (1.2mL·kg⁻¹·min⁻¹) from WBV may be an insufficient stimulus to improve cardiovascular fitness.

Key Words: Elderly, frail, Exercise, Oxygen, Rehabilitation

EXERCISE IS GENERALLY advocated as a countermeasure to offset age-related frailty and to enhance mobility and well-being. It has been widely documented that the natural aging process is associated with reduced muscular and cardiovascular function, bone loss, and increased body fat storage,¹ all of which contribute to a decline in functional performance.² Over time, in combination with a sedentary lifestyle, further deterioration may lead to a greater reduction in mobility, impaired balance, and a higher incidence of falls.³ Furthermore, the decline in muscle function not only involves a loss of muscle strength but also of muscle power. Margaria et al² were the first to report a decline in maximum muscular power with age and found from 20 to 70 years of age muscle power is reduced by about a half, with poor muscle power being a predictor of hospitalization, falls, and fracture.⁴ Although the fact of physiologic decline may not be avoided, it can be mitigated by training, even at a very old age.⁵ However, factors such as time, convenience, poor compliance through dementia, and poor postural control after a stroke often preclude older people from engaging in physical activity.⁶ An exercise modality that is convenient, time efficient, and has the benefits of conventional weight-bearing exercise would be appealing to this group.

One such modality, known as whole-body vibration (WBV) exercise, has recently received some attention as a regimen to overcome these obstacles while producing favorable outcomes.⁷, ⁸, ⁹ WBV requires specialized equipment; however, it can be performed in the convenience of the home and is readily available from commercial companies. Manufactured devices such as a handheld dumbbell and standing and seated oscillating platforms produce the vibration. These devices deliver sinusoidal vibrations to the body at a frequency of 5 to 45Hz. As little as 6 to 10 minutes of WBV a day 3 times a week for 6 to 8 weeks has been shown to increase balance and gait,¹⁰, ¹¹, ¹² improve quality of life,¹² and improve exercise compliance.⁶ Additionally, longer duration (6–12mo) WBV studies in postmenopausal women have documented increases in bone mineral density of the hip¹³ and spine.¹⁴

The mechanism of WBV has yet to be elucidated; however, it has been proposed that WBV involves monosynaptic reflexes that are induced by the stretch-shortening action in the muscles that act over the joints in which the vibration is being absorbed.¹⁵ Electromyographic activity has been shown to increase during WBV,¹⁶, ¹⁷ and it has been purported that WBV elicits muscular activity through evoking sufficient muscular work to raise whole-body oxygen uptake (V̇o₂),¹⁸ which is supported by a linear increase in V̇o₂ with an increasing vibration frequency.¹⁹

Importantly, the acute physiologic responses to WBV have been investigated in the young but not in older people. One might speculate that the responses to WBV are mitigated in older people. Research suggests that aging and disuse attenuates motoneuron excitability and causes structural changes to the muscle spindle²⁰, ²¹; therefore, the muscle spindle in older individuals may be less sensitive to the vibration because of the fiber composition and reflex deterioration that occurs with natural aging.²², ²³ Thus, there is reason to assume that the stimulus for muscular work, either mechanically direct or through the stretch reflex, will be reduced and the metabolic requirement will be decreased in older people. We therefore hypothesized that the increase in V̇o₂, evoked by WBV, will be lower in older people than in the young.

As an attempt to shed some light on WBV-related V̇o₂ in the older and young people, we assessed the effects of the Jendrassik maneuver. This established test involves the person to clasp both hands and pull them apart, and it is thought to facilitate the stretch reflex by presynaptic activation. Doing so typically enhances the reflex amplitude by a factor of 3 after brief sustained contraction.²⁴ As explained previously, it is generally assumed that WBV elicits muscle contractions through the stretch reflex. Therefore, as a secondary hypothesis to be tested in this study, we expected the metabolic rate in both the older and young participants to increase when the Jendrassik maneuver was superimposed with WBV and load.

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Methods 

Vibration and Load 

WBV in standing position involves the musculature from the whole body including the musculature of the trunk and of the shoulder girdle. Therefore, to avoid any involvement of the arm and shoulder musculature in the vibration stimulus, which would influence the Jendrassik maneuver, we constructed a seated version for WBV. To this purpose, a prototype vibration machine consisting of a motorized horizontal leg press with a pin-weighted plate stack^a was fitted with 2 electrically powered 0.15-kW Motovibratori^b to the rear of the footplate of the leg press machine (fig 1). Both units had the capacity to operate at 0 to 3600rpm or 0 to 60Hz at an amplitude of 0.5 to 1.0mm of vibration in the z plane.

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• Fig 1. 

  A schematic diagram of the prototype vibration leg press machine. The footplate angle was fixed at an 80° incline, and the seat was adjusted to a 60° decline.

Pilot work with this equipment found that the optimal frequency and amplitude to elicit maximal increases in V̇o₂ was a frequency of 30Hz and 1-mm amplitude (peak acceleration, 35.2m/s² or 3.6g). This concurs with a previous report¹⁷ that squatting on a vibration platform at 30Hz elicited the highest electromyographic response in the vastus lateralis muscle, and thus we chose a 1-mm amplitude at 30Hz for our study.

The footplate was fixed at an 80° incline, and the participants were instructed to sit in the leg press machine with the seat adjusted to a 60° decline, with both socked feet placed at shoulder width apart placed on a small rubberized footrest of the vibration plate. Participants adjusted their legs to a knee angle of 70° (full extension, 0°), which was verified with an electrogoniometer (see fig 1).

The loading regimen involved the previously described foot placement and knee angle for no load (0% body mass, 20% body mass, 40% body mass). For no load (0% body mass) the participants were required to place their legs on the footrest without any load or additional leg force. For loads of 20% and 40% body mass, a pin selector was inserted into the appropriate weight stack plate of the leg press machine (see fig 1), which was equivalent to 20% and 40% of the participant's body mass. To ensure that no additional leg force was contributing to the various loads, a force transducer was attached to the undercarriage of the leg press seat (see fig 1) and connected to a display unit through an oscilloscope.^c This provided visual feedback to participants to prevent unwarranted increases in isometric leg force, which was continually monitored by the experimenter.

Participants 

Twelve healthy young (mean ± standard deviation [SD], 21.5±2.8y) and 12 healthy older (age, 69.2±7.2y) people matched for sex (6 men, 6 women), weight, and physical activity provided written consent to volunteer for the study. The study protocol was approved by the local ethics committee. Each participant underwent verbal health and medical screening before the study to exclude WBV contraindications of nonconsolidated fractures, bone tumors, herniated disks, deep vein thrombosis, aortic aneurysm, metal implants (leg or vertebral column), diabetes with polyneuropathy, and pregnancy (young women group only). None of the studied participants reported any signs or symptoms that warranted exclusion from participation in the study.

Study Design 

Every participant performed the 9 conditions in a randomized order. The protocol consisted of no vibration and WBV at 30Hz and 3 loads corresponding to (1) no load, 0% body mass, in which the participant placed his/her feet on a small rubberized footrest that was attached to the vibration plate; (2) load of 20% of the participant's body mass; and (3) load of 40% of the participant's body mass (table 1). The rationale for selecting a load of 20% and 40% body mass was based from earlier pilot work that fatigue was minimized as shown by low blood lactate levels in comparison to larger loads. A Jendrassik voluntary contraction (see later) was performed with no vibration and WBV at 30Hz and loads consisting of no load (0% body mass) and a mass of 20% body mass (see table 1). Each condition was 4 minutes in duration and separated by 30 seconds of rest. The rationale for the 4-minute duration was selected on the basis from earlier pilot work that during WBV V̇o₂ produced a steady state during this time. To prevent unwanted leg movement, the participant's knees were restrained by an adjustable elastic band. The participants were asked to place both hands on their knees and to breathe normally during the course of each 4-minute period. A warm-up was prohibited before the start of each testing day to reduce the possibility of influencing the outcome of the study.

Table 1. Variable Settings of the 9 Experimental Conditions

Abbreviations: BM, body mass; 0% BM, no load; 20% BM, load 20% of BM; 40% BM, load 40% of BM; JVC, 10% of Jendrassik maximum voluntary contraction.

A Jendrassik contraction involved pulling with both arms (fig 2) a dual-handle load cell^d that was connected to a computer and acquisition system.^e First, the maximal voluntary isometric force was identified by 2 maximal contractions separated by 15 seconds of rest. The greatest maximal contraction was recorded (table 2), and 10% of this value was then used for a Jendrassik voluntary contraction condition. From earlier pilot work, we knew that levels larger than 10% of a Jendrassik voluntary contraction did not result in a noticeable further reflex augmentation. Therefore, to avoid any possible fatigue effect, we decided to use 10%.

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• Fig 2. 

  The Jendrassik contraction involved pulling a load cell at 10% of maximal voluntary contraction.

Table 2. Mean Physical Characteristics of Men and Women Participants

NOTE. Values are mean ± SD.

Abbreviations: CMV, calf muscle volume; JH, jump height; JMVC, Jendrassik maximum voluntary contraction; PAQ, Physical Activity Questionnaire; PJP, peak jump power; TMV, thigh muscle volume; ΣMV, total muscle volume.

Each participant visited the laboratory on 2 separate occasions with a maximum of 5 conditions being performed with at least 24 hours of rest separating testing days. The participants were asked to refrain from undertaking any vigorous activity 24 hours before the testing; participants performed the protocol at the same time of day. The anthropometric measurements, counter-movement jump, and Jendrassik maximal voluntary contraction were conducted before the commencement of the main study.

The Physical Activity Questionnaire and Anthropometric Measures 

All participants completed a written physical activity questionnaire²⁵ to ascertain the metabolic units spent a week undertaking sport and physical activity (see table 2).

Circumference measurements, skinfold thickness, and limb lengths were used to calculate the thigh muscle volume, calf muscle volume, and total muscle volume (see table 2) from the volumetric method devised by Jones and Pearson.²⁶ The anatomic landmarks of the ankle, knee, and hip were identified and marked. These locations provided reference points for the circumferences, skinfold thickness, and limb lengths. Girth measurements were taken with a nonstretch anthropometric tape, and limb lengths were measured by a Harpenden anthropometer.^f Both girth and limb lengths were taken at the subgluteal fold, thigh, knee, calf, and ankle locations.

Skinfold thickness procedures were conducted in accordance with the International Society for the Advancement of Kinanthropometry protocols. A calibrated skinfold calliper^g was used to measure subcutaneous adipose tissue at the medial and lateral calf, anterior, and posterior thigh.

V̇o₂, Heart Rate, Blood Pressure, and Rating of Perceived Exertion 

V̇o₂ was continually assessed by using the portable K4b² breath by breath pulmonary gas exchange system.^h Before each test, the K4b² was calibrated with ambient air (oxygen, 20.93%; carbon dioxide, .03%) and a known gas concentration mixture (oxygen, 16%; carbon dioxide, 5%). The turbine was calibrated by using a known 3-L volume syringe.^h

A heart rate strapⁱ was attached to the participant's chest and telemetrically interfaced with the K4b² system. Steady-state V̇o₂ was attained in all conditions between 2 to 4 minutes, with the mean value of V̇o₂ (in mL·kg⁻¹·min⁻¹) being used for further analyses. Heart rate was recorded in conjunction with every breath by breath analysis of the K4b², with the mean heart rate being analyzed during the 2- to 4-minute interval.

Blood pressure was assessed at 2 and 4 minutes by an electronic blood pressure monitor,^j and ratings of perceived exertion (RPE)²⁷ were assessed at the 2- and 4-minute interval.

Statistical Analyses 

All analyses were performed by using SPSS software.^k The dependent variables of the physical characteristics were analyzed by analysis of variance (ANOVA). A repeated-measures 2 (no vibration, WBV) by 3 (0% body mass, 20% body mass, 40% body mass) mixed (group, old vs young) ANOVA with post hoc simple contrasts was performed to examine the effects of vibration, load, heart rate, systolic (SBP) and diastolic blood pressure (DBP), RPE, and Jendrassik contraction. For multiple comparisons significance, levels were adjusted by using a Bonferroni adjustment. The level of significance was set at P less than .05.

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Results 

Both vibration and load enhanced (P<.001) V̇o₂ for older and young groups (fig 3), such that WBV increased V̇o₂ by 19.7% compared with no vibration. Furthermore, loads of 20% and 40% body mass increased V̇o₂ by 26.7% and 62.9% in comparison to no load (0% body mass). There was a significant but small interaction effect of vibration and group (P=.045) in which the WBV-related V̇o₂ increase was lower in the old compared with the young. There was a significant load and group interaction (P<.01) such that the younger group increased V̇o₂ to a greater extent with additional load. This difference became significantly detectable at 20% and 40% body mass loads.

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• Fig 3. 

  Mean V̇o₂ ± SD (in mL·kg⁻¹·min⁻¹) of vibration frequency and loads of older and young groups. Vibration and load significantly (P<.001) increased V̇o₂. There was a significant load by group interaction effect (P<.001) between the additional loads of 20% and 40% of body mass (BM) of increased V̇o₂, and there was a small significant interaction of vibration and group (P=.045).

Both WBV and load produced a significant (P<.001) increase in heart rate, with an interaction between load and group (P<.05), implying that the young group exhibited a greater increase in heart rate in response to load compared with the older group. SBP increased significantly (P<.001) with the corresponding increase in loads (0% body mass, 20% body mass, 40% body mass); however, there was no significant effect of vibration influencing SBP (fig 4).

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• Fig 4. 

  Mean ± SD of SBP, DBP, and RPE at 2 and 4 minutes during the various vibration frequency and loads for the older and young groups. Increased loads produced a significant rise (P<.001) in SBP. DBP increased significantly (P<.001) with vibration and a larger load (40% BM). Vibration and load produced a significant increase in RPE. Abbreviations: NV, no vibration; 0% BM, no load; 20% BM, load 20% of BM; 40% BM, load 40% of BM.

Both WBV and load produced a significant increase (P<.001) in DBP, with a significant interaction between vibration and time (P<.05) of vibration (30Hz) producing a higher DBP at 4 minutes compared with 2 minutes (see fig 3). RPE increased significantly (P<.001) with WBV and load, with higher RPEs being recorded at 4 minutes compared with 2 minutes (see fig 4). However, no significant effects were found between young and older groups for SBP, DBP pressure, and RPE.

During WBV, a Jendrassik voluntary contraction produced a significant increase in V̇o₂ of 25.3% (P<.001) compared without a Jendrassik voluntary contraction (table 3); however, there was no statistical difference between groups. RPE, heart rate, SBP, and DBP continued to rise with time during the vibration with a Jendrassik voluntary contraction compared with without a Jendrassik voluntary contraction. RPE and SBP were significantly higher (P<.001) in 4 minutes compared with 2 minutes. However, no statistical differences were found between young and older groups. Moreover, there were no significant differences between sex for V̇o₂, cardiovascular variables, and Jendrassik voluntary contraction.

Table 3. V̇o₂ of Older and Young Participants During the Jendrassik Conditions of Vibration and Loads

NOTE. Values are mean mL·kg⁻¹·min⁻¹ ± SD.

Abbreviations: 0% BM, no load; 20% BM, load 20% of BM; −, without Jendrassik contraction; +, with Jendrassik contraction.

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Discussion 

The main aim of this study was to investigate whether the aerobic metabolism responses to WBV and an additional load of the older population were comparable to those obtained in the young. Our findings suggest that in both young and older people V̇o₂ was significantly enhanced with vibration and an additional load. In qualitative terms, WBV was found to affect V̇o₂ in older and younger people in a very similar way. There was only 1 exception to that rule, in that the increase in V̇o₂ per unit of increment in load was lower in the older group than the young. In quantitative terms, however, the metabolic response to vibration appeared to be slightly lower than in the young. One might therefore argue that older people are less responsive to WBV in terms of aerobic metabolism.

To quantify the increased WBV-related V̇o₂ of the older group and its capability to increase aerobic capacity, an estimation of maximal V̇o₂ (V̇o₂max) percentage can be calculated. Given that 5.2mL·kg⁻¹·min⁻¹ was elicited by WBV and that the V̇o₂max of 21mL·kg⁻¹·min⁻¹ for 68- to 70-year olds is commonly reported,²⁸ the estimate of WBV-related V̇o₂ would be equivalent to 24% of V̇o₂max. However, this would be insufficient to increase aerobic capacity, with at least 40% V̇o₂max being required to elicit the appropriate physiologic changes,²⁹ and confirms that the V̇o₂ elicited by WBV is small; nevertheless, only 1 specific amplitude and frequency was used in the current study.

Although the Jendrassik contraction did elicit an increase in V̇o₂ in all conditions, there was no interaction observed between the Jendrassik contraction and vibration. In fact, the Jendrassik contraction increased V̇o₂ quite uniformly, namely by approximately 1.5 and 2.0mL·kg⁻¹·min⁻¹ in the older and younger groups, respectively, and thus enhanced V̇o₂ quite independently of the vibration modality (WBV).

From the current study, it is inconclusive as to whether the observed response of older versus younger people to vibration is because of differences in reflex activity. However, it is known that the H-reflex is reduced in older individuals because of a decrease in alpha-motoneuron excitability.²⁰ Furthermore, the muscle spindle, which is central to the vibration mechanism, undergoes age-related changes in myosin heavy-chain expression, making it less sensitive to changes in muscle length, and affects its ability to fully activate the motoneurons.²³ Likewise, morphologic changes of thickening spindle capsule and diminished periaxial space occurs from disuse and atrophy.²¹ Therefore, it is plausible that an aging muscle spindle does not have the capacity to activate Ia afferents, which inadvertently affects the excitatory response of the alpha motorneurons.³⁰ Moreover, the lack of Ia afferent or spinal presynaptic inhibitory response from the aging central nervous system may have caused a less effective excitatory response on the alpha motoneuron, which was not capable of eliciting a greater level of V̇o₂.

The body posture (seated vs upright) and the type of body movement (static vs dynamic) may influence V̇o₂. For example, Rittweger et al¹⁸ have reported that standing on a rotating oscillating vibration plate elicits a V̇o₂ of 10.2mL·kg⁻¹·min⁻¹ compared with 5.8mL·kg⁻¹·min⁻¹ in a seated position in the present study. However, squatting at a tempo of 3 seconds up and 3 seconds down on an oscillating plate further increases V̇o₂ to 14mL·kg⁻¹·min⁻¹.¹⁸ For the current study, the seated position was preferred, so the loading of 20% and 40% body mass of the lower limb was able to be conducted in a safe and appropriate manner. Furthermore, a seated position prevented the arm and shoulder muscles from being vibrated which could have influenced the Jendrassik maneuver. Moreover, in the current study, the older participants lead a very active lifestyle, which may not be a true representation of this population.

In the present study, the young adults showed a 1.3mL·kg⁻¹·min⁻¹ increase in V̇o₂ at 30Hz of WBV, which, at a similar frequency, contrasts to the 3.5mL·kg⁻¹·min⁻¹ increase finding by Rittweger et al.¹⁹ The discrepancy can be explained by the different vibration machines used. In the present study, the vibration was administered by a plate moving uniformly up and down in the z plane compared with Rittweger's study¹⁹ in which the vibration was elicited by an oscillating teeterboard that moved about a central axis. Additionally, in the present study, the participants were seated for vibration compared with standing.¹⁹ The reason for the different approach in this study was that, as explained earlier, we wanted to clearly separate upper- and lower-body muscle contractions. However, even though the paradigm applied in the present study differed from the machines that are commercially available for vibration exercise, there is little reason to question the principle finding of this study, namely, that elderly people respond to the vibration in a similar way as younger people.

When contemplating the application of vibration exercise in older people, it is also important to consider the effects on the cardiovascular system. In that sense, the other physiologic variables of heart rate, blood pressure, and RPE that were investigated in this study are of interest. As expected, they showed increases with vibration and also with additional loads. The findings are in line with the view that cardiovascular changes by vibration are comparatively small in relation to muscle activity.³¹ The risk of WBV being a cardiovascular hazard thus appears to be very small in an elderly population. Therefore, WBV exercise for older people may provide some advantages; given the low level of cardiovascular stress, WBV could be performed by those suffering from heart conditions. Additionally, WBV may improve proprioception³² and can be performed at home to increase exercise compliance.

Study Limitations 

Normally, WBV involves standing on an oscillating plate; however, in the current study, we used a prototype vibration machine on which participants were seated, which may have its limitations. Moreover, the older participants in the study lead very active lifestyles; for this reason, a more sedentary group of older subjects might have been a better cohort group to investigate. Despite its limitations, the study had its strengths; WBV exercise for older people may provide some advantages, given the low level of cardiovascular stress, and WBV may be performed by those suffering from heart conditions.

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Conclusions 

Vibration and additional load significantly increased V̇o₂ for old and young people in a similar way, but the elderly responded to an increasing load with a lesser augmentation in V̇o₂ than the young. Likewise, the metabolic rate in both the older and young increased when the Jendrassik maneuver was superimposed with vibration and load.

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Acknowledgments 

We thank Tom McKee, BEng, and Jonathan Howell, MSc, who provided very good technical support. We acknowledge Technogym, who supplied the vibrating leg press.

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• a Technogym, Via Perticari, 2/A, Gambettola, Italy 47035.
• b BM-A; OMB Srl, Via Mariano 3, 41040 Corlo (MO), Italy.
• c 20MHz, HM 203.7; Hameg, Schweinfurter Weg 75, Frankfurt, Germany 60599.
• d FN 3030; FGP Sensors & Instrumentation, ZI - 24 rue des Dames, 78340 Les Clayes sous Bois, France.
• e Acknowledge, version 3.7; Biopac Systems, 42 Aero Camino, Goleta, CA 93117.
• f Holtain Ltd, Crosswell, Crymych PEMBS SA41 3UF, Wales.
• g Baty International, Victoria Rd, Burgess Hill, West Sussex, RH15 9LB, UK.
• h Cosmed, Via Fattiboni Ottone, 214, Rome 00126, Italy.
• i Polar Electro Oy, Professorintie 5, Kempele, FIN-90440, Finland.
• j Adult/Pediatric NIBP monitor; Production Engineering, Medical Equipment Div, 6035 E 38th Ave, Denver, CO 80207.
• k Version 14.0; SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.