Journal of Exercise Physiologyonline

October 2017Volume 20 Number 5

Editor-in-ChiefTommy Boone, PhD, MBAReview BoardTodd Astorino, PhDJulien Baker, PhDSteve Brock, PhDLance Dalleck, PhDEric Goulet, PhDRobert Gotshall, PhDAlexander Hutchison, PhDM. Knight-Maloney, PhDLen Kravitz, PhDJames Laskin, PhDYit Aun Lim, PhDLonnie Lowery, PhDDerek Marks, PhDCristine Mermier, PhDRobert Robergs, PhDChantal Vella, PhDDale Wagner, PhDFrank Wyatt, PhDBen Zhou, PhD

Official Research Journal of the American Society of

Exercise Physiologists

ISSN 1097-9751

Official Research Journal of the American Society of Exercise Physiologists

ISSN 1097-9751

69

JEPonline

Effect of Local Vibration during Resistance Exercise on Muscle Hypertrophy

Marcos D. M. Drummond1, Leszek A. Szmuchrowski1, Roberto Simão2, Alex S. Maior3, Bruno Pena Couto1

1Federal University of Minas Gerais, Belo Horizonte, Brazil, 2Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, 3University Augusto Motta (UNISUAM), Rio de Janeiro, Brazil

ABSTRACT

Drummond DMD, Szmuchrowski LA, Simão R, Maior AS, Couto BP. Effect of Local Vibration during Resistance Exercise on Muscle Hypertrophy. JEPonline 2017;20(5):69-79. The addition of mechanical vibration to resistance training (RT) has been shown to have a positive influence on strength gains and muscle power. The purpose of this study was to determine the influence of local vibration on muscle hypertrophy. The sample included 20 untrained males who were randomly placed into 2 groups. The Vibration Group (VG) trained with the local application of vibration during RT. The Non-Vibration Group (NVG) trained without the application of vibration. Both groups performed resistance training (RT) for 12 wks, 3 times·wk-1. The training protocol was: 4 sets of 8 to 10 repetition maximums of unilateral elbow flexion on a Scott-type bench with 120 sec rest between sets. Parameters of vibration: frequency of 30 Hz and amplitude of 6 mm. Although both groups exhibited significant increases in cross-sectional area from the distal and middle parts of the arm (NVG = 21.04 ± 6.88% and 19.03 ± 8.49%; respectively) at the end of the RT program (VG = 20.90 ± 4.74% and 19.16 ± 10.67%; respectively), the cross-sectional area of the distal arm was higher in the NVG versus the VG (17.41 ± 4.64%; P<0.05). Therefore, the findings indicate that application of local vibration does not need to be included in the RT program of untrained individuals.

Key Words: Cross-Sectional Area, Elbow Flexors Exercise, Muscle Hypertrophy, Vibration

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INTRODUCTION

Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The vibration applied during rehabilitation has been used as a therapeutic strategy to improve the musculoskeletal system (8,24). Also, the application of mechanical vibration during resistance training (RT) has received considerable attention in athletic training and sport science to promote an increase in muscle strength and power (9,10,22,29,32,34).

Two types of training using vibration include whole-body vibration (WBV) and local vibration. WBV is the indirect application of vibrations characterized by vertical sinusoidal oscillations that are transmitted to the applicable muscle through the body tissues (20). In WBV, the vibration is generally transmitted from the foot contact with a vibrating platform. This method is commonly used to add mechanical vibrations to exercise (13,19). The purpose of local vibration training is to direct the vibration stimulus to a specific muscle group or a body segment (16). This action may prevent the loss of the vibration stimuli. Thus the energy that occurs in WBV during the transfer of vibrations across the body tissues, especially in the training of the upper limb muscles (9,10,34).

Silva et al. (32) indicate that the application of local vibration may be more efficient than WBV due to the stimulation of specific muscles that perform the exercise. Moreover, local vibration can also vibrate the cable attached to the resistance bar and the specific hilt of the proposed exercise (10,16,32). This type of local vibration might be more efficient because the addition of vibration generated may produce short eccentric effects in all the muscles that are responsible for the movement (10,32). The increase in strength production with mechanical vibration may be due to the tonic vibratory-like reflex, which resembles the stretch reflex (28,34). This reflex increases neuromuscular activity (25) and the recruitment of motor units through the activation of muscle spindles and polysynaptic pathways that reciprocally inhibit the motor neurons of antagonist muscles (11,28).

The increase in muscle activation and strength production by the application of vibration may increase the loading parameters of RT and may lead to greater muscle hypertrophy (28,34). Additionally, several studies indicate that the application of vibration during RT increases the blood concentration of anabolic hormones, testosterone, and growth hormone (6,15,17), which may contribute to increased muscle hypertrophy (34). However, no studies have investigated the effect of local vibration on muscle hypertrophy or compared the effect of conventional RT to RT with local vibration on muscle hypertrophy. We hypothesized that application of local vibration with RT in the reflex stimulation of motor units can help to increase muscle hypertrophy. Thus, the present study compared the influence of RT and local mechanical vibration of the cable attached to resistance bar to the influence of conventional RT on the muscle hypertrophy of the elbow flexors.

METHODS

SubjectsThis study is a randomized parallel group design in which the subjects were randomly placed into 2 different RT groups: Non-Vibration Group (NVG) (N = 10; 21.3 ± 3.02 yrs, 175 ± 0.09 cm, 69.53 ± 6.24 kg) and Vibration Group (VG) (N = 10; 21.1 ± 2.13 yrs, 176 ± 0.05 cm, 67.81 ± 5.84 kg). There were no losses or exclusions after randomization. The recruitment of subjects was conducted over a period of 3 wks and interrupted at the moment the necessary sample was achieved. None of the subjects participated in any type of RT and had only participated in

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recreational activities for at least 12 months prior to the study. All subjects were instructed to avoid regular sport activities during the study. None of the subjects had a history of injury in the upper limbs or any type of limitation that would affect the completion of training or the 1RM tests. All subjects agreed to participate in the study by signing the Terms of Free and Clear Consent. All procedures were approved by the Ethical Committee for Research at the Federal University of Minas Gerais (CAE. 0159.0.203.000-11). The tests and training sessions were conducted at the same time of day for each subject. The data were collected at the Load Evaluation Laboratory at the Federal University of Minas Gerais. No important changes to the study outcomes occurred after the study commenced. The authors of this study enrolled the subjects, generated the random allocation sequence, and randomly assigned the subjects to the groups.

As inclusion criteria all subjects presented the following nutritional adequacy: (a) ingestion of a normocaloric diet of 50 to 55% of the energy intake from carbohydrate sources; (b) 25 to 30% lipids; and (c) 15 to 20% proteins with 1.2 to 1.7 g of protein per kg of the subject's total body mass. The volunteers were asked to complete and return a 2-day dietary log. The software Dietpro (version 5.1, Dietpro Inc., Viçosa, Minas Gerais, Brazil) was used to analyze the food intake. The subjects were encouraged to maintain their dietary habits during the study period. The subjects’ similar caloric and nutrient intake throughout the experimental training period is similar to that suggested by Volek (35). The procedures were similar to those adopted by Ahtiainen et al. (1) and Buresh et al. (7). The subjects were instructed to avoid anabolic androgenic steroid use and nutritional or pharmacological ergogenic aids.

The following additional exclusion criteria were adopted: (a) use of drugs that may affect cardiorespiratory responses; (b) existence of musculoskeletal diagnosed problems that may limit the execution of elbow flexion exercise on a Scott-type bench; (c) systemic hypertension (≥140/90 mmHg or the use of antihypertensive medication; (d) metabolic disease; and (e) use of exogenous anabolic–androgenic steroids, drugs, and/or medication with potential effects on physical performance.

Training ProceduresInitially, the subjects underwent two familiarization sessions involving unilateral elbow flexion exercises on a Scott-type bench without the application of vibration. The right arm (dominant arm) was used in all the subjects. The NVG performed 4 sets of 8 to 10 repetition maximums (RM) in each training session using a unilateral elbow flexion exercise on a Scott-type bench. The initial weight lifted was 70% of 1RM. During each set in training, the weight lifted was adjusted such that the subject could fulfill the established range of repetitions. When the subject performed 8 RM, the weight lifted in the next set was decreased 0.5 to 1.0 kg. An interval of 120 sec was observed between the sets (1,7,13). Each subject performed 3 weekly sessions, and the minimum recovery interval between the sessions was 48 hrs.

The load system consisted of a column guide for weight displacement that was connected to the Scott-type bench. Weight displacement occurred via a steel cable attached to the specific hilt for the proposed exercise. An adjustable system of washers, rather than plates, was adopted to allow for more precise weight adjustments to be selected (Figure 1).

The VG performed the same training protocol as the NVG, but local mechanical vibrations were applied during the training. The vibrations had a frequency of 30 Hz and peak to peak amplitude of 6 mm at the source of the vibration (20,32). A steel cable joined the column of rings to the hilt, which was connected to a motor via an eccentric shaft (Figure 1). The activation of this system

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enabled the steel cable to be pushed and thereby, generate mechanical vibration transmitted to the cable and subsequently in all the muscles that performed the movement (10,16,32). The transmission of the vibration to the elbow flexors was confirmed by accelerometers positioned on the belly of the biceps brachii (10,32). The accelerometry data were measured by 3-axis accelerometers, biological signals acquisition system (ME6000 Biomonitor), and a specific program (MegaWin, vesão 2.4); all from the brand Mega Electronics Ltd, Finland.

Figure 1. Resistance Training Equipment.

One Repetition Maximum TestingAll subjects performed the 1RM test after one familiarization session. The 1RM test consisted of a unilateral elbow flexion on a Scott-type bench. Two test sessions were performed to ensure the reproducibility of the test (23). The intervals between sessions were 48 hrs. The subjects were instructed not to perform physical activity during the initial test period. To characterize the subjects and prescribe the initial weight lifted, the results of the second test session were used. No pause was allowed between the concentric and eccentric phases of a repetition or between the repetitions. For a repetition to be successful, a complete range of motion for the exercise had to be completed. The range of motion for a successful repetition was defined as elbows beginning in full extension followed by full flexion, while maintaining perfect postural alignment with no torso sway.

The 1RM loads were determined in fewer than five attempts with a rest interval of 5 min between attempts. The weight progression on each attempt was gradual (0.5 to 1.0 kg) and in accordance with the subjective perception of the subjects and evaluators. Each subject was instructed to perform only 1 repetition per attempt. If the full execution of the movement was not accomplished after the recovery interval, the weight lifted on the previous attempt was considered as the maximum weight. The following strategies were utilized to minimize the

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occurrence of errors during the 1RM tests: (a) providing standardized instructions to subjects about the test procedure prior to the performance; (b) verbal stimulation during the execution of the test; and (c) checking the mass of all weights on a precision balance.

Magnetic Resonance ImagingMagnetic Resonance Image (MRI) scans were performed after the completion of 1RM testing to determine the pre-training cross-sectional area (CSA) of the elbow flexors of the subjects’ right arms. The MRI scans were repeated 48 hrs after the end of the last RT session. The MRI images were obtained using Siemens® Espree MRI equipment® (Espree Magneton® model) with experienced researchers who performed all the collection procedures under the supervision of the authors of this study. The equipment was calibrated on each testing day prior to the first test according the manufacturer’s instructions. The right arm was scanned with subjects’ in a supine position with the arm near the trunk and palms facing upwards.

In the MRI, 30 axial slices between the proximal point (proximal humeral epiphysis) and the distal arm (anterior distal point to the elbow joint) in the craniocaudal axis were obtained. The thickness of the slice was 5 mm with a 1.5 mm distance between each slice, and the field of view was 40 x 40 cm. The spin echo pulse sequence was a T1-weighted sequence with a repetition time of 750 ms, echo time of 20 ms and matrix resolution of 230 x 290. The magnetic resonance images were recorded in a digital format for subsequent analysis in a controlled environment. The PACS-Kodak Carestream software (version 11.0, Carestream Health Inc., Rochester, New York) was used to analyze the images and determine the CSA.

The "freehand" tool of the software was used to determine the area of the elbow flexor muscles. This tool allows a specific area to be selected, and the area is determined in cm² (Figure 2). The elbow flexor muscles were identified and selected, and the areas obtained were recorded for subsequent analysis. All muscular components, such as connective tissue and small blood vessels, were included. The same experienced analyst performed all analyses. The CSA of each subject was determined from the average of three medial slices. Specifically, slice numbers 14, 15, and 16 positioned in the medial region of the arm were selected. The procedures were similar to those described by De Souza et al. (12).

Statistical Analyses

The normality of the data was verified using the Shapiro-Wilk test. The intraclass correlation coefficient (ICC) 3.1 and the standard error of measurement (SEM) tests were used to verify the reliability of the 1RM test and CSA measurement (Weir, 2005). The unpaired t-test was used to compare the means for the 1RM tests between groups and the number of repetitions, the duration of each set, and the total volume of training performed by the groups during the training period.

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Figure 2. Standard to Measure Cross-Sectional Area of Distal and Middle Part of the Arm.

A two-way ANOVA with repeated measures (group x time) was used to compare the mean results of the CSA tests prior to and after training. Bonferoni post hoc method was used where appropriate. A P-value of <0.05 was considered significant. The sample size was based on the study of De Souza et al. (12) that compared the chronic effects of two different RT protocols on muscle hypertrophy. An effect size of 25% (pilot study) were determined after 12 wks of training, being considered as zero time reference the initial value of strength production with a coefficient of variation of 20%, an alpha value of 0.95, and beta value of 0.80. Statistical analyses were performed using GraphPad Prism 7.02 (GraphPad Software Inc., San Diego, CA, USA). Descriptive data analyses were also performed.

RESULTS

The 1RM test ICC values and SEM values were 0.93 and 2.8 kg, respectively. The groups exhibited similar results of 1RM tests (P=0.581). The reliability of CSA measurements was evaluated by analyzing each subject’s arm image twice within 6 months. The precision of the CSA measurements was good with an intraclass correlation coefficient of 0.99 and a standard error measure of 0.08 cm² (33). At the end of the training program, scans from the distal and the middle parts of the arm showed a significant (P<0.05) hypertrophy in the NVG (21.04 ± 6.88% and 19.03 ± 8.49%, respectively) and in the VG (20.90 ± 4.74% and 19.16 ± 10.67%, respectively) (Figure 3). Also, after 12 wks of RT the NVG showed a significant increase in the cross-sectional area of the distal arm when compared to the VG (17.41 ± 4.64%; P<0.05).

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Figure 3. Structural Changes in the Distal Arm and the Mid-Arm Before and After 12 Wks of the Resistance Training With and Without Vibration. The values are expressed as mean ± SD. *P<0.05 vs. post-training; **P<0.05 vs. VG group.

No significant differences were observed between the mean number of maximal repetitions performed per set during the training period (P=0.215), the mean duration of each set (P=0.091) or between the means of the groups’ total training volume (total repetitions x total weight lifted) (P=0.136) (Table 1). No adverse events were observed throughout the study.

Table 1. The Results of 1RM Tests, the Number of Repetition Maximums (RM) Performed Per Set, the Duration of Each Set and the Total Volume of Training Performed by the NVG and VG Groups (mean ± SD).

1RM TesT (kg)

Maximum Repetitions

Duration (sec)

Total Volume (kg)

NVG VG NVG VG NVG VG NVG VG

14.4±3.03

13.5±2.68

8.97±0.48

8.69±0.29

26.42±2.68

29.03±2.23

1249.7±324.4

1042.0±141.5

DISCUSSION

This study investigated the chronic effect of RT with local mechanical vibration on the hypertrophy of the elbow flexors. No significant difference in the increase in hypertrophy was observed in the NVG and the VG in relation to the mid-arm, but distal muscle of the arm showed significant increase in the NVG. Thus, the results did not confirm the study hypothesis. To date no study compared the effect of local vibration (by steel cable) on muscle hypertrophy, which

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limits the discussion of the results of the present study. Thus, additional studies in this specific area are necessary.All subjects in the present study were untrained and exhibited high adaptability (2,14). The high adaptability of the VG resulted in a large increase in CSA, similar to the increase observed on the NVG, which also had high adaptability. Thus, untrained individuals may not require a potentiating stimulus to achieve morphological adaptation due to RT. In the present study, muscle hypertrophy was associated with significant changes in muscle architecture, possibly, by addition of sarcomeres in series preceded the development of hypertrophy at the macroscopic level. Another important factor is that eccentric phase can contribute with increase of the girth distal muscle, while in concentric phase show a tendency for increase of the girth of the middle part of the muscle (31). Thus, there was a reduction in tension time in the distal part of the muscle during the eccentric phase with vibration. Further studies in trained subjects should be performed to verify whether the addition of local mechanical vibration to RT may act as differentiated and potentiating stimulus.

In the present study, the addition of local mechanical vibration during RT did not increase the number of maximum repetitions, sets duration, and total training volume. Therefore, the addition of local mechanical vibration during RT did not alter the training stimulus. Moran et al. (26) did not observe acute increases in dynamic muscle strength with the application of local vibration during bicep curls. The failure to increase submaximal dynamic muscle strength production would not lead to an increase in training intensity and, consequently, in total training volume, which occurred in the present study and can partly explain the results. No others studies investigated or compared the effect of local vibration during RT on number of maximal repetitions, sets duration, and total training volume, which limits the discussion of the results of the present study. On the other hand, some studies demonstrated a positive chronic effect of local vibration during RT when using maximal isometric contractions (10,32) or intensity close to 100% of 1 RM (16). However, no other studies have compared the chronic effect of local mechanical vibration during submaximal dynamic RT. The absence of data supports the need for additional studies in this specific area.

No consensus on an ideal vibration protocol has been reached (22,34), and different combinations of varying frequencies and amplitudes of mechanical vibrations had different effects on the development of muscular strength (22). Therefore, while the conditions of 30 Hz and 6 mm that were used in this study may not have generated an increase in RT stimulus and consequently in muscle hypertrophy, other parameters may produce this effect. Some studies commented that low vibration frequency (5-45 Hz) has been efficient to increase EMG activity, muscle force, and power possibly by excitatory responses of the muscle spindle enhance muscle activation that involve a spinal reflex mechanism (6,9,10).

Some studies investigated the effect of WBV on muscle hypertrophy. Machado et al. (21) and Osawa and Oguma (27) observed positive effects of WBV on muscle hypertrophy. Lamont et al. (19) and Von Stengel et al. (36) found that WBV did not result in an increase in CSA of the trained muscle, which is similar to the results of this study. However, different training protocols and different types of training with vibration limit the comparison and the discussion of the results.

CONCLUSIONS

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The results of the present study indicate that muscle hypertrophy was similar between the groups. Therefore, the application of local vibration during RT programs did not potentiate hypertrophy gain and does not need to be included in RT with untrained individuals.

ACKNOWLEDGMENTSThe authors of this study wish to thank the Fundação de Amparo à Pesquisa [Research Protection Foundation] of the state of Minas Gerais (FAPEMIG - Brazil), the Pró-Reitoria de Pesquisa (PRPQ) [Research Pro-Rectory] of the Minas Gerais Federal University and AXIAL - Medicina Diagnóstica [Diagnostic Medicine] of Belo Horizonte, Minas Gerais, Brazil.

Address for correspondence: Professor Bruno Pena Couto, Laboratory of Load Evaluation. Physical Education School, Federal University of Minas Gerais, Antônio Carlos Av. 6.627, Belo Horizonte, Brazil, Email:brunopena@yahoo.com.br. Phone: +5531988779381

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