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Acute Effects of Single Bout of Stretching Exercise and Mechanical Vibration in Hamstring Muscle.

Sara A. Rodrigues1, André S. Rabelo1-2, Bruno P. Couto1, Daisy Motta-Santos1, Marcos D. M. Drummond1, Reginaldo Gonçalves1, Ronaldo A. D. Silva1, Leszek A. Szmuchrowski1

1Federal University of Minas Gerais - UFMG, Belo Horizonte, Brazil,

2Federal University of Maranhão - UFMA, São Luís, Brazil

ABSTRACT

Rodrigues SA, Rabelo AS, Couto BP, Motta-Santos D, Drummond MDM, Gonçalves R, Silva RAD, Szmuchrowski LA. Acute Effects of Single Bout of Stretching Exercise and Mechanical Vibration in Hamstring muscle. JEPonline 2017;20(4):46-57. This study compared the acute responses of ROMmax, Torquemax, ROMfss, Torquefss, Stiffness, and Energy in the static passive hamstrings stretching, hamstrings mechanical vibration, and a combination of both. Twelve male subjects (mean ± SD, age 22.3 ± 1.9 yr, height 176 ± 3 cm, mass 77.3 ± 9.0 kg) not trained in flexibility volunteered to participate in this study. The study was a latin square design with all subjects completing four conditions: (a) control (CON); – no intervention; (b) stretching (ST) - 4 x 30 sec passive static stretching of the hamstrings muscle to 90% of ROMmax; (c) vibration (VIB) – 4 x 30 sec bouts of vibration applied to the hamstring muscle; and (d) Stretching with vibration (ST+VIB) – a combination of the stretching and vibration protocols. Variables performance were assessed using a Flexmachine prior to and after experimental conditions. The results showed no significant difference between the conditions for ROMmax, Torquemax, ROMfss and Torquefss (P>0.05). There was a significant decrease in ST between baseline and after intervention for Stiffness (P = 0.007) and Energy (P = 0.0024). Conventional training and the use of vibration, as specified in this study, did not enhance the subjects’ adaptations to flexibility training. However, for Stiffness and Energy, conventional training seems to reduce both when compared to mechanical vibration.

Key Words: Flexmachine, Mechanical Vibration, Stretching

INTRODUCTION

Flexibility is considered an important component of an athlete’s physical performance. It is a requirement for a good performance in several sports modalities like the artistic gymnastics, taekwondo, and diving (7,8,33).

The evaluation of adaptations in flexibility training is usually done through the measurement of range of motion (ROM) in a joint (28). However, the adaptations have a multidimensional character, and the isolated ROM measurement represents only one of the dimensions (32). It is also necessary to know the area of the transverse section of the elongated muscle, the tension applied to the tissue, and the time during which the tension was applied.

The acute improvement in flexibility is based on mechanical and sensory theories (29,32). A mechanical explanation for flexibility improvement is the viscoelastic deformation (6). Another mechanical explanation is neuromuscular relaxation (32). However, sensory theory justifies the improvement of ROM by increasing the individual's ability to tolerate pain (25) that modifies the sensation of discomfort to stretching (22,32).

The improvement in flexibility is usually the result of stretching muscles using different techniques (8). Proprioceptive neuromuscular facilitation (PNF) and static passive stretching are the two most commonly used stretching techniques in athletics and clinical practice (12,26). Another method that has shown to improve flexibility is the use of mechanical vibrations (7,11,18). Use of mechanical vibration during flexibility training has been verified by numerous studies (1,4,7,17,18,28,30) since the 1970s, and it has been applied in two ways: whole body vibration (WBV) and localized vibration (LV).

Some hypotheses may explain the gain in ROM when the muscle is exposed to mechanical vibration (3,11,17,18) such as the increased pain threshold, the tissue temperature, and the relaxation of the stretched muscles induced by vibration. However, the methodologies employed in the flexibility studies can not prove or refute the hypotheses. There is no relation between cause and effect, since they do not measure sufficient parameters and variables.

We found only two studies that analyzed another adaptation to flexibility training besides ROM. Cronin et al. (5) and Herda et al. (16) also assessed stiffness and found no significant change in the group that was exposed to mechanical vibration. These studies are contrary to the results of the studies by Atha and Wheatley (1); Fagnani et al. (7); Kinser et al. (19); Sands et al. (28); Sands et al. (27), given that they did not identify a significant improvement in ROM.

It is possible that mechanical vibration enhances flexibility. However, there are two important shortcomings. The first one is an investigation that covers the various dimensions of the muscle-tendon unit (MTU) adaptations to the flexibility training, when associated with exposure to mechanical vibration, has not yet been carried out. The second shortcoming is the methodologies used in previous studies. They do not allow for the conclusion that the application of mechanical vibration is more efficient in improving flexibility when compared to conventional training.

Hence, the purpose of this study was to investigate the acute responses of the posterior thigh muscles that result from static passive stretching in association with mechanical vibration. For this purpose we evaluated: Maximal Range of Motion (ROMmax), Maximal Torque (Torquemax), First Sensation of Stretching in the Range of Motion (ROMfss), First Sensation of Stretching in the Torque (Torquefss), Stiffness, and Energy in the static passive stretching of the posterior thigh muscles in four conditions: (a) control (CON) – no intervention; (b) stretching (ST) - 4 x 30 sec passive static stretching of the hamstrings muscle to 90% of ROMmax; (c) vibration (VIB) – 4 x 30 sec bouts of vibration applied to the hamstring muscle; and (d) stretching with vibration (ST+VIB) – a combination of the stretching and vibration protocols. We also investigate whether the application of isolated mechanical vibration can enhance the improvement of flexibility when compared to the static passive stretching of the posterior thigh muscles.

METHODS

Subjects

Twelve healthy men (22.15 ± 0.50 yrs of age; body mass 76.52 ± 2.56 kg; weight of the leg 30.85 ± 1.49 N, not involved in any activity involving flexibility and strength training for lower limbs in the last 12 months) participated voluntarily in this study. All subjects were fully informed of the nature of the study. They signed consent statements, and were aware that they could withdraw from the study at any stage. This project was approved by the Research Ethics Committee of the Universidade Federal de Minas Gerais under the number CAAE: 02556212.9.0000.5149.

Experimental Design

The present study is characterized as an experimental type, using a design with repeated measures, and the experimental situations are distributed in 4X4 Latin square .

Experimental Procedures

All sessions were held at the same time of the day to minimize the effects of temperature variations throughout the day. The first experimental situation was performed with a minimum of 24 hrs and a maximum of 48 hrs after the familiarization session. Among the experimental sessions, a 5-day interval was adopted to guarantee the non-interference of the previous situation (31).

In the familiarization session, anthropometric measurements (body mass in kg and height in cm, Filizola scale with stadiometer - precision of 0.1 kg and 0.5 cm, respectively) were performed to characterize the sample and measure the mass of the foot-leg, for torque correction by gravity. Each subject was positioned on the isokinetic device called a Flexmachine (Figure 1), and all adjustments made to the positioning of the subject in the device were recorded for subsequent days of experimental sections (digital goniometer - Bosch, DWM 40 L).

The subjects were instructed how to operate the Flexmachine: (a) press the start button and the mechanical arm goes up; (b) press the button to register first sensation of stretching (fss); (c) arrival at the maximal ROM; and (d) press the button to go down. This procedure was called the Stretching Maneuver (24). Each stretching maneuver lasted approximately 30 sec (15 sec to ascend and 15 sec to descend). The mechanical arm ascent and descent rates were set at 5°/sec (15). When the subject demonstrated that he understood how to correctly handle the equipment and his torque versus ROM curve format was within the standard, the subject was considered to be familiar with the procedure.

Figure 1. Flexmachine. Source: BIOLAB-CENESP Photo Archive

Control Session (CON)

The control session was divided into three moments: baseline, rest, and after-test. In the baseline and after-test, the subject was positioned in the Flexmachine following the positioning established during the familiarization. Each subject performed the Test of Stretching Maneuvers three times. At rest, the subject remained seated for 4 min (similar time duration to perform the different experimental situations). After this interval, the subject was repositioned in the Flexmachine and performed the after-test. Each subject was self-control. In order to collect the baseline and after-test moments, the subjects used a blindfold in order to avoid establishing a visual point to determine ROMmax. During the Stretching Maneuver the researcher always gave to the subject the following guidance: "Remember that you must go to Maximal ROM.” The second evaluator controlled the computer that recorded the values of ROMmax, Torquemax, ROMFSS, and TorqueFSS. The evaluator also determined if the Test of Stretching Maneuver was valid by examing the curves for ROM and torque.

In the other experimental situations, the procedures adopted for the baseline and after-test moments were identical to those of the control session. Between these moments, the subjects executed each of the experimental interventions.

Experimental Interventions

Experimental Situation 1 (ST) - Stretching

The right lower limb of each subject was submitted to static passive stretching of the posterior thigh muscles. The stretching protocol consisted of 4 series of 30 sec while maintaining 90% of the ROMmax found in the baseline. Each stretching maneuver lasted approximately 30 sec (15 sec to ascend and 15 sec to descend).

Experimental Situation 2 (VIB) - Vibration

The right lower limb of each subject was submitted only to mechanical vibration. The shape of the vibratory stimulus used was f = 30 Hz and amplitude of 3 mm (7,23,36). The vibration application was direct to the muscular belly of the posterior thigh muscles. The vibratory stimulus was applied during 4 sets of 30 sec, with 30 sec interval between the stimuli, time analogous to muscle stretching in ST. The subject was placed in a chair constructed for the present study, which mimics the adjustments allowed in the Flexmachine (Figure 2). This chair had adapted a vibratory device for the training execution with mechanical vibration. Thus, the subject was seated, maintaining only 45° of hip flexion of the limb to be trained and supporting the posterior region of the thigh in the vibrating device as shown in Figure 2 (A, B, and C). The volunteer was instructed to relax the right lower limb during the intervention.

[pic]

Figure 2. Vibrating Chair (A: Front View, B: Side View, *Vibrating Device, C: Position of the Subject, D: Stretching via Flexmachine).

Experimental Intervention 3 (ST+VIB) – Stretching with Vibration

Each subject was simultaneously submitted to the stretching with mechanical vibration. The chair described was used to stretch the subject in a position that mimicked the evaluation position in the Flexmachine. With the subject properly positioned, the leg of the limb to be trained was fitted into a support attached to a steel cable, which passed through a pulley (Figure 2D) controlled by a hand-operated ratchet that allowed the limb to be taken by the researcher to the training ROM. An electrogoniometer (EMG System) was used to monitor the ROMmax to be reached during the intervention (90% of the ROMmax found in the pretest). The subject’s lower limb was raised up to this determined ROM by the researcher with a velocity of less than or equal to 5(/sec (15). The velocity was controlled using Dasylab 11.0 program (DasytecDaten System TechnikGmbH, Germany).

Statistical Analysis

Maximal Range of Motion (ROMmax), Maximal Torque (Torquemax), First Sensation of Stretching in the Range of Motion (ROMfss), and First Sensation of Stretching in the Torque (Torquefss) used for data analysis was the mean of three Stretching Maneuver performed and were expressed as mean ± SD (31). The stiffness used for the data analysis was calculated by the ratio between the torque variation and the ROM, both recorded during the test maneuver. The torque versus ROM curve was divided into three thirds and only the third was taken for data analysis since it is the most linear portion of the curve. The energy used for the data analysis was calculated by the integral of the area below the torque versus the ROM curve.

The normality of all data was verified by the Shapiro-Wilk test. For the comparison of the experimental situations, a Two-Way ANOVA between the baseline and after interventions was performed. If there was a significant difference, a Tukey post hoc was used. The level of significance was set at P ................
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