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Abstract

BACKGROUND:

Local vibration (LV) used as part of the warm-up can stimulate a specific body part and muscle group, potentially increasing muscle flexibility and performance. However, the effect of its combination with static stretching (SS) has not been thoroughly examined.

OBJECTIVE:

To elucidate the acute effectiveness of combining LV and SS (V $+$ S) on the ROM of ankle dorsiflexion, squat jump, counter-movement jump (CMJ) and the dynamic postural stability index (DPSI).

METHODS:

Fifteen healthy men who were regularly involved in recreational sports participated in this study. Static Stretching, V $+$ S, and non-stretching condition (control) were assigned randomly and the intervention period for each condition was five minutes.

RESULTS:

The dorsiflexion improved significantly in SS and V $+$ S compared to the control. The CMJ height decreased significantly following SS compared to V $+$ S and control.

CONCLUSIONS:

This study suggests that V $+$ S improves ankle dorsiflexion ROM without compromising jump performance. Local vibration device could be an effective element in warming up but further research is warranted.

Keywords

Static stretching with local vibration vertical jump dynamic postural stability

1. Introduction

Acute stretching as part of a warm-up, especially static stretching, can cause a loss of maximum strength, rate of force development (RFD), power [1, 2] and reduction in performance capabilities that include dynamic balance after jump and landing [3]. Consequently, establishing a warm-up method that allows for increased muscular flexibility and explosiveness while not decreasing muscle stiffness is important for performance improvement.

In recent years, warm-up has been performed using LV [4, 5, 6, 7, 8]. It has been reported that in field hockey players, peak power and average power increased without changes in the EMG amplitude [7]. On the other hand, using a LV device at a pulsed frequency for 10 minutes had no effect on increasing maximum voluntary contraction (MVC), RFD, or muscle activation in trained healthy men. LV training has been shown to provide direct vibration to the muscle belly and tendons. Muscles with increased length and tension are the most susceptible to vibration [9]. A recent study that addressed the use of LV as part of the warm-up has shown that the anterior split flexibility of male gymnasts is significantly improved [10]. Therefore, the method of a combination of LV and static stretching (SS) as part of a warm-up may contribute to improve muscular flexibility and maintain/improve physical performance including jump and dynamic balance [11].

The purpose of this study was therefore to investigate the acute effects on range of motion, vertical jump ability, and dynamic balance after landing by comparing SS alone and a combination of LV and SS (V $+$ S). We hypothesized that V $+$ S would improve ROM as well as physical performance.

2. Methods

2.1 Participants

Fifteen healthy men (age $=$ 23.5 $\pm$ 2.3 years; height $=$ 172.1 $\pm$ 6.4 cm; body weight $=$ 67.2 $\pm$ 9.9 kg) voluntarily participated in the study. Subjects with a history of a sprain higher than grade II, current ligamentous defects, a history of ligament or joint reconstruction or repair, dysfunction of the vestibular system affecting balance, or trauma (including fracture, myositis ossificans, or burn injuries) were excluded. Three different protocols (SS, V $+$ S, and control) were performed for all subjects in random order on three separate days, with an interval of 24 to 48 hours between tests. This study protocol was approved by Hiroshima University’s Institutional Review Board (study protocol ID number: C-271, date of approval: 2020-6-20). All subjects provided written informed consent before examination.

2.2 Experimental design and procedures

The subjects were randomly allocated to three experimental conditions (SS, V $+$ S, and control). To ensure consistency of data collection among the subjects, stretching of the non-dominant limb was performed for unilateral assessment [12]. The non-dominant limb of each subject was defined by asking about his or her preferred limb when kicking a ball [13]. The warm-up exercise consisted of a 5-min cycling exercise with ergometer air resistance set to 75 W and cadence set to 60 rpm, followed by a complete break of 3-min before the beginning of the test [14].

Stretching was performed with the subjects’ hips and knees in full extension while they stood on a footplate with the ankle at maximum dorsiflexion for both the SS and V $+$ S conditions and with the ankle at an angle of 0 ${}^{\circ}$ for the control condition. For the V $+$ S condition, a vibration device (MYOVOLT ${}^{\text{TM}}$ ; New Zealand) was used with small actuators located on each panel. The vibration frequency passed through a range of 0–170 Hz at amplitude of 0–0.12 mm during the 0.5-s, which created a pulsing effect. The device was placed on the muscle belly of the medial head of the gastrocnemius (GM) of the stretching limb and was held in place with a Velcro strap (Fig. 1). Each panel was activated for 0.5 s and deactivated for 0.5 s with a 5-min duration of vibration using the pulsed mode of the device applied to the stretching limb.

Figure 1.

The application of the vibration device. The vibration frequency passed through a range of 0–170 Hz at amplitude of 0–0.12 mm during the 0.5-s, which created a pulsing effect. The device was placed on the muscle belly of the medial head of the gastrocnemius (GM) of the stretching limb and was held in place with a Velcro strap (Fig. 1).

In this study, an ankle joint exercise device for stretching (Rakkun Walk R-1; Maruzen Industrial Co., Ltd. and Hiroshima University, Japan) was applied (Fig. 2). This computerized device enables to control angle and movement velocity of the ankles joints placed on two steps [15]. The two steps are installed horizontally in the base portion, and two actuators control the left and right vertical movements independently. The inclination angle of the step was used to define the dorsiflexion angle. This device was used for both the intervention and functional evaluation.

Figure 2.

Ankle joint exercise device for stretching. This device can repeatedly move the ankle joint automatically at a constant velocity (10 ${}^{\circ}$ /sec) using a computer program. This computerized device can control the angle and the movement velocity of the ankles placed on two steps.

Figure 3.

Equations for calculation of APSI, MLSI, VSI and DPSI. The DPSI is a composite of the anterior-posterior, medial-lateral, and vertical ground reaction forces, and also provides stability indices for the anterior-posterior (APSI), medial-lateral (MLSI), and vertical (VSI) directions. The DPSI was calculated using the ground reaction forces generated in the first three seconds immediately following initial contact that was identified as the instant when the vertical ground reaction force exceeded 5% of the body mass. The force plate data were normalized to body weight.

2.3 Assessment of maximum ankle dorsiflexion ROM

We measured the degree of maximum ankle dorsiflexion ROM before and after stretching in the SS, V $+$ S, and control protocols to determine the effect of stretching in each stretching condition. Measurements were taken with the participants in a standing position, with the knee fully extended on the footplate. The ROM was measured three times using a stretching device programmed to automatically move the footplate according to pre-specified angle measurements. The mean value of three trials was used for analysis. The angle at which the subjects began to feel discomfort or pain, or raise the heel was defined as the maximum degree of ankle dorsiflexion.

2.4 Assessment of vertical jump

Each subject performed a maximal voluntary vertical jump on the floor with non-dominant limb in two conditions: (1) from a semi-squatting position (squatting jump, SJ) and (2) from an upright standing position with a downward movement before starting to move upward (counter-movement jump, CMJ).

Vertical jump ability was assessed by measuring jump height during the SJ and CMJ using a jump gauge (Myotest SA, Sion, Switzerland). Subjects were instructed to jump vertically and attempt to land with the same body position and in the same location as takeoff to avoid lateral or horizontal displacement. The participants positioned their arms laterally throughout the entire jump and kept their torso in an upright position to emphasize the use of the leg extensor muscles [16]. The participants could recover for 2 minutes between jumps. The average height of the three jumps was used as the outcome value for each jump test. The standard error of the mean for inter-rater reliability of the composite test was 2.4 cm [17, 18].

2.5 Assessment of dynamic postural stability after landing

Dynamic postural stability after landing was evaluated using a two-leg jump and one-leg landing in the forward direction. In a previous study, this approach achieved an intersession reliability [ICC (3, k)] of 0.86 [19]. The jump height was standardized at 30 cm, and the jump distance was normalized to the subject’s body height [19]. The subjects placed 40% of their height from the end of the force plate, and a hurdle with a height of 30 cm was placed at the midpoint between the force plate and the starting position. The subjects performed the following actions three times: jump in the forward direction using both legs over the hurdle with subsequent landing on the force plate on the non-dominant limb, stabilize as quickly as possible, place both hands on the waist once stabilized, and keep still for 10 s while looking forward. They were permitted five practice trials for each condition to become familiar with the one-leg jump, with 2 minutes of rest after testing. The measurements in each condition were conducted on different days to avoid the subject becoming too familiar with the task and to prevent fatigue. The task was repeated if the subject fell upon landing, contacted the hurdle, or failed to jump. Three successful trials were performed for each condition (control, SS, and V $+$ S) and were used for data analysis.

Ground reaction force data was collected at a sampling frequency of 200 Hz. The global reference system was set so that the anterior-posterior axis referred to the y-axis, the medial-lateral axis to the x-axis, and the vertical axis to the z-axis. A Microsoft Excel macro was used to process the ground reaction force data for calculating the DPSI. These data were passed through a zero-lag fourth-order low-pass Butterworth filter with a frequency cutoff of 20 Hz. The dependent variable was the DPSI, is shown in Fig. 3. The DPSI is the resultant of the anterior-posterior, medial-lateral, and vertical ground reaction forces while it also provides stability indices for the anterior-posterior (APSI), medial-lateral (MLSI), and vertical (VSI) directions. The DPSI was calculated using the ground reaction forces generated during the first 3 seconds immediately following initial contact, which was identified as the instant when the vertical ground reaction force exceeded 5% of the body weight. The force plate data was normalized to body weight [18]. We also used raw data signals to calculate the maximum vertical ground reaction force (vGRF max), which was expressed as the magnitude of the peak force in Newtons divided by the subject’s body weight. The average of three successful trials for each condition was used for further analysis [18].

2.6 Statistical analysis

An a priori power analysis by G*Power software (Heinrich-Heine University, Düsseldorf, Germany) revealed that at least 20 subjects were required for a statistical power of 0.75 at an effect size of 0.80 with an alpha level of 0.05 [19]. Repeated-measures 2 (time) $\times$ 3 (stretching condition) analysis of variance (ANOVA) was used to compare changes in ROM in both stretching conditions (SS and V $+$ S) and the control condition. When appropriate, follow-up analyses were performed using paired $t$ -tests between pre- and post-stretching to confirm significant changes within each condition. In addition, repeated-measures 1 (time) $\times$ 3 (stretching condition) ANOVA was used to compare the vertical jump and DPSI (DPSI, MLSI, APSI, VSI, and vGRF max) in both stretching conditions and the control condition. When appropriate, follow-up analyses were performed using post hoc tests. An alpha level of 0.05 was the criterion for rejection of the null hypothesis for all statistical tests. Effect sizes were calculated using the Cohen d statistic [19]. Data analysis was conducted using SPSS for Windows, ver. 20.0 (IBM Japan Co., Tokyo, Japan).

Table 1
Change in ankle dorsiflexion angle between pre and post-measurement ( $\pm$ SD)

Condition	Pre-stretching (degree)	Post-stretching (degree)	$p$ -value
Control	20.3 (2.7)	20.1 (2.8)	0.312
SS	20.4 (2.9)	24.5 (2.7)	$<$ 0.001
V $+$ S	20.1 (2.8)	23.9 (3.1)	$<$ 0.001

Control, control condition; SS, static stretching; V $+$ S, vibration stretching.

Table 2

Values for squat jump and countermovement jump according to stretching condition ( $\pm$ SD)

	Condition			$P$ -value	Effect size	Observed power
	Control	SS	V $+$ S
Squat jump	20.5 (3.3)	19.4 (2.6)	20.5 (3.4)	n.s.	0.13	0.18
Countermovement jump	23.3 (3.2)	21.7 (2.7)	23.7 (3.8)	Control, V $+$ S $>$ SS ${}^{\dagger}$	0.37	0.59

Control, control condition; SS, static stretching; V $+$ S, vibration stretching; vGRF max, maximum vertical grand reaction force; %BW, % body weight. ${}^{\dagger}$ Indicates a significant difference V $+$ S compared with control ( $p<$ 0.05).

Table 3

Values for dynamic postural stability index and vGRF max according to stretching condition ( $\pm$ SD)

	Condition			$P$ -value	Effect size	Observed power
	Control	SS	V $+$ S
Dynamic postural stability index	0.28 (0.06)	0.26 (0.06)	0.26 (0.06)	Control $>$ V $+$ S ${}^{\dagger}$	0.31	0.46
Anterior-posterior stability index	0.13 (0.01)	0.13 (0.01)	0.13 (0.01)	n.s.	0.05	0.10
Medial-lateral stability index	0.02 (0.00)	0.02 (0.00)	0.02 (0.00)	n.s.	0.26	0.39
Vertical stability index	0.24 (0.06)	0.23 (0.06)	0.22 (0.06)	Control $>$ V $+$ S ${}^{\dagger}$	0.36	0.57
vGRF max (%BW)	1.85 (0.54)	1.84 (0.53)	1.80 (0.42)	n.s.	0.04	0.09

3. Results

Repeated-measures ANOVA detected a significant intervention $\times$ time interaction ( $p<$ 0.01). The paired $t$ -test analyses indicated that the SS and V $+$ S conditions were significantly different between pre- and post-stretching. The angle and change in range of dorsiflexion pre- and post-stretching are shown in Table 1. There was no difference in ROM between SS and V $+$ S conditions. The values after SS and V $+$ S were significantly higher than the respective values before. There was no significant difference between the SS and V $+$ S values.

The SJ and CMJ data after the three conditions are shown in Table 2. The height of SJ after the control, SS, and V $+$ S protocols was 20.5 $\pm$ 3.3, 19.4 $\pm$ 2.6, and 20.5 $\pm$ 3.4 cm, respectively. The height of CMJ after the control, SS, and V $+$ S protocols was 23.3 $\pm$ 3.2, 21.7 $\pm$ 2.7, and 23.7 $\pm$ 3.8 cm, respectively. The CMJ after the V $+$ S protocol was significantly higher than that after the SS protocol ( $p<$ 0.05, effect size $=$ 0.37, power $=$ 0.59) while SJ did not differ significantly among the three conditions.

The DPSI, APSI, MLSI, VSI, and vGRF max after the three conditions are shown in Table 3. The DPSI and VSI after the V $+$ S protocol were significantly lower than that after the control protocol ( $p<$ 0.05, effect size $=$ 0.31, power $=$ 0.46; $p<$ 0.05, effect size $=$ 0.36, power $=$ 0.57) and tended to improve compared with the SS condition. The APSI, MLSI, and vGRF max were not significantly different among the three conditions.

4. Discussion

The purpose of this study was to examine the acute effects of V $+$ S on range of motion, vertical jump ability, and dynamic balance after landing in healthy men. The ROM after V $+$ S was significantly larger than that achieved after the control condition, and the effect was similar to that of SS. Vibration stimulation to the body and muscles improves flexibility and has a positive effect on neuromuscular function [20, 21, 22, 23]. This study suggests that local vibration may improve ROM by decreasing muscle stiffness to reduce the number of residual cross bridges caused by increasing muscle tension. Furthermore, a previous study showed that V $+$ S may improve ROM by separating actin-myosin binding and reducing passive muscle stiffness [24]. In this context, the difference in ROM between SS and V $+$ S was considered to be caused by the difference in the mechanism by which the muscle stiffness decreased. Further research is necessary to clarify this issue.

The CMJ was significantly higher after V $+$ S than SS. Previous studies suggested that local vibration stimulation improved the efficiency of tonic vibration reflex [25], increased fiber conduction velocity [26] and recruitment of the motor unit [27]. The tonic vibration reflex is a result of repeated fast and short extension of the musculotendinous unit which may temporarily improve muscle activity and jumping ability [28]. Therefore, it was suggested that V $+$ S affected vertical jumping ability in a different manner compared to SS.

The DPSI and V were significantly lower after V $+$ S than after the control condition and tended to be lower than that after SS. Sell et al. [29] suggested that DPSI score reflected better dynamic postural stability and VSI score was most susceptible to weight fluctuations. The V $+$ S intervention had the most significant influence on dynamic posture control after landing compared with SS and control. Cloak et al. [30] reported that vibration stimulation of the whole body resulted in an improved DPSI among the elite player group and an improved reach distance on the Y-balance test among amateur and elite soccer players. In our study, V $+$ S tended to result in a greater change in dynamic postural stability compared with SS. In addition, there was a tendency for a lower value after V $+$ S compared to SS.

Thus, this is the first study to show an acute effect of V $+$ S in the maintenance or improvement of ROM and explosive physical performance as part of the warm-up for athletes before practice or competition in healthy men.

A few limitations of the present study need to be considered. This study had a small sample size. However, this was a preliminary study to determine the effectiveness of V $+$ S. Second, whether V $+$ S has an acute effect on the passive fascicle stiffness of the MG remains unknown. Thus, it is necessary to clarify the acute effects of V $+$ S on the muscle stiffness and hardness of the GM using in vivo imaging techniques such as ultrasonography. Finally, the long-term effects after V $+$ S were not examined. Further studies are needed to verify the long-term effects of V $+$ S on muscle stiffness and hardness, force potential and dynamic balance.

5. Conclusions

This study examined the effects of V $+$ S on ROM, jump ability, and dynamic postural stability after landing. The results indicate that V $+$ S techniques proved to have a superior effect on jumping performance when compared to SS. A significant improvement in dynamic postural stability after V $+$ S was also observed when compared to non-stretch performance. These findings suggest that V $+$ S improves ROM and postural stability without negatively affecting jumping ability. Additional use of vibration techniques during static stretching might therefore be a viable exercise from in athletic performance.

Author contributions

CONCEPTION: Noriaki Maeda.

PERFORMANCE OF WORK: Somu Kotoshiba, Makoto Komiya and Masanori Morikawa.

INTERPRETATION OR ANALYSIS OF DATA: Yuichi Nishikawa.

PREPARATION OF THE MANUSCRIPT: Noriaki Maeda and Masanori Morikawa.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Junpei Sasadai.

SUPERVISION: Yukio Urabe.

Ethical considerations

This study protocol was approved by Hiroshima University’s Institutional Review Board (study protocol ID number: C-271, date of approval: 2020-6-20). All subjects provided written informed consent before examination.

Funding

The authors report no funding.

Footnotes

Acknowledgments

The authors have no acknowledgments.

Conflict of interest

None to report.

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Acute effects of local vibration stretching on ankle range of motion,vertical jump performance and dynamic balance after landing

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Methods

2.1 Participants

2.2 Experimental design and procedures

2.4 Assessment of vertical jump

2.5 Assessment of dynamic postural stability after landing

2.6 Statistical analysis

Table 1 Change in ankle dorsiflexion angle between pre and post-measurement ( ± SD)

4. Discussion

5. Conclusions

Author contributions

Ethical considerations

Funding

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Change in ankle dorsiflexion angle between pre and post-measurement ( $\pm$ SD)