J Phys Fitness Sports Med, 8 (3): 137-142 (2019)DOI: 10.7600/jpfsm.8.137

JPFSM: Regular Article

Effect of different stretch amplitudes of dynamic stretchingon joint range of motion

Takamasa Mizuno

Received: March 2, 2019 / Accepted: April 16, 2019

Abstract This study examined the effects of different dynamic stretching (DS) amplitudes on joint range of motion (ROM), passive torque (PT), and subjective fatigue. Twelve healthy subjects (age [mean ± SD] = 19.3 ± 1.0 years) underwent three experimental trials: DS at maxi-mal active ankle plantarflexion-dorsiflexion ROM (DS100), DS at 80% maximal active ROM (DS80), or control. Ankle angle and PT were measured before and after DS with the ankle passively dorsiflexed at 1º/s to its maximal ROM. DS consisted of four sets of 30 s of ankle plantarflexion-dorsiflexion at 100 beats/min while standing. Subjective fatigue during DS was measured using the visual-analogue scale. Maximal ankle dorsiflexion angle was significantly increased after DS100 (20.6 ± 3.5º to 23.8 ± 3.8º, P < 0.05); no changes were seen after DS80/control. Subjective fatigue was significantly greater at two (2.6 ± 0.7 mm vs 1.2 ± 0.3 mm), three (3.7 ± 0.9 mm vs 1.3 ± 0.3 mm), and four (5.2 ± 0.9 mm vs 1.6 ± 0.3 mm) sets of DS100 than with DS80 (P < 0.05). PT at maximal dorsiflexion increased from before to after stretch-ing (DS100: 26.3 ± 3.2 Nm to 30.4 ± 3.4 Nm, DS80: 28.8 ± 3.0 Nm to 31.0 ± 3.3 Nm, Control: 26.6 ± 2.8 Nm to 29.1 ± 3.5 Nm, P < 0.05), although there were no significant differences among trials. These results indicated that greater active ROM during DS is important for in-creasing joint ROM, although DS with greater active ROM induces greater subjective fatigue.Keywords : dynamic stretch, amplitude, passive torque, joint flexibility, plantar flexors

Introduction

One of the primary goals of warm-up exercises is to improve exercise performance. Dynamic stretching (DS) performed by moving the limbs through their active range of motion (ROM) by contracting the muscle group that is antagonistic to the target muscle group without bounc-ing can improve muscle strength1), vertical jump height2), sprint time3), leg power4), agility time3), and joint ROM5,6). On the basis of the results of these previous studies, it has recently been recommended that DS should be included in warm-up routines before exercise7). A recent review ar-ticle also highlighted the possible mechanisms underlying DS-induced exercise performance enhancement that have been reported in research articles, which are as follows8): 1) increased heart rate9), 2) increased core temperature10), 3) decreased muscle-tendon unit (MTU) stiffness11), 4) post-activation potentiation4,9), 5) rehearsal of specific movement patterns12), and 6) neural adaptations such as increased motor unit activation or decreased reflex sensi-tivity9,13). However, these mechanisms have not been fully investigated because of limited data8). The optimal protocol for DS to improve exercise perfor-mance has not been established. Some stretching param-

eters, such as stretching duration, stretching velocity, and stretching amplitude, can influence DS-induced effects8). Behm and Chaouachi7) concluded in a review article that force and isokinetic power showed greater enhance-ment following >90 seconds (s) of DS compared to <90 s of DS. However, some previous studies have reported similar DS-induced improvements between shorter and longer DS durations in terms of jump height, velocity, sprint time, and joint ROM5,14,15). Thus, the influence of DS duration is not fully understood. Further, faster DS velocity seems to affect subsequent exercise performance. Fletcher9) found that fast DS at 100 beats/min induced greater increases in jump height than slow DS at 50 beats/min. Indeed, Yamaguchi and Ishii16) clarified that the rate of changes in explosive performance after DS that was performed “as fast as possible” was greater than that for DS performed without the velocity being specified. DS amplitude would also affect DS-induced performance changes. However, most previous studies have reported that DS was performed through the full active ROM; no previous study has examined the effects of DS ampli-tude1,6,9,17,18). Recently, a review article summarized the in-fluence of stretching variables on explosive performance and recommended an optimal protocol for DS16). How-ever, there is no recommendation for an optimal protocol regarding DS-induced flexibility improvement. Correspondence: mizuno@htc.nagoya-u.ac.jp

Research Center of Health, Physical Fitness and Sports, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan

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As mentioned above, the influence of stretching ampli-tude during DS is unclear. However, it is speculated that a narrow stretching amplitude during DS causes less ten-sion to the MTU, resulting in impairment of DS-induced changes. For example, in the case of submaximal active dorsiflexion of the ankle joint, the amount of elongation and tension in the triceps surae muscle might be less than that of maximal active ankle dorsiflexion. In the case of static stretching, a higher stretching intensity causes greater static stretching-induced changes in ROM and passive torque (PT) than a lower stretching intensity19,20). In addition, Freitas et al.20) suggested that the increase in ROM was due to an increase in stretch tolerance (i.e., increased pain threshold), which only occurs at a certain degree of tissue lengthening induced by static stretching. Thus, the extent of tension in the MTU during stretching is one of the important factors related to changes in ROM, stretch tolerance, and passive properties. With the above in mind, the aim of this study was to examine the effects of different DS amplitudes on ROM, PT, and subjective fatigue in testing the hypothesis that stretch amplitude during DS affects DS-induced changes in ROM.

Materials and Methods

Subjects. Twelve healthy male subjects volunteered to participate in the study (mean ± SD age = 19.3 ± 1.0 years, height = 171.3 ± 5.7 cm, weight = 60.4 ± 7.0 kg). No subjects reported any history of recent musculo-skeletal injuries or neuromuscular diseases specific to the lower limbs. All subjects were fully informed of the purpose, procedures, and possible risks of the study. All subjects gave written informed consent for participation in the experiments, which were conducted according to the principles set out in the Declaration of Helsinki and were approved by the Local Ethics Committee of Nagoya University [29-03].

Experimental design. The subjects visited the labora-tory on four occasions, and the visits were separated by more than 24 h. The first visit involved a familiarization session, and the subsequent three visits included the fol-lowing experimental trials: a) DS at maximal active ankle plantarflexion-dorsiflexion ROM (DS100); b) DS at 80% maximal active ankle plantarflexion-dorsiflexion ROM (DS80); c) control condition/resting in a seated position (CON). DS100 was conducted before DS80, whereas CON was performed randomly. During the familiarization session, each subject practiced the passive-dorsiflexion test and DS to minimize any potential learning effects and to adjust to the procedures. During the experimental ses-sions, the subjects underwent two pre-passive dorsiflex-ion tests, DS, and a post-passive dorsiflexion test. During the passive dorsiflexion test, we measured PT, ROM of the ankle joint, and electromyographic (EMG) activities of the medial head of the gastrocnemius (MG) and tibialis

anterior (TA) muscles. A post-passive dorsiflexion test was performed as soon as possible after DS.

Passive dorsiflexion test. To determine PT, ankle ROM, and EMG activity, each subject underwent two passive dorsiflexion tests before DS and one passive dorsiflex-ion test at the post assessment. The passive dorsiflexion test was performed using an approach similar to that described in previous studies21,22). The subjects were se-cured to an isokinetic machine (S-15177; Takei Scientific Instruments, Niigata, Japan) with the right knee at full ex-tension and the footplate fixed to the right foot. The angle of the back of the seat was 75° in relation to the floor. In this study, all reported ankle angles were the angle of the footplate, and the ankle angle was defined as 0° when the footplate was perpendicular to the floor. Values were defined as positive for dorsiflexion. Passive ankle ROM was assessed by passively and isokinetically dorsiflexing the subject’s foot at a rate of 1°/s from −30° to the angle at which the subject felt discomfort and stopped the dy-namometer by activating a safety trigger. The maximal angle of the footplate was defined as the ankle ROM. During this test, the PT generated on the footplate was determined both when the ankle was submaximally dorsi-flexed and at the maximal dorsiflexion angle. Throughout the passive-dorsiflexion test, the subjects were asked to completely relax, to not offer any voluntary resistance. The value from the second assessment during the two pre-passive dorsiflexion tests was used in all subsequent anal-yses. PT and ankle angle were converted from analogue to digital values at a sampling rate of 1.0 kHz (PowerLab 16SP; PowerLab System, AD Instruments Pty Ltd., Aus-tralia). The submaximal PT was determined at every fourth degree during the final 13° (at 1°, 5°, 9°, and 13°) com-mon to both assessment periods (pre- and post-DS)23). The same absolute degree values that were common to each assessment period (within each experimental condition) were used to calculate the submaximal PT for each subject.

Dynamic stretching. Repeated DS was administered to the right lower leg. The ankle angle during DS was mea-sured using an electrical goniometer (DL-210; S&ME, Tokyo, Japan). Each subject was instructed to stand with the knee fully extended and raise the foot from the floor. Then, subjects performed active plantarflexion-dorsiflex-ion at DS100 or DS80 at a rhythm of 100 beats/min set by a metronome. Movement was performed in each direc-tion for each beat. In DS100, subjects were instructed to perform plantarflexion-dorsiflexion in as wide a range as possible. After DS100, each maximal plantarflexion angle, maximal dorsiflexion angle, and DS ROM, which was defined as the range from the maximal plantarflexion angle to maximal dorsiflexion angle, was assessed for all DS that was performed at DS100, and average values were calculated. In DS80, 80% of the DS ROM at DS100

139JPFSM : Dynamic stretching of different amplitudes

was set as the target DS ROM. Actually, the position of the maximal plantarflexion angle in DS80 was set to be the same as that of the average value in DS100, whereas the position of the maximal dorsiflexion angle in DS80 was set at a smaller angle than that of DS100. Therefore, DS ROM at DS80 was regulated to 80% DS ROM at DS100 by depressing the maximal dorsiflexion angle. A monitor displaying the real-time ankle angle and the des-ignated ankle angle line of plantarflexion and dorsiflexion was placed in front of the subject during the DS80. Sub-jects were instructed to match their maximal plantarflex-ion and maximal dorsiflexion angles to the designated angle line at each plantarflexion and dorsiflexion during DS80 as accurately as they could. Before starting DS at DS80, the subjects practiced DS once or twice to match the designated angle. Each DS trial continued for 30 s and was repeated four times, with a 30-s rest between sets. The level of subjective fatigue induced by DS was also recorded using a 10-cm visual-analogue scale before and after each set.

Electromyography. During the passive dorsiflexion test, we measured the EMG activity of the MG and TA using bipolar, disposable surface electrodes (DL-140; S&ME, Tokyo, Japan) placed over the most prominent bulge of the MG and at 1/3 on the line between the tip of the fibula and the tip of the medial malleolus with a 20-mm inter-electrode distance. EMG activity was recorded at a band-width of 5–500 Hz. EMG signals were transmitted to a digital data recorder at a sampling rate of 1.0 kHz. In this study, the EMG amplitudes for the MG and TA during passive-dorsiflexion were calculated using a root mean square (RMS) function for the initial 10° of dorsiflexion and for the final 5° of dorsiflexion, respectively.

Data reliability. The test-retest reliability was calculated using data from two pre-assessments during DS100. The intraclass correlation coefficients (ICCs) and standard er-rors of measurement (SEMs) were calculated to represent the relative and absolute consistencies for each variable, respectively. The ICC values for ankle ROM and PT at maximal dorsiflexion angle were 0.991 (P < 0.001) and 0.978 (P < 0.001), whereas the SEM values were 1.2º and 1.7 Nm, respectively. In addition, there were no signifi-cant differences between measurements taken during two pre-assessments for ankle ROM (t = 0.208, P = 0.839) and PT at maximal ROM (t = 0.013, P = 0.990).

Statistical analyses. A three-way analysis of variance (ANOVA; time [pre or post] × condition [DS100, DS80 or CON] × angle [1°, 5°, 9°, or 13° during the final 13°]) was used to analyze the submaximal PT. A three-way ANOVA (time [pre or post] × condition [DS100, DS80 or CON] × portion [initial 10°, or final 5°]) was used to ana-lyze the EMG amplitudes of the MG and TA. A two-way ANOVA (time [pre or post] × condition [DS100, DS80

or CON]) was used to analyze the ankle ROM and PT at maximal dorsiflexion angle. A two-way ANOVA (stretch-ing repetition [pre, one set, two sets, three sets or four sets] × condition [DS100 or DS80]) was used to analyze subjective fatigue. When appropriate, follow-up analyses were performed using lower-order ANOVA and t-tests with Bonferroni correction. Differences were considered statistically significant at P ≤ 0.05. Unless otherwise specified, all data are reported as means ± SE.

Results

Ankle range of motion during dynamic stretching. The average ROM during four sets of DS for DS80 was 82.1% of DS100.

Ankle range of motion. A significant two-way interac-tion between time and condition was detected for ankle ROM (P < 0.05). Post-hoc testing revealed a significant increase in ankle ROM after DS100 (P < 0.05). However, no significant differences in ankle ROM were seen after either DS80 or CON (Fig. 1). Post-hoc testing also re-vealed that the pre-value of DS80 was higher than that of DS100 (P < 0.05).

Passive torque at maximal dorsiflexion angle. No sig-nificant two-way interactions between time and condi-tion and no significant main effects for condition were detected. However, there was a significant main effect of time (P < 0.05). The marginal means of PT at maximal dorsiflexion angle increased after DS (Fig. 2).

Passive torque during final 13° range of motion. No significant three-way interaction among time, condition, and angle and no significant two-way interactions between

Fig. 1 Stretching-induced changes in ankle range of motion. *Significantly different from the pre-value (P < 0.05).

†Significantly different from pre-value of DS100 (P < 0.05). Data are expressed as means ± SE. CON = con-trol; DS100 = dynamic stretching at 100% of range of motion; DS80 = dynamic stretching at 80% of range of motion.

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time and condition, time and angle, or condition and an-gle were detected for PT. In addition, there were no main effects for condition or time; a significant main effect was observed for angle (P < 0.05). The marginal means for PT during the final 13° of ROM increased with increases in ankle angle (all P < 0.05; Table 1).

Subjective fatigue. A significant two-way interaction be-tween stretching repetition and condition was detected for subjective fatigue (P < 0.05). Post-hoc testing revealed that subjective fatigue induced by DS100 was greater than that induced by DS80 after two, three, and four sets of DS (P < 0.05; Fig. 3). Subjective fatigue during DS100 was higher after three and four sets of DS than that at pre-, one, and two sets (all P < 0.05). Subjective fatigue during DS100 was also higher after four sets of DS than that af-ter three sets (P < 0.05). During DS80, subjective fatigue was higher after one, two, three, and four set of DS than pre-value (all P < 0.05).

Fig. 2 Stretching-induced changes in passive torque at maximal dorsiflexion angle.

*Significantly different from the pre-value (P < 0.05). Data are expressed as means ± SE. CON = control; DS100 = dynamic stretching at 100% of range of motion; DS80 = dynamic stretching at 80% of range of motion.

Fig. 3 Comparisons between conditions for subjective fatigue. *Significantly different from the DS80 value (P < 0.05). aSignificantly different from the pre-value of

DS100 (P < 0.05). bSignificantly different from the first set value of DS100 (P < 0.05). cSignificantly dif-ferent from the second set value of DS100 (P < 0.05). dSignificantly different from the third set value of DS100 (P < 0.05). eSignificantly different from the pre-value of DS80 (P < 0.05). Data are expressed as means ± SE. CON = control; DS100 = dynamic stretching at 100% of range of motion; DS80 = dynamic stretching at 80% of range of motion.

Values represent means ± SE. CON: control; DS100: dynamic stretching at 100% of range of motion; DS80: dynamic stretching at 80% of range of motion.*Significantly different from final1°. **Significantly different from final1° and 5°. ***Significantly different from final1°, 5° and 9°.

Table 1. Passive torque (Nm) before and after dynamic stretching during the final 13º of movement.

141JPFSM : Dynamic stretching of different amplitudes

Electromyography of medial head of gastrocnemius and tibialis anterior. No significant three-way interactions among time, condition, and portion were seen for the EMG values from the MG and TA and no two-way inter-actions for time and condition, time and portion, or condi-tion and portion were detected. In addition, no significant main effects were detected for time or condition, whereas a significant main effect was detected for portion for both the MG and TA (P < 0.05). The marginal means of EMG during the final 5° was greater than that during the initial 10° for both the MG and TA.

Discussion

The present study investigated the effects of different amplitudes of DS on ROM, PT, and subjective fatigue. The main findings of this study were that DS100 in-creased ankle ROM relative to the pre-values, whereas ankle ROM did not change after DS80 and CON. In ad-dition, subjective fatigue during DS100 was greater than that during DS80. This study is the first to demonstrate that the amplitude of DS affects DS-induced changes in joint ROM. The re-sults of this study revealed that ankle ROM significantly increased after DS100 (15.3% increase), although ankle ROM did not change after DS80. This indicates that in order to increase ankle ROM, the amplitude of DS should be >80% of active ankle plantarflexion-dorsiflexion ROM. In previous studies, it was explained that increases in joint ROM after DS were due to changes in mechanical and/or neural factors5,6,11,17). In the present study, mechani-cal factors such as PT did not vary among trials. Although there were no significant differences among trials, the increase in PT at the maximal dorsiflexion angle (i.e., the increase in pain threshold) after DS100 tended to be greater than that after DS80 (15.7% vs. 7.5%). This re-sult means that stretch tolerance tended to increase more in DS100. Therefore, the increase in ankle ROM after DS100 would be due to the increased stretch tolerance. The mechanism underlying the altered stretch tolerance is not fully understood; however, it is possible that no-ciceptive nerve endings in the joint and muscles and the primary somatosensory cortex play a role24,25). A greater increase in subjective fatigue was observed after DS100 compared to DS80. This result indicates the possibility that exercise performance is impaired after DS100. In fact, previous studies demonstrated that a lon-ger duration of DS induced fatigue and impaired muscular endurance, sprint time, and isometric maximal voluntary contraction11,14,15). Although post-activation potentiation, where the previous acute contractile history of a muscle positively affects subsequent muscular performance, is one of the potential mechanisms for improvement in exer-cise performance induced by DS4,10,15,26), this impairment in exercise performance was likely caused by the fact that fatigue cancelled the positive effects of post-activation

potentiation. Thus, Turki et al.15) mentioned that an opti-mal recovery period is needed to maximize the benefits of post-activation potentiation and dissipate fatigue. Simi-larly, in the case of increased joint ROM, it is possible that optimal recovery after DS could improve joint ROM without fatigue. Fortunately, the increase in joint ROM after DS persists for some time after the DS6). Therefore, if the purpose is to increase joint ROM by DS, DS should not be performed just before subsequent exercise. The present study has two key limitations. Firstly, the pre-values of ankle ROM were significantly different between DS80 and DS100. The reason why these values were different is unclear. Because subjects did not per-form any warm-up exercise before measurement, it might be possible that the preconditions were different between DS100 and DS80. However, to achieve the purpose of this study, we focused on changes from pre- to post-DS for each trial. In addition, reliability within a given day was high. Therefore, we believe that the difference in pre-values between DS80 and DS100 did not influence the interpretation of the results. Secondarily, the marginal means of EMG during the final 5° (collapsed across time and condition) was greater than that during the initial 10° for both the MG and TA. However, the increments of EMG were quite little (MG: 0.034 to 0.041 mV, TA: 0.034 to 0.041 mV). In addition, for subjects that could adequately relax their muscles, the EMG activity was less than 0.05 mV above baseline27). Therefore, it was consid-ered that any potential contribution of MG or TA muscle was removed in this study. In conclusion, significant increases in ankle ROM were detected after DS100 relative to pre-values. In contrast, ankle ROM did not significantly increase after DS80 or CON. In addition, subjective fatigue during DS100 was greater than that during DS80. Thus, the present study provides practical evidence that if athletes or practitio-ners use DS to increase ROM, it should be performed at almost maximal active plantarflexion-dorsiflexion ROM; although it should also be noted that subjective fatigue would also increase.

Conflict of Interests

The author declares no conflict of interests.

Acknowledgments

This work was supported by the JSPS KAKENHI Grant-in-Aid for Young Scientists (B) [Grant Number 16K16517].

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