Stretching exercises are incorporated into warm-up protocols of general sports. The purposes are the prevention of sports-related injuries and the improvement of sports performance (23). Recent studies, however, reveal that the static stretching used during general warm-up protocols acutely impairs explosive (2,9,10,17,21) or endurance performance (3,12,17,25). However, several studies (2,9,17,26) have clarified that dynamic stretching acutely improves explosive performance. Only 2 studies (5,29), however, investigated the acute effects of dynamic stretching on endurance running performances. Hayes and Walker (5) found that slow-velocity dynamic stretching did not acutely change running economy during treadmill running at an intensity of 75% maximal oxygen uptake (VO2max) in a well-trained runner. In contrast, Zourdos et al. (29) found that dynamic stretching as 2 sets of 4 repetitions acutely impaired running economy during treadmill running at an intensity of 65% VO2max in a well-trained runner. Zourdos et al. (29), however, indicated that the total distance during running as fast as possible for 30 minutes on a treadmill did not change after the dynamic stretching. Thus, it has not been demonstrated in the previous studies that dynamic stretching acutely improved the endurance running performances in well-trained athletes. Nevertheless, it was recommended to use dynamic stretching during warm-up in endurance running events as if the positive acute effect of dynamic stretching on explosive performance was applied to endurance performance. Actually, endurance athletes and their coaches also use dynamic stretching during actual warm-ups. Judge et al. (8) reported that the coaches of endurance athletes used dynamic stretching (41.5%) or a combination of static stretching and dynamic stretching (44.7%).
The protocols for dynamic stretching in the 2 previous studies (5,29) might not be suitable for acutely improving endurance running performance. Hayes and Walker (5) used slow-velocity dynamic stretching. Zoudors et al. (29) used dynamic stretching in only 2 sets of 4 repetitions. A systematic review (26) investigated the optimal protocol for dynamic stretching to acutely improve explosive performance, but not endurance performance. The review suggested that dynamic stretching should be performed “as quickly as possible” and that the optimal volume of dynamic stretching was “one-two set(s)” of “10–15 repetitions.” The systematic review (26) also indicated that the optimal dynamic stretching improved 2.6–10.6% in jump performances. Hudgins et al. (6) demonstrated that the 3-step jump performance has positive relations with endurance running performance in 800 m (r = 0.83), 3,000 m (r = 0.72), and 5,000 m (r = 0.71). Spurrs et al. (22) revealed that plyometric training improved jump and endurance running performances without any changes in VO2max. These findings let us suppose that the optimal protocol for dynamic stretching to acutely improve explosive performance may acutely improve endurance running performance.
Previous studies have investigated the acute effects of dynamic stretching on running economy at 60% (29) or 75% (5) of VO2max. Furthermore, in a previous study (29) that examined the acute effect of dynamic stretching exercises on endurance running performance, the total running distance for 30 minutes at self-controlled velocity in each subject was evaluated as an index of endurance running performance. The exercise intensity of running was equivalent to approximately 80% VO2max (average VO2 during running · average VO2max−1 × 100). However, high-level endurance runners have to run at higher exercise intensities during actual track-and-field endurance running events (7). For instance, the exercise intensity of the marathon is equivalent to 85% VO2max (7). The exercise intensities of other long- or middle-distance events are equivalent to more than 90% VO2max (7). Therefore, it was reasonable to think that the previous findings might not directly influence performance in the marathon or in long- or middle-distance running events. Thus, the previous studies are not sufficient to infer the acute effects of dynamic stretching techniques on endurance running performances in well-trained long- or middle-distance runners.
The purpose of this study was to clarify the acute effect of the optimal protocol for dynamic stretching to improve explosive performance on endurance running performance in well-trained long- or middle-distance runners. This study examined the acute effect on endurance running performance at an exercise intensity of 90% VO2max, which is assumed to be that achieved in 3,000–5,000-m distance running events (7). We hypothesized that the protocol of dynamic stretching may improve endurance running performance.
Experimental Approach to the Problem
To determine the validity of our hypothesis, experiments consisting of 3 testing days interspersed with more than 2 days of rest were performed. On day 1, each subject visited our laboratory to receive instructions. A test of VO2max with maximum incremental exercise test using a respiratory gas analyzer and a treadmill was conducted to determine each subject's relative running velocity while measuring their endurance running performance. On day 2 (Figure 1), each subject visited the laboratory and rested. After resting, a blood lactate accumulation was assessed and then the mask of the respiratory gas analyzer and transmitter of heart rate were worn. Endurance running performance was assessed after one of the 2 types of pretreatment: (a) nonstretching by resting in a sitting position or (b) performing dynamic stretching of lower extremities. Pretreatment on day 2 was determined at random for each subject. The running velocity during the assessment of the endurance running performance was equivalent to 90% of the VO2max assessed on day 1 for each subject. Each subject continued running to exhaustion on the treadmill set at the running velocity. The time to exhaustion and total running distance were assessed as indices of the endurance running performance. The VO2 from rest to exhaustion was measured as an index of running economy using the respiratory gas analyzer. Immediately after exhaustion, lactate accumulation and heart rate were measured. On day 3, the endurance running performance was also assessed after the opposite pretreatment from day 2. Data were compared between the nonstretching and dynamic stretching pretreatments to examine the acute effects of dynamic stretching on endurance running performance and metabolism. The experiments of both pretreatments for each subject were performed at the same time of day in consideration of circadian rhythm. The temperature of the laboratory was set to 20–24° C throughout all experiments.
Seven healthy well-trained middle- or long-distance male runners (average ± SD: age 21.3 ± 2.1 years [19–24 years]; height 170.3 ± 3.1 cm; body mass 60.0 ± 5.5 kg; VO2max 4.35 ± 0.53 L·min−1; VO2max · body mass−1 72.3 ± 3.7 ml·kg−1·min−1] took part in this study. They belonged to the Track and Field club of our university. All subjects were free of injuries in their lower extremities. All experiments were carried out between February and March. Since the period was off-season, the subjects did not perform any vigorous training. We cautioned each subject to avoid performing intense exercises or training (e.g., running, resistance, or stretching) on the day of each experiment or the previous day. Moreover, we instructed each subject to eat similar meals on the day of each experiment and on the previous day and to finish meal of that day 2 hours before experiment. In addition, we warned each subject to avoid drinking alcohol on the previous day and caffeine on the experimental day. All subjects were informed of the protocol, purpose, and risks of this study, and informed consent was obtained from all subjects. The study was approved by the Ethics Committee of our university.
Maximum Incremental Exercise Test
The maximum incremental exercise test was performed using a motor-driven treadmill (Nishikawa Iron Co. Ltd., Kyoto, Japan) to determine the VO2max and the relative running velocity at 90% VO2max for each subject in reference to the protocols in previous study (24). Each subject continued to run for four minutes at each velocity with a rest period of 1 minute between velocities. The first running velocity was 167 m·min−1 (6 min·km−1). Then, the running velocities were increased as follows: 200 m·min−1 (5 min·km−1), 222 m·min−1 (4 minutes and 30 s·km−1), 250 m·min−1 (4 min·km−1), 273 m·min−1 (3 minutes and 40 s·km−1), 300 m·min−1 (3 minutes and 20 s·km−1), 333 m·min−1 (3 min·km−1), and 364 m·min−1 (2 minutes and 45 s·km−1). The criterion for finishing the test was (a) when the heart rate exceeded the predicted maximal heart rate of each subject (220 b·min−1 – age), (b) when the respiratory quotient exceeded 1.1, or (c) when the subject could not continue to run. All subjects finished by the third criterion. VO2 was measured every 10 seconds by the mixing chamber method using a respiratory gas analyzer (VO2000, S&ME Co. Ltd., Tokyo, Japan) throughout the running test. The maximum VO2 value for 10 seconds in the maximum increment exercise test was assessed as VO2max. Reliability of the VO2max was ascertained by 2 tests interspersed with more than 2 days of rest. The reliability of VO2max was assessed using an interclass correlation coefficient (ICC) and a coefficient of variation (CV). The ICC and CV were 0.787 and 1.9%, respectively. The running velocity at 90% VO2max for each subject was calculated from the relationship between the running velocities and the VO2 obtained by the running test. The average running velocity at 90% VO2max was 280.5 ± 25.6 m·min−1 (3 minutes and 35.4 ± 19.6 s·km−1).
In the dynamic stretching treatment (Figure 2), the subjects performed dynamic stretching of 5 target muscles, i.e., hip extensors and flexors, leg extensors and flexors, and plantar flexors, in upright positions in reference to the protocoloups). The contraction was carried out as quickly and powerfully as possible without bouncing so that subject's target muscle groups were stretched as quickly as possible (27,28). Each stretch was performed for 1 set on both lower extremities and then on the next target muscle group without rest. The total duration of the dynamic stretching treatment was 3 minutes and 37 ± 12 seconds. The endurance running performance was assessed 5 minutes after beginning to perform the dynamic stretching treatment (i.e., 1 minute and 23 ± 12 seconds after dynamic stretching). The order of dynamic stretching is described as follows: (a) hip extensors: the subject leaned forward and raised his foot from the floor with his hip and knee joint lightly flexed. Then, the subject contracted his hip joint extensors and extended his hip joint so that his leg was extended to posterior aspect of his body (Figure 2A); (b) hip flexors: the subject contracted his hip joint flexors with his knee joint flexed and then flexed his hip joint so that his thigh came up to his chest (Figure 2B); (c) leg extensors: the subject contracted his hamstrings and flexed his knee joint so that his heel kicked his buttock (Figure 2C); (d) leg flexors: the subject contracted his hip joint flexors and flexed his hip joint, raising his thigh parallel to the ground with his knee joint flexed at about 90°. Then, the subject contracted his quadriceps with the height of his thigh maintained and then extended his knee joint so that his leg extended to the anterior aspect of his body (Figure 2D); and (e) plantar flexors: the subject raised 1 foot from the floor and fully extended the knee joint. Then, the subject contracted his dorsiflexors and dorsiflexed his ankle joint so that his toe was raised (Figure 2E).
In nonstretching, each subject rested in a sitting position for 5 minutes' that was equivalent to duration in the dynamic stretching treatment. The endurance running performance was assessed immediately after that.
Measurements During Endurance Running Performance
Each subject continued running to exhaustion on the treadmill set at a velocity equivalent to his 90% VO2max. The criterion of exhaustion was (a) when each subject could not continue to run or (b) when each subject could not stay in our defined position for more than 10 seconds. The defined position was a range of anteroposterior 1 m from the center of the treadmill. The continuous time of running to exhaustion was assessed as an index of endurance running performance. The total running distance also was calculated by the running velocity at 90% VO2max·the time to exhaustion. In addition, the VO2 during rest, pretreatment, and running was sampled every 10 seconds with the respiratory gas analyzer (VO2000). In both pretreatments, the average VO2 for 1 minute was calculated at rest for 1 minute before treatment and from the start of running to 1 minute before exhaustion. The VO2 during running was taken as an index of running economy. In the dynamic stretching treatment, the average VO2 while performing dynamic stretching was also calculated. Blood sampling was performed from the earlobe at rest and immediately after running to exhaustion. The blood lactate accumulations were measured with an analyzer (Lactate Pro, LT-1710; Arkray, Kyoto, Japan), and heart rates were measured with transmitter (T31; Polar Oy, Kempele, Finland) and were sampled synchronizing with VO2 to confirm the running intensities and metabolism responses.
All data were normally distributed and homogeneity of variance by using chi-square tests for goodness of fit and Bartlett's tests, respectively. Paired t-tests were used to examine the differences in time to exhaustion and total running distance between the nonstretching and the dynamic stretching treatment. The effect sizes were calculated using Kline's equation (11) (d = mean difference · SD of mean difference−1; small d < 0.50, moderate d = 0.50–0.80, and large d > 0.80) in consideration of using the paired t-test. Repeated-measures analysis of variance (pretreatments × times) was used to compare changes in the VO2, the blood lactate accumulation, and heart rate. The effect sizes were calculated as general η2 (2) (ηg2; small ηg2 = 0.02, moderate ηg2 = 0.13, and large ηg2 = 0.26 (15)). Power (1 − β) of all analyses was calculated. All variable data were expressed as the average ± SD, and the significance level was set at p ≤ 0.05. Reliabilities of measures during endurance running for a constant velocity equivalent to 90% VO2max were assessed using ICCs and CVs comparing repeated-measures test interspersed with more than 2 days of rest. Reliabilities were the time to exhaustion (ICC = 0.982; CV = 8.7%), the total distance (ICC = 0.985; CV = 9.0%), the average VO2 (ICC = 0.995; CV = 1.4%), the blood lactate accumulations at exhaustion (ICC = 0.800; CV = 13.7%), and the heart rate at exhaustion (ICC = 0.957; CV = 1.7%).
The time to exhaustion after the dynamic stretching treatment was longer than that after the nonstretching for all subjects (Figure 3). The average time to exhaustion after the dynamic stretching treatment was 928.6 ± 215.0 seconds, and it was significantly (p < 0.01) longer than that (785.3 ± 206.2 seconds) after the nonstretching (Figure 3). The effect size was large (d = 1.56). The power was 0.93. The total distance for all subjects was also longer after the dynamic stretching treatment, compared with the nonstretching (Figure 4). The average total distance (4,301.2 ± 893.8 m) after dynamic stretching treatment was significantly (p < 0.01) longer than that (3,619.9 ± 783.3 m) after the nonstretching (Figure 4). The effect size was large (d = 1.55). The power was 0.92.
The average relative VO2 was 84% VO2max at 2 minute after beginning to run, 90% VO2max at 3 minutes, and then increased gradually from 92% VO2max to 99% VO2max 4 minutes later (Figure 5). The average VO2 after both pretreatments increased drastically from rest to 2 minutes after beginning to run and then increased slightly (Figure 5). The changes in average VO2 after both pretreatments did not show a significant interaction (pretreatments × times: F = 0.61, p = 0.77). The effect size was small (ηg2 = 0.011). The power was 1.00. The average blood lactate accumulations and heart rate were elevated after both pretreatments from rest to exhaustion (Table 1), although the changes in average blood lactate accumulation and heart rate did not show a significant interaction (blood lactate accumulation, pretreatments × times: F = 0.35, p = 0.57; heart rate, pretreatments × times: F = 0.18, p = 0.67). The effect sizes were small (blood lactate accumulation, ηg2 = 0.014; heart rate, ηg2 = 0.005). The power was 0.99 in blood lactate accumulation and heart rate.
This study investigated the acute effect of dynamic stretching comprising 1 set of 10 repetitions in volume and as quickly as possible in velocity on relative high-intensity endurance running performance in well-trained middle- or long-distance runners. The present results indicated that dynamic stretching acutely prolonged the time to exhaustion (Figure 3; +18.2%) and extended the total distance (Figure 4; +18.9%) of endurance running for a constant velocity equivalent to 90% VO2max. The effect sizes of the improvements in time to exhaustion and total distance were large (d = 1.56 and d = 1.55, respectively), although the number of subjects was small. The VO2, blood lactate accumulation, and heart rate at exhaustion did not differ between the pretreatments (Table 1). It was reasonable to suppose that each subject continued running to exhaustion with a similar effort after the 2 pretreatments. We previously examined acute effects of 15 minutes of warm-up running for a constant velocity equivalent to 70% VO2max recommended generally on time to exhaustion during running equivalent to 90% VO2max in the same well-trained runners as this study (23). The result indicated that the time to exhaustion in warm-up running did not significantly differ from that in no warm-up, i.e., sitting and rest (that is nonstretching in this study), although it tended to improve. The improvement in time to exhaustion (+4.3%) was relatively smaller than that (+18.2%) after dynamic stretching in this study. The average VO2 during the dynamic stretching in this study was 24.9 ± 3.1% VO2max, it was relatively lower and easier than generally recommended intensity (70% VO2max) during warm-up running. The total duration in performing dynamic stretching was three minutes and 37 ± 12 seconds, it was relatively shorter than generally recommended duration (>10 minutes) in warm-up running. From the standpoints of intensity and duration, the dynamic stretching in this study was also superior to general warm-up running. The running intensity of 90% VO2max is equivalent to that of 3,000–5,000-m distance running events in track and field (7). To take our previous study into consideration, the results of this study suggest that using this dynamic stretching protocol during actual warm-up for well-trained runners would improve their endurance running performance in distance running events than using only general warm-up running. This study was the first study to reveal that dynamic stretching acutely improves endurance running performance.
Hayes and Walker (5) compared the acute effects of 5 exercises of dynamic stretching of the lower extremities for 2 sets of 30 seconds and controlled slow-velocity, normal, and progressive static stretching for 2 sets of 30 seconds and nonstretching on VO2 during treadmill running for 10 minutes at an intensity of 75% VO2max. They found that the VO2 did not significantly differ among the pretreatments, suggesting that differences in stretching technique did not acutely affect running economy. In contrast, Zourdos et al. (29) found that 10 exercises of dynamic stretching were performed because 2 sets of 4 repetitions in the lower extremities acutely increased energy expenditure (+4.4%) during treadmill running for 30 minutes at an intensity of 65% VO2max, compared with nonstretching. Zourdos et al. (29) however, indicated that the total distance during running as fast as possible for 30 minutes on a treadmill with the velocity and distance display concealed did not significantly differ between pretreatments. Previous results have thus suggested that the dynamic stretching did not acutely affect endurance running performance, although it impaired running economy during constant velocity running.
We considered 2 reasons for the differences between our findings and those of previous studies (5,29). First, the dynamic stretching protocol in this study differed from those in the previous studies. Hayes and Walker (5) used dynamic stretching controlled at a slow velocity. Zourdos et al. (29) used less dynamic stretching in two sets of four repetitions. A systematic review (26) to find the optimal protocol for dynamic stretching to acutely improve explosive performance suggested that dynamic stretching should be performed “as quickly as possible in velocity” and “one-two set(s) of 10–15 repetitions in volume.” The hypothesis of this study was that the optimal protocol for dynamic stretching to acutely improve explosive performance might also acutely improve the endurance running performance. Our results confirmed the validity of this hypothesis. However, this study investigated a peculiar acute effect of dynamic stretching on endurance running performance. In a general warm-up, athletes usually perform running before dynamic stretching. Moreover, this study used “stationary” dynamic stretching, i.e., without movement. Fletcher and Jones (4) revealed that dynamic stretching with movement acutely significantly improved the 20-m sprint time, although dynamic stretching without movement did not. The results suggested that dynamic stretching with movement was superior to dynamic stretching without movement. Therefore, it was necessary to examine the acute effect of dynamic stretching with movement after warm-up running on endurance running performance. In addition, this study used only 1 set of 10 repetitions as volume of dynamic stretching. The previous systematic review (26) revealed that 1-2 set(s) of 10–15 repetitions as dynamic stretching was an optimal volume to acutely improve explosive performance. Further studies will be needed to clarify more effective protocols as to velocity or volume of dynamic stretching to acutely improve various endurance running performances.
Second, there were differences in the exercise intensities during assessing the endurance running performance. The exercise intensity of the study of Hayes and Walker (5) was 75% VO2max. In the study of Zordous et al. (29), the exercise intensity was 65% VO2max at constant velocity and approximately 80% VO2max at self-controlled velocity. In this study, the endurance running performance was evaluated during running at constant velocity at an exercise intensity equivalent to 90% VO2max. The exercise intensity of 90% VO2max was set based on 3,000–5,000-m running events in track and field (7). To begin with, well-trained runners run at intensities of more than 85% VO2max even in marathons—the lowest intensity running event among middle- and long-distance events (7). It is reasonable to suppose that the present findings are relevant to actual middle- or long-distance running events. Future studies, however, will need to investigate the acute effect of this dynamic stretching protocol on actual running times in 3,000 or 5,000-m time trials.
This study measured VO2 as an index of running economy to consider why dynamic stretching acutely changes endurance running performance. The present results demonstrated that the changes in VO2 did not differ between dynamic stretching treatment and nonstretching (Figure 5). The effect size was also small (ηg2 = 0.011). The present finding suggested that running economy evaluated by VO2 does not explain why dynamic stretching acutely improved the endurance performance. The endurance running performance at the exercise intensity of 90% VO2max or 3,000–5,000-m running is decided by running economy evaluated by not only VO2, but also effective utilization of the stretch-shortening cycle (13,18) or the improvement of neuromuscular activation (14,16). Unfortunately, this study did not measure data for these mechanisms. Future studies need to investigate the contact time or the flight time by analysis of movement and the electromyographic activities of various muscle groups in the lower extremities during performance running and to clarify the reason why the dynamic stretching protocol used in this study acutely improved the endurance running performance at an exercise intensity of 90% VO2max.
This study indicated that the dynamic stretching for 1 set of 10 repetitions as quickly as possible acutely improved endurance running performance at an exercise intensity equivalent to 90% VO2max (7). This finding suggests that this dynamic stretching routine if used during actual warm-ups for well-trained runners might improve their race times in 3,000–5,000-m events in track and field. Thus, we recommend that well-trained runners and their coaches use the dynamic stretching protocol described in this study.
Supported by JSPS KAKENHI Grant number 24700655.
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