There is debate over whether stretching exercises should be included in an athlete's warm-up routine in an effort to maximize athletic performance (19). For instance, static stretching seems to acutely decrease muscle force production capacity in maximal strength and strength endurance events (16). In contrast, dynamic stretching seems to either increase or have no effect on performance of high-intensity movements. Some studies have demonstrated no changes in isometric peak torque (13), and 1 repetition maximal bench press and leg press (3), whereas others have found increases in leg extension power (24) and 20-m sprint performance (9) with dynamic stretching. The performance decrements resulting from static stretching appear to last for at least 60 minutes after the stretching routine (10). Dynamic stretching, however, may be more effective than static stretching for improving athletic performance possibly because of elevated baseline oxygen consumption (V̇O2) before the task (6).
Elevating V̇O2 in the warm-up seems to be particularly important for increasing endurance performance. Indeed, a review by Bishop (5,6) suggested that warm-up protocols that significantly elevated maximal oxygen consumption (V̇O2max) produced improvements in endurance performance (6). Accordingly, we recently demonstrated in a similar population that static stretching increased the energy cost of a 30-minute moderate-intensity run and decreased 30-minute time trial distance. These results may have been obtained because there was no elevation in baseline V̇O2 after the stretching routine and because of a possible decrease in stiffness of the musculoskeletal unit (23). In contrast, dynamic stretching before a race may elevate baseline V̇O2 without compromising running economy. Furthermore, because dynamic stretching has been previously shown to increase athletic performance (9,24), it may have no effect on the stiffness of the musculotendinous unit. We hypothesized that these unique properties of dynamic stretching make it a possible candidate to improve endurance performance when included in a prerun warm-up routine. Therefore, the purpose of this study was to investigate the effects of dynamic stretching on endurance performance and total energy cost measured in calories expended on a treadmill in trained male runners.
Experimental Approach to the Problem
This study had a randomized, crossover design in which the subjects underwent a control and experimental condition in a balanced order. Running energy cost and running performance were assessed after either dynamic stretching (i.e., experimental condition) or quiet sitting (i.e., control condition). The subjects performed 10 different dynamic stretching exercises lasting 15 minutes in the experimental condition while they performed quiet sitting in the control condition. Sit-and-reach performance was assessed before and after each condition. After the sit-and-reach test, the subjects had a 2-minute rest followed by a 30-minute preload run at 65% of their V̇O2max to measure caloric expenditure and a 30-minute performance run at a self-selected speed to measure distance run.
Fourteen trained male runners (23.0 ± 4.3 years, V̇O2max of 63.1 ± 8.3 ml·kg−1·min−1 and percent body fat of 7 ± 2%) were recruited for the study from running and triathlon teams at the Florida State University. Criteria for acceptance in the study included a V̇O2max ≥ 55 ml·kg−1·min−1, a minimum average run of 20 miles·wk−1, recent (≤3 months) participation in a competitive running endurance event (>5 km) and at least 3 years of competition experience. All the runners included stretching exercises on a daily basis as part of their training regimen. The subjects were informed of the experimental risks and signed an informed consent form before the investigation. The investigation was approved by the Florida State University Institutional Review Board for use of human subjects.
The subjects reported to the laboratory on 3 separate occasions, separated by a 1-week interval to control for the specific day and time the experimental protocol was performed. The subjects were instructed to maintain their training routines throughout the experimental period and to refrain from intense exercise for 48 hours before each visit.
On the first visit, the subject's body composition was estimated using the sum of 3 skin-fold measurements (14). V̇O2max was determined on a motor-driven treadmill (Model, Woodway® Waukesha, WI, USA) using a progressive exercise test to exhaustion as described previously (17). Gas exchange, caloric expenditure, and ventilatory parameters were measured by means of indirect calorimetry using a metabolic measurement system (Parvomedics Truemax® 2400, Consentius Technologies, Sandy, UT, USA). Before each test, the gas analyzer was calibrated by using ambient air and a gas of a known composition containing 20.9% O2 and 4 CO2. The turbine flowmeter was calibrated using a 3-L syringe (Hans Rudolph, Inc., Kansas City, MO, USA). The heart rate (HR) was monitored using an HR monitor (Model, Polar™, Lake Success, NY, USA). After the V̇O2max test, the running speed corresponding to 65% of the subjects V̇O2max was determined by walking the subjects at 6.4 km·h−1 for 1 minute, followed by a 0.8-km·h−1 increase each minute until the subject's V̇O2 values reached a steady state at 65% of their previously recorded V̇O2max.
The experimental protocol took place on visits 2 and 3. Initially, the gas analyzer system was attached to the subjects. The average resting V̇O2 values were recorded for 5 minutes before the dynamic stretching protocol and the quiet sitting. The subjects walked for 5 minutes at 3 mph. After the 5-minute walk, a sit-and-reach assessment was performed using a Figure Finder Flex-Tester® sit-and-reach box (Novel Products, Inc., Rockton, IL, USA). Then, the subjects either remained seated for 15 minutes or performed the dynamic stretching protocol (described below). The sit-and-reach performance was reassessed after both the quiet-sitting and the dynamic stretching conditions. Each subject performed 3 trials of the sit-and-reach test of which the best trial was used for analysis. V̇O2 values were also recorded after both the quiet-sitting and dynamic stretching conditions. Finally, the subjects performed a preload run for 30 minutes at an intensity corresponding to 65% of their V̇O2max. The total caloric expenditure was calculated using the sum of the caloric expenditure averages obtained over 30-second intervals (22). Upon completion of the preload run, the treadmill was stopped, and the subjects were disconnected from the metabolic cart and permitted 2 minutes to drink water. The water volume was recorded and used for the next experimental session. During the 30-minute performance run, the subjects were asked to cover their maximal distance possible for 30 minutes. They were allowed to view the time display and to control the treadmill speed but were blinded to the distance covered and the treadmill speed (8). In addition, the HR was recorded every minute, whereas the ratings of perceived exertion (RPE) were assessed every 5 minutes during both the preload and performance runs.
The stretching protocol used in this study consisted of dynamic stretching, focusing on the quadriceps, hamstrings, calves, and hip extensors and flexors (23). A total of 10 different movements were used and completed in 15 minutes by performing 2 sets of 4 repetitions of each movement. The dynamic stretching movements were performed in the following order: (a) Toe and Heel Walks: In these exercises, the subjects walked on their toes for 4 steps followed by walking on their heels for 4 steps to stretch the entire calf complex. (b) Hip Series: The subjects performed a dynamic stretch of the hip flexors and extensors by placing their hands on a wall with their arms fully extended so that their body was at a 45° angle. In this position, each subject lifted his leg off the ground while bringing the knee to the chest and stepping over a hurdle placed laterally before returning to the starting position. (c) Hand Walks: The subjects stretched their calves and hamstrings by beginning in a pushup position and walking their feet as close to their hands while keeping their heels flat. As soon as the subjects' heels came off the ground, they ‘walked’ with their hands back to a pushup position. After the hand walks, the subjects performed a series of walking lunges, including (d) rear lunges, (e) lateral lunges, (f) forward lunges, (g) a knee pull to a lunge, and (h) an ankle pull to a lunge to focus on the quadriceps and gluteus maximus. (i) Walking Groiners: The subjects began this movement in a pushup position and then brought 1 foot next to the same side hand as to perform a groiner. Instead of holding this position, the subjects ‘walked’ their hands out to return to the starting position before performing the action on the opposite leg. (j) Frankensteins: The subjects stood with their feet together and their arms extended straight out in front of them so that their arms were parallel to the ground. While walking, the subjects were instructed to kick 1 leg up to touch the opposite hand to focus on the hamstrings. Every time a step was taken, a kick was made. On nonstretching days, the subjects sat quietly for 15 minutes before the exercise protocol (16).
To control for diet, the subjects kept a record of their diet (all food and beverages) for 72 hours before the first experimental session they participated in. The diet log was then given to the subject with instructions to replicate the food consumption for 72 hours before the second experimental session (2). The subjects were also instructed to maintain current training and not to perform any strenuous exercise 48 hours before all laboratory visits.
The influence of the dynamic stretching routine on the sit-and-reach performance was tested with a 2 × 2 (trial × time) repeated measures analysis of variance (ANOVA). The possible effects of dynamic stretching on total caloric expenditure on both the preload and performance runs were evaluated using paired t-tests (i.e., nonstretching × stretching condition). A number of 2 × 7 (group × time) repeated measures ANOVAs were used to test for the differences in HR and RPE during both the 30-minute preload and 30-minute performance runs. Whenever a significant F-value was obtained, a Tukey post hoc test was performed to localize the effect(s). Data were reported as means and SDs. The statistical procedures were performed using the software Statistica®, and the level of significance was set at p ≤ 0.05.
Sit-and-reach average values increased significantly after the dynamic stretching exercises from 32.3 ± 8.6 to 37.6 ± 8.1 cm (p < 0.05) and did not change (32.5 ± 8.1 to 34.0 ± 8.1 cm) after the quiet sitting. Moreover, poststretching values after dynamic stretching were significantly greater than postsitting values for the control condition (p < 0.05).
Resting V̇O2 and Energy Cost of the 30-Minute Preload Run
The average resting V̇O2 values increased significantly after the dynamic stretching condition from prestretch: 6.2 ± 1.7 vs. poststretch: 8.4 ± 2.1 ml·kg−1·min−1 (p < 0.05) but did not change in the control condition (prestretch: 5.8 ± 1.1 vs. poststretch: 6.1 ± 1.0 ml·kg−1·min−1).
The average velocity that was run at 65% V̇O2max was 10.5 ± 1.9 km·h−1. After the dynamic stretching exercises, the mean energy expended was significantly greater in the stretching (416.7 ± 44.9 kcal) vs. the control (399.3 ± 50.4 kcal) condition (p < 0.05). Figure 1A illustrates the mean caloric expenditure, and Figure 1B shows the individual values for each subject during the 30-minute run at 65% V̇O2max. The effect size for energy cost was 0.4 in favor of the stretching condition. These results demonstrate that significantly more calories were expended after dynamic stretching when compared with those expended after nonstretching with absolute differences ranging from 1 to 77 additional kilocalories.
After the stretching exercises, the mean distance run in the control condition was 6.3 ± 1.1 and 6.1 ± 1.3 km in the stretching condition (p > 0.05). The effect size for the distance run was 0.2 demonstrating little correlation between condition and distance covered. Figure 2A depicts both the mean values, and Figure 2B shows the individuals values for the stretching and control.
Heart Rate and Ratings of Perceived Exertion
There were no group × time interactions for the HR during the preload or the performance runs; however, there were significant time effects for both (p < 0.05). The mean HR values peaked at 162 ± 18 and 168 ± 18 b·min−1 in the stretching and non-tretching control conditions, respectively, during the preload run, and at 189 ± 8 and 189 ± 9 b·min−1 in the stretching and control conditions, respectively, during the performance run. Similarly, no group × time interactions were found for RPE during the preload or the performance runs; however, there were significant time effects for both (p < 0.05). The mean RPE values peaked at 11 ± 3 and 12 ± 3 in the stretching and control conditions, respectively, during the preload run (Figure 3), and at 18 ± 1 vs. 18 ± 1 in the stretching and control conditions, respectively, during the performance runs.
The purpose of this study was to investigate the effects of dynamic stretching on endurance performance and total caloric expenditure on a treadmill run in trained male runners. The main findings in this study were that there was no difference in endurance performance (i.e., distance covered) between the dynamic stretching and control (nonstretching) conditions. Dynamic stretching, however, significantly increased caloric expenditure during the preload run at 65% of V̇O2max (p < 0.05) when compared with the control condition (Figure 1B). These results are likely explained by higher V̇O2 values at the beginning of the preload run because of the increase in metabolic demand during the stretching protocol (23).
Our previous study (23) demonstrated a 17% increase in the sit-and-reach performance after a 16-minute static stretching protocol, which was similar to the 16% increase seen after our dynamic stretching protocol. Although static stretching resulted in a decrease in running performance, our study showed no significant differences in performance with dynamic stretching, despite similar changes in the range of motion (ROM). This finding suggests that dynamic stretching acutely increases joint ROM to the same extent as static stretching does but without deleterious effects on performance.
Dynamic stretching and active warm-up are widely used to elevate core temperature, whereas increasing oxygen consumption and efficiency of substrate use via increased vasodilation of the working muscles (6,18). However, it has been suggested that this increase in the temperature may not be beneficial to endurance performance (6). Furthermore, if the warm-up intensity and duration are too high or >10 minutes, respectively, the warm-up can be detrimental to performance (5,6). For example, Uckert and Joch (21) reported a decrease in performance during a treadmill run up to exhaustion in 20 male runners after a 20-minute warm-up protocol. These results may be attributed to an increased tympanic and skin temperature above baseline levels when compared with a control condition (21). However, they also showed an increase in the runners' time to exhaustion after sitting in a cooling vest for 20 minutes. The cooling vest increased the tympanic temperature greater than the control did, but to a lesser magnitude than the warm-up condition did. Further, the cooling vest also decreased the skin temperature compared with that in the control condition (21). The authors concluded that the increase in the runners' time to exhaustion after wearing the cooling vest was related to the decrease in skin temperature. In addition, Hajoglou et al. (12) noted an increase in 3-km cycling time trial performance after both an easy warm-up of 15 minutes at 70, 80, and 90% ventilatory threshold for 5 minutes each and a hard warm-up of the same protocol followed by 3 minutes of cycling at the respiratory compensation threshold when compared with a no warm-up condition (12). Hajoglou et al. (12) went on to note that a faster rate in V̇O2 elevation at the start of the time trial as a possible mechanism for increased performance in both warm-up conditions (12). These findings suggest that endurance performance may be negatively affected by a long warm-up protocol, whereas intermediate performance (i.e., >5 seconds, but <5 minutes) is improved regardless of the warm-up intensity. The dynamic stretching protocol in this study seems to have some benefits for endurance performance (i.e., increasing baseline V̇O2). However, it also has a controversial length of 15 minutes and a possible elevation in skin temperature, which has been shown to negatively affect endurance performance. Nevertheless, our data suggest that the relatively long duration of our dynamic stretching protocol had no deleterious effect on endurance performance possibly because it produced an increase in V̇O2 values after the dynamic stretching protocol (8.4 ± 2.1 ml·kg−1·min−1).
Other investigators have also proposed that the length and the intensity of the warm-up protocol are important for yielding positive effects on performance (1,4). It has been previously suggested that a warm-up of approximately 70% V̇O2max may be appropriate for intermediate duration exercise (7,20). However, a warm-up of too high an intensity can cause the accumulation of metabolites, negatively affect O2 deficit, deplete glycogen stores, and increase thermoregulatory strain and as a result may not be beneficial for long-term performance (6). For example, Andzel (1) reported an increase in 1-mile run performance when runners had an increased resting V̇O2 at the start of the 1-mile run because of a warm-up, which raised their HR to 140 b·min−1 (1). On the other hand Billat et al. (4) reported a lower total run time in a run to exhaustion in trained long-distance runners because of a fatiguing warm-up protocol (4). Billat et al. used runs >70% in their warm-up protocol (4). This intensity may be too fatiguing because recommended warm-up intensity for improving endurance performance is between 60 and 70% V̇O2max. Additionally, Bishop suggests in his review that a proper warm-up for increasing endurance performance is one which elevates V̇O2, lasts 5–10 minutes, and does not cause thermoregulatory strain nor deplete muscle glycogen stores (6). Furthermore, Gregson et al. (11) reported a decreased time in a run to exhaustion at 70% V̇O2max in well-trained soccer players (11). These findings are consistent with that of Billat et al. because Gregson's study also employed a warm-up of 70% V̇O2max. In this study, the dynamic stretching protocol significantly elevated V̇O2; however, it lasted for 15 minutes, possibly negating positive effects seen from a 5- to 10-minute warm-up. Moreover, most studies, which have reported increases in endurance performance after a warm-up with elevated V̇O2, have consisted of a performance trial between 5 and 25 minutes (6). The performance run in this study lasted for 30 minutes and was always preceded by the same preload run. It is therefore likely that the positive effects of dynamic stretching are not relevant to a run of this particular distance. Finally, even though dynamic exercise performance is increased when the body temperature is elevated, this phenomenon may be more beneficial for short-term performance (e.g., <10 seconds) rather than for endurance performance (6).
Static stretching does not seem to increase resting V̇O2 and results in a decrease in performance in male collegiate runners (23). The decrease in performance with static stretching seems to be caused by a decline in running economy, which is associated with a greater stress-relaxation effect. In fact, the changes in the stress-relaxation property of the muscle tissue resulted in a decreased mechanical efficiency of the stretch shortening cycle (15). On the other hand, dynamic stretching has been reported to increase the performance in anaerobic exercise (9,24). This increase in anaerobic performance as a result of dynamic stretching is likely because of the specificity that dynamic stretching has to the performance activity. Thus, it is reasonable to suggest that dynamic stretching does not result in a decrease of the musculotendinous unit such as in the case of static stretching. This theory is supported by our findings showing dynamic stretching to have no effect on running endurance performance, whereas our previous study demonstrates static stretching to decrease running endurance performance (23).
Reviews on warm-up and performance from Shellock and Prentice (18) and Bishop (5,6) suggest that it is critical to design a specific warm-up protocol for a specific athletic event instead of generalizing the warm-up protocol (6,18). Bishop expanded upon this idea by reporting that an active warm-up, which uses a task-specific burst of activity, may provide ergogenic benefits greater than that of a nonspecific active warm-up for intermediate and long-term exercise performance (6). The stretch shortening cycle is performed and repeated with a greater percentage of maximal force in anaerobic exercise than in long-distance endurance running. It is therefore possible that dynamic stretching is more specific and thus effective at increasing short-term and intermediate duration exercise performance than endurance performance is. Thus, a specific running activity, which increases baseline V̇O2 at the start of the performance trial and is nonfatiguing may be more suitable than dynamic stretching as a method to increase endurance running performance. This theory is supported by Andzel (1) who used a submaximal running warm-up to increase subsequent 1-mile run performance (1).
Caution should be exercised to extrapolate the findings of this study to recreational runners, because we tested only trained male athletes. It is possible that residual fatigue induced by a dynamic stretching protocol may become apparent in a more recreationally trained population or those who are not used to performing stretching exercises. Even though all of the subjects were trained (V̇O2max ≥ 55 ml·kg−1·min−1), some were elite, and some were moderately trained as V̇O2maxs ranged from 55 to 81 ml·kg−1·min−1. Shellock and Prentice (18) indicate that elite athletes may need longer warm-ups to properly prepare, suggesting that a more trained individual needs a longer warm-up because of their thermoregulatory center being more efficient at responding to exercise generated heat (18). With these thoughts, it is interesting to note that our top 2 performance runners both increased their performance under the dynamic stretching condition with the top runner seeing the largest increase in distance covered in the dynamic stretching condition of 0.2 km. Furthermore, the 2 runners in our study who covered the shortest distance performed better during the nonstretching control condition with the worst performance runner seeing the largest decline in performance after the stretching condition (i.e., 0.6 km). It is possible that elite endurance runners need a warm-up protocol of greater intensity and duration than do recreationally trained runners. Additional biomechanical assessments seem necessary, such as changes in stiffness and ground contact times, to have a better understanding on the mechanisms underlying the effects of stretching on both performance and the energy cost of running.
In summary, this study reports 2 important findings on the effects of dynamic stretching on endurance performance in trained male runners. First, it was found that dynamic stretching increases the energy expended during moderate-intensity treadmill exercise most likely because of an increase in O2 consumption. Second, in contrast to static stretching (23), dynamic stretching does not seem to decrease endurance performance and may increase performance in male elite runners during our particular experimental protocol. Further research is needed to ascertain the underlying mechanisms behind our findings possibly with more sophisticated biomechanical and physiological measurements. Further investigations are also necessary using diverse warm-up protocols specific to the endurance events (e.g., types, duration) in different populations (e.g., women, untrained).
The present findings along with our previous research on static stretching (23) suggest that athletes can use both forms of stretching as a mechanism to improve short-term ROM. However, it can be suggested for coaches to consider that static stretching resulted in a 3% decline in endurance performance in trained male runners. If athletes are committed to prerace stretching techniques, coaches may need to consider dynamic stretching because it has no deleterious effect on endurance performance. However, it is also important to note that our findings can be only applicable to the similar populations and conditions specifically tested in our studies.
No external financial support was received to fund this project.
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