The Effect of Static and Dynamic Stretching during Warm-Up on Running Economy and Perception of Effort in Recreational Endurance Runners

s randomized crossover counterbalanced study investigated, in recreational runners, the acute effects of pre-exercise stretching on physiological and metabolic responses, endurance performance, and perception of effort. Eight male endurance runners (age 36 11 years) performed three running-until-exhaustion tests, preceded by three warm-ups, including the following different stretching protocols: static (SS), dynamic (DS), and no-stretching (NS). During the SS and DS sessions, the warm-up consisted of 10 min of running plus 5 min of SS or DS, respectively, while during the NS session, the warm-up consisted of 15 min of running. Physiological and metabolic responses, and endurance running performance parameters, were

three warm-ups, including the following different stretching protocols: static (SS), dynamic (DS), and no-stretching (NS). During the SS and DS sessions, the warm-up consisted of 10 min of running plus 5 min of SS or DS, respectively, while during the NS session, the warm-up consisted of 15 min of running. Physiological and metabolic responses, and endurance running performance parameters, were evaluated. The perception of effort was derived from the rating of perceived exertion (RPE). Running economy signi cantly improved after SS (p< 0.05) and DS (p< 0.01), and RPE values were signi cantly lower in SS (p< 0.05) and DS (p< 0.01), compared to NS. No differences in physiological and metabolic responses among the sessions were found. This study showed that including SS and DS within the warm-up ameliorated running economy and decreased the perception of effort during a running-until-exhaustion test, highlighting the bene ts of stretching on endurance performance. These results should encourage recreational runners to insert stretching during warm-up, to optimize the running energy costs, reducing the perception of effort and making the training sessions more enjoyable. Keywords:stretching; warm-up; time to exhaustion; rate of perceived exertion; running economy 1. Introduction Runners commonly perform a warm-up before an endurance exercise, as it is consid- ered essential to achieve optimal performance [1]. Stretching is frequently integrated into runners' warm-up routines, but its effectiveness in improving physiological and metabolic responses, and endurance running performance parameters, is still debated [2,3]. The effects of stretching on physical performance have been demonstrated to de- pend on different factors, such as stretch modality [4] and duration [5], and the subject's conditioning levels [6]. Among different stretching modalities, SS and DS are the most investigated. SS involves limb movement to the end of the range-of-motion (ROM), holding this position from 15 to 60 s [7], whilst DS requires controlled movements through the ROM, by contracting agonist muscle groups and lengthening antagonist muscle groups, without a held-end position [8]. As concerns stretch duration, recent evidence has highlighted that in SS protocols, usually designed with different durations, a clear dose-response effect Int. J. Environ. Res. Public Health2021,18, 8386.

holding this position from 15 to 60 s [7], whilst DS requires controlled movements through the ROM, by contracting agonist muscle groups and lengthening antagonist muscle groups, without a held-end position [8]. As concerns stretch duration, recent evidence has highlighted that in SS protocols, usually designed with different durations, a clear dose-response effect Int. J. Environ. Res. Public Health2021,18, 8386.

Int. J. Environ. Res. Public Health2021,18, 8386 2 of 12 exists, in which stretch durations that are longer than 60 s per muscle–tendon unit can cause performance impairments, thus adopting shorter durations is recommended. As concerns DS protocols, the current literature reported durations of up to 220 s in total as the most advisable [9]. Regarding the effects induced by SS on physical performance, some studies showed an increase in ROM around the joint, and a signi cant decrease in the risk of muscle injuries [10,11]. However, when investigating the relationship between stretching and injury, some studies showed contrasting data, reporting that SS was not a useful prevention strategy for endurance athletes, as it was unable to reduce the prevalence of muscular– skeletal injuries [12]. A single bout of SS during warm-up has been demonstrated to both impair running performance and running economy [3,12,13], and to reduce maximal voluntary strength and muscle power [8,14], whereas some studies reported no effect on running economy and performance following SS exercises [15–20]. Given the contrasting literature about the effects of SS on performance, an alternative modality, namely, DS, has been proposed. DS has been shown to improve power, sprint and jump performance, and enhance ROM, providing a similar, or greater, increase in exibility than SS [8]. Furthermore, as regards the impact of DS on endurance performance, Yamaguchi et al. (2015) showed that a pre-exercise DS lasting a few minutes, acutely prolonged the time to exhaustion and extended the total running distance, without improving running economy [21], whilst other studies demonstrated no effects of DS, either on running economy [15] or on running performance [22]. In contrast, recently, the same authors showed that a combined warm-up of running plus DS impaired the immediate endurance performance, without affecting running economy [23]. Based on the current literature, the effects induced by pre-exercise stretching on endurance performance, and the most appropriate type of stretching, remain to be clari ed. Therefore, in the present study, we investigated, in recreational runners, the acute effects of two pre-exercise stretching modalities on physiological and metabolic responses, endurance performance and perception of

performance, without affecting running economy [23]. Based on the current literature, the effects induced by pre-exercise stretching on endurance performance, and the most appropriate type of stretching, remain to be clari ed. Therefore, in the present study, we investigated, in recreational runners, the acute effects of two pre-exercise stretching modalities on physiological and metabolic responses, endurance performance and perception of effort during an endurance running performance. To this aim, we compared submaximal continuous running and running-until-exhaustion tests, preceded by three different warm-up routines, including either static or dynamic stretching, or no stretching. Moreover, the assessment of psychophysiological stress experienced by the runners, through the rating of perceived exertion (RPE), was also a focus. In this study, in order to clarify the discrepancies in the previous literature, we inves- tigated whether a general warm-up plus stretching can affect physiological parameters, endurance running performance, and internal workload. Based on previous evidence, we hypothesized that the inclusion of stretching within the warm-up, followed by an appropriate resting period duration [1], would positively in uence endurance running performance. In addition, it is reasonable to hypothesize that stretching exercises, given their bene ts on muscle functions, could be an effective strategy to decrease the perception of effort after an endurance event. At last, considering the contrasting literature about the effects of the different modalities of stretching, we were also interested in comparing the effectiveness of static and dynamic stretching. 2. Materials and Methods 2.1. Subjects Eight recreational male runners, not participating in systematic endurance trainings and with a weekly training volume of about 15 km/week, were enrolled. Estimation of sample size was performed using VO2maxas a physiological response to exercise as one of our primary outcome measures [24,25]. Sample size was estimated using the GPower software (3.1 software Düsseldorf, Germany), applying ANOVA repeated measures (F Test) with a signi cant level of 0.05, a statistical power of 80% to an effect size (ES) of 0.3 [26]. This calculation generated a desired sample size of at least 6 participants. However, we recruited 8 subjects to allow for drop-out during the intervention period.

software (3.1 software Düsseldorf, Germany), applying ANOVA repeated measures (F Test) with a signi cant level of 0.05, a statistical power of 80% to an effect size (ES) of 0.3 [26]. This calculation generated a desired sample size of at least 6 participants. However, we recruited 8 subjects to allow for drop-out during the intervention period.

Int. J. Environ. Res. Public Health2021,18, 8386 3 of 12 Muscle or joint injuries, orthopedic problems, severe visual impairment, cardiovascu- lar diseases, or any other contraindication within three months before the commencement of the study were chosen as exclusion criteria. Participants' characteristics at baseline are reported in Table. Table 1. Subjects' anthropometric and cardiorespiratory characteristics. Data are means standard deviation.Age (years) Weight (kg) Height (cm) VO2max (mL kg 1 min 1 ) 36.00 11.51 71.99 9.65 176.53 6.36 50.13 5.12 VO2max: maximal oxygen uptake. Subjects were asked not to change their sport practice during the intervention period and not to exercise 48 h before the experimental sessions. They were also instructed to avoid the consumption of food in the 3 h prior to the test and to refrain from caffeine and alcohol consumption in the previous 24 h [27]. Before the experimental protocol, all subjects were fully informed about the study aims and procedure, and they gave their written informed consent to participate in the study. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Universit degli Studi di Genova (protocol code: 246 and date of approval: 7 July 2020). 2.2. Experimental Design A randomized crossover repeated measures design was carried out and performed at the same time of the day, one session/week. The experimental protocol consisted of the following four sessions: a cardiopulmonary exercise test (CPET) and three endurance running sessions, differentiated by the warm-up stretching content, as follows: SS, DS, or NS [28]. Before the beginning of the experimental protocol, in order to become accostumed to the treadmill running and maximize the reliability of the running economy measurements, a “treadmill familiarization session” was completed by each participant. During the rst experimental session, subjects performed the CPET to determine their maximal oxygen uptake (VO2max) (mL kg 1 min 1 ), used to quantify the intensity of the running-until-exhaustion session and, in a randomized order, three endurance running tests were completed (NS, SS, DS) between second to fourth session. Each endurance session included 15 min of warm-up followed

participant. During the rst experimental session, subjects performed the CPET to determine their maximal oxygen uptake (VO2max) (mL kg 1 min 1 ), used to quantify the intensity of the running-until-exhaustion session and, in a randomized order, three endurance running tests were completed (NS, SS, DS) between second to fourth session. Each endurance session included 15 min of warm-up followed by 5 min of rest in a standing position [23], then 5 min of a continuous submaximal running and a subsequent running-until-exhaustion test [20]. The randomization was performed in a draw form, on the assessment day (Figure). 2.2.1. Cardiopulmonary Exercise Test Subjects ran 5 min at 7 km/h of speed as a warm-up, then they performed a maximal incremental exercise, with an initial speed of 8 km/h increased by 1 km/h every minute. The gradient of the motorized treadmill (E-motion, Runner, MTC climb 2000, Modena, Italy) was set at 1% to simulate the air resistance that athletes usually experience on an outdoor track [29]. The CPET was performed using an ergospirometer (Sensormedics, Viasys, Irvine, CA, USA) and a mask (Hans Rudolph, INC., Shawnee, KS, USA) with a dead space of 30 mL. Before the measurement, the ergospirometer was calibrated following the recommendation of the manufacturer and the analysis of expired gas was sampled breath by breath. Heart rate (HR) was recorded at 5 s intervals with a Polar heart rate monitor (Polar H7, Electro, Kempele, Finland). Moreover, 2 min after the end of CPET, blood lactate concentration [La] + was measured [30].

Int. J. Environ. Res. Public Health2021,18, 8386 4 of 12Int. J. Environ. Res. Public Health 2021, 18, x FOR PEER REVIEW 4 of 13 Figure 1. Study design. (A): familiarization session; (B): cardiopulmonary exercise test (CPET); (C): no-stretching session (NS); (D): static stretching session (SS); (E): dynamic stretching session (DS). 2.2.1. Cardiopulmonary Exercise Test Subjects ran 5 min at 7 km/h of speed as a warm-up, then they performed a maximal incremental exercise, with an initial speed of 8 km/h increased by 1 km/h every minute. The gradient of the motorized treadmill (E-motion, Runner, MTC climb 2000, Modena, Italy) was set at 1% to simulate the air resistance that athletes usually experience on an outdoor track [29]. The CPET was performed using an ergospirometer (Sensormedics, Viasys, Irvine, CA, USA) and a mask (Hans Rudolph, INC., Shawnee, KS, USA) with a dead space of 30 mL. Before the measurement, the ergospirometer was calibrated following the recommendation of the manufacturer and the analysis of expired gas was sampled breath by breath. Heart rate (HR) was recorded at 5 s intervals with a Polar heart rate monitor (Polar H7, Electro, Kempele, Finland). Moreover, 2 min after the end of CPET, blood lactate concentration [La] + was measured [30]. Subject’s VO 2max was considered to be reached when at least three of the following criteria were fulfilled: i) a steady state of VO 2 despite increasing running velocity (change in VO 2 ≤ 150 mL·kg −1 ·min −1 at VO2max); ii) final respiratory exchange ratio (RER) exceeded 1.1; iii) visible exhaustion; iv) an HR at the end of exercise (HR max) within the 10 bpm of the predicted maximum [210– (0.65 × age)]; v) a lactate concentration at the end of exercise ([La] + ) higher than 8 mmol·L −1 [31]. Furthermore, we also administered the Borg’s CR-10 scale 2 min after the end of CPET. The mean (±SD) value of RPE was 9.25 ± 0.46. The minimal speed needed to elicit VO 2max was considered as vVO2max [32]. The vVO2max was considered as the speed corresponding to the last one-minute step completed during

) higher than 8 mmol·L −1 [31]. Furthermore, we also administered the Borg’s CR-10 scale 2 min after the end of CPET. The mean (±SD) value of RPE was 9.25 ± 0.46. The minimal speed needed to elicit VO 2max was considered as vVO2max [32]. The vVO2max was considered as the speed corresponding to the last one-minute step completed during the CPET. Figure 1. Study design. (A): familiarization session; (B): cardiopulmonary exercise test (CPET); (C): no-stretching session (NS); (D): static stretching session (SS); (E): dynamic stretching session (DS). Subject's VO2maxwas considered to be reached when at least three of the following cri- teria were ful lled: (i) a steady state of VO2despite increasing running velocity (change in VO2 150 mL kg 1 min 1 at VO2max); (ii) nal respiratory exchange ratio (RER) exceeded 1.1; (iii) visible exhaustion; (iv) an HR at the end of exercise (HRmax) within the 10 bpm of the predicted maximum [210– (0.65 age)]; (v) a lactate concentration at the end of exercise ([La] + ) higher than 8 mmol L 1 [31]. Furthermore, we also administered the Borg's CR-10 scale 2 min after the end of CPET. The mean ( SD) value of RPE was9.25 0.46 . The minimal speed needed to elicit VO2maxwas considered as vVO2max[32]. The vVO2max was considered as the speed corresponding to the last one-minute step completed during the CPET. 2.2.2. Endurance Running Sessions All endurance running sessions (SS, DS, NS) were performed on a motorized tread- mill, in a laboratory with controlled temperature and humidity (21–24 C and 44–56%, respectively) [33] and at the same time of the day (11a.m. 1 h) to avoid in uence of the circadian rhythms. Before starting, subjects were fully familiarized with all the procedures. The experimental protocol was generally well tolerated, and subjects completed all the endurance running sessions without complication, not reporting dizziness, light-headiness or nausea symptoms. During endurance sessions, subjects performed 15 min of warm-up including running plus stretching (SS or DS) or not (NS), followed by 5 min of rest. At the end of the rest period, they were asked to perform

experimental protocol was generally well tolerated, and subjects completed all the endurance running sessions without complication, not reporting dizziness, light-headiness or nausea symptoms. During endurance sessions, subjects performed 15 min of warm-up including running plus stretching (SS or DS) or not (NS), followed by 5 min of rest. At the end of the rest period, they were asked to perform 5 min of constant submaximal running at a speed corresponding to 70% VO2maxto evaluate running economy. The mean values of speed at 70% of VO2maxwas 10 km/h. At the end of the submaximal running, the subject continued to run. Then, the speed was increased and the vVO2maxwas reached in about 15 s. From this time point, the time to exhaustion (TTE) was measured with a manual stopwatch [20]. Mean values of the speed corresponding to VO2max(vVO2max) was 14.45 km/h.

Int. J. Environ. Res. Public Health2021,18, 8386 5 of 12 During each running-until-exhaustion test, subjects were blind to time and dis- tance achieved. 2.2.3. No-Stretching Session (NS) In the NS session, the warm-up consisted of 15 min running at an intensity corre- sponding to 60–70% VO2max. 2.2.4. Static Stretching Session (SS) In the SS session, the warm-up consisted of 10 min of running at 60–70% VO2max plus 5 min of SS. The SS exercises focused on the following 5 lower limb muscle groups: quadriceps, hamstrings, hip exors, hip adductors and gluteals [28]. All the static stretches were held at the “point of discomfort” (POD) for 30 s per leg. 2.2.5. Dynamic Stretching Session (DS) In the DS session, the warm-up consisted of 10 min of running at 60–70% VO2max plus 5 min of DS. The DS exercises focused on the same lower limb muscle groups and in the same execution order as the SS protocol. Subjects repeated each DS exercise 30 s per leg and the maximal ROM was achieved, by ensuring a secondary pulling motion with each repetition. Both stretch intensity (100% of the POD) and stretch volume (30 s per leg) were matched for the two stretching protocols. SS and DS exercises and instructions are shown in Figure.Int. J. Environ. Res. Public Health 2021, 18, x FOR PEER REVIEW 6 of 13 Figure 2. Description of static stretching (SS) and dynamic stretching (DS) exercises. Point of discomfort: POD. 2.3. Outcome Measures 2.3.1. Physiological and Metabolic Parameters Maximal oxygen uptake (VO 2max), respiratory exchange ratio (RER), heart rate (HR), and blood lactate concentration ([La] + ) were chosen as dependent variables to describe physiological and metabolic responses [34]. Physiological parameters were continuously monitored during the running-until-exhaustion test. The average VO 2 value, obtained during the last 30 s of the final running stage, was considered as VO 2max. RER was averaged over the last minute of each running velocity and HR max was identified as the highest value recorded during the test [27]. Moreover, according to Assadi and Lepers [30] [La] + was assessed 2 min after the end

The study examines the impact of stretching on running economy and effort perception in recreational runners.