Medicine and Science in Sports, Tunis El Menzah, Tunisia b Laboratory of Functional Neurophysiology and Pathology, Faculty of Sciences Tunis, El

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1 This article was downloaded by: [Auckland University of Technology] On: 20 February 2014, At: 09:41 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK European Journal of Sport Science Publication details, including instructions for authors and subscription information: Eight weeks of dynamic stretching during warm-ups improves jump power but not repeated or single sprint performance Lamia Turki-Belkhiria ab, Anis Chaouachi a, Olfa Turki a, Hamdi Chtourou a, Moktar Chtara a, Karim Chamari a, Mohamed Amri b & David G. Behm c a Tunisian Research Laboratory Sports Performance Optimisation, National Centre of Medicine and Science in Sports, Tunis El Menzah, Tunisia b Laboratory of Functional Neurophysiology and Pathology, Faculty of Sciences Tunis, El Manar, Tunisia c School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, NL, Canada Published online: 15 Oct To cite this article: Lamia Turki-Belkhiria, Anis Chaouachi, Olfa Turki, Hamdi Chtourou, Moktar Chtara, Karim Chamari, Mohamed Amri & David G. Behm (2014) Eight weeks of dynamic stretching during warm-ups improves jump power but not repeated or single sprint performance, European Journal of Sport Science, 14:1, 19-27, DOI: / To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at

2 European Journal of Sport Science, 2014 Vol. 14, No. 1, 1927, ORIGINAL ARTICLE Eight weeks of dynamic stretching during warm-ups improves jump power but not repeated or single sprint performance LAMIA TURKI-BELKHIRIA 1,2, ANIS CHAOUACHI 1, OLFA TURKI 1, HAMDI CHTOUROU 1, MOKTAR CHTARA 1, KARIM CHAMARI 1, MOHAMED AMRI 2,& DAVID G. BEHM 3 Downloaded by [Auckland University of Technology] at 09:41 20 February Tunisian Research Laboratory Sports Performance Optimisation, National Centre of Medicine and Science in Sports, Tunis El Menzah, Tunisia, 2 Laboratory of Functional Neurophysiology and Pathology, Faculty of Sciences Tunis, El Manar, Tunisia, 3 School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John s, NL, Canada Abstract There is abundant research involving the acute effects of stretching on subsequent performance; however, there is little information on dynamic stretch training programmes on range of motion (ROM), power and speed measures. It was the objective of this research to examine the training consequences of active dynamic stretching (ADS) and static dynamic stretching (SDS). A repeated measures design compared the effects of 8 weeks of warm-ups incorporating two dynamic stretch modalities: ADS and SDS on squat jump (SJ), countermovement jump (CMJ), 20-m sprint performances and repeated sprint ability (RSA) and hip ROM in 37 male soccer players. SJ height (SDS: 4.6%; ADS: 5.3%; p B0.05), CMJ height (SDS: 5.3%; ADS: 3.4%; p B0.05), CMJ force (SDS: 7.2%; ADS: 12.7%; p B0.001) and CMJ peak power (SDS: 3.9%; ADS: 3.3%; p B 0.05) increased significantly after SDS and ADS training compared to the control group (no significant change). Sprint performance and RSA were not affected by either of the dynamic stretch training regimens. The SDS and ADS training programmes elicited similar improvements in flexibility (SDS: 57.6%; ADS: 45.1%; p B 0.01) compared to the non-significant changes in the control group. The inclusion of ADS and SDS within the regular warm-up of an 8-week training programme can improve not only flexibility but also jump power measures as well. Keywords: Flexibility, running speed, countermovement jump, squat jumps, repeated spring ability Introduction There is consensus in the literature that dynamic stretching; controlled movement through the active ROM for each joint is preferable to static stretching during the warm-up to prepare for physical activity (Behm & Chaouachi, 2011). Findings from studies implementing an acute bout of dynamic stretching have demonstrated facilitation of power (Yamaguchi, Ishii, Yamanaka, & Yasuda, 2008), jump (Pearce, Dawson, Kidgell, Zois, & Carlson, 2009), sprint (Turki et al., 2012) and agility (Faigenbaum, Bellucci, Bernieri, Bakker, & Hoorens, 2005) performance, as well as an enhanced range of motion (ROM; Khorasani, Abu Osman, & Yusof, 2011). However, it is not clear if these transient improvements can be transferred into sustained enhancements with the incorporation of dynamic stretching into the warm-up before daily training. Despite the growing number of studies documenting the useful immediate effects of dynamic stretching, there is surprisingly limited research examining the chronic training effect of integrating dynamic stretching into the warm-up (Herman & Smith, 2008; Laroche, Lussier, & Roy, 2008; Woolstenhulme, Griffiths, Woolstenhulme, & Parcell, 2006). Woolstenhulme et al. (2006) reported that basketball players who performed 6 weeks of ballistic Correspondence: A. Chaouachi, Tunisian Research Laboratory Sport Performance Optimisation, National Center of Medicine and Science in Sports (CNMSS), Ave Med Ali Akid, 1004 El Menzah, Tunis BP263, Tunisia. anis.chaouachi@ .ati.tn Current address for O. Turki, M. Chtara and K. Chamari: Higher Institute of Sports and Physical Education, Manouba University, Tunis, Tunisia # 2012 European College of Sport Science

3 Downloaded by [Auckland University of Technology] at 09:41 20 February L. Turki-Belkhiria et al. stretching within a warm-up increased flexibility, but did not affect vertical jump height. In a second study (Herman & Smith, 2008), the incorporation of dynamic stretching into the daily pre-season training regimen of wrestlers produced significant longer term or sustained enhancements of power, strength, muscular endurance, anaerobic capacity and agility performance within a 4-week intervention. Finally, Laroche et al. (2008) suggested that 4 weeks of ballistic stretching had little effect on muscle strength, power, work or lengthtension relationship. These conflicting results and few studies evaluating the chronic effect of dynamic stretching on flexibility and muscular performance prompted the present study. To the best of the authors knowledge, there is no research investigating the training effects of dynamic stretching on flexibility and high-speed motor capacities. Since incorporating dynamic stretching into the warm-up is a widespread practice, it is essential to know its chronic or training effects. Previous warm-up protocols have used two types of dynamic stretches: static dynamic stretches (SDSs) and active dynamic stretches (ADSs). SDSs are performed in a stationary position (Yamaguchi & Ishii, 2005), while ADS are completed while moving (e.g. walking or jogging) (Turki et al., 2012). There is equivocation in the literature regarding the effects of dynamic stretching, with a bout of SDS demonstrating either facilitation (Fletcher & Anness, 2007; Yamaguchi et al., 2008) or no effect (Chaouachi et al., 2010; Fletcher & Jones, 2004) on subsequent athletic performance, whereas the same pattern of acute enhancements (Turki et al., 2012), or no effect (Dalrymple, Davis, Dwyer, & Moir, 2010) have also been reported after warm-ups involving ADS. From the limited amount of literature that have directly compared the effects of these two modes of dynamic stretching on performance, ADS seems to be superior to SDS in enhancing subsequent 20-m (Fletcher & Jones, 2004) and 50-m (Fletcher & Anness, 2007) sprint performances. However, these results are limited to the two aforementioned parameters and to the characteristics of subjects who participated in the studies. Pearce et al. (2009) and Curry, Chengkalath, Crouch, Romance, and Manns (2009) combined the two types of dynamic stretching protocols making it difficult to determine the actual contribution of the individual stretching protocols for enhancing subsequent isometric time to peak force knee extension (Curry et al., 2009), and vertical jump (Curry et al., 2009; Pearce et al., 2009) performances. Since SDS does not involve locomotion, it would be presumed that ADS with its greater volume of muscle activity should provide higher heart rates, core temperature and neuromuscular excitation resulting in increased neural conduction velocity, enzymatic activity and decreased tissue viscosity (Young & Behm, 2002). Hence, the purposes of the study were to examine the effects of 8 weeks of SDS and ADS incorporated into the warm-up on squat jump (SJ), countermovement jump (CMJ), 20-m sprint performances, repeated sprint ability (RSA) and flexibility in trained explosive athletes. It was hypothesised that both stretch training programmes would improve ROM. Secondly, based on the lack of strength, power or speed training in the present study, it was hypothesised that the dynamic stretch training programmes would have a null effect on SJ, CMJ, 20-m sprint and RSA measures. Methods Participants This randomised experimental trial with a repeated measures design study was conducted on 37 soccer players pursuing degrees in Exercise Science and Physical Education at the University of Sports of Tunisia. The soccer players were randomly assigned to the ADS (n 11; age years, height cm, body mass kg), the SDS (n 11; age years, height cm, body mass kg) and the control (n15; age , height cm, body mass kg) groups. All subjects were considered experienced soccer players (at least 6 years experience) who trained three times per week for 1.52 hours per session. Training sessions consisted mainly of technical and tactical skill development (80% of the training time) as well as aerobic and anaerobic training. Subjects were accustomed to using both ADS and SDS protocols as part of their warm-up preceding training sessions. Nevertheless, neither the volume nor intensity could be considered as representative of a dynamic flexibility training programme designated to improve flexibility. The mean baseline sit-and-reach scores in this study were less than the mean scores reported in high-level soccer players. Subjects were asked to refrain from any organised stretch training, except for the stretching protocol imposed by the study. There were no other restrictions placed on the subjects activities. The study was conducted during the spring semester (February to April). All the participants gave their informed consent before the investigation. The study was conducted according to the declaration of Helsinki, and the protocol was fully approved by the Ethics Committee of the National Centre of Medicine and Science of Sports of Tunis (CNMSS).

4 Dynamic stretch training improves jump power 21 Downloaded by [Auckland University of Technology] at 09:41 20 February 2014 Procedures Prior to the commencement of the study, all subjects participated in an orientation session to become familiar with the stretching, the specific warm-up exercises and tests. One week after habituation (during week 1), baseline data collection (vertical jump, 20-m sprint, RSA and ROM) measurements were taken on two separate days for each group. No stretches were allowed during the warm-ups before the data collection. The experimental period was 8 weeks in duration and consisted of the three randomly assigned groups completing SDS, ADS or a non-stretching control warm-up conditions (i.e. three times a week for eight consecutive weeks). The ADS and SDS stretching protocols were adapted from the stretching protocol previously used by Turki et al. (2012) and Yamaguchi and Ishii (2005), respectively. The primary investigator led the general and specific warm-up, and two other investigators led the dynamic stretching protocols separately. Post-testing began 48 hours following completion of the 8-week experimental period (week 10) to avoid acute responses. Pre- and posttest SJs, CMJ, 20-m sprint, RSA and ROM measurements were assessed using the same test protocol completed before training. The experimental procedure is summarised in Figure 1. Stretching The dynamic stretching protocol was chosen after an analysis of the warm-up practices performed by subjects prior to typical training sessions, and represents their self-selected, preferred warm-up Control (n=15) 8 Weeks of No Stretching Participants (n=27) SDS (n=11) ADS (n=11) Baseline: Pre -intervention Squat Jump, CMJ, 20m Sprint, RSA, Sit and reach test 8 Weeks of SDS training 8 Weeks of ADS training Post -intervention Squat Jump, CMJ, 20m Sprint, RSA, Sit and reach test Figure 1. Experimental design. SDS, static dynamic stretching; ADS, active dynamic stretching; RSA, repeated sprint ability; CMJ, counter movement jump. modality (Turki et al., 2012). The dynamic stretch protocols consisted of five different active ADS (completed while moving such as walking or jogging (Turki et al., 2012) or SDS (performed in a stationary position (Yamaguchi & Ishii, 2005)) designed to stretch the principal locomotive lower limbs muscle groups (plantar flexors, hip flexors, hamstrings, gluteals and adductors). The ADS and SDS interventions are described in detail in Tables I and II, respectively. The SDS intervention consisted of a series of lower-body controlled movement at a self-selected pace through the active ROM for one or more joints conducted in a stationary position (Yamaguchi & Ishii, 2005). The SDS drills were performed slowly, smoothly and continuously so that no ballistic or abrupt movements occurred at any time. For both the ADS and SDS exercises, the movements were carried out 14 times for each muscle and repeated twice. A 10-second recovery was allowed between exercise sets to minimise any chances of fatigue. The ADS condition consisted of the same movements as were required in the SDS intervention, but the ADS exercises were conducted while walking. All the exercises were performed while walking over a distance of 20 m. Specific warm-up The last section of the warm-up consisted of 57 min soccer specific explosive warm-up composed by incremental intermittent sprint, hops and agility runs (Chaouachi et al., 2010). This specific warm-up included three-quarter pace running: 10-m forward and 5-m sidestepping, repeated twice; 30-m forward, repeated three times; a set of eight single hop jumps; a set of eight alternate leg bounds (side hop) and 45-m forward with 5908 changes of direction, repeated twice. Intensity was then increased: threequarter pace for 10 m and full pace for 20 m, repeated twice, with a walking back recovery (20 m) and full pace for 30 m. Performance measures Both testing sessions (pre- and post-test) took place at the same facility and time of day. Before testing, subjects executed 10-min warm-up progression comprising self-selected exercises in preparation for jumping or sprinting. This warm-up excluded stretching routines so that the possibility of previously reported stretch-induced impairments (Behm & Chaouachi, 2011) would not contaminate the results. The 20-m distance was chosen because it represents the mean sprint distance in field-based team sports (Sim, Dawson, Guelfi, Wallman, & Young, 2009; Turki et al., 2012). The CMJ and SJ were chosen as measures of functional muscle

5 22 L. Turki-Belkhiria et al. Table I. Active dynamic stretching exercises Table II. Static dynamic stretching exercises Muscle groups Active dynamic stretching exercises Muscle groups Static dynamic stretching exercises Gluteals Walking high bringing knee to chest. While walking, lift knee towards chest raise body on the toes of the opposite extended leg Gluteals The subject contracted the hip flexors with knee flexed and flexed the hip joint so that the thigh swung up to the chest Hamstrings Walking while swinging actively the leg to be stretched forward into hip flexion until a stretch is felt in the posterior thigh whilst keeping the knee extended and the ankle in plantar flexion Hamstrings The subject contracted the hip flexors with knee extended and flexed the hip joint so that the leg swung forwards to the anterior aspect of his body Downloaded by [Auckland University of Technology] at 09:41 20 February 2014 Adductors Quadriceps Plantar flexors Hurdler s knee raises forward movement. Whilst travelling forwards, participant raises trailing leg and places hip in flexion (908) in an abducted and externally rotated position, with the knee flexed at 908. In this position the limb is displaced forwards as though participants were stepping over an object just below waist height and returned to normal walking stride position Heel ups. Rapidly kick heels towards buttocks while moving forward Tip-toe walking. Travelling forward whilst completing alternating plantar flexion (tip-toe) with every step forwards. Aim is to raise the body as high as possible through tip-toeing performance. The 620 m was chosen primarily as a measure of RSA. Vertical jump Vertical jump performances were assessed using a portable force platform (Quattro-Jump; Kisler, Winterthur, Switzerland) according to the procedure described by Bosco et al. (1995). Before testing, players performed self-administered sub-maximal CMJ and SJ (two to three repetitions) as a practice and specific additional warm-up. Each jump type was performed three times with 2-min seated rest between each repetition. CMJ and SJ performances considered were jump height, peak power and force. The jump with the greatest height achieved for each type of jump was used for analysis. Adductors Quadriceps Plantar flexors Side-to-side leg swings: The subject leaned against a pole, dynamically adducting and abducting the leg as high as possible The subject contracted the hamstrings and flexed the knee joint so that the heels hit the buttocks Initially the subject raised one foot from the floor and fully extended the knee. Then, the subject contracted the dorsiflexors so that foot/toes were pointing upward Single sprint and repeated sprint ability test The RSA test consisted of 620 m maximal straight-line sprints with 20-s active recovery. During the active recovery, participants slowly jogged back (20 m) to the starting line and waited for the next sprint. Sprint time for 20 m was measured by an infra-red timing system (Brower Timing System, Salt Lake City, UT, USA) located at the starting and finishing line, and the recovery time was controlled by hand-held stopwatch. The participants stood 0.5 m behind the sensor before they commenced each sprint, starting from a standing position. Both mean and total sprint time (sum of six sprints) were determined. Other performance measures included the first and best sprint time of each set. Participants were given strong verbal encouragement throughout all trials to ensure maximal effort. Although several distances have been proposed to assess sprints in team sports, no gold standard protocol is currently available to test players in field conditions (Turki et al., 2012). The 20-m sprint

6 Dynamic stretch training improves jump power 23 Downloaded by [Auckland University of Technology] at 09:41 20 February 2014 performance is considered to be a relevant performance parameter important to success in all sports involving sprints (Devore & Hagerman, 2006; Fletcher, 2010; Turki et al., 2012). The 20-m distance was chosen for three reasons: previous sprint effort studies have employed this or a similar protocol (Fletcher, 2010; Turki et al., 2012), it represents the mean sprint distance in field-based team sports (Sim et al., 2009; Turki et al., 2012) and because these distances were part of the subjects regular fitness testing battery. Flexibility measurement This study focused on flexibility of the hip flexors as constrained by the compliance of the hamstrings and lower back muscle groups. The sit-and-reach test has been shown to be a valid and reliable (Lemmink, Kemper, De Greef, Rispens, & Stevens, 2003) measure of hip flexor flexibility. We used a sit-andreach test device (Acuflex I, Novel Products Inc., USA). Participants sat on a mat with their shoes off, each subject completed three attempts of the sit-andreach test, pushing the slide as far forward on the sitand-reach box as possible while keeping their legs straight. Each subject s best score of the three attempts was used in the statistical analyses. Statistical analyses Means9standard deviations (SD) were used to describe variables. Before using parametric tests, the condition of normal variation was verified using the ShapiroWilk W-test. The data were then analysed using multivariate analysis of variance (32) with repeated measures on the second factor. The factors included three separate groups of training (SDS, ADS and control) and repeated measures of time (pre- and post-training). Because of the slight differences in the initial groups, analysis of covariance with the pre-test values as the covariate was used to determine significant differences between the post-test adjusted means in the groups. Paired t-tests were used to determine the significance of differences in the measured variables after training. Effect sizes (ES: mean of one condition or time mean of other condition or time/average SD) were also calculated and reported (Cohen, 1988) (smallb0.4, moderate , large 0.70). Reliability of the measures (dependent variables) was assessed twice over a number of days with a Cronbach s model interclass-correlationcoefficient (ICC), total error of measurements (TEM) and coefficient of variation (CV) according to the method of Hopkins (Hopkins, 2000). Statistical analyses were performed using SPSS software statistical package (SPSS Inc., Chicago, IL, USA, 16.0), and statistical significance was set at p B0.05. Results The ICC, TEM and CV values for all measures demonstrated high reliability : SJ height (ICC 0.95, TEM 3.8%, CV 1.2%), CMJ height (ICC 0.98, TEM 1.95%, CV 0.4%), sprint (ICC 0.88, TEM B1.8, CV B1%), RSA total time (ICC 0.98, TEM B 1%, CV B1%), flexibility (ICC 0.99, TEM 5.6%, CV 0.8%). Furthermore a paired t-test showed no significant differences between the scores recorded during the test and retest for all the variables measured. Squat jumps The covariance analysis for the SJ height indicated significant differences between the ADS, SDS and control groups (p B0.05). Post hoc analysis indicated that the ADS and SDS groups are similar, and showed significant improvements post-intervention (5.3%; ES 0.83, pb0.05, and 4.6%; ES 1.00, p B0.05, respectively). The SDS group performed significantly (p B0.01) better than the control group (Table III). There were no other significant differences between the three groups for force, and peak power. The control group showed a 2.7% significant (pb0.05; ES 0.23) increase in SJ power from preto post-testing. Countermovement jump A significant group effect was observed for CMJ height (F 4.557; p B0.018), force (F 11.32; p B0.001) and peak power (F 4.43; p B0.02). Significant enhancements were observed in CMJ height in the SDS group (5.3%; ES 1.41) and ADS groups (3.4%; ES 0.37), in comparison to the baseline measurements. The SDS group performed significantly better than the control group. CMJ force increased significantly in both ADS (12.7%; ES 3.6) and SDS (7.2%; ES 2.62) groups. Both ADS and SDS groups performed significantly better than the control group. CMJ peak power increased significantly in both ADS (3.3%; ES 0.85) and SDS (3.9%; ES 1.1) group. The SDS group performed significantly better than the control group (Table III). There were no significant pre- to post-test differences in the control group. 20-m sprint (with 10-m split) There were no significant changes from pre- to posttest in the ADS and SDS groups for the 0- to 10-m and 0- to 20-m sprint times (Table III). The ADS group was significantly better than the control group. The control group had significant deficits pre- to

7 24 L. Turki-Belkhiria et al. Table III. Mean9SD of experimental groups (ADS and SDS) and control group (NS) before and after 8 weeks of dynamic stretching intervention ADS SDS Control Variable (unit) Pre Post Pre Post Pre Post Downloaded by [Auckland University of Technology] at 09:41 20 February 2014 SJ Height (cm) (5.03) (5.22)* (5.99) (4.67)* (5.18) (4.04) Force (kgf/kg) 2.3 (0.2) 2.36 (0.21)* 2.39 (0.11) 2.36 (0.16) 2.38 (0.29) 2.38 (0.37) Power (w/kg) (3.74) 49.3 (4.29)** (3.28) (3.6)** (5.72) (5.63)* CMJ Height (cm) (5.24) (4.41)* (3.63) (4.08)* (4.63) 45.3 (4.65) Force (kgf/kg) 2.27 (0.18) 2.56 (0.18)** 2.37 (0.14) 2.54 (0.15)** 2.33 (0.19) 2.34 (0.22) Power (w/kg) (4.16) (4.09)* (4.67) (3.36)* (4.94) (4.46) Sprint 10 m (s) 1.82 (0.3) 1.84 (0.5) 1.83 (0.7) 1.88 (0.1) 1.85 (0.9) 1.95 (0.12)** 20 m (s) 3.12 (0.7) 3.13 (0.8) 3.12 (0.11) 3.18 (0.12) 3.16 (0.12) 3.24 (0.14)* RSA Best time (s) 3.07 (0.13) 3.08 (0.09) 3.07 (0.13) 3.12 (0.12) 3.17 (0.14) 3.19 (0.14) Total time (s) (0.80) (0.73) (0.88) (0.85) (0.86) (0.74) Decrement (%) 3.65 (1.66) 4.73 (2.03) 2.62 (1.18) 4.60 (2.54) 3.18 (0.94) 3.92 (1.53) Flexibility (cm) (5.59) (4.94)** 8.69 (7.56) 13.7 (6.51)** 7.67 (7.52) 8.31 (6.85) ADS, active dynamic stretching group; SDS, static dynamic stretching group; SJ, squat jump; CMJ, counter movement jump; RSA, repeated sprint ability; kgf, kilogram-force. *Significant differences between pre- and post-conditions for pb0.05; **significant differences between pre- and post-conditions for pb0.01. post-testing in 10-m (pb0.01; ES 0.11) and 20-m (pb0.05; ES 0.66) sprints of 5.4% and 2.5%, respectively (Table III). RSA test ANCOVA revealed no significant group or time effects for all RSA dependent variables: best time, total time and percentage decrement. Flexibility The univariate analysis of variance showed significant (p B0.01) improvements in flexibility in the ADS (45.1%; ES 2.41) and SDS (57.6%; ES 1.59) groups. After the 8-week training period, no changes were observed for the control group (Table III). There were no significant correlations between baseline flexibility (sit-and-reach scores) and changes in flexibility or jumping performance for the two groups. Discussion The primary findings of the study were that the 8-week SDS and ADS interventions elicited similar improvements in sit-and-reach measures. Second, the majority of jumping variables increased after the 8-week SDS and ADS warm-up interventions but were absent in the control group. Third, neither the 20-m sprint performance nor RSA were affected by 8 week of performing ADS and SDS during the warm-up. In agreement with the first hypothesis, both SDS and ADS interventions were equally effective at increasing flexibility as assessed by the sit-and-reach test. This is the first study to investigate the chronic effect of two dynamic stretching modalities (ADS and SDS) on flexibility. There is considerable evidence that ballistic stretching is as effective as static stretching for inducing both acute (Murphy, Di Santo, Alkanani, & Behm, 2010) and chronic gains in flexibility (LaRoche & Connolly, 2006; Woolstenhulme et al., 2006). Weber and Kraus (1949) found that ballistic stretching was more effective than static stretching at increasing flexibility. These results combined with our current findings support the notion that prior ADS and SDS could be used as substitute ROM exercises for static stretching training in order to enhance flexibility. The lack of a correlation between the subjects baseline flexibility and changes in flexibility or performance indicates that these improvements were independent of the subjects initial flexibility (i.e. trained state). Our flexibility results are in agreement with those of numerous other studies reporting increased flexibility after acute (Curry et al., 2009) and chronic (LaRoche & Connolly, 2006; Woolstenhulme et al., 2006) dynamic stretching interventions. The exact mechanisms responsible for chronic or plastic gains in flexibility are controversial; the increases have been primarily attributed to decreased musculotendinous unit (MTU) stiffness (Wilson, Elliott, & Wood, 1992). Kubo, Kanehisa, and Fukunaga (2002) showed that a 3-week stretch training programme for the plantar flexors decreased Achilles tendon hysteresis but had no effect on stiffness indicating a change in tendon viscosity but not elasticity. However, a number of investigations (LaRoche & Connolly, 2006) established that increased flexibility is linked to an enhanced stretch tolerance rather than changes in muscle elasticity,

8 Downloaded by [Auckland University of Technology] at 09:41 20 February 2014 which indicates that there may be minimum longterm adaptations in skeletal muscle elastic properties after a moderate duration (38 week) stretching programme. Indeed, chronic stretching has been reported to lead to apparent but not real changes in muscle extensibility (Halbertsma, Van Bolhuis, & Göeken, 1996; Magnusson, Simonsen, Aagaard, Sørensen, & Kjaer, 1996). Since stretch tolerance and muscle extensibility were not measured directly in the present study, the mechanisms underlying the ROM gains cannot be established. Contrary to the second null hypothesis, the present study revealed that the majority of jumping variables increased significantly after the 8-week SDS and ADS warm-up interventions. These results extend previous reports of acute studies that support the inclusion of warm-ups with a dynamic component, such as SDS (Fletcher & Monte-Colombo, 2010; Woolstenhulme et al., 2006) and ADS (Faigenbaum et al., 2006) in order to enhance vertical jump. These gains have occurred even when ADS routines were combined with SDS exercises (Curry et al., 2009; Pearce et al., 2009). Fletcher and Jones (2004) and Fletcher and Anness (2007) performed a direct comparison between ADS and SDS and reported that ADS were superior for enhancing subsequent 20-m (Fletcher & Jones, 2004) and 50-m (Fletcher & Anness, 2007) sprint performances. However, these conclusions are constrained to acute enhancements in performance outcomes that were evident immediately or shortly after the dynamic warm-up was performed. The present study showed that longer-term enhancements could result when ADS and SDS are incorporated consistently into the warm-ups. A limited number of investigations have investigated the chronic effect of dynamic stretching on vertical jump outcomes. Our results contradict those of Woolstenhulme et al. (2006) who found no effect of 6 weeks of ballistic stretching on CMJ height. The improvement in jumping variables with the present study may be attributed to the more prolonged training duration (8 weeks). Potential mechanisms underlying the vertical jump gains with ADS and SDS are speculative, as direct measurements of these physiological mechanisms were not performed. Potential acute physiological benefits may be related to increases in heart rate and core temperature. Dynamic stretching may enhance skeletal muscle perfusion, enhance MTU stiffness and increase co-ordination of dynamic movement (see review Behm & Chaouachi, 2011). Mann and Jones (1999) suggested that the key attributes of dynamic stretching include enhanced motor unit excitability and improved kinaesthetic sense, leading to improved proprioception and pre-activation. From their training study results, Wilson et al. Dynamic stretch training improves jump power 25 (1992) stated that stretching might be an effective way to increase the re-used elastic energy during exercise involving a stretch-shortening cycle. In accordance with the second hypothesis, the incorporation of ADS and SDS to the warm-up routine for 8 weeks did not negatively affect sprint performance. In conjunction with our results, Nelson and Kokkonen (2001) stated that flexibility training does not improve running economy, indicating that an increased flexibility associated with chronic stretching has little effect on performance. Godges, MacRae, and Engelke (1993) reported that six sessions of stretching performed over a 3-week period were sufficient to improve hip extension ROM and were not associated with corresponding improvements in walking or running-gait economy. Our findings contradict those of previous acute investigations that reported significant increases in sprint performances after warm-up protocols integrating dynamic stretching in highly trained male and female within different sports (Fletcher & Anness, 2007; Turki et al., 2012). These findings show that the stimulus imposed upon the muscle with an acute stretch may be different from the longterm effects of chronic stretching with respect to motor performance. Therefore, it is possible that the chronic use of dynamic stretching does not produce identical acute neuromuscular and mechanical responses but it seems that the long-term effect of either SDS or ADS within the warm-up does not provide detrimental effects on sprinting. Again, in accordance with the second hypothesis, neither SDS nor ADS affected the RSA. These results agree with those of Wong et al. (2011) who found that incorporating static stretching in the daily warm-up routine for three consecutive days had no effect on overall RSA measures. In contrast to these results, Beckett, Schneiker, Wallman, Dawson, and Guelfi (2009) reported a tendency for RSA sprint times to be slower after acute static stretching intervention but this was not supported by statistical significance. It can be speculated that the lack of increase in sprint and RSA performance may be related to the concept of action specificity (Behm & Sale, 1993). Sprints and RSA necessitate rapid stretch-shortening cycle contractions with very brief duration ground contact times. The dynamic stretches were performed slowly, smoothly and continuously without abrupt vertical or horizontal changes of direction and hence would not have placed any such positive training stresses on the subjects. It was noted that the control group had a 2.7% significant (p B0.05; ES 0.23) increase in SJ power, significant deficits in 10 m (5.4%; p B0.01; ES 0.11) and 20 m (2.5%; pb0.05; ES 0.66) sprints and no change in the other measures.

9 Downloaded by [Auckland University of Technology] at 09:41 20 February L. Turki-Belkhiria et al. While statistically significant, the increase in SJ and decrease in 10 m sprint times were of a trivial magnitude. Sporadic changes with control groups are not uncommon in the literature and may be attributed to learning effects (possibly with the SJ) and detraining (possibly with the sprints). Nevertheless the significant findings reported in the present study were in relation to changes found in the control group and should represent changes due to the training programme. Conclusion The present study demonstrates the positive effects of a training programme incorporating ADS and SDS into a warm-up. Not only does ADS and SDS substantially improve flexibility, but also there are improvements in CMJ force, peak power and SJ height. Athletes should incorporate a combination of ADS and SDS into their daily warm-ups. 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