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Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance
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Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance Effets aigus d’étirements de courte durée isolés ou combinés avec des exercices dynamiques sur la performance en force, détente verticale et sprint J. Fortier , G. Lattier , N. Babault ∗ Centre d’expertise de la performance, UFR STAPS, université de Bourgogne, BP 27877, 21078 Dijon cedex, France Received 31 August 2012; accepted 19 November 2012
KEYWORDS Plyometrics; Potentiation; Warm-up; Anaerobic; Power
MOTS CLÉS Pliométrie ;
∗
Summary Objective. — This study aimed to investigate the acute effects of a short-duration isolated static stretching or combined with dynamic plyometric exercises on the performance of some anaerobic parameters (strength, jumping and sprinting). Methods. — During three distinct sessions and after a standardized warm-up, 15 participants randomly performed static stretching exercises alone, static stretching combined with plyometric exercises and no stretch. Total stretch duration was 20 seconds long per muscle group (quadriceps, hamstrings and calf muscles). Tests included maximal quadriceps muscle strength, countermovement jumps and 15 m sprints. Results. — Whatever the condition, maximal strength and sprints were unaltered whereas the vertical jump height significantly decreased (P < 0.05). We conclude that isolated static stretching or combined with plyometric exercises, even with short-duration, were not efficient for strength, jump ability and sprint improvements and should be excluded from warm-up sessions. © 2013 Elsevier Masson SAS. All rights reserved. Résumé Objectifs. — Cette étude explorait les effets aigus d’étirements statiques, isolés ou combinés avec des exercices pliométriques, sur la performance en force, détente verticale et sprint.
Corresponding author. E-mail address: [email protected] (N. Babault).
0765-1597/$ – see front matter © 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.scispo.2012.11.003
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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Potentialisation ; Échauffement ; Anaérobie ; Puissance
Sujets et méthode. — Lors de trois sessions et après un échauffement standardisé, 15 participants ont réalisé de manière aléatoire des exercices d’étirements statiques seuls, étirements statiques combinés avec des exercices pliométriques et pas d’étirements. La durée totale des étirements était de 20 secondes par groupe musculaire (quadriceps, ischios-jambiers et triceps sural). Les tests ont permis d’évaluer la force maximale du quadriceps, la hauteur des sauts avec contre mouvement et des sprints de 15 m. Résultats. — Quelle que soit la condition, la force maximale et les sprints n’ont pas été modifiés tandis que la hauteur maximale de saut a diminué significativement (p < 0,05). Nous avons conclu que des étirements statiques, isolés ou combinés avec des exercices pliométriques, même avec de courtes durées, n’étaient pas efficaces pour améliorer la force, la détente verticale et la vitesse de sprints et doivent par conséquent être exclus des sessions d’échauffement. © 2013 Elsevier Masson SAS. Tous droits réservés.
1. Introduction Stretching exercises could be used before, during and after training for injury prevention, performance improvement and recovery optimization. The usefulness of stretching for improving performance during warm-up remains debated. Numerous studies demonstrated the detrimental acute effects of stretching on the subsequent muscular performance such as maximal voluntary strength and vertical jump ability [1,2]. These performance reductions may originate from neural [3] and mechanical factors [4] that may last until 1 hour post-stretching [5]. Various stretch parameters (e.g., stretch modality, stretch duration) may influence the deleterious stretchinginduced acute effects. Concerning stretching modality, while no statistical difference was observed between static and contract-relax stretches [6], other studies recommended using dynamic rather than static stretching during warm-up (e.g., [7]). Moreover, a dose-response relationship has been suggested [1,2]. Indeed, Kay and Blazevich [2] concluded that stretching durations, commonly performed during preexercise routines (< 30 s), resulted in no performance decreases. Quite similarly, strong evidences exist for performance impairments with total stretch duration longer than 90 seconds whereas more variability is obtained with shorter stretch durations [1]. For instance, Winchester et al. [8] demonstrated that a single 30-s stretch was sufficient enough for strength reductions. During warm-up and whatever the stretching modality or duration, athletes usually combined stretching with dynamic exercises such as plyometrics or maximal voluntary contractions. The aim is to increase muscle temperature but also to induce a post-activation potentiation effect [9]. Some studies previously demonstrated that performing these contractions prior [10] or following muscle stretching [11] could partly reduce the stretch-induced performance impairments. For example, Gelen [11] concluded that static stretching combined with plyometric exercises was efficient to reduce the negative stretch effects on soccer players’ anaerobic performance. However, contrary to dynamic exercises alone, performance was not improved. Generally, these studies applied moderate to long stretch durations, obviously accompanied with performance impairments [1,2], whereas Knudson and Noffal [12] concluded that strength declines appeared with stretch duration longer than 20 seconds (range: 20 to 40 s). Accordingly, it can be questioned whether very short-duration static stretching combined with dynamic exercises could remove the
potential stretch-induced performance reductions and even increase performance. Therefore, the aim of the present study was to investigate the acute effects of an isolated short-duration static stretching or combined with plyometric exercises on muscle strength, vertical jump and sprint performance.
2. Methods 2.1. Experimental approach to the problem The experiment was based on three separate time-matched sessions testing various conditions randomly presented:
• static stretching alone; • static stretching followed by plyometric exercises and; • control condition (no stretch).
These three conditions were applied after a standardized warm-up. Tests performed after the standardized warmup (pre-tests) and immediately after the three different conditions (post-tests), included measurements of the knee extensors maximal isometric strength, vertical jump height and maximal 15-m sprints.
2.2. Participants Fifteen healthy participants (nine men and six women) volunteered for the experiment. Their mean ± standard deviation (SD) age, body mass and height were 22.8 ± 2.0 years, 80.4 ± 10.8 kg, 181 ± 6 cm and 21.3 ± 0.5 years, 60.8 ± 5.0 kg, 162 ± 5 cm for men and women, respectively. All were recreationally active with ∼7 hours training per week and were familiar with stretching as well as explosive type activities such as jumps and sprints. They agreed to participate in the study and signed an informed consent form. The study was conducted according to the declaration of Helsinki, approved by the local committee on human research and followed ethical standards [13]. Participants were asked to refrain from strenuous activity at least 24 hours preceding all testing sessions.
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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Warm-up and static stretching
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Figure 1 Exercises used for stretching on quadriceps (A), hamstring (B) and calf muscles (C). Dynamic exercises following stretches in the Static + Dyn conditions: rapid high knees (D), rapid butt-kicks (E) and rapid ankle flips (F).
2.3. Procedures Each participant performed three testing sessions (randomly presented) in order to study the effects of static stretching alone or combined with dynamic plyometric exercises after a standardized warm-up on strength, vertical jump and sprints. At least 3 days separated each session. A 5 minutes 30 seconds standardized warm-up was performed at the onset of each session. It consisted in ten analytical concentric and eccentric submaximal contractions of lower-limb muscles (quadriceps, hamstrings, gluteus, calf) and various dynamic runs repeated twice over 15 m (rest = walk back to starting position) typically used to prepare athletes for sport participation (high knees, butt kicks, ankle flips, sideway runs, accelerations). After warm-up, participants randomly performed one of the three conditions (static stretching, static stretching combined with dynamic exercises or control) each lasting 4 minutes 30 seconds. Tests were conducted immediately after warm-up (pretests) and immediately after the three different conditions (post-tests). They consisted in measurements of the knee extensors maximal isometric strength, vertical jump height during countermovement jumps (CMJ) and maximal sprints over 15 m.
2.3.1. Static stretching (static) In the present experiment, short stretch duration was tested. Accordingly, 20 seconds static stretches were performed only once on the right and left quadriceps, hamstrings and calf muscles. Muscle groups were randomly chosen but the right side was always stretched first. Participants held each stretch during 20 seconds at the point of discomfort, repeated to the opposite side and then relaxed in a standing static position for 50 seconds before another muscle group. Unassisted exercises were used (Fig. 1). For quadriceps stretch, participants stood and touched a wall for balance. The top ankle or forefoot was grasped from behind and then pulled toward the buttocks. The hip was then straightened by moving the knee backward and held in this position. For hamstrings stretch, participants stood on a flexed leg. The other leg was extended with the heel on the floor. Participants bent at the hip and lower their extended upper torso from the hips onto the extended leg. For calf stretch, participants stood on a raised platform on the balls of one foot, then dropping the heel down toward the floor. Static stretching combined with plyometric exercises (Static + Plyo). During this condition, participants conducted the same stretching exercises as the Static condition (both sides, in a random order and maintained at the point of
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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discomfort). Total stretch duration was similar than the Static condition for each muscle group. However, in order to conduct dynamic plyometric exercises within stretch, stretches were shorter (5 s) and repeated four times. The right, then left sides were alternated and immediately followed by dynamic plyometric exercises performed over 15 m. Dynamic exercises solicited the same muscle group than the preceding stretch (Fig. 1). Rapid high knees, rapid butt kicks and rapid ankle flips were used for quadriceps, hamstrings and calf muscles, respectively. Between each muscle group, participants relaxed 20 seconds in a standing static position. 2.3.2. No stretch (control) During the control condition, participants stayed relaxed (seated and standing static position) during the 4 minutes 30 seconds period after warm-up. 2.3.3. Tests Tests measuring muscle strength, vertical jump and sprint speed were conducted immediately after warm-up (pre-tests) and immediately after the three conditions (posttests). Tests were randomly presented and completed twice. An average value was calculated and retained for statistical analyses. The quadriceps maximal voluntary strength was bilaterally determined using a Myostat strength gauge (Allegro, Sallanches, France). Participants were seated on a leg extension machine (Multiform, La Roque d’Anthéron, France) with a 90◦ knee flexion angle and a 100◦ hip angle. Maximal isometric contractions lasted 4 seconds. During each contraction, the maximal voluntary strength was determined and expressed in Newton (N). The vertical jump height was measured during CMJ using an Optojump system (Optojump, Microgate, Bolzano, Italy) measuring jumps’ fly time. CMJ were performed starting from a standing position, then squatting down to a 90◦ knee angle (± 5◦ ), and then extending the knees in one continuous movement. During CMJ, arms were kept on the hips to minimize their contribution. Maximal running speed was measured with infrared photoelectric cells positioned at 1 m from the floor and 15 m from the start line and controlled by TAC software (Test Atletici Computerizzati, TEL.SI s.r.l., Vignola, Italy). The rear foot was positioned on a contact mat. After a visual signal, participants started from a standing position and ran the 15-m distance as fast as possible. Sprint time started after the rear foot left the mat and did not include reaction time. During all tests, participants were encouraged to express the maximal performance they can. Care was taken to have a minimal rest period between tests and trials.
2.4. Statistical analysis Mean values ± SD were calculated for all dependent variables. Stretching effects were analyzed by using a 2-way analysis of variance (ANOVA) with repeated measures. Time (pre- vs. post-tests) and experimental conditions (Control vs. Static vs. Static + Plyo) were used as repeated measures. Because no gender effect has previously been registered for acute effects of stretching [14], sex differences were not tested during statistics. Subsequent Tukey’s Honestly Significant Difference (HSD) post hoc tests were performed if significant main effects or interactions
Table 1 Maximal strength, vertical jump height and maximal speed measured during pre- and post-tests in the Control, Static and Static + Plyo conditions. Control Strength (N) Pre Post
Static
Static + Plyo
968 ± 345 974 ± 372
947 ± 356 954 ± 342
915 ± 353 935 ± 363
CMJ (cm) Pre Posta
35.1 ± 7.4 33.3 ± 6.2
35.1 ± 7.5 33.6 ± 7.3
34.6 ± 6.5 33.6 ± 6.1
Speed (m.s−1 ) Pre Post
5.57 ± 0.34 5.58 ± 0.38
5.64 ± 0.44 5.74 ± 0.57
5.64 ± 0.44 5.73 ± 0.70
Mean values ± SD; values are averages of men and women; CMJ: countermovement jump. a Significant time main effect (P < 0.0001).
were obtained. Statistical power and effect size (partial eta-squared) associated with the two-way ANOVA were calculated for each variable by our statistics software and shown in results when significant effects were found. The intersession reproducibility of each variable was quantified with intraclass correlation coefficients (ICC) based on the repeated measures ANOVA. The intersession variability of the measurements was assessed by calculating coefficients of variations (CV = SD/mean × 100). ICC and CV were calculated using the three pre-tests values. Statistical significance was accepted at an alpha level of 0.05. Statistics were all performed using Statistica software (version 8.0, Statsoft, Tulsa, USA).
3. Results The two-way ANOVA did not reveal any significant experimental condition effect and interaction effect for CMJ (ICC = 0.992, CV = 2.5%), maximal strength (ICC = 0.992, CV = 6.4%) and speed (ICC = 0.915, CV = 2.4%). A time effect was only obtained for vertical jump height (P < 0.001, power = 0.999, effect size = 0.699) (Table 1). Whatever the condition, CMJ height was significantly lower post-tests as compared to pre-tests (mean decrease: −4.0 ± 3.7%). No time effect was obtained for the maximal isometric strength and maximal running speed.
4. Discussion After a standardized warm-up, the present study demonstrated that short-duration isolated stretching or stretching combined with plyometric exercises have the same effects that a rest period and are ineffective to improve the strength, jump and sprint performance. Also, performing 20 seconds stretches during warm-up did not alter the maximal strength or sprint speed but had detrimental effects on explosive strength as attested by the vertical jump height. Static stretching is not systematically associated with strength production capacity reduction as previously obtained. Indeed, while some authors demonstrated impairments of muscle strength [15], vertical
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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Warm-up and static stretching jump height [16,17] and running velocity [18] immediately after various stretching modalities [6,19], others have not demonstrated stretch-induced deleterious effects [20—22]. These differences could be attributed to the outcome measures [14], to stretch parameters such as duration [23] or modality [24] but also to the inclusion of voluntary contractions [11].
4.1. Outcome measure The outcome measure seemed to be a possible cause for the conflicting results often obtained in the literature. Indeed, in our study, no reduction was registered on muscle strength and sprinting speed while the vertical jump height was impaired. A similar result has previously been obtained following warm-ups with or without static stretching [14]. These opposite effects could be explained by the mechanisms responsible for post-stretching performance reductions and more particularly to mechanical factors. In fact, neural factors, more transient, might play a minor or insignificant role [1]. Indeed, while neural factors may have a large influence following long-duration stretching [4,6], short-duration stretching revealed more equivocal results with some studies obtaining neither electromyographic nor voluntary activation alterations [25,26]. Such finding could partly explain the lack of muscle strength alteration registered here. Mechanical factors originate from a stiffness reduction of the musculo-tendinous unit (MTU, [4]) or a shift of the force/length or torque/angle relationship [19,27,28]. Stiffness alterations negatively impact force transmission and may yield to an increase of the electromechanical delay [29—31]. The vertical jump performance being correlated to both the rate of force development [32] and stiffness [33], MTU stiffness decrease may lower the vertical jump height. This MTU stiffness reduction might also negatively impact the maximal sprint speed [34] and maximal strength production capacity [35]. However, in our study, no stretching effect was observed. This could be explained by the fact that muscular contraction mode are more or less susceptible to stretching alterations [1]. Indeed, these authors indicated in their review that most studies revealed a lack of deficit or even running speed improvements following stretching. Concerning maximal strength, Ikezoe et al. [36] suggested that MTU stiffness reduction was correlated to power reductions rather than muscle strength. Additionally, we can speculate that stretch duration applied here might be too short to produce sufficient MTU stiffness that could significantly affect strength production.
4.2. Stretch parameters Numerous studies previously investigated stretching effects using various stretch modalities [6,16,19,21,24,37,38]. Most results indicated that dynamic stretching has less detrimental effects than static stretching [21,37]. Different stretch durations have also been tested with durations lasting up to 1 hour [39] whereas, during warm-up, stretches shorter than 60 seconds are most commonly used [1]. From the literature, stretch duration appears to have large effects on muscle strength [2]. Static stretches more than 60 seconds demonstrated the largest strength impairments while more variability is obtained with shorter durations [1,2]. In the
5 present study, 20 seconds stretches were only applied per muscle group and could explain the lack of muscle strength and sprint alterations. Few studies have previously used such short duration stretches. While 30 seconds stretches seemed sufficient enough to produce strength reductions [8,40], other studies were unable to show any alteration with a similar duration [41]. Also, 30 seconds stretching seemed long enough to reduce vertical jump height [38] by a reduction of both the neural drive and MTU stiffness. More precisely, after series of 10 seconds static stretching, Knudson and Noffal [12] concluded that strength deficit would appear with stretch durations ranging from 20 and 40 seconds. Therefore, our results are in line with this previous study. Performing 20 seconds stretches during warm-up does not seem to affect muscle strength and speed but should be avoided during activities with vertical jumps.
4.3. Dynamic exercises In our study, stretch-induced effects after a standardized warm-up were similar than passive rest. The two conditions tested here used similar static stretching periods but differed as a result of the dynamic contractions interspersed between stretches. These contractions aimed to lower the detrimental effects of stretching as a result of a postactivation potentiation phenomenon [42] already used by athletes during warm-up. Indeed, using quite similar dynamic contractions for postactivation potentiation as ours (i.e., plyometrics), Gelen [11] concluded that they could partially reduce the detrimental static stretching effects. This combination has not been shown to improve the performance [11] while a performance improvement has previously been obtained combining dynamic exercises with dynamic stretches as compared with isolated static stretches [14]. A difference between conditions was therefore expected in our study. The lack of any difference could be attributed to postactivation potentiation characteristics, to the population tested but also to a potential neuromuscular fatigue. Indeed, postactivation potentiation has been shown to be best obtained after isometric contractions [43] on explosive type athletes [44]. Recently, Kay and Blazevich [10] tested the effect of maximal voluntary contractions performed before static stretching. These authors indicated that isometric contractions removed the acute effects of stretching on muscle strength because contractions realized before stretching, produced a neuromuscular fatigue that had similar effects than stretching [10]. These same authors [45] conducted a similar study but using concentric contractions before stretching. Additional strength reductions, as that obtained following concentric contractions, were registered after stretching. Accordingly, we can conclude that dynamic contractions were unable to produce any significant potentiation effect and therefore were ineffective to remove the deleterious effects of static stretching on anaerobic performance. Static stretching combined with dynamic activities has similar effects than passive rest.
5. Conclusion The present study examined the acute effects of static stretching combined or not with plyometric exercises on
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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strength, speed and vertical jump ability. Our results indicated that short-duration static stretching (20 s per muscle group) will not significantly reduce strength and speed but had negative effects on vertical jump performance. The combination of static stretching with plyometric exercises was ineffective to reduce the deleterious static stretching effects and has similar effects than passive rest. Static stretching, even with very short durations, should be avoided during warm-up for activities including vertical jumps.
Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
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ORIGINAL ARTICLE
Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance Effets aigus d’étirements de courte durée isolés ou combinés avec des exercices dynamiques sur la performance en force, détente verticale et sprint J. Fortier , G. Lattier , N. Babault ∗ Centre d’expertise de la performance, UFR STAPS, université de Bourgogne, BP 27877, 21078 Dijon cedex, France Received 31 August 2012; accepted 19 November 2012
KEYWORDS Plyometrics; Potentiation; Warm-up; Anaerobic; Power
MOTS CLÉS Pliométrie ;
∗
Summary Objective. — This study aimed to investigate the acute effects of a short-duration isolated static stretching or combined with dynamic plyometric exercises on the performance of some anaerobic parameters (strength, jumping and sprinting). Methods. — During three distinct sessions and after a standardized warm-up, 15 participants randomly performed static stretching exercises alone, static stretching combined with plyometric exercises and no stretch. Total stretch duration was 20 seconds long per muscle group (quadriceps, hamstrings and calf muscles). Tests included maximal quadriceps muscle strength, countermovement jumps and 15 m sprints. Results. — Whatever the condition, maximal strength and sprints were unaltered whereas the vertical jump height significantly decreased (P < 0.05). We conclude that isolated static stretching or combined with plyometric exercises, even with short-duration, were not efficient for strength, jump ability and sprint improvements and should be excluded from warm-up sessions. © 2013 Elsevier Masson SAS. All rights reserved. Résumé Objectifs. — Cette étude explorait les effets aigus d’étirements statiques, isolés ou combinés avec des exercices pliométriques, sur la performance en force, détente verticale et sprint.
Corresponding author. E-mail address: [email protected] (N. Babault).
0765-1597/$ – see front matter © 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.scispo.2012.11.003
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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Potentialisation ; Échauffement ; Anaérobie ; Puissance
Sujets et méthode. — Lors de trois sessions et après un échauffement standardisé, 15 participants ont réalisé de manière aléatoire des exercices d’étirements statiques seuls, étirements statiques combinés avec des exercices pliométriques et pas d’étirements. La durée totale des étirements était de 20 secondes par groupe musculaire (quadriceps, ischios-jambiers et triceps sural). Les tests ont permis d’évaluer la force maximale du quadriceps, la hauteur des sauts avec contre mouvement et des sprints de 15 m. Résultats. — Quelle que soit la condition, la force maximale et les sprints n’ont pas été modifiés tandis que la hauteur maximale de saut a diminué significativement (p < 0,05). Nous avons conclu que des étirements statiques, isolés ou combinés avec des exercices pliométriques, même avec de courtes durées, n’étaient pas efficaces pour améliorer la force, la détente verticale et la vitesse de sprints et doivent par conséquent être exclus des sessions d’échauffement. © 2013 Elsevier Masson SAS. Tous droits réservés.
1. Introduction Stretching exercises could be used before, during and after training for injury prevention, performance improvement and recovery optimization. The usefulness of stretching for improving performance during warm-up remains debated. Numerous studies demonstrated the detrimental acute effects of stretching on the subsequent muscular performance such as maximal voluntary strength and vertical jump ability [1,2]. These performance reductions may originate from neural [3] and mechanical factors [4] that may last until 1 hour post-stretching [5]. Various stretch parameters (e.g., stretch modality, stretch duration) may influence the deleterious stretchinginduced acute effects. Concerning stretching modality, while no statistical difference was observed between static and contract-relax stretches [6], other studies recommended using dynamic rather than static stretching during warm-up (e.g., [7]). Moreover, a dose-response relationship has been suggested [1,2]. Indeed, Kay and Blazevich [2] concluded that stretching durations, commonly performed during preexercise routines (< 30 s), resulted in no performance decreases. Quite similarly, strong evidences exist for performance impairments with total stretch duration longer than 90 seconds whereas more variability is obtained with shorter stretch durations [1]. For instance, Winchester et al. [8] demonstrated that a single 30-s stretch was sufficient enough for strength reductions. During warm-up and whatever the stretching modality or duration, athletes usually combined stretching with dynamic exercises such as plyometrics or maximal voluntary contractions. The aim is to increase muscle temperature but also to induce a post-activation potentiation effect [9]. Some studies previously demonstrated that performing these contractions prior [10] or following muscle stretching [11] could partly reduce the stretch-induced performance impairments. For example, Gelen [11] concluded that static stretching combined with plyometric exercises was efficient to reduce the negative stretch effects on soccer players’ anaerobic performance. However, contrary to dynamic exercises alone, performance was not improved. Generally, these studies applied moderate to long stretch durations, obviously accompanied with performance impairments [1,2], whereas Knudson and Noffal [12] concluded that strength declines appeared with stretch duration longer than 20 seconds (range: 20 to 40 s). Accordingly, it can be questioned whether very short-duration static stretching combined with dynamic exercises could remove the
potential stretch-induced performance reductions and even increase performance. Therefore, the aim of the present study was to investigate the acute effects of an isolated short-duration static stretching or combined with plyometric exercises on muscle strength, vertical jump and sprint performance.
2. Methods 2.1. Experimental approach to the problem The experiment was based on three separate time-matched sessions testing various conditions randomly presented:
• static stretching alone; • static stretching followed by plyometric exercises and; • control condition (no stretch).
These three conditions were applied after a standardized warm-up. Tests performed after the standardized warmup (pre-tests) and immediately after the three different conditions (post-tests), included measurements of the knee extensors maximal isometric strength, vertical jump height and maximal 15-m sprints.
2.2. Participants Fifteen healthy participants (nine men and six women) volunteered for the experiment. Their mean ± standard deviation (SD) age, body mass and height were 22.8 ± 2.0 years, 80.4 ± 10.8 kg, 181 ± 6 cm and 21.3 ± 0.5 years, 60.8 ± 5.0 kg, 162 ± 5 cm for men and women, respectively. All were recreationally active with ∼7 hours training per week and were familiar with stretching as well as explosive type activities such as jumps and sprints. They agreed to participate in the study and signed an informed consent form. The study was conducted according to the declaration of Helsinki, approved by the local committee on human research and followed ethical standards [13]. Participants were asked to refrain from strenuous activity at least 24 hours preceding all testing sessions.
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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Warm-up and static stretching
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Figure 1 Exercises used for stretching on quadriceps (A), hamstring (B) and calf muscles (C). Dynamic exercises following stretches in the Static + Dyn conditions: rapid high knees (D), rapid butt-kicks (E) and rapid ankle flips (F).
2.3. Procedures Each participant performed three testing sessions (randomly presented) in order to study the effects of static stretching alone or combined with dynamic plyometric exercises after a standardized warm-up on strength, vertical jump and sprints. At least 3 days separated each session. A 5 minutes 30 seconds standardized warm-up was performed at the onset of each session. It consisted in ten analytical concentric and eccentric submaximal contractions of lower-limb muscles (quadriceps, hamstrings, gluteus, calf) and various dynamic runs repeated twice over 15 m (rest = walk back to starting position) typically used to prepare athletes for sport participation (high knees, butt kicks, ankle flips, sideway runs, accelerations). After warm-up, participants randomly performed one of the three conditions (static stretching, static stretching combined with dynamic exercises or control) each lasting 4 minutes 30 seconds. Tests were conducted immediately after warm-up (pretests) and immediately after the three different conditions (post-tests). They consisted in measurements of the knee extensors maximal isometric strength, vertical jump height during countermovement jumps (CMJ) and maximal sprints over 15 m.
2.3.1. Static stretching (static) In the present experiment, short stretch duration was tested. Accordingly, 20 seconds static stretches were performed only once on the right and left quadriceps, hamstrings and calf muscles. Muscle groups were randomly chosen but the right side was always stretched first. Participants held each stretch during 20 seconds at the point of discomfort, repeated to the opposite side and then relaxed in a standing static position for 50 seconds before another muscle group. Unassisted exercises were used (Fig. 1). For quadriceps stretch, participants stood and touched a wall for balance. The top ankle or forefoot was grasped from behind and then pulled toward the buttocks. The hip was then straightened by moving the knee backward and held in this position. For hamstrings stretch, participants stood on a flexed leg. The other leg was extended with the heel on the floor. Participants bent at the hip and lower their extended upper torso from the hips onto the extended leg. For calf stretch, participants stood on a raised platform on the balls of one foot, then dropping the heel down toward the floor. Static stretching combined with plyometric exercises (Static + Plyo). During this condition, participants conducted the same stretching exercises as the Static condition (both sides, in a random order and maintained at the point of
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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discomfort). Total stretch duration was similar than the Static condition for each muscle group. However, in order to conduct dynamic plyometric exercises within stretch, stretches were shorter (5 s) and repeated four times. The right, then left sides were alternated and immediately followed by dynamic plyometric exercises performed over 15 m. Dynamic exercises solicited the same muscle group than the preceding stretch (Fig. 1). Rapid high knees, rapid butt kicks and rapid ankle flips were used for quadriceps, hamstrings and calf muscles, respectively. Between each muscle group, participants relaxed 20 seconds in a standing static position. 2.3.2. No stretch (control) During the control condition, participants stayed relaxed (seated and standing static position) during the 4 minutes 30 seconds period after warm-up. 2.3.3. Tests Tests measuring muscle strength, vertical jump and sprint speed were conducted immediately after warm-up (pre-tests) and immediately after the three conditions (posttests). Tests were randomly presented and completed twice. An average value was calculated and retained for statistical analyses. The quadriceps maximal voluntary strength was bilaterally determined using a Myostat strength gauge (Allegro, Sallanches, France). Participants were seated on a leg extension machine (Multiform, La Roque d’Anthéron, France) with a 90◦ knee flexion angle and a 100◦ hip angle. Maximal isometric contractions lasted 4 seconds. During each contraction, the maximal voluntary strength was determined and expressed in Newton (N). The vertical jump height was measured during CMJ using an Optojump system (Optojump, Microgate, Bolzano, Italy) measuring jumps’ fly time. CMJ were performed starting from a standing position, then squatting down to a 90◦ knee angle (± 5◦ ), and then extending the knees in one continuous movement. During CMJ, arms were kept on the hips to minimize their contribution. Maximal running speed was measured with infrared photoelectric cells positioned at 1 m from the floor and 15 m from the start line and controlled by TAC software (Test Atletici Computerizzati, TEL.SI s.r.l., Vignola, Italy). The rear foot was positioned on a contact mat. After a visual signal, participants started from a standing position and ran the 15-m distance as fast as possible. Sprint time started after the rear foot left the mat and did not include reaction time. During all tests, participants were encouraged to express the maximal performance they can. Care was taken to have a minimal rest period between tests and trials.
2.4. Statistical analysis Mean values ± SD were calculated for all dependent variables. Stretching effects were analyzed by using a 2-way analysis of variance (ANOVA) with repeated measures. Time (pre- vs. post-tests) and experimental conditions (Control vs. Static vs. Static + Plyo) were used as repeated measures. Because no gender effect has previously been registered for acute effects of stretching [14], sex differences were not tested during statistics. Subsequent Tukey’s Honestly Significant Difference (HSD) post hoc tests were performed if significant main effects or interactions
Table 1 Maximal strength, vertical jump height and maximal speed measured during pre- and post-tests in the Control, Static and Static + Plyo conditions. Control Strength (N) Pre Post
Static
Static + Plyo
968 ± 345 974 ± 372
947 ± 356 954 ± 342
915 ± 353 935 ± 363
CMJ (cm) Pre Posta
35.1 ± 7.4 33.3 ± 6.2
35.1 ± 7.5 33.6 ± 7.3
34.6 ± 6.5 33.6 ± 6.1
Speed (m.s−1 ) Pre Post
5.57 ± 0.34 5.58 ± 0.38
5.64 ± 0.44 5.74 ± 0.57
5.64 ± 0.44 5.73 ± 0.70
Mean values ± SD; values are averages of men and women; CMJ: countermovement jump. a Significant time main effect (P < 0.0001).
were obtained. Statistical power and effect size (partial eta-squared) associated with the two-way ANOVA were calculated for each variable by our statistics software and shown in results when significant effects were found. The intersession reproducibility of each variable was quantified with intraclass correlation coefficients (ICC) based on the repeated measures ANOVA. The intersession variability of the measurements was assessed by calculating coefficients of variations (CV = SD/mean × 100). ICC and CV were calculated using the three pre-tests values. Statistical significance was accepted at an alpha level of 0.05. Statistics were all performed using Statistica software (version 8.0, Statsoft, Tulsa, USA).
3. Results The two-way ANOVA did not reveal any significant experimental condition effect and interaction effect for CMJ (ICC = 0.992, CV = 2.5%), maximal strength (ICC = 0.992, CV = 6.4%) and speed (ICC = 0.915, CV = 2.4%). A time effect was only obtained for vertical jump height (P < 0.001, power = 0.999, effect size = 0.699) (Table 1). Whatever the condition, CMJ height was significantly lower post-tests as compared to pre-tests (mean decrease: −4.0 ± 3.7%). No time effect was obtained for the maximal isometric strength and maximal running speed.
4. Discussion After a standardized warm-up, the present study demonstrated that short-duration isolated stretching or stretching combined with plyometric exercises have the same effects that a rest period and are ineffective to improve the strength, jump and sprint performance. Also, performing 20 seconds stretches during warm-up did not alter the maximal strength or sprint speed but had detrimental effects on explosive strength as attested by the vertical jump height. Static stretching is not systematically associated with strength production capacity reduction as previously obtained. Indeed, while some authors demonstrated impairments of muscle strength [15], vertical
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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Warm-up and static stretching jump height [16,17] and running velocity [18] immediately after various stretching modalities [6,19], others have not demonstrated stretch-induced deleterious effects [20—22]. These differences could be attributed to the outcome measures [14], to stretch parameters such as duration [23] or modality [24] but also to the inclusion of voluntary contractions [11].
4.1. Outcome measure The outcome measure seemed to be a possible cause for the conflicting results often obtained in the literature. Indeed, in our study, no reduction was registered on muscle strength and sprinting speed while the vertical jump height was impaired. A similar result has previously been obtained following warm-ups with or without static stretching [14]. These opposite effects could be explained by the mechanisms responsible for post-stretching performance reductions and more particularly to mechanical factors. In fact, neural factors, more transient, might play a minor or insignificant role [1]. Indeed, while neural factors may have a large influence following long-duration stretching [4,6], short-duration stretching revealed more equivocal results with some studies obtaining neither electromyographic nor voluntary activation alterations [25,26]. Such finding could partly explain the lack of muscle strength alteration registered here. Mechanical factors originate from a stiffness reduction of the musculo-tendinous unit (MTU, [4]) or a shift of the force/length or torque/angle relationship [19,27,28]. Stiffness alterations negatively impact force transmission and may yield to an increase of the electromechanical delay [29—31]. The vertical jump performance being correlated to both the rate of force development [32] and stiffness [33], MTU stiffness decrease may lower the vertical jump height. This MTU stiffness reduction might also negatively impact the maximal sprint speed [34] and maximal strength production capacity [35]. However, in our study, no stretching effect was observed. This could be explained by the fact that muscular contraction mode are more or less susceptible to stretching alterations [1]. Indeed, these authors indicated in their review that most studies revealed a lack of deficit or even running speed improvements following stretching. Concerning maximal strength, Ikezoe et al. [36] suggested that MTU stiffness reduction was correlated to power reductions rather than muscle strength. Additionally, we can speculate that stretch duration applied here might be too short to produce sufficient MTU stiffness that could significantly affect strength production.
4.2. Stretch parameters Numerous studies previously investigated stretching effects using various stretch modalities [6,16,19,21,24,37,38]. Most results indicated that dynamic stretching has less detrimental effects than static stretching [21,37]. Different stretch durations have also been tested with durations lasting up to 1 hour [39] whereas, during warm-up, stretches shorter than 60 seconds are most commonly used [1]. From the literature, stretch duration appears to have large effects on muscle strength [2]. Static stretches more than 60 seconds demonstrated the largest strength impairments while more variability is obtained with shorter durations [1,2]. In the
5 present study, 20 seconds stretches were only applied per muscle group and could explain the lack of muscle strength and sprint alterations. Few studies have previously used such short duration stretches. While 30 seconds stretches seemed sufficient enough to produce strength reductions [8,40], other studies were unable to show any alteration with a similar duration [41]. Also, 30 seconds stretching seemed long enough to reduce vertical jump height [38] by a reduction of both the neural drive and MTU stiffness. More precisely, after series of 10 seconds static stretching, Knudson and Noffal [12] concluded that strength deficit would appear with stretch durations ranging from 20 and 40 seconds. Therefore, our results are in line with this previous study. Performing 20 seconds stretches during warm-up does not seem to affect muscle strength and speed but should be avoided during activities with vertical jumps.
4.3. Dynamic exercises In our study, stretch-induced effects after a standardized warm-up were similar than passive rest. The two conditions tested here used similar static stretching periods but differed as a result of the dynamic contractions interspersed between stretches. These contractions aimed to lower the detrimental effects of stretching as a result of a postactivation potentiation phenomenon [42] already used by athletes during warm-up. Indeed, using quite similar dynamic contractions for postactivation potentiation as ours (i.e., plyometrics), Gelen [11] concluded that they could partially reduce the detrimental static stretching effects. This combination has not been shown to improve the performance [11] while a performance improvement has previously been obtained combining dynamic exercises with dynamic stretches as compared with isolated static stretches [14]. A difference between conditions was therefore expected in our study. The lack of any difference could be attributed to postactivation potentiation characteristics, to the population tested but also to a potential neuromuscular fatigue. Indeed, postactivation potentiation has been shown to be best obtained after isometric contractions [43] on explosive type athletes [44]. Recently, Kay and Blazevich [10] tested the effect of maximal voluntary contractions performed before static stretching. These authors indicated that isometric contractions removed the acute effects of stretching on muscle strength because contractions realized before stretching, produced a neuromuscular fatigue that had similar effects than stretching [10]. These same authors [45] conducted a similar study but using concentric contractions before stretching. Additional strength reductions, as that obtained following concentric contractions, were registered after stretching. Accordingly, we can conclude that dynamic contractions were unable to produce any significant potentiation effect and therefore were ineffective to remove the deleterious effects of static stretching on anaerobic performance. Static stretching combined with dynamic activities has similar effects than passive rest.
5. Conclusion The present study examined the acute effects of static stretching combined or not with plyometric exercises on
Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003
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strength, speed and vertical jump ability. Our results indicated that short-duration static stretching (20 s per muscle group) will not significantly reduce strength and speed but had negative effects on vertical jump performance. The combination of static stretching with plyometric exercises was ineffective to reduce the deleterious static stretching effects and has similar effects than passive rest. Static stretching, even with very short durations, should be avoided during warm-up for activities including vertical jumps.
Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
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Please cite this article in press as: Fortier J, et al. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci sports (2013), http://dx.doi.org/10.1016/j.scispo.2012.11.003