Acute effect of different stretching methods on

PUBBLICAZIONE PERIODICA BIIMESTRALE - POSTE ITALIANE S.P.A. - SPED. IN A. P. D.L. 353/2003 (CONV. IN L. 27/02/2004 N° 46) ART. 1, COMMA 1, DCB/CN - ISSN 0022-4707 TAXE PERÇUE

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EXERCISE PHYSIOLOGY AND BIOMECHANICS ORIGINAL ARTICLES J SPORTS MED PHYS FITNESS 2014;54:683-90

Acute effect of different stretching methods on flexibility and jumping performance in competitive artistic gymnasts G. DALLAS 1, A. SMIRNIOTOU 1, G. TSIGANOS 1, D. TSOPANI 1, A. DI CAGNO 2, 3, CH. TSOLAKIS 1

Aim. The purpose of this study was to investigate the acute effects of 3 different warm up methods of stretching (static, proprioceptive neuromuscular facilitation, and stretching exercises on a Vibration platform) on flexibility and legs powerjumping performance in competitive artistic gymnasts. Methods. Eighteen competitive artistic gymnasts were recruited to participate in this study. Subjects were exposed to each of 3 experimental stretching conditions: static stretching (SS), proprioceptive neuromuscular facilitation stretching (PNF), and stretching exercises on a Vibration platform (S+V). Flexibility assessed with sit and reach test (S & R) and jumping performance with squat jump (SJ) and counter movement jump (CMJ) and were measured before, immediately after and 15 min after the interventions. Results. Significant differences were observed for flexibility after all stretching conditions for S+V (+1.1%), SS (+5.7%) and PNF (+6.8%) (P=0.000), which remained higher 15 min after interventions (S+V (1.1%), SS (5.3%) and PNF (5.5%), respectively (P=0.000). Conclusion. PNF stretching increased flexibility in competitive gymnasts, while S+V maintained jumping performance when both methods were used as part of a warm-up procedure. Key words: Stretching - Vibration - Pliability - Artistic gymnastics.

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tretching before training or competition has been a common practice performed by athletes in most sport activities. It has been suggested that stretching exercises used as part of a warm-up routine increases range of motion (ROM) in various joints 1 minimizing the risk of injury,1, 2 and improves subsequent physical performance.3 Static stretching Corresponding author: G. Dallas, Faculty of Physical Education and Sport Science, National and Kapodistrian University of Athens 41, �� Ethnikis Antistaseos, Dafne, Greece. E-mail: [email protected]

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1National and Kapodistrian University of Athens Department of Physical Education and Sport Science Dafne, Greece 2Department of Health Sciences University of Rome, Rome, Italy 3Department of Medicine and Health Science University of Molise, Campobasso, Italy

(SS), ballistic stretching (BS) and proprioceptive neuromuscular facilitation (PNF) have been shown to increase flexibility. However, it is unclear which method is superior to the others.4 Previous data have showed that SS before physical activity increases flexibility 5 but have a detrimental effect when performance requires maximal force and power production.6, 7 Recently a number of studies have been reported static stretching-induced impairments on subsequent explosive performance while others have not observed significant differences after static stretching interventions of different modes, intensities, frequencies, duration of stretches and recovery prior to performance in participants with different physical level.8 Consequently, some researchers talk against the commonly used practice of static stretching before power demanding activities, such as gymnastics 9 and fencing 10 suggesting the use of different forms of warm-up activities and methods, such as ballistic exercises,11-13 PNF stretching 14, 15 and stretching on vibration platforms.16 The acute effect of PNF on maximal muscular performance has been investigated by a number of comparative studies reporting conflicting re-

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Effect of stretching on flexibility and jumping performance

sults.7, 15, 17-20 Some studies have shown that different volume of PNF stretching decreases vertical jump performance 18, 19 and muscle strength and power output,7 while others found that PNF stretching did not have a significant effect on vertical jump height 17, 20 and knee extension power.15 Thus, further research is needed to determine the effect of PNF on muscular performance. Acute exposure to local or whole-body vibration (WBV) has been recently used as an effective warmup method to improve joint’s flexibility,16, 21, 22 while numerous studies suggest that the various WBV protocols used elicit a potentiation effect improving jumping performance in athletes who participate on explosive events.23-25 However, other studies did not show significant improvement in stretch reflex,26 on maximal voluntary isometric force and rate of force development,27 and in jumping performance after a single bout of WBV.28 Furthermore, WBV when used as a part of an active warm-up in recreational golfers increased flexibility and golf’s specific kinetic patterns 29 while up to our knowledge only one study 30 has examined the simultaneous effect of static stretching and local vibration in flexibility and explosive force in competitive female gymnasts. The results of this study showed that the simultaneously use of vibration in the already elongated muscles by previous execution of static stretching can further increase flexibility without affecting power performance. According to the related literature 8 there is no agreement concerning the effects of different stretching protocols on muscle performance due to differences in methodology, stretching interventions (e.g., time, intensity, recovery time, body position and type of stretching) and performance tasks. In artistic gymnastics success is based on legs’ strength and power supporting the kinetic patterns performed during either training or competition.31 Concentric explosive strength and fast stretchshortening cycles have been associated to gymnastic performance. The ability of the neuromuscular system to produce maximal power output appears to be critical in artistic gymnastics that require optimal combinations of muscle strength, balance and flexibility to maximize performance.31 Moreover, flexibility is a demand at high level athletes, facilitating not only the dynamic competitive requirements but also the movements of the limbs throughout the entire range of motion which is

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necessary in order to achieve high performance scores.31 To the best of our knowledge, this study is the first to compare static (SS), PNF and stretching exercises on a vibration platform (S+V) when the above methods are used as a part of the warm-up routine in competitive artistic gymnasts. Therefore, the purpose of this study was to investigate the acute effects of different stretching interventions (SS, PNF, and S+V) on flexibility and jumping performance in competitive artistic gymnasts. It was hypothesized that all interventions would improve flexibility, while S+V was expected not only to reduce the adverse effects of SS but probably to potentiate jumping ability on the aforementioned group of athletes. Materials and methods Experimental approach to the problem The present study was designed to determine the effect of three different stretching conditions on flexibility and legs’ jumping ability in the same group of competitive artistic gymnasts. All subjects performed three different stretching protocols: static stretching (SS), PNF stretching (PNF) and stretching on vibration platform (S+V), with counterbalanced order on three separate days, with at least 5 days apart between testing days to allow for full recovery. Flexibility (S&R), squat jump (SJ), and counter movement jump (CMJ) were evaluated before, immediately after and 15 min after each stretching intervention to assess changes in neuromuscular functions. Study population Eighteen competitive male and female artistic gymnasts (mean±SD: age 21.83±1.76 years, height 168.44±6.61 cm, body mass 61.61±8.69 kg, % body fat 15.85±6.59) with an athletic competitive experience of approximately 8-10 years, participated in this study. Informed consent was obtained from the subjects before testing after being informed on the purpose and the risks of the experimental design. The study was approved by the local institutional Review Board and all procedures were in accordance with the Helsinki declaration of 1975 as revised in 1996.


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Procedures Subjects had to report to the lab on four separate days. On the first day, they had a familiarization training session and reproduced experimental procedures regarding the stretching techniques and jumping performance tests. Additionally, stature, and body mass was measured at that day. Body mass (kg) was measured to the nearest 0.01 kg (Seca 770 UK), and height (cm) was measured to the nearest 0.1cm using a stadiometer (Seca, Leicester, UK). On the other three days, subjects performed the experimental sessions and were asked to refrain from any strenuous physical activity 48 hours before testing. On each testing day, subjects performed a five-minute warm-up on a cycle ergometer without resistance at a self-selected moderate pace speed arranging from 4.0 to 5.0 km * h-1). Immediately after the warm-up, the subjects completed a series of pre-intervention performance measurements for flexibility: S&R and jumping performance tests: SJ and CMJ in a randomized order. After the initial tests, subjects performed one of the three different lower-body stretching interventions focusing on the hamstrings, quadriceps, soleus muscles and gastrocnemius, in a randomized order. Immediately after the interventions two performance measurements were conducted, the first within 15 seconds and the second 15 min after each intervention. All testing sessions took place at the same time of the day (13:00 to 16:00). Verbal encouragement was given throughout testing trials. Stretching protocol Each subject performed a set of 3 stretching exercises for the knee flexors (hamstrings), knee extensors (quadriceps muscle) and plantar flexors (soleus muscle-gastrocnemius) in each one for the three different warm-up interventions (SS, PNF, S+V) in a randomized order. Each exercise was held for 15 seconds at a point of mild discomfort with 15 seconds rest between each exercise (3 exercises x 15 sec in each warm-up method). The exercise used for each muscle group in each intervention is described below. In the SS of knee flexors, subjects were sitting on a thin gymnastic mat with legs out straight ahead and were instructed to lean forward slowly as far as possible without bending their knees. That position was

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held for 15 seconds at a point of mild discomfort as acknowledged by the subject. In the stretching on vibration platform (S+V) of the knee flexors, subjects were sitting on the ground, supporting their heels on the platform with legs out straight ahead. Subjects executed the same SS protocol as it has been described above. In the PNF intervention for knee flexors, subjects were prone in the floor on a thin mat, with the knee flexed at 90° in a manner that the subjects maintained maximal isometric tension of the leg flexors against a manual resistance applied by the examiner for 15 sec at a point of mild discomfort as acknowledged by the subject. In the SS of knee extensors, subjects stood in an upright position with one hand (left) against a wall for balance, grasping the right ankle with their right hand, fully flexed at the knee joint until the heel touch the buttock at a point of mild discomfort as acknowledged by the subject for 15 s. The same procedure was repeated for the opposite leg. In the stretching on vibration platform (S+V) of knee extensors, subjects took a position with their front leg in lunge, flexed approximately by 120 degrees and with the rear knee supported on a non-operating second platform. Stretching combined with vibration at a point of mild discomfort as acknowledged by the subject was held for 15 s. The same procedure was repeated for the opposite leg. In the PNF intervention of knee extensors, subjects were sat on a desk and maximal isometric tension was applied by themselves against a manual resistance applied by the examiner at a point of mild discomfort as acknowledged by the subject for 15 seconds. In the SS intervention of plantar flexors, subjects stood in an upright position with both hands against a wall for balance, having the frontal part of foot on a raised surface with so that a static stretching of 15 seconds was held at a point of mild discomfort as acknowledged by the subject. In the stretching on vibration platform (S+V) intervention of the plantar flexors, subjects stood upright on the vibration platform trying to push the heel downwards at a point of mild discomfort as acknowledged by the subject for 15 seconds. In the PNF intervention of plantar flexors, from upright position, the subject maintained maximal isometric tension of the plantar leg flexors against a


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manual resistance applied on the athlete’s shoulders by the examiner at a point of mild discomfort as acknowledged by the subject for 15 seconds. Subjects were trying to push upward the heels while the toes of the foot supported in a raised surface. During the S+V method subjects, were exposed to local vertical mechanical Vibration for selected muscles groups at frequency of 30 Hz and amplitude of 2mm, while standing on a Power Plate® Next Generation platform (Power Plate North America, Northbrook, IL, USA). For the proper exercises execution a second vibration non-operating device was used in order to insure similar ground level position for both legs.

with the knees and ankles extended and land in an upright position, while keeping the hands on their hip. The depth for the eccentric phase of the countermovement jump was self selected. Thirty sec of rest was held between each trial and 2 min of rest was allowed between the jumping tests. Three trials were performed for each test and the best result was considered for statistical analysis. Study variables The dependent variables measured were S&R to evaluate flexibility, and SJ and CMJ to evaluate jumping performance. The independent variables were the stretching interventions (SS, PNF, S+V).

Measurements Statistical analysis

Flexibility test Hamstrings flexibility was tested by using a standard sit-and-reach box (Cranlea, UK). Subjects were asked to remove their shoes and sit with their legs extended in front of them against the box. The subjects then placed one hand over the other and stretched forward along the top of the box until they could stretch no further, holding this position for 3 seconds. 30 sec of rest was used between each trial. The best of three trials was evaluated, to the nearest 1.0cm, for further analysis. Jumping performance (Vertical jump tests) Jumping performance tests were conducted on the Optojump device (Microgate, Italy), which allows the measurement of contact and flying times, using an optical acquisition system and calculates the height jumped, according to the theory of Bosco et al.32 The rise of the center of gravity above the ground (h in m) was measured from flight time (tf in seconds) applying ballistic laws: h=tf 2·g·8-1 (m) where g is the acceleration of gravity (9.81 m·s-2).32 Before each test all subjects familiarized with jumping tests. For the SJ the subjects were asked to jump from a semi-squatting position (120°) without counter movement. A hand held Lafayette goniometer was used to ensure the depth of the semi-squatting position. In order to avoid upper body work and to minimize horizontal and lateral displacements the hands were kept on the hips through the test. For the CMJ subjects were instructed to jump

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A two-way repeated measures ANOVA (condition x time) with repeated measures on both factors was used. If significant condition x time interaction were observed, then separate one-way ANOVA were used to assess within differences. Bonferroni posthoc analyses were run when appropriate. ICC was used to determine the between days variability of the data using a 2-way mixed model. According to Richardson,33 partial eta squared was classified as small (0.01 to 0.059), moderate (0.06 to 0.137) and large (>0.138). Statistical significance was accepted at P