High school athletes often begin their exercise with a warm-up protocol, which typically consists of jogging one or two laps around the gym followed by a series of static stretches (Walter et al., 2011). It is widely believed that pre-exercise static stretching (SS) reduces the risk of injury and enhances performance (Woods et al., 2007). However, recent studies reported that pre-exercise SS decreases maximal force production (Leone et al., 2012), jump height (Perrier et al., 2011) and speed (Little and Williams, 2006).
The negative effects of SS are attributed to mechanical factors (e.g. changes in muscle stiffness) and neuromuscular factors such as decreased motor unit activation and altered reflex sensitivity (Avela et al., 2004; Cramer et al., 2005). However, the literature is not unanimous in reporting stretch-induced performance impairments. Recently, a number of studies suggest that SS has no significant effect (Dalrymple et al., 2010; Handrakis et al., 2010) or can improve performance (Costa et al., 2009). The divergent findings are attributed to various factors such as subject's training status (Costa et al., 2009), age (Handrakis et al., 2010), gender, the stretch duration and intensity of the protocol (Behm and Chaouachi, 2011).
The controversy regarding the potential performance impairments of SS, raised the interest for dynamic stretching (DS). DS involves controlled movement through the active range of motion (ROM) for a joint, and incorporates callisthenics movements (e.g. lunging) and running drills that include forward, lateral, and change-of-direction movements (Behm and Chaouachi, 2011). Studies regarding DS reported positive effects on power (Manoel et al., 2008), sprint (Fletcher and Anness, 2007), and jump performance (Perrier et al., 2011). However, these studies have mainly examined the effects of stretching on maximal strength and power performance (squats, bench press, speed, jump etc.). To the authors' knowledge, there is no research investigating the acute effects of DS on balance. Maintaining balance requires fast and accurate movements of upper and lower extremities (armleg coordination). Stretch-induced changes to muscletendon unit (MTU) length and stiffness would be expected to affect the ability to react effectively to stability challenges (Behm et al., 2004).
Currently, limited studies have investigated only the acute effect of SS on balance (Costa et al., 2009). Behm et al. (2004) and Nagano et al. (2006) reported that balance control was impaired after SS. On the contrary, Costa et al. (2009) reported that SS produced a significant improvement in balance compared to the NS condition. The few studies regarding the effect of SS on balance and the absence of studies evaluating the effect of DS on balance was one of the reasons for conducting this study.
Apart from balance, a more compliant MTU due to SS could alter reaction time (RT) and movement time (MT) (Behm et al., 2004). However, only a limited number of studies have investigated this issue. Specifically, Behm et al. (2004) reported impairment in RT and MT after SS, whereas Alpkaya and Koceja (2007) and Perrier et al. (2011) showed no significant effect of SS on RT. The controversial findings and the limited number of studies indicate the importance of additional research on the effects of stretching on RT and MT. Furthermore, the above mentioned studies have examined the effects of stretching on RT of the lower limbs. To the authors' knowledge, no study has compared the effects of DS and SS on RT and MT of the upper limbs. In many sports upper limb RT and MT play an important role for a successful outcome (e.g. basketball, volleyball etc.).
Moreover, RT, MT and agility are often practiced in the same physical education lesson or training unit (Darst and Pangrazi, 2009). Van Gelder and Bartz (2011) reported that a DS protocol for the lower limbs compared to SS improves significantly agility performance. Similar results reported Little and Williams (2006) and McMillian et al. (2006). Conversely, Chaouachi et al. (2010) reported no significant differences between DS and SS regarding agility performance. Generally, agility is defined as a rapid whole-body movement with change of running direction in response to a stimulus (Van Gelder and Bartz, 2011). The movements of the upper and lower limbs are crucial in order for someone to change the running direction rapidly without the loss of balance (Allum et al., 2002). However, none of the conducted studies included a stretching protocol for upper and lower limbs. Furthermore, a stretching protocol of a regular physical education lesson or training unit comprises exercises for the whole-body and not just for the lower-body musculature (National Association for Sport and Physical Education, 2011).
In addition, the literature has focused mainly on the effects of stretching on male subjects (Behm et al., 2011; Handrakis et al., 2010). Only Costa et al. (2009) investigated the effect of SS on balance in adult women. However, the effects of stretching on adolescent females' balance, RT and MT have not been examined. Therefore, the purpose of the present study was to compare the acute effects of a whole-body SS and DS protocol on balance, agility, RT and MT of the upper limbs in adolescent female athletes. Since SS results in a longer and more compliant MTU (Cramer et al., 2005), it was hypothesized that SS would deteriorate balance, agility, RT and MT. In contrast, DS enhances motor unit excitability and kinaesthetic awareness (Jaggers et al., 2008) and therefore it was hypothesized that DS would improve the above mentioned parameters.
Thirty one female high school athletes volunteered to take part in the study (age = 17.3 [+ or -] 0.5 yr, body mass = 55.9 [+ or -] 5.4 kg, height = 1.66 [+ or -] 0.05 m). The students participated in state-mandated physical education program (twice per week for 45 min) and in after-school sport activities, at least 3 times per week (minimum of 1 hour). Eleven participants were basketball players, 8 volleyball, 8 handball and 4 track and field athletes (sprint and long jump). No athlete withdrew because of injury or any other adverse experiences. The procedures used in this study were conducted in accordance to the ethical guidelines of the Aristotle University of Thessaloniki, Greece and informed consent was obtained from both the students and their parents.
Prior to data collection, the participants attended 3 physical education lessons, in which they were familiarized with the stretching procedures. During these orientation sessions they also practiced the tests for balance, agility, RT and MT. All study procedures took place in the gymnasium between 10:00-14:00 hours. After the familiarization period, the participants performed the following protocols counterbalanced, in three different days: (a) 3 min jogging followed by 7 min SS, (b) 3 min jogging followed by 7 min DS, and (c) 3 min jogging without stretching, followed by 7 min of rest (NS). The 3 protocols were administered 2 to 4 days apart. After completing one of the stretching protocols, participants proceeded to the...